BMP / DIB / RLE File Formats

The BMP, DIB, and RLE files are known as "Device Independent Bitmap" files, or "DIB's".

These files exist in two different formats:

1. OS/2 Format
   - The OS/2 formats were the first of the two different formats designed. Images saved using this format may be used with the OS/2 Presentation Manager.
2. Windows Format
   - An enhanced "DIB" file format was released with Microsoft Windows.

These files commonly use different extensions for their file names: BMP, DIB, and RLE, according to where they are used. Although their file name extensions are different, the files themselves are the same (within either OS/2 or Windows).

BMP (Bit-Map) (20,056 bytes)

• BMP is the standard MS-Windows raster format.
• BMP files can be created with Windows' Paintbrush and used as "wallpaper" for the background when running Windows.
• Windows uses a fixed color palette for BMP files which cannot be changed, as doing so would make the screen and border colors change too. This means that transferring an image to the BMP format may result in some color shifts when BMP files are imported into Windows applications.
• Characteristics:
  • BMP - OS/2 - RGB format supports 1, 4, 8, 24 bits per pixel - not compressed.
  • BMP - Windows - RGB format supports 1, 4, 8, 24 bits per pixel - not compressed.
  • BMP - Windows - RLE format supports 4, 8 bits per pixel - RLE compression.

DIB (Device Independent Bitmap)

• DIB files are applied mainly in computer multimedia systems.
• They can also be can be used as image files in the Windows environment.
• Characteristics:
  • DIB - OS/2 - RGB format supports 1, 4, 8, 24 bits per pixel - not compressed.
  • DIB - Windows - RGB format supports 1, 4, 8, 24 bits per pixel - not compressed.
  • DIB - Windows - RLE format supports 4, 8 bits per pixel - RLE compression.

RLE (Run Length Encoding)

• RLE files are actually "DIB" files that use one of the RLE compression routines. A DIB image that has been saved by means of using one of the RLE compression methods would produce an identical file as when saving the same image directly in an RLE format.
• The only difference would be the file name extension.
• Tip: An RLE image file may be used as a replacement opening screen for Windows.n for Windows. (It must be a 4 bit per pixel RLE file.)
• Characteristics:
  • RLE format supports only 4 or 8 bits per pixel.