3.3. Alien Map

Overview

This filter is found in Image>Filters/Colors/Map/Alien Map

This filter renders very modified colors by applying trigonometric functions.

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Preview

This preview displays results of filter application interactively.

Selecting function

You can select there a function, or no function, for each RVB channel.

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.

With Cosine, 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.

With Sine, 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.

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.

Three sliders R, G, B and input boxes with arrow-heads are used to set intensity of each R, G, B channel.