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I have a 4K LG monitor. Model #27UD58. The max resolution supported by the monitor is 3840x2160x32@30 but when I select default for display setting (recommended) in System Preferences > Display it defaults to 1920x1080x32@30. I am puzzled why is that? Under scaled I can see the 3840x2160 option.

I am running Big Sur on Intel based Mac with Radeon GPU in it.

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2 Answers 2

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The default is a factor of exactly 2 (2160/1080 = 2). This is the scaling which makes for the most crisp looking text. So that is the default.

You can, of course, choose something else. If I were to use 3840x2160 on a 27" screen, I would find text looking too small - but if you like it, go for it.

My preference on a 27" screen would be for looks like 2560x1440.

For more detailed answers, read What are the effective scaling modes on OSX with a 4K display? Is an effective real estate of 2560x1440 possible? and some of the others in the 'Related' list on the right.

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  • The text might be crisp but what about video and images? They will not be as sharp and high-frequency content will get aliased. So why does Mac default to a non-native resolution? I am very curious to understand the algorithm it uses to determine what is default for display.
    – morpheus
    Commented Mar 20, 2022 at 3:39
  • @morpheus The default algorithm for hi-res displays is a scale factor of 2. But whatever you select (e.g. 2160x1080 or 2560x1440), applications (including video and image apps) will render to a virtual display which is twice that (e.g. 3840x2160 or 5128x2880) and macOS will, if needed, scale that down to the physical display - 3840x2160 in your case. All that ensures best viewing of both text and video. There is no antialias.
    – Gilby
    Commented Mar 20, 2022 at 5:57
  • @morpheus It is not so that only text gets a special treatment. Video and images are also treated specially, so that in the case of for example a native 3840x2160 resolution being setup for HiDPI 1920x1080, that means that if you play a 4k video - it is displayed in its native resolution without any pixel doubling. Similarly for images that natively have a high resolution - they will be displayed without pixel doubling for maximum clarity.
    – jksoegaard
    Commented Apr 19, 2022 at 11:10
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MacOS IS using the display's full resolution; but objects are scaled to twice the size so it doesn't look tiny.

The 'concept' of it being a 1920 x 1080 display is an abstraction.

The 2x2 pixel block that represents one pixel at the scaled size will almost always have different values in each of the four pixels. Yes, text will be anti-aliased, but images will not.

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