PenTile OLED Screens

About two weeks ago, I finally got around to picking up a Windows Phone 7 phone. After first turning on my new Samsung Omnia 7, my immediate reaction was «crap, I got one with a broken screen!»

Except the screen isn’t broken, at least not in a technical sense. Turns out, there’s a class of OLED screens that use a strange subpixel arrangement called PenTile RGBG. According to Wikipedia, the subpixels on a regular LCD screen are arranged like this:

On a PenTile screen, each pixel only has two subpixels, arranged like this:

While this apparently has some advantages (like a longer lifespan), it has one huge disadvantage: if you have reasonably good eyesight, you can see subpixel rendering artefacts. In other words, a lot of things just don’t look right.

For example, red text on a black background looks like only every other pixel is turned on; this makes straight lines look ragged. Letters look serrated; the letter «S» looks as if it had two little horns sticking out at the top. Solid red areas look like tiny checkerboards. The same applies to blue things, although the effect is less obvious. Straight white lines look like dashed lines. Grey things sometimes look fuzzy.

(Larger version of this image)

It’s kind of hard to believe that, almost a year after Apple’s iPhone 4 basically made individual pixels invisible, a display like this is still considered acceptable.

If you’re designing user interfaces that might be shown on a PenTile device, be sure to test how they actually look. Some combinations of colors just don’t work on these screens.

If you’re considering picking up a device with a PenTile screen, you probably want to look at it in person before buying. Make sure you’re okay with how these things look.

There’s a good article about these displays over at Ars Technica.

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