Photography glossary - G
Galvanography - technique of electroplating a gelatin relief image
created photographically to produce a photomechanical printing
plate.
Gamma - measurement used in sensitometry to describe the
angle made between the straight line portion of the characteristic
curve of the photograph emulsion and the base of the graph. The
gamma is the tangent of the angle so formed.
G curve - average gradient of a characteristic curve, describing
similar characteristics to gamma, but measuring the slope from a
line joining the lower and upper limits of the curve actually used in
practice.
GB- Gigabyte.
Gelatin - natural protein used as a transparent medium to hold
light sensitive silver halide crystals in suspension, binding them to
the printing paper or film, yet swelling to allow entry of processing
solutions.
Gelatin filters - filters cut from dyed gelatin sheets and held in
front of the lens or studio light.
Gelatin sugar process - daylight printing process using paper
with a sugar and dichromate coating, which hardens on exposure
to light.
Ghost images - bright spots of light, often taking the shape of the
aperture, which appear in the camera viewfinder or in the final
photograph when a lens is pointed at a bright light like the sun.
Ghost images have been almost eliminated through the use of
multi layer coatings of the lens elements.
Gigabyte - 1 Gigabyte = 1,024 Megabytes.
GIF - Graphic Interchange Format. A graphic file format limited to 256 colors, which used mainly for web graphics or small animated files.
Glass lens - See Lens
Glossy - Printing paper with grate deal of surface sheen
Glaze - glossy surface produced on some (non resin coated)
printing papers. It is achieved by placing a wet print to to a heated
drum or clean polished surface. Glazed print produce denser
medium blacks than their matte counterparts.
Glazer - machine on which wet fiber base prints are placed face
down in contact with a polished surface, such a chromed steel, and
held by tension. The surface is then heated to dry the print.
Glossy paper - printing paper with a smooth shiny surface finish
to give maximum detail and tonal range.
Gold chloride - soluble chemical used in gold toners.
Gold mean - compositional technique used to determine the
"ideal" position of the main subject in the frame. It is based on
creating a rectangle from a square. A line drawn from the center of
one side of the square to the opposite corner becomes the radius
of an arc. The side of the square is then protracted until it meets
the arc, and from this point a rectangle is constructed. The side of
the square which remains in the rectangle indicates the point at
which the subject should be placed.
GOST - arithmetical system of rating film speed used in Soviet
bloc countries.
GPS - Global Positioning System. The GPS receiver uses satellites to let you determine the exact longitude, latitude, and height above sea level anywhere on earth.
Graduated filter - filter with a colored section, which gradually
reduces in density toward the center of the filter. The rest of the
filter is clear. Also referred to as a Graduated filter
Gradation - tonal contrast range of an image. A smooth transition between black and white, one color and another, or color and no color.
Grade - system of terms and numbers used to denote the contrast
characteristics of black and white printing papers.
Graduate - vessel used for measuring liquids.
Graphics card - Component of a computer that is necessary to display an image on the monitor screen.
Grain - clumps of silver-halide grains in film and paper that
constitute the image. These grains are produced both in the
exposure process (film grain) and in the development process
(paper grain). Unlike film, the grain in printing paper is largely
responsible for the image tone.
Graininess - clumps of silver halide crystals in the emulsion which
are visible to the human eye because of spaces between the
crystals.
Grains - exposed and developed silver halides which have formed
black metallic silver grains, producing the visible photographic
image.
Granularity - objective term describing the amount that silver
halide grains have clumped together within the emulsion.
Gray card - card with an 18 percent gray tint (reflectance) used to
determine exposure by taking a meter reading from subject light
reflected by the card.
Grey scale - A scale of shades ranging from white to black. Devices that can only display data in black and white translate colour differences into various shades of grey.
Gray Level The brightness of a pixel.
Ground glass screen - translucent glass sheet used for viewing
and focusing the image on all large format and some reflex
cameras.
Guide number - term sometimes used to describe a flash factor,
which provides a guide to correct exposure when using flash.
Gum arabic - water soluble gum obtained from the Acacia tree
and used in coatings of a number of photographic processes.
Gum bichromate - contact printing process once very popular for
the manipulative, impressionistic effects it makes possible.
Drawing paper is coated with a mixture of gum, potassium
bichromate and a pigment of any chosen color. This is then
exposed to light behind a negative. Also known as the photo
aquatint process.
Gum platinum process - combination of gum and platinum
printing.
Gyroscopic camera mount - device employing a gyroscope to
help stabilize hand held cameras subject to movement or vibration
from outside sources.
