Display Analysis: The Diamond PenTile Problem

While capable of brilliant images with rich color and the inky blacks only found on OLED-based display panels, I have one major complaint with the Pixel's screen – but it took me some time to be able to define it (and then come up with an argument that supports my impression): Text on this display looks ever so slightly smudged. But why?

The Pixel's AMOLED panel uses what is known as a PenTile layout; a pattern where some of the subpixels are shared, so actual RGB resolution is lower than the rated 1080×1920 if you are comparing to the RGB stripe layout of LCD displays. This sub-pixel layout creates (to this purist, anyway) a worst-case scenario for text clarity at all but the highest resolutions – particulary as all subpixels in this particular display panel are diamond-shaped. Does this sound too harsh? Here is an example from Chipworks, from their look at the Galaxy S5 (the first phone to feature this Samsung display type):

All subpixels are diamond shaped in this PenTile arrangment (Image credit: Chipworks)

In addition to the diamond shape there are simply fewer overall sub-pixels in this arrangement, as not every pixel has its own red, green, and blue subpixel. Another issue for text clarity in particular is that all of these subpixels are positioned at a 45-degree angle. Why does this matter? Text is read horizontally, of course, and standard RGB sub-pixel font smoothing (as found on RGB stripe panels) does not take advantage of this diamond pattern. Here is the Pixel's display up close:

And now an even closer macro shot:

As you see in the photos of the Pixel’s display, text looks rather blurry, with some odd coloration around the edges of some of the letters. This is not the result of chromatic aberration from my camera's lens, as the font smoothing is actually creating these purple and green edges. This is somewhat inconsistent due to the hit-or-miss nature of a shared pixel arrangement like this (particularly a diamond PenTile matrix one), so not every edge is as blurry or discolored. 

I will quickly add a photo of the iPhone 7’s display to show how sub-pixel font smoothing looks on an IPS screen with a standard RGB stripe pattern:

Much better, and this 4.7-inch iPhone has a very low resolution (IPS LCD) display by Android phone standards, with Apple sticking to their bizarre 750×1334 resolution. From the looks of it in person, they aren’t really wrong to do so as text is quite crisp from a normal viewing distance (even though it looks a little blocky in the macro shot above).

I do not dismiss the Pixel's panel technology out of hand, and the issues I have with the phone's display are, in my estimation, related mainly to pixel density. As fickle as I am with smartphones (with most lasting less than six months as I jump ship to the next 'best' thing constantly) I retained a Nexus 6 longer than any other phone in recent memory (still have one, in fact), and its excellent AMOLED display was one strong reason. Yes, even a PenTile subpixel arrangement is quite good for text clarity and overall sharpness if the panel is of sufficient density, and with the Nexus 6 its 1440×2560 resolution – even though it was spread over a 6-inch panel – was sharper. I can't help but think that QHD would be the sweet spot for a 5-inch display, but even the 5.5-inch (IPS LCD) iPhone 7 Plus looks quite good at FHD.

The Pixel XL offers QHD resolution, and should be appreciably better than the standard Pixel in overall display clarity as a result. In short, my theory about display technology and its relationship to resolution is that with an RGB stripe layout (standard with LCD panels) text will appear much sharper at lower resolutions, and AMOLED panels (and this Samsung diamond-shaped PenTile matrix design in particular) seem to need additional resolution to really match IPS LCD for clarity and sharpness.

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