Make a Retinalike display
Make OS X look sharper on a regular monitor by turning on HiDPI mode
Many Apple fans covet the Retina display found on the iMac and MacBook Pro. What many don’t realise is that the special rendering mode OS X this uses to draw the desktop in finer detail is available on Macs with regular displays, too, and that it can have practical benefits. HiDPI mode is enabled by default on Macs that have a built-in Retina display, and that’s why the desktop is drawn at sensible proportions. You won’t see any reference to HiDPI in System Preferences’ Displays pane on these Macs. Rather, clicking the Scaled option reveals settings similar to ‘Looks like 1440x900’. The display itself has many more pixels than that. The scaling options tell OS X to draw things at the same proportions they would appear on a non-Retina display, and to use the extra pixels that are available to draw things in much finer detail. That’s why you see increased detail in icons and text has a much smoother appearance on a Retina display.
If you connect an officially-supported, external 4K display to a Mac, the desktop should appear at similarly sensible proportions. However, some displays cause OS X to display things at a very small size, making text difficult – if not impossible – to read. In this case, it’s essential that you enable HiDPI mode.
HiDPI on low-res
HiDPI mode isn’t only available on displays that genuinely have a high pixel density. It can be enabled on any Mac using a simple Terminal command.
What this won’t do is increase the number of pixels in your display beyond what’s there in the first place. However, when enabled on a 27-inch iMac with a regular display, on which the display has a 2560x1440-pixel resolution, HiDPI enables everything to be drawn at twice the size but with increased fidelity. In effect, this halves the usable workspace on the desktop, so everything is proportioned like it would be on a 1280x720pixel display. You might find this uncomfortable at the distance you normally sit from your Mac. Less fits on the screen – you won’t be able to see as much of a web page or a document at once, for example – but things look clearer. You might find this trade-off between space and clarity is beneficial if you find things are normally a little too small or you have trouble distinguishing characters. You could switch to a lower resolution without enabling HiDPI mode, but OS X will draw the desktop at that resolution and then upscale it to fill the screen, which can make things fuzzy.
Enabling HiDPI is as easy as running a Terminal command (see below), logging out and back in again, then picking a new display resolution.