Glossary of Terms

B (bulb) setting – this function keeps a shutter open as long as the release button remains depressed.

Back-up – A send copy of computer files, or the process of making them, for the purpose of protecting against their loss or damage.

Barn doors – an accessory used with studio light sources to control the direction and spread of the light.

Barrel distortion – a lens aberration that distorts the shape of images. Magnification increases radially inwards, so the straight edges of a square object bow outwards.

Bit-depth – the number of binary digits assigned to each sample in a sequence of data used to represent an image. 8-bit information registers one of a possible 256 values (colours or densities), whereas 16-bit data registers one of 65,536 values.

Bleed – information or material that overflows the edge or trim-line of a printed image.

Boot – to start or restart a computer by loading the basic operating system.

Bounced flash – the diffusion of light from a flashgun by directing it at a suitable reflecting surface such as a white ceiling.

Bracketing – a process of making several shots of the same subject, using incremental changes of aperture or shutter speed, to overcome exposure uncertainties.

Brightness range – the range of tonal variation in an image or scene, usually expressed as a ratio or in f/stops.

Bromoil - an old printing process, patented in the 1850s by Alphonse Poitevin, in which greasy ink on gelatine sensitised by potassium dichromate is used to produce an image.

Buffer – a memory in an output device, such as a digital camera or printer, which stores data temporarily and feeds it to the device at an appropriate rate.

Burning-in – a darkroom or equivalent digital technique for increasing local contrast and density in an image.

Byte – a unit of digital information comprising a number of binary states or bits. Typically, one byte consists of 8 bits. 16-bit values therefore consist of 2 bytes.