Inside Macintosh: Advanced Color Imaging on the Mac OS /

Glossary

absolute colorimetric matching A rendering intent that is used for a device-independent color space in which the result is an idealized print viewed on a perfect paper having a large dynamic range and color gamut. In reality, paper cannot reproduce densities less than a particular minimum density.

abstract profile A profile that allows applications to perform special color effects independent of the devices on which the effects are rendered.

additive color theory The process of mixing red, green, and blue lights, which are each approximately one-third of the visible spectrum. Additive color theory explains how red, green, and blue light can be added to make white light.

animated color A color that the Palette Manager uses for special animation effects. Animated colors work only on devices that have a color table; that is, they do not work on direct devices.

application-owned dialog box A dialog box, created by an application, for presenting a color picker.

brightness A term in color theory used to describe differences in the intensity of light reflected from or transmitted by a color image. The hue of an object may be blue, but the adjectives dark or light distinguish the brightness of one object from another. Compare with hue and saturation.

CIE-based color spaces Color spaces that allow color to be expressed in a device-independent way, unlike RGB colors, which vary with display, and scanner characteristics and CMYK colors, which vary with printer, ink, and paper characteristics. CIE-based color spaces result from work carried out in 1931 by the Commission Internationale d'Eclairage (CIE). These color spaces are also referred to as device-independent color spaces.

CMM See color management module.

color channel See color component.

color component A dimension of a color value expressed as a numeric value. For the ColorSync Manager, depending on the color space, a color value may consist of one, two, three, four, or eight components, also referred to as channels.

color-component value A value that represents the color of a component. Each component of a color space has a color-component value. A color-component value can vary from 0 to 65,535 (0xFFFF), although the numerical interpretation of that range is different for different color spaces. In most cases, color-component intensities are interpreted numerically as varying between 0 and 1.0. See also color space and color value.

color conversion The process of converting colors from one color space to another.

color gamut See gamut.

color management module A component, also referred to as a CMM, that carries out the actual color matching and gamut-checking processes based on requests resulting from calls a program makes to the ColorSync Manager API. An application or driver can supply its own CMM or it can use the robust default CMM that Apple supplies.

Color Manager A set of system software functions that supply color-selection support for Color QuickDraw. Most applications never need to call the Color Manager directly.

color matching The process of adjusting or matching converted colors appropriately to achieve maximum similarity from the gamut of one color space to the other. Color matching always involves color conversion, whereas color conversion may not entail color matching.

color picker Code, implemented as a component, that allows users to select a color from a range of possible colors.

Color Picker Manager A set of system software functions that provide applications with a standard user interface for soliciting color choices from users.

color picker-owned dialog box A dialog box, defined by a color picker, for presenting the color picker.

color space A model for representing color in terms of intensity values; a color space specifies how color information is represented. It defines a multidimensional space whose dimensions, or components, represent intensity values.

color space profile A profile that contains the data necessary to translate color values, such as CIE into RGB or RGB into CIE, as necessary for color matching. Color space profiles provide a convenient means for CMMs to convert between different nondevice profiles.

ColorSync Manager A set of system software functions that provide applications with device-independent color-matching and color conversion services.

color value A complete specification of a color in a given color space. Depending on the color space used, one, two, three, or four color-component values combine to make a color value.

courteous color A color that accepts whatever value the Color Manager determines is the closest match available in the color table. Compare tolerant color.

default system profile The system profile for the display device that the ColorSync Manager includes and uses unless the user selects a different system profile through the ColorSync Manager control panel.

destination profile The profile that describes the characteristics of the output device for which the image is destined. The profile is used to color match the image to the device's gamut.

device-independent color spaces See CIE-based color spaces.

device-linked profile A profile that combines multiple profiles, such as various device profiles associated with the creation and editing of an image.

device profile A structure that provides a means of defining the color characteristics of a given device in a particular state.

event forecasters Warnings sent by an application to a color picker about user actions that might adversely affect the color picker.

explicit color A color that specifies an index value in the devices color table rather than an RGB color.

gamut The range of color that a device can produce, also referred to as the device's color gamut.

HLS space A transformation of RGB space that allow colors to be described in terms more natural to an artist. The name HLS stands for hue, lightness, and saturation.

