ΔE (pronounced “Delta E”)
Represents the degree of difference between two colours. Usually quoted in terms of CIE Lab, it is generally considered that a ΔE of 2 or less is imperceivable visually. In fact, it depends on the colour to which it applies – neutral tones show change far more readily than saturated colours.

Black Point
The density and colour of the darkest black reproducible by a device.

Black Point Compensation
A software setting that maps the black point of the source profile to the black point of the destination profile.

Calibration
The adjustment of the behavior of a device to a standard state.

Characterisation
Finding the relationship between visual colour and a device’s colour before profiling.

CIE
Commission Internationale d’Eclairage. An association of international colour scientists who produced the standards that are used as the basis of the description of colour.

CIE Lab
A device-independent colour space that attempts to uniformly represent colour as we perceive it. ‘L’ is the lightness value, ‘a’ is the red/green opponency and blue/yellow is represented on the ‘b’ axis. It is used as a conversion space (PCS) when transforming from a source profile to a destination profile.

CMM
Colour Management Module, Colour Matching Method or Colour Manipulation Model, this is the engine which performs the transformation from one colour space to another. Different CMMs may produce different colour results.

Colour Space
A representation of a device in which each colour is described as a point in space by a tristimulus value. Each individual device effectively has its own colour space.

Colour Temperature
A description of the colour of the emissions from a light source in ‘kelvins’. Lower values are redder, higher values bluer. The standard colour temperatures for a monitor is 6500ŠK despite the fact that when delivered they are generally in the 9300ŠK to 11000ŠK range. A light box or reflective viewing area should be standardised at 5000ŠK.

Density
The degree to which a surface absorbs light.

Destination Profile
A profile that defines how colours are to be converted from the PCS to the output space (device).

Embedding
Embedding a profile saves a copy of the source profile with the file so that the numeric colour values have some ‘meaning’ when taken to the next stage of the workflow.

Gamma
On a monitor gamma is the relationship between the input voltage and the output luminance. Device gamma is the degree to which the device is non-linear in its tonal behavior.

Gamut
The range of available colours that is reproducible on a specific output device. The gamut of a printer will be different for different ink/paper/profile combinations.

Gamut mapping
The re-mapping of colours from one colour space to another.

Giclee printing (pronounced gee-clay)
A relatively new field of printing that is concerned with the accurate reproduction of artworks from traditional media by means of an inkjet printer. Usually output to canvas or ‘fine art’ papers.

ICC
International Color Consortium. A group of companies who joined forces to produce a set of standards for profile formats. Most profiles are ICC profiles.

ICM
Image Color Management in the Windows implementation of ICC profiles.

Input profile
A profile that describes the way an input device (scanner or digital camera) sees colour. (N.B. A source profile is not necessarily an Input profile).

Linear Response
The relationship between stimulus and response where an increase in stimulus will result in a corresponding increase in response.

Linearisation
The process of making a device deliver a linear response. Entails setting shadow and highlight points and determining the appropriate gamma correction.

Metamerism
More precisely ‘illuminant metamerism’ is where two (spectrally) different colour samples look the same under a particular viewing condition but different under another.

PCS
A Profile Connection Space is the intermediate colour space that is used in the transformation from one profile to another.

Profile
A file that describes the relationship between visual colour and device colour of a specific device. There are many types of profile including input, output, abstract colour space and device link profiles.

Profiling
The process of ‘fingerprinting’ a device to find the relationship between visual colour and the device’s colour. Sometimes called characterization.

Rendering Intents
There are four different rendering intents – Perceptual, Relative colorimetric, absolute colorimetric and saturation. Each reflects a different set of rules for remapping colours between one colour space’s gamut and another. Perceptual is said to be the best intent for photographic use because it maintains the relativity of colour during remapping. It should be used mainly for changes between spaces of similar size. Relative colorimetric leaves in-gamut colours alone and pulls out of gamut colours in. This can result in compression of saturated tones. Absolute colorimetric rendering is the same as Relative except that it will simulate the white point in the output this makes it useful only for proofing. Saturation intent should be ignored.

Soft Proofing Displaying a simulation of the output of a document on your monitor.

Source Profile Defines how a documents colours will be converted between the first colour space to the PCS or visual colour.

Tagging
The process of associating a source profile with a document and can be achieved either by ‘assigning’ a profile within an application or embedding a profile as you save it.

White point
The intensity and colour temperature of the brightest white reproducible by a device. For a monitor this is the colour and intensity when red, green and blue guns are generating their highest output simultaneously.



 

 

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