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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2008-12-06 21:18:58 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2008-12-06 21:18:58 +0000 |
| commit | db5f3dbcf879eb3a55e819147f1ba7a1ee55a535 (patch) | |
| tree | a579ec584ede17644f672a94f7be53f19192cb6b /pngtopam.html | |
| parent | 77bf1e7cd506979ca0679c48a9da3dcf0d948dbd (diff) | |
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git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@785 9d0c8265-081b-0410-96cb-a4ca84ce46f8
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diff --git a/pngtopam.html b/pngtopam.html new file mode 100644 index 00000000..a499ecb8 --- /dev/null +++ b/pngtopam.html @@ -0,0 +1,226 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN"> +<HTML><HEAD><TITLE>Pngtopam User Manual</TITLE></HEAD> +<BODY> +<H1>pngtopam</H1> +Updated: 22 July 2008 +<BR> +<A HREF="#index">Table Of Contents</A> + +<H2>NAME</H2> + +pngtopam - convert a PNG image into a Netpbm image + +<H2 id="synopsis">SYNOPSIS</H2> + +<B>pngtopam</B> +[<b>-verbose</b>] +[<b>-alphapam</b> | <b>-alpha</b> | <b>-mix</b>] +[<b>-background</b>=<i>color</i>] +<BR> +[<b>-gamma</b>=<i>value</i>] +[<b>-text</b>=<i>filename</i>] +[<b>-time</b>] +[<I>pngfile</I>] + +<P>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. + +<H2 id="description">DESCRIPTION</H2> + +<p>This program is part of <a href="index.html">Netpbm</a>. + +<p><b>pngtopam</b> reads a PNG image (Portable Network Graphics) as +input and produces a Netpbm image as output. The type of the output file +depends on the input file - if it's black & white, <b>pngtopam</b> +creates a PBM file. If it's grayscale, <b>pngtopam</b> creates a PGM +file. Otherwise, it creates a PPM file. Except that with the +<b>-alphapam</b> option, it always creates a PAM file. That file has +tuple type GRAYSCALE_ALPHA or RGB_ALPHA depending on whether the input +has color or not. + +<H2 id="options">OPTIONS</H2> + +<DL COMPACT> +<DT><B>-verbose</B> + +<DD>Display various information about the input PNG image and the +conversion process. + +<p>If you want even more information about the PNG image, use +<b>pngcheck</b> (not part of Netpbm). + +<DT><B>-alphapam</B> + +<DD>Produce a single output image containing the main image (foreground) +and the alpha channel or transparency mask. This image is in the PAM +format with tuple type of either GRAYSCALE_ALPHA (which has a depth of +2 channels) or RGB_ALPHA (which has a depth of 4 channels). + +<p>You can specify only one of <b>-alphapam</b>, <b>-alpha</b>, and +<b>-mix</b>. With none of them, <b>pngtopam</b> produces an image of +the foreground of the input image and discards transparency information. + +<P>This option was new in Netpbm 10.44 (September 2008). + +<DT><B>-alpha</B> + +<DD>Output the alpha channel or transparency mask of the image. The +result is either a PBM file or a PGM file, depending on whether +different levels of transparency appear. + +<p><b>pngtopam</b> discards the main image (the foreground). + +<p>You can specify only one of <b>-alphapam</b>, <b>-alpha</b>, and +<b>-mix</b>. With none of them, <b>pngtopam</b> produces an image of +the foreground of the input image and discards transparency information. + +<DT><B>-mix</B> + +<DD>Compose the image with the transparency or alpha mask against a +background. The background color is determined by the bKGD chunk in +the PNG, except that you can override it with <b>-background</b>. +If the PNG has no bKGD chunk and you don't specify <b>-background</b>, +the background color is white. + +<p>You can specify only one of <b>-alphapam</b>, <b>-alpha</b>, and +<b>-mix</b>. With none of them, <b>pngtopam</b> produces an image of +the foreground of the input image and discards transparency information. + +<DT><B>-background=</b><i>color</i> + +<DD> +This option specifies the background color with which to mix the image +when you specify <b>-mix</b>. + +<P><i>color</i> is as described for the <a +href="libppm.html#colorname">argument of the <b>ppm_parsecolor()</b> +library routine</a>. + +<p>Examples: + +<ul> +<li><tt>-background=rgb:01/ff/80</tt> +<li><tt>-background=rgbi:1/255/128</tt> +</ul> + +<p>If you don't specify <b>-background</b>, the background color is what +is specified in the PNG image, and if the PNG doesn't specify anything, +white. + +<p>You cannot specify <b>-background</b> unless you also specify +<b>-mix</b>. Before Netpbm 