In brief my conclusions were:
- PS Luminosity curves preserve Hue in all cases, and increase saturation where luminance is reduced, and reduce saturation where luminance is increased.
- PS Normal and ACR curves do not preserve Hue, and increase saturation in all cases.
In Martin's parrot:
* Point A and B: reduce luminance because of the 'S' curve (and increase Saturation in PS Lum).
* Point C: remains approximately with the same luminance after 'S' curve (and preserves saturation as well in PS Lum).
* Point D: reduces luminance because of the 'S' curve (and reduces Saturation in PS Lum).
Regarding LR, the new one:
- Seems to preserve Hue much better than PS Normal, but still modifies Hue.
- Increases saturation nearly the same as PS Normal.
Again what can be more pleasant to our eyes because of the apparent PS Luminance desaturation, can be PS Normal or LR.
However numbers say PS Luminance preserve better the original parameters.
In fact I wonder, looking at the final parrot point D, if PS Normal and LR could be losing some information (texture) because of the heavy saturation, specially PS Normal. LR seems to keep texture better in that area however.