Method for calibrating the image of a camera

摘要

A method for calibrating the image (3I, 3II) of a camera (1), and, in particular, a traffic-monitoring camera, with respect to its viewing space, such that the camera projection parameters (mk1) of a camera projection of the viewing space onto the image are determined, includes the steps of providing a movable carrier (4) with at least four markings that can be viewed by the camera (1) and that span a volume and that form known first world points (wi) in the viewing space, recording a first image (3I) of the viewing space, shifting the carrier (4) in the viewing space by an unknown offset (v) in order to obtain second world points (wi) dependent on this offset in the viewing space, recording a second image (3II) of the viewing space, detecting the markings in the first image (3I) as first image points (pi) and in the second image (3II) as second image points (pi), and determining the camera projection parameters (mk1), while also determining the offset (v), from the known first world points, the second world points dependent on the offset, the detected first image points, and the detected second image points.

主权项

1. A method for calibrating an image of a stationary camera with respect to a viewing space of the camera, comprising:
providing a movable carrier with at least four markings thereon that can be viewed by the stationary camera and that span a volume, the markings forming known first world points in the viewing space; recording a first image of the markings on the movable carrier in a first position in the viewing space; shifting the carrier with the at least four markings thereon to a second position in the viewing space by an unknown offset, the markings forming second world points which are dependent on this offset in the viewing space; recording a second image of the markings on the movable carrier in the second position in the viewing space; detecting the markings in the first image as first image points and in the second image as second image points; determining the offset and camera projection parameters, which define a projection of world points in the viewing space onto image points in the image, from the known first world points, the second world points dependent on the offset, the detected first image points, and the detected second image points; and calibrating the image of the camera using said camera projection parameters; wherein the step of determining the camera projection parameters is performed using a direct linear transformation (“DLT”) method; and wherein the step of determining the camera projection parameters is performed by solving a DLT equation
D(s,t)·m=p with respect to m, s, and t, wherein;
D(s,t) is a DLT matrix of all world points and image points in which the second world points are expressed by the first world points shifted by the offset (s,t,0); m is a vector of the camera projection parameters; and p is a vector of all image points.