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  • Can No Longer Tolerate iMac After COVID

Hi everyone,

Long-time lurker (and sufferer) here. I’ve read tons of threads, but I’m hoping some of you might be able to at least point me in the right direction.

I got COVID in 2022 and quickly developed several health problems, especially neurological. In hindsight I’ve had issues with Apple screens since the 2017-2019 models of MacBook Pro and iMac Pro, but always wrote it off as a blue light thing or using the computer too much. But I do recall in 2018 when I picked up an iPhone X and iMac Pro just how harsh and uncomfortable they were to use.

Flash forward to July 2022 when I got COVID and I’ve basically been dealing with health issues ever since: POTS and dysautonomia, myoclonic spasms, post-exertional malaise, and likely a connective tissue autoimmune disease. One of my first post-COVID symptoms was my left eye would begin to shut when exposed to certain screens and lights - sort of like when you see a really bright light like police lights and your eyes instinctively try to close. At the time I was using an iPhone 13 Pro, an iMac 21.5-in 2019, and a 14-in MacBook Pro M1 with no issues. Eventually I downgraded to an iPhone 13 which I still use comfortably to this day, albeit on iOS 15.

Over the years I’ve gone to stores to try out different computers - both Apple and Windows. It’s almost like a depressing party trick, but when exposed to screens with high amounts of PWM or dithering my eye will begin to shut. This goes for any kind of screen and certain lights that flicker. It’s a quick way of telling whether a screen is not going to work. I also get a lot of the symptoms you all have described here.

For whatever reason, I can tolerate my iPhone 13 on iOS 15 with no problems. I’ve tried other phones - the same iPhone 13 but on newer OS’s and I get symptoms. I’ve also tried the phones in all the same cases to make sure it’s not placebo, and sure enough I can tell which phone is mine and which isn’t. A family member also had a iPhone 13 on iOS 15 I could use. Once they updated it got more uncomfortable.

Which brings me to my reason for posting. I’ve used an iMac 21.5 intel 2019 on MacOS 10.13. I work in music production so we usually use Macs and I spend a ton of time in front of these screens. I started to develop issues with this computer a few months after my 2022 COVID infection, which is what brought me to this forum. I ended up downloading SwitchResX and the “millions of colors” option ameliorated symptoms enough that I could work on it from Oct 2023-June 2024 with not many problems.

I got COVID again in July 2024 and my health went even more downhill, being in and out of the hospital. As a result I’ve been to ill to work until this week. I just turned on my iMac and it is completely unusable even with SwitchResX. I have an old MacBook Pro 15-in 2015 that I turned on just to test and have no problems at all using it. Interestingly my iPhone 13 I’ve been using all throughout my illness (still on iOS 15 lol) is completely fine. But the iMac I haven’t used for 9 months is not. As it was a lot of my production programs were starting to drop support in favor of the Apple Silicon line. The 2015 MBP is unfortunately too old to be able to support any or the programs and hardware I use (no TB3) otherwise I would use that.

It’s peculiar because the iPhone 13 clearly has PWM yet it’s fine. Something that made me wonder is when I had my eye exam a few months ago, the ophthalmologist said I had a very slight astigmatism. She tried a few lenses just to see what a correction would be like, and all of them - even ones that made it better - caused the same symptoms to appear. I brought up the fact that I understand that the brain compensates with a astigmatism, and it seems post-COVID my brain and nervous system can’t handle certain visual changes. It makes me wonder if because I’ve used my iPhone 13 consistently all these years that I’ve acclimated to the negative aspects. Or maybe I just got lucky with this panel, which is probably more likely given I’m fine with the MBP screen.

So I’m stumped. I need to be able to work but I have tried Stillcolor in store at BestBuy and it doesn’t seem to help on any of the models. It seems like some folks get lucky with certain panels and that’s that. I have no idea what models to even begin looking at. I don’t know if the Radeon 560 graphics card is the problem with my 2019 iMac, but there doesn’t seem to be any way to disable it as it is internal.

Hey,

well it seems it's some 'common' sensitivity to dithering or PWM, if you had it even in 2017 or so. Perhaps try some older LCD devices to see it's not sensitivity to motion or such.

I don't know alot about monitors and so on, but as a starting point, perhaps look into external monitors or some kind.

That would be my strategy anyway. The PWM is removed anyway with an external monitor (I think those iMacs have LCD anyway). And then the temporal dithering…

Besides Stillcolor, did you try out the sRGB color profile on the Mac? (I'm sure there are (better) threads here about it)

That's what comes to my mind anyway : )

    sdkjbfakgljbafkjb

    I did try the sRGB color profile - it actually made it worse, strangely. The MacBook Pro 2015 seems tolerable, so I think you’re right. I’m not sure whether the iMac 21.5in 2019 display has PWM. I thought switching to “millions of colors” would disable dithering with SwitchResX on iMacs, and while I can look at the screen for a few seconds as opposed to not at all when it is not enabled, it doesn’t seem to help. Unfortunately Apple removed the ability to connect these iMacs to an external monitor, so I have no way to test if another display would resolve it.

