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  6.     <title>10.11.┬áNewsprint</title>
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  11.     <link rel="up" href="ch06s10.html" title="10.┬áDistort filters" />
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  17.       <table width="100%" summary="Navigation header">
  18.         <tr>
  19.           <th colspan="3" align="center" id="chaptername">10.┬áDistort filters</th>
  20.         </tr>
  21.         <tr>
  22.           <td width="20%" align="left"><a accesskey="p" href="ch06s10s10.html">Prev</a>┬á</td>
  23.           <th width="60%" align="center" id="sectionname">10.11.┬áNewsprint</th>
  24.           <td width="20%" align="right">┬á<a accesskey="n" href="ch06s10s12.html">Next</a></td>
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  28.     </div>
  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-newsprint"></a>10.11.┬áNewsprint</h3>
  34.           </div>
  35.         </div>
  36.       </div>
  37.       <a id="id3485148" class="indexterm"></a>
  38.       <div class="mediaobject">
  39.         <img src="../images/filters/filters-distort-newsprint.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="id3485169"></a>Overview</h4>
  46.             </div>
  47.           </div>
  48.         </div>
  49.         <p>
  50.             This filter is found in
  51.             <span class="guimenuitem">Image>Filters/Distorts/Newsprin<span class="accel">t</span></span>
  52.           </p>
  53.         <p>
  54.             This filter halftones the image using a clustered-dot
  55.             dither.  Halftoning is the process of rendering an image with 
  56.             multiple levels of grey or colour (i.e. a continuous tone image) 
  57.             on a device with fewer tones; often a bi-level device such as a 
  58.             printer or typesetter.
  59.           </p>
  60.         <p>
  61.             The basic premise is to trade off resolution for greater 
  62.             apparent tone depth (this is known as spatial dithering).
  63.           </p>
  64.         <p> 
  65.             There are many approaches to this, the simplest of which is to 
  66.             throw away the low-order bits of tone information; this is what 
  67.             the posterize filter does. Unfortunately, the results don't look 
  68.             too good. However, no spatial resolution is lost.
  69.           </p>
  70.         <p>
  71.             This filter uses a clustered-dot ordered dither, which reduces 
  72.             the resolution of the image by converting cells into spots which 
  73.             grow or shrink according to the intensity that cell needs to 
  74.             represent.
  75.           </p>
  76.         <p> 
  77.             Imagine a grid super-imposed on the original image.  The image 
  78.             is divided into cells by the grid - each cell will ultimately 
  79.             hold a single spot made up of multiple output pixels in order to 
  80.             approximate the darkness of the original image in that cell.
  81.           </p>
  82.         <p>
  83.             Obviously, a large cell size results in a heavy loss in 
  84.             resolution! The spots in the cells typically start off as 
  85.             circles, and grow to be diamond shaped.  This change in shape is 
  86.             controlled by a <span class="guilabel">spot function</span>.  By using 
  87.             different spot functions, the evolution in the shape of the 
  88.             spots as the cell goes from fully black to fully white may be 
  89.             controlled.
  90.           </p>
  91.       </div>
  92.       <div class="simplesect" lang="en" xml:lang="en">
  93.         <div class="titlepage">
  94.           <div>
  95.             <div>
  96.               <h4 class="title"><a id="id3485258"></a>Options</h4>
  97.             </div>
  98.           </div>
  99.         </div>
  100.         <div class="variablelist">
  101.           <dl>
  102.             <dt>
  103.               <span class="term">Resolution</span>
  104.             </dt>
  105.             <dd>
  106.               <p>
  107.             This group controls the cell size, either by setting the
  108.             input and output resolutions, or directly.
  109.           </p>
  110.               <div class="itemizedlist">
  111.                 <ul type="disc">
  112.                   <li>
  113.                     <p>
  114.                 <span class="guilabel">Input SPI</span>: Resolution of the
  115.                 original input image, in Samples Per Inch (SPI).  This
  116.                 is automatically initialised to the input image's resolution.
  117.               </p>
  118.                   </li>
  119.                   <li>
  120.                     <p>
  121.                 <span class="guilabel">Output LPI</span>: Desired output
  122.                 resolution, in Lines Per Inch (LPI).
  123.               </p>
  124.                   </li>
  125.                   <li>
  126.                     <p>
  127.                 <span class="guilabel">Cell Size</span>: Resulting cell size, in
  128.                 pixels.  Most often you will want to set this directly.
