User's Manual

MediaRich Color Management 183
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White Point Mapping
The color considered to be “white” on each device may not be the same. What is considered
“white” for CMYK devices depends on the paper being used, while “white” on a monitor
depends on the maximum intensities of the red, green, and blue channels. Typically,
monitors have a “white” that is noticeably bluer than paper.
However, when an image displayed on the screen is printed, one does not typically expect
the image to be printed on a blue background. Instead, the “white” of the monitor is
mapped to the “white” of the printer, such that areas displayed as “white” on the monitor
are printed with no ink. This is termed white point mapping.
Color Profiles
Color profiles for a given device can typically be obtained from the device manufacturer,
or may come installed on the operating system. Additionally, software is available that can
be used to characterize a device and create a color profile. The TIFF, JPEG, EPS, and
Photoshop image formats have the ability to store the color profile that describes the image
contents along with the image. This is termed an “embedded profile”.
MediaScript reads embedded profiles from these image formats and will preferentially use
these profiles as the source for color transformations. Additionally, MediaScript has the
ability to save the embedded profile along with the image data.
Rendering Intent
Because of differences in color gamut and white point between differing devices, building
a transformation between devices requires the user to specify how to handle gamut and
white point mapping. This is specified as the rendering intent. The ICC provides four
different intents:
• Perceptual
• Relative Colorimetric
• Absolute Colorimetric
• Saturation
Perceptual
This intent specifies that the white points of the differing device be mapped, and that color
differences for out of gamut colors be preserved. This implies that some compression of
colors that lie inside both gamut be performed to make room for different out-of-gamut
colors. This is usually the best rendering intent for complex images such as photographic
images.
Relative Colorimetric
This intent specifies that colors that lie inside the common color gamut of both devices be
reproduced exactly. Colors that are outside of the destination devices color gamut are
mapped to the gamut boundary. This means that many out of gamut colors may be