Graphics Interchange Format, GIF (CompuServe GIF) is a graphics format widely used on the World Wide Web, both for images and for animations. The format was developed by CompuServe in 1987 to provide a color image format for their file downloading areas, replacing their earlier RLE format in black and white. GIF became popular because they could use the LZW compression algorithm (Lempel Ziv Welch) for compressing the image, which was more efficient than the algorithm Run-length encoding (RLE) used by the PCX and MacPaint formats. Therefore, large images could be downloaded in a reasonable period of time, even with very slow modems.
PCX, standing for Personal Computer Exchange, is an image file format developed by the now-defunct ZSoft Corporation of Marietta, Georgia. It was the native file format for PC Paintbrush and became one of the first widely accepted DOS imaging standards, although it has since been succeeded by more sophisticated image formats, such as BMP, JPEG, and PNG. PCX files commonly stored palette-indexed images ranging from 2 or 4 colors to 16 and 256 colors, although the format has been extended to record true-color (24-bit) images as well. PCX was designed during the early development of PC display hardware and most of the formats it supported are no longer used, Table A shows a list of the most commonly used PCX formats. Contemporary image editing programs may not read PCX files that match older hardware.