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  4.   <head>
  5.     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
  6.     <title>3.┬áChannels dialog</title>
  7.     <link rel="stylesheet" href="gimp-help-plain.css" type="text/css" />
  8.     <link rel="stylesheet" href="gimp-help-screen.css" type="text/css" />
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  10.     <link rel="home" href="index.html" title="GIMP User Manual" />
  11.     <link rel="up" href="ch04.html" title="Chapter┬á4.┬áDialogs" />
  12.     <link rel="previous" href="ch04s02s02.html" title="2.2.┬áLayer masks" />
  13.     <link rel="next" href="ch04s03s02.html" title="3.2.┬áSelection masks" />
  14.   </head>
  15.   <body>
  16.     <div class="navheader">
  17.       <table width="100%" summary="Navigation header">
  18.         <tr>
  19.           <th colspan="3" align="center">3.┬áChannels dialog</th>
  20.         </tr>
  21.         <tr>
  22.           <td width="20%" align="left"><a accesskey="p" href="ch04s02s02.html">Prev</a>┬á</td>
  23.           <th width="60%" align="center">Chapter┬á4.┬áDialogs</th>
  24.           <td width="20%" align="right">┬á<a accesskey="n" href="ch04s03s02.html">Next</a></td>
  25.         </tr>
  26.       </table>
  27.       <hr />
  28.     </div>
  29.     <div class="sect1" lang="en" xml:lang="en">
  30.       <div class="titlepage">
  31.         <div>
  32.           <div>
  33.             <h2 class="title" style="clear: both"><a id="gimp-channel-dialog"></a>3.┬áChannels dialog</h2>
  34.           </div>
  35.         </div>
  36.         <div></div>
  37.       </div>
  38.       <a id="id2960861" class="indexterm"></a>
  39.       <div class="mediaobject">
  40.         <img src="../images/dialogs/dialogs-channel.png" />
  41.       </div>
  42.       <p>
  43.     The Channel dialog is the main interface to edit, modify and manage
  44.     your channels.  Channels have a double usage.  This is why the dialog is
  45.     divided into two parts: the first part for color channels and the
  46.     second part for selection masks.
  47.   </p>
  48.       <p> 
  49.     Color channels: Color channels apply to the image and not to a
  50.     specific layer.  Basically, three primary colors are necessary to
  51.     render all the wide range of natural colors.  As other digital
  52.     software, the<span class="acronym">Gimp</span> uses Red, Green, and Blue as
  53.     primary colors.    The first and primary channels display the
  54.     <span class="guilabel">Red</span>, <span class="guilabel">Green</span>, and
  55.     <span class="guilabel">Blue</span> values of each pixel in your image. In front
  56.     of each channel is a thumbnail displaying a grayscale representation of
  57.     each channel, where white is 100% and black is 0% of the primary color.
  58.     Alternatively, if your image is not a colored but a Grayscale image,
  59.     there is only one primary channel called <span class="guilabel">Gray</span>. For
  60.     an Indexed image with a fixed number of known colors there is also only
  61.     one primary channel called <span class="guilabel">Indexed</span>.  Then there is
  62.     a secondary optionnal channel called <span class="guilabel">Alpha</span>. This
  63.     channel displays transparency values of each pixel in your image.  In
  64.     front of this channel is a thumbnail displaying a grayscale
  65.     representation of the transparency where white is opaque and visible,
  66.     and black is transparent and invisible. If you create your image
  67.     without transparency then the Alpha channel is not present, but you can
  68.     add it from the <a href="ch04s02.html" title="2.┬áLayers dialog">Layers dialog
  69.       menu</a>.  Also, if you have more than one layer in your image,
  70.     Gimp automatically creates an Alpha channel.  
  71.     </p>
  72.       <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
  73.         <table border="0" summary="Note">
  74.           <tr>
  75.             <td rowspan="2" align="center" valign="top" width="25">
  76.               <img alt="[Note]" src="../images/note.png" />
  77.             </td>
  78.             <th align="left">Note</th>
  79.           </tr>
  80.           <tr>
  81.             <td colspan="2" align="left" valign="top">
  82.       Gimp doesn't support  CMYK or YUV color models. 
  83.     </td>
  84.           </tr>
  85.         </table>
  86.       </div>
  87.       <p>
  88.   </p>
  89.       <p>
  90.     Representation of an image with channels:
  91.   </p>
  92.       <p>
  93.       <img src="../images/dialogs/dialogs-channels-example.png" />
  94.   </p>
  95.       <p>
  96.     The right image is decomposed in
  97.     three color channels (red, green, and blue) and the Alpha channel for
  98.     transparency. On the right image the transparency is displayed as a
  99.     gray checkerboard. In the color channel white is always white because
  100.     all the colors are present and black is black. The red hat is visible
  101.     in the red channel but quite invisible in the other channels. This is
  102.     the same for plain green and blue which are visible only in their own
  103.     channels and invisible in others.
