post processing - Astrophotography picture with too much noise. How do I correct this in postprocessing?

This is the Milky Way above Kakadu National Park, Australia, and my first try at astrophotography.

Thirty second exposure, f/4.0 at 17mm with ISO 12800 (!!) which in hindsight probably was way too high and resulted in a lot of noise. I also used Picasa to increase contrast, but I probably went a bit overboard there as well.

This is the original RAW file (.CR2), I am looking for input on how to better postprocess this picture to reduce noise.

Answer

Firstly had you lowered the ISO whilst staying at 30s f/4 you wouldn't have ended up with any less noise.

There's probably nothing you could have done to prevent the noise, I presume f/4.0 was the maximum aperture and if you went any longer than 30 seconds you would get star trails. You might even get less noise if you raise the ISO but that's another story.

However there's plenty you could do to rescue the image, the main thing is reducing chroma (colour) noise. Most noise reduction plug-ins as well as RAW converters give you the option of reducing only colour noise.

Here is the image with some brute force chroma noise reduction (split to LAB in GIMP and then Gaussian blur of 250 to the A and B channels):

The noise reduction has also fixed the magenta cast caused by noise in the red channel. A dedicated noise reduction plugin could do much better than this. A little luminance noise reduction would help too, but not too much in case it mistakes the stars for noise.