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

Elle Stone ellestone at
Wed Nov 15 20:36:38 GMT 2017

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?

Color management and free/libre photography

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