Keep an eye on this software. CinePaint is being ported to Windows as Glasgow. CinePaint, aka Film Gimp, is an opensource software package used by some movie studios for retouching. It has been used on movies such as Harry Potter and The Last Samurai. It is for high fidelity image formats. CinePaint will use 8bit, 16bit or 32bits per channel colors as needed. So, it isn't geared for computer images, which are 8 bits per channel or 8 bits for gifs.

CinePaint Glasgow