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  6.     <title>11.11.¬† Stretch Contrast</title>
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  18.     <div class="navheader">
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  20.         <tr>
  21.           <th colspan="3" align="center">11.11.¬†
  22.     <span lang="en" xml:lang="en">Stretch Contrast</span>
  23.   </th>
  24.         </tr>
  25.         <tr>
  26.           <td width="20%" align="left"><a accesskey="p" href="plug-in-normalize.html"><img src="../images/prev.png" alt="Prev" /></a>¬†</td>
  27.           <th width="60%" align="center">11.¬†
  28.     <span lang="en" xml:lang="en">The ‚Äú<span class="quote">Colors</span>‚Äù Menu</span>
  29.   </th>
  30.           <td width="20%" align="right">¬†<a accesskey="n" href="plug-in-autostretch-hsv.html"><img src="../images/next.png" alt="Next" /></a></td>
  31.         </tr>
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  33.       <hr />
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  35.     <div class="sect2" lang="en" xml:lang="en">
  36.       <div class="titlepage">
  37.         <div>
  38.           <div>
  39.             <h3 class="title"><a id="plug-in-c-astretch"></a>11.11.¬†
  40.     <span lang="en" xml:lang="en">Stretch Contrast</span>
  41.   </h3>
  42.           </div>
  43.           <div>
  44.             <div class="revhistory">
  45.               <table border="1" width="100%" summary="Revision history">
  46.                 <tr>
  47.                   <th align="left" valign="top" colspan="3">
  48.                     <b>Revision History</b>
  49.                   </th>
  50.                 </tr>
  51.                 <tr>
  52.                   <td align="left">Revision $Revision: 2315 $</td>
  53.                   <td align="left">2007-10-17</td>
  54.                   <td align="left">ude</td>
  55.                 </tr>
  56.               </table>
  57.             </div>
  58.           </div>
  59.         </div>
  60.       </div>
  61.       <a id="id2718280" class="indexterm"></a>
  62.       <a id="id2718295" class="indexterm"></a>
  63.       <a id="id2718304" class="indexterm"></a>
  64.       <p>
  65.     The <span class="guimenuitem">Stretch Contrast</span> command automatically
  66.     stretches the histogram values in the active layer. For each channel
  67.     of the active layer, it finds the minimum and maximum values and uses
  68.     them to stretch the Red, Green and Blue histograms to the full contrast
  69.     range. The bright colors become brighter and the dark colors become
  70.     darker, which increases the contrast.
  71.     This command produces a somewhat similar effect to the
  72.     <a class="link" href="plug-in-normalize.html" title="11.10.¬† Normalize">Normalize</a> command, except that
  73.     it works on each color channel of the layer individually. This usually
  74.     leads to color shifts in the image, so it may not produce the desired
  75.     result. ‚Äú<span class="quote">Stretch Contrast</span>‚Äù works on layers of RGB,
  76.     Grayscale and Indexed images. Use ‚Äú<span class="quote">Stretch Contrast</span>‚Äù only
  77.     if you want to remove an undesirable color tint from an image which
  78.     should contain pure white and pure black.
  79.   </p>
  80.       <p>
  81.     This command is also similar to the
  82.     <a class="link" href="gimp-layer-white-balance.html" title="11.8.¬† White Balance">Color Balance</a>
  83.     command, but it does not reject any of the very dark or very bright
  84.     pixels, so the white might be impure.
  85.   </p>
  86.       <div class="sect3" lang="en" xml:lang="en">
  87.         <div class="titlepage">
  88.           <div>
  89.             <div>
  90.               <h4 class="title"><a id="id2718368"></a>11.11.1.¬†
  91.       <span lang="en" xml:lang="en">Activate Command</span>
  92.     </h4>
  93.             </div>
  94.           </div>
  95.         </div>
  96.         <div class="itemizedlist">
  97.           <ul type="disc">
  98.             <li>
  99.               <p>
  100.           This command can be accessed from an image menubar as 
  101.           <span class="guimenu"><span class="accel">C</span>olors</span> ‚Üí <span class="guisubmenu"><span class="accel">A</span>uto</span> ‚Üí <span class="guimenuitem"><span class="accel">S</span>tretch¬†Contrast</span>.
