png-pixel-cmp

Compares two PNGs by decoded pixel values, ignoring encoding-only differences.

Two files that encode the same image are reported as identical even when their bytes differ, so compression level, scanline filters, palette ordering, bit depth and colour type are all ignored. Only the resulting RGBA pixels matter.

Rust

[dependencies]
png-pixel-cmp = { git = "https://github.com/EvenTorset/png-pixel-cmp.git" }

use png_pixel_cmp::compare_png_pixels;

let same = compare_png_pixels(&a, &b)?;

compare_png_pixels returns Result<bool, PngCompareError>. Images with different dimensions are Ok(false) rather than an error; only unreadable data produces an error, and PngCompareError::kind says which of the thirteen failure modes it was.

JavaScript

import { comparePngPixels } from '@cccode/png-pixel-cmp'

const same = await comparePngPixels(a, b)

Supported formats

| Colour type | Bit depths | |---|---| | Greyscale | 1, 2, 4, 8 | | Greyscale + alpha | 8 | | Truecolour | 8 | | Truecolour + alpha | 8 | | Indexed | 1, 2, 4, 8 |

tRNS is honoured for all three of indexed, greyscale and truecolour. 16-bit depths and interlaced images report UnsupportedFormat.