Benchmark results on 1797 different images

Rerun on 2026-10-23 (UTC): 1797 images, 1250.2 megapixels, on an AMD Ryzen 7 7735HS running Linux amd64. Every codec is single-threaded, pinned to CPU 2. Each image has one warmup and 3 measured repetitions; the reported encode and decode times are their separate medians. Codec order rotates between repetitions.

All codecs encode the same normalized 8-bit premultiplied pixels: RGBA for libpng and stb, BGRA for BNG. RGB is premultiplied using (channel * alpha + 127) / 255 with integer division. Compression is lossless relative to those stored pixels, not the original PNG files: premultiplication rounds colours and clears hidden RGB at zero alpha. The one 16-bit source is reduced to its high byte; grayscale sources are expanded to RGBA.

libpng 1.6.55 uses zlib 1.3.1, compression level 6 and all adaptive row filters. stb_image and stb_image_write use their defaults (PNG compression level 8, automatic filtering). BNG uses the linked optimized implementation. The harness was built with GCC 15.2.1, -O3 -DNDEBUG. Source loading, normalization, premultiplication and verification are not timed. BNG scratch/output buffers and libpng output/decode buffers are preallocated; stb allocates internally inside its timed calls. libpng's internal allocations remain timed. These are codec-call measurements, not end-to-end application timings.

Every codec's decoded pixels were compared byte for byte in every repetition, including warmups. PNG outputs were also cross-decoded with the other PNG decoder; BNG fast and reference encoders produced identical files, and both decoders matched. All 1797 source PNGs matched the downloadable corpus by SHA-256. There were no skipped images or pixel mismatches.

One source, screenshot_game/Htdamg_affinity.png, emitted an ancillary iCCP: CRC error warning. It remained included, and both PNG decoders agreed on its pixels.

Overall, BNG is 13.13% smaller than libpng's output, with 29.61× faster encoding and 1.39× faster decoding on this corpus and machine. This is an aggregate comparison, not a guarantee for every image: 666 of the 1797 BNG files were larger than libpng's output.

In the tables, ms and KiB are means per image. MP/s is total pixels divided by the sum of per-image median times; bpp is total encoded bits divided by total pixels. Ratios are calculated from unrounded totals.

The full suite of test images can be downloaded here: bng_benchmark_suite.tar – 1797 PNG source files, ~1.0 GiB

Total

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	8.86	131.63	78.51	5.29	610.1	7.184
stb_image	7.70	64.24	90.32	10.83	870.6	10.252
bng	6.38	4.45	108.99	156.50	530.0	6.241

1797 images, 1250.2 megapixels.

screenshot_game

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	8.21	112.44	81.42	5.94	483.3	5.924
stb_image	7.25	57.64	92.19	11.59	684.3	8.388
bng	5.95	4.43	112.31	150.79	462.0	5.663

568 images, 379.6 megapixels.

pngimg

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	22.51	259.54	83.28	7.22	1247.6	5.453
stb_image	17.12	149.87	109.47	12.51	1817.6	7.944
bng	15.04	9.25	124.58	202.57	1071.1	4.682

171 images, 320.5 megapixels.

photo_tecnick

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	24.60	562.35	58.53	2.56	2414.5	13.736
stb_image	25.88	213.46	55.64	6.75	3533.1	20.099
bng	18.41	15.05	78.21	95.66	1930.9	10.985

100 images, 144.0 megapixels.

screenshot_web

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	81.20	453.39	100.07	17.92	2403.0	2.423
stb_image	44.89	436.72	181.01	18.61	3076.9	3.102
bng	48.76	22.08	166.63	367.94	1975.5	1.992

14 images, 113.8 megapixels.

textures_pk02

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	4.18	89.95	72.66	3.38	421.1	11.357
stb_image	4.43	34.97	68.53	8.69	612.7	16.523
bng	3.63	2.64	83.58	115.12	406.3	10.957

235 images, 71.4 megapixels.

textures_plants

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	12.20	138.30	86.55	7.64	731.9	5.676
stb_image	8.98	81.33	117.69	12.99	1031.5	8.000
bng	8.40	5.24	125.69	201.46	609.8	4.729

59 images, 62.3 megapixels.

icon_512

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	2.18	14.40	120.16	18.20	51.2	1.599
stb_image	1.27	11.80	206.56	22.22	68.8	2.150
bng	1.58	0.81	165.42	322.15	61.8	1.931

213 images, 55.8 megapixels.

photo_wikipedia

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	18.38	413.33	59.00	2.62	2046.3	15.457
stb_image	19.81	164.66	54.74	6.59	2893.9	21.860
bng	14.80	11.34	73.29	95.66	1671.8	12.628

49 images, 53.1 megapixels.

textures_photo

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	16.60	303.32	63.15	3.46	1977.6	15.450
stb_image	17.36	133.39	60.41	7.86	2554.5	19.957
bng	12.58	8.97	83.34	116.94	1283.0	10.023

20 images, 21.0 megapixels.

textures_pk01

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	1.78	29.48	73.18	4.41	163.7	10.324
stb_image	1.73	13.64	74.98	9.53	232.4	14.653
bng	1.41	0.95	92.35	137.37	144.2	9.095

113 images, 14.7 megapixels.

photo_kodak

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	6.63	134.60	59.32	2.92	717.5	14.948
stb_image	7.44	56.92	52.86	6.91	979.4	20.404
bng	5.17	4.34	76.00	90.64	550.8	11.476

24 images, 9.4 megapixels.

textures_pk

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	2.25	20.96	90.59	9.73	223.8	8.993
stb_image	1.97	20.26	103.76	10.07	307.3	12.348
bng	2.00	0.95	101.92	214.27	201.5	8.097

18 images, 3.7 megapixels.

icon_64

	decode ms	encode ms	decode MP/s	encode MP/s	size KiB	bpp
libpng	0.07	0.42	58.15	9.84	3.8	7.628
stb_image	0.05	0.34	86.88	12.00	4.4	8.896
bng	0.05	0.04	83.84	105.22	3.6	7.210

213 images, 0.9 megapixels.

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