[Feature Request] RGB Unsharp mask


#1

Hi! Is it possible to add the choice to apply unsharp mask in rgb color space?


(Mica) #2

Do you want to apply it on each channel separetly? I don’t understand!


#3

I thought in rawtherapee was applied on luminance, it would be nice if we can choose between rgb or luma


#4

The effect of that will be erased when you convert it to JPEG if you let it chroma subsample, just so you know.

Also, you’ll get color fringes where there weren’t any; for example, something red against white would get a green fringe on the white side. It might be visually disturbing.


(Ingo Weyrich) #5

In rt unsharp mask is applied to the L channel of Lab. Why do you want to apply it on rgb?


#6

Because visually I prefer the rgb version, it’s subjective but I don’t think Lab is always the best choice.


(Ingo Weyrich) #7

Can you show an example, please?


#8

I don’t have an example that shows a very visible difference but generally sharpening in rgb gives a well saturated image when instead Lab tends to “desaturate”.
unsharpened


rgb USM

EDIT: wrong file, this is l* a* b* USM :sweat_smile:

l* USM

By the way it isn’t necessary to sharpen in rgb but it’s not an horrible color space for sharpening.
RGB it’s just different from lab not necessary better or wrong :slight_smile:


(Ingo Weyrich) #9

Imho sharpening should be done on the Luminance channel. I’m not the rt dude, but I still think that we won’t implement sharpening on rgb. Maybe I will be wrong.

Ingo


#10

It gets confusing when talking about lightness, luminance and luma, so I will defer to Wikipedia and @elle.


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