OS/2 bitmap family

From Just Solve the File Format Problem
Revision as of 01:13, 13 November 2014 by Jsummers (Talk | contribs)

Jump to: navigation, search
File Format
Name OS/2 bitmap family
Ontology
Extension(s) .bmp, .pm, .bga
PRONOM fmt/115, x-fmt/270

IBM OS/2 BMP (also known as Presentation Manager Bitmap or PM Bitmap) is a family of raster graphics formats used on OS/2. It is closely related to Windows BMP.

The term OS/2 BMP can refer just to the "bitmap" formats (files with a signature of "BM"), or to the family of formats that also includes specialized icon and pointer formats.

There are two major versions of the bitmap format: OS/2 BMP 1.0, and OS/2 BMP 2.0. For details, refer to BMP.

For details about the icon format, see OS/2 Icon.

For details about the pointer format, see OS/2 Pointer.

Contents

Format

All files begin with a 14-byte "file header", of which the first two bytes are an ASCII signature indicating the file type.

Signature Image type Notes
BA Bitmap Array BA format is a kind of container format for one or more images in the other formats (often used with CI format).
BM Bitmap Refer to BMP for more information.
CI Color Icon Refer to OS/2 Icon.
CP Color Pointer Refer to OS/2 Pointer.
IC Icon Refer to OS/2 Icon.
PT Pointer Refer to OS/2 Pointer.

OS/2 BMP vs. Windows BMP

OS/2 BMP 1.0 and Windows BMP v2 are sometimes said to be identical, but apparently that's not quite true. In OS/2 BMP formats, the "Size" field at offset 2 (variously named "cbSize", "FileSize", or "bfSize") is supposed to equal the size of the headers (always 26 for OS/2 1.0; usually 78 for OS/2 2.0). In Windows BMP, it equals the file size.

However, some OS/2 2.0 files have the field set to the file size, Windows-style. And some OS/2 1.0 files that are clearly from OS/2 systems do as well, making them completely identical to Windows BMP v2.

The difference is mostly irrelevant, though it could help to identify some OS/2 2.0 files as such. The Size field is redundant and unreliable, and is ignored by most BMP viewers.

Software

  • Deark can extract the contents of BA files

Specifications

Sample files

BM (1.0)

Refer to BMP (Windows BMP v2).

BM (2.0)

BA/BM

Links

Personal tools
Namespaces

Variants
Actions
Navigation
Toolbox