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How much higher can mobile display resolution go?

Posted: 03 Jan 2014 ?? ?Print Version ?Bookmark and Share

Keywords:smartphone? pixel density? 1080p? PPI? mobile displays?

So even if some individuals are able to discern individual pixels in the latest generation of ultra-high-resolution mobile displays, these screens are indeed already quite good. The question is, how much better can they get?

How to know the unknown
To test the upper limits of our ability to notice resolution differences, we would ideally use actual displays of varying resolutions. But there was a problem. Smartphone displays with pixel densities as high as the 1000 PPI we examined in our study are not available.

So we simulated displays of varying resolutions. We used a photographic process to create backlit transparencies of six different images. These images were downsampled to simulate displays with resolutions of 960x540 (254 PPI), 1280x720 (339 PPI), 1920x1080 (508 PPI), and 3840x2160 (1016 PPI). Each set of six images was produced both as a simulation of aliased and anti-aliased digital images by using Gaussian blur.

Figure 1: Test Images used in experiment, clockwise from top left: Vernier Test Pattern, Text, Web (source: BBC 2012), Family Photo (source: Applied Photography 2012), Video Game (CG) (source: GT5, Sony Computer Entertainment 2010), Kitchen Photo (source: Kitchen Design Perth).

For all but the highest resolution images, print quality very closely mirrored the expected quality of the corresponding digital display. For the purposes of our study, loss of resolution due to optical imperfections and film grain was not, however, statistically significant.

Step right up and see for yourself
We selected 50 subjects at random to participate in our study. Their average vision score was 20/16 based on a near-view Snellen eye test.

In our double blind testing, we asked participants to evaluate the resolution of each of the six image types (vernier pattern, text, website, family photo, video game, and kitchen photo) in a controlled environment. The distance from the simulated displays was 300 mm and was maintained by using a head mount. The subjects were given a time limit of three minutes to rate the images.

The results clearly showed that higher resolution images resulted in significantly better ratings by our subjects for all images and types, both aliased and anti-aliased. Since improvements in ratings were observed for the 1016-PPI images over the corresponding 508-PPI images, we conclude that the perceptible advantage of higher resolution smartphone displays has not been exhausted, even at 1000 PPI.

Figure 2: Interview results: Ranked data (8 C worst, 1, best) showing how subjects perceived the benefit of increased resolution across different image types for a) aliased images, b) anti-aliased images.

The new frontier: 1080p and beyond
Certainly the difference in rankings between the two highest resolutions was not as great as for the lower pixel densities. But the ramifications for future screen development are clear: many consumers can and do perceive differences in resolution far beyond even the latest 440 PPI, 1080p smartphone displays.

To give device manufacturers a visible edge, Sharp has focused considerable resources on pioneering screen technology. Our new IGZO displays make higher resolutions possible while providing efficiency and brilliance. These advances put longer battery life and more immersive experiences within reach for manufacturers.

So no matter how poor your eyesight, one thing is clear: we have yet to see the end of display technology advances in the mobile sector. The enhanced resolution of the next generation of display technology will not be lost on consumers, no matter which way you look at it.

About the author
Lee Spencer is Senior Project Manager at Sharp Devices Europe and a Lead Engineer for LCD solutions.

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