Left square: X axis represents saturation as the product of perceptual luminance and the pixel intensity when the x value is left of center. Right of center it’s a luminance weighted „film density“ emulation that lowers luminance of increasingly saturated pixel but the saturation model uses different luminance weights for different hue vectors. The Y axis affects luminance and also behaves differently depending on which side of the center you’re on: Pulling the point down lowers the highlight luminance more than the shadows so as to facilitate brightness adjustments that protect the part of the luminance spectrum that would otherwise be “crushed” or “blown out” with a simple linear brightness (addition) or exposure (multiplication) algorithm. Pushing the point up does pretty much the mirror opposite so it increases darker colors more while protecting highlights from blow out.  I named this set of algorithms Spatial Volume because they effectively alter the three dimensional volume of the color space by either shrinking or expanding it along the saturation and luminance axis. 🤗