I'm collecting information and samples of proprietary RAW formats from digital still photography devices. Their usage is increasing with the new multi-megapixel cameras.
Simply put, image files in RAW format contain raw data (Bayer array) directly from a CMOS sensor; pure, unprocessed and lossless, opposed to typical JPEGs, where lossy compression is used to reduce file size (and quality).
Unfortunately, there is no universally accepted RAW standard format, so each manufacturer format (even on model basis) differs.
Fortunately, three of the formats are now reverse-engineered.
Support for RAW formats in free software is desirable:
From RAW data, images can be individually customied, different versions of the same image can be created and compared. In addition, any noise in images taken at higher ISO (typically 800 and 1600) can be significantly reduced by saving in RAW format vs. JPEG.
As the CMOS data is stored in a lossless format, no data is thrown away, allthough obfuscated with proprietary compression algorithms. In the case of Canon's RAW formats, they use (until recently secret) proprietary compression algorithm, that reduces the file size greatly. Some RAW formats, like the ones by Nikon in their D1-series cameras, Kodak in their DCS cameras, and Canon in EOS-1D, are disguised as a TIFF, but the data is still proprietary.