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| author | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2018-09-15 19:21:17 +0000 |
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| committer | giraffedata <giraffedata@9d0c8265-081b-0410-96cb-a4ca84ce46f8> | 2018-09-15 19:21:17 +0000 |
| commit | 304813749178ae36a84e54f04211ed25f993d35a (patch) | |
| tree | 23082ad7c739528093da43699e529c2676cb1553 | |
| parent | 299c9b5b698bda893468cf2e4a64a7cf990ddc7f (diff) | |
| download | netpbm-mirror-304813749178ae36a84e54f04211ed25f993d35a.tar.gz netpbm-mirror-304813749178ae36a84e54f04211ed25f993d35a.tar.xz netpbm-mirror-304813749178ae36a84e54f04211ed25f993d35a.zip | |
miscellaneous update
git-svn-id: http://svn.code.sf.net/p/netpbm/code/userguide@3326 9d0c8265-081b-0410-96cb-a4ca84ce46f8
| -rw-r--r-- | directory.html | 3 | ||||
| -rw-r--r-- | pamaltsat.html | 220 | ||||
| -rw-r--r-- | ppmbrighten.html | 1 |
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diff --git a/directory.html b/directory.html index f5d89999..1c34e758 100644 --- a/directory.html +++ b/directory.html @@ -768,6 +768,9 @@ a color map containing all possible colors of given maxval <DT><B><a href=ppmflash.html>ppmflash</a></B> <DD>brighten an image +<DT><B><a href=pamaltsat.html>pamaltsat</a></B> +<DD>change saturation of an image in alternative way + <DT><B><a href=ppmdim.html>ppmdim</a> </B> <DD>dim an image - different way from ppmbrighten diff --git a/pamaltsat.html b/pamaltsat.html new file mode 100644 index 00000000..f03b0af4 --- /dev/null +++ b/pamaltsat.html @@ -0,0 +1,220 @@ +<html><head> +<meta http-equiv="content-type" content="text/html; +charset=windows-1252"><title>Pamaltsat User Manual</title> +</head><body> +<h1>pamaltsat</h1> +Updated: 14 September 2018 +<br> +<a href="#index">Table Of Contents</a> + +<h2>NAME</h2> + +pamaltsat - increase or decrease the saturation of an image using one of +several alternative methods. + +<h2 id="synopsis">SYNOPSIS</h2> + +<b>pamaltsat</b> +[<b>-method</b> <i>name</i>] +[<b>-strength</b> <i>number</i>] +[<b>-linear</b>] +[<i>infile</i>] + +<h2 id="description">DESCRIPTION</h2> + +<p>This program is part of +<a href="http://netpbm.sourceforge.net/doc/index.html">Netpbm</a>. + +<p><b>pamaltsat</b> decreases or increases the saturation of a Netpbm image by +one of various non-standard (<i>alt</i>ernative) methods. + +<p>The input is a Netpbm image from Standard Input or a file named by the +arguments. The output is a Netpbm image in the same format written to +Standard Output. + +<p>The most conventional way to change the saturation of an image is what +<b>ppmbrighten</b> does. + + +<h2 id="examples">EXAMPLES</h2> + +<p>To increase saturation by a factor of 2.1 using the +logarithmic method: + +<pre> +<kdb> + pamaltsat -method log -strength 2.1 test.ppm +</kdb> +</pre> + +<p>To convert a color image to grayscale: + +<pre> +<kbd> + pamaltsat -strength 0 test.ppm +</kbd> +</pre> + + +<h2 id = "methods">SATURATION METHODS</h2> + +<p>The following saturation methods are available. + +<h3>Logarithmic Method</h3> + +<p>This saturation model is inspired by the concept of +<a href="http://www.c-f-systems.com/ColorIntegrity.html">color integrity</a>, +which works with color in terms of intensity ratios, where intensity is a +value of the +<a href="https://en.wikipedia.org/wiki/Luminosity_function">luminosity +function</a>, rather than brightness, or the numercial value of the sample in +the image file. From this viewpoint, it is natural to define the saturation +of a color as the ratio of maximum and minimum intensities of its primary +components. In order, however, to make saturation an additive value and to +endow the <b>-strength</b> parameter with the semantics of a multiplier, +it is convenient to operate on the logarithm of that ratio. The addition of +such saturations acquires physical sense, and multiplication corresponds to +the raising of intensity to the power of the multiplier. + +<p>With this method, <b>pamaltsat</b> raises the intensity of each component +to the power of the <b>strength</b> value. Since the total intensity of the +resulting sample will differ from that of the original, it is thus necessary to +restore it by multiplying the component intensities of the saturated sample by +the ratio of the original intensity to that of the saturated sample. + +<p>Although it is always possible to decrease saturation by any given factor, +there are two cases where it cannot be increased. When the total intensity +(or brightness) of a color is too high for the desired +saturation, <b>pamaltsat</b> applies the maximum possible saturation that +keeps the original intensity. For example, any color with at least one +component at the maxiumum is already fully saturated. When one of the primary +components is zero, the definition of saturation given above no longer works +because of a zero in the denominator. <b>pamaltsat</b> offers no special +treatment of this situation because it does not create discontinuities and +therefore produces no visible defects at