PenTile

PenTile is a family of subpixel matrix layouts for electronic displays in which adjacent pixels share subpixels, so that a panel uses fewer subpixels than the conventional RGB stripe arrangement while keeping the same nominal pixel resolution. The name and the underlying patents are a trademark of Samsung. The most common form is the RGBG layout, which has one green subpixel per pixel but only half a red and half a blue subpixel, with the red and blue shared between neighbouring pixels; this gives roughly one third fewer subpixels than an RGB stripe panel of the same resolution.

PenTile is widely used in OLED panels, including those built for virtual reality head-mounted displays. Because the layout reduces the number of independently lit color elements, it is associated with a lower effective resolution and a more visible screen door effect than an RGB stripe panel at the same pixel count, a trade-off that has shaped the choice of displays in several VR products such as the Samsung Gear VR, the Samsung Odyssey Plus, and the PlayStation VR2.

Origin

The PenTile subpixel layouts were developed by Candice H. Brown Elliott in the early 1990s and were licensed by her company Clairvoyante, Inc. from 2000 to 2008. In March 2008 Samsung Electronics acquired Clairvoyante's PenTile intellectual property and continued development through a Samsung-funded entity, Nouvoyance. Brown Elliott received the Society for Information Display's Otto Schade Prize in 2014 for the development of PenTile subpixel rendering for high-resolution color displays.

The name "PenTile" is short for "pentile", a reference to the pentile (five-tile) geometric arrangement of subpixels in some of the early layouts.

How it works

A conventional display uses the RGB stripe arrangement, in which every pixel has its own red, green, and blue subpixel laid out as three equal vertical bars. PenTile instead shares subpixels between neighbouring pixels and uses a different count for each color.

Two layouts are common:

Layout	Subpixels per pixel	Description
RGBG (RGBG matrix)	2	Used in AMOLED panels. A full green subpixel is paired with alternating red and blue subpixels, so a green subpixel appears in every pixel but red and blue appear in only half. There are twice as many green subpixels as red or blue.
RGBW	4	Used in some LCDs. A clear (white) subpixel is added to red, green, and blue, letting more backlight through for a brighter image at the same power.

The reasoning behind doubling green and halving red and blue is that the human eye derives most of its luminance, and therefore most perceived sharpness, from the green channel, while it is far less sensitive to fine spatial detail in blue. The retina contains nearly equal numbers of long- and medium-wavelength cone cells but many fewer short-wavelength (blue) cones, so reducing the number of blue subpixels has little effect on perceived image quality. To reconstruct a full-color image from the reduced subpixel set, PenTile displays apply subpixel rendering, which distributes the intensity of each input pixel across the available neighbouring subpixels.

In 2013 Samsung introduced a refined RGBG variant, marketed as the Diamond Pixel array, first used in the Galaxy S4. In this arrangement the green subpixels are small and oval while the red and blue subpixels are larger and diamond shaped, again with twice as many green subpixels as red or blue.

Advantages

The reduced subpixel count gives PenTile OLED panels several practical benefits. Fewer subpixels mean lower power draw for a given resolution, and the layout is cheaper and easier to manufacture at high pixel densities than a full RGB stripe OLED. OLED-Info notes that Samsung uses PenTile in essentially all of its high-resolution Super AMOLED displays, generally above about 230 pixels per inch.

A further benefit is panel lifespan. OLED-Info notes that PenTile displays last longer, and the usual explanation is that blue OLED emitters degrade fastest of the three colors, so using fewer and larger blue subpixels, each driven less hard for the same brightness, extends the working life of the display relative to an RGB stripe OLED. As a result, PenTile became widely used in high-end OLED smartphones, and it is found in panels from several vendors beyond Samsung's own Super AMOLED screens.

Criticism

The main drawback of PenTile is that its true subpixel density is lower than its nominal pixel resolution implies. Because red and blue are present at half the rate of green, fine detail and saturated colored text can look grainy, speckled, or slightly blurred, and the gaps between subpixels are more noticeable than on an RGB stripe panel of the same resolution. Display analysts describe PenTile as having a lower effective resolution because of this subpixel grouping. When the Galaxy S III shipped with a PenTile RGBG display in 2012, the layout drew criticism in technology press and from users for visible pixelation compared with the RGB stripe screen of some rivals.

Relevance to virtual reality

The lower effective resolution of PenTile matters more in VR than in a phone or television, because a VR head-mounted display places a small panel a few centimeters from the eye and magnifies it through lenses across a wide field of view. At that magnification the unlit gaps between subpixels become visible as a grid, the artifact known as the screen door effect. An RGB stripe layout, with three full subpixels per pixel, produces a less visible screen door effect than a PenTile layout at the same pixel count, so a higher-resolution PenTile OLED can look softer than a lower-resolution RGB stripe LCD.

Several VR headsets have used PenTile OLED panels. Mobile headsets that reused smartphone-class AMOLED displays, such as the Samsung Gear VR, showed the screen door effect clearly because of both the magnification and the PenTile subpixel layout. The Samsung Odyssey Plus, released in 2018, kept the same 1440 by 1600 per-eye AMOLED resolution as the original Samsung Odyssey but added an "anti-screen-door-effect" diffuser that spreads the light from each pixel into the surrounding gaps, raising the perceived pixel density to about 1,233 pixels per inch and making the gaps far harder to see without increasing the actual resolution.

The PlayStation VR2, released by Sony in 2023, uses OLED panels with a per-eye resolution of 2000 by 2040 at 90 Hz or 120 Hz with HDR. Teardown analysis showed that its panels use a PenTile subpixel arrangement, with a full count of green subpixels but only half as many red and blue, in contrast to the RGB stripe OLED of the original PlayStation VR. The result is a slightly softer image, especially in red and blue detail, and Sony applied a diffusion coating to reduce the screen door effect at a small cost in sharpness.

By contrast, many standalone and PC headsets of the same era moved to LCD panels with an RGB stripe layout precisely to avoid PenTile's softness; examples cited by gHacks include the Meta Quest 2, Pico 4, and HTC Vive XR Elite, which pair around 2,000 by 2,000 pixels per eye with full RGB subpixels. At the high end, Micro-OLED panels used in the Apple Vision Pro and in Varjo headsets reach very small pixel pitch and near-complete fill factor, which largely removes the visible screen door effect regardless of subpixel scheme.

See also

• Screen door effect
• OLED
• Resolution
• Pixels per degree
• Pixel density