R - G - B curve question

I recommend reading the article
http://www.mclelun.com/2019/04/colour-grading-using-curves-and-levels.html

 

Hummm let's see if I can help. With curves and working on the R G and B . On Red, if you raise the curve you are adding Red and removing Cyan, which is the opposite color. With Green, you Add Green (up) and remove Magenta. And with Blue, add (curve up) Blue and remove yellow. If you drag the curve down, you are adding the opposite color of that channel. So you always do this Add Color from that Channel and remove the opposite or Add the Opposite and remove the color of the channel
Now, since R+G gives Yellow because these too combined gives yellow. Same with G+B = C and B+R = M. If you add the same value on the curves, let's say, on Red Input 128 (midtones) and Output 200 and do the same in Green them you have Yellow
If you use the curve on G and B then you are adding Magenta
G+R=Y
R+B=M
B+G=C
On CMYK color model
Y+M=R
Y+C=G
C+M=B

 

thanks... I'm gonna read it

 

thanks a lot... you've helped so much with it.

But I have another question based on your explanation...


if I add the same value on the curves, let's say, on Red Input 128 (midtones) and Output 200 and do the same in Green them you have Yellow

is there any difference between using RED + GREEN to get yellow instead of using direct YELLOW to add color? Idk if you understand my question (english isn't my first language, sorry).

 

Don't worry, English is no mine either.
Well if you use a Direct Yellow them you have to use a Blend mode since Dir Yellow will change all R G and B colors of the image, using what we are talking about is different. In what you will ask? With Curves, you are only "moving" values on 2 channels.

Hummm let's see if this makes sense. Ok, imagine you have sand from the beach and you have a sieve. So you have Red Grains and Green Grains, they all pass and fall on a paper, but the blue grains are bigger, so they stay. But If all your grains are Yellow and they all can pass, then they all fall on the paper