10.27 (March 2005), you could specify +<b>-background</b> without <b>-mix</b> and it was just ignored. (This +caused a usability problem). + + +<DT><B>-gamma=</b><i>value</i> + +<DD>Converts the image to a new display-gamma value. If a gAMA chunk +is present in the <I>png-file</I>, <b>pngtopam</b> uses the specified +image-gamma value. If not, <b>pngtopam</b> considers the image-gamma +to be 1.0. Based on the image-gamma and the display-gamma given with +this option, <b>pngtopam</b> adjusts the colors written to the +<I>pnm-file</I>. + +<p>Because the gammas of uncompensated monitors are around 2.6, which results +in an image-gamma of 0.45, some typical situations are: +when the image-gamma is 0.45 (use -verbose to check) and the picture is too +light, your system is gamma-corrected, so convert with "-gamma 1.0". +When no gAMA chunk is present or the image-gamma is 1.0, use 2.2 to make the +picture lighter and 0.45 to make the picture darker. + +<p>One oddity to be aware of when using <b>-gamma</b> on an image with +transparency: The PNG image specifies that a certain color is +transparent, i.e. every pixel in the image of that color is +transparent. But <b>pngtopam</b> interprets this as applying to the +gamma-corrected space, and there may be less precision in that space +than in the original, which means multiple uncorrected colors map to +the same corrected color. So imagine that the image contains 3 shades +of white and specifies that one of them is transparent. After gamma +correction, those three shades are indistinguishable, so +<b>pngtopam</b> considers pixels of all three shades to be transparent. + +<p>If this is not what you want, don't use <b>gamma</b>. Instead, +use <b>pnmgamma</b> on the output. + + +<DT><B>-text=</b><i>file</i> + +<DD>Writes the tEXt and zTXt chunks to a file, in a format as +described in the <b>pnmtopng</b> user manual. These chunks contain +text comments or annotations. + +<DT><B>-time</B> + +<DD>Prints the tIME chunk to stderr. + +</DL> + +<H2 id="seealso">SEE ALSO</H2> + +<A HREF="pnmtopng.html">pnmtopng</A>, +<A HREF="pngtopnm.html">pnmtopng</A>, +<b>ptot</b>, +<A HREF="pnmgamma.html">pnmgamma</A>, +<A HREF="pnm.html">pnm</A> + +<p>For information on the PNG format, see <a +href="http://schaik.com/png">http://schaik.com/png</a>. + +<H2 id="note">NOTE</H2> + +<p>A PNG image contains a lot of information that can't be represented in +Netpbm formats. Therefore, you lose information when you convert to +another format with "pngtopam | pnmtoxxx". If there is a specialized +converter that converts directly to the other format, e.g. <b>ptot</b> +to convert from PNG to TIFF, you'll get better results using that. + +<H2 id="limitations">LIMITATIONS</H2> + +<p>There could be an option to include PNG comment chunks in the output +image as PNM comments instead of putting them in a separate file. + +<P>The program could be much faster, with a bit of code optimizing. +As with any Netpbm program, speed always takes a back seat to quick +present and future development. + +<h2 id="history">HISTORY</h2> + +<p><b>pngtopam</b> was new in Netpbm 10.44, as a replacement for +<b>pngtopnm</b>. The main improvement over <b>pngtopnm</b> was that +it could generate a PAM image with a transparency channel, whereas +with <b>pngtopnm</b>, you would have to extrac the transparency +channel as a separate file, in a separate run. + +<p><b>pngtopnm</b> was new in Netpbm 8.1 (March 2000), the first big +change to the package in Netpbm's renaissance. It and <b>pnmtopng</b> +were simply copied from the <a +href="http://www.libpng.org/pub/png/apps/pnmtopng.html"> +<b>pnmtopng</b> package</a> by Greg Roelofs. Those were based on +simpler reference applications by by Alexander Lehmann +<alex@hal.rhein-main.de> and Willem van Schaik +<willem@schaik.com> and distributed with their PNG library. + +<p>Nearly all of the code has changed since it was copied from the +<b>pnmtopng</b> package, most of it just to improve maintainability. + + +<H2 id="authors">AUTHORS</H2> + +Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik. + +<HR> +<H2 id="index">Table Of Contents</H2> +<UL> +<LI><A HREF="#synopsis">SYNOPSIS</A> +<LI><A HREF="#description">DESCRIPTION</A> +<LI><A HREF="#options">OPTIONS</A> +<LI><A HREF="#seealso">SEE ALSO</A> +<LI><A HREF="#note">NOTE</A> +<LI><A HREF="#limitations">LIMITATIONS</A> +<LI><A HREF="#history">HISTORY</A> +<LI><A HREF="#authors">AUTHORS</A> +</UL> +</BODY> +</HTML> |