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NAME

       pnmtopng - convert a portable anymap into a Portable Network Graphics file

SYNOPSIS

       pnmtopng [-verbose] [-downscale] [-interlace] [-alpha file]
       [-transparent [=]color] [-background color] [-gamma value]
       [-hist] [-chroma wx wy rx ry gx gy bx by] [-phys x y unit]
       [-text file] [-ztxt file] [-time [yy]yy-mm-dd hh:mm:ss]
       [-filter type] [-compression level] [-force] [pnmfile]

DESCRIPTION

       Reads a portable pixmap as input.  Produces a Portable Network Graphics file as output.

       Color  values  in  PNG  files are either eight or sixteen bits wide, so pnmtopng will automatically scale
       colors to have a maxval of 255 or 65535.  Grayscale files will be produced with bit depths 1, 2, 4, 8  or
       16.  An extra pnmdepth step is not necessary.

OPTIONS

       -verbose
              Display the format of the output file.

       -downscale
              Enables  scaling  of  maxvalues of more then 65535 to 16 bit. Since this means loss of image data,
              the step is not performed by default.

       -interlace
              Creates an interlaced PNG file (Adam7).

       -alpha file
              The alpha channel of pixel (or image) specifies the transparency  of  a  pixel.   To  create  this
              fourth  pixel  value  a  separate  .pbm- or .pgm-file is needed. In this file black (0) stands for
              fully transparant and white (1) will become opaque. The sizes of both  pbm/pgm/ppm-files  must  be
              the  same.   If  the  information  contained  in  the  alpha  mask  can  also  be represented as a
              transparency index, it will be used, since this should result in a smaller image file.

       -transparent color
              ppmtogif marks the specified color as transparent in the PNG image.

              You specify the color as in ppmmake(1).E.g.  red or rgb:ff/00/0d.  If the color you specify is not
              present  in  the image, pnmtopnm selects instead the color in the image that is closest to the one
              you specify.  Closeness is measured as a cartesian distance  between  colors  in  RGB  space.   If
              multiple colors are equidistant, pnmtopnm chooses one of them arbitrarily.

              However, if you prefix your color specification with "=", e.g.

              -transparent =red

              Only the exact color you specify will be transparent.  If that color does not appear in the image,
              there will be no transparency.  pnmtopng issues an information message when this is the case.

       -background color
              To create a background color chunck in the png-file, which  can  be  used  for  subsequent  alpha-
              channel or transparent-color conversions. See -transparent for format of color.

       -gamma value
              Creates an gAMA chunk. By providing the gamma-value of the pnm-file the software that lateron will
              display the png-file will be able to do the necessary gamma-corrections. A good  rule-of-thumb  is
              that when the file is created by a software program (like a CAD-program or a ray-tracer) the value
              is probably 1.0. When the pnm-file looks good on a  non-gamma  corrected  PC  display  (which  has
              itself a gamma-value of 2.2 - 2.8), a value of 0.45 should be given.

       -hist  Use  this parameter to create a chunk that specifies the frequency (or histogram) of the colors in
              the image.

       -chroma white point X and Y, red X and Y, green X and Y, and blue X and Y
              To specify the white point and rgb values following the CIE-1931 spec.

       -phys x y unit
              When your image should not be displayed with square but with rectangular pixels this option should
              be used to create a pHYS chunk. When the unit-value is 0 the x and y only gives the ratio of pixel
              width and height. When it is 1 the x and y specify the number of pixels per meter.

       -text file
              Allows to include comments in the text-chunk of the png-file.  The format of the text-file  is  as
              follows:  when the first column does not contain a blank or a tab, the first word is considered to
              be the keyword.  For keywords to contain spaces, enclose them in double-quotes.
              When the first character on a line is a blank or tab, the rest of the line is a new  line  of  the
              current comment.  Note that the initial spaces are not considered to be part of the comment line.

              Here is an example:
              -------------------------------------------
              Title           PNG-file
              Author          your name
              Description     how to include a text-chunk
                              into a PNG file
              "Creation date" 3-feb-1987
              Software        pnmtopng
              -------------------------------------------

       -ztxt file
              The same as -text, but now the text will be compressed.

       -time yy-mm-dd hh:mm:ss or -time yyyy-mm-dd hh:mm:ss
              This  option  allows  you  to specify the (modification)time. The year parameter can be given as a
              two- or a four-digit value.

       -filter type
              When the types of filters must be restricted you can specify here which filter you  want  to  use.
              Allowed values are: 0 (none), 1 (sub), 2 (up), 3 (avg) and 4 (paeth).

       -compression level
              To  explicitly  set the compression level of zlib use this parameter. Select a level between 0 for
              no compression (max speed) and 9 for maximum compression.

       -force When set, -force limits the optimizations of pnmtopng. A png-file similar to the pnm-input  is  as
              much  as possible enforced. For example no paletted files will be created and alpha-channel images
              will not be converted to images with a transparency chunck.

       All flags can be abbreviated to their shortest unique prefix.

SEE ALSO

       pngtopnm(1), gif2png(1), pnmgamma(1), pnm(5)

NOTE

       Instead of xxxtopnm|pnmtopng, a specific converter should be used,  if  available.   E.g.   gif2png  (GIF
       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                                      pnmtopng(1)