BMP Image Format

The BMP file format is the standard for a Windows 3.0 or later DIB(device independent bitmap) file.

A BMP file contains the following data structures:

HEADER bmfh;
INFOHEADER bmih;
RGBQUAD aColors[];
BYTE aBitmapBits[];

HEADER contains some information about the bitmap file. INFOHEADER contains information about the bitmap such as size, colors. The RGBQUAD array contains a color table. The rest is the image data, which format is specified by the bmih structure.

You can explore more about this and sample codes at
http://astronomy.swin.edu.au/~pbourke/dataformats/bmp/
and
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_2h6a.asp