  129.               </p>
  130.                   </li>
  131.                 </ul>
  132.               </div>
  133.             </dd>
  134.             <dt>
  135.               <span class="term">Screen</span>
  136.             </dt>
  137.             <dd>
  138.               <div class="itemizedlist">
  139.                 <ul type="disc">
  140.                   <li>
  141.                     <p>
  142.                 <span class="guilabel">Separate To RGB, CMYK,
  143.                 Intensity</span>: Select which colourspace you
  144.                 wish to operate in.  In <span class="emphasis"><em>RGB</em></span> mode, no 
  145.                 colourspace conversion is performed. In 
  146.                 <span class="emphasis"><em>CMYK</em></span>, the image is first
  147.                 internally converted to CMYK, then each colour channel is
  148.                 separately halftoned, before finally being
  149.                 recombined back to an RGB image.  
  150.                 In <span class="emphasis"><em>Intensity</em></span> mode, the
  151.                 image is internally converted to greyscale,
  152.                 halftoned, then the result used as the alpha channel
  153.                 for the input image.  This is good for special
  154.                 effects, but requires a little experimentation to
  155.                 achieve best results.  Hint: try CMYK if you don't know
  156.                 which to go for initially.
  157.               </p>
  158.                   </li>
  159.                   <li>
  160.                     <p>
  161.                 <span class="guilabel">Black Pullout (%)</span> When doing
  162.               RGB->CMYK conversion, how much K (black) should be used?
  163.               </p>
  164.                   </li>
  165.                   <li>
  166.                     <p>
  167.                 <span class="guilabel">Angle</span>: Cell grid angle for this channel.
  168.               </p>
  169.                   </li>
  170.                   <li>
  171.                     <p>
  172.                 <span class="guilabel">Spot Function</span>: Spot function to
  173.                 be used for this angle (see preview in blue cell-boxes).
  174.               </p>
  175.                   </li>
  176.                   <li>
  177.                     <p>
  178.                 <span class="guilabel">Lock Channels</span>: Make channel
  179.                 modifications apply to all channels.
  180.               </p>
  181.                   </li>
  182.                   <li>
  183.                     <p>
  184.                 <span class="guilabel">Factory Defaults</span>: Restore the
  185.                 default settings which should give pleasing results.
  186.               </p>
  187.                   </li>
  188.                 </ul>
  189.               </div>
  190.             </dd>
  191.             <dt>
  192.               <span class="term">Antialiasing</span>
  193.             </dt>
  194.             <dd>
  195.               <p>
  196.           Proper halftoning does not need antialiasing: the aim is to
  197.           reduce the colour depth after all!  However, since this
  198.           plugin is mainly for special effects, the results are
  199.           displayed on screen rather than by a black/white printer.
  200.           So it is often useful to apply a little anti-aliasing to
  201.           simulate ink smearing on paper.  If you do want to print the
  202.           resulting image then set the antialising to 1 (ie, off).
  203.           </p>
  204.               <p>
  205.             <span class="guilabel">Oversample</span>:Number of subpixels to
  206.             sample to produce each output pixel.  Set to 1 to disable
  207.             this feature.  Warning: large numbers here will lead to
  208.             very long filter runtimes!
  209.           </p>
  210.             </dd>
  211.           </dl>
  212.         </div>
  213.         <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
  214.           <table border="0" summary="Tip">
  215.             <tr>
  216.               <td rowspan="2" align="center" valign="top" width="25">
  217.                 <img alt="[Tip]" src="../images/tip.png" />
  218.               </td>
  219.               <th align="left">Tip</th>
  220.             </tr>
  221.             <tr>
  222.               <td colspan="2" align="left" valign="top">
  223.                 <p>
  224.         More explanations, illustrative diagrams, a gallery and a
  225.         tutorial are to be found on the plug-in author site:
  226.         <a href="http://www.cl.cam.ac.uk/~and1000/newsprint/" target="_top">
  227.         http://www.cl.cam.ac.uk/~and1000/newsprint/</a>  
  228.         You are strongly encouraged to visit it, since halftoning
  229.         is a large and complex area.
  230.       </p>
  231.               </td>
  232.             </tr>
  233.           </table>
  234.         </div>
  235.         <p>
  236.       Here is an example, from the author's gallery:
  237.     </p>
  238.         <div class="mediaobject">
  239.           <img src="../images/filters/examples/newsprint.png" />
  240.         </div>
  241.       </div>
  242.     </div>
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  244.       <hr />
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  251.           <td width="40%" align="right">┬á<a accesskey="n" href="ch06s10s12.html">Next</a></td>
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  254.           <td width="40%" align="left" valign="top">10.10.┬áShift┬á</td>
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  264.