Text Slightly Blurry at 2560×1440 HiDPI on LG UltraFine 4K 27" - Any Fix or Better Setup?

[apexbains]

Hey everyone,

I'm using BetterDisplay Pro with a 27" LG UltraFine 4K (3840×2160 via USB-C). macOS already offers a 2560×1440 HiDPI option by default, and BetterDisplay correctly detects it too.

The issue: while 2560×1440 HiDPI is selectable, text still appears slightly blurry in apps like Google Sheets, Google Docs, and other text-heavy interfaces. Especially with smaller fonts, the edges aren't crisp. From what I’ve read (and what @waydabber also mentioned), this may be due to macOS internally rendering at 5120×2880 and then scaling it back down to 4K - which causes the blur.

I understand this might be a macOS limitation, but I’m wondering:

Is there any reliable workaround to fix or improve the sharpness?

Would using a virtual display and mirroring it to the real screen help in this case?

Or is there another custom HiDPI setup that gets closer to true 1.5x scaling on a 4K panel?

The goal is to get a native-looking 1440p HiDPI experience with clean, sharp text - not the slightly softened version macOS seems to deliver by default.

Would really appreciate insights from anyone who's solved this or found a better configuration.

Thanks!
Anupal

[Stakker]

There's enough of a resolution difference between 5K and 4K that I personally don't believe the scaling creates artifacts. To test this, I first typed this text in 20 points in Photoshop. Then I scaled the image so that the new image is 75% of the original, as 4K is of 5K. Then I typed the text again in 15 points, matching the size of the scaled text (but without the scaling step).

Which one do you think is the scaled version? :-) There are some super tiny differences, but it's not because of the scaling, but how the hinting of the font happens to align with pixels in Photoshop (I believe). AFAIK, the current macOS font rendering ignores hinting so it doesn't care about aligning with pixels at all, so we can ignore that too. macOS just "brute force" renders the vectors, not caring about how the shapes align with the pixels, instead relying on high resolution to make it look sharp.

Yes, Photoshop font rendering is different from macOS, but my point is that I don't see the scaling creating artifacts. IMO, the reason why 4K looks a bit blurrier is simply the fact that there are less pixels.

(For what it's worth, I use a 5K screen at work and 4K at home, and while I can see the difference, frankly, it's so small that I rarely pay any attention to it.)

But if I'm wrong, and there is something else going on, I would love to learn about it!

[waydabber]

@apexbains - you can't really replicate a clean 2560x1440 image on a 4K panel due to scaling differences as 1:1 pixel mapping in this scenario is simply not possible.
@Stakker - yes, the way desktop compositing works on macOS is that everything is rendered at 5K with your setup. The composited desktop ends up being a flat image (containted by the framebuffer), all vector or font related informations, hints etc are lost by the time the system scales the framebuffer to the actual output, so the scaling entirely uses raster scaling techniques, with some slight sharpening effects added depending on GPU model.

[Stakker]

@waydabber Yes, this is what I'm simulating with Photoshop. However, I noticed TWO errors in my test: I forgot to flatten to bitmap after rendering the first text and I forgot to use Mac style font rendering (no hinting & "fatter"). Here's a properly done 3rd test.

After the three tests, I stick to my original claim :-) There is enough of a resolution difference between 5K and 4K for the scaling to work nicely, even though it is scaling an already rendered (anti-aliased) bitmap. There is a very very tiny difference, but to my eyes it's barely noticeable.

And as I said in the post I deleted earlier, 1:1 pixels don't really matter on macOS these days unless you're doing graphic design work that requires it. Font hinting is ignored so they're not aligned to pixels. Icons are bitmaps so they could be aligned to pixels, but the designers simply scale down from large bitmaps because it's not worth the trouble. Hand-made low resolution icons are a thing of the past, unfortunately. (I have one old app that still has a hand-pixeled low resolution menu icon, and it stands out. Some old menu bar system icons like volume and battery also still have the original hand-pixeled bitmaps. But newer icons like Mission Control or Safari buttons don't.) It's all about brute-force resolution now in Macland :-)

[waydabber]

I agree, I was using a 4K display (scaled from 5K) for coding for many years and (to me) it was fine. But for creating or enjoying pixel art, it might not be ideal. :)

[Stakker]

Yeah… 4K (on a 27" screen) is still a high enough resolution though that it doesn't really matter that much even if you do pixel art IMO. You want to see those image pixels much bigger anyway :-)

I'm super glad we had this discussion, because the main issue with 4K screens used to be that Photoshop thinks it is in 5K (which it technically is). So when you set zoom level to 100% to match image pixels with physical pixels, the image would be shown too small.

But I haven't checked this in a while, so now I did a test pattern image of black and white pixels. And wow, selecting 100% zoom actually matches the image pixels with the physical pixels on my 4K screen :-O I don't know if Apple changed how the OS reports the resolution to apps, or if Adobe fixed this, but it sure looks like Photoshop now understands that I have a 4K screen… Nice :-)