11.14.  Channel Mixer

Revision History
Revision $Revision: 2438 $ 2007-10-20 ude
In RGB mode

In this mode, you have to select an Output Channel . This channel is the one which will be modified. In the dialog window, its default value is 100%, corresponding to the value of the channel in the original image. It can be increased or decreased. That's why slider ends are -200 and 200.

Three RGB sliders let you give a percentage to every channel. For every pixel in the image, the sum of the calculated values for every channel from these percentages will be given to the Output Channel. Here is an example:

In Monochrome mode

When this option is checked, the image preview turns to grayscale, but the image is still a RGB image with three channels, until the filter action is validated.

Here is how the Preserve Luminosity works in the monochrome mode: “ For example, suppose the sliders were Red:75%, Green:75%, Blue:0%. With Monochrome on and the Preserve Luminosity option off, the resulting picture would be at 75%+75%+0% =150%, very bright indeed. A pixel with a value of, say, R,G,B=127,100,80 would map to 127*0.75+100*0.75+80*0=170 for each channel. With the Preserve Luminosity option on, the sliders will be scaled so they always add up to 100%. In this example, that scale value is 1/(75%+75%+0%) or 0.667. So the pixel values would be about 113. The Preserve Luminosity option just assures that the scale values from the sliders always adds up to 100%. Of course, strange things happen when any of the sliders have large negative values ” (from the plug-in author himself).

[Note] Note

Which channel will you modify? This depends on what you want to do. In principle, the Red channel suits contrast modifications well. The Green channel is well adapted to details changes and the Blue channel to noise, grain changes. You can use the Decompose filter.