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<h3 class="title"><a id="plug-in-alienmap"></a>3.3. Alien Map</h3>
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<a id="id3357153" class="indexterm"></a>
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<img src="../images/filters/filters-colormap-alien.png" />
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<p>
This filter is found in
<span class="guimenuitem">Image>Filters/Colors/Map/<span class="accel">A</span>lien Map</span>
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<p>
This filter renders very modified colors by applying trigonometric functions.
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<h4 class="title"><a id="id3357242"></a>Options</h4>
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<span class="term">Preview</span>
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This preview displays results of filter application interactively.
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<span class="term">Selecting function</span>
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<dd>
<p>
You can select there a function, or no function, for each RVB channel.
</p>
<p>
Applying trigonometric functions needs some explanations. Remind trigonometric circle, with
radius +1 (fig.1). M point describes circle counter-clockwise. Its projection on X-axis is
Cosine and its projection on Y-axis is Sine. We can represent sine and cosine variations
graphically (fig.2). Pixel intensity range has been added along X-axis, from darkest (0) to
lightest (255). Resulting pixel color is along Y-axis.
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With <span class="guilabel">Cosine</span>, you can see that pixel 128 (Mid Tone) is mapped to 255
(maximum color) and, more generally, mid tone pixels are subdued, while dark and light
pixels are made more colored.
</p>
<p>
With <span class="guilabel">Sine</span>, color is not much changed in mid tones. Light tones (but not the
lightest) are boosted, and dark tones (but not the darkest ones) are subdued.
</p>
<p>
As pixel color results from the three RGB channels, remaining color appears when a color is
completely subdued. Result of light mixing is not the same as paint mixing, and the color may
look rather odd, but are well explained in RGB space. It will be psychedelic after setting
color intensities.
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<span class="term"> </span>
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<span class="guilabel">Three sliders R, G, B</span> and input boxes with arrow-heads are used to set
intensity of each R, G, B channel.
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