alt Hacker NewsI'll do you one better, which requires no special cameras (most have IR filters) nor double cameras or prisms.
Shoot the scene in 48 or 96 fps. Sync the set lighting to odd frames. Every odd frame, the set lights are on. Every even frame, set lights are off.
For the backing screen, do the reverse. Even frames, the backing screen is on. Odd frames, backing screen is off.
There you go. Mask / normal shot / Mask normal shot / Mask ... you get the idea.
Of course, motion will cause normal image and mask go out of sync, but I bet that can be remedied by interpolating a new frame between every mask frame. Plus, when you mix it down to 24fps you can introduce as much motion blur and shutter angle "emulation" as you want.
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Somebody recently used a variation of this to get good video of welding - basically a camera synced with a very bright (strobe-ish) light, brighter than the weld itself, so you adjust the camera to the ludicrous-but-consistent brightness level and get details of the weld and the surroundings. https://www.youtube.com/watch?v=wSUxK8q4D0Q (Chronos "Helios", from early 2025)
Two problems:
- It'll bleed on fast motion. Hair in the wind would just not work.
- Incandescent lights are out.
You could solve both by having two ghost frames shot very close to the real frame (no need to evenly space the frames, after-all) and using strobing a high powered laser.
You'd need very fast sensor or another one optically on the same position.
Surely this makes your actors feel sick? And wouldn’t it make your motion blur look dashed and also cause artifacts at the edge of the mask if there’s a lot of motion?
this is the approach that stop motion uses, except they get to keep the camera in the same place. its still not perfect because of spill from the background onto the foreground and requires additional masking and cleanup.
Corridor Crew cover this in one of their VFX breakdowns where I can't remember the film but it was supposed to be filmed on a rapidly rotating platfom.
There were a large number of lights around it and each one was blinked on for an instant while the camera shot at an insanely high frame rate - something like 288 frames per second with twelve lights.
This meant that after the fact you could pick any one of the twelve frames for that 1/24th of a second, to choose the angle the light was hitting at.
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This is called “ghost frame” and already exists in Red cameras and virtual production wall tools like Disguise.