blazediff

High-performance image diffing with block-based optimization and SIMD acceleration.

Features

• Block-based optimization - Skip identical regions for massive speedups on similar images
• SIMD acceleration - Native SSE4.1 (x86) and NEON (ARM) implementations
• Multiple formats - PNG, JPEG, and QOI support, via blazediff-shared
• Perceptual diffing - YIQ-based color difference with antialiasing detection
• In-house PNG codec - optional blazediff_png, faster than spng on every fixture, with byte-exact decode parity; opt-in via BLAZEDIFF_PNG_ENABLED
• Cross-platform - Linux, macOS, and Windows support
• Multi-language - Native Rust crate, Node.js (N-API), and Python (PyO3) bindings - all sharing the same core

Installation

Rust (CLI + library)

cargo install blazediff

Node.js - @blazediff/core-native

npm install @blazediff/core-native

N-API bindings shipped as pre-built .node binaries for macOS, Linux, and Windows (arm64 + x64). Built from this crate's napi Cargo feature.

import { compare } from "@blazediff/core-native";

const result = await compare("expected.png", "actual.png", "diff.png", {
  threshold: 0.1,
});

Python - blazediff

pip install blazediff

PyO3 bindings shipped as abi3-py38 wheels for CPython ≥ 3.8 (macOS, Linux manylinux, Windows; arm64 + x86_64). Built from this crate's python Cargo feature.

from blazediff import compare

result = compare("expected.png", "actual.png", "diff.png", threshold=0.1)
if result.match:
    print("identical")
else:
    print(f"{result.diff_count} pixels differ ({result.diff_percentage:.2f}%)")

CLI Usage

# Basic diff
blazediff image1.png image2.png -o diff.png

# With custom threshold (0.0 - 1.0)
blazediff image1.png image2.png -o diff.png -t 0.1

# JSON output for scripting
blazediff image1.png image2.png --json

Library Usage

use blazediff::{diff, DiffOptions};

let options = DiffOptions {
    threshold: 0.1,
    include_anti_aliased: false,
    ..Default::default()
};

let result = diff("image1.png", "image2.png", Some("diff.png"), &options)?;
println!("Different pixels: {}", result.diff_count);

Structural similarity

This crate is a pixel diff: it answers where two images differ. For how alike they look — SSIM, MS-SSIM, Hitchhiker's SSIM — use blazediff-ssim, which stands alone and shares nothing with this crate but the blazediff-shared primitives. It is also what @blazediff/ssim-native wraps.

Interpret

Structured region analysis that produces human-readable change descriptions. It is not part of this crate: it lives in blazediff-interpret, which consumes what diff returns, with its own blazediff-interpret CLI.

The classifier is independent of whatever found the regions. Anything that can say where something changed can drive it: blazediff-ssim by thresholding a score map, or a caller passing boxes directly. Coarse boxes are fine — each is refined against the source pixels before any statistic is computed, so the analysis stays per-pixel.

See INTERPRET.md for the full algorithm documentation - pipeline stages, formulas, classification rules, and output format.

Performance

3-4x faster than odiff, 8x faster than pixelmatch on 4K images.

Image I/O lives in blazediff-shared, shared with the other crates; load_png, save_jpeg and friends are re-exported here unchanged. PNG I/O defaults to spng. Setting BLAZEDIFF_PNG_ENABLED=1 routes decode and stored (level 0) encode through the in-house blazediff_png codec, which is faster than spng on every fixture.

License

MIT