YJK

YJK^[1][2][3] is a proprietary color space implemented by the Yamaha V9958^[4][5][6] graphic chip on MSX2+ computers.^[7][8] 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.^[9] This saves memory, transmission and computing power.

YJK is composed of three components: ${\displaystyle Y}$, ${\displaystyle J}$ and ${\displaystyle K}$. ${\displaystyle Y}$ is similar to luminance (but computed differently), ${\displaystyle J}$ and ${\displaystyle K}$ are the chrominance components (representing the red and green color differences). The ${\displaystyle Y}$ component is a 5-bit value (0 to 31), specified for each individual pixel.

The ${\displaystyle J}$ and ${\displaystyle K}$ components are stored together in 6 bits (-32 to 31) and shared between 4 nearby pixels (4:2:0 chroma sub-sampling).^[10][11][12]

This arrangement allows for the encoding of 19,268 different colors.^[10][11][12]

While conceptually similar to YUV, chroma sampling, numerical relationship between the components, and transformation to and from RGB are different in YJK.