Color Management in PostScript

Keeps color in RGB or device independent space.

Color conversion takes place in device space.

Device profiles used to generate color space arrays (CSA) and color rendering dictionaries (CRD).

A CSA defines the way the RGB values are captured by an input device and is used to convert to a device independent color space.

The CRD converts color into device space.

Black Generation - Color management treats black generation through different profiles for each black generation option.

• This because there are many CMYK values for each CIE value.
• Since black generation is device-dependant, it is handled during the transformation to the output device color space.

Mapping Color Gamuts - Biggest challenge for color management systems is handling out of gamut conversions.

• The gamut of colors displayed on a monitor is greater than the printable gamut.
• Typically, the problem colors are highly-saturated primary colors.
• The problem of mapping to a smaller gamut is referred to as gamut compression.
• Utilizing the CIE color spaces, we can assure colorimetric consistency for in-gamut colors, but there are several possible criteria for out of gamut.

Perceptual - Gamut is compressed in a nearly linear fashion. Good for color images, since it maintains the relative range of colors.

Colorimetric - Gamut is clipped as accurately as possible without compression. Good for matching logos, identity colors.

Saturated - Color pushed toward gamut boundary, giving maximum saturation possible.

PANTONE - Special PANTONE colors are matched as closely as possible.

Source of confusion; is the monitor is an output device or an input device? Really can be either depending upon source of image.

Apple's ColorSync is supported by most CMS and software vendors as well as workstation vendors.

Quality Control - Control elements should be included on press sheet to monitor color quality. In particular these monitor

1. Density -Solid densities measured by densitometer. Need to be ~.1 of target values.

2. Dot Gain - Compare dot size with specified value (and with film since recorder gain may occur).

3. Balance - Print patch of CMY black (c5:m4:y4 for SWOP) to check gray balance. Check with colorimeter or spectrophotometer if available.

4. Tonal value transfer - Include highlight dots and microlines. Should hold 2% dot and 10-11 microline for conventional and 1% and 6-8 microline for stochastic screening.

Profiles can be obtained

1. With CMS.

2. From CMS vendor and third party.

3. From device vendor.

4. Editing existing profiles with a profile editor. (There don't seem to be any profile editors with either ColorSync or KPCMS).