From Just Solve the File Format Problem
RDIB (or RIFF DIB) is a raster image file format based on RIFF and BMP. There are two varieties: "simple RDIB", which is a standard BMP file in a RIFF container, and "extended RDIB", which is more complex.
Files begin with bytes
'R' 'I' 'F' 'F' ?? ?? ?? ?? 'R' 'D' 'I' 'B'.
- RDIB is defined in the RIFF specifications.