Mobius transformation : a step towards "contrast color range" ?

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pierrelabreche
Posts: 414
Joined: January 29th, 2019, 11:47 pm
What is the make/model of your primary camera?: Nikon Z8

Mobius transformation : a step towards "contrast color range" ?

Post by pierrelabreche »

The Mobius transformation is interesting. Could it be useful to let the user manage separately the effect on hue, intensity and saturation?

For example, Nik Collection's effect "contrast color range" would be very welcome as a built-in transformation in PWP.
Perhaps "contrast color range" could be obtained by using an enhanced Mobius effect, whereby saturation and intensity are affected, but not hue.
As usual, a user choice between HSL and HSV models could be useful.
jsachs
Posts: 4203
Joined: January 22nd, 2009, 11:03 pm

Re: Mobius transformation : a step towards "contrast color range" ?

Post by jsachs »

Given the way Mobius works, there is no way to extend it as you suggest.

I played a little with contrast color range, but I have no idea what it is actually doing or how it is implemented.

From what I can make out, the color contrast lets you select some color using the color slider and lightens that color while darkening its complement

I can think of a couple of ways you can achieve this effect in PWP currently:

1) Use Conditional Color Curves to lighten and/or darken selectable hue ranges.

2) Use Selective Color Correction to select colors by hue and saturation and adjust their brightness -- you can also change their hue and saturation at the same time.
Jonathan Sachs
Digital Light & Color
pierrelabreche
Posts: 414
Joined: January 29th, 2019, 11:47 pm
What is the make/model of your primary camera?: Nikon Z8

Re: Mobius transformation : a step towards "contrast color range" ?

Post by pierrelabreche »

jsachs wrote: January 10th, 2022, 3:25 pm I can think of a couple of ways you can achieve this effect in PWP currently:
1) Use Conditional Color Curves to lighten and/or darken selectable hue ranges.
2) Use Selective Color Correction to select colors by hue and saturation and adjust their brightness -- you can also change their hue and saturation at the same time.
Thanks for looking into this. In their current state, these two ways are awkward to use for achieving the desired effect.
The selective color correction is definitely easier to use, because it uses a color wheel rather than a color line.

Suggestion, based on the Selective color correction :
  • Add the ability to constraint a color correction to a pure Saturation vector, i.e., extending along a radial from the central white point.
  • Add the ability to rotate a color correction vector, in addition to moving endpoints. Thus the two endpoints will move by rotation.
  • Add the ability to associate an automatic "color correction twin", which is located opposite the central white point:
    • Hue is shifted by 180 degrees.
    • Saturation of the twin's origin and destination endpoints, are identical to those of the original vector.
    • The brightness change of the twin is the multiplicative inverse (reciprocal). For example, if the original vector increases brightness by 50% (factor 1.50), then the twin decreases brightness by 33.3% (1/1.5 = 66.6% )
  • With the above features, it will be easy to pick the central color of the "contrast color range"; moreover, changing the hue is a simple rotation and the twin endpoints will move automatically.
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