For professionals who use 3D cameras a lot, calibration is not a new concept. It is one of the prerequisites to capture good results. Here some basic knowledge about 3D camera calibration is explained. You will know the definition, purpose and common methods of 3D camera calibration.
What is camera calibration
Camera calibration is a process of establishing the positional relationship between the 3D point coordinates and the corresponding projection on the image plane by calculating the intrinsic and extrinsic camera parameters. Intrinsic parameters refer to the essential nature of cameras which encompass focal length, image sensor format, and distortion. Extrinsic parameters refer to position of camera center and cameraâ€™s orientation in 3D world coordinates.
Why we need calibration
The actual lens often does not offer ideal perspective imaging results. The images captured are distorted due to optical aberration. By calibrating, you can get the actual camera parameters to correct the 3D results.
In object measurement or machine vision applications, camera calibration is a very critical step. The accuracy of the calibration directly affects the accuracy of the results captured by the camera.
There are some different approaches to get the intrinsic and extrinsic camera parameters. One of the most common method is Zhang’s method, the high precision of which makes a frequent method in machine vision. Zhang’s method uses known calibration points and self-calibration technique, which is basically finding the correspondence between the calibration points when they are at different positions. To carry out a full calibration with this method, at least three different images of the calibration gauge need to be captured. The most common calibration gauges include chessboard, square grid and circle grid. Taking Revopointâ€™s 3D intelligent scanner Tanso S1 as an example, three chessboards of different dimensions are offered to scan objects of different sizes and placed at different positions. The whole calibration process takes only 10 seconds. The calibration is friendly for beginners. By a few steps, including place the chessboard at the turntable center and make sure the whole chessboard is captured clearly, users can successfully calibrate the cameras.