International Standards and Conformity Assessment for all electrical, electronic and related technologies
Main title

Colour Management

 

Definitions and links

Ambient illuminance level

The level of light coming from the viewing environment other than the display (screen, scanner, etc). The optimal ambient light conditions should be a grey computer background, white walls, no sunlight and soft artificial lighting.

Black point

The darkest tone in an image.

Charged Couple Device (CCD)

A miniature photometer that detects light intensity and represents the intensity with an analogue voltage. A CCD array is made up of CCD elements, the smallest discrete CCD. They are used in many digital cameras, video cameras and scanners.

Chroma

The saturation of a particular colour or hue. Example: a red apple is high in chroma; pastel colours are low in chroma; black, white and grey have no chroma.

CMOS

A complementary metal-oxide semiconductor.

Colour model

A colour measurement scale or system that numerically specifies the perceived attributes of colour. Used in computer graphics applications and by colour measurement instruments.

Colour profile

A file containing information about the colour reproduction capabilities of a device, such as a scanner, a digital camera, a monitor, or a printer. The source of the image has one profile, which isn’t necessarily the same as the two profiles (source and output) used during a colour matching session.

Colour space

A three-dimensional geometric representation of the colours that can be seen and/or generated using a certain colour model.

Contrast

The level of variation between light and dark areas in an image.

Dither

To simulate a continuous area of colour by using a pattern of small dots of more than one colour. For example, a pattern of discrete, non-overlapping dots of blue and red can be used to simulate purple.

Dots per inch (dpi)

A printer’s term describing the fineness of the mesh or "screen" used to print halftones (a method used in printing to create the effect of continuous tones by varying the size or density of dots). It is frequently and incorrectly used to describe scanner resolution. It is independent of sampling frequency (spi) or the actual pixel count of the image (ppi). The measure dpi represents a user-assigned number of dots per linear inch on hard copy media and it is a standard used to scale media (offset film, prints or a document) to be scanned to a required resolution. Another user-assigned measure, ppi is used to scale the digital image's existing pixels into corresponding colour dots on a printed image. In both cases the dot size is variable with larger dots creating lower resolution and smaller dots creating higher resolution. These two terms are relatively interchangeable. The term dpi is probably most appropriately used when you are scaling media like film or photos to be scanned into a digital image with the required pixel resolution for printing or monitor display. The term ppi is most commonly used to scale existing digital images to a specified print size.

Gamut or workspace

The range of different colours that can be interpreted by a colour model or generated by a specific device.

Hue

The basic colour of an object, such as "red," "green," etc.

Inch

A measure of length, or distance. One inch equals 2,54 cm.

Interpolated resolution

The resolution that a device can yield through interpolation – the process of generating intermediate values based on known values. Most scanners offer an optical resolution of 300 dpi, but an interpolated resolution of up to 4 800 dpi. This means that the scanner can actually capture 90 000 pixels per square inch. Then, based on the values of these pixels, it can add 15 additional pixels in between each pair of known values to yield a higher resolution.

Lines per inch (lpi)

A measure of the resolution of a halftone screen (usually between 55 and 200), referring to the frequency of the horizontal and vertical lines of dots in a printed image.

Optical resolution

The physical resolution at which a device can capture an image. The term is used most frequently in reference to optical scanners and digital cameras.

Pixels per inch (ppi)

Has the same general meaning as "spi" since the pixel is the result of sampling.

Samples per inch (spi)

Describes the number of samples (pixels) both horizontally and vertically in each square inch scanned, or recorded by a digital camera. A 600spi scan of a one inch document would supply 600 pixels horizontally and 600 pixels vertically, a total of 360 000 pixels.

Saturation

The degree of hue in a colour, or a colour's strength. A neutral grey is considered to have zero saturation.

White point

The lightest tone in an image.