Frame Remapping for Virtual Production

One of the benefits of working with a fantastic multi-disciplinary team is range of creative ideas which we come up with. One idea is to utilise the high frame rates of the LED displays to alternate between multiple images, in the same way that stereo shutter glasses alternate between left and right eye images, used in CAVE‘s and the now dead 3D TV‘s. By synchronising the cameras with one or more of the synchronised feeds, a couple of applications arise:

  1. As the virtual camera is rendering the scene from the view point of each physical camera, the view of each camera is different. By alternating between the camera views it is possible to ensure each camera is synchronised with it’s individual virtual camera view, enabling multi-camera configurations. This is particularly relevant in broadcast scenarios.
  2. By alternating between camera view and a chroma green (or any other colour you desire) it is possible to capture a green screen image to assist in post-production VFX.

Like all good ideas, it turns out that this technology has already been integrated into the Brompton controller, and details of this are described here. The feature, snappily titled “frame remapping” allows you to quickly manipulate the signal to the LED wall by applying a frame multiplier which inserts additional frames into the stream. For a video signal of 50Hz, adding an additional frame will double it to 100Hz, doubling the data throughput to the LED display, which is something which needs to be taken into account when configuring the wall. The Brompton also accounts for shutter speed / angle which will improve the alignment of the frames in camera (we found that an additional shutter angle offset was required which was found by trial and error). Note that there can be only one HDMI feed to the SX40 or S8 processors so in order to flip between multiple camera feeds they will need to be sent in a combined feed (for example, concatenated side by side in the x) with an offset applied to separate the signals.

An example of testing (2) is shown below, with the colour image rendered on the Atmos (above) and the green on the camera viewer:

Frame Remapping

Alternating the video feed with chroma green using Brompton’s Frame Remapping technique. Note the LED panel in the display is the ROE Black Onyx 2, although 4 panels were tested. Hay-bale test image and this image courtesy of Rehan Zia.

A few words of caution:

  • This is not easy on the eye, and the Brompton software does clearly warn that this carries a severe epilepsy warning.
  • It is also the case that the display potentially distracting to the actors involved as it may be difficult to elicit the best performance when performers are distracted by constant flickering.
  • Also bear in mind the data rate issue mentioned above, as this may require compromises to your wall layout, colour depth or other parameters to ensure the display receives a complete signal.

We have yet to integrate this technology into a full workflow, and will not be doing so for some time as these LED panels were just on loan for testing. However it does have great potential and I look forward to seeing whether / how VFX studios make use of this feature!

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