I found myself posting this information so frequently on forum threads and in video comments that I wanted to put it all together in one place so that I can share my experience and what I’ve learned with a single link. And, while this is primarily a vintage computing blog, not every post is of that nature. Apologies to my retro-only readers. (Well, there is an Amiga and a Lisa in that second photo down the page, there, so…)
I recently replaced my aging 2017 5K Retina iMac with a Mac Studio, powered by an M1 Max processor and 32GB of RAM. Some months earlier I upgraded my aging laptop to a 2022 M2 MacBook Air. That iMac’s beautiful 27-inch, 5K retina display was hard to part with, and so I wanted to give the new desktop system a very nice screen. And I have, in the form of an LG DualUp 28-inch display.

It’s an unusual display; it is a 16:18 aspect panel with a native resolution of 2560×2880. It is “tall” in its normal orientation, but I’ve chosen to use it rotated which makes it look rather square. A perfect screen for my use cases as a general UNIX system and web development workstation. (I do not game on my desktop Mac nor do I watch feature films, so a more traditional 16:9 aspect ration has little value to me here.) I’ve had this system up and running for two months now and I can say that, of all the displays I’ve ever used, this one is my favorite.
Doing research to spec out the screen for this iMac replacement, I encountered a large number of people lamenting the use of 4K displays with Macs, noting that the Apple 5K displays, with a 218 pixel/inch density, allow for a computationally easy halving of the native display resolution to achieve an ideal desktop rendering. A 5K Apple display has a native resolution of 5120×2880 and the default view mode is a “looks like” 2560×1440 desktop — razor sharp. Halving the native display resolution is easy peasy for GPU hardware — a small lift. This is, presumably, why Apple’s Retina displays are 5K rather than 4K. The thing with 4K displays is that in their typical native 3840×2160 resolution, they present the UI elements far too small, while the system-suggested half-resolution rendering is a sharp “looks like” 1920×1080 display where the UI elements appear too large — there’s too little desktop real estate.
The way around this is to have macOS “scale” the display to a more ideal lower resolution, but choosing that option in display preferences presents a warning: “Using a scaled resolution may affect performance.” What the OS does here is to scale up the chosen resolution to double height and double width (4x the pixels displayed) and then scale them back down to the display’s native resolution — 60 times per second. Indeed, this can be too much for certain older systems out there. But, as you will see, modern Macs should be able to handle the task just fine.
My display, which has a ~140 pixel/inch density (close that of a typical 4K display), is scaling to a “looks like” resolution of 2304×2048. This means that macOS renders my desktop at 4608×4096 (18.9 million pixels) and then scales it down to the panel’s native (rotated) 2880×2560 — 60 times per second. (The “looks like” target for a standard 4K display with a native resolution of 3840×2160 will typically be 2560×1440 and, thus, it gets scaled up 5120×2880 (14.7 million pixels) and then back down to the panel’s native resolution.) This all sounds harrowing, and many threads of concern have been created, talking about the dramatic performance impact that this scaling busywork necessarily has on the system. Among them is this frequently cited video created by a person who indicates that the performance of their M1 MacBook Pro was so dramatically impacted by a scaled 4K display that they returned it and got a more traditional, low-DPI 2K display.
This guy’s experience makes no sense to me.
My LG DualUp display arrived a few weeks before the Mac Studio for which it was purchased. In that time, to test it out, I attached it to my M2 MacBook Air. As expected, the native rendering presented the macOS UI in a far-too-tiny fashion and the system’s suggested HiDPI “looks like” half-resolution of 1280×1440 was too large, too low res. In order to unlock myriad other scaled resolutions to choose from, I reached for the excellent BetterDisplay. This handy app, among various other features, allows you to unlock many additional low- and HiDPI- resolutions in the system display settings to choose from and, in the end, I went with a “just right” resolution of 2304×2048, as mentioned earlier. The M2 Air drove the display perfectly, and everything felt just glass smooth — no performance issues anywhere to be seen.
