Thursday, October 31, 2013

Why curved smartphone screens massively increase image quality, daylight readability

Believe it or not, the curved screen on the Samsung Galaxy Round smartphone isn’t just a marketing gimmick: The curvature actually causes a series of optical effects that result in improved contrast, color accuracy, readability, and overall image quality — especially under ambient light that usually makes smartphone screens almost unreadable, such as daylight or fluorescent office lighting.

This new information about curved displays comes from Raymond Soneira, who is one of the few authorities on display technology, image quality, and color calibration. From the story on his site, it sounds like Samsung gave him a Galaxy Note 3, the Galaxy Round (which is the Note 3 but with a curved display), and a standalone, free-standing OLED display from the Round (which he could bend and flex to his heart’s content). While he hasn’t yet produced his usual slew of images and graphs, it’s clear that he’s very surprised by the massive gain in image quality afforded by the curved display.

For the most part, curved displays are better than their flat siblings due to drastically different reflectance. To begin with, hold your smartphone in front of you, with the screen off. If you’re outside or in the office, you will notice a huge amount of reflections — your face, overhead lighting, etc.

These reflections don’t go away when you turn the screen on; they are merely masked by the patterns displayed on the screen, and the brightness of the display. This is why image quality is generally so atrocious when there’s a lot of ambient light, and why display brightness is valued so highly. Manufacturers are making big strides in reducing reflectance — by introducing new filters, reducing the distance between the display and the protective front glass, etc. — but ultimately, a flat piece of black-backed glass is always going to be pretty reflective.

The Galaxy Round display is only slightly curved along the horizontal plane — the edges are 2.6mm (0.1 inches) higher than the center of the screen — but, believe it or not, this is enough to cause the same magnification as a convex hand mirror. This magnification (and the curvature in general) results in huge improvements almost across the board, from more saturation to better color accuracy and readability.

Most of these gains come from the magnification, which causes three important effects. First, by magnifying your face (by two or more, depending on your viewing distance), less light from behind your face is reflected by the display. Your face is usually shadowed, and doesn’t cause much reflection. Second, the magnification process also dims the reflection of your face (the light is being spread out by the magnification), resulting in less reflectance. Ironically, this also means it isn’t so easy to use a curved display for personal grooming. Finally, at a typical viewing distance of 16 inches (40 cm), the magnification factor is so large that your face becomes a featureless blur, again reducing the amount of noticeable/disruptive reflectance.

Beyond magnification, the simple fact that it’s a curved display means less non-direct light reflects of the screen — and any light from behind you that does hit the screen gets reflected away from your eyes (specular reflection).

All of these factors combine to create a display that, according to Soneira, is massively improved over the Galaxy Note 3 — which itself has a very highly regarded display. The reduced reflectance should also mean that display brightness can be reduced, increasing battery life, though it isn’t clear if the Galaxy Round does this. In fact, from the marketing materials, it isn’t even clear if Samsung is aware of the advantages of curved displays — though, following Soneira’s glowing analysis, the Korean chaebol surely knows now.


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