But most of them, and all of the original negatives, were made using traditional chemical processes.

Crackles and clicks that have blighted the sound have been removed, while dirt, green spots, in the original negatives have been deleted and repaired.

The exhibition comprises about 100 images, including original negatives, and explores the lives and careers of the four, through shared ideas and subjects.

The color of many of the original negatives has degraded.

In the 1980s, the original negatives were lost and feared destroyed.