Behind The Scenes, 7 August 2019: Exploring Film Types
by James Gibbs, Media Technician
In my last few blogs I’ve looked at working with the ‘digital surrogates’ of our films and the post production work we carry out before the films go on display. But what types of film do we work with and how do we create these digital surrogates?
For most people, film is a thing of the past but for us, working with it is an everyday thing. It’s a wonderfully tactile medium – you can touch it, smell it (yep, our film vault has a whole heap of different smells going on!), see the images directly on it and hear it as it moves through the equipment we use. It’s also one of the most robust storage mediums around. If it’s properly looked after, quality film will easily last more than a century.
Motion picture film is made up of a light sensitive emulsion which is applied to a base. The emulsion contains silver halide grains which react with light to produce an image. Colour film has three layers of silver halide, for the yellow, cyan and magenta colours which combine to create a colour image.
Historically, the base was made from cellulose nitrate. This material has the unfortunate side effect of breaking down in to a very flammable gas. Many fires in cinemas have been caused by this and you now need specialist equipment and storage to deal with nitrate film. In the 1930s safety film was introduced with a base made from cellulose triacetate and later again, a polyester base was adopted. Thankfully, it’s rare for us to come across nitrate film.
We work with several common gauges of film:
In the photo above, from left to right we have:
- 35mm 4 perf positive colour print with optical audio track
- 16mm positive colour print with magnetic soundtrack
- 16mm magnetic soundtrack
- 9.5mm positive black and white
- 8mm positive colour
- S8mm positive colour
8mm and Super 8mm are considered an ‘amateur’ gauge and, if you’ve ever huddled round a film projector to watch your grandparents or great grandparents wedding, the chances are it was shot on 8mm. It was developed in the early 1930s and remained popular until the 1980s. Super 8mm has much smaller perforations than 8mm which allows for a larger frame and therefore better image quality.
9.5mm is another amateur gauge, introduced in 1922. The perforations are in the middle of the film, so the image size is much larger than its name suggests.
16mm and S16mm are regarded as professional formats. The majority of our core film collection from the Westward and TSW television companies was shot on 16mm. It’s capable of great quality and had the option to record a magnetic audio track in camera, host combined magnetic or optical tracks and be synchronised for multitrack sound work.
35mm was the cinema standard – with a huge image size, amazing picture quality and the ability to host multiple audio tracks. It was a mainstay of the cinema world for most of the 1900s but has largely been superseded by digital.
So how do we digitise these films? We have a film scanner, capable of digitising all of them and their associated audio tracks. It’s a fairly complicated piece of equipment but the principle is really simple: it’s a camera with a flash.
The film is pulled through a gate and as each frame passes through, a flash fires and a still image is taken. Each of these frames is recorded as a Digital Picture Exchange (DPX) image and when these are played back in succession, we have our motion picture. There are various controls on the scanner for us to adjust for the physical condition of the film and ensure the colour balance is correct and the digital surrogate is the best copy of the film we can produce.
The scanner has a resolution of 2336 x 1752 pixels. This is pretty much the limit of resolution of good 16mm film. The DPX image sequences it produces are huge. An hour-long film results in almost 1.2TB of digital information – enough to fill the hard drive on an average laptop. So, we obviously need lots of storage for our digital media and fast networks, fast media drives and powerful computers to move the files around and work with them. Everything takes time but the benefits of working with such high resolution images, both for post-production and archiving far outweigh the downsides.
So, enough of the technical waffle, let’s see the scanner doing its thing. The film being digitised is an episode of a Westward Television series called ‘Walking Westward’, shot on 16mm with a combined optical audio track.