PCX, standing for PiCture eXchange, was an image file format developed by the now-defunct ZSoft Corporation of Marietta, Georgia, United States. 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 image formats 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. PCX is supported by common image processing software including ACDSee, GIMP, ImageMagick, IrfanView, LView, Netpbm, PaintShop Pro, Photoshop, Visio, PMview, XnView and GraphicConverter. In version 2.1.4 FFmpeg could encode and decode the PCX pixel formats rgb24, rgb8, bgr8, rgb4_byte, bgr4_byte, gray, pal8, and monob. There is a multi-page version of PCX, used by some computer fax and document management programs, with file extension .dcx. A DCX file consists of a header introducing a set of following PCX files. PCX file format PCX files were designed for use on IBM-compatible PCs and always use little endian byte ordering. A PCX file has three main sections, in the following order 128-byte header image data (optional) 256-color palette The PCX file header contains an identifier byte (value 10), a version number, image dimensions, 16 palette colors, number color planes, bit depth of each plane, and a value for compression method. PCX version numbers range from 0 to 5, this originally denoted the version of the PC Paintbrush program used to create the PCX file. The header always has space for 16 colors though the number of colors used depends upon the bit depth of the image. The header is composed of 18 fields: All PCX files use the same compression scheme and the compression value is always 1. No other values have been defined and there are no uncompressed PCX files. One source claims that 0 (uncompressed) is allowed, but not much software supports it. Image data layout PCX image data is stored in rows or scan lines in top-down order. If the image has