Glossary of Terms

Gels – sheets of coloured transparent media used to add various colours to light sources.

Gigabyte (GB) – one thousand million (one billion) bytes of computer data.

Gobo – a cardboard or metal shape used with a suitable light source to project a controlled shadow onto a subject. Gobo are normally used inside a focusing spot lights.

Graduated filter – a filter whose density of colour changes smoothly either from maximum to minimum or from one colour to another.

Grain – the appearance of a single light-sensitive crystal or individual dye cloud in a processed image.

Greyscale – a set of defined brightness steps used by a system. An 8-bit scanner digitizes to a 256-step scale from 0 (black) to 255 (white).

Guide number – a number used in flash photography to obtain a correct lens aperture for subject distance and ISO rating. Guide number for a particular ISO rating, divided by metric distance, gives lens aperture.