Consider blazediff for faster pixel-by-pixel and SSIM comparisons

[teimurjan]

Hey team! I've been working on performance optimization for visual regression testing and wanted to share some benchmarking results that might be of interest to jest-image-snapshot.

Background

I maintain blazediff, a performance-focused image comparison library that started as a pixelmatch optimization. After seeing some performance concerns in the community (like #28), I thought it might be worth proposing as an alternative backend for jest-image-snapshot.

Performance Optimization

I've benchmarked blazediff against the current backends (pixelmatch and ssim.js) on the HuggingFace Img-Diff dataset (50 real-world image pairs):

Pixel-by-pixel comparison:

• blazediff/core: ~1.5x faster than pixelmatch
• Same YIQ perceptual color space and anti-aliasing detection
• Zero memory allocations during comparison
• Block-based optimization with 32-bit integer comparison for quick filtering of unchanged regions

SSIM comparison:

• blazediff/ssim (Gaussian): 3.2x faster than ssim.js Original, 0.9999 correlation with MATLAB reference
• blazediff/ssim (Hitchhiker's): 8.8x faster than ssim.js Original, 0.987 correlation with MATLAB reference
• Uses integral images for O(1) window computatio

Why this might matter

From what I've seen in the issues, folks running large test suites (especially in CI/CD) are hitting performance bottlenecks. The speedup compounds quickly:

• 1000 snapshots taking 30 seconds → 20 seconds (pixel-by-pixel)
  • 1000 identical snapshots taking 30 seconds → 4 seconds (pixel-by-pixel)
• 1000 snapshots taking 30 seconds → 9-3 seconds (SSIM, depending on variant)

Validation

The implementations have been thoroughly validated using the MATLAB implementations from the original papers:

• Pixel-by-pixel: Same algorithm as pixelmatch (YIQ + anti-aliasing), just optimized
• SSIM (Gaussian): 0.9999 correlation with MATLAB reference implementation
• Hitchhiker's SSIM: 0.987 correlation with MATLAB, validated on 50 real-world image pairs

Full benchmarks and validation methodology: IMGDIFF_ANALYSIS.md

Proposal

Would the maintainers be open to:

1. Adding blazediff as an optional comparison backend (similar to how pixelmatch and SSIM are currently options)?
2. Or perhaps just documenting it as a drop-in alternative for users who need the extra performance?

I'm happy to contribute a PR if there's interest. No pressure though—just thought it might help folks dealing with slow test suites!

Repo: https://github.com/teimurjan/blazediff
Docs: https://blazediff.dev/