C

Caustics : The concentrated light reflections caused by refraction through a transparent surface.
Channel : An image component that contains the pixel information for an individual color. A grayscale image has one color channel, an RGB image has three color channels, and a CMYK image has four color channels.
Chroma : (1) A characterization of how much a color differs from both the pure color and the grey of the same intensity. Also called saturation.
(2) The color component of a composite video signal.
(3) The quality of a color that is the combination of hue and brightness. In the Munsell system of color notation, chroma indicates the purity of a color as measured along an axis; the farther from the axis, the purer the color.

CMYK : (Cyan, Magenta, Yellow, and Black) The four-ink colors used in process printing. Cyan, magenta, and yellow are the three subtractive primaries. CMYK colors are simulated on a computer monitor using additive red, green, and blue light. To color separate an image from PhotoShop, convert it to CMYK Color mode.

Color Correction : The adjustment of color in an image to match original artwork or a photograph. Color correction is usually done in CMYK Color mode in preparation for process printing.
Color Keying/Chroma Keying : Using the pixel color of one image to designate that pixel data from another image should replace the first pixel's color. The first image might be a binary image, which would select regions of interest from the second image. Another use is in blue-screening, where an actor works against a blue background. In the output image, the blue pixels get replaced by another image. For example, a weather map can be placed behind the weather presenter who is actually standing in front of a blue screen.

Color Table : The color palette of up to 256 colors of an image in Indexed Color mode.
Compositing : The process of combining multiple images into a single image. Usually this is performed in films to make a computer graphics generated character appear on a previously filmed background. The term is also used in traditional photographic manipulation to refer to the process by which cel animation is recorded onto film under a rostrum camera. In film the 'mechanical' process is usually called matte photography (see color keying), and the process, when used in film sequences is ambiguously called traveling matte.
Compression : The process by which some of an image's data is either stored in patterns or eliminated in order to reduce the images file size.
Continuous-Tone Image : An image, such as a photograph, in which there are gradual transitions between shades or colors.
Contrast : The range of colors in an image. Increasing the contrast of a color palette makes different colors easier to distinguish, while reducing the contrast makes them appear washed out