GIMP User Manual - 3.5. Colormap Rotation

3.5.1. Overview

Figure 11.24. From left to right: Original image, after applying filter

You can find this filter through Filters->Colors->Map->Color Map Rotation.

Colormap Rotation lets you exchange one color range to another range.

3.5.2. Main Options

Figure 11.25. Main Options of the “Color Map Rotation” filter

You have there two color circles, one for the “From” color range and the other for the “To” color range:

From

The Color Circle: Two axis to define "From" range. The curved arrow in angle lets to recognise "From" axis and "To" axis of range. Click-drag these axis to change range.

Switch to Clockwise/Counterclockwise: Sets the direction the range is going.

Change Order of Arrows: Inverts From and To axis. This results in an important color change as colors in selection angle are different.

Select All selects the whole color circle.

From and To boxes display start axis and end axis positions (in rad/PI) which are limiting the selected color range. You can enter these positions manually or with help of arrow-heads.

To

This section options are the same as "From" section ones.

3.5.3. Grey Options

Figure 11.26. Base image for Grey Options

Three sectors are defined for Red, Green and Blue with different saturations. Grey and White colors are represented (0% Sat).

In this tab, you can specify how to treat gray. By default, grey is not considered as a color and is not taken in account by the rotation. Here, you can convert slightly saturated colors into grey and you can also convert grey into color.

Grey Color Circle

At center of this color circle is a small "define circle". At center, it represents grey. If you increase grey threshold progressively, colors with saturation less than this threshold turn to grey.

Then, if you pan the define circle in the color circle, or if you use input boxes, you define Hue and Saturation. This color will replace all colors you have defined as grey. But result depends on Grey Mode too.

Grey Mode

The radio buttons Treat As This and Change As This determine how your previous choices will be treated:

With Change As This, grey will take the color defined by the define circle directly, without any rotation, whatever its position in the color circle.
With Treat As This, grey will take the color defined by the define circle after rotation, according to "From" and "To" choices you made in the Main tab. With this option, you can select color only in the "From" sector, even if it is not visible in Grey tab.

Figure 11.27. Grey Mode

The small circle is on yellow and mode is "Change As This". Blue has changed to yellow. Note that Grey and White did so too.

Gray Threshold

Figure 11.28. Gray Threshold

Grey-threshold is 0.25: the blue sector (sat 0.25) has turned to Grey (Note that Grey and White, that are 0% Sat., are not concerned).

You specify there how much saturation will be considered grey. By increasing progressively saturation, you will see an enlarging circle in color circle and enlarging selected areas in Preview if "Continuous update" is checked. In a black to white gradient,you can see enlarging color replacement as you increase threshold very slowly.

Black to White gradient, progressively filled with color, as threshold increases.

3.5.4. Previews

Original and Rotated

The Original preview displays a thumbnail of the original image and the Rotated preview displays color changes interactively, before they are applied to the Image.

Continuous Update

Continuous Update displays color changes continuously in the Rotated preview.

Area

In this drop down list, you can select between

Entire Layer: works on the whole layer (The image if there is no selection).
Selection: displays selection only,
Context: displays selection in image context.

3.5.5. Units

You can select here the angle unit used to locate colors in the Hue/Saturation circle. This choice is valid only for the current filter session: don"t click on Valid just after selecting unit, return to the wanted tab!