Behind The Scenes, 24 April 2019: Working with different frame rates
by James Gibbs, Media Technician
with thanks to Stacey Anderson, Media Archivist
At the Film and Television Archive we’re digitising a huge amount of film content for the new galleries at The Box. It’s given us a chance to put our film scanner to the test, along with the grading suite we purchased last year, not to mention being a great opportunity to work on some lovely bits of film!
One of these is destined to be one of the many films on display in our ‘Media Lab’ gallery and was shot in 1939 by a Mr Nicholls of Ebrington Street, Plymouth. It’s our earliest known colour film and was captured on 16mm at Gunnislake Carnival, just 6 months before the outbreak of World War II.
Kodak introduced their colour reversal film in 1935 so Mr Nicholls was pretty cutting edge! He must have been a relatively wealthy man too as shooting colour 16mm at this time wouldn’t have been a cheap hobby.
These ‘amateur’ collections throw up an interesting choice for us as Media Technicians: how to deal with differing frame rates. In the UK, we tend to use a frame rate of 25 frames per second (fps) for moving image. Our core collection was shot for broadcast and is all 25fps.
The amateur collections however tend to be shot at a variety of frame rates. Our earliest films were shot on hand cranked cameras, so the frame rate depends on how much porridge the person cracking the handle had for breakfast! Later films are often 16fps, 18fps or 24fps. In the case of Gunnislake Carnival film, it looks like it was shot at 18fps.
Playing these back at the 25fps we use in the UK gives everything a ‘Charlie Chaplin’ feel.
The software we use to grade our films has some clever tricks to convert frame rates though. The simplest, is to duplicate frames. This works for some material, but it can look very jittery.
Next up is frame blending. This looks a lot smoother but can lead to things becoming a bit blurry.
Finally we have optical flow. This is the most ‘clever’ method and takes a fair bit of computing power to achieve. The software looks at each frame and creates an entirely new frame based on what it sees until it has the required 25fps. With the right material, this can look very natural.
With the wrong material, it can look very odd. In this clip, the whole image appears to ripple.
All these methods introduce unwanted artefacts to the final video file but, whichever option we choose, we always have the archived film scan that is a frame for frame digital copy of how it was originally shot.
We’re far from alone in this. Peter Jackson recently released his amazing film of remastered WWI footage and used a similar software technique. This helped contribute to the ‘real’ feel of the footage. Not to mention the painstaking work and expertise he and his team put in to scanning, restoring and colouring the film and the huge amount of visual effects work that must have been required.
Something else that’s rather special about the Gunnislake Carnival film is that the fancy dress takes away some of the clues as to when it was shot. Without the period dress and hairstyles, those could be people from any recent time, enjoying their annual village carnival.