YCC color space

All scanners scan images with red, green and blue filters. Photo CD scanners are not exceptions to this rule. Kodak Photo CD scanners use what is known as a trilinear array, actually three linear CCD (charge-coupled device) arrays lined up next to one another. As the sensor "sees" the image, it is actually recording the three requisite colors through its embedded filters.

Once the scan is made, the data, comprised of hexadecimal (base 16) numbers in three streams from the CCD sensor array, is quickly transformed from the raw red, green and blue data into three color components named Y. C and C and passed over a cable to the Data Manager, a Sun Sparcstation computer that is the brains of the operation .

YCC is a distant relative of a system developed by the broadcast television industry in the early 1950s. At that time the broadcasters were faced with the dilemma of how to send a color picture to millions of black-and-white television owners - while simultaneously making it possible for those with new color sets to receive the same signal - in color. Broadcast television developed an encoding technique called YIQ which is comprised of a black-and-white signal (Y) and two color, or chroma (I and Q) channels that describe the mathematical color coordinates of the color in the image. Kodak's Photo YCC color space is based on the same principle, but with a broader range of mathematical values - thus more room to describe colors and luminance values than a television signal can describe.

Kodak's adoption of YCC makes scanned Photo CD images readily available to television, but also allows for a commodious color space inside of which any image can be recorded without running into the mathematical limits of the space. Think of this color space as an envelope roughly the shape of two pyramids that share the same base surface (hue, or chrominance). The YCC pyramid is larger than the smaller pyramid inside it, which approximately represents the color space of display RGB.

The extra space between the smaller pyramid and the larger is a buffer to accommodate brightness ranges beyond anything that can be seen by the human eye, but which might be recorded on film or recorded by some future imaging technology.

YCC color space can be converted to any of several other color spaces with some reshaping of the mathematical values. One could convert from YCC to CIELAB space with very little loss of image information except those components of YCC that might exceed LAB's brightness values.

The YCC space can also be converted easily, but with some mathematical loss, to the monitor color space, which can be called explant RGB (red, green, blue), and once converted to RGB subsequently converted to the four colors needed for printing - cyan, magenta, yellow and black. It is also possible to convert directly from YCC to CMYK in one pass using a variety of software products.

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