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

Maik Qualmann metzpinguin at
Wed Nov 15 20:48:50 GMT 2017

For the preview to have clean transitions, the option "Preview image is 
converted to 8 bits for a faster viewing" must be disabled.
Can you provide a image to test the color management?


Am Mittwoch, 15. November 2017, 21:36:38 CET schrieb Elle Stone:
> On 11/15/2017 03:16 PM, Andrey Goreev wrote:
> > Try to play with settings in the following tabs:
> > 
> > Settings - Configure digiKam - Image - RAW Behavior
> > Settings - Configure digiKam - Views - Preview
> I set Views/Preview to "Preview shows the full image", and Views/Preview
> Raw Images to "Raw data in half size". Though right now I'm not actually
> looking at raw files, but rather at tiffs and pngs.
> Under Image Editor - RAW Behavior, that's set to "Always open the Raw
> Import Tool to customize settings", but again right now I'm not looking
> at raw files.
> Right now the issue is viewing linear gamma tiffs and pngs:
> The previews are color-managed but have crushed shadow tonality, and the
> smaller the displayed image, the worse the shadow tonality.
> The thumbnails do not look color-managed - instead have a slight magenta
> color cast. The posterized shadows are explained by the fact that the
> thumbnails are 8-bit images.
> > On Wednesday, November 15, 2017 1:08:59 PM MST, Elle Stone wrote:
> >> On 11/15/2017 02:08 PM, Maik Qualmann wrote:
> >>> The thumbnails are color managed. But the color depth of the
> >>> thumbnails is
> >>> only 8 bit, that's probably the cause.
> >> 
> >> Hmm, no, on my monitor, if color management isn't being used, the
> >> image has a slight magenta color cast. All the digiKam thumbnails have
> >> a slight magenta color cast that for example changes the color of blue
> >> skies to make them slightly more purple, and also gives grayscale
> >> images a slight magenta color cast. This is completely separate from
> >> and independent of the crushed/posterized shadows in the thumbnails.
> >> The previews don't have the magenta color cast, but the thumbnails do.
> >> 
> >> But yes, the fact that the thumbnails are 8-bits accounts for the
> >> crushed/posterized shadows for the thumbnails, but hopefully not also
> >> for the previews. Are the previews 8-bits also? Because the tonality
> >> in the previews doesn't have the type of posterized shadows I'd expect
> >> from a linear gamma 8-bit image. Rather the shadows are crushed with
> >> fairly abrupt transitions but not completely posterized tonal shifts.
> >> 
> >> Now that you've explained why the shadows are posterized for the
> >> thumbnails, I should have realized that was the issue - I suspect
> >> thumbnails are only 8-bits fairly universally. But magenta color cast
> >> for the thumbnails is another issue altogether.
> >> 
> >> If you are saying the thumbnails *should* be color-managed (and the
> >> settings would indicate that yes, they should be), how do I
> >> troubleshoot why they are showing the typical (for my monitor, no
> >> doubt not for all monitors) magenta color cast that results when I
> >> view images in non-color-managed applications?

More information about the Digikam-users mailing list