M31 Andromeda Galaxy
This was a real teaser my computer is seriously fast and this file kept me waiting for over 10 minutes to just save and crop at 100% CPU use. I see I now have a file of over 500MB. Not good if you are only using a smaller computer though, this one needs a health warning .....
Right, problem 1) The alignment of the FITS files is a nightmare as the only way I could get Photoshop Elements 2 to stop crashing was to guess the height and width of the files to align the star background. I see that even on your example the star background has a large amount of misalignment.
So to help I have noted the file sizes to assist the others who may follow. The image width is 251.5 cm and the best fit height is 249.24 cm (well good enough for me) remember to uncheck the constraints though. I tried using the 101.15% percent but the computer kept crashing. I found that two of the FITS files needed correction the blue and the red not just the red file as suggested but could just be file handling differences anyway.
Have fun with this and I look forward to see other goes and the comments etc. Just have a look at the star field inside the data it is fantastic the detail you see on the final output (Not this JPEG though this is only a mere 1 MB, best I can do for now. The challenge is ON !!!!
This fits liberator image is not available for sale.
Mike Herbaut & the ESA/ESO/NASA Photoshop FITS Liberator