Subpixel rendering

Subpixel rendering is a way to increase the apparent resolution of a computer's liquid crystal display (LCD) or organic light-emitting diode (OLED) display by rendering pixels to take into account the screen type's physical properties. It takes advantage of the fact that each pixel on a color LCD is actually composed of individual red, green, and blue or other color subpixels to anti-alias text with greater detail or to increase the resolution of all image types on layouts which are specifically designed to be compatible with subpixel rendering.Under the current US regime, any minor improvement to a previous technique can be considered an 'invention' and 'protected' by a patent under the right circumstances (e.g. if it's not totally trivial), If we look at , we see that the Apple II Wozniak patent covering this machine's display technique is listed first in the patents' citations. This shows that both Microsoft and the patent examiner who granted the patents were aware of this 'prior art'.Lower case eLower case isLower case wLower case eLower case isLower case wClear Type activated on a TFTNo subpixel rendering on a TFTA subpixel accurate gradient. Subpixel rendering is a way to increase the apparent resolution of a computer's liquid crystal display (LCD) or organic light-emitting diode (OLED) display by rendering pixels to take into account the screen type's physical properties. It takes advantage of the fact that each pixel on a color LCD is actually composed of individual red, green, and blue or other color subpixels to anti-alias text with greater detail or to increase the resolution of all image types on layouts which are specifically designed to be compatible with subpixel rendering. A single pixel on a color subpixelated display is made of several color primaries, typically three colored elements—ordered (on various displays) either as blue, green, and red (BGR), or as red, green, and blue (RGB). Some displays have more than three primaries, often called MultiPrimary, such as the combination of red, green, blue, and yellow (RGBY), or red, green, blue and white (RGBW), or even red, green, blue, yellow, and cyan (RGBYC). These pixel components, sometimes called subpixels, appear as a single color to the human eye because of blurring by the optics and spatial integration by nerve cells in the eye. The components are easily visible, however, when viewed with a small magnifying glass, such as a loupe. Over a certain resolution threshold the colors in the subpixels are not visible, but the relative intensity of the components shifts the apparent position or orientation of a line. Subpixel rendering is better suited to some display technologies than others. The technology is well-suited to LCDs and other technologies where each logical pixel corresponds directly to three or more independent colored subpixels, but less so for CRTs. In a CRT the light from the pixel components often spreads across pixels, and the outputs of adjacent pixels are not perfectly independent. If a designer knew precisely about the display's electron beams and aperture grille, subpixel rendering might have some advantage. But the properties of the CRT components, coupled with the alignment variations that are part of the production process, make subpixel rendering less effective for these displays. The technique should have good application to organic light emitting diodes (OLED) and other display technologies that organize pixels the same way as LCDs. The origin of subpixel rendering as used today remains controversial. Apple, then IBM, and finally Microsoft patented various implementations with certain technical differences owing to the different purposes their technologies were intended for. Microsoft has several patents in the United States on subpixel rendering technology for text rendering on RGB Stripe layouts. The patents 6,219,025, 6,239,783, 6,307,566, 6,225,973, 6,243,070, 6,393,145, 6,421,054, 6,282,327, 6,624,828 were filed between 1998-10-07 and 1999-10-07, thus should expire in 2019-10-07. Analysis by FreeType of the patent indicates that the idea of subpixel rendering is not covered by the patent, but the actual filter used as a last step to balance the color is. However Microsoft's patent describes the smallest filter possible that distributes each subpixel value to an equal amount of R,G, and B pixels. Any other filter will either be blurrier or will introduce color artifacts. It has been proposed for open source to use a '2-pixel' subpixel rendering, where G is one subpixel, and the R and B of two adjacent pixels are combined into a 'purple subpixel', to avoid the Microsoft patent. This has the claimed advantage of a more equal perceived brightness of the two subpixels, somewhat easier power-of-2 math, and a sharper filter. However it only produces 2/3 the resulting resolution.