Re: [gentoo-user] faded images with Gwenview : solved

[Philip Webb]

210917 Philip Webb wrote:
> It's only when I crop a PNG image in Gwenview
> & save it in place (ie with the same name), that the colors are faded
> & that's only when viewed with Gwenview, not eg with Feh.
> The bad case does look like a Gwenview bug,
> & in fact, as I had forgotten (grimace), I did submit a bug previously :
> KDE Bug 420357 back in April 2020, to which no-one has yet responded.
> I've added a comment & we'll see if there's any response this time.

Tibor Nagy of KDE Bugzilla has replied very promptly :

  My guess this happens due to botched gamma handling.
  Washed out images are a prime symptom of that kind of bugs.
  Seems like when a PNG gAMA chunk is present,
  Gwenview applies the gamma transform in the opposite direction it should,
  thus the washed out images.  Seems to be Qt bug, already fixed in 5.15.x :
  https://github.com/qt/qtbase/commit/de2c3ccd49cb89e0c6912da3b03705a36ef03946

As you can see from the link above, some coder forgot to invert a value,
using 'gamma' when it sb '1/gamma'.

The patch is dated 'June 11', so it make take awhile yet to reach Gentoo.

Meanwhile, I have  2  workarounds which are in fact improvements for me.
I have amended the Imagemagick 'import' command I use for screenshots
to produce them as JPGs, which cb safely cropped already via Gwenview.
Alternatively, Firefox will make screenshots via R-click on its window
& the area to be grabbed cb marked on the screen, so already cropped.

From the beginning, I thought it was a programming bug,
as it appeared suddenly after a KDE update in spring 2020.

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