pngdeer

Smaller PNGs. Same picture. pngdeer is a lossy PNG compressor with no quality slider: for each image it searches palette sizes from 2 to 256 colors, with and without dithering, scores each result with a perceptual metric, and keeps the smallest file that still looks right. At the same quality, the median image comes out 8–12% smaller than with TinyPNG, the best result of any open-source compressor we've measured.

Try it in your browser → Nothing is uploaded: images are compressed on your device.

brew install heydeer/tap/pngdeer
pngdeer input.png -o output.png

• Picks the quality for you: about what TinyPNG would give the image, never above 90 on SSIMULACRA2's scale, which is indistinguishable at 1:1.
• Same bytes everywhere: the command line (macOS and Linux) and the browser (WebAssembly, on every core) run the same Rust code and write identical files.
• Big images too: up to 40 megapixels in the browser, more on the command line.
• JPEG photos too: re-encoded with mozjpeg at the lowest quality that keeps the target, 13% smaller in total than TinyPNG's at its quality (details).
• Animated PNGs stay animated: every frame on one palette and at the target quality, timing kept; 28% of the original size on 12 animated emoji, about even to 16% smaller than TinyPNG (notes).
• Free and open source: MIT.

Leaderboard

We ran pngdeer, TinyPNG and eight open-source quantizers on 180 PNGs: icons, UI screenshots, illustrations, photos, cut-outs and 3D renders. Every output was scored against its original with SSIMULACRA2, a perceptual metric where 90 means indistinguishable at 1:1. TinyPNG is the yardstick:

• Points: median SSIMULACRA2 points above (+) or below (−) TinyPNG when a tool's file is as big as TinyPNG's.
• Reaches: images where a tool can match TinyPNG's quality at all.

Each cell gives the held-out set (71 images) / the tuning set (109 images):

Compressor	Points	Reaches
pngdeer	+1.7 / +2.0	67 / 106
TinyPNG (the yardstick)	0	71 / 109
pngquant	0.0 / +0.3	53 / 87
quantizr	−0.1 / −1.0	39 / 53
exoquant	−3.7 / −5.1	19 / 24
NeuQuant	−6.5 / −9.8	4 / 5
FFmpeg	−7.0 / −8.8	16 / 15
quantette	−7.6 / −9.6	18 / 21
ImageMagick	−11.3 / −14.5	3 / 8
Pillow	−16.8 / −19.5	4 / 4

At TinyPNG's quality, pngdeer's files are 12% smaller on the held-out set and 8% smaller on the tuning set (median image).

• Held out: pngdeer's parameters were tuned on the 109 images; the other 71 were collected afterwards and never used for tuning.
• Generous to the others: each open-source tool gets its best of ten settings per image, picked after the fact. pngdeer's results are what you get, searched at compression time.
• A second opinion: scored with butteraugli instead, which the search never looks at, pngdeer's files are still 6–9% smaller than TinyPNG's at the same quality.
• TinyPNG ran through its API in October 2026. bench/ reruns everything; the website screenshots in the sets aren't ours to share, so a rerun covers 155 of the 180 images.

WebP

pngdeer also writes WebP (an output name ending in .webp, or the switch in the browser): the smaller of its palette image stored losslessly and the lowest lossy quality that keeps the target (a JPEG photo: below). Against TinyPNG's WebP on 120 of the images, the size each tool needs to match TinyPNG's quality (median image / in total), and how many images it can bring up to that quality:

Compressor	Size at TinyPNG's quality	Reaches
pngdeer	95.0% / 93.9%	118
TinyPNG (the yardstick)	100%	120
cwebp, best of 27 settings	97.9% / 110.2%	120
pngquant + cwebp, best of 10	135.0% / 212.1%	115

• cwebp is libwebp's own encoder, the library Squoosh, sharp and Pillow encode with. It gets its best of 27 settings per image, picked after the fact: 13 qualities with and without the auto filter, and lossless. pngquant + cwebp stores pngquant's palette image as lossless WebP, TinyPNG's palette route from open-source parts.
• At TinyPNG's file size, on the 40 images where all three can be compared, pngdeer scores 2.6 SSIMULACRA2 points above TinyPNG, pngquant + cwebp 1.9, cwebp −0.3.
• Out of the box, cwebp's default quality makes files 6% bigger than TinyPNG's on the median image, and slightly worse. pngdeer's automatic quality makes them 5% smaller, as good.
• WebP's settings were chosen on these 120 images. On the other 60, against a stand-in that matches TinyPNG's WebP on these (same size and score, median), pngdeer is 4% smaller. The WebP notes have the details.

