Bug 506496

Summary:	RGB Full value is not applied
Product:	[Plasma] kwin	Reporter:	David Rubio <david.alejandro.rubio>
Component:	output configuration	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	david.alejandro.rubio, nate, xaver.hugl
Priority:	NOR
Version First Reported In:	6.4.2
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Screen showing YCbCr4:4:4 insteaqd of Full RGB

Description David Rubio 2025-07-02 15:51:04 UTC

SUMMARY
Setting "RGB Range" to "Full" still keeps monitor at YCbCr 4:4:4 which looks *bad*. Both Windows and macOS are able to use RGB Full 8-bit on this monitor. I am unsure what logs I should attach here, so please let me know. Just in case I thought it could be a link speed issue, I tried at 60Hz, and it does YCbCr 4:4:4 10-bit color instead for... some reason. I don't find any way to force it on the command line, nor can I use wayland-xrandr to set it (which does work on Window Managers)

STEPS TO REPRODUCE
1. Set "RGB Range" to Full
2. Nothing changes, screen doesn't even flash.

OBSERVED RESULT
[See attachment]

EXPECTED RESULT
Screen uses RGB Full range.

SOFTWARE/OS VERSIONS
Linux: 6.15.4
KDE Plasma Version: 6.4.2
KDE Frameworks Version: 6.15.0
Qt Version: 6.9.1

ADDITIONAL INFORMATION

Comment 1 David Rubio 2025-07-02 15:52:24 UTC

Created attachment 182868 [details]
Screen showing YCbCr4:4:4 insteaqd of Full RGB

Comment 2 Zamundaaa 2025-08-20 19:25:39 UTC

The RGB range setting does not change the display encoding. It's quite simply not what it's meant to do...

Comment 3 David Rubio 2025-08-20 19:31:03 UTC

I would argue it's a bit misleading then. Still, how would I set my
screen to Full RGB then? KWin is the only compositor where for some
reason it's stuck on 4:4:4.

El mié, 20 ago 2025 a las 15:25, Zamundaaa
(<bugzilla_noreply@kde.org>) escribió:
>
> https://bugs.kde.org/show_bug.cgi?id=506496
>
> Zamundaaa <xaver.hugl@kde.org> changed:
>
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|REPORTED                    |RESOLVED
>          Resolution|---                         |NOT A BUG
>
> --- Comment #2 from Zamundaaa <xaver.hugl@kde.org> ---
> The RGB range setting does not change the display encoding. It's quite simply
> not what it's meant to do...
>
> --
> You are receiving this mail because:
> You reported the bug.
> You are on the CC list for the bug.

Comment 4 Zamundaaa 2025-08-21 12:56:25 UTC

There's no way to do that, it's unfortunately completely up to the driver. No other compositor can do it either.
The only approach I know of is to modify the EDID of the display, to claim that it just doesn't support YCbCr.

FWIW, YCbCr 4:4:4 should look exactly identical to RGB 4:4.4, if it doesn't, something else is wrong. You can report that problem to your graphics vendor.