Dithering/FRC tests on external monitor with MacBook Pro M2 and Intel

madmozg

Hey guys, I decided to test FRC/Dithering when connecting M2 or Intel based macbooks to my external 2K 8bit display with DP and HDMI. I used basic microscope from amazon. I also created a custom grayscale gradient image with a line, to put microscope on exactly the same place for each test.

Devices which I used:

USB-C DisplayPort cable 1.2
High speed HDMI with an apple dongle connection to USB-C
Monitor ASUS VG27AQ (8bit panel) 144hz
Macbook Pro M2 13 TB
Macbook Pro 15 Intel 2018
Carson 100x-250x LED MicroFlip Pocket Microscope MP-250

Youtube: https://youtu.be/LZMWduGGJvk?si=UpL-XtRg5GFHIwrK (youtube of course has a bad compression, so its better to take a look on a video from dropbox, but please like the video to share it on youtube.)

Dropbox: https://www.dropbox.com/scl/fi/n42xpz4oyr78qe7ikytp3/gray_frc_tests.mov?rlkey=njx3nlwaw08bcg3o8tvcfwcnm&dl=0

My conclusion

With HDMI connection it looks like FRC is visible at refresh rates 60/100/120, but not at 144. With Display Port its still bad at 60 and 100 hertz, but 120 looks much better and at 144hz it looks normal. At 144hz it flickers on video I think only because iphone camera is using 240fps and it detects the inconsistency/desynchronization with 144hz.

@aiaf @DisplaysShouldNotBeTVs So looks like it does proof that the cable and connection type really affect the FRC/Dithering on external displays.

Btw, even with 144hz enabled, when I'm connecting any apple silicon laptops top this monitor, it gives me weird light symptoms like FRC is enabled, don't know why.

Also I did some testing with StillColor app enabled/disabled and didn't see any changes at all.

I also can be wrong with my conclusions, because i've spent maybe 6-7 hours looking at these flickering pixels lmao..

photon78s

madmozg

Great comparison video. So if your input signal does not have temporal dithering and somehow pixel flicker is still present on your 8 bit (true 8 bit with no FRC) monitor, then I think that would leave pixel inversion as the cause?

DisplaysShouldNotBeTVs

madmozg Also I did some testing with StillColor app enabled/disabled and didn't see any changes at all.

this is weird, because I can see obvious differences and changes in flicker when toggling Stillcolor even through with my own eyes when connecting M1 Macs to monitors.

(especially 6-bit+FRC monitors, because on those, before Stillcolor existed, some transparency effects would literally visibly flash to the point anyone could see it. Stillcolor finally fixed that more "obvious" issue for both me and even some other non-sensitive users I talked to online too)

I even can notice a difference on internal displays, I can literally see very subtle flicker and "moving waves" stop and start if I'm "directly looking at a gray background" on m1air or M2 TB's internal panel while disabling and enabling dithering back and forth.

madmozg

photon78s I think so too. I asked chatgpt and claude about it, like if your display doesn't have FRC tech, is any external device can force it to use FRC, and the answer was no. So possibly it can be inversion.

DisplaysShouldNotBeTVs

madmozg like if your display doesn't have FRC tech, is any external device can force it to use FRC

I mean the GPU-level FRC that M1 Macs use (before Stillcolor existed) effectively does this IMO

async

This is super nice. You could consider trying to record in a slightly different fps to see it it makes any difference. Some third party apps support this.