Possible ColorSync discontinuity bug introduced in OS 10.14.6 with display "r/g/bTRC" tags?
Possible ColorSync discontinuity bug introduced in OS 10.14.6 with display "r/g/bTRC" tags?
- Subject: Possible ColorSync discontinuity bug introduced in OS 10.14.6 with display "r/g/bTRC" tags?
- From: William Hollingworth via colorsync-users <email@hidden>
- Date: Mon, 12 Aug 2019 22:21:05 -0500
I'm starting to get reports of a severe banding problem that seems to be
related to the recent macOS 10.14.6 update which includes some (unknown)
changes to ColorSync.
I've duplicated this and what I'm seeing is that when a display profile
has the r/g/bTRC "curv" tag encoded as a "simple gamma" value rather
than an array of points (typically 256), then there can be a big
luminance discontinuity between level RGB=0 and RGB=1 - depending on the
gamma value. I'm using a simple grayscale test image in the Preview app.
The canned "Adobe RGB (1998)" profile encodes the 2.2 gamma as a "simple
gamma" and this issue is evident when selected as a display profile.
However the "Generic RGB Profile" encodes gamma 1.8 this way also but
the discontinuity isn't very obvious. So higher gamma values make this
more obvious.
Re-encoding the profile's response curve as an array of points instead
of a single "simple gamma" value seems to avoid the issue. However it
was perfectly OK in previous macOS versions.
Is anyone else experiencing this issue? It looks like X-Rite encode
their TRCs as an array of points regardless, so probably most people
won't see it.
Anyone at Apple aware of this?
Thanks
Will Hollingworth
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