GIMP opens RAW images, with UFRaw
GIMP won’t open raw image data files, unless you install a plugin. UFRaw (Unidentified Flying Raw) is a tool you can use as a Gimp plug-in. It reads raw images. It can read Nikon’s tone curves. It supports most of the existing raw formats (any format supported by DCRaw).
UFRaw reads raw images, using dcraw as a back end, and supports color management via LittleCMS, allowing the user to apply input, output, and display color profiles. This allows UFRaw to support a large number of raw image formats.
Install UFRaw and forget about it! To work it needs some files that GIMP won’t use anymore, therefore, if you try to open it directly you will receive messages such as “The code execution cannot proceed because libgdk_pixbuf-2.0-0.dll was not found. Reinstalling the program may fix this problem.”
Just download UFRaw, install it and forget about it! Open GIMP and in the Open File dialogue you will now be able to open RAW images.