PNGNQ(1) User Manuals PNGNQ(1)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 val-
ues 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@gmail.com>
SEE ALSO png(5)Linux MAY 2009 PNGNQ(1)
Check Out this Related Man Page
pngtopnm(1) General Commands Manual pngtopnm(1)NAME
pngtopnm - convert a Portable Network Graphics file into portable anymap
SYNOPSIS
pngtopnm [-verbose] [-alpha | -mix] [-background color]
[-gamma value] [-text file] [-time] [pngfile]
DESCRIPTION
Reads a Portable Network Graphics as input. Produces a portable anymap as output. The type of the output file depends on the input file -
if it's black & white, a pbm file is written, else if it's grayscale a pgm file, else a ppm file.
OPTIONS -verbose
Display the format of the input file and the type of the output file. If the chunks are part of the png-file, the alpha, trans-
parency and gamma-values will be indicated.
-alpha Output the alpha channel or transparency mask of the image. The result is either a pbm file or pgm file, depending on whether dif-
ferent levels of transparency appear.
-mix Compose the image with the transparency or alpha mask against a the background. When a background chunk is available that color is
taken, else black will do.
-background color
If no background color chunck is present in the png-file, or when another color is required this parameter can be used to set the
background color of images. This is especially useful for alpha-channel images or those with transparency chunks. The format, to
specify the color in, is either (in the case of orange) "1.0,0.5,0.0", where the values are floats between zero and one, or with the
syntax "#RGB", "#RRGGBB" or "#RRRRGGGGBBBB" where R, G and B are hexa-decimal numbers.
-gamma value
Converts the image to a new display-gamma value. When a gAMA chunk is present in the png-file, the image-gamma value will be used.
When not, the image-gamma is considered to be 1.0. Based on the image-gamma and the display-gamma given with this option the colors
written to the pnm-file will be adjusted.
Because the gamma's of uncompensated monitors are around 2.6, which results in an image-gamma of 0.45, some typical situations are:
when the image-gamma is 0.45 (use -verbose to check) and the picture is too light, your system is gamma-corrected, so convert with
"-gamma 1.0". When no gAMA chunk is present or the image-gamma is 1.0, use 2.2 to make the picture lighter and 0.45 to make the
picture darker.
-text file
Writes the tEXt and zTXt chunks to a file, in a format as described in the pnmtopng man-page. These chunks contain text comments or
annotations.
-time Prints the tIME chunk to stderr.
All flags can be abbreviated to their shortest unique prefix.
SEE ALSO pnmtopng(1), ptot(1), pnmgamma(1), pnm(5)NOTE
Instead of pngtopnm|pnmtoxxx, a specific converter should be used, if available. E.g. ptot (PNG to TIFF conversion), etc.
BUGS
There could be an option to read the comment text from pnm comments instead of a separate file.
The program could be much faster, with a bit of code optimizing.
AUTHORS
Copyright (C) 1995-1997 by Alexander Lehmann
and Willem van Schaik.
6 January 1997 pngtopnm(1)