  104.   </p>
  105.       <div class="simplesect" lang="en" xml:lang="en">
  106.         <div class="titlepage">
  107.           <div>
  108.             <div>
  109.               <h3 class="title"><a id="id2961013"></a>Dialog call</h3>
  110.             </div>
  111.           </div>
  112.           <div></div>
  113.         </div>
  114.         <p>
  115.       The Channel dialog can be called in many ways :
  116.       </p>
  117.         <div class="itemizedlist">
  118.           <ul type="disc">
  119.             <li>      
  120.           from the toolbox-menu:
  121.           <span class="guimenuitem"><span class="accel">F</span>ile</span>/
  122.           <span class="guimenuitem"><span class="accel">D</span>ialogs</span>/
  123.           <span class="guimenuitem"><span class="accel">C</span>hannels</span></li>
  124.             <li>
  125.           from the image-menu:
  126.           <span class="guimenuitem"><span class="accel">D</span>ialogs</span>/
  127.           <span class="guimenuitem"><span class="accel">C</span>hannels</span></li>
  128.             <li>
  129.           from another dialog-menu:
  130.           <span class="guimenuitem"><span class="accel">A</span>dd Tab</span>/
  131.           <span class="guimenuitem"><span class="accel">C</span>hannels</span></li>
  132.           </ul>
  133.         </div>
  134.         <p>
  135.     </p>
  136.       </div>
  137.       <div class="simplesect" lang="en" xml:lang="en">
  138.         <div class="titlepage">
  139.           <div></div>
  140.           <div></div>
  141.         </div>
  142.         <div class="variablelist">
  143.           <p class="title">
  144.             <b>Using the Channeldialog</b>
  145.           </p>
  146.           <dl>
  147.             <dt>
  148.               <span class="term">Overview</span>
  149.             </dt>
  150.             <dd>
  151.               <p>
  152.             The top channels are the color channels and the optional Alpha
  153.             channel. They are always organized in the same order and they
  154.             cannot be erased. Selection masks are described below and
  155.             displayed as a list in the dialog.  Every channel appears in
  156.             the list in form of a thumbnail.  A right-click in a channel
  157.             thumbnail opens the <a href="ch04s03.html#gimp-channel-menu" title="3.1.┬áChannels Menu">channel
  158.               menu</a>.
  159.           </p>
  160.             </dd>
  161.             <dt>
  162.               <span class="term">Channel attributes</span>
  163.             </dt>
  164.             <dd>
  165.               <p>
  166.             Every channel is shown in the list with its own attributes. The
  167.             main attribute is the name of the channel itself. You can edit
  168.             selection masks by double-clicking on their name. A
  169.             double_click on the thumbnail opens a full dialog where you can
  170.             also set the visual aspect of the channel in the image window.
  171.             In front of the thumbnail there is an eye icon: 
  172.             <span class="guiicon">
  173.               <img src="../images/dialogs/dialogs-icon-eye.png" />
  174.             </span>
  175.             by clicking on it you define whether the channel is visible or
  176.             not.  As a result of this visibility, the view of the image
  177.             changes in the image window and a white image becomes yellow if
  178.             you remove the view of the blue because yellow is the
  179.             complementary color for blue.  If you remove the view of the
  180.             Alpha channel, everything becomes transparent and nothing else
  181.             than a grey checkerboard is visible. The aspect of this virtual
  182.             background can be changed in the 
  183.             <a href="">Preferences</a>.
  184.             The chain icon           
  185.             <span class="guiicon">
  186.               <img src="../images/dialogs/dialogs-icon-vchain.png" />
  187.             </span>
  188.             enables grouping of channels for operations on multiple channels.
  189.           </p>
  190.               <div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;">
  191.                 <table border="0" summary="Caution">
  192.                   <tr>
  193.                     <td rowspan="2" align="center" valign="top" width="25">
  194.                       <img alt="[Caution]" src="../images/caution.png" />
  195.                     </td>
  196.                     <th align="left">Caution</th>
  197.                   </tr>
  198.                   <tr>
  199.                     <td colspan="2" align="left" valign="top">
  200.             Activated channels appear highlighted in blue in the dialog. If
  201.             you click on a channel in the list you toggle activation of the
  202.             corresponding channel.  Disabling a color channel red, blue, or
  203.             green has severe consequencies. For instance if you disable the
  204.             blue channel, all pixels from now on added to the image will
  205.             not have blue component, and so a white pixel will have the
  206.             yellow complementary color.
