.TH pngtopnm 1 "6 January 1997"
.IX pngtopnm
.SH NAME
pngtopnm - convert a Portable Network Graphics file into portable anymap
.SH SYNOPSIS
.B pngtopnm
.RB [-verbose]
[-alpha | -mix]
[-background color]
.br
[-gamma value]
[-text file]
[-time]
.RI [ pngfile ]
.SH DESCRIPTION
Reads a Portable Network Graphics as input.
.IX png
Produces a portable anymap as output.
The type of the output file depends on the input file - if it's
black & white, a
.I pbm
file is written, else if it's grayscale a
.I pgm
file, else a
.I ppm
file.
.SH OPTIONS
.TP
.B -verbose
Display the format of the input file and the type of the output file. If
the chunks are part of the
.I png-file,
the alpha, transparency and gamma-values will be indicated.
.TP
.B -alpha
Output the alpha channel or transparency mask of the image. The result is either a
.I pbm
file or
.I pgm
file, depending on whether different levels of transparency appear.
.TP
.B -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.
.TP
.B -background color
If no background color chunck is present in the 
.I 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.
.TP
.B -gamma value
Converts the image to a new display-gamma value. When a gAMA chunk is present
in the
.I 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
.I pnm-file
will be adjusted. 
.br
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.
.TP
.B -text file
Writes the tEXt and zTXt chunks to a file, in a format as described in the
.I pnmtopng
man-page.  These chunks contain text comments or annotations.
.TP
.B -time
Prints the tIME chunk to stderr.
.PP
All flags can be abbreviated to their shortest unique prefix.
.SH "SEE ALSO"
pnmtopng(1), ptot(1), pnmgamma(1), pnm(5)
.SH NOTE
Instead of pngtopnm|pnmtoxxx, a specific converter should be used, if
available. E.g.
.I ptot
(PNG to TIFF conversion), etc.
.SH BUGS
There could be an option to read the comment text from pnm comments instead
of a separate file.
.PP
The program could be much faster, with a bit of code optimizing.
.SH AUTHORS
Copyright (C) 1995-1997 by Alexander Lehmann
.br
                        and Willem van Schaik.
.\" Permission to use, copy, modify, and distribute this software and its
.\" documentation for any purpose and without fee is hereby granted, provided
.\" that the above copyright notice appear in all copies and that both that
.\" copyright notice and this permission notice appear in supporting
.\" documentation.  This software is provided "as is" without express or
.\" implied warranty.
.\"
.\" This man-page was derived from rasttopnm.1 by Jef Poskanzer