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pnmtopng Updated: June 2002 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] Obsolete options: [-filter type] You may abbreviate any option to its shortest unique prefix. DESCRIPTION This program is part of Netpbm. 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 specification. pnmtopng does not necessarily repre- sents 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. Specify the color (color) as described for the argu- ment 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 equidistant, pnm- topng 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 trans- parency. 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 -transpar- ent. -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 in- put 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 informa- tion helps describe how the color values in the PNG must be inter- preted. 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 speci- fied 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 This option determines the aspect ratio of the individ- ual pixels of your image as well as the physical resolution of it. unit is either 0 or 1. When it is 1, the option spec- ifies 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 occu- py 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 -phys, pnmtopng creates the im- age with no pHYS chunk, which means square pixels of no absolute resolu- tion. -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 di- vided into lines, delimited by newline characters. The last line need not end with a newline character. A group of consecutive lines repre- sents a comment. A "delimiter character" is a blank or tab or null char- acter. The first line representing a comment must not start with a delimiter character. Every other line in the group is a "continu- ation 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 Col- umn 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 key- word. The first line of the comment text is all the text in the file line beginning after the keyword and any delimiter charac- ters after it. immediately 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 com- ment 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 key- word 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 pa- rameter 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 permit- ted 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 optimiza- tions. 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. -libversion This option causes pnmtopng to do nothing but display version information about the libraries it uses. 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. _________________________________________________________________ Table Of Contents * NAME * SYNOPSIS * DESCRIPTION * OPTIONS * SEE ALSO * AUTHORS
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