| Gutter | The blank space between columns on a page or the inner edges of a book page. |
| Guides | appear as lines that float over the entire image and do not print. You can move, remove, or lock a guide to avoid accidentally moving it. |
| Guide Number | A number used to represent the illuminating power of a photographic flash for comparison of efficiency with other flash units. |
| Grayscale | This mode uses up to 256 shades of gray. Every pixel of a grayscale image has a brightness value ranging from 0 (black) to 255 (white). Grayscale values can also be measured as percentages of black ink coverage (0% is equal to white, 100% to black). |
| Graphic Pen | Uses fine, linear ink strokes to capture the details in the original image and is especially striking with scanned images. The filter replaces color in the original image, using the foreground color for ink and background color for paper. |
| Graphic | Any non-text element like a photo, a piece of clip art, or a graph. |
| grain | (AKA granularity) is the unwanted random optical texture |
| Gradient tool | Fills a closed object with a range of colors that fade into each other. |
| Gradiation | Often used as a screen printing term, the gradual changing of color across a substrate. |
| Gloss | The shine or luster of a paper. |
| global light | Using global light gives the appearance of a consistent light source shining on the image. |
| Glitch | Video noise appearing on the TV screen |
| GIGO | Garbage In, Garbage Out |
| Gigabyte | A term applied to the size of an image, hard drive, or storage unit. A gigabyte is 1,024 megabytes of data (roughly one million bytes). |
| GIF | The CompuServe Graphics Interchange Format [pronounced Jif] is the file format commonly used to display 256 color graphics and images in web pages on the Internet. Not good for photos, good for graphics. |
| Ghosting | During the print process, a shadow that appears in the print that is generally undesirable. |
| Generation | Each stage of a reproduction as it is changed from its original state. |
| GCR | Gray Component Replacement is an extension of UCR in that it replaces the neutral colors in the image as well as the colored areas with equal amounts of cyan, magenta, and yellow throughout the tonal range of the image. |
| GB | GigaByte - 1,024 MegaBytes |
| Gaussian Blur | A filter used for defocusing a digital image |
| Gamut | The gamut of a color system is the range of colors that can be displayed or printed. The spectrum of colors that can be viewed by the human eye is wider than any method of reproducing color. The RGB gamut is greater than that of the CMYK model. |
| Galleries | A managed collection of images displayed in a conveniently accessible form |
| Gain Control | An electronic control that prevents under or over exposure |
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