The Digital Film Restoration Process

The digital film restoration system LIMELIGHT was developed by Joanneum Research (Graz) and has been successfully applied to restoring parts of the Austrian film 'Opernball'. The split-screen image shows the heavily distorted original on the left half and the restored frame on the right. Frame 1

The restoration process starts with the conversion of each frame to a digital image with a high resolution film scanner. The size of a digital color image is up to 45 MBytes per frame.

The next phase includes the detection of cuts and scratches parallel to the direction of film transport, which are the first defects to be removed. In each shot or scene a reference frame is automatically chosen for the brightness correction.

Frame 2

Furthermore a motion analysis ( local and dominant ) is performed to enable the detection of single frame anomalies by motion compensated frame differencing as well as camera movement necessary for detecting image vibrations. The final restoration phase consists of the removal of single frame artefacts, of noise suppression and image stabilisation.

While all these steps are performed automatically, there is also the possibility for an operator to make changes if necessary. The parameter settings and the choice of reference frames can be modified on operator request.

The last step can be either the transformation of the image sequences back to celluloid film or the storage on proper digital media.

Removable Classes of Artefacts:

A Sample Dust Mask

The upper left image shows the original frame - maybe the artefacts due to dust are hard to see on your display. During the restoration process the pixel differences to a previously generated reference frame are calculated, resulting in the dust mask (middle right image).

Frame 3

The pixel differences due to the actor's motion must not be taken into account. This is achieved by tracking the motion of neighbouring pixels through subsequent frames and compensating for pixel changes due to the detected motion.

The pixels indicated by the dust mask are eventually restored using an average value from the previous and next frames. The result is shown in the bottom image.