  102.         </p>
  103.             </li>
  104.           </ul>
  105.         </div>
  106.       </div>
  107.       <div class="sect3" lang="en" xml:lang="en">
  108.         <div class="titlepage">
  109.           <div>
  110.             <div>
  111.               <h4 class="title"><a id="id2718422"></a>11.11.2.¬†
  112.       <span lang="en" xml:lang="en">‚Äú<span class="quote">Stretch Contrast</span>‚Äù Example</span>
  113.     </h4>
  114.             </div>
  115.           </div>
  116.         </div>
  117.         <div class="figure">
  118.           <a id="id2718436"></a>
  119.           <p class="title">
  120.             <b>Figure¬†15.145.¬†
  121.         <span lang="en" xml:lang="en">Original image</span>
  122.       </b>
  123.           </p>
  124.           <div class="figure-contents">
  125.             <div class="mediaobject">
  126.               <img src="../images/menus/alice.png" alt="Original image" />
  127.               <div class="caption">
  128.                 <p>
  129.             The layer and its Red, Green and Blue histograms before
  130.             ‚Äú<span class="quote">Stretch Contrast</span>‚Äù.
  131.           </p>
  132.               </div>
  133.             </div>
  134.           </div>
  135.         </div>
  136.         <br class="figure-break" />
  137.         <div class="figure">
  138.           <a id="id2718476"></a>
  139.           <p class="title">
  140.             <b>Figure¬†15.146.¬†
  141.         <span lang="en" xml:lang="en">Image after the command</span>
  142.       </b>
  143.           </p>
  144.           <div class="figure-contents">
  145.             <div class="mediaobject">
  146.               <img src="../images/menus/c-stretch.png" alt="Image after the command" />
  147.               <div class="caption">
  148.                 <p>
  149.             The layer and its Red and Green and Blue histograms after
  150.             ‚Äú<span class="quote">Stretch Contrast</span>‚Äù.
  151.             The pixel columns do not reach the right end of the histogram
  152.             (255) because of a few very bright pixels, unlike
  153.             ‚Äú<span class="quote">White Balance</span>‚Äù.
  154.           </p>
  155.                 <p>
  156.             Histogram stretching creates gaps between the pixel columns,
  157.             giving it a striped look.
  158.           </p>
  159.               </div>
  160.             </div>
  161.           </div>
  162.         </div>
  163.         <br class="figure-break" />
  164.       </div>
  165.     </div>
  166.     <div class="navfooter">
  167.       <hr />
  168.       <table width="100%" summary="Navigation footer">
  169.         <tr>
  170.           <td width="40%" align="left"><a accesskey="p" href="plug-in-normalize.html"><img src="../images/prev.png" alt="Prev" /></a>¬†</td>
  171.           <td width="20%" align="center">
  172.             <a accesskey="u" href="gimp-imagewindow-menus-colors.html">
  173.               <img src="../images/up.png" alt="Up" />
  174.             </a>
  175.           </td>
  176.           <td width="40%" align="right">¬†<a accesskey="n" href="plug-in-autostretch-hsv.html"><img src="../images/next.png" alt="Next" /></a></td>
  177.         </tr>
  178.         <tr>
  179.           <td width="40%" align="left" valign="top"><a accesskey="p" href="plug-in-normalize.html">11.10.¬†
  180.     <span lang="en" xml:lang="en">Normalize</span>
  181.   </a>¬†</td>
  182.           <td width="20%" align="center">
  183.             <a accesskey="h" href="index.html">
  184.               <img src="../images/home.png" alt="Home" />
  185.             </a>
  186.           </td>
  187.           <td width="40%" align="right" valign="top">¬†<a accesskey="n" href="plug-in-autostretch-hsv.html">11.12.¬†
  188.     <span lang="en" xml:lang="en">Stretch HSV</span>
  189.   </a></td>
  190.         </tr>
  191.       </table>
  192.     </div>
  193.   </body>
  194. </html>
  195.