Originally Posted by Richard Lane
That's one way to think of it. Personally, I see it as more of a 9 to 1, and I'll explain why:
* Uncompressed 14-bit raw in the camera (27 MB)
* Lossless CR2 compression (like ZIP) in the camera (20-24 MB, depending on the scene)
* Raw file is decompressed and demosaiced to 16-bits in the raw converter (91 MB)
* Converted to JPEG (10 MB in your case).
So the JPEG doesn't really know that your image originally came from a 22 MB raw file -- all it knows about is the 91 MB image that is in your raw converter (e.g. DPP). It has to do the work of compressing 91 MB to 10 MB, so I see it as 9:1.
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