pngnq (1) - Linux Manuals

pngnq: quantize png images

NAME

pngnq - quantize png images

SYNOPSIS

pngnq [-vfhV][-s sample_factor ][-Q dither ][-g gamma ][-e extension ][-d dir ][-n colors ][ inputfiles ]

DESCRIPTION

pngnq Quantizes a 32-bit RGBA PNG image to an 8 bit RGBA palette PNG using the neuquant algorithm. The output file name is the input file name extended with "-nq8.png" or a specified extension.

OPTIONS

-v

Verbose mode. Prints status messages.

-f

Force ovewriting of files.

-s sample factor

Sample factor. The neuquant algorithm samples pixels stepping by this value. The default value of 3 gives good results. Higher values sample less of the image pixels and thus are faster but less accurate. A factor of 1 samples every image pixel.

-n colors

Specifies the number of colors to quantize to. Defaults to 256 which is the maximum. The minimum here is 2.

-Q dither

Choose a dithering method: n = no dither (default), f = Floyd Steinberg dithering.

-g gamma

Set the image gamma correction. If not present, uses the png file's gamma or defaults to 1.0.

-e extension

Specifies the new filename extension. Defaults to "-nq8.png". Pngnq drops .png from the original filenames. If you set the argument of the -e option to .png and choose the -f option the input file will be overwritten.

-d dir

Tells pngnq to put output files in a directory other than the one the input files are in.

input files

The png files to be processed. Defaults to standard input if not specified. If standard input is being processed the output is sent to standard output.

-h

Print program help.

-V

Print version number and library versions.

BUGS

Does not deal correctly with greyscale alpha images with low bit depths, but these wont benefit from quantizing.

AUTHOR

Stuart Coyle <stuart.coyle [at] gmail.com>