[argyllcms] Re: Black crush on macOS - some advise?
- From: Florian Höch <lists+argyllcms@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Thu, 14 Mar 2019 14:20:31 +0100
Am 13.03.2019 um 15:03 schrieb aufonddulac@xxxxxxx:
There is a black crush bug reported that means we must use special
profile only: single curve + Matrix with black point compensation.
Florian Hoch tells us this is a fix.
Apple applications like Preview and QuickLook are affected by this macOS
bug. Other applications like ColorSync Utility (which can also be used
to view images), as well as 3rd party applications that implement their
own color management (like Adobe Creative Suite), are not affected.
The effect of the bug is black crush and posterization in dark areas
when cLUT type profiles, or matrix profiles with individual shaper
curves, or calibration (vcgt) with input zero not mapping to output
zero, or profiles where black is not scaled to zero, e.g. no baked-in
black point compensation, are used (or any combination thereof).
This bug has been around since at least Mac OS X Mavericks, with no fix
from Apple in sight even after all these years. The profiling software
used does not matter, only the criteria listed above.
The workaround is as described, create a single shaper curve (or single
gamma) and matrix profile, with baked-in black point compensation, and
calibration that maps input zero to output zero, or do not use any of
the affected applications.
But some of us are seeing and reporting that even this profile is not
working now, and Florian Hoch is not able to offer a new bug fix suggestion.
That's not what I have found - in all the instances where people thought
the workaround didn't work and had me look into it, they did create a
type of profile or used a non-default combination of settings that is
affected by the macOS bug.
Creating a type of profile in DisplayCAL that will work with Preview and
QuickLook is easy: Use the defaults (settings -> select "Default" if you
have changed anything). Note that these defaults differ from the ones
used under Windows.
What you _cannot_ do if you wish to use buggy Apple software like
Preview or QuickLook (not a complete list, just common pitfalls):
- Use calibration black point correction (creates a calibration that
doesn't necessarily map input zero to output zero)
- Use any profile type other than single curve + matrix or single gamma
- Turn off baked-in black point compensation
- Use the "Photo" preset (creates a calibration that doesn't necessarily
map input zero to output zero)
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