Pnmtopng User Manual(0)                 Pnmtopng User Manual(0)



Table Of Contents

NAME
       pnmtopng - convert a PNM image to PNG


SYNOPSIS
       pnmtopng  [-verbose]  [-downscale]  [-interlace] [-alpha
       file]  [-transparent   [=]color]   [-background   color]
       [-palette  palettefile]  [-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] [-nofilter]
       [-sub]  [-up]  [-avg]  [-paeth]   [-compression   level]
       [-force] [-version] [pnmfile]


OPTION USAGE
       Obsolete options:

       [-filter type]

       You  may  abbreviate  any  option to its shortest unique
       prefix.


DESCRIPTION
       This program is part of Netpbm(1).

       pnmtopng reads a PNM image as input and produces  a  PNG
       image 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
               This  specifies the transparency (alpha channel)
              of the image.  You supply the alpha channel as  a
              standard PGM alpha mask (see the PGM(1)specifica-
              tion.pnmtopngdoesnot necessarily  represents  the
              transparency  information  as an alpha channel in
              the PNG format.  If it can represent  the  trans-
              parency information through a palette, it will do
              so in order to make a smaller PNG file.  pnmtopng
              even  sorts the palette so it can omit the opaque
              colors from the transparency part of the  palette
              and save space for the palette.


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

              Specify the color (color) as  described  for  the
              argument  of the ppm_parsecolor() library routine
              .  E.g. red or rgb:ff/00/0d.  If  the  color  you
              specify  is  not  present  in the image, pnmtopng
              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 equidis-
              tant, pnmtopng 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 trans-
              parent.  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
              Causes  pnmtopng  to  create  a  background color
              chunk in the PNG output which  can  be  used  for
              subsequent  alpha  channel  or  transparent color
              conversions.   Specify  color  the  same  as  for
              -transparent.


       -palette palettefile
              This  option  specifies  a  palette to use in the
              PNG.  It forces pnmtopng to create  the  paletted
              (colormapped)  variety  of  PNG  -- if that isn't
              possible, pnmtopng fails.   If  the  palette  you
              specify doesn't contain exactly the colors in the
              image, pnmtopng fails.  Since pnmtopng will auto-
              matically generate a paletted PNG, with a correct
              palette, when appropriate, the  only  reason  you
              would  specify the -palette option is if you care
              in what order the colors appear in  the  palette.
              The  PNG  palette has colors in the same order as
              the palette you specify.

              You specify the palette by naming a PPM file that
              has one pixel for each color in the palette.

              Alternatively,  consider  the  case  that  have a
              palette and you want to make sure your  PNG  con-
              tains only colors from the palette, approximating
              if necessary.  You don't care  what  indexes  the
              PNG  uses  internally  for  the  colors (i.e. the
              order of the PNG palette).   In  this  case,  you
              don't need -palette.  Pass the Netpbm input image
              and your palette PPM  through  pnmremap.   Though
              you  might think it would, using -palette in this
              case wouldn't even save pnmtopng any work.


       -gamma value
              Causes pnmtopng to create an  gAMA  chunk.   This
              information  helps  describe how the color values
              in the PNG must be interpreted.  Without the gAMA
              chunk,  whatever interprets the PNG must get this
              information separately (or just assume  something
              standard).   If  your  input is a true PPM or PGM
              image, you should specify -gamma .45.  But  some-
              times people generate images which are ostensibly
              PPM except  the  image  uses  a  different  gamma
              transfer function than the one specified for PPM.
              A common case of this is when the image  is  cre-
              ated by simple hardware that doesn't have digital
              computational ability.  Also,  some  simple  pro-
              grams  that  generate  images  from scratch do it
              with a gamma transfer in which the gamma value is
              1.0.


       -hist  Use  this parameter to create a chunk that speci-
              fies 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 This option
              specifies the white point and rgb values  follow-
              ing the CIE-1931 spec.


