Provided by: netpbm_11.07.00-2_amd64 bug

NAME

       pnmtopng - convert a PNM image to PNG

SYNOPSIS

       pnmtopng  [-verbose]  [-downscale] [-interlace] [-alpha=file] [-transparent=[=]color] [-background=color]
       [-palette=palettefile] [-gamma=value] [-hist] [-text=file] [-ztxt=file] [-rgb='wx wy
         rx ry gx gy bx by'] [-size='x y unit'] [-srgbintent=intent] [-modtime='[yy]yy-mm-dd
         hh:mm:ss']   [-nofilter]   [-sub]   [-up]   [-avg]   [-paeth]   [-compression=n]    [-comp_mem_level=n]
       [-comp_strategy={huffman_only|filtered}]           [-comp_method=deflated]          [-comp_window_bits=n]
       [-comp_buffer_size=n] [-force] [-libversion] [pnmfile]

OPTION USAGE

       Obsolete options:

       [-filter n]

       Options available only in older versions:

       [-chroma wx wy rx ry gx gy bx by] [-phys x y unit] [-time [yy]yy-mm-dd
         hh:mm:ss]

       Minimum unique abbreviation of option is acceptable.  You may use double 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).

       pnmtopng reads a PNM image as input and produces a PNG image as output.

       Color component 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.

       For  a  grayscale  image, pnmtopng produces a PNG bit depth 1, 2, 4, 8 or 16.  When the input image has a
       small maxval, the output PNG image has a correspondingly small bit depth.  But in mapping the PNM  maxval
       to  the  PNG  maxval  (which  is by definition the maximum value that can be represented in the number of
       bits), a fair amount of distortion happens with these low maxvals.  For example, with a PNM maxval  of  5
       and  a  PNG  maxval  of 7, the input sample 2 becomes the output sample 3.  The input brightness is 2/5 =
       .40, while the output brightness is 3/7 = .43.  Note that this is not a problem if you view the maxval as
       a  precision,  because  in .4 and .43 are identical within the precision implied by maxval 5.  Indeed, if
       you convert this PNG back to a maxval 5 PGM, the pixel's value  will  again  be  2,  exactly  as  it  was
       originally.   But  if you need precisely the same colors in the output PNG as in the input PNM, make sure
       your input PNM has a maxval which is a power of two minus one.  If you can't do  that,  then  convert  it
       with  pamdepth  to something with a large maxval that is a power of two minus one (255 and 65535 are good
       choices) to minimize the error.

OPTIONS

   Note: Option Syntax of Older Versions
       pnmtopng changed in Netpbm 10.30 (October 2005) to use the standard Netpbm command line  syntax.   Before
       that, you could not use double hyphens to denote an option and could not use an equal sign to separate an
       option name from its value.  And the options had to come before the non-option program arguments.

       Furthermore, the options  -chroma,  -phys,  and  -time  were  replaced  by  -rgb,  -size,  and  -modtime,
       respectively.   The  only  difference,  taking  -phys/-size  as  an example, is that -phys takes multiple
       program arguments as the option argument, whereas -size takes a single program argument which is composed
       of multiple words.  E.g. the old shell command

          pnmtopng -phys 800 800 0 input.pnm > output.png

       is equivalent to the new shell command

          pnmtopng -size "800 800 0" input.pnm > output.png

       If  you're  writing  a  program that needs to work with both new and old , have it first try with the new
       syntax, and if it fails with "unrecognized option," fall back to the old syntax.

   Current Options
       In addition to the options common to all programs based on libnetpbm (most notably -quiet, see
        Common Options ⟨index.html#commonoptions⟩ ), pnmtopng recognizes the following command line options:

       -verbose
              This causes pnmtopng to display information about the format of the output file.

       -downscale
              This enables pnmtopng to scale maxvalues of more then 65535 to 16 bits. Since this means  loss  of
              image data, pnmtopng does not do it by default.

       -interlace
              This causes the PNG file to be interlaced, in Adam7 format.  The interlaced format is one in which
              the raster data starts with a low-resolution representation of the entire  image,  then  continues
              with  additional  information  for the entire image, then even more information, etc.  In Adam7 in
              particular, there are seven such passes of the whole image.  This is useful when you are receiving
              the  image  over a slow communication line as someone is waiting to see it.  The simplest thing to
              do in that case is wait for the entire image to arrive and then display it instantly, but then the
              user  is  wasting  time staring at a blank space until the whole image arrives.  With the standard
              non-interlaced format, the data arrives row-by-row starting at the top,  so  the  displayer  could
              display  each  row of the image as it arrives and gradually paint down to the bottom.  But with an
              interlaced image, the displayer can start by showing a low-resolution version of the  image,  then
              gradually improve the display as more data arrives.

       -alpha=filename
              This specifies the transparency (alpha) channel of the image.  You supply the transparency channel
              as a standard PGM transparency mask (see the PGM(1) specification.  pnmtopng does not  necessarily
              represents  the  transparency  information as a transparency channel in the PNG format.  If it can
              represent the transparency 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  pnm_parsecolor()  library  routine
              ⟨libnetpbm_image.html#colorname⟩  .   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 equidistant, 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 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
              Causes pnmtopng to create a background color chunk in  the  PNG  output  which  can  be  used  for
              subsequent  transparency  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
              automatically  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 contains
              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 a 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=.52.  But sometimes 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 created by simple  hardware  that  doesn't  have  digital
              computational  ability.  Also, some simple programs 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 specifies the frequency (or histogram) of the colors  in
              the image.

       -text=filename
              This option lets you include arbitrary text strings in the PNG output, as tEXt chunks.

              filename is the name of a file that contains your text strings.

              The output contains a distinct tEXt chunk for each entry in the file.

              Here is an example of a text string file:

                   Title           PNG file
                   Author          John Doe
                   Description     how to include a text chunk
                                      PNG file
                   "Creation Date" 2015-may-11
                   Software        pamtopng

              The file is divided into entries, each entry comprising consecutive lines of text.  The first line
              of an entry starts in the first column (i.e. the first column is not white space) and every  other
              line  has white space in the first column.  The first entry starts in the first line, so it is not
              valid for the first line of the file to have white space in its first column.

              The first word in an entry is the key of the text string (e.g. 'Title').  It begins in column  one
              of  the  line  and continues up to, but not including, the first delimiter character or the end of
              the line, whichever is first.  You can enclose the key in double quotes in which case the key  can
              consists  of  multiple  words.  The quotes are not part of the key.  The text string per se begins
              after the key and any delimiter characters after it, plus  the  text  in  subsequent  continuation
              lines.

              There  is no limit on the length of a file line or entry or key or text string.  There is no limit
              on the number of entries.

       -ztxt=filename
              The same as -text, except the text string is compressed in the PNG  output.   pnmtopng  uses  zTXt
              chunks  instead of a tEXt chunks, unless the key for the text string starts with 'A' or 'T'.  This
              odd exception exists for backward compatibility; we don't know  why  the  program  was  originally
              designed this way, except that the distinction was meant to roughly identify the keys 'Author' and
              'Title'.

       -rgb=chroma_list
              This option specifies how red, green, and blue component values of a pixel  specify  a  particular
              color,  by  telling  the  chromaticities  of  those  3 primary illuminants and of white (i.e. full
              strength of all three).

              The chroma_list value is a blank-separated list of 8 floating point decimal numbers:  the CIE-1931
              X and Y chromaticities (in that order) of each of white, red, green, and blue, in that order.

              This information goes into the PNG's cHRM chunk.

              In a shell command, make sure you use quotation marks so that the blanks in chroma_list don't make
              the shell see multiple command arguments.

              This option was new in Netpbm 10.30 (October 2005).  Before that, the option -chroma does the same
              thing, but with slightly different syntax.

       -size="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, -size="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 resolution.

              This information goes into the PNG's pHYS chunk.

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

              This option was new in Netpbm 10.30 (October 2005).  Before that, the option -phys does  the  same
              thing, but with slightly different syntax.

