Color Management

The human eye can distinguish millions of different colors, all of which arise from two types of light mixtures: additive or subtractive. Computer monitors use an additive system, while print color is subtractive. This fundamental difference can complicate both accurate reproduction on a computer monitor of the colors of an original work and accurate printing of a digital image. Over time a variety of systems have been developed to reproduce color.

RGB 
Any device that uses light to record or display color (such as a camera or monitor) uses three colors – red, green, and blue – to create all the colors in an image. This is called “RGB.”.

CMYK
When printing, one standard system uses four colors  — cyan, magenta, yellow, and black – to create all other colors.  This is called “CMYK.”

Color Mode Standards

Any image intended for printing either commercially or on an ink jet or color laser, should be saved in the CMYK mode.

Any image intended for viewing on a monitor should saved in the RGB mode.

Digital images may be produced in black and white (bitonal), grayscale, or color.
Color capture is recommended for most photographs (even those that are black and white to retain subtleties of tone), but this choice depends on the project. For example, bitonal would likely be the best choice for scanning black and white newspaper cartoons.

Color Profiles

Color profiles provide translation between an input or output device – e.g., a monitor, camera, scanner, or printer – and the digital information within an image file.  Profiles instruct a device how to produce the color in an image.  Profiles should be set both when an image is captured and in preparation for output.  Note: Color profiles should be set on derivative files; the master file should be preserved for future conversions.

Color Space

A color space is a three-dimensional geometric representation of the colors that can be discerned and/or created by a particular color model (the two expressions may be used interchangeably).  The term may also refer to the range of possible colors that can be produced by a particular output device-such as a monitor, color printer, photographic film, or printing press.  

Color Space Standards

For input (e.g., scan or digital photograph): Adobe RGB (1998)
For output: Adobe RGB (1998)
For digital presentation such as Web or through a projector: sRGB
For print output (e.g., photographic prints or publication use), color specifications should be set according to the output device being used.  Most labs, printers, etc. will provide color specification settings or do the color space conversion on-site.

Bit Depth

Bit depth refers to the number of bits used to construct the color of each pixel. The greater the bit depth, the greater the number of tones that can be represented.  A bit depth setting of eight signifies that there are eight bits for each of the three color channels: red, green, and blue (RGB). 

Note: bit depth numbers are sometimes referred to as the sum of the bits in the three channels.  Therefore eight bit can be referred to as twenty-four bit, and sixteen bit can be referred to as forty-eight bit.

Bit Depth Standards

See resolution standards.