How to change a colour?

farss wrote on 3/29/2008, 8:06 PM
Here's my problem.
I have a static background that the client created. I want to replace it with much the same thing but animated. I have a suitable DJ HD Jumback. Both it and the original are one colour with only variation in luminance making up the image, it's actually just bubbles underwater. Now I want to make the water in the Jumpack the same colour as the still. I can sample both colours to get either HSL or R'G'B'. The only FX that will do what I want is the Channel Blend, CC primary or secondary are the wrong tools and for sure I tried them as they're simple to use.

So what I cannot get my head around is how to calculate the RGB matrix coefficients for the Channel Blend FX to shift from one known colour to another known colour. What I have got my head around is that I need to be careful not to shift what is the Y' value in the process.

Sorry to ask such a technical question on a Sunday morning but I think the answer to this could help a lot of us. This goes right back to the Technicolor Challenge. Someone did ask back then how the correct coefficients were derived but there was never an answer.

Bob.

Comments

GlennChan wrote on 3/29/2008, 8:46 PM
You can't just use the secondary CC fx and use the "hue" and "saturation" controls?

Or just de-saturate the sucker, and then use the normal CC filter and use the wheels to add the tint you want (or gradient map).
farss wrote on 3/29/2008, 10:44 PM
Tried using hue controls but they didn't seem to come close.
Didn't try your second option but that should work.
Managed to nail it pretty close with channel blend doing it by eyeball and 'succesive approximation' while monitoring where I was going. Switching on Normalise Rows made it much easier.

As much an exercise in trying to understand how things work than anything.

Bob.
GlennChan wrote on 3/30/2008, 9:58 AM
Well you can figure out the algebra of what you're trying to get.

Eyeballing it would work too.
Grazie wrote on 3/30/2008, 10:36 PM
Send me a sample still? G