Claude Skill

compare-screenshots

Compare screenshots against the intended design, distinguishing approved references from historical baselines. Use for iterative implementation matching, before/after visual review, objective image telemetry, or checking a lone capture for flat, empty, or badly framed content.

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Part of dzhng/skills — 32 skills

Install

skills CLI npx skills add https://github.com/dzhng/skills/tree/main/skills/visual/compare-screenshots
Claude Code claude plugin marketplace add https://llmmart.ai/marketplace.json && claude plugin install dzhng-skills@llmmart
Git git clone https://github.com/dzhng/skills.git

The skills CLI installs just this skill, for any of its supported agents. Claude Code installs the whole dzhng/skills collection as a plugin from our marketplace. Git is the plain clone.

Skill manifest

Compare Screenshots

Judge images against the intended result. A user-approved design is the target; a historical baseline is only an earlier attempt and may be wrong. Metrics locate differences, never decide correctness. Use design-with-images for the full exploration-to-implementation loop.

Workflow

  1. Establish the target. Use the user-approved reference and stated design requirements when available; do not replace them with your own taste. Otherwise derive the target from the visual requirement, what the thing depicts in reality and the domain skill that owns the look. Write it down in one or two concrete sentences ("low sun should cast long shadows east; trees fill the canopy; labels stay legible at this zoom").
    • If the right answer isn't clear — competing valid readings, a taste or product-intent call, a tradeoff only the owner can settle — stop and ask the user what the correct answer should be. Show them the comparison. Do not quietly default to the baseline to avoid asking; that bakes in whatever the baseline got wrong.
  2. Confirm comparability so the differences you see are real, not capture artifacts: same viewport, DPR, route/page, frozen time/tick, camera intent, UI state, data, fonts/assets where they matter. If not comparable, fix capture setup or compare only a crop/feature where the mismatch is harmless.
  3. Measure the approved design. For reference matching, read and complete Reference Landmarks before changing code or accepting a candidate. Then generate artifacts sized to the question: side-by-side, key-feature crops/zooms, grayscale, absolute grayscale heatmap, pixelmatch diff, per-image Sobel/edge maps, edge-difference heatmap, JSON metrics.
  4. Inspect boundaries before judging the whole. For every changed visual effect, inspect all sides at native scale and in matched detail crops. Include the effect's full fade and surrounding space; a crop ending at the component box hides spill. Compare top/right/bottom/left extents separately, anchored to visible text, rules or silhouettes rather than inferred CSS bounds. Check every foreground feature crossed by the effect (lines, icons, text, adjacent panels): brightness, color, sharpness and continuity must match the target. A readable line can still be incorrectly dimmed. Record each check as reference observation → candidate observation → pass/fix/uncertain, with its crop. Use the landmark table to resolve local distances and contrast; full-frame averages cannot settle a local defect.
  5. Judge each divergence against the target. For every place the two images differ, name what is actually there in plain terms — missing content, wrong camera, bad hierarchy, weak contrast, wrong depth, text overlap, layout shift, clipped edge, unexpected blur, style mismatch — and decide which side is closer to correct. The answer can be the candidate, the baseline, both wrong, or a genuine toss-up.
  6. Get a neutral second opinion for disputed or high-stakes calls: a fresh subagent given only the two images and neutral labels, per references/subagent-visual-review.md.
  7. Resolve mismatches to an approved target. When implementing a selected design, record material differences in spacing, shape, softness, typography and hierarchy; revise, recapture and repeat until resolved or the user changes the target. Do not silently exempt a difference because the code is simpler.
  8. Conclude with one verdict: candidate is less wrong (accept, and re-bless the baseline if one exists), baseline is less wrong (reject), both wrong (another pass needed — say what's still off), or unclear (ask the user). Accept only when every boundary/overlap check passes or has an explicit user-approved deviation; uncertainty requires closer evidence, not a pass. Overall resemblance or a positive second opinion cannot cancel a local defect. Never accept on a lower score alone or reject on a higher one. Never hide content, blur detail, crop away differences, or make the capture less truthful to move a number.

Useful Metrics

Pick metrics that answer the question. For full visual comparisons, report:

  • mae: mean absolute grayscale difference, 0..255, lower is closer.
  • rmse: grayscale root mean square error, lower is closer.
  • diffRatio16, diffRatio32, diffRatio64: fraction of pixels over each grayscale delta threshold.
  • pixelmatchRatio: mismatch ratio from pixelmatch over grayscale images.
  • edgeEnergyCurrent and edgeEnergyCandidate: average Sobel edge strength.
  • edgeEnergyRatio: candidate/current. Far below 1 usually means missing geometry, props, labels, or terrain; far above 1 usually means noisy or incorrect detail.
  • edgeDiffRatio32: fraction of pixels whose Sobel edge differs materially.
  • avgLuminanceCurrent, avgLuminanceCandidate, avgLuminanceDelta: average brightness and delta. Use when a render is visibly too dark/light even if a broader distance score improves.
  • Content proxies relevant to the scene: black/void ratio, terrain-like ratio, water-like ratio, team-color ratio, label/text mask ratio.

For UI/document/layout reviews, also use crop bounds, text/foreground mask coverage, contrast checks, edge clipping, element positions, and before/after dimensions when those beat global pixel distance.

Single-Image Metrics

Every metric above measures one image against another, so none of them can answer "is this capture worth anything" when there is nothing to compare it to — and the pair score is symmetric, so an enormous distance never says which side is the empty frame. A few absolute numbers do, computed on a coarse grid from a single PNG:

  • colorEntropyBits under ~3.0, or dominantColorShare over ~0.6: one colour owns the frame. A sparse scene, an unlit one, or a subject that never drew.
  • edgeDensity under ~0.04: almost no form anywhere. Empty framing, a primitive-dominant scene, or the subject sitting outside the crop.
  • luminanceContrast under ~60: fog, darkness, or haze compressing the whole frame into one band.
  • transparentShare above 0 on a capture that should be opaque: the capture itself is wrong. A transparent pixel keeps whatever RGB it was left with, so an invisible frame can look rich until it is composited — the scene metrics composite before measuring, and name the invisible share rather than letting you infer it. The pair metrics above still read stored RGB, so this field is where transparency gets told either way.

These are thresholds for suspicion, not gates. A deliberately minimal design, a night scene, an empty-state screen, and a whiteboard all trip them honestly. Use them to decide where to look, then say what the frame is actually doing — never adjust a capture to raise a number, which is the same failure as cropping away a difference.

Distance Score

When a single fixed-pair number is useful, this default works for structural changes:

distance = 0.35 * diffRatio32 + 0.25 * pixelmatchRatio + 0.25 * edgeDiffRatio32 + 0.15 * min(1, abs(log2(edgeEnergyRatio)))

It measures distance from the other image, nothing more. Because the baseline can be wrong, a distance of 0 is not success and a large distance is not failure — a richer scene, clearer models, stronger labels, real depth, or better lighting all legitimately raise it. Use the score to find where the images move; decide who is right in step 5. Name the field for what it measures (distance, not "parity") so no one reads it as a verdict.

Report the full-frame score and, when UI dominates the shot, a labeled world-crop score. Use the world-crop score to locate renderer movement and keep the full-frame score so UI/camera mistakes stay visible.

Score Discipline

  • Quote the previous and new distance for the same pair each iteration, then say whether the movement is toward the target, away from it, or diagnostic noise.
  • Prefer edge metrics for missing-content bugs. A flat top-down map can show a deceptively moderate grayscale diff while edge energy proves trees, roads, city forms, or army silhouettes are absent.
  • Segment out stable UI when it dominates and the question is the world render; keep a full-frame score too, labeled.
  • If the camera is wrong, pixel scores are diagnostic only. Fix camera intent first, then judge the render.

Tooling

Keep comparison scripts inside the skill or a temporary workspace, not in product code, unless the product genuinely needs screenshot comparison at runtime.

  • scripts/visual-parity-diff.mjs is a reusable local helper. Its PNG and pixel-diff runtime is bundled with the skill, so target repositories do not need pngjs or pixelmatch. Run it with REFERENCE_DIR=<png-folder>, CANDIDATE_DIR=<png-folder>, and optional OUT_DIR=<artifact-folder>. REPORT_ORDER=a,b,c pins ordering; CROPS_JSON=<file> adds labeled crops (keyed by image id, each crop in pixels or { "unit": "ratio" } normalized bounds). Pair reports carry a sceneMetrics block per side.
  • Drop REFERENCE_DIR to run the same helper on a folder with no counterpart: it writes scene-metrics.json with the single-image numbers above and no diff artifacts. Use it on a lone screenshot, on a full capture set before anyone reviews it, or to find which side of a large distance is the empty one.
  • scripts/visual-parity-diff.eval.mjs is the helper's own eval: it generates fixtures whose correct answer is known by construction — empty, transparent, primitive-dominant, authored, degenerate — and asserts the classification, the invariances, and the CLI contract. Run it with the same REPO_ROOT after changing the script. Never satisfy a failing check by loosening a threshold until you have shown the fixture, not the code, is what's wrong.
  • For other tasks, adapt the same artifact set rather than adding one-off scripts to the application. Extend the helper if a needed pair is uncovered.

References

  • references/subagent-visual-review.md: neutral subagent prompt/config for an independent judgment when history could bias you.
Files (skills)
  • references
    • reference-landmarks.md 2.9 KB
      # Reference Landmarks
      
      Read before implementing or accepting a match to an approved image.
      
      1. **Measure the reference first.** Pick visible anchors for each requested
         relationship: glyph bounds, line endpoints, icon edges, solid silhouettes.
         Record a small table: feature | reference relationship/range | candidate
         measurement | delta | pass/fix/uncertain. Fill the reference column before
         changing code; never calibrate the target from the latest candidate.
      2. **Separate core from fringe.** A soft edge has no single boundary. Locate the
         dark/opaque core, its transition and the faint outer tail on each side. Say
         where a foreground stroke meets that profile. “Full width” may mean the
         visible core, not every pixel of blur; resolve shorthand against the supplied
         image before translating it into a percentage or a hard clip. For example,
         compare a rule's ends to both the text bounds and the fade, and compare the
         last glyph-to-rule gap separately from the tail below the rule.
      3. **Keep scale honest.** Preserve original captures at the actual application
         scale, with viewport and DPR recorded. If a generated reference has different
         raster dimensions, record the mapping from its source capture; if unknown,
         compare ratios to stable landmarks such as glyph height and state uncertainty.
         Label any derived alignment image. Never resize the application, typography
         or evidence merely to make the pair agree. Native captures remain the proof.
      4. **Isolate ambiguous effects.** When terrain, texture or lighting could be
         mistaken for shadow, capture the same frozen state with only that effect
         toggled. Use the difference to locate its contribution; keep the normal
         capture beside it. Use local contrast/falloff samples across an edge rather
         than whole-frame similarity. If no clean reference baseline exists, report
         the inferred range instead of inventing an exact opacity or endpoint.
      5. **Keep the whole feature in the crop.** Include both endpoints, all fade
         tails and surrounding context. Recheck crop bounds after every geometry
         change; an old crop can hide a newly extended edge. Zoomed crops supplement
         native-size evidence, never replace it.
      6. **Close every discrepancy.** A reviewer saying “slightly wider,” “minor gap”
         or “uncertain extent” has identified unfinished comparison work. Measure and
         resolve it, or record a demonstrated rasterization limit or user-approved
         deviation. Do not convert those words into a pass because the overall image
         looks good. Validate test assertions against these reference relationships,
         not a convenient CSS mechanism or the last verbal interpretation.
      
      After a user catches a missed detail, revisit the whole landmark table. Recheck
      neighbors after the fix: restoring a bright line can erase the dark support
      above it; extending that line can overshoot the reference's fading edge. Finish
      with the updated table and current captures, not a repeated general verdict.
      
    • subagent-visual-review.md 3.6 KB
      # Subagent Visual Review
      
      Use this when history or prior conclusions could bias the main agent's visual
      judgment.
      
      ## Spawn Config
      
      - `agent_type`: `default`
      - `fork_context`: `false`
      - Attach the two screenshots as `local_image` items.
      - For an approved-design comparison, identify `Reference` and `Candidate` and
        supply the intended design requirements. For an open preference comparison,
        use `Image A` and `Image B` without declaring a target.
      - Supply full frames and matched detail crops including surrounding space.
        Withhold previous verdicts, implementation details and the author's preferred
        answer; do not withhold the target needed to judge fidelity.
      - Give it a shell only if you want numbers back. Images alone buy a description;
        a judge asked for measurements it has no way to take answers in the register
        the question was posed in and invents them.
      
      ## Prompt
      
      ```text
      You are doing an unbiased visual review of two screenshots for the same visual target. You have no prior context.
      
      Compare Image A and Image B. Report:
      
      1. Whether they appear to show the same viewport/state/content.
      2. Major visible differences in camera/view, layout, content, missing details,
         labels/text, icons, color, lighting, depth/layering, clipping, artifacts,
         readability, or style.
      3. Inspect every changed effect at all four boundaries, including its full fade
         beyond the component. Compare extent relative to visible anchors on each
         side. Check brightness, color, sharpness and continuity of every foreground
         feature it crosses. Report local discrepancies even if everything is legible.
      4. Give a per-feature reference observation → candidate observation →
         pass/fix/uncertain record. Distinguish solid/core edges from faint fringe;
         locate endpoints and gaps relative to visible anchors, in words unless you
         quote the command and output that measured them. Verify crops include
         the entire feature. Request paired effect-on/off captures when background
         texture makes extent ambiguous. A small discrepancy still needs resolution;
         do not label it acceptable merely because the whole looks similar.
      5. A concise verdict on whether the images preserve the intended visual
         relationship or need another pass.
      
      When an approved reference is identified, judge fidelity to it. Otherwise do not
      assume either image is the target. Overall attractiveness does not excuse a
      local mismatch. Judge only from visible pixels and supplied design requirements.
      
