How to choose the calibration board?

As we all know, in machine vision applications, such as measurement, photogrammetry, 3D reconstruction and other applications, calibration plates are required. Because the main function of the calibration target is to correct lens distortion, determine the conversion relationship between physical size and pixels, and determine the relationship between the three-dimensional geometric position of a point on the surface of the object and its corresponding point in the image, so as to establish a camera imaging system. geometric model. So do you know how to select the calibration board? Here is the introduction:

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Selection of calibration target:

1. Select the size of the calibration board:

Select the appropriate calibration plate according to the size of the field of view. It is recommended in the halcon document that the size of the calibration plate pattern should be at least larger than 1/4 of the field of view and smaller than the entire field of view, and take 15-20 calibration images; it is recommended that the pattern of the calibration plate be larger than 1/3 of the field of view , less than the entire field of view, the number of calibration images depends on the requirements; for the calibration board of the halcon12 version, it is recommended that the pattern of the calibration board be larger than the field of view area, and about 5 calibration images with different attitudes; the calibration board of the halcon12 version currently only supports halcon12, but halcon12 Version software can use calibration boards from previous versions.

2. Select the calibration plate material:

Please choose a ceramic/metal calibration plate for the front light source to avoid reflection. The backlight source can choose optical glass material.

3. Select the content of the calibration board drawing:

The content of the calibration board drawings needs to be attached with the above materials: accuracy, external dimension tolerance, thickness, production effect drawings (the distinction between positive and negative plates, etc.), detailed CAD drawings (drawings do not draw scale drawings).

In summary, it is the selection of the calibration board. Only by selecting a good calibration target, the calibration board can greatly improve the detection and measurement accuracy indicators, thus effectively ensuring that the machine vision system calibration can fully play its role in precision measurement and detection applications.