  207.           </td>
  208.                   </tr>
  209.                 </table>
  210.               </div>
  211.             </dd>
  212.             <dt>
  213.               <span class="term">Managing channels</span>
  214.             </dt>
  215.             <dd>
  216.               <p>
  217.             Under the channel list is a set of buttons allowing you to
  218.             perform some basic operations on channel list.
  219.           </p>
  220.               <p>
  221.             </p>
  222.               <div class="itemizedlist">
  223.                 <ul type="disc">
  224.                   <li>
  225.                     <p>
  226.                   <img src="../images/dialogs/dialogs-icon-edit.png" />
  227.                   <a id="gimp-channel-edit"></a>
  228.                   <span class="guilabel">Edit channel attributes</span>, only
  229.                   available for selection masks. Here you can change the
  230.                   <span class="guilabel">Channel name</span>.  The other two
  231.                   parameters affect channel is visibility in the image
  232.                   window; they control <span class="guilabel">Opacity</span> and
  233.                   color used for the mask in the image window.  A click on
  234.                   the color button displays the Gimp color selector and
  235.                   then you can change the mask color.
  236.                 </p>
  237.                   </li>
  238.                   <li>
  239.                     <p>
  240.                   <img src="../images/dialogs/dialogs-icon-new.png" />
  241.                   <a id="gimp-channel-new"></a>
  242.                   <span class="guilabel">New channel</span>: you can create here a
  243.                   new channel available to save a selection.  Displayed
  244.                   dialog lets you change <span class="guilabel">Opacity</span> and
  245.                   mask color used in the image to represent the selection.
  246.                 </p>
  247.                   </li>
  248.                   <li>
  249.                     <p>
  250.                   <img src="../images/dialogs/dialogs-icon-raise.png" />               
  251.                   <a id="gimp-channel-raise"></a>
  252.                   <span class="guilabel">Raise channel</span>, only available for
  253.                   selection masks : you can here put the channel up a level
  254.                   in the list.  Press <span><b class="keycap">Shift</b></span> key to move
  255.                   channel to top of the list.
  256.                 </p>
  257.                   </li>
  258.                   <li>
  259.                     <p>
  260.                   <img src="../images/dialogs/dialogs-icon-lower.png" />   
  261.                   <a id="gimp-channel-lower"></a>
  262.                   <span class="guilabel">Lower channel</span>:
  263.                   You can here put the channel down a level in the list.
  264.                   Press the <span><b class="keycap">Shift</b></span> key to move the channel
  265.                   to bottom of the list.
  266.                 </p>
  267.                   </li>
  268.                   <li>
  269.                     <p>
  270.                   <img src="../images/dialogs/dialogs-icon-duplicate.png" />
  271.                   <a id="gimp-channel-duplicate"></a>
  272.                   <span class="guilabel">Duplicate channel</span>: You can create
  273.                   here a copy of the active channel. Name of new channel is
  274.                   suffixed with a number.
  275.                 </p>
  276.                     <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
  277.                       <table border="0" summary="Tip">
  278.                         <tr>
  279.                           <td rowspan="2" align="center" valign="top" width="25">
  280.                             <img alt="[Tip]" src="../images/tip.png" />
  281.                           </td>
  282.                           <th align="left">Tip</th>
  283.                         </tr>
  284.                         <tr>
  285.                           <td colspan="2" align="left" valign="top">
  286.                   You can also duplicate a color channel or the Alpha
  287.                   channel.  It's an easy way to keep a copy of them and to
  288.                   use them later as a selection in an image.
  289.                 </td>
  290.                         </tr>
  291.                       </table>
  292.                     </div>
  293.                   </li>
  294.                   <li>
  295.                     <p>
  296.                   <img src="../images/dialogs/dialogs-icon-delete.png" />   
  297.                   <a id="gimp-channel-selection-delete"></a> 
  298.                   <span class="guilabel">Delete channel</span>,only available for
  299.                   selection masks: you can here delete the active channel.
  300.                 </p>
  301.                   </li>
  302.                   <li>
  303.                     <p>
  304.                   <img src="../images/dialogs/dialogs-icon-selection.png" />
  305.                   <a id="gimp-channel-selection-replace"></a>
  306.                   <span class="guilabel">Channel to selection</span>: here you can
  307.                   transform the channel to become a selection. By default
  308.                   the selection derived from a channel replaces any
  309.                   previous active selection. It's possible to change this
  310.                   by clicking on control keys.