      Describe what you see in words. State no pixel value, luminance, percentage,
      ratio, count, or offset unless you ran a command that produced it and you quote
      that command and its output beside the number. "Image B reads clearly darker
      along the lower edge" is a finding; a luminance mean you did not measure is a
      fabrication.
      ```
      
      ## How To Use The Result
      
      - Treat the subagent result as independent evidence about which image is less
        wrong, not a replacement for metrics or your own inspection — and not a vote
        for whichever image is the baseline.
      - Run the returned review through the receipts checker that ships with
        `screenshot-critique` before you read it, and strike whatever it flags. An
        unsupported number reads as the strongest evidence in the review precisely
        because it is numeric, so it has to be removed before it can persuade you.
      - If the subagent flags wrong camera, mismatched state, missing content, or
        visible artifacts, fix capture/rendering quality before judging the rest.
      - Preserve the findings, not just the headline verdict. A “pass” accompanied
        by an unresolved local discrepancy is not acceptance; finish the landmark
        check before calling the feature done.
      
  • scripts
    • visual-parity-diff.eval.mjs 13.6 KB · in bundle
    • visual-parity-diff.mjs 23.1 KB · in bundle
  • test
    • fixtures
      • target-without-helper-packages
        • candidate
          • fixture.png 297 B · in bundle
        • reference
          • fixture.png 297 B · in bundle
        • README.md 70 B
          Fixture repository intentionally has no package.json or node_modules.
          
    • visual-parity-diff.test.mjs 2.5 KB · in bundle
  • vendor
    • pixelmatch
      • index.js 11.7 KB
        /**
         * Compare two equally sized images, pixel by pixel.
         *
         * @param {Uint8Array | Uint8ClampedArray} img1 First image data.
         * @param {Uint8Array | Uint8ClampedArray} img2 Second image data.
         * @param {Uint8Array | Uint8ClampedArray | void} output Image data to write the diff to, if provided.
         * @param {number} width Input images width.
         * @param {number} height Input images height.
         *
         * @param {Object} [options]
         * @param {number} [options.threshold=0.1] Matching threshold (0 to 1); smaller is more sensitive.
         * @param {boolean} [options.includeAA=false] Whether to skip anti-aliasing detection.
         * @param {number} [options.alpha=0.1] Opacity of original image in diff output.
         * @param {[number, number, number]} [options.aaColor=[255, 255, 0]] Color of anti-aliased pixels in diff output.
         * @param {[number, number, number]} [options.diffColor=[255, 0, 0]] Color of different pixels in diff output.
         * @param {[number, number, number]} [options.diffColorAlt=options.diffColor] Whether to detect dark on light differences between img1 and img2 and set an alternative color to differentiate between the two.
         * @param {boolean} [options.diffMask=false] Draw the diff over a transparent background (a mask).
         * @param {boolean} [options.checkerboard=true] Whether to blend semi-transparent pixels against a checkerboard pattern (true) or plain white (false) when comparing.
         *
         * @return {number} The number of mismatched pixels.
         */
        export default function pixelmatch(img1, img2, output, width, height, options = {}) {
            const {
                threshold = 0.1,
                alpha = 0.1,
                aaColor = [255, 255, 0],
                diffColor = [255, 0, 0],
                checkerboard = true,
                includeAA, diffColorAlt, diffMask
            } = options;
        
            if (!isPixelData(img1) || !isPixelData(img2) || (output && !isPixelData(output)))
                throw new Error('Image data: Uint8Array, Uint8ClampedArray or Buffer expected.');
        
            if (img1.length !== img2.length || (output && output.length !== img1.length))
                throw new Error(`Image sizes do not match. Image 1 size: ${img1.length}, image 2 size: ${img2.length}`);
        
            if (img1.length !== width * height * 4) throw new Error(`Image data size does not match width/height. Expecting ${width * height * 4}. Got ${img1.length}`);
        
            // check if images are identical
            const len = width * height;
            const a32 = new Uint32Array(img1.buffer, img1.byteOffset, len);
            const b32 = new Uint32Array(img2.buffer, img2.byteOffset, len);
            let identical = true;
        
            for (let i = 0; i < len; i++) {
                if (a32[i] !== b32[i]) { identical = false; break; }
            }
            if (identical) { // fast path if identical
                if (output && !diffMask) {
                    for (let i = 0, pos = 0; i < len; i++, pos += 4) drawGrayPixel(img1, pos, alpha, output);
                }
                return 0;
            }
        
            // maximum acceptable square distance between two colors;
            // 35215 is the maximum possible value for the YIQ difference metric
            const maxDelta = 35215 * threshold * threshold;
            const [aaR, aaG, aaB] = aaColor;
            const [diffR, diffG, diffB] = diffColor;
            const [altR, altG, altB] = diffColorAlt || diffColor;
            let diff = 0;
        
            // compare each pixel of one image against the other one
            for (let i = 0, pos = 0; i < len; i++, pos += 4) {
                // squared YUV distance between colors at this pixel position, negative if the img2 pixel is darker
                const delta = a32[i] === b32[i] ? 0 : colorDelta(img1, img2, pos, pos, checkerboard);
        
                // the color difference is above the threshold
                if (Math.abs(delta) > maxDelta) {
                    const x = i % width;
                    const y = (i / width) | 0;
                    // check it's a real rendering difference or just anti-aliasing
                    const isExcludedAA = !includeAA && (antialiased(img1, x, y, width, height, a32, b32, checkerboard) || antialiased(img2, x, y, width, height, b32, a32, checkerboard));
                    if (isExcludedAA) {
                        // one of the pixels is anti-aliasing; draw as yellow and do not count as difference
                        // note that we do not include such pixels in a mask
                        if (output && !diffMask) drawPixel(output, pos, aaR, aaG, aaB);
        
                    } else {
                        // found substantial difference not caused by anti-aliasing; draw it as such
                        if (output) {
                            if (delta < 0) {
                                drawPixel(output, pos, altR, altG, altB);
                            } else {
                                drawPixel(output, pos, diffR, diffG, diffB);
                            }
                        }
                        diff++;
                    }
        
                } else if (output && !diffMask) {
                    // pixels are similar; draw background as grayscale image blended with white
                    drawGrayPixel(img1, pos, alpha, output);
                }
            }
        
            // return the number of different pixels
            return diff;
        }
        
        /** @param {Uint8Array | Uint8ClampedArray} arr */
        function isPixelData(arr) {
            // work around instanceof Uint8Array not working properly in some Jest environments
            return ArrayBuffer.isView(arr) && arr.BYTES_PER_ELEMENT === 1;
        }
        
        /**
         * Check if a pixel is likely a part of anti-aliasing;
         * based on "Anti-aliased Pixel and Intensity Slope Detector" paper by V. Vysniauskas, 2009
         * @param {Uint8Array | Uint8ClampedArray} img
         * @param {number} x1
         * @param {number} y1
         * @param {number} width
         * @param {number} height
         * @param {Uint32Array} a32
         * @param {Uint32Array} b32
         * @param {boolean} checkerboard
         */
        function antialiased(img, x1, y1, width, height, a32, b32, checkerboard) {
            const x0 = Math.max(x1 - 1, 0);
            const y0 = Math.max(y1 - 1, 0);
            const x2 = Math.min(x1 + 1, width - 1);
            const y2 = Math.min(y1 + 1, height - 1);
            const pos4 = (y1 * width + x1) * 4;
            // cache the center pixel's RGBA once instead of re-reading it on every neighbor comparison
            const cr = img[pos4];
            const cg = img[pos4 + 1];
            const cb = img[pos4 + 2];
            const ca = img[pos4 + 3];
            let zeroes = x1 === x0 || x1 === x2 || y1 === y0 || y1 === y2 ? 1 : 0;
            let min = 0;
            let max = 0;
            let minX = 0;
            let minY = 0;
            let maxX = 0;
            let maxY = 0;
        
            // go through 8 adjacent pixels
            for (let x = x0; x <= x2; x++) {
                for (let y = y0; y <= y2; y++) {
                    if (x === x1 && y === y1) continue;
        
                    // brightness delta between the center pixel and adjacent one
                    const delta = brightnessDelta(img, pos4, (y * width + x) * 4, cr, cg, cb, ca, checkerboard);
        
                    // count the number of equal, darker and brighter adjacent pixels
                    if (delta === 0) {
                        zeroes++;
                        // if found more than 2 equal siblings, it's definitely not anti-aliasing
                        if (zeroes > 2) return false;
        
                    // remember the darkest pixel
                    } else if (delta < min) {
                        min = delta;
                        minX = x;
                        minY = y;
        
                    // remember the brightest pixel
                    } else if (delta > max) {
                        max = delta;
                        maxX = x;
                        maxY = y;
                    }
                }
            }
        
            // if there are no both darker and brighter pixels among siblings, it's not anti-aliasing
            if (min === 0 || max === 0) return false;
        
            // if either the darkest or the brightest pixel has 3+ equal siblings in both images
            // (definitely not anti-aliased), this pixel is anti-aliased
            return (hasManySiblings(a32, minX, minY, width, height) && hasManySiblings(b32, minX, minY, width, height)) ||
                   (hasManySiblings(a32, maxX, maxY, width, height) && hasManySiblings(b32, maxX, maxY, width, height));
        }
        
        /**
         * Check if a pixel has 3+ adjacent pixels of the same color.
         * @param {Uint32Array} img
         * @param {number} x1
         * @param {number} y1
         * @param {number} width
         * @param {number} height
         */
        function hasManySiblings(img, x1, y1, width, height) {
            const x0 = Math.max(x1 - 1, 0);
            const y0 = Math.max(y1 - 1, 0);
            const x2 = Math.min(x1 + 1, width - 1);
            const y2 = Math.min(y1 + 1, height - 1);
            const val = img[y1 * width + x1];
            let zeroes = x1 === x0 || x1 === x2 || y1 === y0 || y1 === y2 ? 1 : 0;
        
            // go through 8 adjacent pixels
            for (let x = x0; x <= x2; x++) {
                for (let y = y0; y <= y2; y++) {
                    if (x === x1 && y === y1) continue;
                    zeroes += +(val === img[y * width + x]);
                    if (zeroes > 2) return true;
                }
            }
            return false;
        }
        
        /**
         * Calculate color difference according to the paper "Measuring perceived color difference
         * using YIQ NTSC transmission color space in mobile applications" by Y. Kotsarenko and F. Ramos.
         * Caller guarantees the two pixels differ, so the early-zero check is omitted.
         * @param {Uint8Array | Uint8ClampedArray} img1
         * @param {Uint8Array | Uint8ClampedArray} img2
         * @param {number} k
         * @param {number} m
         * @param {boolean} checkerboard
         */
        function colorDelta(img1, img2, k, m, checkerboard) {
            const r1 = img1[k];
            const g1 = img1[k + 1];
            const b1 = img1[k + 2];
            const a1 = img1[k + 3];
            const r2 = img2[m];
            const g2 = img2[m + 1];
            const b2 = img2[m + 2];
            const a2 = img2[m + 3];
        
            let dr = r1 - r2;
            let dg = g1 - g2;
            let db = b1 - b2;
            const da = a1 - a2;
        
            if (a1 < 255 || a2 < 255) { // blend pixels with background
                let rb = 255, gb = 255, bb = 255;
                if (checkerboard) {
                    rb = 48 + 159 * (k % 2);
                    gb = 48 + 159 * ((k / 1.618033988749895 | 0) % 2);
                    bb = 48 + 159 * ((k / 2.618033988749895 | 0) % 2);
                }
                dr = (r1 * a1 - r2 * a2 - rb * da) / 255;
                dg = (g1 * a1 - g2 * a2 - gb * da) / 255;
                db = (b1 * a1 - b2 * a2 - bb * da) / 255;
            }
        
            const y = dr * 0.29889531 + dg * 0.58662247 + db * 0.11448223;
            const i = dr * 0.59597799 - dg * 0.27417610 - db * 0.32180189;
            const q = dr * 0.21147017 - dg * 0.52261711 + db * 0.31114694;
        
            const delta = 0.5053 * y * y + 0.299 * i * i + 0.1957 * q * q;
        
            // encode whether the pixel lightens or darkens in the sign
            return y > 0 ? -delta : delta;
        }
        
        /**
         * Specialized brightness-only color delta for the anti-aliasing detector,
         * with the center pixel's RGBA hoisted out of the neighbor loop.
         * @param {Uint8Array | Uint8ClampedArray} img
         * @param {number} k center pixel offset
         * @param {number} m neighbor pixel offset
         * @param {number} r1
         * @param {number} g1
         * @param {number} b1
         * @param {number} a1
         * @param {boolean} checkerboard
         */
        function brightnessDelta(img, k, m, r1, g1, b1, a1, checkerboard) {
            const r2 = img[m];
            const g2 = img[m + 1];
            const b2 = img[m + 2];
            const a2 = img[m + 3];
        
            let dr = r1 - r2;
            let dg = g1 - g2;
            let db = b1 - b2;
            const da = a1 - a2;
        
            if (!dr && !dg && !db && !da) return 0;
        
            if (a1 < 255 || a2 < 255) {
                let rb = 255, gb = 255, bb = 255;
                if (checkerboard) {
                    rb = 48 + 159 * (k % 2);
                    gb = 48 + 159 * ((k / 1.618033988749895 | 0) % 2);
                    bb = 48 + 159 * ((k / 2.618033988749895 | 0) % 2);
                }
                dr = (r1 * a1 - r2 * a2 - rb * da) / 255;
                dg = (g1 * a1 - g2 * a2 - gb * da) / 255;
                db = (b1 * a1 - b2 * a2 - bb * da) / 255;
            }
        
            return dr * 0.29889531 + dg * 0.58662247 + db * 0.11448223;
        }
        
        /**
         * @param {Uint8Array | Uint8ClampedArray} output
         * @param {number} pos
         * @param {number} r
         * @param {number} g
         * @param {number} b
         */
        function drawPixel(output, pos, r, g, b) {
            output[pos] = r;
            output[pos + 1] = g;
            output[pos + 2] = b;
            output[pos + 3] = 255;
        }
        
