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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)