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You're absolutely right that RGB differences are not very meaningful to humans. I chose to stick with the easiest approach for educational purposes, but I'd love to hear if anyone tries out a different color difference function.

Note that the authors tried other types of energy functions in their original papers, ones that didn't simply use color differences. No one energy function seemed to be perfect across a variety of images.

Completely agree with this. In my experience, LAB space really makes an observable difference in perception-based applications, as compared to the mostly arbitrary RGB cube space.

RGB values in images are de-facto sRGB, which is reasonably close to human perception (sRGB gamma curve is close to Munsell lightness curve).

In this case applying gamma correction to compute the color difference in linear light would make things worse, as it'd model physical properties of the light, rather than human perception.