Reverse engineering Adobe’s gamut mapping

I’ve been working on gamut mapping for the last couple of weeks. I started with what felt like a pretty solid set of rules. Zeroth rule: leave no fingerprints. The mapping must be visually transparent. No banding, contouring, discontinuities, or global biases. The transform should be smooth and well-behaved, ideally continuous with bounded slope, so that small input differences remain small everywhere. First rule: place every color inside the output gamut. All output colors must be realizable by the destination device, without exception. Otherwise, the device will apply its own mapping, which is uncontrolled and may violate the other rules. Second rule: minimize perceived hue shift. Preserve hue as much as possible, recognizing that exact constancy is not always achievable under compression. Hue errors should be minimized in a perceptual space, not a device space. Third rule: preserve local contrast, especially near the gamut boundary. Do not collapse structure in highly saturated…