3D LUT magic

Alright, let start with a little video for 2021, happy new year y’all!

This was graded in Resolve with no LUTs, and no taste.

As we were discussing the other day with some amazing colorists and color scientists on our Discord server about LUTs and how stupid they were, I realized I missed the explanation in my stupid LUTs article. Despite the fact that some people sell some on internet and that some people like to wave their (black) magic wand like it’s containing some dark science, let’s build some 3D LUT together and have some fun.

So let’s say that we want to build the simplest LUT in the world. We’ll cover the range from 0 to 1, in 1 step, on the 3 input values separated by spaces, here we go:

1: 0 0 0

2: 0 0 1

3: 0 1 0

4: 0 1 1

5: 1 0 0

6: 1 0 1

7: 1 1 0

8: 1 1 1

So we have the input values, and if we write them as is, we have the smallest unity 3D LUT we can think of. It’s unity because the machine that reads those values expects to have that structure of incrementation of the input code values, and will look in the same place for the output value, for example if on a RGB LUT the input for full red which is line 5 it will look at the code values for R and find 1, for G it will be 0 and for B it will be 0.

If our LUT was doing a basic operation like a 0.5 gain, it would look like :

1: 0 0 0

2: 0 0 0.5

3: 0 0.5 0

4: 0 0.5 0.5

5: 0.5 0 0

6: 0.5 0 0.5

7: 0.5 0.5 0

8: 0.5 0.5 0.5

and then for full red on line 5 it would read 0.5 0 0 and would make a 0.5 value on the red output. So that’s it, you made your first 3D LUT!

So obviously you would want more steps to go from 0 to 1, in that case in the LUT metadata you would find a number that says something like LUT size, it’s just the number of steps.

You may even want to go further than 1, some formats would allow for it

So as you could see, it’s very dumb, again. But there’s magic. Yes. Because in a LUT, you can store stuff you can’t understand, that you can’t modelize. It’s a quantic machine. Or it’s a silver machine, like film!

We have amazing peeps on our Discord server, and amazing sharing of knowledge. Feel free to comment in the dedicated Rockflowers Q&A channel