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<th colspan="3" align="center" id="chaptername">5.6. Levels tool</th>
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<h3 class="title"><a id="gimp-tool-levels"></a>5.6. Levels tool</h3>
</div>
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<div class="mediaobject">
<img src="../images/toolbox/tools-levels.png" />
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<p>
The Level tool provides features similar to the Histogram tool but can
also change the intensity range of the active layer or selection.
</p>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3330173"></a>Activate Tool</h4>
</div>
</div>
</div>
<p>
The Level Tool can be called in the following
order, from the image-menu:
<span class="guimenuitem"><span class="accel">T</span>ools</span>/
<span class="guimenuitem"><span class="accel">C</span>olor
Tools</span>/<span class="guimenuitem"><span class="accel">L</span>evels
</span>.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3330271"></a>Options</h4>
</div>
</div>
</div>
<div class="variablelist">
<dl>
<dt>
<span class="term">Modify Levels for Channel</span>
</dt>
<dd>
<p>
You can select the specific channel which will be modified by the
tool: Value makes changes to the luminosity of all pixels in the
image. Color channels allow to change saturation. Alpha channel
works on transparency. <span class="guilabel">Initialize channel</span>
cancels changes to the selected channel.
</p>
</dd>
<dt>
<span class="term">Input Levels</span>
</dt>
<dd>
<p>
The main area is a graphic representation of image dark, mid and
light tones content. They are on abscissa from level 0 (black) to
level 255 (white). Pixel number for a level is on ordinate axis.
The curve surface represents all the pixels of the image for the
selected channel. A well balanced image is an image with levels
(tones) distributed all over the whole range. An image with a
blue predominant color, for example, will produce a histogram
shifted to the left in Green and Red channels, signified by green
and red lacking on highlights.
</p>
<p>
Level ranges can be modified in three ways:
</p>
<div class="itemizedlist">
<ul type="opencircle">
<li style="list-style-type: circle">
<p>
Three triangles as sliders: one black for dark tones, one grey
for midtones (often called Gamma value), one white for light
tones.
</p>
</li>
<li style="list-style-type: circle">
<p>
Three eyedroppers: use the left one to pick the darkest
color, the mid one to pick the mid tone color, the right one
to pick the lightest color on the image. You can use
View/Info Window to find these colors.
</p>
</li>
<li style="list-style-type: circle">
<p>
Three input boxes to enter values directly.
</p>
</li>
</ul>
</div>
</dd>
<dt>
<span class="term">Output Levels</span>
</dt>
<dd>
<p>
Output Levels allows manual selection of a constrained output level
range. There are also arrow-heads located here that can be used to
interactively change the Output Levels.
</p>
</dd>
<dt>
<span class="term">All Channels</span>
</dt>
<dd>
<p>
<span class="guilabel">Load</span>: This button allows you to select a file
holding level settings.
</p>
<p>
<span class="guilabel">Save</span>: Allows you to save any levels you have set
to a file that can be loaded later.
</p>
<p>
<span class="guilabel">Auto</span>: Performs an automatic setting of the
levels.
</p>
<p>
<span class="guilabel">Three eyedroppers</span>: These three
controls determine three points on the grayscale. Any
level below the "Black Point" is black; any point above
the "White Point" is white. The "Gray Point", which must
be between the other two, determines the middle level of
Gray. All shades of gray are calculated from these three
levels.
</p>
</dd>
<dt>
<span class="term">Preview</span>
</dt>
<dd>
<p>
The Preview button makes all changes to the levels dynamically so
that the new level settings can be viewed straight away.
</p>
</dd>
</dl>
</div>
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