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.

       The "input files" defaults to standard input if not specified. If standard input is  being
       processed the output is sent to standard output.

OPTIONS

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

       -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.

       -f     Force overwriting of files.

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

       -h     Print program help.

       -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.

       -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.

       -v     Verbose mode. Prints status messages.

       -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@gmail.com>

SEE ALSO

       png(5)