GEF
Graphics Exchange Format replaces the pattented LZW
compression in GIF89a code with unpattented LZHUF code. A
GIF89a/LZHUF file is almost as small as the original
GIF89a/LZW while maintaining full format compatibility.
GEM
Graphics data-format used by Ventura Publisher. On DOS/Windows systems, they use the filename extension of: .GEM; on MacOS systems it is .IMG.
.GIF, GIFf
Graphics Interchange Format designed by CompuServe with LZW "lossless" compression technology patented by Unisys. (Software developers must be licensed by either CompuServ or Unisys.) This general graphics data-format is used by most online services for users of DOS/Windows, MacOS and other operating systems. This standard supports files of interlaced and non-interlaced onscreen graphics with 2, 4, 8, 16, 32, 128, or 256 colors.
A file may have multiple image "cells." Typically, cells have: a 4 bit depth, 1 byte per pixel, 1 pixel per byte, and 320 pixel width by 200 pixel height. The maximum is 8 bits per pixel. Translations usually output to a non-interlaced form. Files have a filename extension of: .GIF. Viewer utilities: CompuShow (DOS), giffer (MacOS).
GIF89 a is a Web animation file which includes multiple images. By displaying one image while another is loaded, the animation can be played as it downolads via a Web browser like Netscape Navigator 2.0+ or Microsoft Internet Explorer.
Embedding animated GIFs in HTML documents is similar to referencing standard GIF images. Use a tool like the GIF Construction Set that recoginzes the file's extended attributes (including multiple images and control blocks for handling delays and sequencing loops).
Another tool,GIFBuilder 0.4, can be used to transform a large QuickTime movie into a much smaller animated GIF file. (JPEGs cannot be used to create primitive animations. JPEG images are smaller than GIFs because they use a higher compression ratio, but the JPEG's lossy compression could reduce its image quality. )
GL
DOS motion video file format. Player utility: GRASPRT (DOS shareware).
Grayscale It denotes an image's lack of color value, or hue, and the representation of them by a spectrum-range of shades of black. If an image must be converted to grayscale and also scaled to a different size, do the grayscaling first.
Grayscale printing. How fine or coarse an image is printed is determined by Screen Ruling. Expressed in the number of lines per inch (lpi); typically, rulings are lines of dots. Screen Type is the dots or lines which compose an image. The printed Screen Angle affects the alignments of lines, including lines of dots. Alignment is measured in degrees clockwise from 3 o'clock, which equals 0°. The default setting is usually 45°. (For gray areas within an image, aligning the dots at 45°, 135°, 255°, or 315° will results in the identical fills.) Print Resolution is the number of printed dots per inch (dpi).
High screen rulings generally produce sharp images, but with fewer shades of gray--between white and solid black--than lower screen rulings. Lower rulings produce more shades of gray, but less distinct images. For best results:
- If printer resolution is 300 dpi, set screen ruling to 53 to 60 lpi, to produce an image with 25 to 40 shades of gray.
- If printer resolution is 600 dpi, set screen ruling to 71 to 85 lpi, to produce an image with 40 to 100 shades of gray.
- If printer resolution is 1270 dpi, set screen ruling to 90 to 128 lpi, to produce an image with 100 to 200 shades of gray.
- If printer resolution is 1693 dpi, set screen ruling to 80 to 120 lpi, to produce an image with up to 256 gray shades.
- If printer resolution is 2540 dpi, set screen ruling to 90 to 150 lpi, to produce an image with up to 256 gray shades.
Grays are created by screen cells of dots. For example, if there are 25 dots per screen cell, each one may be either turned on or off to produce 25 different shades of gray, plus a white screen.
To determine the approximate number of gray shades that can be printed at a given screen ruling and printer resolution use this formula: gray shades = (printer resolution in dpi / screen ruling in lpi)2 + 1 (white)
.GZ
Unix compression/decompression (codec) format. Use Aladdin's free StuffIt Expander to decode files for MacOS compatibility.
References are samples only. Each one is presented in greater detail in the
Technical Research Assistant for 2001
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