Bug 511047

Summary:	The "background contrast" added in the blur effect does not, in fact, help with contrast
Product:	[Plasma] kwin	Reporter:	Tech-Tac <im.tech.tac>
Component:	effects-various	Assignee:	KWin default assignee <kwin-bugs-null>
Status:	RESOLVED DUPLICATE
Severity:	normal	CC:	nate, pavel23dob, putr4.s
Priority:	NOR
Version First Reported In:	6.5.0
Target Milestone:	---
Platform:	Other
OS:	Linux
See Also:	https://bugs.kde.org/show_bug.cgi?id=510818
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description Tech-Tac 2025-10-24 20:23:33 UTC

It may even give negative results, specifically in dark mode.

"background contrast" was previously a separate toggleable effect but now it's been merged into the blur effect.
As far as I can tell it mainly just lightens the background behind blurred windows, as to make the assumingly darker text contrast more. This however does the complete opposite when the text is light.

I suggest to make it toggleable once more. Or, even better, deprecate it completely, as in my opinion, I think it is already up the application to decide how contrasting it wants its background to be, given that it controls the opacity of the background color, which should already provide enough contrast to the content.

For example an app can have a dark translucent background with light text (E.g. terminal apps), this can be and often is in disregard to the global color theme. If the application is configured to add blur to the background, no additional tinting is required as the translucent background is added to the blur behind darkens it. While the background contrast filter would attempt to lighten it.

Comment 1 Tech-Tac 2025-10-24 20:38:32 UTC

Forgot to mention it also doesn't play nice with KWin software brightness, it's always too bright.

Comment 2 Prajna Sariputra 2025-10-26 07:17:51 UTC

Bug 510818 is about the blur effect being brighter than it used to be (and has a lot of comments and duplicates already), so perhaps this bug should be marked as duplicate of that one? A developer did respond there noting that the cause of the change is the blur and background contrast plugins being merged in 6.5.

Comment 3 Tech-Tac 2025-10-26 14:32:35 UTC

That indeed appears to be about the same issue.
But the problem isn't new with 6.5, the background contrast filter was always ugly but it was optional so no one complained. I'm more asking to make it more adaptive/flexible (at the very least optional again).
The contrast effect is nice really, but it doesn't work in dark mode due to how it's implemented.

Comment 4 Pavel Dobiáš 2025-10-26 21:11:01 UTC

I agree, for me using a custom dark theme also yields WORSE results than before the merge, especially in menus and such. The overall background color now becomes lighter which certainly isn't a contrast improvement with white text.

Comment 5 Nate Graham 2025-10-29 21:25:39 UTC

The background contrast effect was always an implementation detail exposed to the user, which is why it was collapsed into the Blur effect in Plasma 6.5.

It's definitely the case that the end result is for the blurred area to be too light. That's tracked in Bug 510818.

*** This bug has been marked as a duplicate of bug 510818 ***