pngtopnm

   Updated: 6 January 1997
   Table Of Contents

NAME

   pngtopnm - convert a PNG image into a PNM image

SYNOPSIS

   pngtopnm [-verbose] [-alpha | -mix] [-background color]
   [-gamma value] [-text file] [-time] [pngfile]

DESCRIPTION

   This program is part of Netpbm.

   pngtopnm  reads a PNG image (Portable Network Graphics) as in-
put and produces
   a PPM image as output. The type of the output file depends  on
the input file
   -  if it's black & white, pngtopnm creates a PBM file. If it's
grayscale,
   pngtopnm creates a PGM file. Otherwise, it creates a PPM file.

OPTIONS

   -verbose
	  Display  various  information about the input PNG image
and the
	  conversion process.
	  If you want even more information about the PNG  image,
use pngcheck
	  (not part of Netpbm).
   -alpha
	  Output  the  alpha  channel or transparency mask of the
image. The
	  result is either a PBM file or a PGM file, depending on
whether
	  different levels of transparency appear.
   -mix
	  Compose  the	image with the transparency or alpha mask
against a
	  background. When a background chunk is available,  png-
topnm uses the
	  color it specifies. Otherwise, pngtopnm uses black.
   -background color
	  If  no  background  color chunck is present in the png-
file or when
	  another color is required, you can use  this	parameter
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 floating point dec-
imal between
	  zero	and  one, or with the syntax "#RGB", "#RRGGBB" or
"#RRRRGGGGBBBB"
	  where R, G and B are hexadecimal numbers.
   -gamma value
	  Converts the image to a new display-gamma value.  If	a
gAMA chunk is
	  present  in  the  png-file, pngtopnm uses the specified
image-gamma
	  value. If not, pngtopnm considers the image-gamma to be
1.0. Based on
	  the  image-gamma  and the display-gamma given with this
option,
	  pngtopnm adjusts the colors written to the pnm-file.
	  Because the gammas of uncompensated monitors are around
2.6, which
	  results  in an image-gamma of 0.45, some typical situa-
tions 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 user manual. These chunks contain text
comments or
	  annotations.
   -time
	  Prints the tIME chunk to stderr.

   All options can be abbreviated to their shortest  unique  pre-
fix.

SEE ALSO

   pnmtopng, ptot, pnmgamma, pnm

   For	information on the PNG format, see http://schaik.com/png.

NOTE

   A PNG image contains a lot of information that can't be repre-
sented in
   Netpbm  formats. Therefore, you lose information when you con-
vert to another
   format with "pngtopnm | pnmtoxxx". If there is  a  specialized
converter that
   converts  directly  to  the other format, e.g. ptot to convert
from PNG to
   TIFF, you'll get better results using that.

LIMITATIONS

   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 optimiz-
ing. As with any
   Netpbm program, speed  always  takes	 a  back  seat	to  quick
present and future
   development.

AUTHORS

   Copyright  (C)  1995-1997  by Alexander Lehmann and Willem van
Schaik.
     _________________________________________________________________



Table Of Contents

     * NAME
     * SYNOPSIS
     * DESCRIPTION
     * OPTIONS
     * SEE ALSO
     * NOTE
     * LIMITATIONS
     * AUTHORS

UNIX/Linux commands referenced on this page:

1. convert
2. as
3. file
4. more
5. make
6. pnmtopng
7. pnmgamma