What is parallax?
Parallax is defined as the difference in alignment between two objects, when looking at them from a different viewpoint or angle. You can experience it simply, by looking at close objects with your left and right eyes separately, and observe the difference of alignment of the objects in front of you.
Stitching blends the different video streams into a full 360 video. Parallax error is introduced by the slightly different points of view of each camera.
To have a perfect stitch, each camera and lenses would have to be at the same position, which is physically impossible.
How does parallax impact 360 video calibration and output ?
Parallax introduces stitching errors, making seams more visible after stitching, usually on objects close to the camera.
The effect of parallax can be compared to that of focus on a regular camera : Focus can be done on a specific distance, and things get blurry when they are closer/further away than the focusing point. Similarly, you will get a perfect stitch at a specific distance from the camera (typically, where control points have been detected or manually added) and the further away the object are from the optimal stitching distance on a specific seam, the worst stitching errors will get on the object.
Can I avoid parallax ?
It's impossible to remove it entirely, but there are different ways to reduce it and make less invisible:
- The rig should be as compact as possible, and the distance between the lenses ca should be the closest the one from the others.
- Reducing the number of cameras/lenses in your rig helps in getting a compact setup and reduce the amount of stitching lines.
- The closest the objects are from the camera, the more likely parallax effect will be visible. Usually, parallax effect is more or less invisible after 2 meters, and starts to be very noticeable to less than 1 meter.
- If you need to have a very close object from the camera, the parallax effect will not be visible if it's in front of just one lens. If it's on the overlap between several lenses, then parallax will be more visible.