Automatic Projector Calibration

Johnny Lee presented on his thesis work an interesting way to automatically calibrate a projector by embedding optical sensors into the projection surface.
The procedure consists in detecting the individual pixels illuminating the optical sensors.
This is done by projecting a series of gray-coded binary patterns on the target surface. These patterns are coded in a way to detect every pixel projected on the screen. The amount of patterns to project depends on the resolution of the projector. For a 1024x768 resolution each pixel can be uniquely detected with only twenty patterns.

Once the key pixels have been detected on the target surface it is posible to find the homography that transforms the screen pixels to the projected locations. Once this transformation is known, pre-warped images may be transmitted to the projector.

This project has many applications besides projector calibration.
It can be used for creating a large display using tiled projection. This is known as stitching.
It can also be used to project multiple versions of the same content on a surface to reduce the shadows when one projector is blocked.
Finally, another of the possible uses is to register the orientation of a 3D surface. This requires the geometry of the surface to be known and the optical sensors to be in the visibility range from the projector.

A video explaining the usage and other details of the implementation can be seen here.