YJK
YJK is a proprietary color space implemented by the Yamaha V9958 graphic chip on MSX2+ computers. It has the advantage of encoding images by implementing less resolution for color information than for brightness, taking advantage of the human visual systems' lower acuity for color differences. This saves memory, transmission and computing power. YJK is composed of three components: , and . is similar to luminance (but computed differently), and are the chrominance components (representing the red and green color differences). The component is a 5-bit value (0 to 31), specified for each individual pixel. The and components are stored together in 6 bits (-32 to 31) and shared between 4 nearby pixels (4:2:0 chroma sub-sampling). While conceptually similar to YUV, chroma sampling, numerical relationship between the components, and transformation to and from RGB are different in YJK. (Wikipedia).
