It’s no secret that phone displays are getting big—much bigger than they used to be. The iPhone got bumped up a notch (from 3.5 inches to 4 inches), Nokia’s Lumia display is gargantuan (4.3 inches), and some of the Android phones launching this quarter come with 4.7-inch displays. Even Sharp and LG have begun manufacturing 5-inch displays with more than 446 pixels per inch (ppi), and those displays are expected to come with a 1920×1080 resolution, giving them the same resolution as HDTVs and pitting them against contenders like the iPhone's 326 ppi Retina display and the HTC One X's 312 ppi. But when 1080p is crammed into such a relatively small package, does it really matter to the human eye?
We took this question to Dr. Raymond Soneira, president and CEO of DisplayMate, a company that produces calibration software for displays of all types. Dr. Soneira has also been known to publish display shoot-outs that pit the latest smartphones against each other in the battle for the best display.
When it comes to 1080p on a smartphone, he admits that it might not matter for the most casual users. "For some people, it is possible to tell the difference if we were to sit down and study a [1080p] display and a [720p] display, side-by-side," he said in a phone interview with Ars. "If you’re really a fanatic and you study images, or you have some professional applications and you’re really into displays, then it may make a visual difference for you."
For most people, though, it won't matter. Photos are inherently fuzzy, so it won’t matter whether they’re viewed on a 1920×1080 or 1280×720 smartphone display; you’ll still see their imperfections. "Even the tiniest image detail in a photograph is always spread over more than one pixel," Dr. Soneira explained in a follow-up e-mail. "The image detail is never perfectly aligned with the pixel structure of the display." Videos are even worse: not only are they fuzzy like photographs, but the pictures are constantly moving. Even if the images were sharp, the human brain couldn’t zero in on content that’s appearing for only a fraction of a second on such a small display. "For ordinary viewing of videos, 1920×1080 is really not going to make a visual difference," adds Dr. Soneira.
Where a 1080p smartphone display could really make an impact is with computer-generated content—that is, the user interface, buttons, and text. "Only computer-generated images make full use of the pixel resolution of the display," says Dr. Soneira. "For graphics and text, maybe you want that kind of sharpness." Like desktop computers, smartphone displays can also utilize sub-pixel rendering, which helps improve the visual sharpness of computer-generated graphics.
A 1080p display might also be useful for simply viewing 1920×1080 content and not worrying about scaling. "Every time you rescale content that’s scaled for some other resolution, it’s not going to look as good. So there’s an advantage to living with 1920×1080 even if your eye can’t appreciate the fine details, because you don’t have the rescaling artifacts," he says.
For most uses, however, the extra sharpness of a 1080p display is wasted. In Dr. Soneira's third-generation iPad display shoot-out, he explains that because most adults don't actually have true 20/20 vision—even with glasses or contact lenses—when they view a display further away than recommended, the eyes can no longer fully resolve the sharpness. The iPhone’s Retina display makes a good example of this. "If you use the legal definition for 20/20 vision, the resolution for the iPhone at 326 ppi becomes a ‘retina’ display at 10.5 inches," says Dr. Soneira, because that’s the viewing distance where the image on the screen will appear optimally sharp. After about 15 inches, "the much higher 326 ppi is 'wasted' because the eye can't resolve sharpness above 229 ppi." The further away a person gets, the more gradual the reduction in perceived image sharpness.
In the end, whether 1080p is worth it on a smartphone display depends on each individual use case. If you're using it to watch video or scroll through photos on Facebook, it might not matter too much whether you're doing so on a 1080p display. But if you devour e-books on the train ride home or have content that's catered to a 1920×1080 resolution, it may prove worth it. It's also important to keep in mind that all of those added pixels come at a cost. "It takes energy, computer power, and electricity to rescale an image,” says Dr. Soneira. "That uses CPU power and battery power and neither of those [things] are good."
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