High DPI Displays: Do You Really Need Them?

Ever since the “Retina” display was launched, the topic of high-resolution display became a big deal in the context of phones, tablets, and even laptops. While “regular” PC monitors still have a pixel density of ~72 PPI (aka DPI), High-density displays for smartphones reach anywhere between 300 and 550 PPI.

High-DPI (aka HiDPI) displays in the context of phones should be understood a bit differently. The handset world is mainly divided between 1080p (1920×1080 or FHD/Full HD) and 1440p (2560×1440 or QHD/Quad HD). There is a lot of debate as for whether or not going from HD to QHD is perceptible, worth it or even detrimental. The answer is… “it depends”, and here’s why:

Pixel per inch describes how many pixels there are per inch of screen. Screen resolution describes how many pixels there are in total on the screen surface. For a given resolution, various screen sizes will yield various PPI density (large screen = lower PPI).

Screen size

300 PPI is a starting bar for HiDPI displays and that the human eye is capable of perceiving more details than that. “How much” varies for every person, so it’s best to check different screens to know what PPI is “good enough” for your vision.

The context in which the screen is used greatly affects whether higher PPI contributes to a better experience. For example, if you are watching a movie, going from 70 PPI to 150 PPI is highly perceptible, but going from 150 to 300 starts to show a diminishing return.

If you read, especially fine prints, a higher PPI brings a much higher visual comfort. This is particularly true for Chinese characters or pictographs, and it’s not rare to be able to perceive differences between 300PPI and 400 PPI or 500 PPI. The same is true for looking at photos. Going from a 300 PPI screen to a 450PPI one can be perceptible. Going from 450 PPI to 550 PPI is often not as obvious.

Virtual Reality (VR) changes everything

Virtual Reality is the game changer for HiDPI displays naysayers. While going from 420 to 550 PPI may not be very noticeable in a normal application, it makes a world of difference for VR apps. That’s because VR is experienced through optical lenses that magnify the screen’s pixels, PPI count is critical for that use case.

Having 50% more pixels adds a lot of perceived sharpness to the VR experience, and it is undeniable that we would need to reach, or go beyond, 1000 PPI to make the sharpness “Good enough”. We discussed this topic with Dr. Ramchan Woo, LG Electronics’ VP of product planning during the Game Developers Conference 2016.

Conclusion

In the context of smartphone displays, going from a standard 72-PPI to 300PPI makes a world of difference. If HiDPI starts at 300 PPI, then, yes, everyone needs a HiDPI screen. Now, the question is “what’s the point of diminishing returns?”

Going from ~326 PPI (iPhone 6s) to 425 PPI (Huawei P9) can be noticeable by many users. Going from 425 PPI to 575 PPI (Galaxy S7) is harder to notice, except in specific situations like HD photos or small text. VR makes that last difference much more obvious. To recap:

• 72 PPI : low density for handsets. “Basic” density for PCs
• ~300 PPI: entry-level HiPDI display
• ~425 PPI: perceptible difference with 300 PPI
• ~550 PPI: relatively hard to perceive the difference with 425 PPI, except in VR, HD photos and tiny text
• ~1000 PPI: not useful for handsets or laptops, but ideal for VR because of the lens magnification

VR aside, we would consider 425+ PPI to provide a very good experience for a handset. For PCs, anything above 300 PPI is already excellent. If you go beyond that, you just need to make sure that applications will adapt properly so that you won’t end up with tiny icons that make everything unusable (legacy Windows apps).

For reference:

• The Galaxy S7 has a 5.1” display, a resolution of 2560×1440 which leads to 576 PPI in density, for 3.7M pixels
• The Huawei P9 has a 5.2” display, a resolution of 1920×1080 which leads to 425 PPI in density, for 2M pixels
• The iPhone 6s has a 4.7” display, a resolution of 1334×750 which leads to 326 PPI in density, for 1M pixels

Hubert Nguyen
Categories: Cellphones
Tags: displays