What is HiDPI

and Why Does it Matter?


Pixel Doubling

At the heart of HiDPI is pixel doubling: drawing an image with twice as many physical pixels in each dimension than requested in virtual pixels.

1× vs 2× (HiDPI). With 4× as many pixels. HiDPI allows crisper shapes and better aliasing.

Half Pixels are a Lie

So, why pixel doubling and not just increasing the density on a 15" display from, say, 1080p to something like 2880×1620? To get you user interface at the same physical size* as on the 1080p display, you would have to scale it by 1.5×. That means a dot that is requested to be drawn at 1 virtual pixel now has to be drawn at 1.5 physical pixels.

1×, 2×, and 1.5× scaling drawing a 1px dot. On 1× and 2×, the dots look identical. On 1.5×, software has to compensate and aliases, creating a fuzzy edge.

4K? Quad HD? 5K? UHD? Retina? HiDPI?

HiDPI is a great idea, but it’s a hard concept to explain to customers (and some manufacturers don’t even seem to get the benefits, see the next section). So the industry has come up with several different buzzwords in an effort to pitch it it customers, with varying success.

Retina

Arguably the most effective of these efforts comes from Apple with their Retina branding. They describe Retina as meaning so pixel-dense that the human retina can’t discern the individual pixels at a normal viewing distance. That’s accurate, but also a bit of marketing speak compared to how they use it in practice. For Apple, Retina seems to simply mean pixel-doubled.

4K, Quad HD, 5K, and UHD

Technically, 4K, Quad HD, 5K, and UHD have nothing at all to do with pixel density and HiDPI. However, since they’re the terms used to sell projectors and TVs, computer manufacturers like to use them to upsell from the “lowly HD” displays they’re replacing.

HiDPI

In the desktop Linux world (and it would seem in Windows land as well), the term HiDPI is being adopted as the manufacturer-independent version of pixel-doubling or “Retina.” Few manufacturers are actively using this term (System76 is!), but software developers tend to know and use it. I’d love to see it picked up as an industry standard term if used properly.

Some Manufacturers Make Poor Decisions

Higher resolution is not always better. In an effort to upsell from their lower-resolution displays, some manufacturers are jumping on the 4K bandwaggon without considering the phyiscal size and how pixel doubling works.

The Takeaway

  • HiDPI ideally means pixel-doubling
  • Half pixels are a lie
  • 4K does not mean HiDPI, and might not always be the best resolution
  • Some manufacturers make poor decisions

elementary

We design and develop the fast, open, and privacy-respecting replacement for Windows and macOS

Cassidy James Blaede

Written by

Co-founder & UX Architect at elementary, Inc. He/him/his.

elementary

We design and develop the fast, open, and privacy-respecting replacement for Windows and macOS