        /**
         * @param {Uint8Array | Uint8ClampedArray} img
         * @param {number} i
         * @param {number} alpha
         * @param {Uint8Array | Uint8ClampedArray} output
         */
        function drawGrayPixel(img, i, alpha, output) {
            const val = 255 + (img[i] * 0.29889531 + img[i + 1] * 0.58662247 + img[i + 2] * 0.11448223 - 255) * alpha * img[i + 3] / 255;
            drawPixel(output, i, val, val, val);
        }
        
      • LICENSE 738 B · in bundle
      • package.json 904 B
        {
          "name": "pixelmatch",
          "version": "7.2.0",
          "type": "module",
          "description": "The smallest and fastest pixel-level image comparison library.",
          "main": "index.js",
          "types": "index.d.ts",
          "bin": {
            "pixelmatch": "bin/pixelmatch"
          },
          "files": [
            "bin/pixelmatch",
            "index.d.ts"
          ],
          "dependencies": {
            "pngjs": "^7.0.0"
          },
          "devDependencies": {
            "eslint": "^10.2.1",
            "eslint-config-mourner": "^4.1.0",
            "typescript": "^6.0.3"
          },
          "scripts": {
            "pretest": "eslint",
            "test": "tsc && node --test"
          },
          "repository": {
            "type": "git",
            "url": "git+https://github.com/mapbox/pixelmatch.git"
          },
          "keywords": [
            "image",
            "comparison",
            "diff"
          ],
          "author": "Volodymyr Agafonkin",
          "license": "ISC",
          "bugs": {
            "url": "https://github.com/mapbox/pixelmatch/issues"
          },
          "homepage": "https://github.com/mapbox/pixelmatch#readme"
        }
        
    • pngjs
      • lib
        • bitmapper.js 6.3 KB
          "use strict";
          
          let interlaceUtils = require("./interlace");
          
          let pixelBppMapper = [
            // 0 - dummy entry
            function () {},
          
            // 1 - L
            // 0: 0, 1: 0, 2: 0, 3: 0xff
            function (pxData, data, pxPos, rawPos) {
              if (rawPos === data.length) {
                throw new Error("Ran out of data");
              }
          
              let pixel = data[rawPos];
              pxData[pxPos] = pixel;
              pxData[pxPos + 1] = pixel;
              pxData[pxPos + 2] = pixel;
              pxData[pxPos + 3] = 0xff;
            },
          
            // 2 - LA
            // 0: 0, 1: 0, 2: 0, 3: 1
            function (pxData, data, pxPos, rawPos) {
              if (rawPos + 1 >= data.length) {
                throw new Error("Ran out of data");
              }
          
              let pixel = data[rawPos];
              pxData[pxPos] = pixel;
              pxData[pxPos + 1] = pixel;
              pxData[pxPos + 2] = pixel;
              pxData[pxPos + 3] = data[rawPos + 1];
            },
          
            // 3 - RGB
            // 0: 0, 1: 1, 2: 2, 3: 0xff
            function (pxData, data, pxPos, rawPos) {
              if (rawPos + 2 >= data.length) {
                throw new Error("Ran out of data");
              }
          
              pxData[pxPos] = data[rawPos];
              pxData[pxPos + 1] = data[rawPos + 1];
              pxData[pxPos + 2] = data[rawPos + 2];
              pxData[pxPos + 3] = 0xff;
            },
          
            // 4 - RGBA
            // 0: 0, 1: 1, 2: 2, 3: 3
            function (pxData, data, pxPos, rawPos) {
              if (rawPos + 3 >= data.length) {
                throw new Error("Ran out of data");
              }
          
              pxData[pxPos] = data[rawPos];
              pxData[pxPos + 1] = data[rawPos + 1];
              pxData[pxPos + 2] = data[rawPos + 2];
              pxData[pxPos + 3] = data[rawPos + 3];
            },
          ];
          
          let pixelBppCustomMapper = [
            // 0 - dummy entry
            function () {},
          
            // 1 - L
            // 0: 0, 1: 0, 2: 0, 3: 0xff
            function (pxData, pixelData, pxPos, maxBit) {
              let pixel = pixelData[0];
              pxData[pxPos] = pixel;
              pxData[pxPos + 1] = pixel;
              pxData[pxPos + 2] = pixel;
              pxData[pxPos + 3] = maxBit;
            },
          
            // 2 - LA
            // 0: 0, 1: 0, 2: 0, 3: 1
            function (pxData, pixelData, pxPos) {
              let pixel = pixelData[0];
              pxData[pxPos] = pixel;
              pxData[pxPos + 1] = pixel;
              pxData[pxPos + 2] = pixel;
              pxData[pxPos + 3] = pixelData[1];
            },
          
            // 3 - RGB
            // 0: 0, 1: 1, 2: 2, 3: 0xff
            function (pxData, pixelData, pxPos, maxBit) {
              pxData[pxPos] = pixelData[0];
              pxData[pxPos + 1] = pixelData[1];
              pxData[pxPos + 2] = pixelData[2];
              pxData[pxPos + 3] = maxBit;
            },
          
            // 4 - RGBA
            // 0: 0, 1: 1, 2: 2, 3: 3
            function (pxData, pixelData, pxPos) {
              pxData[pxPos] = pixelData[0];
              pxData[pxPos + 1] = pixelData[1];
              pxData[pxPos + 2] = pixelData[2];
              pxData[pxPos + 3] = pixelData[3];
            },
          ];
          
          function bitRetriever(data, depth) {
            let leftOver = [];
            let i = 0;
          
            function split() {
              if (i === data.length) {
                throw new Error("Ran out of data");
              }
              let byte = data[i];
              i++;
              let byte8, byte7, byte6, byte5, byte4, byte3, byte2, byte1;
              switch (depth) {
                default:
                  throw new Error("unrecognised depth");
                case 16:
                  byte2 = data[i];
                  i++;
                  leftOver.push((byte << 8) + byte2);
                  break;
                case 4:
                  byte2 = byte & 0x0f;
                  byte1 = byte >> 4;
                  leftOver.push(byte1, byte2);
                  break;
                case 2:
                  byte4 = byte & 3;
                  byte3 = (byte >> 2) & 3;
                  byte2 = (byte >> 4) & 3;
                  byte1 = (byte >> 6) & 3;
                  leftOver.push(byte1, byte2, byte3, byte4);
                  break;
                case 1:
                  byte8 = byte & 1;
                  byte7 = (byte >> 1) & 1;
                  byte6 = (byte >> 2) & 1;
                  byte5 = (byte >> 3) & 1;
                  byte4 = (byte >> 4) & 1;
                  byte3 = (byte >> 5) & 1;
                  byte2 = (byte >> 6) & 1;
                  byte1 = (byte >> 7) & 1;
                  leftOver.push(byte1, byte2, byte3, byte4, byte5, byte6, byte7, byte8);
                  break;
              }
            }
          
            return {
              get: function (count) {
                while (leftOver.length < count) {
                  split();
                }
                let returner = leftOver.slice(0, count);
                leftOver = leftOver.slice(count);
                return returner;
              },
              resetAfterLine: function () {
                leftOver.length = 0;
              },
              end: function () {
                if (i !== data.length) {
                  throw new Error("extra data found");
                }
              },
            };
          }
          
          function mapImage8Bit(image, pxData, getPxPos, bpp, data, rawPos) {
            // eslint-disable-line max-params
            let imageWidth = image.width;
            let imageHeight = image.height;
            let imagePass = image.index;
            for (let y = 0; y < imageHeight; y++) {
              for (let x = 0; x < imageWidth; x++) {
                let pxPos = getPxPos(x, y, imagePass);
                pixelBppMapper[bpp](pxData, data, pxPos, rawPos);
                rawPos += bpp; //eslint-disable-line no-param-reassign
              }
            }
            return rawPos;
          }
          
          function mapImageCustomBit(image, pxData, getPxPos, bpp, bits, maxBit) {
            // eslint-disable-line max-params
            let imageWidth = image.width;
            let imageHeight = image.height;
            let imagePass = image.index;
            for (let y = 0; y < imageHeight; y++) {
              for (let x = 0; x < imageWidth; x++) {
                let pixelData = bits.get(bpp);
                let pxPos = getPxPos(x, y, imagePass);
                pixelBppCustomMapper[bpp](pxData, pixelData, pxPos, maxBit);
              }
              bits.resetAfterLine();
            }
          }
          
          exports.dataToBitMap = function (data, bitmapInfo) {
            let width = bitmapInfo.width;
            let height = bitmapInfo.height;
            let depth = bitmapInfo.depth;
            let bpp = bitmapInfo.bpp;
            let interlace = bitmapInfo.interlace;
            let bits;
          
            if (depth !== 8) {
              bits = bitRetriever(data, depth);
            }
            let pxData;
            if (depth <= 8) {
              pxData = Buffer.alloc(width * height * 4);
            } else {
              pxData = new Uint16Array(width * height * 4);
            }
            let maxBit = Math.pow(2, depth) - 1;
            let rawPos = 0;
            let images;
            let getPxPos;
          
            if (interlace) {
              images = interlaceUtils.getImagePasses(width, height);
              getPxPos = interlaceUtils.getInterlaceIterator(width, height);
            } else {
              let nonInterlacedPxPos = 0;
              getPxPos = function () {
                let returner = nonInterlacedPxPos;
                nonInterlacedPxPos += 4;
                return returner;
              };
              images = [{ width: width, height: height }];
            }
          
            for (let imageIndex = 0; imageIndex < images.length; imageIndex++) {
              if (depth === 8) {
                rawPos = mapImage8Bit(
                  images[imageIndex],
                  pxData,
                  getPxPos,
                  bpp,
                  data,
                  rawPos
                );
              } else {
                mapImageCustomBit(
                  images[imageIndex],
                  pxData,
                  getPxPos,
                  bpp,
                  bits,
                  maxBit
                );
              }
            }
            if (depth === 8) {
              if (rawPos !== data.length) {
                throw new Error("extra data found");
              }
            } else {
              bits.end();
            }
          
            return pxData;
          };
          
        • bitpacker.js 4.6 KB
          "use strict";
          
          let constants = require("./constants");
          
          module.exports = function (dataIn, width, height, options) {
            let outHasAlpha =
              [constants.COLORTYPE_COLOR_ALPHA, constants.COLORTYPE_ALPHA].indexOf(
                options.colorType
              ) !== -1;
            if (options.colorType === options.inputColorType) {
              let bigEndian = (function () {
                let buffer = new ArrayBuffer(2);
                new DataView(buffer).setInt16(0, 256, true /* littleEndian */);
                // Int16Array uses the platform's endianness.
                return new Int16Array(buffer)[0] !== 256;
              })();
              // If no need to convert to grayscale and alpha is present/absent in both, take a fast route
              if (options.bitDepth === 8 || (options.bitDepth === 16 && bigEndian)) {
                return dataIn;
              }
            }
          
            // map to a UInt16 array if data is 16bit, fix endianness below
            let data = options.bitDepth !== 16 ? dataIn : new Uint16Array(dataIn.buffer);
          
            let maxValue = 255;
            let inBpp = constants.COLORTYPE_TO_BPP_MAP[options.inputColorType];
            if (inBpp === 4 && !options.inputHasAlpha) {
              inBpp = 3;
            }
            let outBpp = constants.COLORTYPE_TO_BPP_MAP[options.colorType];
            if (options.bitDepth === 16) {
              maxValue = 65535;
              outBpp *= 2;
            }
            let outData = Buffer.alloc(width * height * outBpp);
          
            let inIndex = 0;
            let outIndex = 0;
          
            let bgColor = options.bgColor || {};
            if (bgColor.red === undefined) {
              bgColor.red = maxValue;
            }
            if (bgColor.green === undefined) {
              bgColor.green = maxValue;
            }
            if (bgColor.blue === undefined) {
              bgColor.blue = maxValue;
            }
          
            function getRGBA() {
              let red;
              let green;
              let blue;
              let alpha = maxValue;
              switch (options.inputColorType) {
                case constants.COLORTYPE_COLOR_ALPHA:
                  alpha = data[inIndex + 3];
                  red = data[inIndex];
                  green = data[inIndex + 1];
                  blue = data[inIndex + 2];
                  break;
                case constants.COLORTYPE_COLOR:
                  red = data[inIndex];
                  green = data[inIndex + 1];
                  blue = data[inIndex + 2];
                  break;
                case constants.COLORTYPE_ALPHA:
                  alpha = data[inIndex + 1];
                  red = data[inIndex];
                  green = red;
                  blue = red;
                  break;
                case constants.COLORTYPE_GRAYSCALE:
                  red = data[inIndex];
                  green = red;
                  blue = red;
                  break;
                default:
                  throw new Error(
                    "input color type:" +
                      options.inputColorType +
                      " is not supported at present"
                  );
              }
          
              if (options.inputHasAlpha) {
                if (!outHasAlpha) {
                  alpha /= maxValue;
                  red = Math.min(
                    Math.max(Math.round((1 - alpha) * bgColor.red + alpha * red), 0),
                    maxValue
                  );
                  green = Math.min(
                    Math.max(Math.round((1 - alpha) * bgColor.green + alpha * green), 0),
                    maxValue
                  );
                  blue = Math.min(
                    Math.max(Math.round((1 - alpha) * bgColor.blue + alpha * blue), 0),
                    maxValue
                  );
                }
              }
              return { red: red, green: green, blue: blue, alpha: alpha };
            }
          
            for (let y = 0; y < height; y++) {
              for (let x = 0; x < width; x++) {
                let rgba = getRGBA(data, inIndex);
          
                switch (options.colorType) {
                  case constants.COLORTYPE_COLOR_ALPHA:
                  case constants.COLORTYPE_COLOR:
                    if (options.bitDepth === 8) {
                      outData[outIndex] = rgba.red;
                      outData[outIndex + 1] = rgba.green;
                      outData[outIndex + 2] = rgba.blue;
                      if (outHasAlpha) {
                        outData[outIndex + 3] = rgba.alpha;
                      }
                    } else {
                      outData.writeUInt16BE(rgba.red, outIndex);
                      outData.writeUInt16BE(rgba.green, outIndex + 2);
                      outData.writeUInt16BE(rgba.blue, outIndex + 4);
                      if (outHasAlpha) {
                        outData.writeUInt16BE(rgba.alpha, outIndex + 6);
                      }
                    }
                    break;
                  case constants.COLORTYPE_ALPHA:
                  case constants.COLORTYPE_GRAYSCALE: {
                    // Convert to grayscale and alpha
                    let grayscale = (rgba.red + rgba.green + rgba.blue) / 3;
                    if (options.bitDepth === 8) {
                      outData[outIndex] = grayscale;
                      if (outHasAlpha) {
                        outData[outIndex + 1] = rgba.alpha;
                      }
                    } else {
                      outData.writeUInt16BE(grayscale, outIndex);
                      if (outHasAlpha) {
                        outData.writeUInt16BE(rgba.alpha, outIndex + 2);
                      }
                    }
                    break;
                  }
                  default:
                    throw new Error("unrecognised color Type " + options.colorType);
                }
          
                inIndex += inBpp;
                outIndex += outBpp;
              }
            }
          
            return outData;
          };
          
