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  6.     <title>6.7.┬áUnsharp Mask</title>
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  11.     <link rel="up" href="ch06s06.html" title="6.┬áEnhance filters" />
  12.     <link rel="prev" href="ch06s06s06.html" title="6.6.┬áSharpen" />
  13.     <link rel="next" href="ch06s07.html" title="7.┬áGeneric filters" />
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  18.         <tr>
  19.           <th colspan="3" align="center" id="chaptername">6.┬áEnhance filters</th>
  20.         </tr>
  21.         <tr>
  22.           <td width="20%" align="left"><a accesskey="p" href="ch06s06s06.html">Prev</a>┬á</td>
  23.           <th width="60%" align="center" id="sectionname">6.7.┬áUnsharp Mask</th>
  24.           <td width="20%" align="right">┬á<a accesskey="n" href="ch06s07.html">Next</a></td>
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  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>
  37.       <a id="id3479642" class="indexterm"></a>
  38.       <div class="mediaobject">
  39.         <img src="../images/filters/filters-enhance-unsharpmask.png" />
  40.       </div>
  41.       <div class="simplesect" lang="en" xml:lang="en">
  42.         <div class="titlepage">
  43.           <div>
  44.             <div>
  45.               <h4 class="title"><a id="id3479663"></a>Overview</h4>
  46.             </div>
  47.           </div>
  48.         </div>
  49.         <p>
  50.       This filter is found in 
  51.       <span class="guimenuitem">Image>Filters/Enhance/<span class="accel">U</span>nsharp Mask</span>
  52.     </p>
  53.         <p>
  54.       Out-of-focus photographs but also most of digitized images need
  55.       correction of sharpness.  This is due to digitizing process that
  56.       must chop a color continuum up in points with slightly different
  57.       colors: elements thiner than sampling frequency will be averaged
  58.       into an uniform color. So sharp borders are rendered a little
  59.       blurred. The same phenomenon appears when printing color dots on
  60.       paper.
  61.     </p>
  62.         <p>
  63.       The Unsharp Mask filter (what an odd name!) sharpens edges of the
  64.       elements without increasing noise or blemish. It is the king of
  65.       the sharpen filters.
  66.     </p>
  67.         <p>
  68.       Some scanners apply a sharpen filter while scanning. It's worth to
  69.       disable it so that you 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="id3479714"></a>Options</h4>
  77.             </div>
  78.           </div>
  79.         </div>
  80.         <div class="variablelist">
  81.           <dl>
  82.             <dt>
  83.               <span class="term">Parameters setting</span>
  84.             </dt>
  85.             <dd>
  86.               <p>
  87.             </p>
  88.               <div class="itemizedlist">
  89.                 <ul type="disc">
  90.                   <li>
  91.                     <p>
  92.                 <span class="guilabel">Radius</span>: slider and input boxes
  93.                 (0.1-120) allow you to set how many pixels on either
  94.                 side of an edge will be affected by sharpening. High
  95.                 resolution images allow higher radius. Y'd better to
  96.                 always sharpen an image at its final resolution.
  97.               </p>
  98.                   </li>
  99.                   <li>
  100.                     <p>
  101.                 <span class="guilabel">Amount</span>: slider and input boxes
  102.                 (0.00-5.00) allow you to set strength of sharpening. 
  103.               </p>
  104.                   </li>
  105.                   <li>
  106.                     <p>
  107.                 <span class="guilabel">Threshold</span>: slider and input boxes
  108.                 (0-255) allow you to set the minimum difference in pixel
  109.                 values that indicates an edge where sharpen must be
  110.                 applied. So you can protect areas of smooth tonal
  111.                 transition from sharpening, and avoid creation of
  112.                 blemishes in face, sky or water surface.
  113.               </p>
  114.                   </li>
  115.                 </ul>
  116.               </div>
  117.               <p>
  118.           </p>
  119.             </dd>
  120.           </dl>
  121.         </div>
  122.       </div>
  123.       <div class="simplesect" lang="en" xml:lang="en">
  124.         <div class="titlepage">
  125.           <div>
  126.             <div>
  127.               <h4 class="title"><a id="id3479783"></a>More informations</h4>
  128.             </div>
  129.           </div>
  130.         </div>
  131.         <p>
  132.             To prevent color distorsion while sharpening, Decompose your
  133.             image to HSV and work only on Value. Then Compose the image
  134.             to HSV. This is well explained at <a href="http://www.gimpguru.org" target="_top">gimpguru.org</a>
  135.           </p>
  136.       </div>
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  141.         <tr>
  142.           <td width="40%" align="left"><a accesskey="p" href="ch06s06s06.html">Prev</a>┬á</td>
  143.           <td width="20%" align="center">
  144.             <a accesskey="u" href="ch06s06.html">Up</a>
  145.           </td>
  146.           <td width="40%" align="right">┬á<a accesskey="n" href="ch06s07.html">Next</a></td>
  147.         </tr>
  148.         <tr>
  149.           <td width="40%" align="left" valign="top">6.6.┬áSharpen┬á</td>
  150.           <td width="20%" align="center">
  151.             <a accesskey="h" href="index.html">Home</a>
  152.           </td>
  153.           <td width="40%" align="right" valign="top">┬á7.┬áGeneric filters</td>
  154.         </tr>
  155.       </table>
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  157.   </body>
  158. </html>
  159.