Solution for blurry effect on 4k 27" with WQHD resolution on DisplayLink?

[jonyking]

Hello everyone,

I hope you can help me a little bit. I've got the problem that the resolution is very blurry behalf the Full HD resolution. Is it possible to fix that?

I've got an MacBook Pro 13" with m1 and connected two 4k 27" displays (Philips 276E8VJSB) over a DisplayLink USB-C Dockingstation from HP.

Full HD ist working great without any blurry text.

[waydabber]

Hi, can you make some photos on what do you mean by blurry text? On a 4K display anything that is not 1920x1080 or 3840x2160 will look somewhat blurry due to scaling / supersampling and the necessary misalignment of framebuffer and physical pixels in the intermediate resolutions. This works this way by design on macOS. On a 27" display the optimal resolution should be 2560x1440 HiDPI but for that to be pixel perfect you'd need a display with a 5K panel (this is why Apple uses 5K displays for 27" iMacs or in the UltraFine displays made by LG for Apple). 4K displays are definitely a compromise on macOS. When Apple engineers devised how scaling and HiDPI should work on MacOS they were inspired by iOS and probably did not foresee that 4K displays will become mainstream in the 27"-32" space. Honestly, Windows PCs are now in a much better position in this regard right now.

[waydabber]

But the "somewhat blurry" still looks OK for most ppl. If yours is superblurry, then the OS probably scales a non-hidpi WQHD resolution which would look bad indeed on a 4K display. :)

[jonyking]

Thanks for the fast and detailed answer!

For me it is not HiDPI, so the text is not sharp enough. But as I described below I've a similar setup at home with my mac mini m1.

I have the same setup with my mac mini over hdmi and usb-c with two 31" 4K displays (of course without any third party software). There is a very clear font at the resolution of 2560x1440 HiDPI.

I've attached two pictures one with Full HD and one with 2560x1440.
1920x1080

2560x1440

[waydabber]

Both of these are HiDPI, but these are screenshots (which show the framebuffer state), it is not obvious how it shows on the display and in what way it is blurry.

But I just re-read your original message and now I see that it is DisplayLink. I think DL might not support interim scaled resolutions (or maybe there is a beta driver that does). Others successfully used BetterDummy to alleviate this issue, you can contact @jb-ks as he has a DisplayLink setup and experimented a lot with it to figure out how things works best. :)

See this: #274

[jb-ks]

In #173 (comment) I made some photos from my 4k screen attached with DisplayLink:

• 4k native (as reference)

• LowRes 2560 x 1440

• mirrored

• full screen stream

The result was that mirrored HiDPI is much better than LowRes, but still clearly inferior to native HiDPI.

Full screen streaming, however, is very close to native HiDPI (but still not identical).

In normal use with full screen streaming, there is no noticeable difference between my directly connected monitor and the one connected with DisplayLink.