G'MIC exercises

[afre (Alan)]

@Stampede asked about Mixer [PCA] and I gave an uninformed answer.

GIMP 2.10.x tips and tricks

This might help: http://setosa.io/ev/principal-component-analysis/. Basically the mixer considers 3 PCA components. The primary contains most of variation of the image, followed by the secondary and finally the tertiary. I.e., you could remove the tertiary and still see most of the original image. My first impression is that factor is the weight of the components, shift is the intensity and twist is the hue shift.

I know people who frequent this thread can do better than that. Additional thoughts:

1. I was curious what the command would be in CLI and so output the command to the layer name. The command is kind of lengthy; are those values for the gradients?

[G'MIC] Mixer [PCA]: fx_mix_pca 0,0,0,-1.5,0,0,-1.5,0,0,0,3,248,98,2325.2000000000003,111.79512900164166,114.29732606890039,67.953656912764956,2315.6918711327867,1198.1961603337977,1119.5840052975143,1198.1961603337977,1460.9525680609997,972.14804576863651,1119.5840052975143,972.14804576863651,1028.2088564317926,0,50,50

If so, they don’t require user input at all. Should they belong to the argument list?

2. It would be great if we could get a rgb2pca and pca2rgb, though I don’t know if that is meaningful or useful. If anything, it would be an educational demonstration on how to get to and back from 3 PCA components.

3. I guess the input for PCA manipulation isn’t limited to RGB. It could be any number of channels, right? Does the number of input channels correspond to the number of PCA components we get? Or could we decompose the input image to any number of components, sort of like split_details?

Apologies for asking so many questions, especially when many of you are busy people. I hope I don’t tempt you away from your important work.