Strictly speaking this post won't directly address you question Mike, but it might help to get to know IRIS...
I found the Sloan Digital Sky Survey site some time ago and they have a series of Basic and Advanced Projects on there. The Basic ones look like they might be aimed a school kids, and the Advanced ones at enthusiasts and uni students. One of the Advanced Projects is Image Processing - and they use IRIS.
I started working through this some time ago, but I haven't kept it up. The tutorial is for an older version of IRIS, but it's not too hard to work out how to adapt to the new version.
http://cas.sdss.org/dr5/en/
From the above page, under "Science Projects" select "Advanced". One the next page you'll see a project on "Image Processing".
While it doesn't directly answer your question about RAWs, the project is quite well written to step you through getting used to IRIS. Once you get past the initial steep learning curve, it may become obvious
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Al.