G

gamma

A measurement of midtone brightness for a monitor. The gamma value defines the slope of that curve halfway between black and white. Gamma values range from 1.0 to about 2.5. The Macintosh has traditionally used a gamma of 1.8, which is relatively flat compared to television. Windows PCs use a 2.2 gamma value, which has more contrast and is more saturated .

gamut

The range of viewable and printable colors for a particular color model, such as RGB (used for monitors ) or CMYK (used for printing). When a color cannot be displayed or printed, Photoshop can warn you that the color is out of gamut. In terms of color working spaces, the gamut of a monitor is a triangular space with its corners in the red, green, and blue areas of an industry-standard color gamut chart. The gamut chart plots the device s available colors compared to the gamut of colors that humans can see.

GIF87a and GIF89a

The Graphics Interchange Formats (GIFs), used for Web applications and for saving animations produced in ImageReady. GIF is a lossless-compression format that compresses the image through reduction of the available colors. GIF87a does not support transparency. GIF89a is used to omit the visibility of selected colors on a Web browser.

gradient

Variations of color that subtly blend into one another. Photoshop gradients blend multiple colors into each other or into transparency over a specified distance.

gradient fill

A fill that displays a gradual transition from the foreground color to the background color. In Photoshop, gradient fills are added with the Gradient tool or a Gradient Fill layer.

gray-component replacement (GCR)

An operation that removes a neutral mixture of cyan, magenta , and yellow from colored and neutral areas, and replaces them with black. GCR is generally more extreme and uses more black than the related undercolor removal (UCR) separation method.

grayscale image

An image that use an 8-bit system, in which any pixel can be one of 256 shades of gray. Each pixel contains 8 bits of information. Each bit can be either on (black) or off (white), which produces 256 possible combinations.

Grayscale mode

A Photoshop color mode that displays black-and-white images. A grayscale image is composed of one channel consisting of up to 256 levels of gray, with 8 bits of color information per pixel. Each pixel has a brightness value from 0 (black) to 255 (white). Grayscale pixels can also be measured in percentages of black ink, from 0 percent (white) to 100 percent (black). When color images are converted to Grayscale mode, their hue and saturation information is discarded and their brightness (or luminosity) values remain .

grid

In Photoshop, a series of equally spaced horizontal and vertical lines that create a visual matrix. A grid helps you see the global relations between aligned elements on a page. Grids do not print.

GUI (graphical user interface)

A software program s way of interacting with users. The GUI (pronounced gooey ) of Photoshop lets you perform virtual operations that mimic real-world tasks such as painting, compositing, or filtering.

guide

In Photoshop, a horizontal or vertical line that can be positioned anywhere on the image s surface. Guides do not print.