1. COMPUTER VISION D10K-7C02 CV05: Edge Detection Dr. Setiawan Hadi, M.Sc.CS. Program Studi S-1 Teknik Informatika FMIPA Universitas Padjadjaran

2. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Edge detection Goal: Identify sudden changes (discontinuities) in an image – Intuitively, most semantic and shape information from the image can be encoded in the edges – More compact than pixels Ideal: artist’s line drawing (but artist is also using object-level knowledge)

3. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Origin of edges Edges are caused by a variety of factors: depth discontinuity surface color discontinuity illumination discontinuity surface normal discontinuity

4. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Characterizing edges An edge is a place of rapid change in the image intensity function image intensity function (along horizontal scanline) first derivative edges correspond to extrema of derivative

5. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Derivatives with convolution For 2D function f(x,y), the partial derivative is: For discrete data, we can approximate using finite differences: Source: K. Grauman

6. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Partial derivatives of an image Which shows changes with respect to x? -1 1 1 -1 or -1 1

7. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Finite difference filters Other approximations of derivative filters exist:

8. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Canny Edge Detector 1.Filter image with derivative of Gaussian 2.Find magnitude and orientation of gradient 3.Non-maximum suppression: – Thin wide “ridges” down to single pixel width 4.Linking and thresholding (hysteresis): – Define two thresholds: low and high – Use the high threshold to start edge curves and the low threshold to continue them J. Canny, A Computational Approach To Edge Detection, IEEE Trans. Pattern Analysis and Machine Intelligence, 8:679-714, 1986.A Computational Approach To Edge Detection

9. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Canny Edge Detection in C# http://www.codeproject.com/Articles/93642/Canny- Edge-Detection-in-C

10. Computer Vision Teknik Informatika-Semester Ganjil 2015-2016 Computer Vision Website Computer Vision Demonstration Website – http://users.ecs.soton.ac.uk/msn/book/new_demo/ http://users.ecs.soton.ac.uk/msn/book/new_demo/ Computer Vision Online – http://www.computervisiononline.com/ http://www.computervisiononline.com/ The Computer Vision Homepage – http://www.cs.cmu.edu/~cil/vision.html http://www.cs.cmu.edu/~cil/vision.html The Computer Vision Industry – http://www.cs.ubc.ca/~lowe/vision.html http://www.cs.ubc.ca/~lowe/vision.html CVonline: The Evolving, Distributed, Non-Proprietary, On-Line Compendium of Computer Vision – http://homepages.inf.ed.ac.uk/rbf/CVonline/