New Technologies Amplify Judder

Day 2 was tight on time for all of the speakers – Welsh announced at the start of the day that, if they overran, he would sound a horn and they’d have to leave the stage no matter what they were doing. “It’s a blood sport, you’ll love it,” he told the audience.

Tony Davis of RealD talked about frame rates. Even back in the 1800s, when motion imaging was first invented, judder was a problem – but manageable. As new technologies like HFR and UltraHD have been added, the problem has become more obvious.

Judder is often left in for aesthetic reasons: removing it completely makes images appear “too soft”. The camera shutter function is key to judder: the artefact is caused by the way that the shutter represents moving images in a single frame. Other artefacts include strobing (caused by the way the projector reproduces motion stored in a sequence of frames), exposure and noise. Shooting at short exposure times raises image noise, especially if camera gain is also brought up (as it often is in this work).

Davis showed a very good demonstration of 24fps video compared to 60fps, with various basebands and either 180° or shaped shutters. The content (a moving car) became progressively better – and then much worse. When asked what was wrong with the last clip, he revealed that it was the original 24fps sample!