~/imallett (Ian Mallett)

# Subpixel Zoo

## A Catalog of Subpixel Geometry

### Introduction and Definitions

Pixels are in-reality not magical little squares that have a color associated with them.

For displays, the color needs to be represented by discrete "subpixel"s (usually but not always three: some kind of red, green, or blue). The perceived color is then the addition of the subpixels' emissions.

Sensors in the photography and display world are made of little elements called "sensel"s or "photosite"s. These sensels may have color filters over them, limiting what wavelengths of light they respond to. As far as I can tell, an arrangements of sensels is called a "color filter array" (CFA), and when the arrangement is of red, green, and blue filters, the CFA is called a "Bayer filter" (pronounced [ˈba͡ɪ̯ˌəɹ]: BYE-er). This usage is sometimes inconsistent in the real-world, with non-Bayer CFAs erroneously being called Bayer.

In some cases, CFA sensels are similar to subpixels: detecting the colors that will later be emitted. In other cases, demosaicing algorithms are used to reconstruct full color values over each sensel by using information from neighboring sensels. In this case, the sensels serve the function of (and are called) "pixel"s. When researching a given arrangement, it is usually difficult to determine which of the two options was intended. In this document, I'll use the display-centric "subpixel" terminology.

Working in graphics (where knowing the particulars of such things is sometimes important) has brought my attention to the fact that there are a huge number of arrangements of subpixels and, shocked to find that there is no centrally located database of subpixels, I decided to categorize and name them myself. This page intends to exhaustively list all subpixel geometries that are used in-practice. They are drawn procedurally by the same program, with an outline describing each pixel (in some cases, multiple pixels must be outlined to show a tileable pattern). Click on any for a larger image. Relevant links and common products are also provided for some patterns.

If you have verifiable evidence (e.g. a close-up picture) of a screen with a subpixel geometry not listed here, or spot an error, please contact me to let me know! You can also help contribute by adding new (or not implemented) geometries to the program.

### Square Geometries

Name Geometry Notes Known Products References
Basic The model most people think of for pixels: a small square where the color is represented everywhere. Incorrect, since no display technology actually does this. Provided for completeness.
RGB Arrangement with three subpixels per pixel. Most common type of LCD monitor.
BGR Same as RGB, except horizontally reversed.
Alternating RBG Reverses red and green every other row, with blue apparently sandwiched in the middle. Hard to tell which way the first pixel is, whether blue is in the middle, and indeed whether any such arrangement is used in real products.
Chevron RGB Same as RGB, but subpixels are chevron-shaped, presumably to widen useful area.
• Dell TFT LCD 1905FP
Quattron RGBY Adds a yellow subpixel to better display yellows.
• "AQUOS XU" series TVs
VRGB Same as RGB, except rotated.
VBGR Same as RGB, except rotated (the other way).
• Sony R510C
• Sony W650D
• Steam Deck
RGGB Arrangement with four subpixels per pixel. Two green subpixels, since green is most perceptually important. Note: the same as Bayer GRBG, but shifted a half pixel.
BGBR Arrangement with three subpixels per pixel, with the blue subpixel being elongated.
• Samsung Galaxy Note II
Shift BRBG Similar to BGBR, except the blue subpixel shifts and the red/green subpixels are swapped.
• Samsung Galaxy Tab S 10.5
Alternating BGBR Same as BGBR, except the pattern flips horizontally (or shifts) every row.
Alternating PenTile RGWRGB Strange filter used in some cameras.
• Samsung Galaxy (Camera)
Alternating PenTile RGBW Classic PenTile matrix. Allows for finer resolution at the expense of making each pixel only able to represent two colors.
Alternating PenTile RGBG Another PenTile matrix, without using white.
• Samsung Galaxy S3
• Samsung Galaxy Nexus
• (Many More)
Diagonal PenTile GRGB A diagonal version of pentile.
• Samsung Galaxy Note 3
Rotated Triangles A diamond blue pixel bordered by four triangles. This may just be a prototypical PenTile pattern.
XO-1 LCD Arrangement used by the OLPC XO-1. Note: pixel sizings may be inaccurate, but this suggests each pixel is "sub-sampled by three".
GRBG (Bayer Filter) Note: the same as RGGB, but shifted a half pixel.
WRBG (CFA) WRBG components arranged in a 2x2 square.
CRBG (CFA) Similar to GRBG (Bayer) by with one of the primaries replaced by cyan ("emerald").
CYGM (CFA) Arrangement using different primaries. The advantage is higher quantum efficiency of the filters. The disadvantage is loss of color fidelity.
CYYM (CFA) Another arrangement. See CYGM (Bayer).
Kodak RGBW 4a (CFA) RGBW components arranged in a 4x4 square. Filter supposedly used by Kodak. Note: pixel sizes may be off; source poor.
Kodak RGBW 4b (CFA) RGBW components arranged in a 4x4 square. Filter supposedly used by Kodak. Note: pixel sizes may be off; source poor.
Kodak RGBW 4c (CFA) RGBW components arranged in a 4x4 square. Filter supposedly used by Kodak. Note: pixel sizes may be off; source poor.
Fujifilm X-Trans (Bayer Filter) Arrangement claimed to be more resistant to Moire patterns.
Fujifilm RGGB EXR (Bayer Filter) Filter with color channels arranged in stripes. Pixels can be defined as the combination of adjacent photosites, or as overlapping RGGB filters. See reference.

### Triangular Geometries

Some geometries cannot be described by square symmetry, and must be described by triangular symmetry. These were common for color cathode ray tube (CRT) displays, and have since made a resurgence in mobile device OLED displays.

The most immediate concern is how the 2D square grid of the pixel data maps onto the non-square display. I haven't found anyone willing to say definitively what happens, but probably it's done by resampling, explicitly or implicitly—not by e.g. shifting alternate rows of the grid and squashing. Evidence in favor of this is the claim that CRT monitors are inherently multisync, and have no native resolution, as well as my own experiments on PenTile displays which showed that neighboring pixels can contribute to the same subpixel.

Let's look at CRTs for an example. Color CRT displays work by sending three electron beams toward a triangular grid of holes. After the beams pass through a hole, they spread out slightly, to land on one of three phosphors (see diagram). It is tempting to think of these triangular clusters as "pixel"s, but in reality, as far as I can tell, the pixels still come from a rectangular scan of the beams. In particular, one image pixel might cover multiple, one, or less than one phosphor clusters—there is not a simple relationship between them. Each beam can only hit the correct color phosphor, but other than that, the difference between the rectangular image and the triangular subpixels is ignored (which we can interpret as resampling).

Name Geometry Notes Known Products References
Horizontal Column Dot Triangular grid of phosphors. CRT examples tend to be perfect circles.
• RG280M (?)
Vertical Column Dot Triangular grid of phosphors.
Vertical Column Horizontal RGB Triangular grid of pixels that can be thought of as shifting alternate columns of a rectangular grid. Each cell then has three vertical RGB elements like basic RGB. The cell size can vary as well; e.g. the Wikipedia example has shorter cells.