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  6.     <title>5.6.¬† Levels</title>
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  14.     <link rel="prev" href="gimp-tool-threshold.html" title="5.5.¬† Threshold" />
  15.     <link rel="next" href="gimp-tool-curves.html" title="5.7.¬† Curves" />
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  19.       <table width="100%" summary="Navigation header">
  20.         <tr>
  21.           <th colspan="3" align="center">5.6.¬†
  22.     <span lang="en" xml:lang="en">Levels</span>
  23.   </th>
  24.         </tr>
  25.         <tr>
  26.           <td width="20%" align="left"><a accesskey="p" href="gimp-tool-threshold.html"><img src="../images/prev.png" alt="Prev" /></a>¬†</td>
  27.           <th width="60%" align="center">5.¬†
  28.     <span lang="en" xml:lang="en">Color Tools</span>
  29.   </th>
  30.           <td width="20%" align="right">¬†<a accesskey="n" href="gimp-tool-curves.html"><img src="../images/next.png" alt="Next" /></a></td>
  31.         </tr>
  32.       </table>
  33.       <hr />
  34.     </div>
  35.     <div class="sect2" lang="en" xml:lang="en">
  36.       <div class="titlepage">
  37.         <div>
  38.           <div>
  39.             <h3 class="title"><a id="gimp-tool-levels"></a>5.6.¬†
  40.     <span lang="en" xml:lang="en">Levels</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: 2429 $</td>
  53.                   <td align="left">2008-01-17</td>
  54.                   <td align="left">j.h</td>
  55.                 </tr>
  56.               </table>
  57.             </div>
  58.           </div>
  59.         </div>
  60.       </div>
  61.       <a id="id2645598" class="indexterm"></a>
  62.       <a id="id2645611" class="indexterm"></a>
  63.       <a id="id2645625" class="indexterm"></a>
  64.       <p>
  65.     The Level tool provides features similar to the Histogram tool but can
  66.     also change the intensity range of the active layer or selection in every
  67.     channel. This tool is used to make an image lighter or darker, to change
  68.     contrast or to correct a predominant color cast.
  69.   </p>
  70.       <div class="sect3" lang="en" xml:lang="en">
  71.         <div class="titlepage">
  72.           <div>
  73.             <div>
  74.               <h4 class="title"><a id="id2645644"></a>5.6.1.¬†
  75.       <span lang="en" xml:lang="en">Activate the Tool</span>
  76.     </h4>
  77.             </div>
  78.           </div>
  79.         </div>
  80.         <p>
  81.       You can get to the Level Tool in the image-menu through:
  82.       <span class="guimenu"><span class="accel">T</span>ools</span> ‚Üí <span class="guisubmenu"><span class="accel">C</span>olor Tools</span> ‚Üí <span class="guimenuitem"><span class="accel">L</span>evels</span>, or
  83.       <span class="guimenu">Colors</span> ‚Üí <span class="guimenuitem">Levels</span>,
  84.     </p>
  85.         <p>
  86.       or by clicking the
  87.       <span class="guiicon">
  88.         <span class="inlinemediaobject"><img src="../images/toolbox/stock-tool-levels-22.png" /></span>
  89.       </span>
  90.       icon in Toolbox if this tool has been installed there. For this, go to
  91.         <a class="link" href="gimp-dialogs-misc.html#gimp-tools-dialog" title="5.1.¬† Tools Dialog">Tools Dialog</a>.
  92.     </p>
  93.       </div>
  94.       <div class="sect3" lang="en" xml:lang="en">
  95.         <div class="titlepage">
  96.           <div>
  97.             <div>
  98.               <h4 class="title"><a id="id2645740"></a>5.6.2.¬†
  99.       <span lang="en" xml:lang="en">Options</span>
  100.     </h4>
  101.             </div>
  102.           </div>
  103.         </div>
  104.         <div class="figure">
  105.           <a id="id2645751"></a>
  106.           <p class="title">
  107.             <b>Figure¬†13.128.¬†
  108.         <span lang="en" xml:lang="en">Level tool options</span>
  109.       </b>
  110.           </p>
  111.           <div class="figure-contents">
  112.             <div class="mediaobject">
  113.               <img src="../images/toolbox/tools-levels.png" alt="Level tool options" />
  114.             </div>
  115.           </div>
  116.         </div>
  117.         <br class="figure-break" />
  118.         <div class="variablelist">
  119.           <dl>
  120.             <dt>
  121.               <span class="term">Channel</span>
  122.             </dt>
  123.             <dd>
  124.               <p>
  125.             You can select the specific channel which will be modified by the
  126.             tool:
  127.             </p>
  128.               <div class="itemizedlist">
  129.                 <ul type="disc">
  130.                   <li>
  131.                     <p>
  132.                   <span class="guilabel">Value</span> makes changes to the value of
  133.                   all RGB channels in the image: the image becomes darker or
  134.                   lighter.
