Glossary of Terms

C-41 – the chemistry used to process most colour negative films.

Cable release – a flexible cable used to release a camera shutter without causing movement and consequent blurring of an image.  It is normally used in conjunction with a tripod and a slow shutter speed.

Cache – RAM used to hold computer data recently read from a mass storage device. Its purpose is to speed up processing.

Camera movement – movement of a camera during the exposure period, perhaps causing loss of detail or blurring.

Catch-light – small specular reflections of a light source usually seen in the eyes in portraiture. Lack of catch lights in portraits may be regarded as a deficiency.

Capacity – the quantity of computer data that can be held by a storage device, usually quoted in MB or GB.

CCD – silicon chip used as an electronic sensor to replace film in a digital camera. It has electrodes arranged in a rectangular array. The electrodes a light sensitive and correspond to pixels. The light level measured by each electrode is turned into a digital code.

CD-R – compact disk used as a read-only memory (CD-ROM). Data can be written onto it only once.

CD-RW – a “rewritable” compact disk onto which data can be written any number of times.

Centre-weighted metering – exposure determination system commonly found in SLRs giving greater emphasis to brightness in the centre of the field of view.

Changing bag – a light-proof black fabric bag used to handle film and other light-sensitive materials in daylight. Most have two separate layers equipped with zips, and a pair of sleeves with elastic armholes.

Chroma – the purity of a colour measured as a product of hue and brightness, or the degree of departure of a colour from the neutral. Colours having a low chroma value are usually described as weak, whereas those with a high chroma are said to be strong or highly saturated.

Chromogenic films – B&W films that can be processed using standard C41 colour chemistry to produce monochrome prints.

Circle of confusion – the diameter of a spot that cannot be distinguished from a point in an image at a normal viewing distance of 250mm. This measurement is an essential element in calculating depth of field.

Cloning – copying one part of an image directly to another area.

Colorimeter – an instrument for measuring colour, and used to calibrate a computer monitor.

Colour balance – an adjustment made in a photographic process to ensure that neutral greys in a subject remain neutral in an image.

Colour cast – a false predominance or bias of a particular colour spread evenly throughout an image, and usually most apparent in light neutral tones.

Colour gamut – the range of colours a particular device or reproduction system is able to produce.

Colour management – the process of controlling the colours in an image reproduction system such that they are repeatable and acceptably accurate. Key components of colour management are monitor and printer calibration.

Colour space – a defined range of colours producible by an output device.

Colour temperature – measure of the colour of a light source in terms of physical temperature (degrees Kelvin) of a black body radiator. Daylight approximates to 5,400^oK and a sunset to 2,800^oK.

Complementary colours –pairs of colours of light which, when combined in equal proportions, produce white light – ie cyan and red, yellow and blue.

Compression – the process of encoding digital files in a space-efficient manner. Compression algorithms remove unnecessary information from files in a way that allows it later to be replaced. No compression of physical storage is involved.

Contact sheet – a same-size print of all the negatives on a roll of film used to select images for enlargement.

Contrast – the brightness range in a scene, or the difference in brightness between adjacent areas of tone. Also, the rate at which processed film density increases with greater exposure.

Convergence – the appearance of parallel lines in a view, as seen in an image, when photographed from an angle.

Crop – to use or remove part of an image typically to improve composition or make it fit a given space.

Cropped sensor – a sensor in a digital camera having dimensions smaller than those of the comparable film-based format.

Cut and paste – to remove a selected part of an image, or other digital file, and store it temporarily in a memory before reusing in, or pasting it to, another location.