reasonable strength levels. When, +however, strength approaches infinity, each color tends to its primary +component with the highest intensity. + + +<h3>Spectral Method</h3> + +<p>This is the default method. It treats color as a spectrum with three +bands: one for the intensity of each primary component. Since neutral gray +has a uniform (constant) spectrum, saturation can be measured as the +difference of the spectrum of the given color from the uniform spectrum of the +same total intensity. The spectral method uses one of the simplest measures +of such a difference: the diffirence between the highest and lowest component +intensities, which is an additive value and therefore amenable to +multiplication with good physical sense. Although a complete hue-saturation +model can be dervied from this approach, <b>pamaltsat</b> need not concern +itself with it because it always preserves both hue and total intensity. + +<p>In order to change saturation, <b>pamaltsat</b> first multiplies the +intensity of each component by the desired strength. The saturation of the +result is the strength times the saturation of the original, and likewise the +total intensity, but it is then restored by subtraction of the neutral gray +with a suitable intensity. + +<p>The effect of this method on each component intensity may be expressed in +the following equation: +<center> +<tt>sat = orig * strength - Iorig * (strength - 1)</tt> +</center> +<br> +where <tt>sat</tt> is the saturated sample, <tt>orig</tt> the original sample, +and <tt>Iorig</tt> the total intensity of the original color. + +<p>The method is also related to color integrity because both its operations +are part of that concept: multiplication of component intensities by the same +quotient is an important operation because changes brightness but keeps color +balance, and subtraction of a constant from all component intensities is +described by the inventor of color integrity as "subtraction of +white." + +<p>This procedure may produce both negative and over-unity component +intensities. For such samples, <b>pamaltsat</b> decreases the strength to the +highest value that keeps the resulting color in range. + + +<h2 id="options">OPTIONS</h2> + +<dl> +<dt><b>-method</b> <i>method</i> +<dd>specifies the saturation method to use: +<table> +<tr><th>method name</th><th>option value</th></tr> +<tr><td>Logarithmic</td><td><tt>log </tt></td></tr> +<tr><td>Spectral </td><td><tt>spectrum</tt></td></tr> +</table> + +<P>The default is <b>spectrum</b> + +<dt><b>-strength</b> <i>strength</i> + +<dd>This specifies a real nonnegative factor whereby to modify saturation. A +value greater than unity will increase saturation, whereas a value less than +unity will decrease it. Unity will leave the image unchanged, and zero will +produce greyscale output according to Rec 709. + +<b>pamaltsat</b> preserves the total intensity of each pixel and never +affects neutral gray pixels. + +<p>This option is mandatory. + +<dt><b>-linear</b> + +<dd>This tells <b>pamaltsat</b> that the input is the intensity-linear +variation of a Netpbm image forat, in which the samples are proportional to +light intensity rather than to brightness, as they are in true—or +gamma-adjusted— Netpbm image formats. +</dl> + +<h2 id="unotes">USAGE NOTES</h2> + +<p>Since <b>pamaltsat</b> does not affect neutral colors, you should adjust +the color balance before saturation. You can do this with <b>pamlevels</b>. + + +<h2 id="ext">EXTENSIBILITY</h2> + +<b>pamaltsat</b> is written with an eye to extending it with new saturation +methods, which programmers are welcome to contribute. The only requirement is +that every new method depend on a single strength parameter with the semantics +described under the <b>-strength</b> command-line option. + + +<h2 id="seealso">SEE ALSO</h2> + +<p> +<A HREF="ppmbrighten.html">ppmbrighten</A>, +<A HREF="ppmflash.html">ppmflash</A>, + + +<h2 id="author">AUTHOR</h2> + +<p>This program was first submitted by Anton Shepelev +(<a href="mailto:anton.txt@gmail.com">anton.txt@gmail.com</a>). + +<h2 id="history">HISTORY</h2> + +<p><b>pamaltsat</b> was new in Netpbm 10.84 (September 2018). + + +<h2 id="index">Table Of Contents</h2> +<ul> +<li><a href="#synopsis" >SYNOPSIS</a> +<li><a href="#description">DESCRIPTION</a> +<li><a href="#examples" >EXAMPLES</a> +<li><a href="#methods" >SATURATION METHODS</a> +<li><a href="#options" >OPTIONS</a> +<li><a href="#unotes" >USAGE NOTES</a> +<li><a href="#ext" >EXTENSIBILITY</a> +<li><a href="#seealso" >SEE ALSO</a> +<li><a href="#author" >AUTHOR</a> +<li><a href="#history" >HISTORY</a> +</ul> + + +</body> +</html> + diff --git a/ppmbrighten.html b/ppmbrighten.html index a9657ac6..6b84db3d 100644 --- a/ppmbrighten.html +++ b/ppmbrighten.html @@ -125,6 +125,7 @@ with a bogus error message. <A HREF="ppmdim.html">ppmdim</A>, <A HREF="pamfunc.html">pamfunc</A>, <A HREF="ppmflash.html">ppmflash</A>, +<A HREF="pamaltsat.html">pamaltsat</A>, <A HREF="pamdepth.html">pamdepth</A>, <A HREF="pnmgamma.html">pnmgamma</A>, <A HREF="ppmhist.html">ppmhist</A>, |