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Some color spaces are not device-dependent, but instead represent how a viewer sees colors, such as CIE Lab
or CIECAM02. These color spaces are defined by the CIE (Commission Internationale de l’Éclairage). The
advantage of these spaces is that if two objects have the same CIELAB values, they look the same when
viewed under the same conditions. Values in these spaces can be obtained from measuring the light emitted
or reflected by an object.
The solution: color management
Many colors from an RGB-controlled device cannot be reproduced in a CMYK-controlled device, and vice
versa. These colors are called “out-of-gamut” colors.
1. Describe the color behavior of a device as accurately as possible by using an ICC profile. The color
behavior of a device can be described by taking various RGB or CMYK combinations, sending them to a
device, measuring the resulting output, and expressing it in a device-independent color space (for
example, CIE Lab). The resulting relationship is stored in an ICC profile, which is a standard file that
translates the color space of a device(CMYK or RGB) to a device-independent color space (for example
CIE Lab). The process of generating an ICC profile is called profiling.
2. Convert colors as effectively as possible by using a Color Management System (CMS). A CMS is
software that uses information from ICC profiles to transform the color space of one device (defined by
a source profile) into the color space of another device (defined by a destination profile). In this
solution, difficulties arise with the colors that exist in the gamut that one device uses and that the other
does not use.
The following four settings describe a CMS:
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CMS: Color Management System. The software that converts the color information that is stored in the
input image (defined by a source profile) into an output image that has the color space specified by a
destination profile. Many different CMSs are on the market: in software programs, in operating systems,
and in printing software, including the Z6200 internal RIP.
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Source profile: a description of the color behavior of the input device
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Destination profile: a description of the color behavior of the output device
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Rendering intent: the most difficult challenge in color management is when a color in the source gamut
does not correspond directly to a color in the destination gamut. When a perfect match is not possible,
choices must be made about how to treat gamut differences. These choices are called rendering intent.
There are four different possibilities depending on the final output that you want to achieve.
◦
Use Perceptual for the most pleasing final output. It is suitable for photographic content.
◦
Use Saturation for vivid final output. It is suitable for business graphics (charts, presentations,
and so on), but is not recommended for color matching.
98 Chapter 7 Color management ENWW