Video pass-through
Video passthrough, also known as camera passthrough, is a capability of a headset to pass through a video feed to the user on the headset's display. It shows the outside world to the user so he does not become disoriented. It is also known as "video passthrough". It can be used in a mixed-reality headset.
Monochrome passthrough with correct geometry can be done using a depth camera, and reprojecting the point cloud.
The idea of video passthrough was brought into the AR arena largely by Virtual Fixtures. More recently, the Lynx R1, and was popularized by the Quest 2 and Quest Pro.
One of the difficulties of doing passthrough right is the positional difference between cameras on the outside of a headset and the eyes of the user. So the image has to go through a distortion process. On the Quest Pro and Quest 3, this uses a neural network. Other gadgets potentially also use a neural network.
It is possible to use a light field camera to capture an image and reproject it at a different transform.
It is also possible to have a camera offset from the headset and facing the headset, and put a mirror on the headset.