When Samsung launched the GS4, they said the Super AMOLED display uses PenTile. Back in January, it was reported that Samsung will adopt a new subpixel scheme that uses diamond sub-pixels, but up until now we didn't hear anything official from Samsung. Today the company finally did acknowledge the new design, and published two closeup photos of the GS4 display.
Diamond Pixel, as Samsung's calls their new design, is a PenTile subpixel scheme, in which there are twice as many green subpixels as there are blue and red ones. The green subpixels are oval and small while the red and blue ones are diamond-shaped and larger (the blue subpixel is slightly larger than the red one). DisplayMate says that this is because green is the most efficient (and long lasting) OLED emitter while the blue has the shortest lifetime.
According to DisplayMate, the diamond shapes were chosen to maximize the sub-pixel packing and achieve the highest possible PPI (the GS4's OLED has 441 PPI). The greens are oval because they are squeezed between the larger red and blue ones. In any case, reviews of this display has been terrific, so this design seems to be a very good one.