Question

In the 4 * 5 array that makes up a colour matrix, what do ALL the values do?

All I have found is basically this:

0, 0, 0, 0, 0 <-R

0, 0, 0, 0, 0 <-G

0, 0, 0, 0, 0 <-B

0, 0, 0, 0, 0 <-A

What does each thing do?

Answer 1

Lifted directly from Adobe’s ColorMatrix docs:

“The color matrix filter separates each source pixel into its red, green, blue, and alpha components as srcR, srcG, srcB, srcA. To calculate the result of each of the four channels, the value of each pixel in the image is multiplied by the values in the transformation matrix. An offset, between -255 and 255, can optionally be added to each result (the fifth item in each row of the matrix). The filter combines each color component back into a single pixel and writes out the result. In the following formula, a[0] through a[19] correspond to entries 0 through 19 in the 20-item array that is passed to the matrix property:”

redResult   = (a[0]  * srcR) + (a[1]  * srcG) + (a[2]  * srcB) + (a[3]  * srcA) + a[4]
greenResult = (a[5]  * srcR) + (a[6]  * srcG) + (a[7]  * srcB) + (a[8]  * srcA) + a[9]
blueResult  = (a[10] * srcR) + (a[11] * srcG) + (a[12] * srcB) + (a[13] * srcA) + a[14]
alphaResult = (a[15] * srcR) + (a[16] * srcG) + (a[17] * srcB) + (a[18] * srcA) + a[19]

And definitely test out the example in the docs. Beyond that, see the blog post by Emanuele Feronato, which is pretty good at showing how to use the matrix to adjust colors.