Still, I saw such concerned discussion about macOS scaling, in various places online, that I wanted more assurance. I noticed that the author of BetterDisplay has a Discord channel to support users of the app. I joined it and had a number of conversations with him about my concerns. I showed him the aforelinked video of the distressed YouTube user reporting to have experienced such dire 4K performance issues on his M1 MacBook Pro. He felt surely that something else must be amiss with his configuration.
He explained,
The M1/M2 is specifically designed to be super efficient when it comes to macOS desktop rendering. M1 Pro+ macs can drive multiple 5K displays alongside a 4K display simultaneously, all with scaling involved so that can result in huge framebuffers. So I think driving a single display with a 5K-6K framebuffer with scaling is way below the limitations of these machines.
…
If we try to make sense of it, a 5K framebuffer has about 15 million pixels. So at 60fps about 900 million pixels must be processed. Let’s say 1 billion pixels. If we say that scaling is done super inefficiently, let’s say every pixel requires 5 floating point operations to be scaled. That is 5 billion operations per second. Now the M1 Pro can do about 5 teraflops — that is 5 trillion (5 000 billion) operations per second. That means that all the scaling stuff will consume 0.1% of the capabilities of the GPU. Even if there are additional inefficiencies and super wasteful processing, so everything requires 10x as much processing, then the desktop scaling will keep occupied the GPU 1%.
Even if somehow the 1% would turn into 10%, still 90% of the GPU is free. So surely scaling will not make a smooth video playback drop to 1fps in any circumstance. It would be such an obvious issue that I think everybody would know about it.
As I stated, the M2 Air drove the DualUp display without incident. I viewed 60fps 4K videos, ran a few games, scrolled wildly through my massive photo gallery, swiped through five different virtual desktops — all smooth. My own observations of what was happening right in front of me revealed zero cause for concern, and the sound reasoning I heard in that Discord further put me at ease. And, as you might guess, the Mac Studio where the DualUp now lives also handles the scaled display, along with an unscaled secondary display, with complete ease.
A recent video by Kyle Erickson, whose tech videos I enjoy, should also help allay such concerns for those who have them.
It seems to be the case that recent, modern Macs — and not just those with Apple Silicon — can handle HiDPI scaling without issue.
Great write up and hopefully will make concerned folks stop worrying. This whole issue has been blown way out of reality; it’s taken on MaxTech levels of hyperbole with people freaking out over nothing!
It should be quite obvious that this isn’t a significant burden as lots of apple laptops use scaled resolutions by default even in older and way less powerful intel processors.
Thanks for the explanation helped me a lot!
I would like to know about text clarity. Does text look crisp/clear on LG DualUp comparing with iMac 5K screen or LG Ultrafine 5K Display?
Scaled properly, it looks very clear, but it is not as absolutely razor sharp as a 5K or 6K display.
The issue isn’t the performance (Although it’s annoying as well)
The issue is that the screen is scaled. It’ll look blurry and uneven. This defeats the purpose of a high-dpi screen in the first place.
Why not get a lower dpi screen that is cheaper, faster and looks sharper on macOS?
Rendering a 5k image onto a 4k screen
won’t be slower than rendering a 5k image onto a 5k screen.
But it’ll look worse then rendering a 1440p image onto a 1440p screen.
And that last part is the frustrating one.
Well, performance isn’t a particular issue for modern systems as I’ve tried to illustrate with this blog post. And as for your suggestion that it will look “blurry and uneven,” that would indeed be the case if the image was not rendered at a much higher resolution that the native 4K screen resolution and then scaled down to that native resolution. That’s the “HiDPI” macOS scaling we’re talking about here.
My screen is basically a 4K as far as its DPI, but it’s an odd aspect ratio. So, let’s take a more typical 4K screen, which is 3840×2160 pixels @ 16:9 aspect ratio. macOS sees this screen and defaults it to a “HiDPI” mode of 1920×1080. If it rendered at the native 3840×2160, on the typical ~27-inch 4K display, the UI elements and text would be much too small for most people’s liking. The “HiDPI” label indicates that it’s internally rendering the desktop at twice the height and twice the width (4x the pixels) of the 1920×1080 (which happens to be the native resolution of the display) and scales it down to the panel’s native resolution, which is exactly half the height and width of the internal upscale which, being exactly 50% on both axes, makes the image razor sharp. But the UI elements are now too big; there’s too little real estate on the desktop for most people’s liking.
