Digitally remastering old films
MORE THAN two million films languish in vaults around the world, some of them so dadly damaged they can no longer be screened If nothing is done. They could disappear for good, like half the films made in the U.S. before 1950.
But research at the University of La Rochelle in France and Monash University in Clayton, Victoria promises an automated technique to restore these old films to their former glory.
Films can be cleaned chemically or by using ultrasound. But this is time consuming and expensive,and chemicals also damage the original.
Another Appraoch is to digitize the film and then clean upthe digital version frame by frame – daunting job. These computer aided techniques remain ery expensive, says Samia Boukir., who started work on an automated system in La Rochelle but has now moved to Monas.
Only an automated system can hope salvage the archive of deteriorating film.
Once a film has been scanned in, the first stage of the process is to correct flicker cuased by the film sliping- the result of damage to its perforation. The software picks out distinct features in a pair of frames such as prominent pieces of background, and measures movement of the features between the frames and again notes the difference. Then it moves on to the next page and again notes the differene.
Using this information, the system works out if two frames are unusually close together or far apart and corrects any anomalies.
Dust spots usually occur only on single frames, as the system looks for small specks that are visible on one frame and absent on its neighbour.
The software repairs the image by sampling the unspoilt area of the image on the adjacent frames and replacing the dust spot with an average of the sampled pixels.
Detecting scratches is more complicated because they may run over several frames and can be confused with vertical lines that are part of the film.
But a telltale pattern often gives them away: scratches are normally caused by the mechanical parts of a projector rubbing on the film, so they tend to repeat at regular intervals.
Having identified the scratch and its duration the software then repairs the damage by taking pixels from undamaged frames before and after the scratch.
This smoothing effect avoids any sharp edges in the restored image, says Boukir. Finally, film grain is added back.
When detecting dust particles, says Boukir, 95 per sent accuracy is acceptable. But with line scratches it has to be better.
Because of this, some level of human intervention will be needed, but it is likely to be little more than an operator accepting or rejecting a change.
She says that instead of trying to enhance the whole image on a frame, it is better to concentrate on repairing damage.
Once restored, the digitized films can be viewed by future generations without risking more damage to be original be running it through a projector. And films are very vulnerable.
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