James White

Here's an interesting  interview with BFI restoration supervisor James White:

Some Came Running// Film Restoration in the Digital Domain

White's philosophy is to remain true to the film's aesthetic history and make sure the restoration is an accurate representation of how the film would have looked when it was originally shown at the cinema.

Frames can be cleaned up and flicker removed but the actual level of detail within the image is dependent on the original elements.  In some instances films have been over polished and the de-grain process has been pushed so far that the end product looks more like an oil painting or a PlayStation game than a film. In the case of The Wizard of Oz the digital cleanup was so sharp it allowed audiences to see things that the filmmakers at the time had never intended to be seen, such as the wires holding up the scarecrow.