- OpenCV - GUI
- OpenCV - Writing an Image
- OpenCV - Reading Images
- OpenCV - Storing Images
- OpenCV - Environment
- OpenCV - Overview
- OpenCV - Home
Types of Images
Image Conversion
Drawing Functions
- OpenCV - Adding Text
- OpenCV - Drawing Arrowed Lines
- OpenCV - Drawing Convex Polylines
- OpenCV - Drawing Polylines
- OpenCV - Drawing an Ellipse
- OpenCV - Drawing a Rectangle
- OpenCV - Drawing a Line
- OpenCV - Drawing a Circle
Blur
Filtering
- OpenCV - Image Pyramids
- OpenCV - Morphological Operations
- OpenCV - Erosion
- OpenCV - Dilation
- OpenCV - Filter2D
- OpenCV - SQRBox Filter
- OpenCV - Box Filter
- OpenCV - Bilateral Filter
Thresholding
Sobel Derivatives
Transformation Operations
Camera and Face Detection
Geometric Transformations
Miscellaneous Chapters
OpenCV Useful Resources
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
OpenCV - Canny Edge Detection
Canny Edge Detection is used to detect the edges in an image. It accepts a gray scale image as input and it uses a multistage algorithm.
You can perform this operation on an image using the Canny() method of the imgproc class, following is the syntax of this method.
Canny(image, edges, threshold1, threshold2)
This method accepts the following parameters −
image − A Mat object representing the source (input image) for this operation.
edges − A Mat object representing the destination (edges) for this operation.
threshold1 − A variable of the type double representing the first threshold for the hysteresis procedure.
threshold2 − A variable of the type double representing the second threshold for the hysteresis procedure.
Example
Following program is an example demonstrating, how to perform Canny Edge Detection operation on a given image.
import org.opencv.core.Core; import org.opencv.core.Mat; import org.opencv.imgcodecs.Imgcodecs; import org.opencv.imgproc.Imgproc; pubpc class CannyEdgeDetection { pubpc static void main(String args[]) throws Exception { // Loading the OpenCV core pbrary System.loadLibrary(Core.NATIVE_LIBRARY_NAME); // Reading the Image from the file and storing it in to a Matrix object String file = "E:/OpenCV/chap17/canny_input.jpg"; // Reading the image Mat src = Imgcodecs.imread(file); // Creating an empty matrix to store the result Mat gray = new Mat(); // Converting the image from color to Gray Imgproc.cvtColor(src, gray, Imgproc.COLOR_BGR2GRAY); Mat edges = new Mat(); // Detecting the edges Imgproc.Canny(gray, edges, 60, 60*3); // Writing the image Imgcodecs.imwrite("E:/OpenCV/chap17/canny_output.jpg", edges); System.out.println("Image Loaded"); } }
Assume that following is the input image canny_input.jpg specified in the above program.
![Canny Input](/opencv/images/canny_input.jpg)
Output
On executing the above program, you will get the following output −
Image Processed
If you open the specified path, you can observe the output image as follows −
![Canny Output](/opencv/images/canny_output.jpg)