Bug 512496

Summary:	sRGB Colour Intensity seems to be inverted
Product:	[Plasma] kwin	Reporter:	Wedge009 <wedge009>
Component:	colour-management	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	CONFIRMED ---
Severity:	normal	CC:	nethshanperis, xaver.hugl
Priority:	NOR
Version First Reported In:	6.5.2
Target Milestone:	---
Platform:	Kubuntu
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	AlderLake system StoneyRidge system SyncMaster 204B

Description Wedge009 2025-11-23 03:09:49 UTC

I had a look around and couldn't find anything existing that's related.

I mainly use Kubuntu LTS on my more capable machines (so still on Plasma 5), but for a few machines I'm using Plasma 6 from non-LTS Kubuntu. I recently noticed the 'sRGB colour intensity' slider in the Display Configuration.

I calibrate all my displays, so in each case a colour profile is used. When the 'sRGB colour intensity' slider is set to 100%, it seems noticeable _less_ intense/saturated than when the slider is set to 0%, which seems back-to-front to me.

Selecting 'Prefer colour accuracy' or 'Prefer efficiency' appears to make no difference.

I'm observing this on a variety of systems:
* Intel Alder Lake iGPU with built-in screen.
* AMD Stoney Ridge with Vega iGPU on built-in screen.
* AMD Barts (Radeon HD 6870) desktop GPU on desktop monitor.

I don't think any of these displays are HDR-capable. Is it the case that not many people use colour profiles?

1. Enter Display Configuration settings
2. Use a colour profile
3. Observe sRGB colour intensity/saturation at 0% is greater than at 100%

Linux/KDE Plasma: 
KDE Plasma Version: Currently Plasma 6.5.2 and 6.5.3, but possibly since whenever this slider was introduced.
KDE Frameworks Version: 6.20.0
Qt Version: 6.9.2

Comment 1 Wedge009 2025-11-23 03:15:37 UTC

> Is it the case that not many people use colour profiles?

I tried using the 'built-in' colour profile. On the old desktop monitor I don't notice any difference between 0 and 100% intensity, but on the Alder Lake display, 0% looks slightly more intense than 100%.

Comment 2 Zamundaaa 2025-11-24 13:09:57 UTC

Is the native gamut of your screens perhaps smaller than sRGB? Please attach the ICC profile in question

Comment 3 Wedge009 2025-11-24 21:14:25 UTC

According to my records, the built-in screens registered at about 55% and 75% sRGB coverage/volume. But the desktop monitor, is about 95% sRGB coverage and 105% volume.

Comment 4 Wedge009 2025-11-24 21:14:58 UTC

Created attachment 187131 [details]
AlderLake system

Comment 5 Wedge009 2025-11-24 21:15:13 UTC

Created attachment 187132 [details]
StoneyRidge system

Comment 6 Wedge009 2025-11-24 21:15:32 UTC

Created attachment 187133 [details]
SyncMaster 204B

Comment 7 Zamundaaa 2025-12-05 17:07:25 UTC

Okay, that makes sense then. The slider goes from correct sRGB (0%) to native primaries (100%). That works very intuitively with HDR screens, but not so much with screens that don't cover all of sRGB.

We have two options there I think, one would be to set some minimum gamut that "100%" will always expand to, the other would be to hide and disable the option if the screen doesn't cover all of sRGB. The former will cause some clipping and color shifts if used on such a screen, but it's at least worth experimenting with it.

Comment 8 Wedge009 2025-12-05 21:52:32 UTC

When Kubuntu 26.04 is available and I switch to Plasma 6 across all my machines, I can see what happens on my screens with sRGB > 100% coverage.

For older/inferior screens with sRGB < 100%, I'll keep a watch for any new developments. This isn't high priority, from my perspective, but I appreciate the acknowledgement.

Comment 9 nethshanperis 2025-12-06 05:39:24 UTC

similarly, my vendor srgb profile seems desaturated when i upgraded to 6.5.3. Im not sure about the other profiles however like the dci-p3 one because it looks fine. The srgb profile for some reason is not only desaturated than p3 but also has a weird overly punchy yet dark look especially on bright reds and oranges and the srgb intensity level worsens it. this could be related to that. please let me know if i must attach the profile here or whether to open a new report.

Comment 10 Wedge009 2026-01-03 02:50:40 UTC

I belatedly realised Plasma was using the 'dark mode' version of the wallpaper because I had left it at the defaults. When I forced it to use 'light mode', the sRGB intensity inversion doesn't appear to be so bad.

I don't know why this should make a difference, but I suppose this is all rather subjective anyway.