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PCX is an image file format that uses a simple form of run-length encoding (a type of lossless compression algorithm). See also Category:Graphics file formats Here is a summary of the most common graphics file formats: Some file formats, e. ...
Run-length encoding (RLE) is a very simple form of data compression in which runs of data (that is, sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. ...
Lossless data compression is a class of data compression algorithms that allows the original data to be reconstructed exactly from the compressed data. ...
PCX developed by the ZSoft Corporation of Marietta, Georgia, USA. It was the native file format for their PC Paintbrush graphics program, which was one of the first popular DOS graphics programs for early PCs. The acronym DOS stands for disk operating system, an operating system component for computers that provides the abstraction of a file system resident on hard disk or floppy disk secondary storage. ...
The tower of a personal computer. ...
Most PCX files use a color palette, but the format has also been extended to allow 24-bit images. PCX was quite popular on early DOS and Windows systems, but is nowadays rare, having been largely replaced by formats which support better compression, such as GIF, JPEG and PNG. Microsoft Windows is a range of operating environments for personal computers and servers. ...
A rotating globe in GIF format GIF (Graphics Interchange Format) is a bitmap image format for pictures and animations that use 256 (or fewer) distinct colors. ...
A photo of a flower compressed with successively higher compression ratios from left to right. ...
PNG (Portable Network Graphics) is a lossless bitmap image format. ...
Because colors 0x00..0xc0 are compressed better than colors 0xc1..0xff, good palette sorting is important. It's usually (but not always) enough to move the most-common colors into palette positions 0x00..0xc0, and least-used to palette positions 0xc1..0xff. The complete algorithm for sorting the palette is to count how many times a color appears 63N+1 (for nonnegative integer N) in a row, as it's only possible in such cases to use unprefixed color values to improve compression, and move colors with higher count into indexes 0x00..0xc0, and all others to 0xc1..0xff. This is warranted to produce optimal results.
This compression algorithm is very fast and takes very little memory, but is not very efficient, especially in compressing real-world images.
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