  135.                 </p>
  136.                   </li>
  137.                   <li>
  138.                     <p>
  139.                   <span class="guilabel">Red</span>, <span class="guilabel">Green</span> and
  140.                   <span class="guilabel">Blue</span> work on a particular color
  141.                   channel: the image gets more or less color. Remember that
  142.                   adding or removing a color result in removing or adding
  143.                   the complementary color
  144.                 </p>
  145.                   </li>
  146.                   <li>
  147.                     <p>
  148.                   <span class="guilabel">Alpha</span> works on semi-transparent layers
  149.                   or selections: here, dark means more transparency, and
  150.                   white is fully opaque. Your image must have an Alpha
  151.                   Channel, otherwise this option is disabled.
  152.                 </p>
  153.                   </li>
  154.                   <li>
  155.                     <p>
  156.                   <span class="guilabel">Initialize channel</span> cancels changes to
  157.                   the selected channel.
  158.                 </p>
  159.                   </li>
  160.                 </ul>
  161.               </div>
  162.               <p>
  163.           </p>
  164.             </dd>
  165.             <dt>
  166.               <span class="term">Input Levels</span>
  167.             </dt>
  168.             <dd>
  169.               <p>
  170.             The main area is a graphic representation of the active layer or
  171.             selection dark (Shadows), mid and light (Highlight)tones content
  172.             (the Histogram). They are on abscissa from level 0 (black) to
  173.             level 255 (white). Pixel number for a level is
  174.             on ordinate axis. The curve surface represents all the pixels of
  175.             the image for the selected channel. A well balanced image is an
  176.             image with levels (tones) distributed all over the whole range.
  177.             An image with a blue predominant color, for example, will produce
  178.             a histogram shifted to the left in Green and Red channels,
  179.             signified by green and red lacking on highlights.
  180.           </p>
  181.               <p>
  182.             Level ranges can be modified in three ways:
  183.           </p>
  184.               <div class="itemizedlist">
  185.                 <ul type="opencircle">
  186.                   <li style="list-style-type: circle">
  187.                     <p>
  188.                 Three triangles as sliders: one black for dark tones
  189.                 (Shadows), one grey for midtones (Gamma), one white for light
  190.                 (Highlights) tones.
  191.               </p>
  192.                     <p>
  193.                 The black slider determines the <span class="emphasis"><em>black point
  194.                 </em></span>: all pixels with this value or less
  195.                 will be black (no color with a color channel selected /
  196.                 transparent with the Alpha channel selected).
  197.               </p>
  198.                     <p>
  199.                 The white slider determines the <span class="emphasis"><em>white point
  200.                 </em></span>: all pixels with this value or
  201.                 higher, will be white (fully colored with a color channel
  202.                 selected / fully opaque with the Alpha channel selected).
  203.               </p>
  204.                     <p>
  205.                 The gray slider determines the <span class="emphasis"><em>mid point</em></span>.
  206.                 Going to the left, to the black, makes the image lighter
  207.                 (more colored / more opaque) . Going to the right, to the
  208.                 white, makes the image darker (less colored / more
  209.                 transparent).
  210.               </p>
  211.                   </li>
  212.                   <li style="list-style-type: circle">
  213.                     <p>
  214.                 Two eye-droppers: when you click them, the mouse pointer
  215.                 becomes an eye-dropper. Then clicking on the image determines
  216.                 the black or the white point according to the chosen
  217.                 eye-dropper. Use the left, dark one  to determine the
  218.                 black-point; use the right, white one to determine the white
  219.                 point.
  220.               </p>
  221.                   </li>
  222.                   <li style="list-style-type: circle">
  223.                     <p>
  224.                 Three numeric text boxes to enter values directly.
  225.               </p>
  226.                   </li>
  227.                 </ul>
  228.               </div>
  229.               <p>
  230.             Input Levels are used to lighten highlights (bright tones),
  231.             darken shadows (dark tones), change the balance of bright and
  232.             dark tones. Move sliders to the left to increase lightness
  233.             (increase the chosen color / increase opacity). Move the sliders
  234.             to the right to lessen lightness (lessen the chosen color /
  235.             lessen opacity)).
