Thread: CC3 --- How do I use the RGB Matrix?

http://www.graficaobscura.com/matrix/index.html describes the general idea. If you look at the RGB Matrix Data Entry dialog, it tells you that

R = []*R + []*G + []*B + []
G = []*R + []*G + []*B + []
B = []*R + []*G + []*B + []

where [] is a number that you enter (different number for each []). The key to understanding this is that every color has a red, a green, and a blue component (thus, RGB). This filter processes an input RGB color into an output RGB color. Fully labeling the above equations gives

outputR = []*inputR + []*inputG + []*inputB + []
outputG = []*inputR + []*inputG + []*inputB + []
outputB = []*inputR + []*inputG + []*inputB + []

Why aren't they fully labeled on the dialog? I'm going to claim that I didn't want the dialog to get too wide. Yeah, that's it! I didn't want the dialog to get too wide!

Anyhow, the first row defines the output red component of the color as the weighted sum of the input RGB components. If you want to get rid of all red in your drawing, use 0, 0, 0, 0 for the 4 numbers on the outputR line. If you want the output red to have no relation to the input RGB color, but just be a solid red, then use 0, 0, 0, 1. If you want a perceptually gray color to replace the output, use the numbers 0.3, 0.59, 0.11, 0 for all of the output RGB components (these values are the Gray predefine value from the dialog). The sum of the numbers that you enter across a row should be 1.

A couple of other things you could do with the tool include shuffling your channels and doing color correction. For instance, if you wanted to see only the grayscale red channel, you could enter 1,0,0,0 into all three lines. Each channel would then be replaced with the red channel.

Color correction: Say you want the image to be slightly yellower. In additive color theory, yellow is complementary to blue, so that means you need to reduce the blue information in the matrix. Give the blue line 0, 0, .9, 0 That will reduce the blue by 10%, which effectively increases the yellow.

A color wash, like the sepia preset, can be achieved by starting with the grayscale preset, then nudging the numbers in the direction you want to go. Notice that sepia is pretty close to the numbers for gray. The blue has been pushed down, and both red and green raised, red a bit more than green. It will likely take a lot of experimentation to hit the numbers you want, but starting with a good understanding of additive color theory will help.

Incidentally, this matrix is frequently used to construct Photoshop filters, as is the Spatial Matrix Process.

My method is to find a resource that provides swatches, and then google the name of the swatch to find the RGB coordinate. Wikipedia is a pretty good resource for more basic colours, but Dulux can be pretty helpful too!