NAME

pngquant — PNG converter and lossy image compressor

SYNOPSIS

DESCRIPTION

pngquant converts 32-bit RGBA PNGs to 8-bit (or smaller) RGBA-palette PNGs, optionally using Floyd-Steinberg dithering. The output filename is the same as the input name except that it ends in ‘-fs8.png’ or ‘-or8.png’ (unless the input is stdin, in which case the quantized image will go to stdout). The default behavior if the output file exists is to skip the conversion; use --force to overwrite.

OPTIONS

-o out.png, --output out.png

Writes converted file to the given path. When this option is used only single input file is allowed.

--ext new.png

File extension (suffix) to use for output files instead of the default ‘-fs8.png’ or ‘-or8.png’.

-f, --force

Overwrite existing output files. “--ext .png --force” can be used to convert files in place (which is unsafe).

--nofs, --ordered

Disable Floyd-Steinberg dithering.

--floyd [=N]

Set dithering level using fractional number between 0 (none) and 1 (full, the default).

-s N, --speed N

1 (brute-force) to 11 (fastest). The default is 3. Speed 10 has 5% lower quality, but is about 8 times faster than the default. Speed 11 disables dithering and lowers compression level.

-Q min-max, --quality min-max

min and 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 (or if outputting to stdin, 24-bit original will be output) and pngquant will exit with status code 99.

--skip-if-larger

If conversion results in a file larger than the original, the image won't be saved and pngquant will exit with status code 98. Additionally, file size gain must be greater than the amount of quality lost. If quality drops by 50%, it will expect 50% file size reduction to consider it worthwhile.

--posterize bits

Truncate number of least significant bits of color (per channel). Use this when image will be output on low-depth displays (e.g. 16-bit RGB). pngquant will make almost-opaque pixels fully opaque and will reduce amount of semi-transparent colors. When this option is enabled the default filename suffix is ‘-ie-fs8.png’ / ‘-ie-or8.png’.

--strip

Remove optional chunks (metadata) from PNG files.

--transbug

Workaround for readers that expect fully transparent color to be the last entry in the palette.

-v, --verbose

Enable verbose messages showing progress and information about input/output. Opposite is --quiet. Errors are output to stderr regardless of this option.

-V, --version

Display version on stdout and exit.

-h, --help

Display help and exit.

EXAMPLE

Creating a new image with the number of colors reduced to 64:

The resulting image will have 64 colors and will be saved as image-fs8.png.

Overwriting image in-place if it can be reduced without too much quality loss:

AUTHOR

pngquant is developed by Kornel Lesinski <kornel@pngquant.org> based on code by Greg Roelofs <newt@pobox.com>.

pngquant homepage.