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MacOS scaling and 27-inch 4K monitors: What graphic designers should know

The goal of this article is to let graphic designers know how MacOS handles UI scaling, and how Photoshop responds to different scaling options on 4K displays or Retina displays from Apple.

Most of the MacOS UI scaling options should produce sharp and detailed looking UI elements (e.g. text, fonts, icons, palettes) on a 4K monitor. However, for optimal scaling and sharpness, you should probably go with a 27-inch 5K display, and unfortunately this size and resolution combination is not common. 27-inch 4K displays are more common.

There's an article on bjango that explains why 27-inch 5K is better than 27-inch 4K. Just to summarise that article, MacOS works best when the resolution of the display is close to either 110 PPI or 220 PPI. So before you buy any monitor, just use a PPI calculator online to calculate the PPI.

The scaling issues mentioned below are from 27-inch 4K displays.

There are some issues with zoom with Photoshop on MacOS depending on the UI scaling option you use. Whether you care about it is really personal preference. This affects Affinity Photo on MacOS too. This zoom issue does not happen with Windows.

Some people care about it, while some people don't care. The zoom issues are there which is why I'm able to show them to you with screenshots.

With certain MacOS UI scaling options, within Photoshop and Affinity Photo when zooming to 100%, your file will not show you a 1:1 pixel representation.

It's a minor issue that doesn't prevent me from doing my work. It's certainly not an issue that will affect photographers, digital artists, 99.9% of users.

Let's look at one example on a 15.6-inch 4K display (282 PPI). The MacOS UI scaling options available are:

  • 1920 x 1080
  • 1680 x 945
  • 1504 x 846
  • 1280 x 720
  • 1152 x 648

When you hold the Alt key and press on the Scaled word just beside the radio button, more UI scaling options will appear. Not that in this case, there's no 4K UHD option (1:1 no scaling) available, probably because the UI will be too tiny at this option.

Here's how a file measuring 3840 x 2160 pixel looks on a 15.6-inch 4K UHD monitor with the 1080P UI workspace. The UI elements look big and comfortable to see. At 100% zoom, you also get a true 1:1 pixel representation. In other words, a 3840 x 2160 pixel file fills a 4K UHD display.

By the way, 1080P UI workspace is the optimal option for a 15.6-inch 4K monitor.

Say you want to scale up the UI to the next option 1680 x 945 (above) because you want to see larger UI elements. With this option, you can still zoom to 100% in Photoshop but you're not going to get a true 1:1 pixel representation as shown above.

This happens because MacOS has changed the resolution to 3360 x 1890 but using a 1680 x 945 UI workspace. The 1:1 pixel representation happens at 3360 x 1890, which is why you see the 4K UHD file has cropped off because it's too big for the 3360 x 1890 resolution.

Here are screenshots for the same file on the other UI workspaces: 1504 x 846, 1280 x 720, 1152 x 648.

That's how MacOS UI scaling works with 15.6-inch 4K UHD display.

Now say you have a 27-inch 4K UHD monitor (163 PPI) which is quite a common resolution and display size combination. Because using native (no scaling) resolution will give you tiny UI elements, you have to scale the UI and the comfortable option is the 1440P UI workspace.

By choosing the 1440P workspace, MacOS will scale the resolution to 5120 x 2880. That's why you see the 4K UHD file only taking up a portion of the display, even though a 4K UHD file should fill the whole 4K UHD display.

These issues with zoom also affects "Export as" and "Save for Web" functions within Photoshop.

How can it affect your graphic design work?

Let's use the 27-inch 4K UHD monitor as example. Let's say I want to export a photo to 500px wide to use on my blog. All the pictures you see above are all 500px wide by the way.

When I view the 500px wide file on the 1440P UI workspace, the 500px file is actually set against 5120 x 2880 resolution so it's going to look really small, kinda difficult to see if there is text on it. 500px vs 5120px wide is quite a huge difference.

On a 27-inch 1440P monitor (108 PPI), the same 500px file is set against a 2560 x 1440 resolution and is much bigger. Pixels are bigger, more chunky with more pixelation.

Of course most designers will just use "Fit to Screen CMD+0" to view their work up close on their 4K or Retina display, or just zoom to 200%. So this zoom issue may not matter.