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  4.   <head>
  5.     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
  6.     <title>6.7.┬áUnsharp Mask</title>
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  11.     <link rel="up" href="ch05s06.html" title="6.┬áEnhance filters" />
  12.     <link rel="previous" href="ch05s06s06.html" title="6.6.┬áSharpen" />
  13.     <link rel="next" href="ch05s07.html" title="7.┬áGeneric filters" />
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  15.   <body>
  16.     <div class="navheader">
  17.       <table width="100%" summary="Navigation header">
  18.         <tr>
  19.           <th colspan="3" align="center">6.7.┬áUnsharp Mask</th>
  20.         </tr>
  21.         <tr>
  22.           <td width="20%" align="left"><a accesskey="p" href="ch05s06s06.html">Prev</a>┬á</td>
  23.           <th width="60%" align="center">6.┬áEnhance filters</th>
  24.           <td width="20%" align="right">┬á<a accesskey="n" href="ch05s07.html">Next</a></td>
  25.         </tr>
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  29.     <div class="sect2" lang="en" xml:lang="en">
  30.       <div class="titlepage">
  31.         <div>
  32.           <div>
  33.             <h3 class="title"><a id="plug-in-unsharp-mask"></a>6.7.┬áUnsharp Mask</h3>
  34.           </div>
  35.         </div>
  36.         <div></div>
  37.       </div>
  38.       <a id="id2975875" class="indexterm"></a>
  39.       <div class="mediaobject">
  40.         <img src="../images/filters/filters-enhance-unsharpmask.png" />
  41.       </div>
  42.       <div class="simplesect" lang="en" xml:lang="en">
  43.         <div class="titlepage">
  44.           <div>
  45.             <div>
  46.               <h4 class="title"><a id="id2975896"></a>Overview</h4>
  47.             </div>
  48.           </div>
  49.           <div></div>
  50.         </div>
  51.         <p>
  52.       This filter is found in 
  53.       <span class="guimenuitem">Image>Filters/Enhance/<span class="accel">U</span>nsharp Mask</span>
  54.     </p>
  55.         <p>
  56.       Out-of-focus photographs but also most of digitized images need correction of sharpness. 
  57.       This is due to digitizing process that must chop a color continuum up in points with 
  58.       slightly different colors: elements thiner than sampling frequency will be averaged into 
  59.       an uniform color. So sharp borders are rendered a little blurred. The same phenomenon 
  60.       appears when printing color dots on paper.
  61.     </p>
  62.         <p>
  63.       The Unsharp Mask filter (what an odd name!) sharpens edges of the elements without 
  64.       increasing noise or blemish. It is the king of the sharpen filters. It's a pity we 
  65.       don't have any preview! 
  66.     </p>
  67.         <p>
  68.       Some scanners apply a sharpen filter while scanning. It's worth to disable it so that you 
  69.       keep control on your image.
  70.     </p>
  71.       </div>
  72.       <div class="simplesect" lang="en" xml:lang="en">
  73.         <div class="titlepage">
  74.           <div>
  75.             <div>
  76.               <h4 class="title"><a id="id2975948"></a>Options</h4>
  77.             </div>
  78.           </div>
  79.           <div></div>
  80.         </div>
  81.         <div class="variablelist">
  82.           <dl>
  83.             <dt>
  84.               <span class="term">Parameters setting</span>
  85.             </dt>
  86.             <dd>
  87.               <p>
  88.             </p>
  89.               <div class="itemizedlist">
  90.                 <ul type="disc">
  91.                   <li><span class="guilabel">Radius</span>: slider and input boxes (0.1-120) allow you to set how 
  92.                 many pixels on either side of an edge will be affected by sharpening. High 
  93.                 resolution images allow higher radius. Y'd better to always sharpen an image at 
  94.                 its final resolution.
  95.               </li>
  96.                   <li><span class="guilabel">Amount</span>: slider and input boxes (0.00-5.00) allow you to set 
  97.                 strength of sharpening. 
  98.               </li>
  99.                   <li><span class="guilabel">Threshold</span>: slider and input boxes (0-255) allow you to set 
  100.                 the minimum difference in pixel values that indicates an edge where sharpen must 
  101.                 be applied. So you can protect areas of smooth tonal transition from sharpening, 
  102.                 and avoid creation of blemishes in face, sky or water surface.
  103.               </li>
  104.                 </ul>
  105.               </div>
  106.               <p>
  107.           </p>
  108.             </dd>
  109.           </dl>
  110.         </div>
  111.       </div>
  112.       <div class="simplesect" lang="en" xml:lang="en">
  113.         <div class="titlepage">
  114.           <div>
  115.             <div>
  116.               <h4 class="title"><a id="id2976008"></a>More informations</h4>
  117.             </div>
  118.           </div>
  119.           <div></div>
  120.         </div>
  121.         <div class="variablelist">
  122.           <dl>
  123.             <dt></dt>
  124.             <dd>
  125.               <p>
  126.             To prevent color distorsion while sharpening, Decompose your image to HSV and work only on 
  127.             Value. Then Compose the image to HSV. This is well explained at
  128.             <a href="/cgi-bin/olink?sysid=">
  129.             <i class="citetitle">gimpguru.org</i></a>
  130.           </p>
  131.             </dd>
  132.           </dl>
  133.         </div>
  134.       </div>
  135.     </div>
  136.     <div class="navfooter">
  137.       <hr />
  138.       <table width="100%" summary="Navigation footer">
  139.         <tr>
  140.           <td width="40%" align="left"><a accesskey="p" href="ch05s06s06.html">Prev</a>┬á</td>
  141.           <td width="20%" align="center">
  142.             <a accesskey="u" href="ch05s06.html">Up</a>
  143.           </td>
  144.           <td width="40%" align="right">┬á<a accesskey="n" href="ch05s07.html">Next</a></td>
  145.         </tr>
  146.         <tr>
  147.           <td width="40%" align="left" valign="top">6.6.┬áSharpen┬á</td>
  148.           <td width="20%" align="center">
  149.             <a accesskey="h" href="index.html">Home</a>
  150.           </td>
  151.           <td width="40%" align="right" valign="top">┬á7.┬áGeneric filters</td>
  152.         </tr>
  153.       </table>
  154.     </div>
  155.   </body>
  156. </html>
  157.