Example for the “Channel Mixer” filter
This command combines values of the RGB channels. It works with images
with or without an alpha channel. It has monochrome mode and a preview.
Activate the command
You can find this command through
→ → .
“Channel Mixer” command options
From this menu you select the channel to mix to. Choices are
Red, Green, or Blue. It is insensitive when
Monochrome option is checked.
Red, Green, Blue
These three sliders set the contribution of red, green or blue
channel to output. Can be negative. These sliders are graduated
from -200 to 200. They represent the percentage which will be
attributed to the output channel. 100% corresponds to the value of
the channel of the studied pixel in the image.
This option converts the RGB image into a gray-scale RGB image.
The Channel Mixer command is often used with this aim in view,
because it often provides a better result than the other ways
(see Grayscale in
Glossary). Makes the Output Channel menu
The 21%, 72%, 7% settings give you the same gray luminosity
(Value) as the Grayscale command in Image/Mode. (They were 30%,
59%, 11% in v2.2).
Calculations may result in too high values and an image too much
clear. This option lessens luminosities of the color channels
while keeping a good visual ratio between them. So, you can change
the relative weight of the colors without changing the overall
Load settings from a file.
Save settings to a file.
Set default settings.
How does Channel Mixer work?
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:
The original image and its channels
Output channel is red. Green Channel +50
Output channel is red. Green Channel +50%. The Preserve
Luminosity option is checked.
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
command action is validated.
Monochrome option checked. Red: 100% Green: 50% Blue: 0%.
Preserve Luminosity unchecked.
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
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).
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