Most users would desire a 2560×1440 desktop in this scenario. Here, a user could set the Mac to output a literal, non-HiDPI (not scaled internally) 2560×1440 to the 3840×2160 panel. In this scenario, the panel hardware itself would upscale the video to its native resolution and, given that this is not an exactly-twice-resolution upscale, it will look somewhat as you say “blurry and uneven.” (It’s also the case that macOS probably upscales images more cleanly than the firmware routines in said panel, even in this non-HiDPI scenario.)
The solution is to choose a HiDPI resolution of 2560×1440 in macOS. What this does is render the desktop at 5120×2880 internally and then scale it down (60 times per second) to the native panel resolution of 2840×2160. Here, the resulting image does not look “blurry and uneven” and it looks significantly better than a lower dpi screen with a native 2560×1440 panel. Trust me on this; I have a lower dpi, 2560×1440 native display sitting two inches to the right of my Mac’s display here on the desk, which is attached to a Windows PC that I use exclusively for gaming.
I use this LG DualUp display (which, for the purposes of this conversation, is a “4K display”) every day, all day. I write code on it (job) and do all manner of other things (typical use), etc. I use lots of small-text terminal windows, what’s more.
I directly replaced my 27-inch 5K Retina iMac with this Mac Studio and this display and I can say with conviction that this display looks negligibly less clear to me than the iMac’s 5K Retina display did. I wear glasses, and with them on my vision is perfect. It looks incredibly sharp and uniform and I find the fidelity of the image shockingly good, and a nice bonus is that this is a matte screen and so lacks the high reflective glare of the iMac’s display. If I get very close to the screen and look at the individual pixels of text on the display, I can see that the 5K (when scrutinized at so close a range) was sharper, but only on such close inspection can I feel this.
That said, I like the unique aspect ratio of this display so much more than the typical 16:9, that I consider this to be the best display I have ever used. For me, the aspect ration makes far more sense than a widescreen display. The hint of a difference between it and a true 5K under 5-inches-from-the-screen observation is so irrelevant and typically unnoticeable to me that it is not a factor at all.
I hope this helps.
Thank you for collecting all this information. I personally use 2k gaming monitors and had initially thought about changing monitors because I was seeing blurry text at the native resolution of 2560x1440p. Then I discovered BetterDummy, now BetterDisplay and set a resolution of 2048 x 1152 which translates to 4096 x 2304 HiDPI. This seems to me to be the best option for a 27” 2k monitor and I can even take advantage of the 100 hz of the display without having experienced any performance drops.
Nevertheless, I find it really sad that apple does not handle scaling without third-party software, although BetterDisplay is a great OpenSource software.
I just got the Dual Up & downloaded the software you mentioned. However, I could not seems to find the HiDPI resolution of 2560×1440. The max I got is 1440 x1280 under HiDPI. Can you tell me what I am missing? I am using Mac M1 by the way. In addition,I have to rotate 170 degree to get the orientation similar to your picture. Thanks!
If you haven’t solved the issue yet, try this: go to BetterDisplay settings, to the App menu tab, find the resolution section and check the show all resolutions option.
I still didn’t see it. I can only find show additional resolution option, but even then I couldn’t find 2560 x1440 under HiDPI. I can see it under non-HiDPI though.
It took me 2 weeks from the time I visited the Apple store to find out why all the Macbook Air screens looked blurry to me. After that 2 weeks of research, and from what I can tell, it seems the issue is Apple display scaling. To me the picture looks like someone is sharing their screen over teams, like there is some compression or resizing that screws up the sharpness.
Blake, Thank you! Yours is the best post I’ve seen on this “scaling” math/physics quagmire. I got A’s in upper level calculus but was still having difficulty understanding the issues of monitor “scaling”. I’m looking to update to an M2 but without a budget or creative need for an Apple monitor. The question of what monitor to buy left me swimming in the wormhole threads about 4K scaling. Thank you for throwing me a life raft to help float me to a monitor purchase decision.