of course one cannot really get the most from a digital image capture without using the most of the data, and to do that, one need RAW, and of course RAW convertor before one can do any more image PP on them, and while many commercial ones are available. These followings are not to be dismissed. In fact many are more powerful ( and also difficult to master ) than like of commercial offering. But then they also are all capable to simple and straight forward working of RAW captures
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http://ufraw.sourceforge.net/Install.html - UFRaw
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http://www.i-graph.com/?q=node/2 - RAWConvert
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http://rawstudio.org/compatibility.php - RAWstudio
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http://www.rawtherapee.com/ - RAW Therapee
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http://bluemarine.tidalwave.it/ - blueMarine
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http://www.astrosurf.com/buil/us/iris/iris.htm - IRIS ( only for Astro photography )