"Resolutions" for the New Year

Happy New Year!

This post is not going to be about the "less coffee; more exercise" type of resolutions for the new year. Instead, let's discuss display resolutions and how they are shaping up for 2014.

A few years ago, Apple introduced the "Retina Display" as a marketing term. The thought was that the resolution of the display is so high that when held in the typical viewing distance, the pixel density is practically as high as can be distinguished by the naked eye, and thus increasing the resolution for that viewing distance won't generate any benefits.

Let's run through the numbers. 25cm (10 inches) is considered to be closest comfortable viewing distance for most people. The visual acuity of the eye - assuming 20/20 vision - is considered to be 1 arcmin/pixel or approximately 60 pixels per degree. At a distance of 25 cm, 1 degree takes up 25*tan(1 degree) or about 0.44 cm. Thus, if 60 pixels take up 0.44 cm, 1 inch would require 60*2.54/0.44 = 346 pixels/inch, sometimes referred to as 346 DPI (dots per inch) or PPI (pixels per inch) at this distance of 25 cm . Indeed, Apple has 326 DPI in the iPhone 4, so pretty close.

Some have argued that Apple's claim is misleading and that a display needs to have at 477 DPI to truly have eye-limiting resolution. So, when new 5" 1080p flat panel displays - such as those from Sharp - came with 433 DPI, that should have been nearly enough, right?

Now, we are hearing about 538 DPI flat-panel screens, 2560x1440 resolution, that are coming out in smartphone or small tablet form factor. Where are all these people that can tell apart 443 DPI but can't tell apart 538 DPI? Other than the "my display has more pixels than your display" claim, is there really a tangible benefit for phones to have higher and higher DPI?

If you make goggles that use smartphone displays, you love these higher display resolutions. Goggles magnify displays so when a 1080p display gets magnified to - for the sake of examples - 90 degrees wide, the pixel density is 1920/90=21.3 pixels/degree, so still far from eye-limiting. a 2560x1440 display magnified the same way will produce 28.4 pixels/degree, providing a tangible improvement. To get to eye-limiting resolution at 90 degrees, you'd need a screen that is physically small enough to be worn on the head yet has 5400 pixels across. Good luck finding the GPU that can drive interactive content for that display!

Several years ago, my company developed the xSight HMD which used a unique optical tiling system to combine multiple 800x600 OLED displays into one large virtual display that had about 1920x1080 pixels. Today, similar performance can be achieved without tiling.

Thus, as long as goggle makers can ride the smartphone wave, they can get better and better resolutions, but since even 2560x1440 sounds like somewhat of an overkill, what's next? Will the next-generation goggles continue to use flat panel displays or will they gravitate towards other technologies?

It should be a fascinating 2014. Happy New Year!