"One of the things that is particularly difficult to work out is what is good and what is better," Catherine Higgitt, Principal Scientific Officer at the National Gallery, tells BBC Culture. "We're separating an image into two hypothetical images, but what is it we're trying to get? Is that something useful to a conservator – interested in damage, cracks and subsurface details – or something that looks as close to the image at the surface as possible?"
