Overview
Introduction
This tool answers a precise question two similar-looking PNGs often raise: are they actually identical, and if not, exactly how much do they differ?
Both images are decoded and compared locally in your browser; neither file is uploaded anywhere.
What Is PNG Images Comparator?
A pixel-level PNG comparison tool that checks two decoded images across all four RGBA channels and reports whether they match exactly, plus detailed difference figures when they don't.
It's an exact byte-level comparison, not a perceptual similarity score, so it will flag even single-pixel, sub-visible differences.
How PNG Images Comparator Works
Both uploaded PNGs are decoded into RGBA pixel buffers via canvas; if their dimensions don't match, the comparison stops there and reports the mismatch.
Otherwise, a pure lib function loops over both buffers together, comparing all four channels of each corresponding pixel pair and tracking how many pixels differ at all and the single largest per-channel difference found.
When To Use PNG Images Comparator
Use it to verify two exports of the same source image are pixel-identical, catching unintended changes from a re-save, re-compression, or tool upgrade.
It's also useful for visually debugging a rendering pipeline by confirming exactly how much output changed after a code change.
Often used alongside PNG Analyzer and PNG Transparency Checker.
Features
Advantages
- Gives an exact, deterministic answer rather than a fuzzy visual similarity guess.
- Reports both how many pixels changed and how large the biggest single change was, distinguishing subtle recompression from substantial edits.
- Runs entirely client-side, so neither image is uploaded anywhere.
Limitations
- Requires both images to have identical dimensions to run a pixel comparison; resizing one to match the other first is necessary if they started at different sizes.
- This is an exact, not perceptual, comparison — two images that look identical to the human eye due to imperceptible recompression differences will still report as non-identical if any byte differs.
Examples
Best Practices & Notes
Best Practices
- Use this after any automated image-processing step to confirm only the intended region of an image changed.
- If dimensionsMatch is false, resize one image to match the other explicitly before re-running the comparison, rather than assuming they're unrelated.
Developer Notes
The pixel-by-pixel comparison is a pure function over two plain Uint8ClampedArray pixel buffers, fully unit-tested without any canvas dependency; only decoding both uploads into those buffers happens in the browser-only component.
PNG Images Comparator Use Cases
- Verifying a re-export or re-compression didn't unintentionally change any pixels
- Debugging a rendering pipeline by measuring exactly how much output changed after a code change
- Confirming an automated edit only affected the intended region of an image
Common Mistakes
- Expecting a 'similarity score' — this tool reports exact pixel/channel differences, not a perceptual closeness percentage.
- Comparing two images of different dimensions and expecting a partial pixel-by-pixel diff; resize to match first.
Tips
- A low differencePercent with a high maxChannelDifference usually means a small, sharp, localized change (like an added element); a high differencePercent with a low maxChannelDifference usually means broad, subtle changes (like recompression).
- Pair with the PNG Analyzer on each image individually if you need more context on what might explain a difference.