guided blend mask blur not guiding anything in some modules (works only between input and output color profile)
The guided mask blur is awesome when it works, but seems to work only for modules in the Lab space, i.e. after the input color profile application and before the output color profile.
Try the exposure or profiled denoise (before input profile), or channel mixer (output profile), and there the "feathering radius" is almost equivalent to the "bluring radius" slider.
#3 Updated by Heiko Bauke about 2 months ago
As far as I can tell, there is no bug in the implementation of the feathering algorithm. For some (many?) images, however, the LAB representation (where brightness and color information are separated into different channels) is much more suitable to guide the mask.
#4 Updated by Matthieu Moy about 2 months ago
I didn't test with many images, but I tested specifically with a high-contrast image (black rock on white snow) and the effect of guiding is not even visible. It starts being visible if I overexpose the image (like +2EV or more).
My guess is that it should be possible to make the algorithm work for these images by applying some coefficients to the channels before doing the blur (e.g. if applying +2EV works, multiplying the guide by 2 could work). Not sure whether there's an easy way to do that without ruining the performance. At worse, obviously, a conversion to Lab would do the trick but that's probably overkill.
In the current situation, the problem is that a user trying the feathering slider on the wrong module will most likely give up and decide that the slider is useless. Pascal had trouble understanding how it worked, it took me stg like 1 hour to understand why I was not getting anything interesting out of it. If there's no way to get it to work on non-Lab modules, I'd be in favor of hiding the slider in these modules to avoid misunderstanding.
#5 Updated by Pascal Obry about 2 months ago
I'm just trying to know if this has a chance to be fixed today and then I can delay a bit the rc0 otherwise it will be in the rc1. As it is a new feature, I would really like to see this fixed for the rc0. Let me know what you think and what is the status. Thanks.
#7 Updated by Pascal Obry about 2 months ago
For RC0 if we do not have a fix I'll do that : https://github.com/darktable-org/darktable/pull/1868
Does that sounds ok to you?
#9 Updated by Matthieu Moy about 2 months ago
AFAIU, the Lab values are meant to be in [0.0, 100.0], while pre-input-color profile see values in [0.0, 1.0]. If so, would a multiplication by 100.0 do the trick?
Good that RC0 is there, and good that you (Pascal) have deactivated the slider temporarily. I just hope we'll get it back before the final release :-).
#10 Updated by Pascal Obry about 2 months ago
- Priority changed from Low to Medium
- % Done changed from 0 to 50
- Status changed from New to In Progress
- Category set to Darkroom
And indeed I just tried it on Lab based module and it works great and is very impressive. As I said before all my testing during integration check was done with the exposure module and I was never able to get it working properly! Now I understand why all others said that it was impressive and quite a nice addition :)
Anyway, let's hope a fix can be found for RGB based modules.