  311.                   </p>
  312.                     <div class="itemizedlist">
  313.                       <ul type="circle">
  314.                         <li>
  315.                           <p>
  316.                         <a id="gimp-channel-selection-add"></a>
  317.                         <span><b class="keycap">Shift</b></span>: the selection derived from a
  318.                         channel is added to the previous active selection.
  319.                         The final selection is merged from both.
  320.                       </p>
  321.                         </li>
  322.                         <li>
  323.                           <p>
  324.                         <a id="gimp-channel-selection-subtract"></a>
  325.                         <span><b class="keycap">Ctrl</b></span>: the final selection is the
  326.                         substraction of selection derived from a channel from
  327.                         the previously active one.
  328.                       </p>
  329.                         </li>
  330.                         <li>
  331.                           <p>
  332.                         <a id="gimp-channel-selection-intersect"></a>
  333.                         <span><b class="keycap">Shift Ctrl</b></span>: the final selection is
  334.                         the intersection of selection derived from a channel
  335.                         with the previously active one. Only common parts are
  336.                         kept. 
  337.                       </p>
  338.                         </li>
  339.                       </ul>
  340.                     </div>
  341.                     <p>
  342.                 </p>
  343.                   </li>
  344.                 </ul>
  345.               </div>
  346.               <p>
  347.           </p>
  348.             </dd>
  349.           </dl>
  350.         </div>
  351.       </div>
  352.       <div class="sect2" lang="en" xml:lang="en">
  353.         <div class="titlepage">
  354.           <div>
  355.             <div>
  356.               <h3 class="title"><a id="gimp-channel-menu"></a>3.1.┬áChannels Menu</h3>
  357.             </div>
  358.           </div>
  359.           <div></div>
  360.         </div>
  361.         <div class="variablelist">
  362.           <div class="mediaobject">
  363.             <img src="../images/dialogs/dialogs-channel-menu.png" />
  364.           </div>
  365.           <dl>
  366.             <dt></dt>
  367.             <dd>
  368.               <p>
  369.             You can get the channel context menu by right clicking on a
  370.             channel thumbnail. This menu gives the same operations on channels
  371.             as those available from dialog buttons. The only difference concerns
  372.             transformation to selection operations, each of them having its own
  373.             entry in the menu.
  374.           </p>
  375.               <p>
  376.             </p>
  377.               <div class="itemizedlist">
  378.                 <ul type="disc">
  379.                   <li>
  380.                     <p>
  381.                   <span class="guilabel">Edit channel attributes</span>, 
  382.                   <span class="guilabel">New channel</span>,
  383.                   <span class="guilabel">Raise channel</span>,
  384.                   <span class="guilabel">Lower channel</span>,
  385.                   <span class="guilabel">Duplicate channel</span>, 
  386.                   <span class="guilabel">Delete channel</span>:
  387.                   see <a href="ch04s02.html#gimp-layer-menu" title="2.1.┬áLayers Menu">Managing channels</a>.
  388.                 </p>
  389.                   </li>
  390.                   <li>
  391.                     <p>
  392.                   <span class="guilabel">Channel to selection</span>:
  393.                   Selection derived from channel replaces any previous active selection. 
  394.                 </p>
  395.                   </li>
  396.                   <li>
  397.                     <p>
  398.                   <span class="guilabel">Add to selection</span>:  
  399.                   Selection derived from channel is added to previous active 
  400.                   selection. Final selection is merging of both.
  401.                 </p>
  402.                   </li>
  403.                   <li>
  404.                     <p>
  405.                   <span class="guilabel">Substract from selection</span>:  
  406.                   Final selection is substraction of selection derived from 
  407.                   a channel from previous active selection. 
  408.                 </p>
  409.                   </li>
  410.                   <li>
  411.                     <p>
  412.                   <span class="guilabel">Intersect with selection</span> :  
  413.                   Final selection is intersection of selection derived from a
  414.                   channel with the previous active selection. Only common parts are kept.
  415.                 </p>
  416.                   </li>
  417.                 </ul>
  418.               </div>
  419.               <p>
  420.           </p>
  421.             </dd>
  422.           </dl>
  423.         </div>
  424.       </div>
  425.     </div>
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  441.           <td width="40%" align="right" valign="top">┬á3.2.┬áSelection masks</td>
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  447.