@aiaf Tested and WORKING for an external monitor on M1 Max MacBook Pro with Sonoma 14.2.1. This is one of the best releases this community has seen in a long time, I am eternally grateful.
BTW I'll definitely get in touch with you soon — although I'm not experienced with reverse engineering, I've learned quite a lot of interesting info on how macOS does dithering and color management recently, and would love to provide any info I know that would help in creating an Intel version. Is it best to DM you here or on your Twitter?
My experience:
I have an ancient CCFL monitor with DVI in (Samsung SyncMaster 906BW) which I connect to the M1 Mac through a USBC»HDMI cable to an HDMI»DVI adapter.
(Fun fact: DVI displays provide RGB EDID to Macs by default, so the whole "force RGB instead of YbCbCr" ordeal infamous with HDMI monitors isn't actually necessary here!)
I'm pretty sure this monitor is native 6-bit with no FRC, since even when connecting to a M1 Mac with default "10-bit" settings, banding appears. (I was wrong, it's actually the monitor's own FRC pattern conflicting with Apple's dithering pattern, see my newer reply)
However, what's really funny is because of this limited hardware, it makes Apple Silicon temporal dithering EXTREMELY obvious.
Typically, connecting the 906BW to the M1 causes totally noticeable checkerboard patterns on some colors, and other colors will actually visibly flicker to the extent someone who's not sensitive could notice it. These get even more intense while I'm continuously moving my head.
For a while I thought this was either the ancient monitor starting to fail, a bad cable, LCD pixel inversion, or FRC that the monitor itself was producing… until I plugged it into an old Windows PC, and all those issues stopped happening.
For the first time ever, Stillcolor has immediately solved this issue. The moment it's enabled, all of these moving patterns disappear and the M1 finally gets clean external monitor output. Changing gamma and contrast with BetterDisplay finally causes obvious banding shifts, which it wasn't able to before.
So if anyone is dealing with "checkerboard pattern on dark mode backgrounds with external monitor on M1 Mac" — which I've seen some people in generic Apple communities mention before, Stillcolor resolves this issue too!! It is caused by temporal dithering.
And of course, enabling Stillcolor significantly reduces eye strain on the external monitor for me!
(Edit: The monitor still has its own FRC, but I'm definitely less sensitive to it than Apple's dither pattern — after all, I wasn't getting the same level of significant eye strain using this same monitor back when Windows XP was current.
However, I might have been running Windows XP back then in true 6-bit output mode, which I really wish was possible on a modern OS…
However I DO notice the monitor's FRC and find it a bit annoying, and am now trying to seek out a non-FRC monitor so I can use macOS 100% dither-free.)
Here's why it doesn't seem as effective on the internal XDR display though…
Mini-LED XDR MacBook Pros have some aspects of color calibration built into the display itself, that's why the display preferences looks different on these models and tries to push seemingly limited "Reference Modes" over color profiles.
This also means that certain aspects like gamma are processed by the display panel instead of the GPU as Macs usually so.
So on XDR Macs, even though Stillcolor actually does cause some changes in colors on the internal display, it doesn't solve dithering on the laptop screen entirely. Because if gamma is adjusted with BetterDisplay here — unlike with an external monitor, no banding shifts will happen and gradients will remain "just as smooth" (i.e. dithering) at any gamma level. Of course the internal screen has some PWM too.
(I suspect) that there's two layers of dithering on XDR Macs 😱 one at GPU level (which Stillcolor does disable) and one at display panel level (which it can't disable).
Or perhaps, if it's not dithering, this "second layer" is due to individual brightness control of the mini-LEDs (AKA different PWM rates per each area of the display) to achieve different gamma levels without seeming to affect the amount of available colors.
However, LCD Macs like M2 Air, and the low-end "Touch Bar" Pros, use standard color profiles (where only the GPU is involved) instead of this hardware-level color management. This is why people here with MacBook Airs are reporting great results, but MacBook Pro users are more hesitant.
In summary, Stillcolor has the same great effects on external monitors on both Air and Pro, but only will be able to fully improve the laptop display on LCD models like the Air.
(BTW, I'm guessing that forcing external output EDID to RGB mode is probably neccessary for Stillcolor to fully improve an HDMI monitor. This wasn't an issue for me though because my monitor uses DVI.)
Since this app exists now, and based on what I've just written above… I'm honestly about to start considering selling my M1 XDR Pro and swapping it for an M2 Air instead 😄
For now, at least I can finally use my M1 Pro as a desktop!