    It’s bewildering to me that I can tolerate my iPhone 13 which does have PWM. Perhaps I’m just used to the frequency and waveform of this particular display. I tried the M2-M4 MacBook Airs in store and it didn’t agree with me. I remember tolerating a MacBook Pro 14in M1 in 2022 that I later sold. I wonder if it’s about finding something that mimics my phone as opposed to just trying to find a flicker free display. But it’s impossible to test these computers before buying them. I’ve looked at Windows computers in Best Buy as well and they’re even worse than the Macs for me. I’m stumped!

      "This model (iMac 21.5 2019) has a 21.5" 4096x2304 LED-backlit 16:9 widescreen IPS DCI-P3 "Retina 4K" display"

      Well DCI-P3 (color space) and billions of colors, there you go. So certainly lots of dithering (not sure what of this is new to you). Not sure if the backlight has PWM but I'm sure there's some info out there

      Well perhaps if you tolerated the MBP 14 M1 you could get that again?. Perhaps with returns (some on ebay have that) because of the panel lottery. But yeah if it's "just so-so" works it's a bit annoying

      Btw "font smoothing" is another option to disable in settings; because it also uses dithering in newer Macs

      Clokwork

      I will describe two cases: temporal dithering at the GPU level and at the monitor level.

      To begin with, I will provide a general concept of temporal dithering.

      Temporal dithering is a technology used to improve color representation on a screen. If a device (such as a monitor or graphics card) cannot accurately display a specific color due to limitations, it rapidly alternates between neighboring shades, creating the illusion of the desired color. This process happens so quickly that the human eye perceives a blended color rather than individual flickers.

      Temporal dithering at the GPU level

      The GPU processes frames before sending them to the monitor. The temporal dithering algorithm, which is typically implemented at the GPU level in this case, makes changes to the frames that will be displayed on the monitor. Therefore, the maximum frequency of temporal dithering cannot exceed the current frame rate of the monitor.

      What about the minimum frequency? This is a bit more complex. Temporal dithering is applied only to those areas of the frames where additional color simulation is required. If the frames already matches the desired color palette, the algorithm may be completely disabled. In other words, the minimum frequency of temporal dithering depends on whether the algorithm needs to be applied and can be zero if temporal dithering is not used.

      Temporal dithering at the monitor level

      If we talk about FRC, it is one of the forms of temporal dithering used in displays. Everything I described above also applies to FRC. The only difference is that it operates not at the GPU level, but at the monitor level.

          Thanks. Yeah I think the dithering too complex to somehow "remove" away per framerate. Who knows at what rates it dithers and what part of the picture, and so on

          WhisperingWind

          Pardon my ignorance, so does a program like Stillcolor essentially override dithering at the system level so it never turns on? Or can programs themselves still trigger it? I wonder why some people don’t have luck with Stillcolor. Is this an indication that you can’t actually at this point disable dither permanently on MacOS?

          Or is this an indication that PWM and dithering are not the sole factors for discomfort, and if so, that complicates things. Using my iMac as an example; I have SwitchResX running with “millions of colors” selected which is supposed to disable dithering. I do indeed notice a difference when it is not running, but it is not enough to resolve my issues with this screen. I don’t believe the screen has PWM. So all that leaves is the Radeon Pro 560X graphics card. I wonder if SwitchResX is unable to fully disable dithering because this Mac is not using intel integrated graphics. This is just a guess as I don’t know the inner workings of either. Or perhaps I’ve just become more sensitive to screens since I haven’t used a computer in 9 months. I recall people having problems with iMacs in the late 2010s, so perhaps I’m missing something.

              WhisperingWind Thanks for that. With some preliminary readings that I am getting from the flicker meter that I purchased, I am starting to notice that one part of the equation affecting me is the amplitude of the dips/peaks when the flicker happens. This is very apparent with many OLED panels.

              I'm thinking that in combination with FRC is what's troubling me. I just need to prove it.

              @sdkjbfakgljbafkjb I wish I knew what algorithms were being used. I wonder if the flickering is only between two shades or is it more?

                AshX

                does a program like Stillcolor essentially override dithering at the system level so it never turns on?

                StillColor and BetterDisplay disable temporal dithering at the GPU level. There is no other source of temporal dithering in macOS.

                Some internal displays of MacBooks and iMacs may have their own temporal dithering (FRC), but there’s nothing we can do about it. I always use an external monitor with my MBP M1, as the internal display causes discomfort even without PWM, but because of dithering.

                Or can programs themselves still trigger it?

                This is unlikely because triggering temporal dithering requires access to the frame buffer. Such access is not available to regular applications, only to system components. As mentioned above, temporal dithering is primarily a GPU prerogative.

                But in theory, the case I will describe below is possible; this description should be taken with a grain of salt, as it is just an assumption.

