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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 3.2//EN">
<html>
<head><title>Pamtopng User Manual</title></head>
<body>
<h1>pamtopng</h1>
Updated: 28 June 2015
<BR>
<a href="#index">Table Of Contents</a>
<h2>NAME</h2>
pamtopng - convert a Netpbm image to PNG
<h2 id="synopsis">SYNOPSIS</h2>
<b>pamtopng</b>
[<b>-verbose</b>]
[<b>-transparent=</b><i>color</i>]
[<b>-background=</b><i>color</i>]
[<b>-gamma=</b><i>value</i>]
[<b>-chroma="</b><i>wx</i> <i>wy</i>
<i>rx</i> <i>ry</i> <i>gx</i> <i>gy</i> <i>bx</i> <i>by</i><b>"</b>]
[<b>-srgbintent=</b><i>intent</i>]
[<b>-time=</b>[<i>yy</i>]<i>yy</i><b>-</b><i>mm</i><b>-</b><i>dd</i>
<i>hh</i><b>:</b><i>mm</i><b>:</b><i>ss</i>]
[<b>-text=</b><i>file</i>]
[<b>-ztxt=</b><i>file</i>]
[<b>-itxt=</b><i>file</i>]
[<I>pnmfile</i>]
<?makeman .SH OPTION USAGE ?>
<p>Minimum unique abbreviation of option is acceptable. You may use double
hyphens instead of a 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>pamtopng</b> reads a Netpbm image as input and produces a PNG image as
output.
<p>Color component values in PNG files are either 8 or 16 bits wide, so where
necessary <b>pamtopng</b> scales colors to have a maxval of 255 or 65535.
In that case, it will add an sBIT chunk to indicated the original bit-depth.
<p><b>pamtopng</b> works only on images with maxval 1, 3, 15, 255, or 65535.
You can use <b>pamdepth</b> to convert an image with some other maxval to one
of these.
<p><b>pamtopng</b> produces a color PNG from a color PAM, even if the
only colors in the image are shades of gray. To create a graycale PNG,
from such an image (which might be slightly smaller), you can use other
Netpbm programs to convert the input to grayscale.
<h3 id="pnmtopng">Alternative: <b>pnmtopng</b></h3>
<p>Netpbm contains another program for generating PNG images: <b>pnmtopng</b>.
<b>pnmtopng</b> is a much older program - it is in fact the first program in
the world that could generate a PNG. <b>pnmtopng</b> is a complex,
feature-laden program. It lets you control various arcane aspects of the
conversion and create PNGs with various arcane features. It does various
transformations on the image to create the greatest compression possible, to a
degree that probably doesn't make any difference in the modern world.
<p>Because <b>pnmtopng</b> has been around virtually forever, programs and
procedures that use it are more portable than those that use <b>pamtopng</b>.
Its age and popularity also probably make it have fewer bugs.
<p><b>pamtopng</b> does not have any way to do what the following do in
<b>pnmtopng</b>:
<ul>
<li><b>-palette</b>
<li><b>-history</b>
<li><b>-filter</b>
<li><b>-size</b>
<li><b>-paeth</b>
<li><b>-hist</b>
<li><b>-nofilter</b>
<li><b>-sub</b>
<li><b>-up</b>
<li><b>-avg</b>
<li><b>-force</b>
<li><b>-libversion</b>
<li><b>-compression</b>
<li><b>-comp_</b><i>xxx</i>
</ul>
<p>These are some of the other functions of <b>pnmtopng</b>
that <b>pamtopng</b> lacks:
<ul>
<li>When you specify a transparent or background color that is not in the
image, <b>pnmtopng</b> can optionally choose the closest one that is in
image. <b>pamtopng</b> always uses the exact color you specify.
</ul>
<p>Features that exist in both programs are controlled by largely the same
command syntax. But there are these differences:
<ul>
<li><b>pnmtopng</b>'s <b>-rgb</b> option is <b>-chroma</b> in <b>pamtopng</b>.
<b>-chroma</b> is a better name, and in fact was the name that <b>pnmtopng</b>
used originally, but we had to change it when we had to change the syntax
of the option value to conform to the rest of Netpbm.
<li><b>pnmtopng</b>'s <b>-modtime</b> option is <b>-time</b> in
<b>pamtopng</b>. The origin of <b>-modtime</b> is analogous to that of
<b>-rgb</b>.
</ul>
<h2 id="options">OPTIONS</h2>
<dl compact>
<dt><b>-transparent=</b><i>color</i>
<dd>
<b>pamtopng</b> marks the specified color as transparent in the PNG image.
<P>Specify the color (<i>color</i>) as described for
the <a href="libppm.html#colorname">argument of the <b>ppm_parsecolor()</b>
library routine</a>. E.g. <B>red</B> or <B>rgb:ff/00/0d</B>.
<dt><b>-background=</b><i>color</i>
<dd>
This causes <b>pamtopng</b> to create a background color chunk in the PNG
output which can be used for subsequent transparency channel or transparent
color conversions. Specify <i>color</i> the same as for <b>-transparent</b>.
<dt><b>-gamma=</b><i>value</i>
<DD>This causes <b>pnmtopng</b> 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 <b>-gamma=.45</b>. 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.
<dt><b>-chroma=</b><i>chroma_list</i>
<dd>
<DD>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).
<p>The <i>chroma_list</i> 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.
<p>This information goes into the PNG's cHRM chunk.
<p>In a shell command, make sure you use quotation marks so that the
blanks in <i>chroma_list</i> don't make the shell see multiple command
arguments.
<dt><b>-srgbintent=</b><i>intent</i>
<dd>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 <b>pamtopng</b> 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.
