Mac external displays for designers and developers, part 2

Since writing about Mac external displays in 2016, not much has changed. LG, Dell, Samsung, and other display makers have either never catered for the specs many Mac designers and developers want, or they’ve reluctantly produced products that have been short-lived or compromised.

In 2019, Apple announced their return to the display market, with an incredible product carrying an incredible price tag. The Pro Display XDR surpasses the specs many Mac users need, which unfortunately also puts it out of reach for many financially.

2019 also saw an update to LG’s 4K UltraFine display, increasing its size from 21.5-inch to 23.7-inch, but lowering its resolution pixel density. This effectively left the market with a single option — the LG 5K UltraFine. Not only that, but the LG 5K UltraFine has been going in and out of stock globally. It’s unclear to me if the product still exists as a going concern.

Thankfully, Apple’s new Studio Display now provides a great option.

Photo of Apple Studio Display

Spec wise, it’s incredibly similar to LG’s 5K UltraFine, and the display of the now discontinued 27-inch iMac, even though it’s not using the same panel. The Studio Display is precisely what I and many others have been asking Apple for — an iMac without the computer. It’s definitely true the Studio Display could have included local dimming, HDR, 120Hz refresh rate and other niceties, but I think that would have been the wrong choice if it meant a higher price. The Studio Display hits an incredibly important target, and it can now be the default choice for discerning Mac designers and developers.

With that in mind, what are the criteria for a good external Mac display in 2022?

Pixel density #

macOS has been designed to be legible and usable with a pixel density of about 218PPI (pixels per inch) for “Retina” class desktop displays. If a display’s PPI is higher, text and the macOS user interface will be smaller. If a display’s PPI is lower, text and the macOS user interface will be larger. Stray too far from 218PPI and macOS becomes unusable.

Apple’s laptops have slightly higher pixel density, at 227PPI and 254PPI for the MacBook Air and 16-inch MacBook Pro respectively. This trades a little legibility for screen real estate, while also catering for the closer viewing distance (the closer you get to a display, the larger things look). These choices dictate how physically large text and interface elements appear on the respective devices.

Everything above assumes macOS is being run without display scaling. Display scaling is a system preferences setting that renders your Mac’s screen to a virtual buffer that is larger or smaller than your display, and then scales the final result to fit. This allows Macs to work with a wide range of displays with different pixel densities.

However, display scaling comes with some significant caveats, including a blurrier picture, shimmering when scrolling, moiré patterns, worse GPU performance, and worse battery life if you’re using a laptop. Display scaling also undoes dithering, which can mean gradients aren’t as smooth. With those issues in mind, it’s far, far better to run macOS at the pixel density it was designed for.

The comparisons below are made by simulating a Studio Display on the left and a 4K UHD (3840×2160 pixel) 27-inch display on the right, with macOS display scaling set so text and elements are the same size. The 4K display represents a common high-end display, with a pixel density of around 163PPI. The images are also presented larger to make the issues more pronounced, but these problems can definitely be seen with the naked eye, once you know what to look for. Please note that browser zoom, display scaling and other settings may make it harder to see the differences in the examples below.

The main issue is that everything’s just blurrier with display scaling enabled.

A comparison of 218PPI vs simulated 163PPI, showing the 163PPI display being blurrier

When pixels aren’t mapped 1:1 with the macOS window buffer, scrolling means edges and thin lines shimmer when moving.

A comparison of 218PPI vs simulated 163PPI, showing the 163PPI display shimmering as fine lines are scrolled

Even when elements aren’t moving, fine details can form moiré patterns. The example below shows a checkerboard being turned into a bit of a lumpy mess.

A comparison of 218PPI vs simulated 163PPI, showing the 163PPI display with a moiré pattern

Here’s a couple of photos of a 14-inch MacBook Pro’s screen, taken at the same distance from the display. The example on the left shows 1×1 pt checkerboard pattern with the “default for display” option. The example on the right shows the same pattern with the “more space” display scaling option.

Two close-up photos of a MacBook Pro screen

Not everyone’s going to see these issues or be annoyed by them, but they are very real. There’s also very legitimate reasons for using display scaling, or purchasing displays that can’t run macOS with 1:1 pixel mapping. It’s just good to be aware of the compromises. If you’re after a cheaper option, buying a non-Retina display could be a good choice. For that, you’d want a display that’s around 109PPI. It will look more pixelated though.

