It is well known that calibration plates are required in machine vision applications, such as measurement, photogrammetry, 3D reconstruction, etc. Because the calibration plate is mainly used to correct lens distortion, determine the conversion relationship between physical dimensions and pixels, and determine the relationship between the three-dimensional geometric position of a point on the surface of a space object and its corresponding point in the image, so as to establish the geometric model of camera imaging. Do you know how to select the calibration plate? Here's a brief introduction:
Model selection of calibration plate:
1. Select the calibration board size:
Select an appropriate calibration plate according to the size of the field of view. In the Halcon document, it is recommended that the pattern size of the calibration plate should be at least greater than 1/4 of the field of view and smaller than the entire field of view, and 15-20 calibration images should be taken; It is recommended that the calibration plate pattern should be larger than 1/3 of the field of view and smaller than the entire field of view. The number of calibration images depends on the requirements; For the calibration plate of Halcon 12, it is recommended that the pattern of the calibration plate should be larger than the field of view, and there are about 5 calibration images with different attitudes; The calibration board of Halcon12 only supports Halcon12 at present, but the software of Halcon12 can use the calibration board of the previous version.
2. Select the calibration plate material:
Please select ceramic/metal calibration plate for front light source to avoid reflection. The backlight source can be made of optical glass.
3. Select the contents of the calibration plate drawing:
The contents of the calibration plate drawing shall be attached with the above materials: precision, overall dimension tolerance, thickness, and production effect drawings (classification of positive and negative plates) Detailed CAD drawings (do not draw scale drawings).
To sum up, it is the selection of calibration plate. Only when we have selected a good calibration board, we can greatly improve the detection and measurement accuracy indicators, so as to effectively ensure that the machine vision system calibration can fully play its role in precision measurement and detection applications.