<p><i>intent</i> is one of:
<ul>
<li><b>perceptual</b>
<li><b>relativecolorimetric</b>
<li><b>saturation</b>
<li><b>absolutecolorimetric</b>
</ul>
<dt><b>-text=</b><i>filename</i>
<dd>
This option lets you include comments in text chunks of the PNG output.
<i>filename</i> is the name of a file that contains your text comments.
<p>The output contains a distinct tEXt chunk for each comment.
<p>Here is an example of a comment file:
<pre>
Title PNG file
Author John Doe
Description how to include a text chunk
PNG file
"Creation Date" 2015-may-11
Software pamtopng
</pre>
<p>The first line representing a comment must not start with a delimiter
character (a blank, tab or null). Every other line in the group is a
continuation line and must start with a delimiter character.
<p>The first word in a comment line is the keyword of the comment. 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 keyword in double quotes in which case the keyword can consists of
multiple words. The quotes are not part of the keyword. The comment text
begins after the keyword and any delimiter characters after it, plus the text
in subsequent continuation lines.
<p>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, the size
of the comment or the number of comments in the file.
<dt><b>-ztxt=</b><i>filename</i>
<dd>The same as <b>-text</b>, except <b>pamtopng</b> will compress the
comment, except that when the keyword is "Title", "Author" or "Language".
<dt><b>-itxt=</b><i>filename</i>
<dd>Similar to <b>-text</b>, but the comments can be in a language other than
English. The PNG image indicates what language that is and includes the
comment key both in English and that language.
<p>The input file must start with a record that identifies the comment
language. Its key is "Language".
<p>For each record, you must give the key both in English and in the comment
language.
<p>Example:
<pre>
Language Taal nl-NL
Title Titel PNG file
Author Auteur Pietje Puk
Description Omschrijving Tekst in het Nederlands.
</pre>
<p>The language specification is based on the ISO 639-1 standard, see
http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes for the valid codes.
The format is either a two character "nl" or an extended code like "en-US".
<dt><b>-time="</b>[<i>yy</i>]<i>yy-mm-dd hh:mm:ss</i><b>"</b>
<dd>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 or four
digit value.
<dt><b>-verbose</b>
<dd>
This causes the program to display various facts about the conversion.
</dl>
<h2 id="seealso">SEE ALSO</h2>
<a href="pngtopam.html">pngtopam</a>,
<a href="pnmtopng.html">pnmtopng</a>,
<a href="pam.html">pam</a>,
<a href="pnm.html">pnm</a>
<p>For information on the PNG format, see
<a href="http://www.w3.org/TR/PNG/">http://www.w3.org/TR/PNG/</a>,
<a href="http://libpng.org/pub/png/">http://libpng.org/pub/png/</a>,
<a href="http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes">http://en.wikipedia.org/wiki/List_of_ISO_639-1_codes</a> and
<a href="http://schaik.com/png/">http://schaik.com/png/</a>.
<h2 id="history">HISTORY</h2>
<p><b>pamtopng</b> was new in Netpbm 10.70 (June 2015).
<p>Before <b>pamtopng</b>, the two ways to create PNG images with Netpbm
were <b>pnmtopng</b> and <b>pamrgbatopng</b>. The history of the former is
discussed above. The latter was added to Netpbm in 2005 as a cheap way to
fill a significant need that <b>pnmtopng</b> did not: the ability to turn the
alpha channel in a PAM image into the alpha channel in a PNG image.
<p>Handling of the alpha channel with <b>pnmtopng</b> is very cumbersome (as
was dealing with alpha channels in general before the introduction of the PAM
format). <b>pamrgbatopng</b> could do what people wanted with the alpha
channel, but nothing else. It was a very small program with literally no
command line options.
<p>The goal in those days was eventually to expand <b>pnmtopng</b> to do the
PAM alpha channel thing, rename it to <B>pamtopng</B>, and retire
<b>pamrgbatopng</b>. But <b>pnmtopng</b> is such a complex program, because
of its dizzying array of features and its need for backward compatibility,
that adding that one capability to it was a daunting task and for ten years
nobody attempted it.
<p>In 2015, one of the authors of the original <b>pnmtopng</b> (from before it
was even part of Netpbm -- a program that shared essentially no lines of code
with <b>pnmtopng</b> of 2015) decided to go in a different direction. While
many features of <b>pnmtopng</b> were pretty important and easy to implement,
many others were probably of no use in the modern world or at least not
important enough to justify the complexity they lent to the code. (The
features thought to be outdated were ones that were intended to make the PNG
output slightly smaller - something considerably less important with the
declining cost of computer resources).
<p>And there was an opportunity to drop those features: We could use the new
name "pamtopng" for a new program, keep the existing program under
the name "pnmtopng", and avoid most backward compatibility trouble.
<p>Therefore, Willem van Schaik wrote an intermediate level program that had
all the most important features of <b>pnmtopng</b>, plus the alpha channel
handling of <b>pamrgbatopng</b>, with nice, simple code. That was
<b>pamtopng</b>.
<p>Because <b>pamrgbatopng</b> had no options, <b>pamtopng</b> was backward
compatible with it without even trying. Therefore, as soon as we
added <b>pamtopng</b> to Netpbm, we removed <b>pamrgbatopng</b> and
recommended that <b>pamtorgbatopng</b> be installed as an alias for
<b>pamtopng</b>.
<h2 id="author">AUTHOR</h2>
Copyright (C) 1995-1997 by Alexander Lehmann and Willem van Schaik.
<br>
Copyright (C) 2015 by 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="#history">HISTORY</a>
<li><a href="#author">AUTHOR</a>
</ul>
</body>
</html>
|