  236.           </p>
  237.               <div class="mediaobject">
  238.                 <img src="../images/toolbox/levels-input-1.png" />
  239.                 <div class="caption">
  240.                   <p>
  241.                 A gray-scaled image. Three stripes: Shadows (64), Mid Tones
  242.                 (127), Highlights (192). The histogram shows three peaks,
  243.                 one for each of the three tones.
  244.               </p>
  245.                 </div>
  246.               </div>
  247.               <div class="figure">
  248.                 <a id="id2646034"></a>
  249.                 <p class="title">
  250.                   <b>Figure¬†13.129.¬†
  251.               <span lang="en" xml:lang="en">Example for Input Levels</span>
  252.             </b>
  253.                 </p>
  254.                 <div class="figure-contents">
  255.                   <div class="mediaobject">
  256.                     <img src="../images/toolbox/levels-input-2.png" alt="Example for Input Levels" />
  257.                     <div class="caption">
  258.                       <p>
  259.                   The Value channel is selected.
  260.                   The black slider (Shadows) has been moved up to the
  261.                   Shadows peak. The 64 value became 0 and the Shadows
  262.                   stripe became black (0). The Gamma (mid tones) slider is
  263.                   automatically moved to the middle of the tone range. Mid
  264.                   tones are made darker to 84 and Highlights to 171.
  265.                 </p>
  266.                     </div>
  267.                   </div>
  268.                   <div class="mediaobject">
  269.                     <img src="../images/toolbox/levels-input-3.png" alt="Example for Input Levels" />
  270.                     <div class="caption">
  271.                       <p>
  272.                   The white slider (highlights) has been moved up to the
  273.                   highlight peak. The 192 value became 255 and the highlight
  274.                   stripe became white. The Gamma (mid tones) slider is
  275.                   automatically moved to the middle of the tone range. Mid
  276.                   tones are made lighter to 169 and Shadows to 84.
  277.                 </p>
  278.                     </div>
  279.                   </div>
  280.                 </div>
  281.               </div>
  282.               <br class="figure-break" />
  283.             </dd>
  284.             <dt>
  285.               <span class="term">Output Levels</span>
  286.             </dt>
  287.             <dd>
  288.               <p>
  289.             Output Levels allows manual selection of a constrained output
  290.             level range. There are also numeric text boxes with arrow-heads
  291.             located here that can be used to interactively change the Output
  292.             Levels.
  293.           </p>
  294.               <p>
  295.             Output levels force the tone range to fit the new limits you have
  296.             set.
  297.           </p>
  298.               <div class="itemizedlist">
  299.                 <ul type="disc">
  300.                   <li>
  301.                     <p>
  302.                 Working with Value: values are compressed and look more
  303.                 alike; so contrast is reduced. Shadows are made lighter:
  304.                 new details can show up but contrast is less; a compromise
  305.                 is necessary. Highlights are made darker.
  306.               </p>
  307.                   </li>
  308.                   <li>
  309.                     <p>
  310.                 Working with Color channels: if you the use the green
  311.                 channel for example and set the output levels between 100
  312.                 and 140, all pixels with some green, even a low value, will
  313.                 have their green channel value shifted between 100 and 140.
  314.               </p>
  315.                   </li>
  316.                   <li>
  317.                     <p>
  318.                 Working with Alpha channel: all Alpha values will be
  319.                 shifted to the range you have set.
  320.               </p>
  321.                   </li>
  322.                 </ul>
  323.               </div>
  324.               <div class="figure">
  325.                 <a id="id2646184"></a>
  326.                 <p class="title">
  327.                   <b>Figure¬†13.130.¬†
  328.               <span lang="en" xml:lang="en">Example for Output Levels</span>
  329.             </b>
  330.                 </p>
  331.                 <div class="figure-contents">
  332.                   <div class="mediaobject">
  333.                     <img src="../images/toolbox/levels-output-1.png" alt="Example for Output Levels" />
  334.                     <div class="caption">
  335.                       <p>
  336.                   <span class="bold"><strong>Original image</strong></span>:
  337.                   A RGB gradient from black (0;0;0) to white (255;255;255).
  338.                   Output Levels has no histogram; here, we used
  339.                   <span class="guimenu">Dialogs</span> ‚Üí <span class="guimenuitem">Histogram</span>.
  340.                 </p>
  341.                     </div>
  342.                   </div>
  343.                   <div class="mediaobject">
  344.                     <img src="../images/toolbox/levels-output-2.png" alt="Example for Output Levels" />
  345.                     <div class="caption">
  346.                       <p>
  347.                   Value channel selected.
  348.                   The black slider has been moved to 63 and the white slider
  349.                   to 189. The Histogram shows the compression of pixels. No
  350.                   pixel is less than 63, and no pixel is more than 189. In
  351.                   the image, Shadows are lighter and Highlights are darker:
  352.                   contrast is reduced.
