Ultrawide Centre Seam

[m4nea]

Ultrawide 3440x1440, and there is a visible seam down the middle of the monitor, cutting it exactly in half. When I move items past it, they "fold" over it sort of like the pages of a book, one pixel wide. Text is also weirdly blurry at full resolution.
This is an intermittent issue I am seeing. I can actually fix it if I unplug the monitor a couple of times (sometimes), but I'm not sure I want to be flickering my display on and off this much. Not sure if this is just a crummy dongle I have...
Any ideas? Can't find anyone else with this issue at the moment. This does not happen on my windows machine, just M2 macbook air.

[m4nea]

Just a self-update. I can force proper resolution display by changing the colour to 8-bit only. Could this just be a bug with 10-bit colour on base M2?

[waydabber]

Hi there - not sure to be honest. A seam in the middle of the screen might indicate displayport MST tiling (when the video data are sent as two tiles if the bandwidth does not allow the video data to be sent using SST) and some timing related issue with this - however this is not common and should not be required for low resolutions like 3440x1440. It might simply be a display board issue that manifests itself when the display gets 10-bit data. It is extremely unlikely that it is a general bug in M2. 8-bit color requires less bandwidth so if MST tiling is used for 10-bit, it is possible that it is not used with 8-bit or internally the display can handle things better (more likely explanation) and this specific bug just does not manifest itself. I recommend using 8-bit, it is very unlikely you'll notice any difference especially as macOS uses GPU side dithering - most probably your display can't support true 10-bit anyway and just uses FRC (display side temporal dithering) to make up for that, so going 8bit + GPU side dithering will result in the same/similar quality.

[m4nea]

Hi, thanks for the response! This is good to know about the way this tiling is done. I think you are right on the money about this panel not being proper 10-bit.
I was thinking it could also be my cheap HDMI dongle having trouble with the bandwidth, do you think it would be worth trying another one to see if there is improvement?
In the meantime I have the colour mode setting protected to 8-bit, so the problem is solved for now. I don't do any important colour-accurate work on this display, and nothing beyond rec709, anyways.