       -phys x y unit
              This  option  determines  the aspect ratio of the
              individual pixels of your image as  well  as  the
              physical resolution of it.

              unit  is either 0 or 1.  When it is 1, the option
              specifies the physical resolution of the image in
              pixels per meter.  For example, -phys 10000 15000
              1 means that when someone displays the image,  he
              should make it so that 10,000 pixels horizontally
              occupy  1  meter  and  15,000  pixels  vertically
              occupy  one  meter.   And even if he doesn't take
              this advice on the overall size of the  displayed
              image,  he  should  at least make it so that each
              pixel displays as 1.5 times as high as wide.

              When unit is 0, that means there is no advice  on
              the  absolute  physical  resolution;  just on the
              ratio of horizontal to vertical physical  resolu-
              tion.

              This  information goes into the PNG's pHYS chunk.

              When you don't specify  -phys,  pnmtopng  creates
              the  image with no pHYS chunk, which means square
              pixels of no absolute resolution.


       -text file
              This option lets you include comments in the text
              chunk  of  the PNG output.  file is the name of a
              file that contains your text comments.

              Here is an example of a comment file:
                         Title           PNG file

                         Author          Bryan Henderson

                         Description     how to include a text chunk
                                         PNG file
                         "Creation date" 3-feb-1987

                         Software        pnmtopng

              The format of the file is as follows:   The  file
              is divided into lines, delimited by newline char-
              acters.  The  last  line  need  not  end  with  a
              newline  character.  A group of consecutive lines
              represents a comment.

              A "delimiter character" is a blank or tab or null
              character.  The first line representing a comment
              must not start with a delimiter character.  Every
              other  line in the group is a "continuation line"
              and must start with a delimiter character.

              The first line representing a comment consists of
              a  keyword  and  the  first line of comment text.
              The keyword begins in Column 1 of the  file  line
              and continues up to, but not including, the first
              delimiter character, or  the  end  of  the  line,
              whichever  is  first.  Exception: you can enclose
              the keyword in double quotes and spaces and  tabs
              within the double quotes are part of the keyword.
              The quotes are not part of the  keyword.   A  NUL
              character is not allowed in a keyword.

              The  first  line  of  the comment text is all the
              text in the file line beginning after the keyword
              and  any  delimiter characters after it.  immedi-
              ately after the delimiter  character  that  marks
              the end of the keyword.

              A  continuation line defines a subsequent line of
              the comment.  The comment line is all the text on
              the  continuation  line  starting  with the first
              non-delimiter character.

              There is one newline character between every  two
              comment  lines.   There  is  no newline character
              after the last line of comment text.

              There is no limit on the length of a file line or
              keyword  or  comment  text  line or comment text.
              There is no limit on the number  of  comments  or
              size of or number of lines in the file.


       -ztxt file
              The  same as -text, except pnmtopng considers the
              text 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 value to be
              placed in the PNG output.  You  can  specify  the
              year  parameter  either  as  a  two digit or four
              digit value.


       -filter type
              This option is  obsolete.   Before  Netpbm  10.22
              (April  2004), this was the only way to specify a
              row filter.  It specifies a single  type  of  row
              filter, by number, that pnmtopng must use on each
              row.

              Use -nofilter, -sub, -up,  -avg,  and  -paeth  in
              current Netpbm.


       -nofilter

       -sub

       -up

       -avg

       -paeth Each of these options permits pnmtopng to use one
              type of row filter.  pnmtopng  chooses  whichever
              of  the permitted filters it finds to be optimal.
              If you specify none of these options, it  is  the
              same  as  specifying all of them -- pnmtopng uses
              any row filter type it finds optimal.

              These options were new with Netpbm  10.22  (April
              2004).   Before  that,  you could use the -filter
              option to specify one permitted row filter  type.
              The  default, when you specify no filter options,
              was the same.


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


       -force When  you specify this, pnmtopng limits its opti-
              mizations.  The resulting PNG output is as  simi-
              lar  to  the Netpbm input as possible.  For exam-
              ple, the PNG output will not be paletted and  the
              alpha channel will be represented as a full alpha
              channel even if the information could  be  repre-
              sented more succinctly with a transparency chunk.



       -libversion
              This option causes pnmtopng  to  do  nothing  but
              display  version  information about the libraries
              it uses.




SEE ALSO
       pngtopnm(1), pnmremap(1), pnmgamma(1), pnm(1)

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


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



netpbm documentation       June 2002    Pnmtopng User Manual(0)
