A LUT is a simple way of describing any possible colour transform and has a lot of good uses. So all a 3D LUT is doing is taking a set of RGB values and returning different RGB values. Then looks those up in a table and you get a resulting RGB value. What a 3D LUT is doing is similar, but it takes 3 values as input, a R, G and B colour value usually. We’ll come back to this later on.Ī 3D LUT is where the ‘issues’ can start. Of course you can see that a LUT has a well defined start and finishing value, whereas a mathematical curve could be infinite. You can have multiple 1D LUTs, one for each R, G and B but that's less usual. So if you have a 10 bit number going in (1024 possible values) then that is the size of your table (1024 entries) and you’re good to go. So if you wanted to change a log curve to a gamma curve there is a pure mathematical equation that could be used, but actually it is quicker to work out what all the values are ahead of time and store them in a table. It’s a very quick way of converting between sets of values. All a 1D LUT does is convert one value into another - you have an input value, that is looked up in the table and an output value is found. One is a 1D (one dimensional) LUT and the other is a 3D Cube LUT.Ī 1D LUT is very simple, very useful and not a problem. Lets define a few terms before we dive into what’s going on.

This post will attempt to show you what a LUT does and when it doesn’t do it very well. The truth, as always, is somewhere in between.

LUTs have been seen as the holy grail and the very embodiment of the devil itself.

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