       -srgbintent=intent
              This  asserts  that  the input is a pseudo-Netpbm image that uses an sRGB color space (unlike true
              Netpbm) and indicates how you intend for the colors to be rendered.  It causes pnmtopng to include
              an  sRGB  chunk in the PNG image that specifies that intent, so see the PNG documentation for more
              information on what this really means.

              intent is one of:

       •      perceptualrelativecolorimetricsaturationabsolutecolorimetric

              This option was new in Netpbm 10.71 (June 2015).  Before that, pnmtopng never  generates  an  sRGB
              chunk.

       -modtime="[yy]yy-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.

              This option was new in Netpbm 10.30 (October 2005).  Before that, the option -time does  the  same
              thing, but with slightly different syntax.

       -filter=n
              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=n
              This option sets set the compression level of the zlib compression.  Select a level from 0 for  no
              compression (maximum speed) to 9 for maximum compression (minimum speed).

              The default is the default of the zlib library.

       -comp_mem_level=n
              This  option  sets  the  memory  usage  level  of the zlib compression.  Select a level from 1 for
              minimum memory usage (and minimum speed) to 9 for maximum memory usage (and speed).

              The default is the default of the zlib library.

              This option was new in Netpbm 10.30 (October 2005).

       -comp_strategy={huffman_only|filtered}
              This options sets the compression strategy of the zlib compression.  See  Zlib  documentation  for
              information on what these strategies are.

              The default is the default of the zlib library.

              This option was new in Netpbm 10.30 (October 2005).

       -comp_method=deflated
              This  option  does  nothing.   It  is  here for mathematical completeness and for possible forward
              compatibility.  It theoretically selects the compression method of the zlib compression, but the Z
              library knows only one method today, so there's nothing to choose.

              The default is the default of the zlib library.

              This option was new in Netpbm 10.30 (October 2005).

       -comp_window_bits=N
              This  option  tells how big a window the zlib compression algorithm uses.  The value is the base 2
              logarithm of the window size in bytes, so 8 means 256 bytes.  The value must be from 8 to 15 (i.e.
              256 bytes to 32K).

              See Zlib documentation for details on what this window size is.

              The default is the default of the zlib library.

              This option was new in Netpbm 10.30 (October 2005).

       -comp_buffer_size=N
              This  option  determines  in  what size pieces pnmtopng does the zlib compression.  One compressed
              piece goes in each IDAT chunk in the PNG.  So the bigger this value, the fewer  IDAT  chunks  your
              PNG  will have.  Theoretically, this makes the PNG smaller because 1) you have less per-IDAT-chunk
              overhead, and 2) the compression algorithm has more data  to  work  with.   But  in  reality,  the
              difference will probably not be noticeable above about 8K, which is the default.

              The value n is the size of the compressed piece (i.e. the compression buffer) in bytes.

              This option was new in Netpbm 10.30 (October 2005).

       -force When  you specify this, pnmtopng limits its optimizations.  The resulting PNG output is as similar
              to the Netpbm input as possible.  For example, the  PNG  output  will  not  be  paletted  and  the
              transparency  channel  will  be represented as a full transparency channel even if the information
              could be represented more succinctly with a transparency chunk.

       -libversion
              This option causes pnmtopng to display version information about itself and the libraries it uses,
              in  addition  to  all  its  normal  function.   Do  not confuse this with the Netpbm common option
              -version, which causes the program to display version information about the Netpbm library and  do
              nothing else.

              You  can't  really  use  this  option  in  a program that invokes pnmtopng and needs to know which
              version it is.  Its function has changed too much over the history of  pnmtopng.   The  option  is
              good only for human eyes.

SEE ALSO

       pngtopam(1), pamtopng(1), pnmremap(1), pnmgamma(1), pnm(1)

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

AUTHOR

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

DOCUMENT SOURCE

       This  manual  page was generated by the Netpbm tool 'makeman' from HTML source.  The master documentation
       is at

              http://netpbm.sourceforge.net/doc/pnmtopng.html