Checkerboard is the calibration target. Any checkerboard of different sizes and different internal corners can be used. Eg: You can use the following attached pdf. It has 7 internal corners horizontally and 9 internal corners vertically. https://drive.google.com/file/d/1mTR8HTpvROE1Pv0rmXEBVLSxs_yMDnvf/view?usp=sharing
With the Stereo-Camera in a fixed position, take images of a checkerboard from the cameras. Take shots of the checkerboard at different positions with the stereo-camera. A minimum of 25 images is recommended to get good results. Save the images in different folders on your PC.
Also, record the length of one of the squares on the checkerboard, and also the count of horizontal and vertical corners inside the checkerboard.
It is recommended that you name the files with pairing information in the name itself. For example, name the image from the left and right cameras as ‘left01.jpg’ and ‘right01.jpg’ in case of jpg files, and so on. Keep in mind, there is no need to change the extension while renaming the files. This step is purely to help you pair the images when you upload the images to the calibration tool.
Here is an example set of files used during this calibration process. Here, the count of horizontal corners is 9 and vertical corners are 7.
It is recommended to also have calculated the intrinsics parameters for the left and right cameras of the stereo-camera to be filled in the Stereo-calibration App with data specifically collected for intrinsic calibration of those cameras. Although an on the fly calculation of intrinsics is supported by the tool, it uses the images uploaded for stereo-calibration, which tends to raise inaccuracies in the intrinsics calibration and overall stereo-calibration results.