Author Topic: Remapping Colors like Lookup Table  (Read 4956 times)

Hi folks!

I'm trying to simulate the color change that happens when inks are exposed to UV radiation—the reds and purples all turn to magenta, the yellows disappear, and the blues mostly stay.

What I essentially need is a color lookup table (LUT), if you're familiar with the concept from film color correction. I need to say, "If the input image has this color, remap to this other color".

HSL won't work because I need to affect the colors unevenly. It's possible curves might work but they're tricky to control and I'd like to have more control over the output. I've tried replace and match color nodes and I don't think they do what I want.

Here's an example setup kind of illustrating what I want. The desired output is "faked" because it's being built from a grayscale, where I need to be creating it from a given input image's colors. I suspect gradients won't actually be the way to accomplish this, but it was worth trying.

This SEEMS like something that shouldn't be that hard for Designer, but maybe I'm underestimating the problem. TBH I'm not sure how I'd accomplish it in Photoshop, either.



I maybe found a way close to what you want to achieve. Well, it is not a LUT and i don't think it's perfect but it seems to do the job in a way.
I've just divide the color by a yellow solid color and just control the power of the yellow amount by adjusting the alpha channel of the uniform color node.

this is rather trivial inside a pixel processor. the image above only remaps based on hue - if you want to also have saturation and lightness factor into this it becomes a bit more involved, but is also possible.

You should try the "Gradient Dynamic" node. I think it does exactly what you describe in your first image.
Product Manager - Allegorithmic

Thanks all!

I appreciate all your feedback. I haven't messed with pixel processors but I need to learn!

@cgvinny on Twitter replied to me and brought his LUT node to my attention—good if you have a LUT that you want to use, plus they're easily made in Photoshop.

Here it is if it helps anyone: