Removing the tripod or other rigging from an immersive media video improves the sense of presence for the viewer in a virtual scene.
Nadir tripod removal techniques Image: Light Sail VR
Read Time: 15 Minutes
Visually removing the camera support in post production is common when creating an immersive video. It can be distracting to see the tripod, rover, rail or cable supporting the camera in 360 or 180 video. Inevitably there will be stitching artifacts from that support hardware. Observing those set elements in an immersive video is distracting and can break the sense of being present in the story.
For 3D-180 media it's possible to mount the camera so that the tripod and film gear is hidden from the view of the camera, but for 360 there will typically be a visible tripod or other rig holding the camera. Removing this will help fully immerse the audience in the virtual world.
Some productions choose to blur the tripod area or composite a black void or circular logo where the camera sits. This is an acceptable method for productions without the time or resources to paint out or mask out the rigging on every shot. Many high quality immersive video projects employ the black void technique, as it provides the audience a platform to sit or stand upon while watching.
High end immersive video productions traditionally composite clean plate information which was captured during the shoot. Compositing a still frame or a short range of video frames as the nadir plate provides a more natural sense of presence than a blur, void, or logo.
The clean plate can be either a static image or a short sequence of captured video frames of the floor or ground where the rig would have been, with the same lighting as during the shoot. Capturing clean plate information is very important for floors or surfaces with complex details or patterns. As part of the production workflow, the clean plate is composited into the stitched video before any color grading occurs.
Note: A static clean plate frame can induce a perception that the patch appears frozen; to avoid this, capture a short range of frames with non-cohesive sensor noise to composite as the nadir patch.
If the camera is moving, while mounted to a rover as an example, the path of the rover and camera can be tracked over time using dedicated tracking software. A mask is generated which can be used to hide the rover frame by frame. Floor or surface image data in front of the moving rover is sampled as it moves. This sampled data is used to interpolate the fill plate, matching the perspective of the sample in relation to the rover and camera. Additional clean plates can be generated during the tracking process and can then be composited into a stitched version of the video.
Mocha Pro is an example of a software tool which can readily accomplish this. Our Create and track masks in Mocha Pro article will help you learn more about Mocha Pro's tracking and masking for removing moving cameras.
Rig removal in monoscopic video is easier than with stereoscopic video as there is only a single equirectangular frame in mono and no disparity issues vs a left-right pair of stereoscopic frames with disparity which must be carefully matched.
Rig removal with stereoscopic immersive media is challenging as the clean plate or patching content must match the stereo disparity of the original shot perfectly or stereo artifacts will appear. Stitched video from most current 3D 360 camera rigs is feathered at the poles and converges to monoscopic; compositing clean plate information is a time consuming process that benefits from experience in dedicated immersive video software tools and an expertise in stereoscopic immersive video.
Below is an example of a professional removal workflow using Nuke Cara VR to eliminate rigging in the left eye frame and then use the stereo tools in Nuke to reproject the left eye over the right eye with the proper disparity. The technique produces very high quality results but it is time consuming: Using Nuke to replace a blank nadir.
Here are links to articles which review specific tools and their methodologies for removing the tripod or other set equipment:
Mistika Boutique is another tool used for immersive media creation. Here is a tutorial from SGO on rig removal that can be done during the stitching process