Yeah, you can use principle component analysis to figure out the transform to make the colour space "optimal" for compression of a specific image. I tried that

Yeah, you can use principle component analysis to figure out the transform to make the colour space "optimal" for compression of a specific image. I tried that once: https://bainbridgecode.wordpress.com/2012/04/24/beating-png-part-2/ https://bainbridgecode.wordpress.com/2012/04/24/beating-png-... and https://bainbridgecode.wordpress.com/2012/05/07/beating-png-part-3-remembering-a-level-maths/ https://bainbridgecode.wordpress.com/2012/05/07/beating-png-... There are plots at the end of part 3 showing the image channels separately for YCrCb and my custom PCA derived space. They clearly show that there's a lot less duplication of data between channels with the latter. And that in turn is obviously good for compression.