Subpixel rendering

Subpixel rendering is a method used to increase the effective resolution of a color display device.

Microsoft's patent describes the smallest filter possible that distributes each subpixel value to an equal amount of R,G, and B pixels.

[4] A single pixel on a color display is made of several subpixels, typically three arranged left-to-right as red, green, and blue (RGB).

Steve Gibson has claimed that the Apple II, introduced in 1977, supports an early form of subpixel rendering in its high-resolution (280×192) graphics mode.

Color is instead created as an artifact of the NTSC color encoding scheme, determined by horizontal position: pixels with even horizontal coordinates are always purple (or blue, if the flag bit is set), and odd pixels are always green (or orange).

The flag bit in each byte affects color by shifting pixels half a pixel-width to the right.

)[10] FreeType, the library used by most current software on the X Window System, contains two open source implementations.

The original implementation uses the ClearType antialiasing filters and carries the following notice: "The colour filtering algorithm of Microsoft's ClearType technology for subpixel rendering is covered by patents; for this reason the corresponding code in FreeType is disabled by default.

Note that subpixel rendering per se is prior art; using a different colour filter thus easily circumvents Microsoft's patent claims.

[11] Since version 2.8.1, a second implementation exists, called Harmony, that "offers high quality LCD-optimized output without resorting to ClearType techniques of resolution tripling and filtering".

Adobe created their own subpixel renderer called CoolType, allowing them to display documents the same way across various operating systems: Windows, MacOS, Linux etc.