https://bugs.kde.org/show_bug.cgi?id=468706
Bug ID: 468706
Summary: Color corrections behavior is either incorrect or
misleading
Classification: Applications
Product: gwenview
Version: 23.04.0
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: normal
Priority: NOR
Component: general
Assignee: gwenview-bugs-n...@kde.org
Reporter: adam.m.fontenot+...@gmail.com
Target Milestone: ---
SUMMARY
I was under the impression until I happened to check the settings just now that
Gwenview didn't support color corrections (mapping the color profile of an
image into the color profile of the screen). It apparently does, but (a)
applying color corrections should probably be the default behavior (as in
digikam, eog, etc), and (b) the message under the setting is very confusing.
Go to Settings > Configure > Advanced. You'll find the setting "Color profile":
"Apply only the profile embedded in the image file". Some text under this says
"Assume that system-wide color correction already applies monitor profile."
That's not how color corrections work, at least under X11. colord is capable of
applying white point and gamma correcting curves to the video card gamma table
(VCGT). But after that, the screen is still not color corrected. The ICC
profile contains the display character of the screen *after* applying the VCGT,
but it is then (under X11) up to applications to read that color profile and
render colors appropriately.
Some professional screens *can* be calibrated to a particular target, but in
that case you would not set an ICC profile for the screen in colord, because
there would then be no color corrections to do!
It's also unclear what this setting actually does. *How* is it handling
embedded color profiles? What is the target profile when this setting is
enabled? Does it take e.g. a ProPhoto or AdobeRGB image and then squish it into
an sRGB profile, under the assumption that my screen targets sRGB?
Note 1: even if there were a way to do system-wide color corrections (under
X11), this would be undesirable unless all applications could be made to target
some wide gamut intermediate color space like Rec. 2020 (or maybe P3). If the
system-wide color corrections require applications to be sRGB, you will lose
the ability to show wide gamut colors.
Note 2: None of this applies to Wayland. AFAIK it doesn't even support profiled
color corrections yet, but my understanding is that the protocol for color
corrections that's being worked on would allow windows to have color-tagged
paint areas, which could then be managed correctly by the compositor.
Operating System: Arch Linux
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.105.0
Qt Version: 5.15.9
Kernel Version: 6.2.11-arch1-1 (64-bit)
Graphics Platform: X11
ADDITIONAL INFORMATION
My suggestion would be to invert the meaning of the setting, enable it by
default, and have it read something like:
[x] Enable Color Corrections
Use color profile from colord or automatically detected for your screen to
display corrected colors for images.
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