Here’s an overview of the pixel density for Apple’s current displays and some other external display options. You can use Sven Neuhaus’s PPI calculator to work out the pixel density of any display you’re interested in.

List of external displays and their respective PPI (pixels per inch) values

Colour space #

The range of colours a display can produce is often noted by its colour space. In 2016, I stated “if you only need sRGB, buy an sRGB only display”. Wider gamut content is more common now, and purchasing something that covers Display P3 or Adobe RGB might be a good idea, especially if you’re looking to keep your display for a while. It’s a bit of a moot point though — all the displays that meet the pixel density requirement cover the Display P3 colour space.

Future displays will likely cover wider and wider ranges of colours, until the point we hit the limits of human perception (ACES). The next stop on the train for consumer displays might be Rec.2020.

Bit depth #

Support for wider gamuts increases the need for more steps when expressing colours as digital values. Standard gamut (sRGB) displays typically use 8 bits per component (red, green, and blue, with a total of 256 steps of intensity for each), which results in around 16.7 million different possible colours.

To avoid issues like gradient banding, 10 bits per component is needed for wide gamut displays. As far as I can tell, the Studio Display, Pro Display XDR, and LG 5K UltraFine all accept 10 bits per component. In Apple’s tech specs, this is typically noted as “1 billion colours”. I believe this means 10 bits per component is sent to the display, but the panel itself may use fewer bits in combination with temporal dithering and other techniques to make the most of the hardware.

For a wide gamut display, 10 bits per component is a good idea. Once again, the Studio Display meets this requirement. The 24-inch M1 iMac and M1-based 14-inch and 16-inch MacBook Pros also list their displays as supporting “1 billion colours”. The 13-inch MacBook Pro and MacBook Air are both listed as “millions of colours”.

Brightness #

I barely venture beyond 50% brightness on any Mac desktop display I use. I know others have a different opinion, and some friends use maximum brightness. Your working environment will likely dictate your brightness requirements.

Local dimming #

Splitting a display’s backlight into individually controllable zones can increase the contrast ratio and provide deeper black levels. This is usually called local dimming or mini-LED. The Pro Display XDR, 12.9-inch iPad Pro, 14-inch MacBook Pro, and 16-inch MacBook Pro all have local dimming. I believe Apple denotes this feature as “XDR display” in their tech specs, because using mini-LED backlights provides local dimming, and it can assist with HDR support.

Local dimming is a great feature, and this is the first improvement I’d like to see on a revised Studio Display in the future (the current Studio Display doesn’t have local dimming). I don’t think local dimming is essential though.

High dynamic range #

HDR (high dynamic range) support is nice to have, but is only critical if you’re viewing or editing high dynamic range content. This may be important for editing video or photos, but is probably not important for most designers and developers.

Refresh rate #

120Hz refresh rate would be nice to have, but there is no display I’m aware of that meets the macOS pixel density requirement while also providing faster refresh rates. The Studio Display, LG 5K UltraFine and Pro Display XDR are all 60Hz. I believe 5K at 120Hz and 10 bit per component should be technically possible over Thunderbolt 3 with Display Stream Compression, but I may have messed up the calculations.

Bandwidth calculations for 5K 120hz using Display Stream Compression

True Tone and Night Shift #

True Tone and Night Shift both move the display’s colours away from the truth. They make what you’re seeing less accurate. When you’re doing any work with colour, I think they should be both turned off. I also think it’s wise to consider your environment, and try to minimise how much variation there is in lighting changes throughout your work day. Human perception is notoriously relative, but I believe constant exposure to a neutral and fixed environment can build muscle memory for colours. The more consistent your space is, the better. There’s a reason video edit suites and colour grading suites have minimal, neutral lighting, often even carefully choosing paint colours for walls.

The health benefits of Night Shift seem to be inconclusive at best. If you enjoy using it, great. Just turn it off when you’re doing colour critical work.

My setup #

I’m currently using a Pro Display XDR, but I would have definitely purchased a Studio Display if it was available when I needed a display. I’m using the default reference mode of P3-500 nits, with True Tone off, Night Shift off, and automatic brightness adjustment off.

Published 1 April 2022.