pngtopnm



Pngtopnm User Manual(0)                                Pngtopnm User Manual(0)




NAME

       pngtopnm - convert a PNG image into a PNM image



SYNOPSIS

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

       Minimum unique abbreviation of option is acceptable.  You may use  dou-
       ble  hyphens  instead  of single hyphen to denote options.  You may use
       white space in place of the equals sign to separate an option name from
       its value.



DESCRIPTION

       This program is part of Netpbm(1).

       pngtopnm  reads  a  PNG  image (Portable Network Graphics) as input 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.  The background color  is  determined  by  the  bKGD
              chunk  in  the  PNG, except that you can override it with -back-
              ground.  If the PNG has no bKGD  chunk  and  you  don’t  specify
              -background, the background color is white.


       -background=color
              This option specifies the background color with which to mix the
              image when you specify -mix.

              color is as described for the argument of  the  ppm_parsecolor()
              library routine .

              Examples:



       ·      -background=rgb:01/ff/80

       ·      -background=rgbi:1/255/128


              If  you  don’t specify -background, the background color is what
              is specified in the PNG image, and if the  PNG  doesn’t  specify
              anything, white.

              You  cannot  specify  -background  unless you also specify -mix.
              Before Netpbm 10.27 (March 2005), you could specify  -background
              with  -mix  and  it  was just ignored.  (This caused a usability
              problem).



       -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 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 user  manual.   These  chunks  contain
              text comments or annotations.


       -time  Prints the tIME chunk to stderr.





SEE ALSO

       pnmtopng(1), ptot, pnmgamma(1), pnm(1)

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



NOTE

       A  PNG image contains a lot of information that can’t be represented in
       Netpbm formats.  Therefore, you lose information when  you  convert  to
       another  format  with "pngtopnm | pnmtoxxx".  If there is a specialized
       converter that converts directly to the other format, e.g. ptot to con-
       vert 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  optimizing.   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.



netpbm documentation             24 March 2005         Pngtopnm User Manual(0)

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