Windows 3.11 Paintbrush Image File Format

Microsoft Windows 3.11 featured Paintbrush as its built-in raster graphics editor, which primarily utilized the Windows Bitmap (BMP) and PCX file formats. While the Windows Bitmap format served as the default standard for the operating system, Paintbrush maintained native support for the PCX format due to the software's historical development. This article outlines the specific roles of BMP and PCX in Windows 3.11, their technical characteristics, and why these formats were chosen.

The Default Format: Windows Bitmap (BMP)

The primary and default file format for saving raster graphics in Windows 3.11 Paintbrush was the Windows Bitmap format, denoted by the .bmp file extension. Paintbrush also supported the closely related Device-Independent Bitmap (.dib) extension.

Microsoft designed the BMP format to ensure that graphics could be displayed consistently across different video hardware and display adapters. In Windows 3.11 Paintbrush, BMP files supported several color depths:

  • Monochrome (1-bit): Black-and-white images with two possible colors.
  • 16 Colors (4-bit): The standard color palette supported by baseline VGA hardware.
  • 256 Colors (8-bit): Used indexed palettes compatible with Super VGA (SVGA) drivers.
  • 24-bit Color: True color capabilities, limited mainly by the user's installed graphics card.

BMP files stored raw, uncompressed pixel arrays or utilized simple Run-Length Encoding (RLE) for 4-bit and 8-bit images, making them computationally lightweight for the hardware of the era.

The Legacy Format: PCX

The secondary raster format natively supported by Windows 3.11 Paintbrush was PCX (.pcx). Paintbrush was originally developed by ZSoft Corporation under the name "PC Paintbrush." Microsoft licensed a customized version of this software to bundle with early editions of Windows, retaining the software's native PCX file handling.

PCX was one of the earliest widely accepted raster image formats on the IBM PC platform. It natively used byte-oriented Run-Length Encoding (RLE) to compress image data, which typically produced smaller file sizes than uncompressed BMP files. Paintbrush allowed users to both open and save graphics in the PCX format, ensuring backward compatibility with DOS-based graphics software and desktop publishing suites of the early 1990s.

Summary

Users creating raster graphics in Microsoft Windows 3.11 Paintbrush saved their work primarily as BMP files or alternatively as PCX files. The adoption of BMP anchored the graphics directly into the Windows display subsystem, while PCX compatibility provided interoperability with legacy PC software until Microsoft introduced the modernized MS Paint in Windows 95.