Browser-local comparison method

Image difference checker

An image difference checker compares two same-size images pixel by pixel. Peelaway’s checker decodes both files locally, reports the pixels whose RGBA channel difference exceeds your chosen threshold, and renders a difference heatmap. It does not upload either image, align mismatched photos, or judge whether an AI edit is semantically correct.

Open the image editor

Interactive checker

Compare two same-size images

Choose two files and a threshold. A pixel is counted as changed only when its largest red, green, blue, or alpha-channel delta is greater than that threshold.

JPEG, PNG, or WebP · 12 MP maximum

JPEG, PNG, or WebP · 12 MP maximum

The files are decoded and compared in this browser tab. Peelaway does not upload them, and analytics receives no image bytes, filenames, dimensions, pixel values, heatmap, or calculated result.

Published method

Exact RGBA threshold formula

For each pixel, the checker calculates the absolute difference for R, G, B, and A, then takes the largest of those four values. The pixel changes when:

max(|R₁−R₂|, |G₁−G₂|, |B₁−B₂|, |A₁−A₂|) > threshold

Changed share

Changed pixels divided by total pixels, reported as a percentage.

Mean RGBA delta

The sum of every absolute channel delta divided by four times the pixel count.

Maximum delta

The largest single-channel absolute difference observed anywhere in the pair.

Two-pixel verification fixture

This deliberately small fixture makes the strict greater-than rule independently checkable. At threshold 4, a delta of 4 is unchanged and a delta of 10 is changed.

Known pixel differences and expected classification
PixelOnly changed channelMaximum deltaClassification
1R: 10 → 144Unchanged
2G: 100 → 11010Changed
Expected result1 of 2 pixels changed (50%); mean RGBA delta 1.75; maximum 10.

Interpretation boundaries

What pixel difference can and cannot show

Useful for

  • • Checking deterministic rendering or export regressions.
  • • Locating changed pixels in already aligned images.
  • • Measuring exact or thresholded RGBA differences.

Not evidence of

  • • Perceptual image quality or aesthetic preference.
  • • Instruction adherence or semantic edit correctness.
  • • Correct alignment, object preservation, or a good AI edit.

Alignment: a one-pixel shift can make most of an otherwise identical image differ. This checker rejects mismatched dimensions and does not register or align content.

Lossy encoding: JPEG can introduce small channel changes even when two images look similar. Thresholds can suppress small deltas but cannot prove visual equivalence.

Alpha and color space: decoded Canvas values include alpha, and browser color conversion can affect returned pixel values. The HTML specification defines Canvas pixel access and its default sRGB behavior; it does not make separately encoded files byte- or pixel-identical.

Source ledger

Sources and first-party evidence

Sources checked August 11, 2026. The threshold formula, two-pixel fixture, heatmap rule, and browser implementation are Peelaway’s published method. The sources below define the browser primitive and the boundary between raw differences and context-aware edit evaluation.

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