Colors:Color management

This article is intended to serve as a crude introduction to the color management.

It also covers some intricate aspects of dealing with conversion of color between different color models and color spaces, highlighting certain aspects which may be handled quite differently in different software.

Definitions

Definitions according to the Wikipedia:

• Color management – In digital imaging systems, color management (or colour management) is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printers, offset presses, and corresponding media.

• Color profile (ICC profile) – In color management, an ICC profile is a set of data that characterizes a color input or output device, or a color space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the color attributes of a particular device or viewing requirement by defining a mapping between the device source or target color space and a profile connection space (PCS). This PCS is either CIELAB (L*a*b*) or CIEXYZ. Mappings may be specified using tables, to which interpolation is applied, or through a series of parameters for transformations.

• Color space – A color space is a specific organization of colors. In combination with physical device profiling, it allows for reproducible representations of color, in both analog and digital representations. A color space may be arbitrary, with particular colors assigned to a set of physical color swatches and corresponding assigned color names or numbers (such as with the Pantone collection), or structured mathematically (as with the NCS System, Adobe RGB and sRGB).

• Color model – A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components. When this model is associated with a precise description of how the components are to be interpreted (viewing conditions, etc.), the resulting set of colors is called "color space".

Conversion

Color conversion is a complex topic which often causes confusion, and may result in discrepancies between different vendors and products.

Photoshop and other professional graphics editing software offer a wide range of features to deal with color management, which include assigning a color profile to an image, interpreting embedded color profile within an image, and converting between different color profiles and color modes. Photoshop uses predetermined default color profiles for different color modes, which can also be adjusted in the Color Settings, where you can select a color profile and other attributes for different color modes (or color models), e.g. RGB, CMYK, Gray.

Color profiles (or ICC profiles) describe the characteristics of color input and output devices by means of well defined conversions to/from a profile connection space (PCS), which is used as a common intermediate space when converting between two different color profiles.

The Colors product does not currently deal with color profiles. Conversions between different color models are performed using common linear remapping algorithms, i.e. simple maths. In contrast, conversions performed in Photoshop would use color space remapping according to the selected color profiles.

A conversion sequence using linear remapping algorithms:

RGB -> [linear remapping algorithm] -> CMYK

A conversion sequence using color profiles:

RGB -> [sRGB / IEC 61966-2-1:1999] -> LAB -> [Coated FOGRA39 / ISO 12647-2:2004] -> CMYK

References

Noteworthy:

• (Wikipedia) Color
• (Wikipedia) RGB color model
• (Wikipedia) CMYK color model conversion
• (Adobe Photoshop) Color modes
• (Adobe Photoshop) Color settings
• (Adobe Photoshop) Working with color profiles

Footnotes: