182 Appendix B
•
•
•
•
Color Management Overview
MediaScript uses the ICC (International Color Consortium) methodology for color
management, where the color characteristics of each color reproduction device to be used
is stored in a color profile. Converting an image from one device to another involves setting
up a color transformation between the source profile and the destination profile. This
transformation is then used to convert each pixel in the image from the source device to the
destination device. Detailed information regarding ICC color management can be found at
the ICC web site.
Colorspaces
Different color reproduction devices use different types of color representation
(colorspaces) for color reproduction. Most color reproduction devices fall into three basic
categories. Each category is represented by a different image colorspace.
Grayscale colorspace devices use a single intensity corresponding to the
darkness/lightness desired. In MediaScript, a grayscale value of 0 represents black, while
a grayscale level of 255 represents white.
RGB colorspace devices (typically monitors) use red, green, and blue intensities which
combine to form the color. The value combined additively; when all three components are
0, the color is the darkest the device can represent; and when all three components are 255,
the color is the brightest.
CMYK colorspace devices (typically printers) use the intensity of the cyan, magenta,
yellow, and black inks to represent the color. When no ink is used, (all components 0), the
color is the color of the paper. When the maximum intensities are used, the color is at its
darkest. Note that most printers cannot print using the maximum value of all four
channels.
Converting colors between these different types of devices fundamentally changes the
nature of the image data. For example, the color white on an RGB device is typically
represented by setting all three channels to 255. However, on a CMYK device, white is
typically represented by setting all four channels to 0. It is therefore important to know
which colorspace an image is represented in.
Color Gamut
Different devices may not be able to reproduce the same range of colors. The range of colors
that a given device can reproduce is called its “gamut”. RGB devices typically have a
significantly different gamut than CMYK devices. Therefore, converting an image from an
RGB colorspace to a CMYK colorspace or vice-versa typically involves a loss of
information as different colors in the source colorspace may map to the same color in the
destination colorspace. For this reason, it is advisable to keep the number of color
conversions to a minimum.
