G-type lenses

Nikkor AF-D lenses introduced in 2000. They don't have an aperture ring. Aperture setting is made through a "Sub-Command Dial" on modern auto bodies. G lenses were designed to weight less and be less expensive than their counterparts with an aperture ring. AF bodies without a "Sub-Command Dial" can use G-type lenses in Program and Shutter priority modes only. The first was the 70-300mm f/4-5.6G AF.

Gamma

The values produced by a monitor from black to white are nonlinear. If you graph the values, they form a curve, not a straight line. Gamma defines the slope of that curve at halfway between black and white. Gamma adjustment compensates for the nonlinear tonal reproduction of output devices such as monitor tubes. Gray Gamma 1.8 matches the default grayscale display of Mac OS computers. Gray Gamma 2.2 matches the default grayscale display of Windows computers.

Gamut

The total range of colors produced by a device. A color is said to be "out of gamut" when its position in one device's color space cannot be directly translated into another device's color space. For example, the total range of colors that can be reproduced with ink on coated paper is greater than that for uncoated newsprint, so the total gamut for uncoated newsprint is said to be smaller than the gamut for coated stock. A typical CMYK gamut is generally smaller than a typical RGB gamut. The most appropriate gamut for Internet display is sRGB.

GIF

CompuServe Graphics Image Format. A raster-oriented file type for image sharing across multiple platforms, either 1-bit or 8-bit, rendering from 2 to 256 colors or shades of gray.

Gradation

The tonal contrast range of an image. Also the range of light and dark tones in a scene that a film or digital sensor is capable of registering, and gradual changing of one tint or shade into another in very small degrees.

Grade

Refers to the contrast rating of black and white enlargement papers. Zero is the lowest contrast and 5 is the maximum contrast.

Graduated Filter Or “Gradated” Filter.

A filter that is not uniformly dense, but that gradually changes its density across the filter’s field. A Graduated neutral density filter is clear from one edge to approximately the middle of the filter, then gradually increase in density towards the opposite edge. Colored gradated filters gradually change color density across the filter’s field. Used to balance the light of a scene with overly bright highlights.

Grain

Exposed and processed silver halides on the film emulsion that turn black and form miniature "grain" that make up the image on a piece of film. The equivalent efect at high ISO in digital photography -which is grainless- is "noise".

Gray Scale

An image made up of varying tones of black and white, containing no color, so grayscale is synonymous with black and white. The 256 gray levels system divides the gray scale into 256 sections with black at 0 and white at 255.

Ground Glass

Frosted glass used as a viewing mechanism in cameras without prisms. The glass is placed so that the lens projects the image against the glass for focusing and composition purposes.

Guide Number

A number used to describe the output capacity of a flash. Usually measured using an ISO sensitivity or speed of 100. Divided by the distance from flash to subject it yields aperture.