HSV space A transformation of RGB space that allow colors to be described in terms more natural to an artist. The name HSV stands for hue, saturation, and value.

hue The name of the color that places the color in its correct position in the spectrum. For example, if a color is described as blue, it is distinguished from yellow, red, green, or other colors. Compare with brightness and saturation.

indexed color space The color space used when drawing with indirectly specified colors.

inhibited color A color that is prevented from appearing on particular screens. Colors can be specifically inhibited on a 2-bit, 4-bit, and 8-bit color or grayscale screen.

interchange color space
Device-independent color spaces that are used for the interchange of color data from the native color space of one device to the native color space of another device.

inverse table A special data structure arranged by the Color Manager in such a manner that, given an arbitrary RGB color, the Color Manager can very rapidly look up its pixel value.

L*a*b* space A nonlinear transformation (that is, a third-order approximation) of the Munsell color-notation system designed to match perceived color difference with quantitative distance in color space.

L*u*v* color space A nonlinear transformation of XYZ space used to create a perceptually linear color space. This color space was designed to match perceived color difference with quantitative distance in color space.

named color space A color space in which each color has a name; colors are generally ordered so that each has an equal perceived distance from its neighbors in the color space.

new color In a color picker dialog box, the latest color selected by the user.

original color In a color picker dialog box, the color that the user is about to change.

palette A set of colors optimized for use on display devices with a limited number of colors. A palette defines a set of RGB colors, how they are to be used, and the tolerances within which they must be matched.

perceptual matching A rendering intent in which all the colors of a given gamut may be scaled to fit within another gamut. The colors maintain their relative positions, so the relationship between colors is maintained.

pixel value A number used by system software and a graphics device to represent a color. The translation from the color that an application specifies in an RGBColor data structure to a pixel value is performed at the time the application draws the color. The process differs for indexed and direct devices.

profile A structure that may contain measurements representing a color gamut, including information such as the lightest and darkest possible tones, and maximum densities for red, green, blue, cyan, magenta, and yellow. The International Color Consortium defines several different types of profiles. Each of these types of profiles must include a different required set of information, but all of these profile types follow the same format.

profile chromaticities Color values that define the extremes of saturation that the device can produce for its primary and secondary colors (red, green, blue, cyan, magenta, yellow).

profile identifier An abbreviated data structure that uniquely identifies, and possibly modifies the rendering intent for, a profile in memory or on disk

reference white point A specific definition of what is considered white light represented in terms of XYZ space and usually based on the whitest light that can be generated by a given device.

relative colorimetric matching A rendering intent in which the colors that fall within the gamuts of both devices are left unchanged. Relative colorimetric matching allows some colors in both images to be exactly the same, which is useful when colors must match quantitatively. A disadvantage of relative colorimetric matching is that many colors may map to a single color resulting in tone compression.

rendering intent The approach taken when a CMM maps or translates the colors of an image to the color gamut of a destination device. Each profile supports four different rendering intents: perceptual matching, relative colorimetric matching, saturation matching, and absolute colorimetric matching.

RGB space A three-dimensional color space whose components are the red, green, and blue intensities that make up a given color.

saturation The degree of hue in a color or a color's strength. A neutral gray is considered to have zero saturation. A saturated red would have the a color similar to apple red. Compare with brightness and hue.

saturation matching A rendering intent in which the relative saturation of colors is maintained from gamut to gamut. Colors outside the gamut are usually converted to colors with the same saturation, but different lightness, at the edge of the gamut.

source profile The profile that is associated with the image and describes the characteristics of the device on which the image was created.

subtractive color theory The process of combining subtractive colorants such as inks or dyes. In this theory colorants of cyan, magenta, and yellow are used to subtract a portion of the white light that is illuminating an object.

system-owned dialog box The default dialog box provided by system software for applications that create custom dialog boxes for color pickers. Applications can make this a box modal, modeless, or moveable modal dialog box.

system profile The profile that defines the color characteristics for the system's display device. The ColorSync Manager provides a control panel to allow the user to specify the system profile for the current display device.

tolerant color A color that accepts--within a specified range--the value that the Color Manager determines is the closest match available in the color table. If there is no match within the specified range, the Palette Manager loads the required color. Compare courteous color.

tristimulus values An hypothetical set of primaries, XYZ, set up by the CIE that correspond to the way the eye's retina behaves. The term tristimulus comes from the fact that color perception results from the retina of the eye responding to three types of stimuli. After experimentation, the CIE set up a hypothetical set of primaries, XYZ, that correspond to the way the eye's retina behaves.

XYZ color space The fundamental CIE-based color space that allows colors to be expressed as a mixture of the three tristimulus values X, Y, and Z.

Yxy color space A color space belonging to the XYZ base family that expresses the XYZ values in terms of x and y chromaticity coordinates, somewhat analogous to the hue and saturation coordinates of HSV space.