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Bug #10903

Channel mixer in gray values weird results

Added by Joe Giampaoli over 4 years ago. Updated over 4 years ago.

Status:
New
Priority:
Low
Assignee:
-
Category:
Darkroom
Target version:
-
Start date:
02/01/2016
Due date:
% Done:

0%

Estimated time:
Affected Version:
git development version
System:
Debian
bitness:
64-bit
hardware architecture:
amd64/x86

Description

Correct me if I'm wrong, but I don't know if the channel mixer is rendering weird results when playing with the values for specific channels. For example in the video capture I am including, I activate the channel mixer in B&W and when I start pulling down the blue channel to make the sky darker it appears that the trees (with lot's of green) start becoming brighter and then when making the blue brighter the trees become darker. Is this correct? Is it expected to work this way? I know that with color zones I can be more precise with the colors I want to darken or brighten, but it seems to me that in the sample video capture I am providing, the trees must share some of the blue in a way for the greens, why do they respond in an opposite manner?

Thanks

out.ogv (7.82 MB) out.ogv Joe Giampaoli, 02/01/2016 01:52 PM
out-1.ogv (8.99 MB) out-1.ogv Joe Giampaoli, 02/03/2016 01:24 PM
GIMP.ogv (7.3 MB) GIMP.ogv Joe Giampaoli, 02/03/2016 01:39 PM

History

#1 Updated by Joe Giampaoli over 4 years ago

I just want to simplify in a way that cutting down on certain values shouldn't necessarily boost others. I'm not sure how a channel mixer works, is it trying to maintain a "whole" equal value? Maybe I'm just a bit confused since I also work with audio and I'm used to EQ-ing a track, if I need to cut down on specific frequencies I don't expect others to go up. :)

Thanks

#2 Updated by Joe Giampaoli over 4 years ago

I just played with the same picture in GIMP with the mono mixer and yes, it responds more as expected (trees become darker when pulling down the blue channel) unless I activate the "Preserve Luminosity" box, then it does the weird results that I see in DT. So is this what's happening? It's preserving the luminosity? Is there a way I could do this without that? In GIMP this is not a default setting, could this feature be disabled or removed or add that "preserve luminosity" to the Channel Mixer module?. Also in that mode it renders a lot more noise sometimes....

Thanks

#3 Updated by Tobias Ellinghaus over 4 years ago

Channelmixer is next to unusable for me, it has different defaults for double clicking a slider vs. resetting the module, has strange effects for different sliders (try moving red to <= 0 for lightness and then the same with green) and many other problems. I fear a rewrite is the only sane thing to do. And while we are at it we should also move it out of output color space.

#4 Updated by Joe Giampaoli over 4 years ago

Wow! That bad? OK, well at least it's not my "picky" me... lol

Well, I guess I'll keep doing it either with color zones or just do that as a final step in GIMP.

Thanks for your reply!

#5 Updated by Roman Lebedev over 4 years ago

Please try https://github.com/darktable-org/darktable/pull/1061
Is there any difference?

#6 Updated by Joe Giampaoli over 4 years ago

Roman Lebedev wrote:

Please try https://github.com/darktable-org/darktable/pull/1061
Is there any difference?

Sorry for my ignorance, but how do I pull or merge 1061 to my local git repository from terminal?

Thanks!

EDIT: I get

fatal: repository 'https://github.com/darktable-org/darktable/pull/1061/' not found

#7 Updated by Roman Lebedev over 4 years ago

Joe Giampaoli wrote:

Roman Lebedev wrote:

Please try https://github.com/darktable-org/darktable/pull/1061
Is there any difference?

Sorry for my ignorance, but how do I pull or merge 1061 to my local git repository from terminal?

Thanks!

EDIT: I get

fatal: repository 'https://github.com/darktable-org/darktable/pull/1061/' not found

See https://help.github.com/articles/checking-out-pull-requests-locally/ and https://gist.github.com/piscisaureus/3342247

#8 Updated by Joe Giampaoli over 4 years ago

OK, just tried it. No, there's no difference with "Preserve Luminance" Unchecked. If I activate it, it seems to exaggerate the results...

Attaching another screen video capture with this test so you can see my results.

Thanks

#9 Updated by Joe Giampaoli over 4 years ago

Here's a sample video of the results I get in GIMP with the mono channel mixer just so you get an idea of what I was expecting. As you can see the greys in the trees pretty much retain the same values and the results aren't as harsh until I activate "Preserve Luminosity" there...

Thanks again!

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