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Bug #11985

Modules which operate in Lab may create visible artifacts even when configured as no-op (all sliders at zero / straight curves)

Added by Sarge Borsch over 1 year ago. Updated over 1 year ago.

Status:
Closed: won't fix
Priority:
Low
Assignee:
-
Category:
Darkroom
Target version:
Start date:
01/31/2018
Due date:
% Done:

0%

Affected Version:
2.4.1
System:
Mac OS X
bitness:
64-bit
hardware architecture:
amd64/x86

Description

I've found some problem samples which cause certain modules ("contrast brightness saturation", "tone curve" when not in RGB or XYZ mode) cause visible artifacts (violet dot clusters in this case) when enabled, even if they are configured to do nothing (which is the default).

Steps to reproduce:
1: Open the raw sample in darkroom mode, optionally use the supplied minimal xmp profile (it has only base curve and exposure and nothing else)
2: Enable "contrast brightness saturation" or "tone curve" with default(no-op) settings
Then look at the changes in blue areas
I also tested the previous release (2.4.0), there's no difference.

Also, the artifacts are not visible when gamut clipping in "input profile" is enabled, but this is a crude workaround, I'd rather not have to simply throw away potentially useful information early in processing pipe (if something is out of gamut, it can be brought in by reducing saturation or something else, am I right?).

I am also attaching the in-camera JPEG for reference. (reduced by jpegtran, so no metadata, but it can be read from the raw file if needed)

Right now I have 2 more similar raw files which exhibit the same problem, feel free to ping me if I should upload them too, or do something else to help debugging this.

DSC00420.ARW.xz (22.1 MB) Sarge Borsch, 01/31/2018 09:42 PM

DSC00420.ARW.xmp (1.8 KB) Sarge Borsch, 01/31/2018 09:43 PM

DSC00420.JPG - jpeg from camera, except metadata (3.67 MB) Sarge Borsch, 01/31/2018 09:43 PM

screenshot_cbs.png - c.b.s. enabled without any gamut clipping (2.83 MB) Sarge Borsch, 01/31/2018 10:03 PM

screenshot_nothing.png - c.b.s. disabled (2.81 MB) Sarge Borsch, 01/31/2018 10:03 PM

screenshot_gamut_clipping.png - "gamut clipping" with "rec2020" (c.b.s. makes no difference) (2.55 MB) Sarge Borsch, 01/31/2018 10:04 PM

History

#1 Updated by Roman Lebedev over 1 year ago

Please attach both screenshots.
Looking at this screenshot, isn't this again gamut clipping issue?

Try setting "gamut clipping" (!! NOT the color profile itself) in "input color profile" to "rec2020"

#2 Updated by Sarge Borsch over 1 year ago

it seems that the exposure also affects the result: artifacts are hard to see at the default exposure setting, and very easy to see if it's +1.2EV or higher.

#3 Updated by Roman Lebedev over 1 year ago

  • Status changed from New to Closed: won't fix

Tried locally, it is standard "deep saturated blues" problem, which is described in usermanual.
Setting gamut clipping to rec2020 helps.

#4 Updated by Sarge Borsch over 1 year ago

Roman Lebedev wrote:

Please attach both screenshots.
Looking at this screenshot, isn't this again gamut clipping issue?

Try setting "gamut clipping" (!! NOT the color profile itself) in "input color profile" to "rec2020"

Done. Also, tried "gamut clipping" with "rec2020", it removes the difference but it itself visibly changes the image in a different way. I'm attaching all 3 screenshots.

#5 Updated by Sarge Borsch over 1 year ago

Roman Lebedev wrote:

Tried locally, it is standard "deep saturated blues" problem, which is described in usermanual.
Setting gamut clipping to rec2020 helps.

Shouldn't it be the default setting then?

#6 Updated by Roman Lebedev over 1 year ago

Sarge Borsch wrote:

Roman Lebedev wrote:

Tried locally, it is standard "deep saturated blues" problem, which is described in usermanual.
Setting gamut clipping to rec2020 helps.

Shouldn't it be the default setting then?

Not really, it isn't essential/required to get some base image to be displayed.
Also, adds some memory/computational overhead.

You can, as usual, create auto appliable preset with whatever params you want.

#7 Updated by Roman Lebedev over 1 year ago

  • Target version set to 2.6.0

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