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GELATIN - A nearly transparent substance, obtained by boiling animal tissue in water, used as (1) the medium for suspending light-sensitive silver halide crystals on photographic film, and (2) in the manufacture of gelatin filters.
GELATIN FILTER - Also known as “gelatin slide” and “gel,” a thin sheet of translucent colored gelatin for placing over lights to obtain lighting effects, and in the manufacture of photographic filters for lenses. Gels are available in a wide color and density variety.
GELS - Generic term used in reference to any colored translucent material (color media) that is used to color a light, whether the material is made from gelatin, glass or plastic.
GHOST IMAGE - In time (or long) exposure photography, an object that is only partially recorded on the film and therefore has a translucent, ghost-like appearance. Ghosting also occurs when using electronic flash at a slow shutter speed, and a second image is captured on the film by ambient light. Some people also refer to “flare” as a ghost image.
GIF - (Graphics Interchange Format) is a small image file format that is constrained to a maximum of 256 colors, generally making it a poor choice for your digital images. When it was created, most computer video cards were able to display no more than 256 colors. It is used mainly on the internet for graphic images that don't require subtle or gradual change in tones. It was created for viewing online images from the CompuServe network, and is also known as a "CompuServe GIF."
GLOSSY PAPER - Shiny-surfaced, photo-sensitive paper used in making photographic prints.
GN - Abbreviation for Guide Number.
GOBO - A light-blocking device that falls under the general category of "Grip equipment." Generally used in a studio to prevent illumination from a studio light striking a portion of a scene. A "gobo" can be a simple piece of opaque cardboard or a sophisticated material in a specific shape, often a rectangle or square. "Barn doors" are gobos.
The rectangle defined by the GOLDEN MEAN.
GOLDEN HOUR - The time an hour or less before the sun goes down and around fifteen minutes after the sun has set. Sunlight is usually warmer and more complimentary to skin tones at this time, and the angle of the light can provide depth to portraits and landscape photography. This quality of light is also sometimes referred to as "Photographer's light."
GOLDEN MEAN - Also referred to as the “Golden section” and the “Gold mean,” the Golden mean is an ancient fine arts formula that mathematically defines a rectangle of specific proportions. This rectangle, called the “Golden rectangle,” is believed to frame objects in pleasing proportions. (See Rule of Thirds for more information.)
GOLDEN RECTANGLE - A rectangle of specific mathematical proportions that are closely approximated in the shape of a 35 mm film’s frame or the viewframe of a digital camera.
GOST - GOST is a standardization system developed by the All-Russian Scientific and Research Institute for Certification. Its coding system for film speeds, although similar to the ISO system, uses different numbers.
GRADATION - (1) An image’s tonal contrast range. (2) The range of light and dark tones in a subject that a film is capable of showing (i.e. how a film reproduces contrast). (3) The gradual changing of one tint or shade to another by very small degrees.
GRADATED FILTER - Also called a “Graduated” filter. A filter that is not uniformly dense, but that gradually changes its density across the filter’s field. A Gradated neutral density filter is clear from one edge to approximately the middle of the filter, then gradually increases in density towards the opposite edge. Colored gradated filters gradually change color density across the filter’s field.
GRADATED GRAY FILTER - Another name for a Gradated neutral density filter.
GRADATED NEUTRAL DENSITY FILTER - See definition in "Gradated filter" above.
GRADE - A system of classifying the contrast of photographic papers used in making black and white prints, ranging from 0 (soft) to 5 (hard).
GRADUATED FILTER - See Gradated filter above.
GRAIN - Minute crystals of silver halides in the light-sensitive emulsion of film that react when exposed to light, turning black, are called “grains.” (See Graininess of film.)
GRAININESS - Graininess occurs when clumps of individual grains are large and irregularly spaced out in the negative. They are visible to the naked eye in the finished print, particularly enlargements, as sand-like particles. When this occurs, the picture appears “grainy.” Graininess in digital images is caused by "noise," which usually appears in shadow areas and is generally unwanted and unattractive.
GRANULARITY - Describes a negative or film that shows a granulated structure, usually used to describe the degree of granularity that is visible.
The GRAY CARD is a simple but effective aid in determining proper exposure.
GRAY CARD - Also known as the “Kodak neutral test card,” a gray card is an 8" X 10" (20 cm by 25.5 cm) card, about 1/8" thick, that is uniformly gray on one side. The gray side reflects precisely 18% of the white light that strikes it (corresponding to the calibration of a reflected-light meter). It is uniformly white on the other side, which reflects 90% of the light.
GRAY FILTER - Another name for a neutral density filter, or ND filter.
GROUND GLASS SCREEN - Flat sheet of glass in a camera treated so that it can be used for viewing and focusing an image, also known as the “Viewing screen.”
GUIDE NUMBER - A number which serves as a guide to proper exposure when using flash. Also known as “Flash factor.” The number is based on a flash unit's light output and a digital camera's ISO sensitivity setting or a traditional camera's film speed. When the guide number is divided by the flash-to-subject distance, the correct aperture for proper exposure is determined. Guide numbers may be quoted in meters or feet, according to which system is used for the measurement of distance.