OpenTelecine, OpenCV, image processing

The two biggest challenges to overcome in the OpenTelecine project are optics and image processing. In previous blogs, we discussed some accomplishments in image processing for the rectangular geometries found in 8mm film frames and film spool holes. In this blog, we shall discuss the failures and upcoming challenges in configuring the camera and OpenTelecine optics to illuminate and capture 8mm frames.

The first image is a prototype of a projector using a SparkFun cardboard box, Petzl LED headlight, and an existing projector optical focus. An unusual attribute of this prototype is the lack of a well defined aperture. In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. In our case, the aperture was cut out to be a large rectangular hole that spans multiple 8mm frames. Another unusual characteristic is that the film rests on a adjustable back-plane. This allows for the projector to have two optical parameters to adjust: the optical focus and the distance to the back-plane.



The prototype projector was set up in a dark room to project the 8mm film on a whiteboard. A Nikon D90 camera was set off to the side and capture a 10 second exposure of this image. Notice the imperfection in this photo, where the center spool hole is in perfect focus, whereas the left and right spool holes are not. Another unexpected discovery is that the images smear and streak off between frames, which is caused by the mechanical shutter and film transition. This is solved in practice by reducing the aperture size. 8mm film cameras generally have larger apertures then the projector, which causes a projector to display only a subset of each original frame. Striving to capture the maximum available frame in the OpenTelecine will be difficult because the frames will not have perfectly shaped rectangular frames and spool holes. The top of each frame will be smeared and streaked, whereas the spool holes are rounded rectangles.




Instead of capturing the film off the whiteboard, the camera and projector were placed inline to face each other directly. Notice that the images captured by using this approach are completely and totally unacceptable. Is this project doomed to fail?

Reflection, refraction, and chromatic dispersion are well understood, and there are precise mathematical solutions to this problem. My next attempt will come by a recommendation, which is to place the camera and project perpendicular to each, with a mirror between them at a 45 degree angle.

The project currently uses Ubuntu 11.04 (simular to Microsoft Windows), OpenCV, gimp (similar to Adobe), GNU gcc (similar to Microsoft .NET), and Eclipse. Photos are generally taken with a Nikon D90 or Sprint HTC Evo running CyanogenMod (simular to Windows mobile cell phone and iPhone).