In our previous post we looked at fixing a super 8 film projector. While watching filme with a real projector has its own charm, it is inconvenient to say the least. First of all you make the entire room properly dark or you can't see anything. This is regardless of the fact that the projector bulb is consuming 100 watts of power to show the image. Even if you manage not to burn the film merely running it through the projector causes wear, scratches and tearing. While film typically ages very well, eventually it will turn into magenta goop or gets eaten by vinegar syndrome. Thus you'd really want to convert all these films into high quality digital files.
There are several companies that offer this service. If you only have a few rolls, using those is the smart thing to do. I, on the other hand, have so much material that using a commercial service would cost thousands (possibly tens of thousands) of euros. Fortunately, this is a fairly common problem and there are dozens of existing projects on the Internet to be inspired by.
The main technical problem with super 8 film is that it is very small. A sequence of 10 super 8 images is approximately as long as a matchstick. The fact that projectors can display 18 frames per second with sub millimeter registration is an astounding achievement of mechanical engineering. How do they do that? Very difficultly.
Many of the DIY solutions start by taking an existing projector and modifying it to run slower. Then you remove the projection lens and aim a digital camera with a macro lens at the gate. This yields incredible results quality-wise but requires a fairly expensive macro lens and typically the modification on the projector is destructive. So that's out. Some more searching eventually lead me to this Github project.
The basic idea is simple. Instead of using a projector or trying to replicate a film transport (which proper tension and all that) instead rely on the basic stiffness on film and drive it directly with stepper motor. Film is not aligned mechanically but instead by detecting the sprocket hole with some straightforward machine vision code. Time to fire up the ol' 3D printer and order components. This is what the end result looks like after assembly
The thing at the top left that looks like a space cannon prop from a scifi movie is actually a microscope lens. Not only can it do > 1x optical magnification, it can do so at a cost of about 25 euros. The downside is noticeable chromatic aberration. The small flat thing on the other end is the Raspberry Pi HQ camera module that can do 4k at 12 bits per channel. The whole thing is run via a single Raspberry Pi 3 with a stepper motor hat. The board at the bottom is used to distribute 12V DC power to the lamp and motors.
Before going further, let's just spend some time appreciating just how awesome colors look in this film. Props to the chemical engineers at Kodak. And remember, the original image is about one third of the size of your smallest fingernail.
The Github repo says that you probably need to adapt the code to your setup. I basically ended up rewriting all of it from scratch. In the process I learned that OpenCV has its own GUI toolkit which is both simple (one could even say simplistic) and perfect for this use case. The first attempt took nine hours to process one 3.5 minute reel of film. Then I realized that trying to do 4k on material that physically maxes out at approximately 2k with the processing power of a potato is not a recipe for success. Halving the capture resolution and a few other optimizations brought the runtime down to about one hour per reel.
With this, some more custom software for image processing and stabilization coupled with FFmpeg scripts one can start to go through the archive of films. Doing so raises a fair bit of questions. For example:
Is that a 3 year old child driving a jury-rigged go-kart on a frozen lake on his own without even wearing a helmet?
Yes it is. A bit later an adult drives the car but he is too heavy so the ice cracks under him. No one seems particularly concerned. This may seem strange to us but you have to understand that this was the very early 70s. The concept of safety had not been invented yet.
