Using Edge Points in Mistika VR

Edge Points are a unique feature in Mistika VR that provide precise, fine tuning during the stitch process. They can help resolve issues with optical flow and overlapping image pixels between lenses, and are a great tool for challenging stitching projects.

Edge Points are a powerful stitching feature unique to Mistika VR. They are added between adjacent lenses to reduce optical flow artifacts and overlapping pixel misalignment on scene elements which are moving between camera lenses. They are also an effective tool for maintaining good stitching on important scene elements, such as the talent's face between two lenses. Edge Points can be positioned in a fixed location, or animated for scene elements in motion, or during a moving camera shot. Edge Points provide a high level of precision for fine tuning complex stitches. Understanding how to use them is crucial when stitching using Mistika VR.

We introduced the concept of edge points in the Stitching with Mistika VR article when discussing ghosting artifacts that may appear when optical flow is activated. Optical flow is a powerful method for aligning overlapping image pixels between adjacent lenses in an immersive video, however there are a number of scenarios where it may produce undesirable artifacts such as ghosting, misalignment or rippling. To address these, a single edge point may be sufficient, or multiple edge points may need to be added. They can be scaled, feathered and repositioned as needed, and their parameters can be animated over time to remove artifacts as scene elements move across the shot.

To work with edge points, first toggle on both the Camera Overlay and Feather Overlay from the menu at the bottom of the Visual Editor. The overlay displays the camera areas and their names as C1, C2, C3, etc. and also shows the feather line between adjacent cameras. Cameras can be interactively selected by clicking on them in overlay display in the Visual Editor. The overlay indicates which camera is currently active when adding, selecting and editing edge points.

To add an Edge Point select the camera closest to an area in the image with optical flow artifacts, in this case, the flight deck crew member. In the Edge Point pop-up menu at the bottom of the Clip Stack in Mistika VR, select Add Edge Point. Additional edge points can be added, or removed from this pop-up menu. Edge points will be named to correspond to the active camera number, for example, all edge points added to Camera 1 (C1) will all be named P1 regardless of how many of them have been added to that camera.

In Camera Controls, the Edge Points control panel displays each edge point’s parameters: Yaw, Pitch, Size and Feather. By default edge points are large and centered in the lens area. Click on the circular edge point controller to drag it over the area of the image with artifacts. The Yaw and Pitch values will change interactively as the edge point is repositioned. Size and Feather are both manually controlled numerical parameters. In this example, the edge point size has been reduced from the default 25 to 12.

In the example below, the flight deck crew member is no longer in frame once the helicopter takes off. By keyframing the position and scale parameters, the edge point was moved inside the lens and scaled down in size.

The image below is an example of how multiple edge points can be added per camera to reduce overlap artifacts and improve optical flow pixel alignment in a complex shot. As the helicopter moved through the shot, some of the edge points were keyframed into the lens area and rescaled small as they were no longer needed. The process is time consuming, but in a complex stitching project like this, edge points provide the best solution for addressing optical flow and overlapping pixel artifacts.