210914 Philip Webb wrote:

210913 David Haller wrote:

Gwenview uses color-management via media-libs/lcms, feh does not.
See "Rendering intent" and "Color profile" under "Advanced"
in Gwenview's configure dialog. HTH.

That cb relevant, but I've explored further & have some results.

When I crop a JPG image with Fotoxx or Gwenview,
then view it with Gwenview, the colors remain vivid ;
this is true whether I rename the new version in Gwenview or not.

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.

So I can avoid the problem either by cropping only with Fotoxx
or by renaming them whenever I do it with Gwenview
or by converting PNGs to JPGs before cropping them.

I have reconfirmed this.

The bad case does look like a Gwenview bug,
but KDE bugs tend to disappear into the ocean, if reported.

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.

Thanks for the comments. I will try redoing the faded versions,
tho' that will mean getting them from the I/net again.

I managed to do that & now have images which cb seen via Gwenview.

Any further suggestions re causes of the bad case are welcome.

They still are, but it does seem to be a bug.

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========================,,============================================
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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.

--
========================,,============================================
SUPPORT ___________//___, Philip Webb
ELECTRIC /] [] [] [] [] []| Cities Centre, University of Toronto
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On Sun, 19 Sep 2021 00:01:51 -0400, Philip Webb wrote:

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.

5.15.2 is already in testing, which explains why I was unable to
reproduce this in the way it hit you, but there was still one washed out
image I saw.


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Neil Bothwick

667 - The FAX number of the beast

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210919 Neil Bothwick wrote:

On Sun, 19 Sep 2021 00:01:51 -0400, Philip Webb wrote:

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

5.15.2 is already in testing, which explains why I was unable
to reproduce this in the way it hit you,
but there was still one washed out image I saw.

I'm using Qt 5.15.2-r3 , which is stable, but -r10 is still testing.
Probably, the correct version wb part of 5.15.3 or 5.16.1 or similar.

Meanwhile, the advice has to be don't manipulate PNGs using Gwenview :
convert them to JPG first.

--
========================,,============================================
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ELECTRIC /] [] [] [] [] []| Cities Centre, University of Toronto
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Am Sun, Sep 19, 2021 at 05:37:20AM -0400 schrieb Philip Webb:

Meanwhile, the advice has to be don't manipulate PNGs using Gwenview : convert them to JPG first.

Rather, manipulate them with something other than gwenview, which is always better than to use JPG due to compression artifacts (even on very high
quality settings).

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