Calibrate optic parameters ========================== A camera device have to be calibrated to compensate its optical distorsion. ![Optic parameters calibration](../../img/optic_calibration.png) ## Print calibration board The first step to calibrate a camera is to create an [ArUcoBoard](../../argaze.md/#argaze.ArUcoMarkers.ArUcoBoard) like in the code below: ``` python from argaze.ArUcoMarkers import ArUcoMarkersDictionary, ArUcoBoard # Create ArUco dictionary aruco_dictionary = ArUcoMarkersDictionary.ArUcoMarkersDictionary('DICT_APRILTAG_16h5') # Create an ArUco board of 7 columns and 5 rows with 5 cm squares with 3cm ArUco markers inside aruco_board = ArUcoBoard.ArUcoBoard(7, 5, 5, 3, aruco_dictionary) # Export ArUco board with 300 dpi resolution aruco_board.save('./calibration_board.png', 300) ``` !!! note There is **A3_DICT_APRILTAG_16h5_3cm_35cmx25cm.pdf** file located in *./src/argaze/ArUcoMarkers/utils/* folder ready to be printed on A3 paper sheet. Let's print the calibration board before to go further. ## Capture board pictures Then, the calibration process needs to make many different captures of an [ArUcoBoard](../../argaze.md/#argaze.ArUcoMarkers.ArUcoBoard) through the camera and then, pass them to an [ArUcoDetector](../../argaze.md/#argaze.ArUcoMarkers.ArUcoDetector.ArUcoDetector) instance to detect board corners and store them as calibration data into an [ArUcoOpticCalibrator](../../argaze.md/#argaze.ArUcoMarkers.ArUcoOpticCalibrator) for final calibration process. ![Calibration step](../../img/optic_calibration_step.png) The sample of code below illustrates how to: * load all required ArGaze objects, * detect board corners into a Full HD camera video stream, * store detected corners as calibration data then, * once enough captures are made, process them to find optic parameters and, * finally, save optic parameters into a JSON file. ``` python from argaze.ArUcoMarkers import ArUcoMarkersDictionary, ArUcoOpticCalibrator, ArUcoBoard, ArUcoDetector # Create ArUco dictionary aruco_dictionary = ArUcoMarkersDictionary.ArUcoMarkersDictionary('DICT_APRILTAG_16h5') # Create ArUco optic calibrator aruco_optic_calibrator = ArUcoOpticCalibrator.ArUcoOpticCalibrator() # Create ArUco board of 7 columns and 5 rows with 5 cm squares with 3cm aruco markers inside # Note: This board is the one expected during further board tracking expected_aruco_board = ArUcoBoard.ArUcoBoard(7, 5, 5, 3, aruco_dictionary) # Create ArUco detector aruco_detector = ArUcoDetector.ArUcoDetector(dictionary=aruco_dictionary, marker_size=3) # Assuming that live Full HD (1920x1080) video stream is enabled ... # Assuming there is a way to escape the while loop ... # Capture images from video stream while video_stream.is_alive(): image = video_stream.read() # Detect all board corners in image aruco_detector.detect_board(image, expected_aruco_board, expected_aruco_board.markers_number) # If all board corners are detected if aruco_detector.board_corners_number == expected_aruco_board.corners_number: # Draw board corners to show that board tracking succeeded aruco_detector.draw_board(image) # Append tracked board data for further calibration processing aruco_optic_calibrator.store_calibration_data(aruco_detector.board_corners, aruco_detector.board_corners_identifier) # Start optic calibration processing for Full HD image resolution print('Calibrating optic...') optic_parameters = aruco_optic_calibrator.calibrate(aruco_board, dimensions=(1920, 1080)) if optic_parameters: # Export optic parameters optic_parameters.to_json('./optic_parameters.json') print('Calibration succeeded: optic_parameters.json file exported.') else: print('Calibration failed.') ``` Below, an optic_parameters JSON file example: ```json { "rms": 0.6688921504088245, "dimensions": [ 1920, 1080 ], "K": [ [ 1135.6524381415752, 0.0, 956.0685325355497 ], [ 0.0, 1135.9272506869524, 560.059099810324 ], [ 0.0, 0.0, 1.0 ] ], "D": [ 0.01655492265003404, 0.1985524264972037, 0.002129965902489484, -0.0019528582922179365, -0.5792910353639452 ] } ```