        • chunkstream.js 4.1 KB
          "use strict";
          
          let util = require("util");
          let Stream = require("stream");
          
          let ChunkStream = (module.exports = function () {
            Stream.call(this);
          
            this._buffers = [];
            this._buffered = 0;
          
            this._reads = [];
            this._paused = false;
          
            this._encoding = "utf8";
            this.writable = true;
          });
          util.inherits(ChunkStream, Stream);
          
          ChunkStream.prototype.read = function (length, callback) {
            this._reads.push({
              length: Math.abs(length), // if length < 0 then at most this length
              allowLess: length < 0,
              func: callback,
            });
          
            process.nextTick(
              function () {
                this._process();
          
                // its paused and there is not enought data then ask for more
                if (this._paused && this._reads && this._reads.length > 0) {
                  this._paused = false;
          
                  this.emit("drain");
                }
              }.bind(this)
            );
          };
          
          ChunkStream.prototype.write = function (data, encoding) {
            if (!this.writable) {
              this.emit("error", new Error("Stream not writable"));
              return false;
            }
          
            let dataBuffer;
            if (Buffer.isBuffer(data)) {
              dataBuffer = data;
            } else {
              dataBuffer = Buffer.from(data, encoding || this._encoding);
            }
          
            this._buffers.push(dataBuffer);
            this._buffered += dataBuffer.length;
          
            this._process();
          
            // ok if there are no more read requests
            if (this._reads && this._reads.length === 0) {
              this._paused = true;
            }
          
            return this.writable && !this._paused;
          };
          
          ChunkStream.prototype.end = function (data, encoding) {
            if (data) {
              this.write(data, encoding);
            }
          
            this.writable = false;
          
            // already destroyed
            if (!this._buffers) {
              return;
            }
          
            // enqueue or handle end
            if (this._buffers.length === 0) {
              this._end();
            } else {
              this._buffers.push(null);
              this._process();
            }
          };
          
          ChunkStream.prototype.destroySoon = ChunkStream.prototype.end;
          
          ChunkStream.prototype._end = function () {
            if (this._reads.length > 0) {
              this.emit("error", new Error("Unexpected end of input"));
            }
          
            this.destroy();
          };
          
          ChunkStream.prototype.destroy = function () {
            if (!this._buffers) {
              return;
            }
          
            this.writable = false;
            this._reads = null;
            this._buffers = null;
          
            this.emit("close");
          };
          
          ChunkStream.prototype._processReadAllowingLess = function (read) {
            // ok there is any data so that we can satisfy this request
            this._reads.shift(); // == read
          
            // first we need to peek into first buffer
            let smallerBuf = this._buffers[0];
          
            // ok there is more data than we need
            if (smallerBuf.length > read.length) {
              this._buffered -= read.length;
              this._buffers[0] = smallerBuf.slice(read.length);
          
              read.func.call(this, smallerBuf.slice(0, read.length));
            } else {
              // ok this is less than maximum length so use it all
              this._buffered -= smallerBuf.length;
              this._buffers.shift(); // == smallerBuf
          
              read.func.call(this, smallerBuf);
            }
          };
          
          ChunkStream.prototype._processRead = function (read) {
            this._reads.shift(); // == read
          
            let pos = 0;
            let count = 0;
            let data = Buffer.alloc(read.length);
          
            // create buffer for all data
            while (pos < read.length) {
              let buf = this._buffers[count++];
              let len = Math.min(buf.length, read.length - pos);
          
              buf.copy(data, pos, 0, len);
              pos += len;
          
              // last buffer wasn't used all so just slice it and leave
              if (len !== buf.length) {
                this._buffers[--count] = buf.slice(len);
              }
            }
          
            // remove all used buffers
            if (count > 0) {
              this._buffers.splice(0, count);
            }
          
            this._buffered -= read.length;
          
            read.func.call(this, data);
          };
          
          ChunkStream.prototype._process = function () {
            try {
              // as long as there is any data and read requests
              while (this._buffered > 0 && this._reads && this._reads.length > 0) {
                let read = this._reads[0];
          
                // read any data (but no more than length)
                if (read.allowLess) {
                  this._processReadAllowingLess(read);
                } else if (this._buffered >= read.length) {
                  // ok we can meet some expectations
          
                  this._processRead(read);
                } else {
                  // not enought data to satisfy first request in queue
                  // so we need to wait for more
                  break;
                }
              }
          
              if (this._buffers && !this.writable) {
                this._end();
              }
            } catch (ex) {
              this.emit("error", ex);
            }
          };
          
        • constants.js 662 B
          "use strict";
          
          module.exports = {
            PNG_SIGNATURE: [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a],
          
            TYPE_IHDR: 0x49484452,
            TYPE_IEND: 0x49454e44,
            TYPE_IDAT: 0x49444154,
            TYPE_PLTE: 0x504c5445,
            TYPE_tRNS: 0x74524e53, // eslint-disable-line camelcase
            TYPE_gAMA: 0x67414d41, // eslint-disable-line camelcase
          
            // color-type bits
            COLORTYPE_GRAYSCALE: 0,
            COLORTYPE_PALETTE: 1,
            COLORTYPE_COLOR: 2,
            COLORTYPE_ALPHA: 4, // e.g. grayscale and alpha
          
            // color-type combinations
            COLORTYPE_PALETTE_COLOR: 3,
            COLORTYPE_COLOR_ALPHA: 6,
          
            COLORTYPE_TO_BPP_MAP: {
              0: 1,
              2: 3,
              3: 1,
              4: 2,
              6: 4,
            },
          
            GAMMA_DIVISION: 100000,
          };
          
        • crc.js 853 B
          "use strict";
          
          let crcTable = [];
          
          (function () {
            for (let i = 0; i < 256; i++) {
              let currentCrc = i;
              for (let j = 0; j < 8; j++) {
                if (currentCrc & 1) {
                  currentCrc = 0xedb88320 ^ (currentCrc >>> 1);
                } else {
                  currentCrc = currentCrc >>> 1;
                }
              }
              crcTable[i] = currentCrc;
            }
          })();
          
          let CrcCalculator = (module.exports = function () {
            this._crc = -1;
          });
          
          CrcCalculator.prototype.write = function (data) {
            for (let i = 0; i < data.length; i++) {
              this._crc = crcTable[(this._crc ^ data[i]) & 0xff] ^ (this._crc >>> 8);
            }
            return true;
          };
          
          CrcCalculator.prototype.crc32 = function () {
            return this._crc ^ -1;
          };
          
          CrcCalculator.crc32 = function (buf) {
            let crc = -1;
            for (let i = 0; i < buf.length; i++) {
              crc = crcTable[(crc ^ buf[i]) & 0xff] ^ (crc >>> 8);
            }
            return crc ^ -1;
          };
          
        • filter-pack.js 4.2 KB
          "use strict";
          
          let paethPredictor = require("./paeth-predictor");
          
          function filterNone(pxData, pxPos, byteWidth, rawData, rawPos) {
            for (let x = 0; x < byteWidth; x++) {
              rawData[rawPos + x] = pxData[pxPos + x];
            }
          }
          
          function filterSumNone(pxData, pxPos, byteWidth) {
            let sum = 0;
            let length = pxPos + byteWidth;
          
            for (let i = pxPos; i < length; i++) {
              sum += Math.abs(pxData[i]);
            }
            return sum;
          }
          
          function filterSub(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let val = pxData[pxPos + x] - left;
          
              rawData[rawPos + x] = val;
            }
          }
          
          function filterSumSub(pxData, pxPos, byteWidth, bpp) {
            let sum = 0;
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let val = pxData[pxPos + x] - left;
          
              sum += Math.abs(val);
            }
          
            return sum;
          }
          
          function filterUp(pxData, pxPos, byteWidth, rawData, rawPos) {
            for (let x = 0; x < byteWidth; x++) {
              let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
              let val = pxData[pxPos + x] - up;
          
              rawData[rawPos + x] = val;
            }
          }
          
          function filterSumUp(pxData, pxPos, byteWidth) {
            let sum = 0;
            let length = pxPos + byteWidth;
            for (let x = pxPos; x < length; x++) {
              let up = pxPos > 0 ? pxData[x - byteWidth] : 0;
              let val = pxData[x] - up;
          
              sum += Math.abs(val);
            }
          
            return sum;
          }
          
          function filterAvg(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
              let val = pxData[pxPos + x] - ((left + up) >> 1);
          
              rawData[rawPos + x] = val;
            }
          }
          
          function filterSumAvg(pxData, pxPos, byteWidth, bpp) {
            let sum = 0;
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
              let val = pxData[pxPos + x] - ((left + up) >> 1);
          
              sum += Math.abs(val);
            }
          
            return sum;
          }
          
          function filterPaeth(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
              let upleft =
                pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
              let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);
          
              rawData[rawPos + x] = val;
            }
          }
          
          function filterSumPaeth(pxData, pxPos, byteWidth, bpp) {
            let sum = 0;
            for (let x = 0; x < byteWidth; x++) {
              let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
              let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
              let upleft =
                pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
              let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);
          
              sum += Math.abs(val);
            }
          
            return sum;
          }
          
          let filters = {
            0: filterNone,
            1: filterSub,
            2: filterUp,
            3: filterAvg,
            4: filterPaeth,
          };
          
          let filterSums = {
            0: filterSumNone,
            1: filterSumSub,
            2: filterSumUp,
            3: filterSumAvg,
            4: filterSumPaeth,
          };
          
          module.exports = function (pxData, width, height, options, bpp) {
            let filterTypes;
            if (!("filterType" in options) || options.filterType === -1) {
              filterTypes = [0, 1, 2, 3, 4];
            } else if (typeof options.filterType === "number") {
              filterTypes = [options.filterType];
            } else {
              throw new Error("unrecognised filter types");
            }
          
            if (options.bitDepth === 16) {
              bpp *= 2;
            }
            let byteWidth = width * bpp;
            let rawPos = 0;
            let pxPos = 0;
            let rawData = Buffer.alloc((byteWidth + 1) * height);
          
            let sel = filterTypes[0];
          
            for (let y = 0; y < height; y++) {
              if (filterTypes.length > 1) {
                // find best filter for this line (with lowest sum of values)
                let min = Infinity;
          
                for (let i = 0; i < filterTypes.length; i++) {
                  let sum = filterSums[filterTypes[i]](pxData, pxPos, byteWidth, bpp);
                  if (sum < min) {
                    sel = filterTypes[i];
                    min = sum;
                  }
                }
              }
          
              rawData[rawPos] = sel;
              rawPos++;
              filters[sel](pxData, pxPos, byteWidth, rawData, rawPos, bpp);
              rawPos += byteWidth;
              pxPos += byteWidth;
            }
            return rawData;
          };
          
        • filter-parse-async.js 558 B
          "use strict";
          
          let util = require("util");
          let ChunkStream = require("./chunkstream");
          let Filter = require("./filter-parse");
          
          let FilterAsync = (module.exports = function (bitmapInfo) {
            ChunkStream.call(this);
          
            let buffers = [];
            let that = this;
            this._filter = new Filter(bitmapInfo, {
              read: this.read.bind(this),
              write: function (buffer) {
                buffers.push(buffer);
              },
              complete: function () {
                that.emit("complete", Buffer.concat(buffers));
              },
            });
          
            this._filter.start();
          });
          util.inherits(FilterAsync, ChunkStream);
          
        • filter-parse-sync.js 483 B
          "use strict";
          
          let SyncReader = require("./sync-reader");
          let Filter = require("./filter-parse");
          
          exports.process = function (inBuffer, bitmapInfo) {
            let outBuffers = [];
            let reader = new SyncReader(inBuffer);
            let filter = new Filter(bitmapInfo, {
              read: reader.read.bind(reader),
              write: function (bufferPart) {
                outBuffers.push(bufferPart);
              },
              complete: function () {},
            });
          
            filter.start();
            reader.process();
          
            return Buffer.concat(outBuffers);
          };
          
        • filter-parse.js 4.7 KB
          "use strict";
          
          let interlaceUtils = require("./interlace");
          let paethPredictor = require("./paeth-predictor");
          
          function getByteWidth(width, bpp, depth) {
            let byteWidth = width * bpp;
            if (depth !== 8) {
              byteWidth = Math.ceil(byteWidth / (8 / depth));
            }
            return byteWidth;
          }
          
          let Filter = (module.exports = function (bitmapInfo, dependencies) {
            let width = bitmapInfo.width;
            let height = bitmapInfo.height;
            let interlace = bitmapInfo.interlace;
            let bpp = bitmapInfo.bpp;
            let depth = bitmapInfo.depth;
          
            this.read = dependencies.read;
            this.write = dependencies.write;
            this.complete = dependencies.complete;
          
            this._imageIndex = 0;
            this._images = [];
            if (interlace) {
              let passes = interlaceUtils.getImagePasses(width, height);
              for (let i = 0; i < passes.length; i++) {
                this._images.push({
                  byteWidth: getByteWidth(passes[i].width, bpp, depth),
                  height: passes[i].height,
                  lineIndex: 0,
                });
              }
            } else {
              this._images.push({
                byteWidth: getByteWidth(width, bpp, depth),
                height: height,
                lineIndex: 0,
              });
            }
          
            // when filtering the line we look at the pixel to the left
            // the spec also says it is done on a byte level regardless of the number of pixels
            // so if the depth is byte compatible (8 or 16) we subtract the bpp in order to compare back
            // a pixel rather than just a different byte part. However if we are sub byte, we ignore.
            if (depth === 8) {
              this._xComparison = bpp;
            } else if (depth === 16) {
              this._xComparison = bpp * 2;
            } else {
              this._xComparison = 1;
            }
          });
          
          Filter.prototype.start = function () {
            this.read(
              this._images[this._imageIndex].byteWidth + 1,
              this._reverseFilterLine.bind(this)
            );
          };
          
          Filter.prototype._unFilterType1 = function (
            rawData,
            unfilteredLine,
            byteWidth
          ) {
            let xComparison = this._xComparison;
            let xBiggerThan = xComparison - 1;
          
            for (let x = 0; x < byteWidth; x++) {
              let rawByte = rawData[1 + x];
              let f1Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
              unfilteredLine[x] = rawByte + f1Left;
            }
          };
          
          Filter.prototype._unFilterType2 = function (
            rawData,
            unfilteredLine,
            byteWidth
          ) {
            let lastLine = this._lastLine;
          
            for (let x = 0; x < byteWidth; x++) {
              let rawByte = rawData[1 + x];
              let f2Up = lastLine ? lastLine[x] : 0;
              unfilteredLine[x] = rawByte + f2Up;
            }
          };
          
          Filter.prototype._unFilterType3 = function (
            rawData,
            unfilteredLine,
            byteWidth
          ) {
            let xComparison = this._xComparison;
            let xBiggerThan = xComparison - 1;
            let lastLine = this._lastLine;
          
            for (let x = 0; x < byteWidth; x++) {
              let rawByte = rawData[1 + x];
              let f3Up = lastLine ? lastLine[x] : 0;
              let f3Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
              let f3Add = Math.floor((f3Left + f3Up) / 2);
              unfilteredLine[x] = rawByte + f3Add;
            }
          };
          
          Filter.prototype._unFilterType4 = function (
            rawData,
            unfilteredLine,
            byteWidth
          ) {
            let xComparison = this._xComparison;
            let xBiggerThan = xComparison - 1;
            let lastLine = this._lastLine;
          
            for (let x = 0; x < byteWidth; x++) {
              let rawByte = rawData[1 + x];
              let f4Up = lastLine ? lastLine[x] : 0;
              let f4Left = x > xBiggerThan ? unfilteredLine[x - xComparison] : 0;
              let f4UpLeft = x > xBiggerThan && lastLine ? lastLine[x - xComparison] : 0;
              let f4Add = paethPredictor(f4Left, f4Up, f4UpLeft);
              unfilteredLine[x] = rawByte + f4Add;
            }
          };
          
          Filter.prototype._reverseFilterLine = function (rawData) {
            let filter = rawData[0];
            let unfilteredLine;
            let currentImage = this._images[this._imageIndex];
            let byteWidth = currentImage.byteWidth;
          
            if (filter === 0) {
              unfilteredLine = rawData.slice(1, byteWidth + 1);
            } else {
              unfilteredLine = Buffer.alloc(byteWidth);
          
              switch (filter) {
                case 1:
                  this._unFilterType1(rawData, unfilteredLine, byteWidth);
                  break;
                case 2:
                  this._unFilterType2(rawData, unfilteredLine, byteWidth);
                  break;
                case 3:
                  this._unFilterType3(rawData, unfilteredLine, byteWidth);
                  break;
                case 4:
                  this._unFilterType4(rawData, unfilteredLine, byteWidth);
                  break;
                default:
                  throw new Error("Unrecognised filter type - " + filter);
              }
            }
          
            this.write(unfilteredLine);
          
            currentImage.lineIndex++;
            if (currentImage.lineIndex >= currentImage.height) {
              this._lastLine = null;
              this._imageIndex++;
              currentImage = this._images[this._imageIndex];
            } else {
              this._lastLine = unfilteredLine;
            }
          
            if (currentImage) {
              // read, using the byte width that may be from the new current image
              this.read(currentImage.byteWidth + 1, this._reverseFilterLine.bind(this));
            } else {
              this._lastLine = null;
              this.complete();
            }
          };
          
        • format-normaliser.js 2.3 KB
          "use strict";
          
          function dePalette(indata, outdata, width, height, palette) {
            let pxPos = 0;
            // use values from palette
            for (let y = 0; y < height; y++) {
              for (let x = 0; x < width; x++) {
                let color = palette[indata[pxPos]];
          
                if (!color) {
                  throw new Error("index " + indata[pxPos] + " not in palette");
                }
          
                for (let i = 0; i < 4; i++) {
                  outdata[pxPos + i] = color[i];
                }
                pxPos += 4;
              }
            }
          }
          
          function replaceTransparentColor(indata, outdata, width, height, transColor) {
            let pxPos = 0;
            for (let y = 0; y < height; y++) {
              for (let x = 0; x < width; x++) {
                let makeTrans = false;
          
                if (transColor.length === 1) {
                  if (transColor[0] === indata[pxPos]) {
                    makeTrans = true;
                  }
                } else if (
                  transColor[0] === indata[pxPos] &&
                  transColor[1] === indata[pxPos + 1] &&
                  transColor[2] === indata[pxPos + 2]
                ) {
                  makeTrans = true;
                }
                if (makeTrans) {
                  for (let i = 0; i < 4; i++) {
                    outdata[pxPos + i] = 0;
                  }
                }
                pxPos += 4;
              }
            }
          }
          
          function scaleDepth(indata, outdata, width, height, depth) {
            let maxOutSample = 255;
            let maxInSample = Math.pow(2, depth) - 1;
            let pxPos = 0;
          
            for (let y = 0; y < height; y++) {
              for (let x = 0; x < width; x++) {
                for (let i = 0; i < 4; i++) {
                  outdata[pxPos + i] = Math.floor(
                    (indata[pxPos + i] * maxOutSample) / maxInSample + 0.5
                  );
                }
                pxPos += 4;
              }
            }
          }
          
          module.exports = function (indata, imageData, skipRescale = false) {
            let depth = imageData.depth;
            let width = imageData.width;
            let height = imageData.height;
            let colorType = imageData.colorType;
            let transColor = imageData.transColor;
            let palette = imageData.palette;
          
            let outdata = indata; // only different for 16 bits
          
            if (colorType === 3) {
              // paletted
              dePalette(indata, outdata, width, height, palette);
            } else {
              if (transColor) {
                replaceTransparentColor(indata, outdata, width, height, transColor);
              }
              // if it needs scaling
              if (depth !== 8 && !skipRescale) {
                // if we need to change the buffer size
                if (depth === 16) {
                  outdata = Buffer.alloc(width * height * 4);
                }
                scaleDepth(indata, outdata, width, height, depth);
              }
            }
            return outdata;
          };
          
        • interlace.js 2 KB
          "use strict";
          
          // Adam 7
          //   0 1 2 3 4 5 6 7
          // 0 x 6 4 6 x 6 4 6
          // 1 7 7 7 7 7 7 7 7
          // 2 5 6 5 6 5 6 5 6
          // 3 7 7 7 7 7 7 7 7
          // 4 3 6 4 6 3 6 4 6
          // 5 7 7 7 7 7 7 7 7
          // 6 5 6 5 6 5 6 5 6
          // 7 7 7 7 7 7 7 7 7
          
          let imagePasses = [
            {
              // pass 1 - 1px
              x: [0],
              y: [0],
            },
            {
              // pass 2 - 1px
              x: [4],
              y: [0],
            },
            {
              // pass 3 - 2px
              x: [0, 4],
              y: [4],
            },
            {
              // pass 4 - 4px
              x: [2, 6],
              y: [0, 4],
            },
            {
              // pass 5 - 8px
              x: [0, 2, 4, 6],
              y: [2, 6],
            },
            {
              // pass 6 - 16px
              x: [1, 3, 5, 7],
              y: [0, 2, 4, 6],
            },
            {
              // pass 7 - 32px
              x: [0, 1, 2, 3, 4, 5, 6, 7],
              y: [1, 3, 5, 7],
            },
          ];
          
          exports.getImagePasses = function (width, height) {
            let images = [];
            let xLeftOver = width % 8;
            let yLeftOver = height % 8;
            let xRepeats = (width - xLeftOver) / 8;
            let yRepeats = (height - yLeftOver) / 8;
            for (let i = 0; i < imagePasses.length; i++) {
              let pass = imagePasses[i];
              let passWidth = xRepeats * pass.x.length;
              let passHeight = yRepeats * pass.y.length;
              for (let j = 0; j < pass.x.length; j++) {
                if (pass.x[j] < xLeftOver) {
                  passWidth++;
                } else {
                  break;
                }
              }
              for (let j = 0; j < pass.y.length; j++) {
                if (pass.y[j] < yLeftOver) {
                  passHeight++;
                } else {
                  break;
                }
              }
              if (passWidth > 0 && passHeight > 0) {
                images.push({ width: passWidth, height: passHeight, index: i });
              }
            }
            return images;
          };
          
          exports.getInterlaceIterator = function (width) {
            return function (x, y, pass) {
              let outerXLeftOver = x % imagePasses[pass].x.length;
              let outerX =
                ((x - outerXLeftOver) / imagePasses[pass].x.length) * 8 +
                imagePasses[pass].x[outerXLeftOver];
              let outerYLeftOver = y % imagePasses[pass].y.length;
              let outerY =
                ((y - outerYLeftOver) / imagePasses[pass].y.length) * 8 +
                imagePasses[pass].y[outerYLeftOver];
              return outerX * 4 + outerY * width * 4;
            };
          };
          
        • packer-async.js 1.1 KB
          "use strict";
          
          let util = require("util");
          let Stream = require("stream");
          let constants = require("./constants");
          let Packer = require("./packer");
          
          let PackerAsync = (module.exports = function (opt) {
            Stream.call(this);
          
            let options = opt || {};
          
            this._packer = new Packer(options);
            this._deflate = this._packer.createDeflate();
          
            this.readable = true;
          });
          util.inherits(PackerAsync, Stream);
          
          PackerAsync.prototype.pack = function (data, width, height, gamma) {
            // Signature
            this.emit("data", Buffer.from(constants.PNG_SIGNATURE));
            this.emit("data", this._packer.packIHDR(width, height));
          
            if (gamma) {
              this.emit("data", this._packer.packGAMA(gamma));
            }
          
            let filteredData = this._packer.filterData(data, width, height);
          
            // compress it
            this._deflate.on("error", this.emit.bind(this, "error"));
          
            this._deflate.on(
              "data",
              function (compressedData) {
                this.emit("data", this._packer.packIDAT(compressedData));
              }.bind(this)
            );
          
            this._deflate.on(
              "end",
              function () {
                this.emit("data", this._packer.packIEND());
                this.emit("end");
              }.bind(this)
            );
          
            this._deflate.end(filteredData);
          };
          
        • packer-sync.js 1.2 KB
          "use strict";
          
          let hasSyncZlib = true;
          let zlib = require("zlib");
          if (!zlib.deflateSync) {
            hasSyncZlib = false;
          }
          let constants = require("./constants");
          let Packer = require("./packer");
          
          module.exports = function (metaData, opt) {
            if (!hasSyncZlib) {
              throw new Error(
                "To use the sync capability of this library in old node versions, please pin pngjs to v2.3.0"
              );
            }
          
            let options = opt || {};
          
            let packer = new Packer(options);
          
            let chunks = [];
          
            // Signature
            chunks.push(Buffer.from(constants.PNG_SIGNATURE));
          
            // Header
            chunks.push(packer.packIHDR(metaData.width, metaData.height));
          
            if (metaData.gamma) {
              chunks.push(packer.packGAMA(metaData.gamma));
            }
          
            let filteredData = packer.filterData(
              metaData.data,
              metaData.width,
              metaData.height
            );
          
            // compress it
            let compressedData = zlib.deflateSync(
              filteredData,
              packer.getDeflateOptions()
            );
            filteredData = null;
          
            if (!compressedData || !compressedData.length) {
              throw new Error("bad png - invalid compressed data response");
            }
            chunks.push(packer.packIDAT(compressedData));
          
            // End
            chunks.push(packer.packIEND());
          
            return Buffer.concat(chunks);
          };
          
        • packer.js 3.6 KB
          "use strict";
          
          let constants = require("./constants");
          let CrcStream = require("./crc");
          let bitPacker = require("./bitpacker");
          let filter = require("./filter-pack");
          let zlib = require("zlib");
          
          let Packer = (module.exports = function (options) {
            this._options = options;
          
            options.deflateChunkSize = options.deflateChunkSize || 32 * 1024;
            options.deflateLevel =
              options.deflateLevel != null ? options.deflateLevel : 9;
            options.deflateStrategy =
              options.deflateStrategy != null ? options.deflateStrategy : 3;
            options.inputHasAlpha =
              options.inputHasAlpha != null ? options.inputHasAlpha : true;
            options.deflateFactory = options.deflateFactory || zlib.createDeflate;
            options.bitDepth = options.bitDepth || 8;
            // This is outputColorType
            options.colorType =
              typeof options.colorType === "number"
                ? options.colorType
                : constants.COLORTYPE_COLOR_ALPHA;
            options.inputColorType =
              typeof options.inputColorType === "number"
                ? options.inputColorType
                : constants.COLORTYPE_COLOR_ALPHA;
          
            if (
              [
                constants.COLORTYPE_GRAYSCALE,
                constants.COLORTYPE_COLOR,
                constants.COLORTYPE_COLOR_ALPHA,
                constants.COLORTYPE_ALPHA,
              ].indexOf(options.colorType) === -1
            ) {
              throw new Error(
                "option color type:" + options.colorType + " is not supported at present"
              );
            }
            if (
              [
                constants.COLORTYPE_GRAYSCALE,
                constants.COLORTYPE_COLOR,
                constants.COLORTYPE_COLOR_ALPHA,
                constants.COLORTYPE_ALPHA,
              ].indexOf(options.inputColorType) === -1
            ) {
              throw new Error(
                "option input color type:" +
                  options.inputColorType +
                  " is not supported at present"
              );
            }
            if (options.bitDepth !== 8 && options.bitDepth !== 16) {
              throw new Error(
                "option bit depth:" + options.bitDepth + " is not supported at present"
              );
            }
          });
          
          Packer.prototype.getDeflateOptions = function () {
            return {
              chunkSize: this._options.deflateChunkSize,
              level: this._options.deflateLevel,
              strategy: this._options.deflateStrategy,
            };
          };
          
          Packer.prototype.createDeflate = function () {
            return this._options.deflateFactory(this.getDeflateOptions());
          };
          
          Packer.prototype.filterData = function (data, width, height) {
            // convert to correct format for filtering (e.g. right bpp and bit depth)
            let packedData = bitPacker(data, width, height, this._options);
          
            // filter pixel data
            let bpp = constants.COLORTYPE_TO_BPP_MAP[this._options.colorType];
            let filteredData = filter(packedData, width, height, this._options, bpp);
            return filteredData;
          };
          
          Packer.prototype._packChunk = function (type, data) {
            let len = data ? data.length : 0;
            let buf = Buffer.alloc(len + 12);
          
            buf.writeUInt32BE(len, 0);
            buf.writeUInt32BE(type, 4);
          
            if (data) {
              data.copy(buf, 8);
            }
          
            buf.writeInt32BE(
              CrcStream.crc32(buf.slice(4, buf.length - 4)),
              buf.length - 4
            );
            return buf;
          };
          
          Packer.prototype.packGAMA = function (gamma) {
            let buf = Buffer.alloc(4);
            buf.writeUInt32BE(Math.floor(gamma * constants.GAMMA_DIVISION), 0);
            return this._packChunk(constants.TYPE_gAMA, buf);
          };
          
          Packer.prototype.packIHDR = function (width, height) {
            let buf = Buffer.alloc(13);
            buf.writeUInt32BE(width, 0);
            buf.writeUInt32BE(height, 4);
            buf[8] = this._options.bitDepth; // Bit depth
            buf[9] = this._options.colorType; // colorType
            buf[10] = 0; // compression
            buf[11] = 0; // filter
            buf[12] = 0; // interlace
          
            return this._packChunk(constants.TYPE_IHDR, buf);
          };
          
          Packer.prototype.packIDAT = function (data) {
            return this._packChunk(constants.TYPE_IDAT, data);
          };
          
          Packer.prototype.packIEND = function () {
            return this._packChunk(constants.TYPE_IEND, null);
          };
          
        • paeth-predictor.js 372 B
          "use strict";
          
          module.exports = function paethPredictor(left, above, upLeft) {
            let paeth = left + above - upLeft;
            let pLeft = Math.abs(paeth - left);
            let pAbove = Math.abs(paeth - above);
            let pUpLeft = Math.abs(paeth - upLeft);
          
            if (pLeft <= pAbove && pLeft <= pUpLeft) {
              return left;
            }
            if (pAbove <= pUpLeft) {
              return above;
            }
            return upLeft;
          };
          
        • parser-async.js 4.3 KB
          "use strict";
          
          let util = require("util");
          let zlib = require("zlib");
          let ChunkStream = require("./chunkstream");
          let FilterAsync = require("./filter-parse-async");
          let Parser = require("./parser");
          let bitmapper = require("./bitmapper");
          let formatNormaliser = require("./format-normaliser");
          
          let ParserAsync = (module.exports = function (options) {
            ChunkStream.call(this);
          
            this._parser = new Parser(options, {
              read: this.read.bind(this),
              error: this._handleError.bind(this),
              metadata: this._handleMetaData.bind(this),
              gamma: this.emit.bind(this, "gamma"),
              palette: this._handlePalette.bind(this),
              transColor: this._handleTransColor.bind(this),
              finished: this._finished.bind(this),
              inflateData: this._inflateData.bind(this),
              simpleTransparency: this._simpleTransparency.bind(this),
              headersFinished: this._headersFinished.bind(this),
            });
            this._options = options;
            this.writable = true;
          
            this._parser.start();
          });
          util.inherits(ParserAsync, ChunkStream);
          
          ParserAsync.prototype._handleError = function (err) {
            this.emit("error", err);
          
            this.writable = false;
          
            this.destroy();
          
            if (this._inflate && this._inflate.destroy) {
              this._inflate.destroy();
            }
          
            if (this._filter) {
              this._filter.destroy();
              // For backward compatibility with Node 7 and below.
              // Suppress errors due to _inflate calling write() even after
              // it's destroy()'ed.
              this._filter.on("error", function () {});
            }
          
            this.errord = true;
          };
          
          ParserAsync.prototype._inflateData = function (data) {
            if (!this._inflate) {
              if (this._bitmapInfo.interlace) {
                this._inflate = zlib.createInflate();
          
                this._inflate.on("error", this.emit.bind(this, "error"));
                this._filter.on("complete", this._complete.bind(this));
          
                this._inflate.pipe(this._filter);
              } else {
                let rowSize =
                  ((this._bitmapInfo.width *
                    this._bitmapInfo.bpp *
                    this._bitmapInfo.depth +
                    7) >>
                    3) +
                  1;
                let imageSize = rowSize * this._bitmapInfo.height;
                let chunkSize = Math.max(imageSize, zlib.Z_MIN_CHUNK);
          
                this._inflate = zlib.createInflate({ chunkSize: chunkSize });
                let leftToInflate = imageSize;
          
                let emitError = this.emit.bind(this, "error");
                this._inflate.on("error", function (err) {
                  if (!leftToInflate) {
                    return;
                  }
          
                  emitError(err);
                });
                this._filter.on("complete", this._complete.bind(this));
          
                let filterWrite = this._filter.write.bind(this._filter);
                this._inflate.on("data", function (chunk) {
                  if (!leftToInflate) {
                    return;
                  }
          
                  if (chunk.length > leftToInflate) {
                    chunk = chunk.slice(0, leftToInflate);
                  }
          
                  leftToInflate -= chunk.length;
          
                  filterWrite(chunk);
                });
          
                this._inflate.on("end", this._filter.end.bind(this._filter));
              }
            }
            this._inflate.write(data);
          };
          
          ParserAsync.prototype._handleMetaData = function (metaData) {
            this._metaData = metaData;
            this._bitmapInfo = Object.create(metaData);
          
            this._filter = new FilterAsync(this._bitmapInfo);
          };
          
          ParserAsync.prototype._handleTransColor = function (transColor) {
            this._bitmapInfo.transColor = transColor;
          };
          
          ParserAsync.prototype._handlePalette = function (palette) {
            this._bitmapInfo.palette = palette;
          };
          
          ParserAsync.prototype._simpleTransparency = function () {
            this._metaData.alpha = true;
          };
          
          ParserAsync.prototype._headersFinished = function () {
            // Up until this point, we don't know if we have a tRNS chunk (alpha)
            // so we can't emit metadata any earlier
            this.emit("metadata", this._metaData);
          };
          
          ParserAsync.prototype._finished = function () {
            if (this.errord) {
              return;
            }
          
            if (!this._inflate) {
              this.emit("error", "No Inflate block");
            } else {
              // no more data to inflate
              this._inflate.end();
            }
          };
          
          ParserAsync.prototype._complete = function (filteredData) {
            if (this.errord) {
              return;
            }
          
            let normalisedBitmapData;
          
            try {
              let bitmapData = bitmapper.dataToBitMap(filteredData, this._bitmapInfo);
          
              normalisedBitmapData = formatNormaliser(
                bitmapData,
                this._bitmapInfo,
                this._options.skipRescale
              );
              bitmapData = null;
            } catch (ex) {
              this._handleError(ex);
              return;
            }
          
            this.emit("parsed", normalisedBitmapData);
          };
          
        • parser-sync.js 2.5 KB
          "use strict";
          
          let hasSyncZlib = true;
          let zlib = require("zlib");
          let inflateSync = require("./sync-inflate");
          if (!zlib.deflateSync) {
            hasSyncZlib = false;
          }
          let SyncReader = require("./sync-reader");
          let FilterSync = require("./filter-parse-sync");
          let Parser = require("./parser");
          let bitmapper = require("./bitmapper");
          let formatNormaliser = require("./format-normaliser");
          
          module.exports = function (buffer, options) {
            if (!hasSyncZlib) {
              throw new Error(
                "To use the sync capability of this library in old node versions, please pin pngjs to v2.3.0"
              );
            }
          
            let err;
            function handleError(_err_) {
              err = _err_;
            }
          
            let metaData;
            function handleMetaData(_metaData_) {
              metaData = _metaData_;
            }
          
            function handleTransColor(transColor) {
              metaData.transColor = transColor;
            }
          
            function handlePalette(palette) {
              metaData.palette = palette;
            }
          
            function handleSimpleTransparency() {
              metaData.alpha = true;
            }
          
            let gamma;
            function handleGamma(_gamma_) {
              gamma = _gamma_;
            }
          
            let inflateDataList = [];
            function handleInflateData(inflatedData) {
              inflateDataList.push(inflatedData);
            }
          
            let reader = new SyncReader(buffer);
          
            let parser = new Parser(options, {
              read: reader.read.bind(reader),
              error: handleError,
              metadata: handleMetaData,
              gamma: handleGamma,
              palette: handlePalette,
              transColor: handleTransColor,
              inflateData: handleInflateData,
              simpleTransparency: handleSimpleTransparency,
            });
          
            parser.start();
            reader.process();
          
            if (err) {
              throw err;
            }
          
            //join together the inflate datas
            let inflateData = Buffer.concat(inflateDataList);
            inflateDataList.length = 0;
          
            let inflatedData;
            if (metaData.interlace) {
              inflatedData = zlib.inflateSync(inflateData);
            } else {
              let rowSize =
                ((metaData.width * metaData.bpp * metaData.depth + 7) >> 3) + 1;
              let imageSize = rowSize * metaData.height;
              inflatedData = inflateSync(inflateData, {
                chunkSize: imageSize,
                maxLength: imageSize,
              });
            }
            inflateData = null;
          
            if (!inflatedData || !inflatedData.length) {
              throw new Error("bad png - invalid inflate data response");
            }
          
            let unfilteredData = FilterSync.process(inflatedData, metaData);
            inflateData = null;
          
            let bitmapData = bitmapper.dataToBitMap(unfilteredData, metaData);
            unfilteredData = null;
          
            let normalisedBitmapData = formatNormaliser(
              bitmapData,
              metaData,
              options.skipRescale
            );
          
            metaData.data = normalisedBitmapData;
            metaData.gamma = gamma || 0;
          
            return metaData;
          };
          
        • parser.js 7.5 KB
          "use strict";
          
          let constants = require("./constants");
          let CrcCalculator = require("./crc");
          
          let Parser = (module.exports = function (options, dependencies) {
            this._options = options;
            options.checkCRC = options.checkCRC !== false;
          
            this._hasIHDR = false;
            this._hasIEND = false;
            this._emittedHeadersFinished = false;
          
            // input flags/metadata
            this._palette = [];
            this._colorType = 0;
          
            this._chunks = {};
            this._chunks[constants.TYPE_IHDR] = this._handleIHDR.bind(this);
            this._chunks[constants.TYPE_IEND] = this._handleIEND.bind(this);
            this._chunks[constants.TYPE_IDAT] = this._handleIDAT.bind(this);
            this._chunks[constants.TYPE_PLTE] = this._handlePLTE.bind(this);
            this._chunks[constants.TYPE_tRNS] = this._handleTRNS.bind(this);
            this._chunks[constants.TYPE_gAMA] = this._handleGAMA.bind(this);
          
            this.read = dependencies.read;
            this.error = dependencies.error;
            this.metadata = dependencies.metadata;
            this.gamma = dependencies.gamma;
            this.transColor = dependencies.transColor;
            this.palette = dependencies.palette;
            this.parsed = dependencies.parsed;
            this.inflateData = dependencies.inflateData;
            this.finished = dependencies.finished;
            this.simpleTransparency = dependencies.simpleTransparency;
            this.headersFinished = dependencies.headersFinished || function () {};
          });
          
          Parser.prototype.start = function () {
            this.read(constants.PNG_SIGNATURE.length, this._parseSignature.bind(this));
          };
          
          Parser.prototype._parseSignature = function (data) {
            let signature = constants.PNG_SIGNATURE;
          
            for (let i = 0; i < signature.length; i++) {
              if (data[i] !== signature[i]) {
                this.error(new Error("Invalid file signature"));
                return;
              }
            }
            this.read(8, this._parseChunkBegin.bind(this));
          };
          
          Parser.prototype._parseChunkBegin = function (data) {
            // chunk content length
            let length = data.readUInt32BE(0);
          
            // chunk type
            let type = data.readUInt32BE(4);
            let name = "";
            for (let i = 4; i < 8; i++) {
              name += String.fromCharCode(data[i]);
            }
          
            //console.log('chunk ', name, length);
          
            // chunk flags
            let ancillary = Boolean(data[4] & 0x20); // or critical
            //    priv = Boolean(data[5] & 0x20), // or public
            //    safeToCopy = Boolean(data[7] & 0x20); // or unsafe
          
            if (!this._hasIHDR && type !== constants.TYPE_IHDR) {
              this.error(new Error("Expected IHDR on beggining"));
              return;
            }
          
            this._crc = new CrcCalculator();
            this._crc.write(Buffer.from(name));
          
            if (this._chunks[type]) {
              return this._chunks[type](length);
            }
          
            if (!ancillary) {
              this.error(new Error("Unsupported critical chunk type " + name));
              return;
            }
          
            this.read(length + 4, this._skipChunk.bind(this));
          };
          
          Parser.prototype._skipChunk = function (/*data*/) {
            this.read(8, this._parseChunkBegin.bind(this));
          };
          
          Parser.prototype._handleChunkEnd = function () {
            this.read(4, this._parseChunkEnd.bind(this));
          };
          
          Parser.prototype._parseChunkEnd = function (data) {
            let fileCrc = data.readInt32BE(0);
            let calcCrc = this._crc.crc32();
          
            // check CRC
            if (this._options.checkCRC && calcCrc !== fileCrc) {
              this.error(new Error("Crc error - " + fileCrc + " - " + calcCrc));
              return;
            }
          
            if (!this._hasIEND) {
              this.read(8, this._parseChunkBegin.bind(this));
            }
          };
          
          Parser.prototype._handleIHDR = function (length) {
            this.read(length, this._parseIHDR.bind(this));
          };
          Parser.prototype._parseIHDR = function (data) {
            this._crc.write(data);
          
            let width = data.readUInt32BE(0);
            let height = data.readUInt32BE(4);
            let depth = data[8];
            let colorType = data[9]; // bits: 1 palette, 2 color, 4 alpha
            let compr = data[10];
            let filter = data[11];
            let interlace = data[12];
          
            // console.log('    width', width, 'height', height,
            //     'depth', depth, 'colorType', colorType,
            //     'compr', compr, 'filter', filter, 'interlace', interlace
            // );
          
            if (
              depth !== 8 &&
              depth !== 4 &&
              depth !== 2 &&
              depth !== 1 &&
              depth !== 16
            ) {
              this.error(new Error("Unsupported bit depth " + depth));
              return;
            }
            if (!(colorType in constants.COLORTYPE_TO_BPP_MAP)) {
              this.error(new Error("Unsupported color type"));
              return;
            }
            if (compr !== 0) {
              this.error(new Error("Unsupported compression method"));
              return;
            }
            if (filter !== 0) {
              this.error(new Error("Unsupported filter method"));
              return;
            }
            if (interlace !== 0 && interlace !== 1) {
              this.error(new Error("Unsupported interlace method"));
              return;
            }
          
            this._colorType = colorType;
          
            let bpp = constants.COLORTYPE_TO_BPP_MAP[this._colorType];
          
            this._hasIHDR = true;
          
            this.metadata({
              width: width,
              height: height,
              depth: depth,
              interlace: Boolean(interlace),
              palette: Boolean(colorType & constants.COLORTYPE_PALETTE),
              color: Boolean(colorType & constants.COLORTYPE_COLOR),
              alpha: Boolean(colorType & constants.COLORTYPE_ALPHA),
              bpp: bpp,
              colorType: colorType,
            });
          
            this._handleChunkEnd();
          };
          
          Parser.prototype._handlePLTE = function (length) {
            this.read(length, this._parsePLTE.bind(this));
          };
          Parser.prototype._parsePLTE = function (data) {
            this._crc.write(data);
          
            let entries = Math.floor(data.length / 3);
            // console.log('Palette:', entries);
          
            for (let i = 0; i < entries; i++) {
              this._palette.push([data[i * 3], data[i * 3 + 1], data[i * 3 + 2], 0xff]);
            }
          
            this.palette(this._palette);
          
            this._handleChunkEnd();
          };
          
          Parser.prototype._handleTRNS = function (length) {
            this.simpleTransparency();
            this.read(length, this._parseTRNS.bind(this));
          };
          Parser.prototype._parseTRNS = function (data) {
            this._crc.write(data);
          
            // palette
            if (this._colorType === constants.COLORTYPE_PALETTE_COLOR) {
              if (this._palette.length === 0) {
                this.error(new Error("Transparency chunk must be after palette"));
                return;
              }
              if (data.length > this._palette.length) {
                this.error(new Error("More transparent colors than palette size"));
                return;
              }
              for (let i = 0; i < data.length; i++) {
                this._palette[i][3] = data[i];
              }
              this.palette(this._palette);
            }
          
            // for colorType 0 (grayscale) and 2 (rgb)
            // there might be one gray/color defined as transparent
            if (this._colorType === constants.COLORTYPE_GRAYSCALE) {
              // grey, 2 bytes
              this.transColor([data.readUInt16BE(0)]);
            }
            if (this._colorType === constants.COLORTYPE_COLOR) {
              this.transColor([
                data.readUInt16BE(0),
                data.readUInt16BE(2),
                data.readUInt16BE(4),
              ]);
            }
          
            this._handleChunkEnd();
          };
          
          Parser.prototype._handleGAMA = function (length) {
            this.read(length, this._parseGAMA.bind(this));
          };
          Parser.prototype._parseGAMA = function (data) {
            this._crc.write(data);
            this.gamma(data.readUInt32BE(0) / constants.GAMMA_DIVISION);
          
            this._handleChunkEnd();
          };
          
          Parser.prototype._handleIDAT = function (length) {
            if (!this._emittedHeadersFinished) {
              this._emittedHeadersFinished = true;
              this.headersFinished();
            }
            this.read(-length, this._parseIDAT.bind(this, length));
          };
          Parser.prototype._parseIDAT = function (length, data) {
            this._crc.write(data);
          
            if (
              this._colorType === constants.COLORTYPE_PALETTE_COLOR &&
              this._palette.length === 0
            ) {
              throw new Error("Expected palette not found");
            }
          
            this.inflateData(data);
            let leftOverLength = length - data.length;
          
            if (leftOverLength > 0) {
              this._handleIDAT(leftOverLength);
            } else {
              this._handleChunkEnd();
            }
          };
          
          Parser.prototype._handleIEND = function (length) {
            this.read(length, this._parseIEND.bind(this));
          };
          Parser.prototype._parseIEND = function (data) {
            this._crc.write(data);
          
            this._hasIEND = true;
            this._handleChunkEnd();
          
            if (this.finished) {
              this.finished();
            }
          };
          
        • png-sync.js 252 B
          "use strict";
          
          let parse = require("./parser-sync");
          let pack = require("./packer-sync");
          
          exports.read = function (buffer, options) {
            return parse(buffer, options || {});
          };
          
          exports.write = function (png, options) {
            return pack(png, options);
          };
          
        • png.js 4.3 KB
          "use strict";
          
          let util = require("util");
          let Stream = require("stream");
          let Parser = require("./parser-async");
          let Packer = require("./packer-async");
          let PNGSync = require("./png-sync");
          
          let PNG = (exports.PNG = function (options) {
            Stream.call(this);
          
            options = options || {}; // eslint-disable-line no-param-reassign
          
            // coerce pixel dimensions to integers (also coerces undefined -> 0):
            this.width = options.width | 0;
            this.height = options.height | 0;
          
            this.data =
              this.width > 0 && this.height > 0
                ? Buffer.alloc(4 * this.width * this.height)
                : null;
          
            if (options.fill && this.data) {
              this.data.fill(0);
            }
          
            this.gamma = 0;
            this.readable = this.writable = true;
          
            this._parser = new Parser(options);
          
            this._parser.on("error", this.emit.bind(this, "error"));
            this._parser.on("close", this._handleClose.bind(this));
            this._parser.on("metadata", this._metadata.bind(this));
            this._parser.on("gamma", this._gamma.bind(this));
            this._parser.on(
              "parsed",
              function (data) {
                this.data = data;
                this.emit("parsed", data);
              }.bind(this)
            );
          
            this._packer = new Packer(options);
            this._packer.on("data", this.emit.bind(this, "data"));
            this._packer.on("end", this.emit.bind(this, "end"));
            this._parser.on("close", this._handleClose.bind(this));
            this._packer.on("error", this.emit.bind(this, "error"));
          });
          util.inherits(PNG, Stream);
          
          PNG.sync = PNGSync;
          
          PNG.prototype.pack = function () {
            if (!this.data || !this.data.length) {
              this.emit("error", "No data provided");
              return this;
            }
          
            process.nextTick(
              function () {
                this._packer.pack(this.data, this.width, this.height, this.gamma);
              }.bind(this)
            );
          
            return this;
          };
          
          PNG.prototype.parse = function (data, callback) {
            if (callback) {
              let onParsed, onError;
          
              onParsed = function (parsedData) {
                this.removeListener("error", onError);
          
                this.data = parsedData;
                callback(null, this);
              }.bind(this);
          
              onError = function (err) {
                this.removeListener("parsed", onParsed);
          
                callback(err, null);
              }.bind(this);
          
              this.once("parsed", onParsed);
              this.once("error", onError);
            }
          
            this.end(data);
            return this;
          };
          
          PNG.prototype.write = function (data) {
            this._parser.write(data);
            return true;
          };
          
          PNG.prototype.end = function (data) {
            this._parser.end(data);
          };
          
          PNG.prototype._metadata = function (metadata) {
            this.width = metadata.width;
            this.height = metadata.height;
          
            this.emit("metadata", metadata);
          };
          
          PNG.prototype._gamma = function (gamma) {
            this.gamma = gamma;
          };
          
          PNG.prototype._handleClose = function () {
            if (!this._parser.writable && !this._packer.readable) {
              this.emit("close");
            }
          };
          
          PNG.bitblt = function (src, dst, srcX, srcY, width, height, deltaX, deltaY) {
            // eslint-disable-line max-params
            // coerce pixel dimensions to integers (also coerces undefined -> 0):
            /* eslint-disable no-param-reassign */
            srcX |= 0;
            srcY |= 0;
            width |= 0;
            height |= 0;
            deltaX |= 0;
            deltaY |= 0;
            /* eslint-enable no-param-reassign */
          
            if (
              srcX > src.width ||
              srcY > src.height ||
              srcX + width > src.width ||
              srcY + height > src.height
            ) {
              throw new Error("bitblt reading outside image");
            }
          
            if (
              deltaX > dst.width ||
              deltaY > dst.height ||
              deltaX + width > dst.width ||
              deltaY + height > dst.height
            ) {
              throw new Error("bitblt writing outside image");
            }
          
            for (let y = 0; y < height; y++) {
              src.data.copy(
                dst.data,
                ((deltaY + y) * dst.width + deltaX) << 2,
                ((srcY + y) * src.width + srcX) << 2,
                ((srcY + y) * src.width + srcX + width) << 2
              );
            }
          };
          
          PNG.prototype.bitblt = function (
            dst,
            srcX,
            srcY,
            width,
            height,
            deltaX,
            deltaY
          ) {
            // eslint-disable-line max-params
          
            PNG.bitblt(this, dst, srcX, srcY, width, height, deltaX, deltaY);
            return this;
          };
          
          PNG.adjustGamma = function (src) {
            if (src.gamma) {
              for (let y = 0; y < src.height; y++) {
                for (let x = 0; x < src.width; x++) {
                  let idx = (src.width * y + x) << 2;
          
                  for (let i = 0; i < 3; i++) {
                    let sample = src.data[idx + i] / 255;
                    sample = Math.pow(sample, 1 / 2.2 / src.gamma);
                    src.data[idx + i] = Math.round(sample * 255);
                  }
                }
              }
              src.gamma = 0;
            }
          };
          
          PNG.prototype.adjustGamma = function () {
            PNG.adjustGamma(this);
          };
          
        • sync-inflate.js 3.7 KB
          "use strict";
          
          let assert = require("assert").ok;
          let zlib = require("zlib");
          let util = require("util");
          
          let kMaxLength = require("buffer").kMaxLength;
          
          function Inflate(opts) {
            if (!(this instanceof Inflate)) {
              return new Inflate(opts);
            }
          
            if (opts && opts.chunkSize < zlib.Z_MIN_CHUNK) {
              opts.chunkSize = zlib.Z_MIN_CHUNK;
            }
          
            zlib.Inflate.call(this, opts);
          
            // Node 8 --> 9 compatibility check
            this._offset = this._offset === undefined ? this._outOffset : this._offset;
            this._buffer = this._buffer || this._outBuffer;
          
            if (opts && opts.maxLength != null) {
              this._maxLength = opts.maxLength;
            }
          }
          
          function createInflate(opts) {
            return new Inflate(opts);
          }
          
          function _close(engine, callback) {
            if (callback) {
              process.nextTick(callback);
            }
          
            // Caller may invoke .close after a zlib error (which will null _handle).
            if (!engine._handle) {
              return;
            }
          
            engine._handle.close();
            engine._handle = null;
          }
          
          Inflate.prototype._processChunk = function (chunk, flushFlag, asyncCb) {
            if (typeof asyncCb === "function") {
              return zlib.Inflate._processChunk.call(this, chunk, flushFlag, asyncCb);
            }
          
            let self = this;
          
            let availInBefore = chunk && chunk.length;
            let availOutBefore = this._chunkSize - this._offset;
            let leftToInflate = this._maxLength;
            let inOff = 0;
          
            let buffers = [];
            let nread = 0;
          
            let error;
            this.on("error", function (err) {
              error = err;
            });
          
            function handleChunk(availInAfter, availOutAfter) {
              if (self._hadError) {
                return;
              }
          
              let have = availOutBefore - availOutAfter;
              assert(have >= 0, "have should not go down");
          
              if (have > 0) {
                let out = self._buffer.slice(self._offset, self._offset + have);
                self._offset += have;
          
                if (out.length > leftToInflate) {
                  out = out.slice(0, leftToInflate);
                }
          
                buffers.push(out);
                nread += out.length;
                leftToInflate -= out.length;
          
                if (leftToInflate === 0) {
                  return false;
                }
              }
          
              if (availOutAfter === 0 || self._offset >= self._chunkSize) {
                availOutBefore = self._chunkSize;
                self._offset = 0;
                self._buffer = Buffer.allocUnsafe(self._chunkSize);
              }
          
              if (availOutAfter === 0) {
                inOff += availInBefore - availInAfter;
                availInBefore = availInAfter;
          
                return true;
              }
          
              return false;
            }
          
            assert(this._handle, "zlib binding closed");
            let res;
            do {
              res = this._handle.writeSync(
                flushFlag,
                chunk, // in
                inOff, // in_off
                availInBefore, // in_len
                this._buffer, // out
                this._offset, //out_off
                availOutBefore
              ); // out_len
              // Node 8 --> 9 compatibility check
              res = res || this._writeState;
            } while (!this._hadError && handleChunk(res[0], res[1]));
          
            if (this._hadError) {
              throw error;
            }
          
            if (nread >= kMaxLength) {
              _close(this);
              throw new RangeError(
                "Cannot create final Buffer. It would be larger than 0x" +
                  kMaxLength.toString(16) +
                  " bytes"
              );
            }
          
            let buf = Buffer.concat(buffers, nread);
            _close(this);
          
            return buf;
          };
          
          util.inherits(Inflate, zlib.Inflate);
          
          function zlibBufferSync(engine, buffer) {
            if (typeof buffer === "string") {
              buffer = Buffer.from(buffer);
            }
            if (!(buffer instanceof Buffer)) {
              throw new TypeError("Not a string or buffer");
            }
          
            let flushFlag = engine._finishFlushFlag;
            if (flushFlag == null) {
              flushFlag = zlib.Z_FINISH;
            }
          
            return engine._processChunk(buffer, flushFlag);
          }
          
          function inflateSync(buffer, opts) {
            return zlibBufferSync(new Inflate(opts), buffer);
          }
          
          module.exports = exports = inflateSync;
          exports.Inflate = Inflate;
          exports.createInflate = createInflate;
          exports.inflateSync = inflateSync;
          
