# pnmtopng

Updated: June 2002
Index

## 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] [-filter type] [-compression level] [-force] [pnmfile]

## DESCRIPTION

Reads a PPM, PGM, or PBM image as input. 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 specification. pnmtopng does not necessarily represents the transparency information as an alpha 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.

  You specify the color as in ppmmake.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 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 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.

  If you have a palette and you want to make sure your PNG contains only colors from the palette, approximating if necessary, pass the Netpbm input image and your palette PPM through pnmremap. There's no need to use -palette on pnmtopng in this case. It doesn't 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 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.
-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 following the CIE-1931 spec.
-phys x y unit
  When your image should not be displayed with square but with rectangular pixels, use this option to create a pHYS chunk. When unit is 0, x and y give only the ratio of pixel width and height. When it is 1, x and y specify the number of pixels per meter.
-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.

  The format of the file is as follows: When the first column does not contain a blank or a tab, the first word is considered to be a keyword. For a keyword to contain spaces, enclose it 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. 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
                                 PNG file
                 "Creation date" 3-feb-1987

                 Software        pnmtopng

-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
  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 (maximum speed) and 9 for maximum compression (minimum speed).
-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 alpha channel will be represented as a full alpha channel even if the information could be represented more succinctly with a transparency chunk.

All options can be abbreviated to their shortest unique prefix.

## SEE ALSO

pngtopnm, pnmremap, pnmgamma, pnm

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

## AUTHORS

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

## Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
SEE ALSO
AUTHORS