Hi William, I hope you're keeping well So, am I reading this right please? An LUT profile would be OK and a "MATRIX" not, in this setting. Is an LUT what you are calling "encoded as - - an array of points" I guess a 16 bit LUT may be OK? I am just thinking about basICColor display. Are you able to communicate with Apple about it - now John Zimmerer's gone I've no idea who'd be in charge of Colorsync? I saw a post from Steve about his NEC on the Adobe forum [compressed blacks] and I think he may have been chatting with you about the issue? https://forums.adobe.com/thread/2645572?prevContainerType=14&prevContainerID... Best Regards, Neil Barstow Imaging & Colour Management Specialist http://www.colourmanagement.net proud to be part of: http://www.colormanagementgroup.com www.colormanagement.com On Tue, Aug 13, 2019 at 4:21 AM William Hollingworth via colorsync-users < colorsync-users@lists.apple.com> wrote:
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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