Shaper LUTs vs. CDLs

[Hrvoje Simic]

Math operations are certainly not practical when you live in a world that denies the existence of CDLs. However, in a software product that does ostensibly support CDLs, it should be moderately preferable to have a workflow that need only attach 3 32-bit numbers (Slope, Offset, and Power) to a gamma adjustment, rather than lugging around 160KB of approximations. Or at least it would be preferable if the software that supported CDLs did so in a way that made them as easy to use and specify as LUTs, rather than treating them as if they were made of Vibranium. Or worse, Kryptonite.

CDL although useful in specific workflows is a rudimentary image shaping compared to a potential of a 3DLUT.

 

[Steven Abrams]

it should be moderately preferable to have a workflow that need only attach 3 32-bit numbers (Slope, Offset, and Power) to a gamma adjustment

A pow() function for every RGB(A) pixel value in an image can be more expensive than a 1D look up (with lerping). Depends on the system and implementation. It's not always practical, potentially just from a legacy implementation (or even just workflow) point of view. I prefer math based when it suits also, just saying shaper LUTs can be very useful when used in the right way at the right time. To completely rule them out for a single workflow preference is to ignore the bigger picture.

100x higher precision than 33^3 is irrelevant for grading. 64^3 reaches limits of discerning ability.

For linear conversions? No.
Shaper LUTs adjust the range of the input to suit the expected input range of a 3DLUT, or perform gamma/linear conversions. We're not talking about creative grading here.

Gamma mapping LUT alone used for creative shaping basis can be a setback for grading compared to 3DLUT because manipulating the rest of the image aspects will be predetermined with operators and color space. There are scenarios where a 3DLUT treating all the signal aspects together is a better starting point. It all depends on a creative approach and workflow priorities but there is no free lunch just because gamma mapping is more precise.

I don't know if it's the language barrier, but this has nothing to do with what I'm speaking about. You've suddenly introduced the words "creative" and "grading" into the discussion. Which is a different topic to Shaper LUTs. And you seem to be arguing that 3D LUTs are better for color space conversions than 1DLUTs, which no one made the argument against or even proposed. It's like you're not actually in the same discussion but a slightly different one, yet still responding to this one.

CDLs or math based expressions have their place. 1DLUTs have their place. 3DLUTs have their place.