Method for generating an array of 3-D points
A method that estimates the coordinates of the calibration points in the projector image plane using local homographies obtained from the imaging camera. First, a dense set of correspondences between projector and camera pixels is found by projecting onto the calibration object an identical pattern sequence as the one later projected when scanning the target, reusing most of the software components written for the scanning application. Second, the set of correspondences is used to compute a group of local homographies that allow projection back of any of the points in the calibration object onto the projector image plane with sub-pixel precision. In the end, the data projector is then calibrated as a normal camera.
1. A stereo system comprising:
a calibration object having known dimensions and a plurality of points having known relationships to one another and that are identifiable in images of the object;
a projector configured to project a sequence of structured-light patterns that code corresponding projector coordinates in the structured-light patterns;
a camera to capture a plurality of images of the object at each of a plurality of orientations of the object with the object being illuminated by the sequence of structured-light patterns at each of the plurality of orientations; and
a computer having a storage medium for storing the plurality of images and at least one processor configured to:
identify each of the plurality of points in each of the plurality of images and determine a camera coordinate for each of the plurality of points identified in the plurality of images;
automatically determine projector coordinates for each of a plurality of pixels in each of the plurality of image from the structured light patterns in each of the plurality of images;
compute a local homography for each point identified in the plurality of images, each local homography determined from the projector coordinates determined from pixels in a neighborhood of the respective point identified in the plurality of images, each local homography providing a local transformation from camera coordinates to projector coordinates;
transform the camera coordinate of each point identified in the plurality of images to a respective projector coordinate using the corresponding local homography;
determine intrinsic camera parameters using the known dimensions of the object and the determined camera coordinates of each of the plurality of points identified in the plurality of images;
determine intrinsic projector parameters using the known dimensions of the object and the projector coordinates transformed from the respective camera coordinates by the respective local homography; and
determine a transformation that relates locations of the camera and the projector to calibrate the projector-camera pair of the stereo system.
2. The system of claim 1 , wherein the sequence of structured-light patterns comprise binary patterns.
3. The system of claim 1 , wherein the sequence of structured-light patterns comprise Gray codes.
4. The system of claim 1 , wherein the sequence of structured-light patterns comprise phase shifting patterns.
5. The system of claim 1 , wherein the calibration object comprises a checkerboard of known dimensions and wherein the plurality of points are corners of said checkerboard.