What is PCX? PiCture eXchange Format Explained
An early DOS-era raster format from ZSoft's PC Paintbrush, using run-length encoding compression.
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What is PCX?
PCX, short for PiCture eXchange, is a raster image file format developed by the now-defunct ZSoft Corporation of Marietta, Georgia. ZSoft introduced it in 1985 as the native format for its PC Paintbrush program, and it became one of the first widely accepted DOS imaging standards.
A PCX file consists of a 128-byte header describing dimensions, color planes, and palette information, followed by image data compressed with a simple byte-wise run-length encoding (RLE) scheme. In the RLE method, the two most significant bits of a byte signal whether it is a run-length count or a literal pixel value, allowing repeated pixels to be stored compactly.
How PCX Works
A PCX file opens with a fixed 128-byte header recording a manufacturer byte, version, the image's window dimensions, resolution, bits per pixel, the number of color planes, and palette data.[1] Image data follows as scanlines compressed with a byte-oriented run-length encoding: if a byte's two most significant bits are set, its lower six bits give a repeat count for the following byte; otherwise the byte is a literal pixel value.[2]
Color and Palettes
Early PCX versions handled monochrome and 16-color EGA images using a palette stored in the header.[2] Version 5 added support for 256-color images via an additional 256-entry, 768-byte VGA palette appended at the end of the file, marked by a leading 0x0C byte, as well as 24-bit truecolor stored across three planes.[1]
History and Legacy
ZSoft introduced PCX in 1985 as the native format of its PC Paintbrush program, making it one of the earliest widely supported raster formats on DOS systems.[1] Its simple RLE scheme is fast but compresses poorly on detailed images, and the format was gradually displaced by GIF, PNG, and JPEG; it is now largely of legacy and archival interest.[3]
MKV Technical Specifications
PCX vs Other Image Formats
| Feature | PCX | BMP | PNG |
|---|---|---|---|
| Type | Raster | Raster | Raster |
| Compression | RLE[1] | None or RLE | Lossless |
| Color depth | Up to 24-bit[2] | Up to 32-bit | Up to 16-bit |
| Transparency | No[2] | Limited | Yes |
| Era | Legacy DOS/PC[1] | Windows | Modern web |
| Best for | Legacy paint files | Windows images | Web graphics |
PCX was a widely used early PC paint format with simple RLE compression, but it has largely been superseded by BMP and PNG.
Advantages & Disadvantages
Advantages
PCX applies simple run-length encoding that reduces file size on images with runs of identical pixels without discarding data.
Its fixed header and straightforward RLE scheme make PCX easy to parse and implement.
As an early DOS standard, PCX was supported by a wide range of legacy graphics and paint software.
The format handles indexed-color images with embedded palettes as well as multi-plane color data.
Disadvantages
PCX has been superseded by formats such as BMP, JPEG, and PNG and is rarely used in modern workflows.
Its byte-wise RLE is ineffective on complex or photographic images, where it can offer little size benefit.
Many contemporary applications no longer read or write PCX without specialized tools.
Common Use Cases
PCX is encountered mainly when working with legacy DOS-era graphics.
Legacy file recovery | FileFormer
PCX support is needed to open images created by older PC Paintbrush and DOS applications.
Retro and archival graphics | FileFormer
The format appears in archives of vintage software, clip art, and game assets.
Simple indexed images | FileFormer
PCX can still serve as a straightforward container for palette-based images with run-length compression.
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Try Image Converter FreeFrequently Asked Questions
What does PCX stand for?
PCX stands for PiCture eXchange, the native image format of ZSoft's PC Paintbrush program.
Who developed PCX and when?
It was developed by ZSoft Corporation and introduced in 1985 for PC Paintbrush.
Does PCX use compression?
Yes. PCX requires its image data to be compressed using a simple byte-wise run-length encoding (RLE) scheme, which is lossless.
Is PCX still used today?
Rarely. It has largely been replaced by BMP, JPEG, and PNG, and survives mostly for opening legacy files and archival material.
Can PCX store color images?
Yes. PCX supports indexed-color images with embedded palettes and multi-plane color data, in addition to monochrome and grayscale.