PNG Codec Benchmarks

A from-scratch PNG codec in Rust — blazediff-png — against spng , image-rs (png), and zune-png . Decode and encode are timed (best-of, size-scaled iteration counts) over the full fixture corpus (36 PNGs, 342.8 MPx), single-threaded on Apple Silicon. Lower is better.

Encode is measured at two settings so the speed/size trade-off is explicit and zune’s stored-only encoder is compared fairly: no compression (stored deflate blocks) and half compression (half of each codec’s own max deflate level — libdeflate 12 → 6, zlib 9 → 4).

Speed here, correctness elsewhere. These are timing numbers. Byte-identical decode parity with spng is verified separately on a large public-image corpus — Urban100, BSD100, Set14, Set5 (real high-res photos) plus the full PngSuite  (every format corner and the intentionally-malformed files), ~395 files — by the corpus_differential test: every file decodes byte-identically to spng at RGBA8 and at every SPNG_FMT_*, malformed files reject in lockstep, and every accepted image survives a blazediff encode → decode round-trip. Fetch the corpus with crates/blazediff-png/scripts/fetch-corpus.sh and run with BLAZEDIFF_PNG_CORPUS set; the Benchmark PNG GitHub workflow runs the benchmark and this verification.

Decode

blazediff decodes ~1.39× faster than spng across the corpus.

Encode — No Compression

Levels: blazediff stored · spng stored · image-rs stored · zune stored.

blazediff encodes ~6.67× faster than spng (stored) across the corpus.

Encode Size — No Compression

Output bytes per codec; the final row is each codec’s total as a percentage of spng’s (the de-facto reference). zune-png has no compressed mode, so it always writes stored output — far larger than the rest.

Encode — Half Compression

Levels: blazediff libdeflate 6 · spng zlib 4 · image-rs flate2 4 · zune stored.

blazediff encodes ~3.75× faster than spng (zlib 4) across the corpus.

Encode Size — Half Compression

Output bytes per codec; the final row is each codec’s total as a percentage of spng’s (the de-facto reference). zune-png has no compressed mode, so it always writes stored output — far larger than the rest.