  353.                 </p>
  354.                     </div>
  355.                   </div>
  356.                 </div>
  357.               </div>
  358.               <br class="figure-break" />
  359.             </dd>
  360.             <dt>
  361.               <span class="term">All Channels</span>
  362.             </dt>
  363.             <dd>
  364.               <p>
  365.             <span class="guilabel">Open</span>: This button allows you to
  366.             select a file holding level settings.
  367.           </p>
  368.               <p>
  369.             <span class="guilabel">Save</span>: Allows you to save any levels
  370.             you have set to a file that can be loaded later.
  371.           </p>
  372.               <p>
  373.             <span class="guilabel">Auto</span>: Performs an automatic setting
  374.             of the levels.
  375.           </p>
  376.               <p>
  377.             <span class="guilabel">Three eyedroppers</span>: These three buttons
  378.             respectively represent a white, a gray and a black eye-dropper.
  379.             When you click one of these buttons, the mouse pointer takes the
  380.             form of the eye-dropper it represents. Then, when clicking the
  381.             image, the clicked pixel determines the <span class="emphasis"><em>white point
  382.             </em></span>, the <span class="emphasis"><em>black point</em></span> or the
  383.             <span class="emphasis"><em>mid point</em></span> according to the eye-dropper you
  384.             chose. Works on all channels, even if a particular channel is
  385.             selected.
  386.           </p>
  387.               <div class="figure">
  388.                 <a id="id2646357"></a>
  389.                 <p class="title">
  390.                   <b>Figure¬†13.131.¬†
  391.               <span lang="en" xml:lang="en">Example for Levels eye-droppers</span>
  392.             </b>
  393.                 </p>
  394.                 <div class="figure-contents">
  395.                   <div class="mediaobject">
  396.                     <img src="../images/toolbox/levels-eyedrop.png" alt="Example for Levels eye-droppers" />
  397.                     <div class="caption">
  398.                       <p>
  399.                   At the bottom, a gradient from black to white. Down, the
  400.                   result after clicking with the white eye-dropper: all
  401.                   pixels with a value higher than that of the clicked pixel
  402.                   turned to white.
  403.                 </p>
  404.                     </div>
  405.                   </div>
  406.                 </div>
  407.               </div>
  408.               <br class="figure-break" />
  409.             </dd>
  410.             <dt>
  411.               <span class="term">Preview</span>
  412.             </dt>
  413.             <dd>
  414.               <p>
  415.             The Preview button makes all changes to the levels dynamically so
  416.             that the new level settings can be viewed straight away.
  417.           </p>
  418.             </dd>
  419.           </dl>
  420.         </div>
  421.       </div>
  422.       <div class="sect3" lang="en" xml:lang="en">
  423.         <div class="titlepage">
  424.           <div>
  425.             <div>
  426.               <h4 class="title"><a id="id2646423"></a>5.6.3.¬†
  427.       <span lang="en" xml:lang="en">Tool Options dialog</span>
  428.     </h4>
  429.             </div>
  430.           </div>
  431.         </div>
  432.         <div class="variablelist">
  433.           <p>
  434.         Although this tool is not present in Tool box, nevertheless it has a
  435.         Tool Option Dialog under the Toolbox. These options are described here:
  436.       </p>
  437.           <dl>
  438.             <dt>
  439.               <span class="term">Histogram Scale</span>
  440.             </dt>
  441.             <dd>
  442.               <p>
  443.             These two options have the same action as the logarithmic and
  444.             Linear buttons in the Levels dialog.
  445.           </p>
  446.             </dd>
  447.             <dt>
  448.               <span class="term">Sample Average</span>
  449.             </dt>
  450.             <dd>
  451.               <p>
  452.             This slider sets the ‚Äú<span class="quote">radius</span>‚Äù of the color-picking
  453.             area. This area appears as a more or less enlarged square when
  454.             you maintain the click on a pixel.
