I’m too tired to write a long rant, go see this thread for more. Here are the basics:
I’m creating a print of Procastination, and I may as well use the print-in-progress as an example. The original file is a 16-bit tiff in ProPhoto RGB (its the colourspace Lightroom uses) . It renders thus in Photoshop:
(Apologies for the small file size, these are taken from screen caps)
I then opened the file as-is in the Gimp:
It looks like ass, frankly.
I then went back to Photoshop, converted the photo to standard sRGB and downscaled it to 8 bit. The photo looks much better, but still like ass in comparison to the original: