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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, transparency 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 different 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 re‐
              quired this parameter can be used to set the background color of images. This is espe‐
              cially 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  im‐
              age-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)