  455.           </p>
  456.             </dd>
  457.           </dl>
  458.         </div>
  459.       </div>
  460.       <div class="sect3" lang="en" xml:lang="en">
  461.         <div class="titlepage">
  462.           <div>
  463.             <div>
  464.               <h4 class="title"><a id="id2646492"></a>5.6.4.¬†
  465.         <span lang="en" xml:lang="en">Actual practice</span>
  466.       </h4>
  467.             </div>
  468.           </div>
  469.         </div>
  470.         <div class="figure">
  471.           <a id="id2646505"></a>
  472.           <p class="title">
  473.             <b>Figure¬†13.132.¬†
  474.         <span lang="en" xml:lang="en">A very under-exposed image</span>
  475.       </b>
  476.           </p>
  477.           <div class="figure-contents">
  478.             <div class="mediaobject">
  479.               <img src="../images/filters/examples/colors-retinex1.png" alt="A very under-exposed image" />
  480.               <div class="caption">
  481.                 <p>Original image</p>
  482.               </div>
  483.             </div>
  484.             <div class="mediaobject">
  485.               <img src="../images/toolbox/levels-ex1b.png" alt="A very under-exposed image" />
  486.               <div class="caption">
  487.                 <p>
  488.             The histogram shows a predominance of Shadows and missing
  489.             Highlights.
  490.           </p>
  491.               </div>
  492.             </div>
  493.           </div>
  494.         </div>
  495.         <br class="figure-break" />
  496.         <div class="figure">
  497.           <a id="id2646565"></a>
  498.           <p class="title">
  499.             <b>Figure¬†13.133.¬†
  500.         <span lang="en" xml:lang="en">Setting the white point</span>
  501.       </b>
  502.           </p>
  503.           <div class="figure-contents">
  504.             <div class="mediaobject">
  505.               <img src="../images/toolbox/levels-ex2a.png" alt="Setting the white point" />
  506.               <div class="caption">
  507.                 <p>
  508.             The white slider has been moved to the start of well marked
  509.             Highlights. The image lightens up.
  510.           </p>
  511.               </div>
  512.             </div>
  513.             <div class="mediaobject">
  514.               <img src="../images/toolbox/levels-ex2b.png" alt="Setting the white point" />
  515.               <div class="caption">
  516.                 <p>
  517.             The resulting histogram (down) shows Highlights now, but Shadows
  518.             are still predominant.
  519.           </p>
  520.               </div>
  521.             </div>
  522.           </div>
  523.         </div>
  524.         <br class="figure-break" />
  525.         <div class="figure">
  526.           <a id="id2646627"></a>
  527.           <p class="title">
  528.             <b>Figure¬†13.134.¬†
  529.         <span lang="en" xml:lang="en">
  530.           Setting the balance between Shadows and Highlights
  531.         </span>
  532.       </b>
  533.           </p>
  534.           <div class="figure-contents">
  535.             <div class="mediaobject">
  536.               <img src="../images/toolbox/levels-ex3a.png" alt="Setting the balance between Shadows and Highlights" />
  537.               <div class="caption">
  538.                 <p>
  539.             The mid slider has been moved to the left. This results in
  540.             reducing the proportion of Shadows and increasing the proportion
  541.             of Highlights.
  542.           </p>
  543.               </div>
  544.             </div>
  545.             <div class="mediaobject">
  546.               <img src="../images/toolbox/levels-ex3b.png" alt="Setting the balance between Shadows and Highlights" />
  547.               <div class="caption">
  548.                 <p>
  549.             The resulting histogram (down) confirms the reduction of Shadows.
  550.           </p>
  551.               </div>
  552.             </div>
  553.           </div>
  554.         </div>
  555.         <br class="figure-break" />
  556.       </div>
  557.     </div>
  558.     <div class="navfooter">
  559.       <hr />
  560.       <table width="100%" summary="Navigation footer">
  561.         <tr>
  562.           <td width="40%" align="left"><a accesskey="p" href="gimp-tool-threshold.html"><img src="../images/prev.png" alt="Prev" /></a>¬†</td>
  563.           <td width="20%" align="center">
  564.             <a accesskey="u" href="gimp-tools-color.html">
  565.               <img src="../images/up.png" alt="Up" />
  566.             </a>
  567.           </td>
  568.           <td width="40%" align="right">¬†<a accesskey="n" href="gimp-tool-curves.html"><img src="../images/next.png" alt="Next" /></a></td>
  569.         </tr>
  570.         <tr>
  571.           <td width="40%" align="left" valign="top"><a accesskey="p" href="gimp-tool-threshold.html">5.5.¬†
  572.     <span lang="en" xml:lang="en">Threshold</span>
  573.   </a>¬†</td>
  574.           <td width="20%" align="center">
  575.             <a accesskey="h" href="index.html">
  576.               <img src="../images/home.png" alt="Home" />
  577.             </a>
  578.           </td>
  579.           <td width="40%" align="right" valign="top">¬†<a accesskey="n" href="gimp-tool-curves.html">5.7.¬†
  580.     <span lang="en" xml:lang="en">Curves</span>
  581.   </a></td>
  582.         </tr>
  583.       </table>
  584.     </div>
  585.   </body>
  586. </html>
  587.