RGB colour encodings (colour spaces)
Image courtesy of Jegsworks
RGB – or red, green and blue – colour encodings are used by most multimedia equipment to communicate colour, such as computer screens, digital cameras, scanners, and consumer and office printers. These devices need standard colour encodings for open, unambiguous, and reliable data exchange. IEC work in this area defines standard RGB encodings, which enable the unambiguous communication of colour information.
IEC 61966-2-1 specifies the default RGB colour encoding – sRGB – which specifies the colours produced by sRGB digital values on a reference CRT display. Colors encoded as sRGB should represent the desired appearance on the reference display when viewed in the reference viewing conditions. Source devices are required to perform any conversions necessary to produce sRGB image data. Receiving devices interpret sRGB image data as the desired appearance on the reference display, and perform conversions as necessary to produce reproductions. Such conversions may involve color space conversions, and color re-rendering of the image to optimize it for reproduction media different from the reference display.
IEC 61966-2-2 specifies the scRGB colour encoding, which is an extended dynamic range, extended gamut colour encoding for scene colors. It is based on the same ITU-R BT.709 HDTV RGB primaries as sRGB, so that simple tone curve color rendering is an option when converting scRGB image data to sRGB.
IEC 61966-5 specifies a colour image encoding similar to the sRGB encoding, but based on a wider gamut colour space than sRGB. A display that has a colour gamut wider than conventional displays has been selected as the “Reference image display system characteristics” in this standard. These wider colour gamut displays provide advantages in commercial printing industry workflows and are intended to be used by professional photographers, prepress industry including DTP and designers.
Luminance-chrominance (YCC) transformations are also provided for both the sRGB and scRGB color encodings.