What GIF (Graphics Interchange Format) is
Developed by CompuServe, using file compression technology from Unisys, this is a graphics file format used on the Internet. It was originally referred to as a "CompuServe Bitmap" but it stands for "Graphics Interchange Format." You may hear GIF mentioned as "GIF format" (this is redundant, but it is widely used). On Web pages, the images (or pictures) you see are usually in GIF because the files are small and can be downloaded quickly. Another type of graphics format commonly used online is JPG; these files download even faster and contain a better resolution. However, JPGs cannot be "interlaced," so many Web authors use GIFs instead, to get that "melting onto the screen" effect that happens with interlaced images. Following are special kinds of GIF:
Animated GIF - a series of static images are displayed one after another or on top of each other, giving the effect of motion or animation.
Interlaced GIF - these appear first with poor resolution and then gain resolution once the entire image has arrived, as opposed to arriving linearly from the top row to the bottom row. This type of format is good for giving the user a quick idea of what the entire image will look like while they're waiting for the rest of the image to load.
Transparent GIF - useful because they appear to blend in smoothly with the Web page's background, even if the user has set a background color that differs from the one the developer expected. To make a GIF see-through or appear to be the same color as the background, you must assign one color to be transparent; if the Web browser supports transparency, that color will be replaced by the browser's background color, whatever it may be.
The meaning of Raster graphics
Also known as "bitmapped graphics" these programs store images in the form of patterns of screen pixels. Unlike "draw programs" (vector graphics), these "paint programs" can create detailed patterns of shading that convey an artistic touch, but any attempt to rescale or resize the image may result in unacceptable distortion. Raster-based graphics have become a standard technology and are popularly known by their GIF and JPG formats. Raster graphics use pixel-by-pixel definitions as opposed to vector graphics which use computer algorithms to describe shapes, lines, animation, etc.
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