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


       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]


       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.


              Display the format of the output file.

              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.

              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.


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


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


       There could be an option to read the comment text from pnm comments instead of a  separate

       The program could be much faster, with a bit of code optimizing.


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

                                          6 January 1997                              pnmtopng(1)