Adjustment brush with color - can't get the color I set.

[kbFRL]

Hi all -
I'd appreciate an explanation of how colored adjustment brushes work.

What I see is that even when I have an absolutely white area
(R,G.B)= (100,100,100)%
on the histogram,
and I select brush color as
H=0;S=100,
which gives a seemingly pure Red, my brush with
(Feather-0, Flow=100 and Density=100) creates
area with
(R,G,B)=(46.5,32,31.6)%
when Exposure = -4.0
or
(83,71.2, 71.0)
when Exposure = -2.0, etc.

So what's behind this, and why it's apparently impossible to get the color set in the "Select the color" box for the brush?
My LR version is 6.5
Best,
--K.

 

[Johan Elzenga]

Colors are overlaid (mixed with the underlying pixels) on the picture, because otherwise you would get a complete opaque colored area without any detail (as if you spilled paint on the image). That is why the result always depends on what's underneath the painted area.

 

[kbFRL]

Thank you, Johan.
I do understand that there's a mixture, but in my case the area underneath is completely white, so there is no detail whatsoever, and the second component of the mixture is neutral.
The practical case in question is that I got a picture where a street lamp, which is yellow-orange in reality, was rendered by the camera as purely white due to a too wide exposure range,
I tried to color it properly using an adjustment brush - and couldn't...

 

[Johan Elzenga]

A common misunderstanding. You think about white as 'no color', but it is 'maximum color'. White is RGB 255, 255, 255, so if you overlay colors on white, that is what happens.

 

[kbFRL]

Whether white is called "maximum" color or "no color", is not an issue here (I called in "neutral", though it, probably, better describes grey).
The issue is that the color selected by (H,S) pair (and with L assumed to be 50%, I think) and shown as such as the brush color, does not correspond to the observed results.

For reasons unknown to me, LR, mixing Red=RGB(255,0,0)=HSL (0,100,50(?)) with White=RGB(255,255,255)=HSL (0,0,100), gives
Exp=-0->RGB(255,255,255)= HSL(0,0,100)
Exp=-1->RGB(241.7,227.4,227.2)=HSL(0,36.6.92)
Exp=-2 ->RGB=(212,182,181)= HSL(2,26.5.77.1)
Exp=-3->RGB=(167,127, 126)= HSL(1,18.9,57.5)
Exp=-4-> RGB=(116,82,81)= HSL(2,17.8,38.6)

The practical question remains - how to get the color one wants to - using a colored adjustment brush?

 

[Rob_Cullen]

As I understand 'Brush Color'-
Replace the word 'Color' with 'Tint'
When you brush with a color set in the brush it will only apply a tint that is affected by the luminance of the underlying pixels. It does not seem possible to brush color on white areas of an image.
It does not work in the same way that a pixel editor brush would work (eg. in Photoshop)
So for practical purposes, all expressions of RGB values are meaningless.
If you want full color (255,0,0) then you will need to edit in Photoshop.

 

[kbFRL]

I agree with you on all points, except " It does not seem possible to brush color on white areas of an image."
It is possible, if you get exposure down, but the color will be not the one you selected for the brush - for R, it will be mixed with G and B in some proportion.
I understand that in "normal" cases this does not matter - one could probably find a brush color which will satisfy one's needs, but when an area is washed out completely - then one must use a different tool, as you mentioned.

 

[kbFRL]

I found this old thread:
Adjustment Brush - Color Matching | Adobe Community
which discusses almpost the same topic and offers a way to replace one color with another.