Ricoh AP 306D [75/77] Printing guideline for ricoh color products 2 1

Printing Guideline for Ricoh Color Products 2.01

be seen or generated by a certain color model.

Densitometer

This is a density reading device that is used in calibration processes. Usually a CMYK

patch page representing the actual status of a printer is printed and then read by a

densitometer. The result is fed back to the system or software, which compares it to

the target densities (or gamma curve) and calculates and applies a correction.

Gamut

The gamut of a color device is the total range of colors that it can produce (read,

display or print). RGB devices generally have larger gamuts than CMYK devices, but

the size of a CMYK gamut is also very much dependent on the media used. A color

is called out-of-gamut, if it cannot be produced within a device‘s gamut. Certain colors

of a photo scanned on a RGB scanner for example may be out-of-gamut of a printer.

It is task of a color management system to translate colors from one gamut to another

in a way that compensates for such differences in gamut.

Gamut Mapping

This is the process of converting colors from one gamut into another. As gamuts

usually are different in size and shape, there are several methods to do such

a conversion, which emphasise the accuracy of a single color or the perception

of the whole range of colors. In a color management system these methods are

called rendering intents and are optimised for different type of data such as images,

graphics or logos.

ICC ProÞ le

An ICC proÞ le describes the gamut of a particular color device or color space in

relation to a device independent color space like L*a*b* in a standard Þ le format

developed by the ICC. It is used by a color management system in order to convert

colors from one color space to another.

International Color Consortium (ICC)

A group established by eight industry vendors in order to develop an open, vendor-

neutral, cross-platform color management system architecture. The ICC for example

introduced the standard Þ le format for proÞ les used in color management sytsems.

For more information, see www.color.org.

L*a*b*

A device-independent color model is based on the model proposed by the

Commission Internationale d’Eclairage (CIE) in 1931 as an international standard

for color measurement. In 1976, this model was reÞ ned and named CIE L*a*b. ICC

proÞ les describe the device‘s gamut in relation to the device-independent L*a*b* color

space, which allows conversions from any source color space to any destination color

space via the L*a*b* color space.

Perceptual

The perceptual rendering intent preserves the impression of an image and gives the

most pleasing reproduction of an image within the capabilities of the output device‘s

gamut. Single colors may not be reproduced exactly in order to keep gradations and

the relation between colors.