This is the official
pngquant converts 24/32-bit RGBA PNGs to 8-bit palette with alpha channel preserved. Such images are compatible with all modern browsers, and a special compatibility setting exists which helps transparency degrade well in Internet Explorer 6.
Quantized files are often 40-70% smaller than their 24/32-bit version.
This utility works on Linux, Mac OS X and Windows.
- batch conversion of multiple files:
- Unix-style stdin/stdout chaining:
… | pngquant - | …
Generated files are both smaller and look much better.
Significantly better quality of quantisation
- more accurate remapping of semitransparent colors
- special dithering algorithm that does not add noise in well-quantized areas of the image
- uses variance instead of popularity for box selection (improvement suggested in the original median cut paper)
- feedback loop that repeats median cut for poorly quantized colors
- additional colormap improvement using Voronoi iteration
- supports much larger number of colors in input images without degradation of quality
- gamma correction (output is always generated with gamma 2.2 for web compatibility)
More flexible commandline usage
- number of colors defaults to 256
- long options and standard switches like
Refactored and modernised code
- C99 with no workarounds for old systems
- floating-point math used throughout
- Intel SSE optimisations
- multicore support via OpenMP
- quantization moved to standalone libimagequant
pngquant -h for full list.
max are numbers in range 0 (worst) to 100 (perfect), similar to JPEG. pngquant will use the least amount of colors required to meet or exceed the
max quality. If conversion results in quality below the
min quality the image won't be saved (if outputting to stdin, 24-bit original will be output) and pngquant will exit with status code 99.
pngquant --quality=65-80 image.png
Set custom extension (suffix) for output filename. By default
-fs8.png is used. If you use
--ext=.png --force options pngquant will overwrite input files in place (use with caution).
Speed/quality trade-off from 1 (brute-force) to 11 (fastest). The default is 3. Speed 10 has 5% lower quality, but is 8 times faster than the default. Speed 11 disables dithering and lowers compression level.
Disables Floyd-Steinberg dithering.
Workaround for IE6, which only displays fully opaque pixels. pngquant will make almost-opaque pixels fully opaque and will avoid creating new transparent colors.
Print version information to stdout.
Read image from stdin and send result to stdout.
Stops processing of arguments. This allows use of file names that start with
-. If you're using pngquant in a script, it's advisable to put this before file names:
pngquant $OPTIONS -- "$FILE"