#pngquant

This the official new pngquant.

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.

##Usage

• batch conversion of multiple files: pngquant 256 *.png
• Unix-style stdin/stdout chaining: … | pngquant 16 | …

To further reduce file size, you may want to consider optipng or ImageOptim.

##Improvements since 1.0

• Significantly better quality of quantisation

  • 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
  • more accurate remapping of semitransparent colors
  • special dithering algorithm that does not add noise in well-quantized areas of the image
  • gamma correction (output is always generated with gamma 2.2 for web compatibility)

• More flexible commandline usage

  • number of colors defaults to 256
  • standard switches like -- and - are allowed

• Refactored and modernised code

  • C99 with no workarounds for old systems
  • floating-point math used throughout
  • Intel SSE3 optimisations

##Options

See pngquant -h for full list.

###-ext new.png

Set custom extension (suffix) for output filename. By default -or8.png or -fs8.png is used. If you use -ext .png -force options pngquant will overwrite input files in place (use with caution).

###-speed N

Speed/quality trade-off from 1 (brute-force) to 10 (fastest). The default is 3. Speed 10 has 5% lower quality, but is 8 times faster than the default.

###-iebug

Workaround for IE6, which only displays fully opaque pixels. pngquant will make almost-opaque pixels fully opaque and will avoid creating new transparent colors.

###-version

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"