Example Calibrate Planar Stereo

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  Image of a stereo pair before calibration.

• 

  Image of a calibrated stereo pair. Radial distortion has been removed.

This example demonstrate how to calibrate a stereo camera system using a high level interface which automatically detects calibration targets in a set of stereo images. After calibration the intrinsic parameters of each camera is found as well as their extrinsic relationship with each other. Both the square grid and chessboard patterns are supported by this example. For a full description of the calibration process and instruction on how to do it yourself see the tutorial linked to below.

Example File: ExampleCalibrateStereoPlanar.java

Calibration Tutorial: Wikipage

Concepts:

• Camera calibration
• Lens distortion
• Intrinsic parameters
• Stereo Vision

Relevant Applets:

• Stereo Calibration

Related Examples:

• Calibrated Stereo Rectification
• Monocular Camera Calibration
• Removing Lens Distortion

Example Code

/**
 * Example of how to calibrate a stereo camera system using a planar calibration grid given a set of images.
 * Intrinsic camera parameters are estimated for both cameras individually, then extrinsic parameters
 * for the two cameras relative to each other are found   This example does not rectify the images, which is
 * required for some algorithms. See {@link ExampleRectifyCalibratedStereo}. Both square grid and chessboard targets
 * are demonstrated in this example. See calibration tutorial for a discussion of different target types and how to
 * collect good calibration images.
 *
 * All the image processing and calibration is taken care of inside of {@link CalibrateStereoPlanar}.  The code below
 * loads calibration images as inputs, calibrates, and saves results to an XML file.  See in code comments for tuning
 * and implementation issues.
 *
 * @see ExampleRectifyCalibratedStereo
 * @see CalibrateStereoPlanar
 *
 * @author Peter Abeles
 */
public class ExampleCalibrateStereoPlanar {

	// Detects the target and calibration point inside the target
	PlanarCalibrationDetector detector;

	// Description of the target's physical dimension
	PlanarCalibrationTarget target;

	// List of calibration images
	List<String> left;
	List<String> right;

	// Many 3D operations assumed a right handed coordinate system with +Z pointing out of the image.
	// If the image coordinate system is left handed then the y-axis needs to be flipped to meet
	// that requirement.  Most of the time this is false.
	boolean flipY;

	/**
	 * Square grid target taken by a PtGrey Bumblebee camera.
	 */
	public void setupBumblebeeSquare() {
		// Use the wrapper below for square grid targets.
		detector = FactoryPlanarCalibrationTarget.detectorSquareGrid(new ConfigSquareGrid(3,4));
		// Target physical description
		target = FactoryPlanarCalibrationTarget.gridSquare(3, 4, 30,30);

		String directory = "../data/evaluation/calibration/stereo/Bumblebee2_Square";

		left = BoofMiscOps.directoryList(directory, "left");
		right = BoofMiscOps.directoryList(directory, "right");

		flipY = false;
	}

	/**
	 * Chessboard target taken by a PtGrey Bumblebee camera.
	 */
	public void setupBumblebeeChess() {
		// Use the wrapper below for chessboard targets.  The last parameter adjusts the size of the corner detection
		// region.  TUNE THIS PARAMETER FOR OPTIMAL ACCURACY!
		detector = FactoryPlanarCalibrationTarget.detectorChessboard(new ConfigChessboard(3,4));
		// Target physical description
		target = FactoryPlanarCalibrationTarget.gridChess(3, 4, 30);

		String directory = "../data/evaluation/calibration/stereo/Bumblebee2_Chess";

		left = BoofMiscOps.directoryList(directory, "left");
		right = BoofMiscOps.directoryList(directory, "right");

		flipY = false;
	}

	/**
	 * Process calibration images, compute intrinsic parameters, save to a file
	 */
	public void process() {
		// Declare and setup the calibration algorithm
		CalibrateStereoPlanar calibratorAlg = new CalibrateStereoPlanar(detector, flipY);
		calibratorAlg.configure(target, true, 2);

		// ensure the lists are in the same order
		Collections.sort(left);
		Collections.sort(right);

		for( int i = 0; i < left.size(); i++ ) {
			BufferedImage l = UtilImageIO.loadImage(left.get(i));
			BufferedImage r = UtilImageIO.loadImage(right.get(i));

			ImageFloat32 imageLeft = ConvertBufferedImage.convertFrom(l,(ImageFloat32)null);
			ImageFloat32 imageRight = ConvertBufferedImage.convertFrom(r,(ImageFloat32)null);

			if( !calibratorAlg.addPair(imageLeft, imageRight) )
				System.out.println("Failed to detect target in "+left.get(i)+" and/or "+right.get(i));
		}

		// Process and compute calibration parameters
		StereoParameters stereoCalib = calibratorAlg.process();

		// print out information on its accuracy and errors
		calibratorAlg.printStatistics();

		// save results to a file and print out
		BoofMiscOps.saveXML(stereoCalib, "stereo.xml");
		stereoCalib.print();
	}

	public static void main( String args[] ) {
		ExampleCalibrateStereoPlanar alg = new ExampleCalibrateStereoPlanar();

		// Select which set of targets to use
		alg.setupBumblebeeChess();
//		alg.setupBumblebeeSquare();

		// compute and save results
		alg.process();
	}
}