Example Video Mosaic

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An image mosaic is created by combining numerous images together to create one large one. In this example, it is demonstrated how to create a mosaic from a video image in real-time using a high level interface which hides much of the complexity. The mosaic is created by tracking image features and fitting a motion model (affine or homography) to the feature's location in each frame.

Example File: ExampleVideoMosaic.java

Concepts:

  • Image Stitching
  • Image Mosaic
  • 2D image motion

Relevant Videos:

Related Examples:

Example Code

/**
 * Example of how to create a mosaic from a video sequence using StitchingFromMotion2D.  Mosaics work best
 * when the scene being observed is far away or a flat surface.  The camera motion should typically be rotational only,
 * but translation can work depending on the scene's geometry.  Motion blur and cheap cameras in general will degrade
 * performance significantly with the current algorithm.  This example just demonstrates a gray scale image, but
 * with additional work color images can also be processed.
 *
 * @author Peter Abeles
 */
public class ExampleVideoMosaic {
	public static void main( String[] args ) {
		// Configure the feature detector
		ConfigPointDetector configDetector = new ConfigPointDetector();
		configDetector.type = PointDetectorTypes.SHI_TOMASI;
		configDetector.general.maxFeatures = 300;
		configDetector.general.radius = 3;
		configDetector.general.threshold = 1;

		// Use a KLT tracker
		PointTracker<GrayF32> tracker = FactoryPointTracker.klt(4, configDetector, 3, GrayF32.class, GrayF32.class);

		// This estimates the 2D image motion
		// An Affine2D_F64 model also works quite well.
		ImageMotion2D<GrayF32, Homography2D_F64> motion2D =
				FactoryMotion2D.createMotion2D(220, 3, 2, 30, 0.6, 0.5, false, tracker, new Homography2D_F64());

		// wrap it so it output color images while estimating motion from gray
		ImageMotion2D<Planar<GrayF32>, Homography2D_F64> motion2DColor =
				new PlToGrayMotion2D<>(motion2D, GrayF32.class);

		// This fuses the images together
		StitchingFromMotion2D<Planar<GrayF32>, Homography2D_F64>
				stitch = FactoryMotion2D.createVideoStitch(0.5, motion2DColor, ImageType.pl(3, GrayF32.class));

		// Load an image sequence
		MediaManager media = DefaultMediaManager.INSTANCE;
		String fileName = UtilIO.pathExample("mosaic/airplane01.mjpeg");
		SimpleImageSequence<Planar<GrayF32>> video =
				media.openVideo(fileName, ImageType.pl(3, GrayF32.class));

		Planar<GrayF32> frame = video.next();

		// shrink the input image and center it
		Homography2D_F64 shrink = new Homography2D_F64(0.5, 0, frame.width/4, 0, 0.5, frame.height/4, 0, 0, 1);
		shrink = shrink.invert(null);

		// The mosaic will be larger in terms of pixels but the image will be scaled down.
		// To change this into stabilization just make it the same size as the input with no shrink.
		stitch.configure(frame.width, frame.height, shrink);
		// process the first frame
		stitch.process(frame);

		// Create the GUI for displaying the results + input image
		ImageGridPanel gui = new ImageGridPanel(1, 2);
		gui.setImage(0, 0, new BufferedImage(frame.width, frame.height, BufferedImage.TYPE_INT_RGB));
		gui.setImage(0, 1, new BufferedImage(frame.width, frame.height, BufferedImage.TYPE_INT_RGB));
		gui.setPreferredSize(new Dimension(3*frame.width, frame.height*2));

		ShowImages.showWindow(gui, "Example Mosaic", true);

		boolean enlarged = false;

		// process the video sequence one frame at a time
		while (video.hasNext()) {
			frame = video.next();
			if (!stitch.process(frame))
				throw new RuntimeException("You should handle failures");

			// if the current image is close to the image border recenter the mosaic
			StitchingFromMotion2D.Corners corners = stitch.getImageCorners(frame.width, frame.height, null);
			if (nearBorder(corners.p0, stitch) || nearBorder(corners.p1, stitch) ||
					nearBorder(corners.p2, stitch) || nearBorder(corners.p3, stitch)) {
				stitch.setOriginToCurrent();

				// only enlarge the image once
				if (!enlarged) {
					enlarged = true;
					// double the image size and shift it over to keep it centered
					int widthOld = stitch.getStitchedImage().width;
					int heightOld = stitch.getStitchedImage().height;

					int widthNew = widthOld*2;
					int heightNew = heightOld*2;

					int tranX = (widthNew - widthOld)/2;
					int tranY = (heightNew - heightOld)/2;

					Homography2D_F64 newToOldStitch = new Homography2D_F64(1, 0, -tranX, 0, 1, -tranY, 0, 0, 1);

					stitch.resizeStitchImage(widthNew, heightNew, newToOldStitch);
					gui.setImage(0, 1, new BufferedImage(widthNew, heightNew, BufferedImage.TYPE_INT_RGB));
				}
				corners = stitch.getImageCorners(frame.width, frame.height, null);
			}
			// display the mosaic
			ConvertBufferedImage.convertTo(frame, gui.getImage(0, 0), true);
			ConvertBufferedImage.convertTo(stitch.getStitchedImage(), gui.getImage(0, 1), true);

			// draw a red quadrilateral around the current frame in the mosaic
			Graphics2D g2 = gui.getImage(0, 1).createGraphics();
			g2.setColor(Color.RED);
			g2.drawLine((int)corners.p0.x, (int)corners.p0.y, (int)corners.p1.x, (int)corners.p1.y);
			g2.drawLine((int)corners.p1.x, (int)corners.p1.y, (int)corners.p2.x, (int)corners.p2.y);
			g2.drawLine((int)corners.p2.x, (int)corners.p2.y, (int)corners.p3.x, (int)corners.p3.y);
			g2.drawLine((int)corners.p3.x, (int)corners.p3.y, (int)corners.p0.x, (int)corners.p0.y);

			gui.repaint();

			// throttle the speed just in case it's on a fast computer
			BoofMiscOps.pause(50);
		}
	}

	/**
	 * Checks to see if the point is near the image border
	 */
	private static boolean nearBorder( Point2D_F64 p, StitchingFromMotion2D<?, ?> stitch ) {
		int r = 10;
		if (p.x < r || p.y < r)
			return true;
		if (p.x >= stitch.getStitchedImage().width - r)
			return true;
		if (p.y >= stitch.getStitchedImage().height - r)
			return true;

		return false;
	}
}