Image Processing Reference
In-Depth Information
Input image
transformed to
L*a*b* using
source profile
TRC
(gray balance,
channel-independent
linearization, etc.)
Calibrated
CM YK
CMY
CMYK
UCR/GCR
3-D LUT
Output image
shown in
L*a*b*
Halftoning
Marker
Hardcopy
Print engine
FIGURE 8.1
Image path with input and output in device-independent color space, L*a*b*
(UCR: under color removal; GCR: gray component replacement).
8.2 PRINCIPLES OF COLOR MANAGEMENT
Consider a digital imaging system with variety of color devices such as a digital
camera, image scanner, cathode ray tube (CRT) or liquid crystal display (LCD)
monitor, digital printer, and offset press. A color management system will make the
color conversion and reproduction among these devices as accurate as possible. This
includes pro
ling and calibration of different devices to provide nearly identical
reproduction across them. For example, if an image is scanned by a scanner,
displayed on an LCD monitor, and then printed on a digital printer, we would like
the printed image to be perceived as being identical to what we see on the monitor.
This is called what you see is what you get (WYSIWYG). Obviously, this is not
possible across all the imaging systems due largely to physical limitations on
reproducibility of each device. Our goal is to make the reproduction process as
accurate as possible (within physical limits) so that output is device, media, and
halftone independent. For example, consider the image reproduction system shown
in Figure 8.2, where a digital camera captures an image that is displayed on an LCD
monitor and then printed on a digital printer.
The image captured by the digital camera is in RGB color space. The camera is
generally calibrated and hence it complies to some calibrated RGB space (e.g.,
sRGB). These RGB values are generally displayed for visualization on a computer
FIGURE 8.2 (See color insert following page 428.)
Image reproduction system.
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