Turns out that macOS uses temporal dithering to achieve additional color depth when connected to external displays and most of the Dell monitors are “sensitive” to level 16 of gray (which actually fluctuates between levels 15 and 17) as it happens at the threshold of the monitor’s Image Compensation Algorithm (ICA) causing it to turn on/off rapidly.
So a feature designed to prevent image retention and uneven brightness ends up causing the flickering and retention of image (ghosting) as confirmed by Dell after years of users complaining and trying every possible workaround.
Here is an approximate visualization of that range of gray:
The root of the problem is the advertised “1.07 billion colors” (10-bit color depth) even though the panel only supports 8-bit color range which it reports to macOS over EDID, which then triggers the YCbCr dithering on macOS GPU output, which in turn triggers the monitor’s Image Compensation Algorithm (ICA) threshold bug.
It might be possible to resolve this with a firmware update for the monitor but none of the recent updates (such as M3F102) have fixed the issue for me.
How to Fix it?
There are two ways to fix this — enforce RGB mode for the monitor video signal input (instead of the default YCbCr) or disable the temporal dithering on the macOS output.
1. Set RGB Input Color Format in Monitor Settings
Use the button at the back to open the monitor settings and set the “Input Color Format” under “Color” to RGB (instead of YCbCr):
Unplug and reconnect the USB-C cable after making the change to enforce a fresh EDID handshake. Consider resetting all settings to factory defaults before making the change.
This will make macOS send a full 10-bit RGB color data on the output instead of the capped 8-bit stream with temporal dithering.
2. Disable macOS Temporal Dithering
Use the Stillcolor app to disable the macOS temporal dithering if you want to keep using the YCbCr mode for some reason. Importantly, the app will not affect the built-in display color rendering (since it supports the full color range) so it can be left enabled at all times.
Impacted Dell Monitor Models
This fix is needed for the following Dell monitor models (I’m using U2723QE from Amazon):
- G series: G3223D
- C series: C1422H, C2422HE, C2722DE, C3422WE
- S series: S2422HZ, S2722DZ, S2722QC, S2723HC, S3423DWC
- P series: P2421DC, P2721Q, P3221D, P2422HE, P2722HE, P3222QE, P2423DE, P2723DE, P2723QE, P3223DE, P3223QE, P1424H, P2424HEB, P2724DEB, P3424WE, P5524QT, P6524QT, P8624QT
- U series: U2421E, U2421HE, U2721DE, U3421WE, U3821DW, U4021QW, U2722D, U2722DE, U2722DX, U2723QE, U2723QX, U3023E, U3223QE, U3223QZ, U3423WE, U4323QE, U2424H, U2424HE, U2724D, U2724DE, U3224KB, U3824DW, U4924DW
Best Dell Monitor for Mac
Having a monitor that can also charge your computer and serve as a USB hub over a single USB-C cable is really convenient. If buying today, I would get the 27-inch Dell U2725QE which is also Amazon best-seller and an updated model of what I have currently:
- same 3840×2160 resolution
- higher refresh rate at 120Hz (previously 60Hz)
- higher contrast of 3000:1 (previously 2000:1)
- higher USB-PD output power of 140W (previously 90W)
Using the available downstream USB-C port you can also power a charging station/stand for your iPhone, Apple Watch and AirPods such as this Belkin 25W 3-in-1 charger (foldable and great for travel). Note that there are a lot of cheaper options available but all of them have slower charging speeds (7W vs. 15W or 25W) and most are not Apple MFi-certified which will cause your phone to show a warning message every time you put it down for charging.