        • sync-reader.js 1.1 KB
          "use strict";
          
          let SyncReader = (module.exports = function (buffer) {
            this._buffer = buffer;
            this._reads = [];
          });
          
          SyncReader.prototype.read = function (length, callback) {
            this._reads.push({
              length: Math.abs(length), // if length < 0 then at most this length
              allowLess: length < 0,
              func: callback,
            });
          };
          
          SyncReader.prototype.process = function () {
            // as long as there is any data and read requests
            while (this._reads.length > 0 && this._buffer.length) {
              let read = this._reads[0];
          
              if (
                this._buffer.length &&
                (this._buffer.length >= read.length || read.allowLess)
              ) {
                // ok there is any data so that we can satisfy this request
                this._reads.shift(); // == read
          
                let buf = this._buffer;
          
                this._buffer = buf.slice(read.length);
          
                read.func.call(this, buf.slice(0, read.length));
              } else {
                break;
              }
            }
          
            if (this._reads.length > 0) {
              throw new Error("There are some read requests waitng on finished stream");
            }
          
            if (this._buffer.length > 0) {
              throw new Error("unrecognised content at end of stream");
            }
          };
          
      • LICENSE 1.1 KB · in bundle
      • package.json 1.8 KB
        {
          "name": "pngjs",
          "version": "7.0.0",
          "description": "PNG encoder/decoder in pure JS, supporting any bit size & interlace, async & sync with full test suite.",
          "contributors": [
            "Alexandre Paré",
            "Gaurav Mali",
            "Gusts Kaksis",
            "Kuba Niegowski",
            "Luke Page",
            "Pietajan De Potter",
            "Steven Sojka",
            "liangzeng",
            "Michael Vogt",
            "Xin-Xin Wang",
            "toriningen",
            "Eugene Kulabuhov"
          ],
          "homepage": "https://github.com/lukeapage/pngjs",
          "keywords": [
            "PNG",
            "decoder",
            "encoder",
            "js-png",
            "node-png",
            "parser",
            "png",
            "png-js",
            "png-parse",
            "pngjs"
          ],
          "engines": {
            "node": ">=14.19.0"
          },
          "main": "./lib/png.js",
          "directories": {
            "lib": "lib",
            "example": "examples",
            "test": "test"
          },
          "files": [
            "browser.js",
            "lib/"
          ],
          "scripts": {
            "build": "yarn prepublish",
            "prepublish": "yarn browserify",
            "browserify": "browserify lib/png.js --standalone png > browser.js",
            "coverage": "nyc --reporter=lcov --reporter=text-summary tape test/*-spec.js",
            "test": "yarn lint && yarn prettier:check && tape test/*-spec.js | tap-dot && node test/run-compare",
            "lint": "eslint .",
            "prettier:write": "prettier --write .",
            "prettier:check": "prettier --check ."
          },
          "repository": {
            "type": "git",
            "url": "git://github.com/pngjs/pngjs.git"
          },
          "license": "MIT",
          "bugs": {
            "url": "https://github.com/pngjs/pngjs/issues"
          },
          "devDependencies": {
            "browserify": "17.0.0",
            "buffer-equal": "1.0.1",
            "connect": "3.7.0",
            "eslint": "8.34.0",
            "eslint-config-prettier": "8.6.0",
            "nyc": "15.1.0",
            "prettier": "2.8.4",
            "puppeteer": "19.7.1",
            "serve-static": "1.15.0",
            "tap-dot": "2.0.0",
            "tape": "5.6.3"
          }
        }
        
  • SKILL.md 10.4 KB
    ---
    name: compare-screenshots
    description: Compare screenshots against the intended design, distinguishing approved references from historical baselines. Use for iterative implementation matching, before/after visual review, objective image telemetry, or checking a lone capture for flat, empty, or badly framed content.
    ---
    
    # Compare Screenshots
    
    Judge images against the intended result. A user-approved design is the target;
    a historical baseline is only an earlier attempt and may be wrong. Metrics locate
    differences, never decide correctness. Use
    [design-with-images](../design-with-images/SKILL.md) for the full exploration-to-implementation loop.
    
    ## Workflow
    
    1. **Establish the target.** Use the user-approved reference and stated design
       requirements when available; do not replace them with your own taste. Otherwise
       derive the target from the visual requirement, what the thing depicts in reality
       and the domain skill that owns the look. Write it down in one or two
       concrete sentences ("low sun should cast long shadows east; trees fill the
       canopy; labels stay legible at this zoom").
       - If the right answer isn't clear — competing valid readings, a taste or
         product-intent call, a tradeoff only the owner can settle — **stop and ask
         the user** what the correct answer should be. Show them the comparison.
         Do not quietly default to the baseline to avoid asking; that bakes in
         whatever the baseline got wrong.
    2. **Confirm comparability** so the differences you see are real, not capture
       artifacts: same viewport, DPR, route/page, frozen time/tick, camera intent,
       UI state, data, fonts/assets where they matter. If not comparable, fix
       capture setup or compare only a crop/feature where the mismatch is harmless.
    3. **Measure the approved design.** For reference matching, read and complete
       [Reference Landmarks](references/reference-landmarks.md) before changing code
       or accepting a candidate. Then generate artifacts sized to the question:
       side-by-side, key-feature crops/zooms, grayscale, absolute grayscale heatmap,
       pixelmatch diff, per-image Sobel/edge maps, edge-difference heatmap, JSON
       metrics.
    4. **Inspect boundaries before judging the whole.** For every changed visual
       effect, inspect all sides at native scale and in matched detail crops. Include
       the effect's full fade and surrounding space; a crop ending at the component
       box hides spill. Compare top/right/bottom/left extents separately, anchored to
       visible text, rules or silhouettes rather than inferred CSS bounds. Check
       every foreground feature crossed by the effect (lines, icons, text, adjacent
       panels): brightness, color, sharpness and continuity must match the target.
       A readable line can still be incorrectly dimmed. Record each check as
       reference observation → candidate observation → pass/fix/uncertain, with its
       crop. Use the landmark table to resolve local distances and contrast;
       full-frame averages cannot settle a local defect.
    5. **Judge each divergence against the target.** For every place the two images
       differ, name what is actually there in plain terms — missing content, wrong
       camera, bad hierarchy, weak contrast, wrong depth, text overlap, layout
       shift, clipped edge, unexpected blur, style mismatch — and decide which side
       is closer to correct. The answer can be the candidate, the baseline, both
       wrong, or a genuine toss-up.
    6. **Get a neutral second opinion** for disputed or high-stakes calls: a fresh
       subagent given only the two images and neutral labels, per
       `references/subagent-visual-review.md`.
    7. **Resolve mismatches to an approved target.** When implementing a selected
       design, record material differences in spacing, shape, softness, typography
       and hierarchy; revise, recapture and repeat until resolved or the user changes
       the target. Do not silently exempt a difference because the code is simpler.
    8. **Conclude with one verdict:** candidate is less wrong (accept, and re-bless
       the baseline if one exists), baseline is less wrong (reject), both wrong
       (another pass needed — say what's still off), or unclear (ask the user).
       Accept only when every boundary/overlap check passes or has an explicit
       user-approved deviation; uncertainty requires closer evidence, not a pass.
       Overall resemblance or a positive second opinion cannot cancel a local defect.
       Never accept on a lower score alone or reject on a higher one. Never hide
       content, blur detail, crop away differences, or make the capture less
       truthful to move a number.
    
    ## Useful Metrics
    
    Pick metrics that answer the question. For full visual comparisons, report:
    
    - `mae`: mean absolute grayscale difference, 0..255, lower is closer.
    - `rmse`: grayscale root mean square error, lower is closer.
    - `diffRatio16`, `diffRatio32`, `diffRatio64`: fraction of pixels over each
      grayscale delta threshold.
    - `pixelmatchRatio`: mismatch ratio from pixelmatch over grayscale images.
    - `edgeEnergyCurrent` and `edgeEnergyCandidate`: average Sobel edge strength.
    - `edgeEnergyRatio`: candidate/current. Far below 1 usually means missing
      geometry, props, labels, or terrain; far above 1 usually means noisy or
      incorrect detail.
    - `edgeDiffRatio32`: fraction of pixels whose Sobel edge differs materially.
    - `avgLuminanceCurrent`, `avgLuminanceCandidate`, `avgLuminanceDelta`: average
      brightness and delta. Use when a render is visibly too dark/light even if a
      broader distance score improves.
    - Content proxies relevant to the scene: black/void ratio, terrain-like ratio,
      water-like ratio, team-color ratio, label/text mask ratio.
    
    For UI/document/layout reviews, also use crop bounds, text/foreground mask
    coverage, contrast checks, edge clipping, element positions, and before/after
    dimensions when those beat global pixel distance.
    
    ## Single-Image Metrics
    
    Every metric above measures one image against another, so none of them can
    answer "is this capture worth anything" when there is nothing to compare it to
    — and the pair score is symmetric, so an enormous distance never says *which*
    side is the empty frame. A few absolute numbers do, computed on a coarse grid
    from a single PNG:
    
    - `colorEntropyBits` under ~3.0, or `dominantColorShare` over ~0.6: one colour
      owns the frame. A sparse scene, an unlit one, or a subject that never drew.
    - `edgeDensity` under ~0.04: almost no form anywhere. Empty framing, a
      primitive-dominant scene, or the subject sitting outside the crop.
    - `luminanceContrast` under ~60: fog, darkness, or haze compressing the whole
      frame into one band.
    - `transparentShare` above 0 on a capture that should be opaque: the capture
      itself is wrong. A transparent pixel keeps whatever RGB it was left with, so
      an invisible frame can look rich until it is composited — the scene metrics
      composite before measuring, and name the invisible share rather than letting
      you infer it. The pair metrics above still read stored RGB, so this field is
      where transparency gets told either way.
    
    These are thresholds for *suspicion*, not gates. A deliberately minimal design,
    a night scene, an empty-state screen, and a whiteboard all trip them honestly.
    Use them to decide where to look, then say what the frame is actually doing —
    never adjust a capture to raise a number, which is the same failure as cropping
    away a difference.
    
    ## Distance Score
    
    When a single fixed-pair number is useful, this default works for structural
    changes:
    
    `distance = 0.35 * diffRatio32 + 0.25 * pixelmatchRatio + 0.25 * edgeDiffRatio32 + 0.15 * min(1, abs(log2(edgeEnergyRatio)))`
    
    It measures **distance from the other image**, nothing more. Because the
    baseline can be wrong, a distance of 0 is not success and a large distance is
    not failure — a richer scene, clearer models, stronger labels, real depth, or
    better lighting all legitimately raise it. Use the score to find *where* the
    images move; decide who is right in step 5. Name the field for what it measures
    (distance, not "parity") so no one reads it as a verdict.
    
    Report the full-frame score and, when UI dominates the shot, a labeled
    world-crop score. Use the world-crop score to locate renderer movement and keep
    the full-frame score so UI/camera mistakes stay visible.
    
    ## Score Discipline
    
    - Quote the previous and new distance for the same pair each iteration, then say
      whether the movement is toward the target, away from it, or diagnostic noise.
    - Prefer edge metrics for missing-content bugs. A flat top-down map can show a
      deceptively moderate grayscale diff while edge energy proves trees, roads,
      city forms, or army silhouettes are absent.
    - Segment out stable UI when it dominates and the question is the world render;
      keep a full-frame score too, labeled.
    - If the camera is wrong, pixel scores are diagnostic only. Fix camera intent
      first, then judge the render.
    
    ## Tooling
    
    Keep comparison scripts inside the skill or a temporary workspace, not in
    product code, unless the product genuinely needs screenshot comparison at
    runtime.
    
    - `scripts/visual-parity-diff.mjs` is a reusable local helper. Its PNG and
      pixel-diff runtime is bundled with the skill, so target repositories do not
      need `pngjs` or `pixelmatch`. Run it with `REFERENCE_DIR=<png-folder>`,
      `CANDIDATE_DIR=<png-folder>`, and optional `OUT_DIR=<artifact-folder>`.
      `REPORT_ORDER=a,b,c` pins ordering;
      `CROPS_JSON=<file>` adds labeled crops (keyed by image id, each crop in pixels
      or `{ "unit": "ratio" }` normalized bounds). Pair reports carry a
      `sceneMetrics` block per side.
    - Drop `REFERENCE_DIR` to run the same helper on a folder with no counterpart:
      it writes `scene-metrics.json` with the single-image numbers above and no
      diff artifacts. Use it on a lone screenshot, on a full capture set before
      anyone reviews it, or to find which side of a large distance is the empty
      one.
    - `scripts/visual-parity-diff.eval.mjs` is the helper's own eval: it generates
      fixtures whose correct answer is known by construction — empty, transparent,
      primitive-dominant, authored, degenerate — and asserts the classification,
      the invariances, and the CLI contract. Run it with the same `REPO_ROOT` after
      changing the script. Never satisfy a failing check by loosening a threshold
      until you have shown the fixture, not the code, is what's wrong.
    - For other tasks, adapt the same artifact set rather than adding one-off
      scripts to the application. Extend the helper if a needed pair is uncovered.
    
    ## References
    
    - `references/subagent-visual-review.md`: neutral subagent prompt/config for an
      independent judgment when history could bias you.
    

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