JPEG

pngdeer also takes JPEG photos (pngdeer photo.jpg -o smaller.jpg, or drop them in the browser) and writes a smaller JPEG: re-encoded with mozjpeg at the lowest quality that keeps the target, never bigger than the photo. On 60 photos from Wikimedia Commons, 30 web-size copies and 30 camera originals, the size each tool needs to match TinyPNG's quality (median photo / in total), and how many photos it can bring up to that quality:

Compressor	Size at TinyPNG's quality	Reaches
pngdeer	87.8% / 85.4%	60
TinyPNG (the yardstick)	100%	60
jpegli, best of 12 settings	89.2% / 87.2%	60
mozjpeg, best of 7 qualities	94.2% / 89.1%	59

• jpegli is Google's JPEG encoder from the JPEG XL project, mozjpeg Mozilla's, which Squoosh uses. Each gets its best setting per photo, picked after the fact: qualities 40–90, jpegli also at 4:2:0. pngdeer's files are pooled the same way (its encoder, mozjpeg with its MS-SSIM-tuned table at 4:2:0, at qualities 50–85, and its own runs), as in the PNG and WebP tables. The file it writes with TinyPNG's score as the target is 89.5% / 86.7% of TinyPNG's size.
• At TinyPNG's file size, pngdeer scores 3.3 SSIMULACRA2 points above TinyPNG on the median photo, jpegli 3.1, mozjpeg 1.8.
• At its automatic quality, pngdeer's files are 82% of TinyPNG's size on the median photo (84% in total), scoring about the same (median +0.2 points). mozjpeg's default quality makes them 7% bigger than TinyPNG's, 5 points better.
• Like TinyPNG, pngdeer gives big photos a lower quality than small ones: a large photo is seen scaled down. Unlike TinyPNG, it keeps the color profile (unless sRGB) and the orientation, and drops the rest of the camera's metadata.
• WebP from a JPEG (pngdeer photo.jpg -o photo.webp, or the switch in the browser): turned upright, at the same automatic quality. At TinyPNG's WebP quality it needs 95.3% / 91.3% of TinyPNG's WebP size; cwebp, given its best of 13 settings per photo, about the same. At equal quality it is no smaller than pngdeer's own JPEG (99% on the median photo), so it is there for sites that want WebP.
• The JPEG notes have the details. TinyPNG ran through its API in October 2026.

How it works

• Searches the palette: palette sizes from 2 to 256 colors, each tried a few ways (with and without Floyd–Steinberg dithering, with neighbour smoothing, with a second palette builder), and the smallest file that reaches the target wins.
• Scores what you'd see: SSIMULACRA2, measured in-process. Colors are matched in Oklab, smooth gradients are always dithered, and transparent pixels are judged over light and dark backgrounds.
• Stays fast on big images: large images are searched on a downscaled preview and checked at full size.

The research notes follow every step, from the first comparison with TinyPNG to today's defaults.

Command line

pngdeer input.png -o output.png              # automatic quality
pngdeer input.png -o output.png --target 85  # a fixed SSIMULACRA2 quality
pngdeer input.png -o output.webp             # WebP, automatic quality
pngdeer photo.jpg -o photo.min.jpg           # JPEG, automatic quality
pngdeer photo.jpg -o photo.webp              # a JPEG as WebP
pngdeer --help

From source: cargo build --release, and the binary is target/release/pngdeer.

Browser

The web app runs the same code compiled to WebAssembly. To run it locally (web/build.sh lists the toolchain it needs):

sh web/build.sh
python3 web/serve.py   # http://localhost:8770

License

MIT. Dependencies keep their own licenses (web/THIRD_PARTY_LICENSES.txt), as do the test and sample images (the SOURCES.md next to them). JPEG output is encoded with mozjpeg: this software is based in part on the work of the Independent JPEG Group.