Nowadays, in the field of machine vision applications, the use of calibration plates is often indispensable. Because the camera calibration technology needs accurate camera internal and external parameters as the input and precondition of the reconstruction algorithm, the camera projection matrix can be calculated through the calibration algorithm, and the three-dimensional measurement information of the scene can be provided. Without the absolute translation, rotation and scaling parameters of the real scene, the measure reconstruction at the level of similar transformation can be achieved. Do you know what to pay attention to when using the calibration plate? Here's a brief introduction:
Pay attention to the following items when using the calibration plate:
1. The number of calibration images is usually between 15 and 25. The number of images is too small, which is easy to lead to inaccurate calibration parameters.
2. The number of pixels of circle or ring features should be as large as 20, and the imaging size of the calibration plate should account for approximately 1/4 of the whole picture.
3. Use the auxiliary light source to polish the calibration plate to ensure that the brightness of the calibration plate is sufficient and uniform.
4. The calibration plate imaging shall not be over exploded, which will lead to the offset of feature contour extraction, thus leading to inaccurate circle center extraction.
5. The calibration plate feature imaging cannot have obvious defocusing distance. When defocusing occurs, the distance of the calibration plate, the size of the aperture and the image distance can be adjusted by adjusting (for the fixed focus lens, focusing usually means adjusting the image distance).
6. During the calibration process, the aperture and focal length of the camera cannot be changed, which requires re calibration.
7. The number of calibration plate images shall cover the whole measurement space and the whole measurement field of view. The camera image shall be divided into four quadrants. It shall be ensured that the captured calibration plate images are evenly distributed in the four quadrants. In each quadrant, it is recommended to tilt twice in different directions.
To sum up, we should pay attention to some matters in the process of using the calibration plate. In order to ensure the effect, we should not only pay attention to the above matters, but also place the calibration plate in an appropriate position, so that we can play a greater role in the calibration plate.
