Nexus One PenTile Matrix OLED Display

Miahi Preda at Mihai Mobile wrote an interesting piece titled, Nexus One display and subpixel pattern. What is so interesting? It highlights the sub-pixel format of the OLED display used in the Nexus One. The sub-pixel format is called PenTile Matrix and is manufactured by Samsung using the technology from Clairvoyante, a company that Samsung purchased not too long ago. The PenTile Matrix is a 2×2 sub-pixel structure and is different from the usual 3×1 sub-pixel structure of a typical display. The 2×2 sub-pixel structure was used for two main purposes.

Aging: First OLED phosphors continue to exhibit differential aging with the blue aging most quickly. The blue sub-pixel (as well as the red) takes up a larger area than the green. With a larger area the blue sub-pixel does not need to be driven with as much current to generate the brightness levels needed. And because it isn’t driven as hard it doesn’t age as fast. I’m not certain why red has such a large area.

Second the 2×2 sub-pixel structure allows for less complicated driver ICs. Simpler driver ICs mean less cost but it also means less power.

800×480? Technically the 800×480 “resolution” on the Nexus One OLED display is incorrect. I tend not to use the term resolution as it refers to density and not a format. I prefer to use the phrase “pixel format” to make sure that readers know what I am referring to. For instance, 100 ppi (pixels per inch) would be referring to the resolution of a display. On the other hand 1920×1080 would be pointing to the pixel format of the display. So back to the Nexus One.

The PenTile Matrix sub-pixel structure on the OLED display used in the Nexus One certainly does not have a 800×480 pixel format. I’m actually unsure as to what the pixel format is, but a simple calculation by a non-math major yields a pixel format equivalent of 533×480 based on the standard assumption that a pixel is composed of a 3 x 1 sub-pixel structure. That’s because each 4 pixel cluster in a PenTile Matrix has 8 sub-pixels going across and 4 sub-pixels going down. A regular 3×1 sub-pixel pixel has 12 sub-pixels going across and 4 down. But that’s sub-pixels.

Update 2010.02.23: I had the pleasure of meeting Candice Brown Elliott, Founder and CEO of Nouvoyance, Joel Pollack, Sr. VP of Strategic Sales and Marketing, and Tony Botzas, Director of System Apps and Engineering on February 3rd. I came out of the 2 1/2-hour meeting impressed and convinced that the 3.7-inch PenTile Matrix OLED display used in the Nexus One does indeed have a resolution that is equivalent to a 3.7-inch TFT LCD with a 800×480 pixel format using red, green, blue 3×1 striped sub-pixels. Read Display Showdown Part Ia: Nexus One for more information.

Resolution: I’ve spoken several times with Joel Pollack, Senior VP of Strategic Sales and Marketing at Nouvoyance, which was Clairvoyante prior to its acquisition by Samsung, and what I get from Joel is this: what is important is what the eyes see not the hardware sub-pixel structure. According to Clairvoyante at the time and now Nouvoyance, the resolution (and this is why making the distinction between resolution and pixel format becomes all the more important) is equivalent to a 800×480 pixel format display with a 3×1 sub-pixel structure. That means even though the PenTile Matrix OLED display has less sub-pixels it looks like it has the same number of sub-pixels as a typical 3×1 sub-pixel format LCD. But does it really?

I’m not 100% convinced that you can get the same visual resolution with less sub-pixels. It is interesting to see a comment on Mihai Mobile by a user named Bergamot:

That explains why the Nexus screen seemed visibly “dotty” in a way I’ve never seen an LCD look.

With less sub-pixels I am not surprised that a keen set of eyes sense a difference between the PenTile OLED display and a typical LCD. I have not seen the OLED display on a Nexus One for myself (at the time of this writing) but I would be very surprised if I didn’t feel the dotty-ness as well. As far as I know almost all Samsung smartphones with an OLED display sporting a 800 x 480 “resolution” makes use of the PenTile Matrix 2×2 sub-pixel structure.

Daring Fireball’s John Gruber:

In short, I love the pixel density and brightness (and, so far, the battery life), but I do not like the color reproduction.

I won’t get into a discussion regarding color reproduction here but it is interesting John notes the pixel density. Hopefully I’ve laid out a fairly clear argument that explains the PenTile Matrix OLED used in the Nexus One has less resolution, ergo less pixel density, compared to a LCD with a 800 x 480 pixel format using a 3×1 sub-pixel format.

We might be at a crossroads. 800×480: what does that mean? In light of different sub-pixel structures, 800×480 means almost nothing unless you get a bit more technical and show how the sub-pixels are arranged. Maybe it is time we shift our focus from technical specifications to actual experience. But then we would want to quantify the quality of our experience, wouldn’t we.