Saturation Thresholding...

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Postby leeharper_admin » Mon Apr 04, 2011 6:13 pm

In thinking about ways of getting the maximum saturation into the image without hitting the gamut boundary walls (and therefore flattening out the image detail), I've been thinking that there is an additional interface tweak that would be really useful.

As has been discussed, it will be useful if the HSB Saturation curve could be displayed (via a radio button) either horizontal (for altering saturation on a hue-by-hue basis) or diagonal (for altering saturation on an intensity basis - as is the case in CM3).

I think that it will be immensely helpful if the threshold feature available in Lab (L channel) and HSB (B channel) is also made available for the HSB Saturation channel when the channel display is set to 'Intensity' (diagonal).

This will allow us to use the threshold to get 100% saturation into areas in the image without driving large areas out-of-gamut (and therefore crushing the detail).

In conjunction with an L parabola mask (and a version of HSB based on Lab), this thresholding Saturation option could make HSB the go-to color mode for color enhancement.


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Postby ggroess » Mon Apr 04, 2011 10:49 pm

OK I think my mind just went Bang.....
Let me think on this one a bit.

something feels out of place on this...

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Postby leeharper_admin » Tue Apr 05, 2011 10:24 am

I think that this seems dodgy because in CM3 the Saturation channel is so noisy - so the idea of using it to boost (rather than reduce) saturation seems dangerous. However, if Mike recreates HSB using Lab as he has mentioned, the Saturation channel would then be a really good place to add saturation to an image.

If someone (me ;)) is going to use the Saturation curve (in 'Intensity' mode - i.e., diagonal curve orientation) to add saturation to the image, CM4 should have a method for ensuring that large areas within the image are not clipped to 100% saturation (by an extreme move to the curve endpoint) - because that clipping will effectively be reducing saturation contrast in the image.

Of course, there may be situations in which it may be appropriate to clip a large area to 100% saturation (studio backgrounds?/blue skies) - so I'd like the clipping preview to be a guide, rather than a limit. CM3's Threshold preview perfectly fits the bill for this...


This then begs the question of how to fit the Saturation curve into our Color Variation process. As I see it this allows for two approaches:

  • Lab A/B contrast pin move for hue and saturation variation, with adjustments to the HSB Saturation curve to cut back areas that have been over-saturated by the contrast pin move.

  • Lab A/B contrast pin move for hue variation only (the UI could have a radio button to enable this: i.e., 'Hue and Saturation', 'Hue-only', 'Saturation-only'), followed by adjustments to the HSB Saturation curve to increase saturation variation.

Which method is best? Conceptually, controlling these two color components with separate adjustments is appealing; practically though, I think it remains to be seen as to which approach is best. The trouble is that we can't test both approaches well until the Saturation channel is cleaner...


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