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2<!DOCTYPE sect2 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
3                       "http://www.docbook.org/xml/4.3/docbookx.dtd">
4<!-- section history:
5
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7<!-- id is still used by GIMP, do not change! -->
8<sect2 id="gimp-layer-equalize">
9  <title>Equalize</title>
10
11  <indexterm>
12    <primary>Colors</primary>
13    <secondary>Equalize</secondary>
14  </indexterm>
15  <indexterm>
16    <primary>Equalize</primary>
17  </indexterm>
18  <para>
19    The <guimenuitem>Equalize</guimenuitem>
20    command automatically adjusts the brightness of colors across the active
21    layer so that the histogram for the Value channel is as nearly flat as
22    possible, that is, so that each possible brightness value appears at about
23    the same number of pixels as every other value. You can see this in the
24    histograms in the example below, in that pixel colors which occur
25    frequently in the image are stretched further apart than pixel colors
26    which occur only rarely. The results of this command can vary quite a bit.
27    Sometimes <quote>Equalize</quote>
28    works very well to enhance the contrast in an image, bringing out details
29    which were hard to see before. Other times, the results look very bad. It
30    is a very powerful operation and it is worth trying to see if it will
31    improve your image. It works on layers from RGB and Grayscale images. If
32    the image is Indexed, the menu entry is insensitive and grayed out.
33  </para>
34
35  <sect3>
36    <title>Activate the Command</title>
37    <para>
38      You can access this command from the image menubar through
39      <menuchoice>
40        <guimenu>Colors</guimenu>
41        <guisubmenu>Auto</guisubmenu>
42        <guimenuitem>Equalize</guimenuitem>
43      </menuchoice>
44    </para>
45  </sect3>
46
47  <sect3>
48    <title><quote>Equalize</quote> example</title>
49    <figure>
50      <title>Original image</title>
51      <mediaobject>
52        <imageobject>
53          <imagedata format="PNG"
54            fileref="images/menus/colors/auto/alice.png"/>
55        </imageobject>
56        <caption>
57          <para>
58            The active layer and its Red, Green, Blue histograms before
59            <quote>Equalize</quote>.
60          </para>
61        </caption>
62      </mediaobject>
63    </figure>
64    <figure>
65      <title>Image after the command</title>
66      <mediaobject>
67        <imageobject>
68          <imagedata format="PNG"
69            fileref="images/menus/colors/auto/equalize.png"/>
70        </imageobject>
71        <caption>
72          <para>
73            The active layer and its Red, Green, Blue histograms after
74            treatment.
75          </para>
76          <para>
77            Histogram stretching creates gaps between pixel columns giving it
78            a striped look: colors that occur frequently are stretched.
79          </para>
80        </caption>
81      </mediaobject>
82    </figure>
83  </sect3>
84
85</sect2>
86