Started with a pure JS implementation (still the fastest JS image diff), but wanted to push performance further. I rewrote the core in Rust to make it the fastest open-source single-threaded image diff. On 4K images (5600×3200): ~327ms vs odiff's ~1215ms. Binaries are ~3x smaller too (~700KB vs ~2MB).
The core insight: make the cold pass smarter to make the hot pass do less work. Instead of simple pixel equality, the cold pass scans dynamic-sized blocks and marks "problematic" ones - blocks that might contain differences. The hot pass then only runs YIQ perceptual diff and antialiasing check on those problematic blocks, skipping everything else entirely. PNG I/O uses spng (C library) via Rust bindings. SIMD throughout - NEON on ARM, SSE4.1 on x86. Drop-in replacement for odiff with the same API.