You can use the colour toning module in mode colour correction regions to do that
ccregions.pp3 (13.0 KB)
Well, it does the job here.
If you apply this CL curve:
you may see that we have tweaked the darkest pixels in the image (look at the lower, grayscale bar), and by dragging them down we have effectively lowered its saturation (look at the left bar).
E.g. This is a crop of an image (original, without CL curve applied):
and by applying the previous curve:
as you may see, the darkest parts of the fruits have been almost completely desaturated
(Donât forget to turn on the tool)
No again.
The behavior you obtain in this way is just âsomethingâ about the relation between L and C, but itâs not âgoodâ. At least is not what you obtain with other software that have such tool and itâs not what you obtain in GIMP by changing saturation with a layer mask based on luminosity.
Hard to me to explain.
HH or CC or even LL curve has a function y=F(x) and its neutral function yâ=x itâs obviously a diagonal.
Now, which is the meaning of a diagonal where x and y are different and indipendent things?
This is well treated by LH and CH tools, made in the only way they can work.
Why not for LC and CL?
Which is the meaning of a (i.e.) 20,20 point where the y is C and the x is L?
A point with L=20 could have every values of C.
What I expect from a C by L tool is a Câ=f(C) for each different value of L.
A curve C=f(L) does not have too much sense. Sure it has âaâ behavior but not the one expected by a tool called C by L.
The evidence is that actually, in a 0-100 L scale, is not possible to decrease saturation for a 0 (do you prefer 1?) luminosity point, as it is not possible to increase saturation for a 100 (99?) L point.
I canât explain better.
Thatâs what the colour correction module does. Did you try the pp3 I attached? Currently the answer seems to be no again
âŠ
Example: Enable color toning, set saturation to -100, set mask to L equalizer
and draw the curve you want, like this (left is original, right is with desaturated shadows)
Then add a second correction to saturate the parts you want and set saturation to +100:
Draw the curve to define the regions you want to saturate, et voila:
It is I who conceived this type of heretical curve (about 6 years ago) , which in fact is not heretical.
This system works as well as a horizontal curve and makes it easier to use BĂ©ziers curves
It applies to any chromaticity for a given luminance, and the derivative function yâ = x has nothing to do with it
But as says Ingo, itâs probably not this transformation that you want to achieve
Jacques
Sorry, I did not noticed you attached a pp3.
Anyway thank you, but I did not want to know how to do what I need.
I only wanted to point out what it seems to me a bad (I mean no sense) bahavior of the LC/CL tool.
If you tell me itâs OK as it is, Iâm fine. Thank you again.
@bluc The question from op was
How would one approach selecting (varying) degrees of shadows and desaturating them?
Then you asked: How do you think to desaturate the shadows or to saturate the highlights?
Please excuse I gave an answer
@jdc I can't understand LC and CL tools
at the bottom of the picture, how SNSHDR work. Easy to understand what it do.
With the diagonal, you donât have a good (I would say any) control at the edges, for shadow and hilights.
Anyway, Iâm fine with your answer. You think itâs OK, I think not, but for what I paid Iâm full satisfied
I think I donât follow you, but I donât even care about formulae or graphs in a user interface. I just seek results: how do you remove color (desaturate) black?
Again, how do you increase saturation of white, or an already saturated channel? I donât mind what a user interface pretends to do. It simply canât do that.
How do you increase 70 to a channel that already has a value of 254 (clipping at 255)?
How do you remove 125 from pure black (0,0,0)?
I think itâs not what somebody say here, but what could be done or not. It doesnât matter what a user interface makes you to believe.
About pure black and pure white I said 0-100 (or 1-99). 1 and 99 deserve their saturation level, but for all you wrote, I have to admit that you are fully right.
I was talking about LCH while I was thinking about HSV. My bad.
Thank you and sorry.
Also thanks and sorry to Ingo.
@jdc, hi Jacques, a question please.
Suppose you have the neutral 45 degree CL line and consider a point with x value = N.
Now you lower the curve in this area so that for x=N, y is now 0.9N, say.
What happens to the C values for all pixels with luminosity N? Are they -
a) reduced by a factor, that is, a multiplication
b) reduced by a fixed value, a subtraction, and bounded to zero, or
c) something else!
Thanks.
As @jdc is an expert in Munsell colors, may I ask if that transformation is perceptually uniform? That is, the same apparent color, with lower saturation?
Applying a simple multiplication of channels doesnât always lead to that results.
If I recall correctly, he factors in the shift with many LUTs.
@RawConvert
As says Ingo, itâs a)
@XavAL
the answer is in the use of âavoid color shiftâ
- if desabled, nothing is done !!
- if enabled
- first, with relative colorimetry (personal algoritm whithout using LCMS), C and if necessary L are modified to be in the gamut
- second, a Munsell correction is applied with 195 LUTf, essentialy where Lab is âfalseâ : red-yellow, blue-pirple, and some greens. Munsell tables have the reputation of being the ones that best render color perception
jacques
You can read Rawpedia
http://rawpedia.rawtherapee.com/Color_Management_addon#The_.22Munsell.22_correction
Thanks for the info @jdc. I was just playing with a test image to help my understanding. One small point - the tooltip for âred and skin tones protectionâ (and Rawpedia) says it works for the C slider and CC curve, but it clearly works for CL also.
Iâd have to agree with bluc on this controversy. Although I definitely understand how to use the CL tool as a diagonal, through having to figure it out, it would allow for much more precise and intuitive manipulation as a flat boost/cut equalizer orientation.