Issue with monitor on MacBook Air

I have a 4K monitor on my Mac. In Displays Preferences, I can choose to display "UI looks like" "resolution" options as a simplified list of radio buttons ("Larger Text" … "More Space"), or as a list of resolutions.

It helps to understand that there are three sets of resolutions .

• The "UI looks like" "resolution" – the one that you select in Displays Preferences. Applications use this for sizing text and objects. Legacy (non-Retina-aware) applications believe that this is the actual resolution of the screen. Retina-aware applications know that if the display is in a Retina mode, they can draw things in finer detail.
• The internal drawing canvas resolution. In Retina modes, this has 2x as many pixels (in each direction) as the "UI looks like" resolution.
• The resolution of the signal sent to the screen.

For these five choices, on my system, the corresponding resolutions are

• (1920x1080) => (3840x2160) => (3840x2160)   Retina mode (“Larger Text”)
• (2560x1440) => (5120x2880) => (3840x2160)   Retina mode
• (3008x1692) => (6016x3384) => (3840x2160)   Retina mode
• (3360x1890) => (6720x3780) => (3840x2160)   Retina mode
• (3840x2160) => (3840x2160) => (3840x2160)   Non-Retina mode ("More Space")

I normally run my 27" 4K monitor in the "UI looks like 2560x1440" mode, so text and objects are the same size that they would be on a 27" 2.5K monitor. Applications draw things at a 5K level of detail. The Mac then downscales the 5K image to fit on the actual 4K screen.

All five of these modes use the full 4K resolution of the screen. They just make different tradeoffs as to text / object size vs. "workspace".

This is something I can see easily using

• The Graphics/Displays section of System Information (Option- / System Information…) and
• The display on my Dell monitor which tells me the resolution of the signal it is receiving from the computer

In a resolution list like this one, "(low resolution)" implies that the mode in question is not a Retina mode.

Thus,

• If I select "2560 x 1440", the computer will draw on a 5K canvas, and send a 4K signal to the monitor.
• If I select "1920 x 1080 (Default)", the computer will draw on a 4K canvas, and send a 4K signal to the monitor.
• If I select "1920 x 1080 (low resolution)", the computer will draw on a 1920x1080 canvas, and text will be much fuzzier. Interestingly enough, even in this mode, my Dell monitor reports receiving a 4K signal! I take it that the Mac is doing the upscaling; but the result would be the same if the Mac sent a 1920x1080 signal to the monitor, and the monitor did the (1920x1080) => (3840x2160) upscaling.

If you go back and forth between the two "1920 x 1080" modes while you have a window with a lot of text open on the screen, the difference in quality (in favor of the Retina mode) will be very obvious.

Presumably "1920 x 1080 (Default)" is listed as a "(Default)" because (2 x 1920) = 3840 and (2 x 1080) = 2160 … on most Retina Macs, the default is either the resolution that results in perfect 2x integer scaling, or a setting one notch higher than that, which gets a little bit more "stuff" onto the screen (at the expense of text/object size).

I believe that Windows handles this a different way. Instead of Retina scaling modes and "UI looks like" resolutions, there's a system-wide scaling factor.

So for a 27" 4K display,

• Retina "UI looks like 2560x1440" mode on a Mac, and
• A 150% scaling factor + resolution setting of 4K on Windows

would presumably produce similar results.

The thing about the Windows approach is that it relies on applications to honor that 150% (or whatever) setting. My impression was that, in the early days of high-PPI displays, many Windows applications didn't. So you'd set up your nice new 4K display and text in some of your applications would shrink to minuscule size.

Apple's approach is a bit more complex, but the idea was to make legacy applications "just work" properly with the high-PPI displays. If they thought that a 4K display only had 1920x1080 pixels, but the operating system knew that they were legacy applications and that the real resolution was higher, it could transparently map their drawing calls into ones that would put things of expected sizes at expected places on the screen. The legacy applications might not take advantage of the extra resolution, but at least they'd still be usable.

These days, just about every Mac application is Retina-aware, but I am pretty sure that backwards compatibility is one of the reasons why the Mac's Displays Settings controls are designed the way that they are.

One thing that came up in another thread is that the MacBook Air's "up to" resolutions seem to apply to the internal canvas resolution.

• (1920x1080) => (3840x2160) => (3840x2160)   Retina mode (“Larger Text”)
• (2560x1440) => (5120x2880) => (3840x2160)   Retina mode
• (3008x1692) => (6016x3384) => (3840x2160)   Retina mode
• (3360x1890) => (6720x3780) => (3840x2160)   Retina mode
• (3840x2160) => (3840x2160) => (3840x2160)   Non-Retina mode ("More Space")

On a M3 MacBook Air (different model than yours), closing the lid lets you use two displays – one with a resolution of up to 6K, another with a resolution of up to 5K.

Someone with that MacBook Air reported that they could not select "like 3008x1692" for the second display. They could select "like 2560x1440" or "3840x2160" – but not "like 3008x1692" (or "like 3360x1890"). If you take a look at the internal canvas resolutions for those modes (resolutions which exceed 5K), that explains why. It makes sense when you think about it, but it's not exactly well-documented.

Your MacBook Air supports "one external display with up to 6K resolution at 60Hz" – so I am guessing that the "like 3008x1692" and "like 3360x1890" Retina modes will be available to you.

MacBook Air (M1, 2020) - Technical Specifications - Apple Support

drizzydraker wrote:

I have an M1 MacBook Air. Got a Dell 27” 4K (S2721QS) today, which I thought was plenty of spec for me. I’ve since been introduced to the resolution/scaling/etc situation with MacBooks and monitors, but I’m far from techy enough to pretend to understand.

I don’t even know what question to ask... Why is 1920x1080 the default setting? Why is 3840x2160 labeled as low resolution? Why does selecting that 4K setting make everything super small with no option to scale it up?

First things first. The reason that everything is super-small when you select 3840x2160 ("More Space") is that applications traditionally have sized things in terms of pixels. A regular 27" monitor has 2560x1440 pixels, and those pixels are packed together a bit more tightly than the ones on a regular 24" 1920x1080 monitor. So when running those two monitors "at native resolution", text and objects are a bit smaller on the 27" 2.5K monitor than they are on the 24" 1080p one. Your monitor has 50% more pixels each way than a 27" 2.5K monitor – but it has the same physical size. So at the 3840x2160 setting, text is only 2/3rd as wide and 2/3rd as high – and takes up only 4/9th as much area – as text on a regular 27" 2560x1440 monitor.

Basically, all the increased resolution is going to cramming more, and smaller, stuff onto the display. It's as if you bought a book that was printed in 5-point type just because commercial book printing machines have the sort of resolution that would allow them to do that.

This is why Apple invented Retina scaling modes, and why you probably want to use one.

(To be continued)