AMOLED

As you know, I love new technology. But new technology for its own sake is only of limited interest. That's why I'm so confused at all the love people are giving to Samsung's Active Matrix Organic Light Emitting Diode display, as featured in the Samsung Galaxy S, HTC Nexus One, and HTC Incredible phones (among others.) OLED has a lot of promise: to me the biggest advantage is that it can use less power since it doesn't need a backlight. However, it has a lot of disadvantages, too. One of the biggest disadvantages is that the pixels of an OLED display can only shine for so long before they dim significantly. The blue OLED subpixels are especially prone to this, which is why the AMOLED display that is getting all the attention in the media uses the "Pentile" subpixel layout, as shown in the image to the right.

Traditionally, color displays have three equally sized subpixels per pixel, so that each pixel can display the same color range, blended between the three primary colors: red, green and blue. However, an OLED display which used a traditional subpixel layout would be handicapped because the blue subpixels would fade noticeably before the red and green subpixels, which means that over a year or so, your display would get increasingly yellow-gray, eventually losing the ability to show blue and white colors at all. To overcome this problem, the Pentile subpixel layout provides two kinds of pixels, a green + big red pixel, and a green + big blue pixel. If you look under the water droplet in the picture to the right, you'll see the small green subpixels all lined up, and the big blue and red subpixels alternating. Since the big blue pixel is twice as big as the green pixel, it can last twice as long without fading. This keeps the overall life of the display long, despite the limitations of OLED blue subpixels.

For viewing photos and television, this tradeoff is ok. You can't really notice the different flavors of subpixel, since the pixels are so small. However, for viewing text, this is unacceptable. I've ranted about bad applications of subpixel antialiasing before, but to recap: since text has lots of tiny, sharp lines that don't usually line up with the pixel grid, modern displays use subpixel antialiasing to give the illusion of sharp lines by slightly changing the colors of the boundary pixels of each letter, taking advantage of the fact that our eyes are more sensitive to brightness than color. Having the fringes of text colored slightly funky is better looking than having the text squished into a rigid pixel grid.

The Pentile layout defeats subpixel antialiasing, because the pixels are not the same, and because the subpixels are not the same size! This leads to horrible looking text: vertical edges of text are crenellated like the roof of a castle as the text rendering engine struggles with the Pentile display layout. This is really grating to look at.

Since I use my smartphone mostly for reading text, bad text rendering is completely unacceptable. I don't understand how Samsung can defend their current AMOLED display against the iPhone 4 display - the only thing I can say is that some people are just insensitive to visual detail. These are the same people that made Powerpoint equation rendering so ugly, and they probably watch 4:3 aspect ratio SDTV stretched on their 16:9 HDTVs because they don't notice that everyone and everything is now 33% fatter. It's fine that some people don't perceive visual details - live and let live. But if you're deaf, don't offer your services as a music critic.

Let's put the disparity in plain objective terms that everyone can understand. The new iPhone display has 960*640*3 subpixels, in a display of 5.65 in^2. The Samsung AMOLED in the Galaxy S has 800*400*2 subpixels, in a display of 7.06 in^2. This means that the subpixel density of the new iPhone display is THREE TIMES DENSER than the Samsung Galaxy S display. This has a huge impact on text rendering fidelity. I don't understand how you can just write off this 3x disparity as negligable.

And this is without going into AMOLED's very poor color fidelity and complete unreadability outdoors.

In summary, I'm really glad Apple is resisting the OLED buzzword campaign and sticking with an incredibly high resolution LCD screen for now, instead of jumping on a buzzword bandwagon. OLED is not quite ready for primetime, for anyone that cares about how text looks.

PS. Apple calls their display a "Retina display". This is a buzzword fail on their part, since the resolution of the iPhone display is still not as fine as the retina can perceive.

More on the Pentile display
More on Samsung's claims that AMOLED is better than LCD

PPS. Anandtech did a nice comparison between the Droid's LCD, which has 2/3rds the pixels of the new iPhone, and the AMOLED from Samsung in the HTC Incredible. Take a look at this image from Google maps and tell me which you prefer. Now imagine the LCD with 50% more pixels in the same area - that's what the new iPhone display will give. Samsung marketing, you are just crazy.