                In OpenGL, there is an option to enable spatial dithering. However, its interpretation depends on the graphics card driver. For example, in Linux, it is completely ignored for Intel-based graphics cards. I am not sure how it works in macOS. If some app uses OpenGL instead of Metal for hardware acceleration, then theoretically, spatial dithering could occur in the area where hardware-accelerated rendering is running. However, it is highly unlikely (almost impossible) that this would involve temporal dithering.

                I wonder why some people don’t have luck with Stillcolor. Is this an indication that you can’t actually at this point disable dither permanently on MacOS?

                A significant role here may be played by the monitor, the sensitivity level of the eyes, various image post-processing by different graphics cards, and different versions of macOS. It's difficult for me to say anything until I get my hands on such a device and can study it.

                I have SwitchResX running with “millions of colors” selected which is supposed to disable dithering

                I don't think it can reliably disable dithering, as there are dithering algorithms that don't improve color reproduction but smooth out gradients. They will still work on an 8-bit monitor when an 8-bit signal is sent to it from the graphics card.

                Some MacBook and iMac displays may have an extended color gamut. For this, KSF phosphor might be used (KSF phosphor is highly efficient at converting blue or near-UV light from LEDs into red light), which by itself puts a lot of strain on my eyes even without PWM and dithering. Such displays always appear slightly reddish to me.

                Such a display was in my old iMac 2019 (Radeon Pro 560X, 5K). I couldn't do anything with it in macOS, Linux, or Windows. I sold it.

                    WhisperingWind This is unlikely because triggering temporal dithering requires access to the frame buffer. Such access is not available to regular applications, only to system components. As mentioned above, temporal dithering is primarily a GPU prerogative.

                    I mean, not neccesarily, for all I know the WindowServer could be telling the GPU various things if an app requests HDR/EDR mode, or if an app requests it should be rendered with a specific color profile

                    i.e. how some video editing apps and some non-native GUI toolkits are configured to map #FF0000 to full P3 red even though the surrounding apps only understand #FF0000 to be the less saturated sRGB red instead, implying each app has a different idea of what "256 shades" means.

                    So possibly, when both apps are running, the graphics card (or the WindowServer itself, independent of the graphics card) decides to use dithering to ensure each app can still display what "looks like" 256 distinct shades even when both apps display simultaneously.

                    In addition, I've found that some apps like Blender cause the entire desktop of LCD Apple Silicon MacBooks like M1 Air to fade to a slightly different calibration for the entire duration the app window is visible in any way (even if it's dragged all the way to a corner), and then fade back to "normal" when the app is completely minimized. This is especially noticeable with Stillcolor as the banding shift is really obvious on the desktop wallpaper. It seems to be connected to the HDR/EDR mode being activated.

                    This may also invoke different graphics card functionality, without the app specifically requesting dithering etc. itself.

                    Finally, color profiles on Apple Silicon Macs seem to be running at a higher bit depth than the desktop itself, even with Stillcolor. If you put a transparent black overlay over the whole screen using a standard app window, and slowly increase the opacity (e.g. BetterDisplay Overlay Dimming mode) — you will notice more prominent banding shifts than if you dim the internal display in the same manner using a color profile (e.g. BetterDisplay Color Profile Adjustments mode).

                    This makes me think color profiles are always running at 10-bit and the desktop at 8-bit?

                        WhisperingWind

                        WhisperingWind are dithering algorithms that don't improve color reproduction but smooth out gradients. They will still work on an 8-bit monitor when an 8-bit signal is sent to it from the graphics card.

                        Some MacBook and iMac displays may have an extended color gamut. For this, KSF phosphor might be used (KSF phosphor is highly efficient at converting blue or near-UV light from LEDs into red light), which by itself puts a lot of strain on my eyes even without PWM and dithering. Such displays always appear slightly reddish to me.

                        Such a display was in my old iMac 2019 (Radeon Pro 560X, 5K). I couldn't do anything with it in macOS, Linux, or Windows. I sold it.

                        Interesting. My iMac has the same specs except it’s 4K. I also tested a family member’s MacBook Pro 15” 2015 and while it’s moderately better than the iMac, it’s still uncomfortable. As soon as I look at my iPhone 13 I’m relaxed and it’s comfortable. I couldn’t detect PWM on the iMac or the MBP so your other possibilities make sense.

                        I also wonder if my brain has adapted to the iPhone 13’s PWM and screen, and maybe it just can’t tolerate different patterns in dithering or PWM. It could be post-COVID weirdness and maybe for my personal situation, I have to try to find a screen as similar to what I’m used to for now. Or maybe it’s smaller size is more tolerable. Truly bizarre. I wish there was a neutral device to test against, but I can’t say I’ve found any sort of laptop or monitor in a computer store that is comfortable when I’ve gone to check them out. If I knew what screen manufacturer my iPhone was using, that may be a clue.

                        I had a MacBook Pro M1 at the same time as this phone was purchased that was comfortable (May 2022) so I wonder if I may have to try picking up a used one and revert it to the MacOS at the time. Can’t say I’m holding my breath for MacBook Air M4’s coming out next week, but I’ll take a look at them, too.

                            dev