[konsole] [Bug 510947] New: Transparent background blur color reproduction is wildly off

[Oded Arbel]

https://bugs.kde.org/show_bug.cgi?id=510947

            Bug ID: 510947
           Summary: Transparent background blur color reproduction is
                    wildly off
    Classification: Applications
           Product: konsole
      Version First 25.08.2
       Reported In:
          Platform: Other
                OS: Linux
            Status: REPORTED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: konsole-devel at kde.org
          Reporter: oded at geek.co.il
  Target Milestone: ---

Created attachment 186035
  --> https://bugs.kde.org/attachment.cgi?id=186035&action=edit
screenshot showing the effect with 30% transparency, compared to the actual
wallpaper that was used (image was scaled down)

SUMMARY
When using "transparent background" in the Konsole appearance, with "blur
background" enabled, the effect massively mutes almost all colors but over
saturates red and similar colors. See attachments.

I've noticed this effect after the update to 6.5 - so I think this is the
likely cause as this effect is really jarring, so much that I had to turn off
blur to continue working, that I think it is new to Plasma 6.5

STEPS TO REPRODUCE
1.  In Konsole, click Settings -> Edit current profile -> Appearance -> Edit
2. Check "Blur background", and set "Background transparency to 100%"
3. Click Apply

OBSERVED RESULT
Any red in the background is brightened while any non-red is muted (the
background usually just the wallpaper, but this also affects whatever window is
behind Konsole).

EXPECTED RESULT
There shouldn't be massive change in colors just from blurring.

SOFTWARE/OS VERSIONS
Operating System: KDE neon User Edition
KDE Plasma Version: 6.5.0
KDE Frameworks Version: 6.19.0
Qt Version: 6.9.2
Kernel Version: 6.14.8-061408-generic (64-bit)
Graphics Platform: Wayland
Processors: 20 × 12th Gen Intel® Core™ i7-12700H
Memory: 32 GiB of RAM (31.0 GiB usable)
Graphics Processor: Intel® Iris® Xe Graphics

ADDITIONAL INFORMATION
A. See attached screenshots
B. I ran the color picker on the konsole rendering, with blur on and off, and
here are some numbers:

Redish area: unblurred HSV (RGB) = 6, 241, 236 (236, 38, 13) ; blurred HSV
(RGB) = 13, 215, 255 (255, 87, 40)
Light gray area: unblurred HSV (RGB) = 26, 25, 181 (181, 171, 163); blurred HSV
(RGB) = 20, 51, 175 (175, 152, 140)

We can see that there's a slight shift towards red, in general, but also that
reds are brightened by quite a lot (~7%, but its clamped so it could be more)
while gray areas are actually darkened a bit (-3% in this example, which from
testing multiple gray light levels - appears representative).

This effect is very jarring.

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