For months I've wrestled with the ongoing process of finding the best possible images of Richard Amsel's artwork for use in the film. Many of these are from scans of newly acquired transparencies, while many others required my actually buying old posters and cleaning them up.
Sometimes it's easy. THE LITTLE PRINCE, for example, was rather simple to do. The final poster art of THE BIG SLEEP, however, was a bit of a nightmare. I bought an original poster from 1978, scanned it piece by piece, "puzzled" it together (a long, laborious process)...but ultimately, I had to give up. The reason: the multitone color printing process used on some older posters causes a whirlwind of issues when scanning, even at high resolution (over 400 pixels per inch). This causes a "banding" effect in images that is difficult to fix, especially when the overall image is itself a stitched collage of multiple scans.
Ultimately, I had to rely on a best quality image available, "uprez" it to a larger size for editing, and then do my best to clean up and color correct.