Example Canny Edge

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  Left) Input image. Right) Found contours using canny edge detector

Edge or contour detection is a basic computer vision problem. The Canny edge detector is a popular algorithm for detecting edges in an image which uses hystersis thresholding. In BoofCV the Canny edge detector can produce different kinds of output. A binary image containing every pixel which is identified as an edge or a tree graph containing all the selected edge pixels.

Example Code:

• ExampleCannyEdge

Concepts:

• Object contours/edges

Relevant Examples:

• Binary Image Processing

Example Code

/**
 * Demonstration of the Canny edge detection algorithm. In this implementation the output can be a binary image and/or
 * a graph describing each contour.
 *
 * @author Peter Abeles
 */
public class ExampleCannyEdge {

	public static void main( String[] args ) {
		BufferedImage image = UtilImageIO.loadImageNotNull(UtilIO.pathExample("simple_objects.jpg"));

		GrayU8 gray = ConvertBufferedImage.convertFrom(image, (GrayU8)null);
		GrayU8 edgeImage = gray.createSameShape();

		// Create a canny edge detector which will dynamically compute the threshold based on maximum edge intensity
		// It has also been configured to save the trace as a graph. This is the graph created while performing
		// hysteresis thresholding.
		CannyEdge<GrayU8, GrayS16> canny = FactoryEdgeDetectors.canny(2, true, true, GrayU8.class, GrayS16.class);

		// The edge image is actually an optional parameter. If you don't need it just pass in null
		canny.process(gray, 0.1f, 0.3f, edgeImage);

		// First get the contour created by canny
		List<EdgeContour> edgeContours = canny.getContours();
		// The 'edgeContours' is a tree graph that can be difficult to process. An alternative is to extract
		// the contours from the binary image, which will produce a single loop for each connected cluster of pixels.
		// Note that you are only interested in external contours.
		List<Contour> contours = BinaryImageOps.contourExternal(edgeImage, ConnectRule.EIGHT);

		// display the results
		BufferedImage visualBinary = VisualizeBinaryData.renderBinary(edgeImage, false, null);
		BufferedImage visualCannyContour = VisualizeBinaryData.renderContours(edgeContours, null,
				gray.width, gray.height, null);
		BufferedImage visualEdgeContour = new BufferedImage(gray.width, gray.height, BufferedImage.TYPE_INT_RGB);
		VisualizeBinaryData.render(contours, (int[])null, visualEdgeContour);

		ListDisplayPanel panel = new ListDisplayPanel();
		panel.addImage(visualBinary, "Binary Edges from Canny");
		panel.addImage(visualCannyContour, "Canny Trace Graph");
		panel.addImage(visualEdgeContour, "Contour from Canny Binary");
		ShowImages.showWindow(panel, "Canny Edge", true);
	}
}