better lut3d placement in the pipeline

[jakubfi]

Related to issue #3062

If we consider how the available GMIC LUTs are supposed to be used, default lut3d module placement in dt's pipeline should be different. I'd say it should go right before colorout. Take a look at the following examples prepared using one of GMIC LUTs with various software:

Image processed with rt's film simulation:

Image processed with dt's lut3d (current placement)

Image processed with dt's lut3d (fixed placement - right before colorout):

And, for reference, unprocessed image ("clean" edit exported from dt) put through LUT with GMIC:

[jakubfi]

P.S. I've checked the module order once more. Before monochrome would be a better placement for lut3d, or maybe even before color reconstruction - I'm not sure about that one.

[junkyardsparkle]

Doesn't this depend quite a bit on specific use case? The LUT is a fixed transform, so I would tend to think it would make more sense early in the pipe, allowing following modules to perform further action on its output. If you only want the effect of the LUT, it doesn't really matter where it is, because you won't have other stuff enabled. ;-)

(TBH, my insight is limited here, because I don't really see the point of using something so primitive in software with so many other, more flexible color tools... OTOH, I have used darktable to produce haldcluts for use in ffmpeg, etc; I think of them as more useful in that workflow - using a software which makes adjustment easy to apply a transform in software which doesn't).

[jakubfi]

@junkyardsparkle You're correct about this depending on a use case. My concern is that lut3d is most likely going to be used for applying GMIC LUTs, which are well-known and readily available, and this is going to be the main use case here. For this to work correctly out of the box lut3d shoud be later in the pipe, so that most users get the desired results instead of "this looks weird".

In other words: lut3d position in the pipe isn't fixed by definition. Some users will have to change its position anyway. I would like to allow most users get good results easily, and leave messing with the pipe order to (most likely) more knowledgeable users.

Either way it should be made very clear (only doc? or maybe popup hints?) that lut3d position may need adjusting depending on the type of LUT used.

[github-actions]

This issue did not get any activity in the past 30 days and will be closed in 7 days if no update occurs. Please check if the master branch has fixed it since then.