Thumbnails not color-managed + severely distorted shadow tonality for thumbs, previews

Elle Stone ellestone at
Thu Nov 16 17:07:16 GMT 2017

On 11/16/2017 08:00 AM, Elle Stone wrote:
> Also in the version of digiKam that I installed from git, the thumbnails 
> are color-managed. Of course the shadows are still posterized from being 
> linear gamma 8-bit thumbnails, but that is to be expected.
> There is one more variable (setting or not setting the system monitor 
> profile) that I want to double-check, that might affect the display of 
> the thumbnails: When using the version of digiKam from Gentoo Portage, I 
> had set the system monitor profile upon starting X. But this morning, 
> testing my modified "git" version of digiKam, I also unset the system 
> monitor profile and set the digiKam monitor profile from disk, so that 
> the digiKam color management settings and GIMP/Krita color management 
> settings would match as closely as possible. I can't imagine how this 
> would affect display of thumbnails but not the previews, but maybe it 
> somehow does.

Hmm, experimenting, I can deliberately produce not-color-managed 
thumbnails by setting/unsetting the system monitor profile while digiKam 
is running, and then changing the digiKam color management monitor 
profile setting. Restarting digiKam makes the thumbnails be color-managed.

So I'm guessing that there was something in how my system monitor 
profile was being set when I was running digikam 5.7.0 from Gentoo 
Portage, that somehow resulted in the thumbnails not being 
color-managed. So my apologies! for saying the thumbnails aren't 
color-managed. They weren't on my system, but I think this was strictly 
a function of when/how the system monitor profile was being set.

As already noted, the problem with the preview image shadow tonality is 
completely eliminated by changing 
"core/libs/dimg/filters/icc/icctransform.cpp" line 58 from 
"transformFlags = 0;" to "transformFlags = cmsFLAGS_NOOPTIMIZE;" before 
compiling and installing digiKam.


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