User manual

11 • Modifying an image
ColorQuartet 5.0 Pro
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Advantages of LCH
One reason why the LCH color model is so useful is that it employs uniform units of distance in
all three dimensions, making it possible to define colors that are evenly spaced within the
model. Another reason is that its parameters are the ones that people intuitively use when they
talk about color: hue, lightness and saturation. Once you get a feeling for which LCH values cor-
respond to which colors, you may therefore find that the model’s linearity makes it easy to work
in ColorQuartet using LCH values, as opposed to CMYK values, which are logarithmic and
therefore take much more practice to master.
LCH and IT8 calibration
The above mentioned characteristics of the LCH model also led the American National Stan-
dards Institute (ANSI) to use it as a basis for their IT8 color calibration standard and test targets,
which are now the industry standard for calibrating scanners, imagesetters and other prepress
devices. The test targets consist of 288 systematically arranged color fields that represent the
entire color space, from fully saturated colors to near neutrals, at both highlight, mid-tone and
shadow portions of the lightness scale.
Calibrating your scanner to the IT8 standard lets you save scans in TIFF Lab format. This is a
device-independent, calibrated file format that can be transferred between different image han-
dling programs and prepress devices without losing information. When the file is output, its
color data are reconverted from the global LCH (Lab) color space to the color space of the out-
put device.
>>> Related topics:
D
ensitometer window
Checking and changing tonal range with the LCH text fields
Saturation