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Color conversion is the process of converting colors from one color space to another. Color matching , which entails color conversion, is the process of selecting colors from the destination gamut that most closely approximate the colors from the source image. Color matching always involves color conversion, whereas color conversion may not entail color matching. Rendering intent refers to the approach taken when a CMM maps or translates the colors of an image to the color gamut of a destination device--that is, a rendering intent specifies a gamut-matching strategy.
Different imaging devices (scanners, displays, printers) work in different color spaces and each is capable of producing a different range of colors. Although color displays from different manufacturers all use RGB colors, each will typically have a different RGB gamut. Printers that work in CMYK space vary drastically in their gamuts, especially if they use different printing technologies. Even a single printer's gamut can vary significantly with the ink or type of paper it uses. It's easy to see that conversion from RGB colors on an individual display to CMYK colors on an individual printer using a particular paper type can lead to unpredictable results.
When an image is output to a particular device, the device displays only those colors that are within its gamut. Likewise, when an image is created by scanning, all colors from the original image are reduced to the colors within the scanner's gamut. Devices with different gamuts cannot reproduce each other's colors exactly, but careful shifting of the colors used on one device can improve the visual match when the image is displayed on another.
Figure 1-7 Color gamuts for two devices expressed in Yxy space
Figure 1-7 shows examples of two devices' color gamuts, projected onto Yxy space. Both devices produce less than the total possible range of colors, and the printer gamut is restricted to a significantly smaller range than the RGB gamut. The problem illustrated by Figure 1-7 is to display the same image on both devices with a minimum of visual mismatch. The solution to the problem is to match the colors of the image using profiles for both devices and one or more color management modules. A profile is a structure that provides a means of defining the color characteristics of a given device in a particular state. For more information, see Profiles .