“Video Look” vs. “Film Look”
The next subject is the cause of a lot of discussion among cinematographers, which is “video look” vs. “film look”. Here’s what generally makes the difference on the timing front.
- Most “video” cameras used to shoot at 29.97 frames/second (or 59.94 interlaced fields/second), resulting in a very characteristic look.
- Film cameras shoot at 24 frames per second, and film is projected at 24 fps with a triple bladed mechanical shutter that blinks the image on and off a couple of times per frame.
- Most electronic cameras that are set up for digital motion picture shooting actually operate at 23.976 frames per second (called 23.98p). Even when the camera is advertised as 24p, if it’s an electronic camera it’s 99.9% likely that it’s actually shooting at 23.976 frames/second. This is so that the signal remains compatible with the 29.97 frames/second rate that is used by most video playback systems.
- Almost all video cameras that are shooting 23.976 frames per second transmit the data over a serial digital connection called HD-SDI. (High Definition Serial Digital Interface.) The frame is captured in one shot at the sensor (called “progressive scan”) and transmitted in two separate fields. This progressive capture/segmented field combination is called 23.976 PsF. It’s used on every Sony camera (F23, F35, F900, F950), the Panavision Genesis, and most other digital motion picture cameras.
A few cameras use a 2:3 pulldown, where they shoot 23.976 frames per second progressively, then put this into an output stream at 59.94 interlaced fields/second, by repeating fields. Since Previzion expects a steady stream of frames, the uneven frame timing causes problems. We have some code that can perform a reverse pulldown, and extract the progressively scanned frames, but it’s painful to deal with, and you’ll need to externally “genlock” the camera to our sensors to get it to sync properly.
The RED cameras shoot internally at a 4k resolution, but have a live video output that has a 2:3 pulldown that is placed into a 720p 59.94 video stream. The Previzion RED input setting automatically removes the pulldown, so that the correct frames are shown. This also requires an external genlock to get the sensors to sync properly. (Genlock is discussed below.)
Synchronization with the RED is still experimental. It works, but intermittently.