lec11

# lec11 - Announcements Generalized Hough Transform line...

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1 CSE152, Spr 11 Intro Computer Vision Generalized Hough Transform, line fitting Introduction to Computer Vision CSE 152 Lecture 11a CSE152, Spr 11 Intro Computer Vision Announcements • Assignment 2: Due today • Midterm: Thursday, May 5 in class CSE152, Spr 11 Intro Computer Vision What is region like if: 1. λ 1 = 0? 2. λ 2 = 0? 3. λ 1 = 0 and λ 2 = 0? 4. λ 1 > 0 and λ 2 > 0? Corner Detection C ( x , y ) = I x 2 I x I y I x I y I y 2 Ρ Σ ΢ ΢ Τ Φ Υ Υ CSE152, Spr 11 Intro Computer Vision So, to detect corners Filter image with a Gaussian. Compute the gradient everywhere. Move window over image and construct C over the window. Use linear algebra to find λ 1 and λ 2 . If they are both big, we have a corner. 1. Let e(x,y) = min( λ 1 (x,y), λ 2 (x,y) ) 2. (x,y) is a corner if it’s local maximum of e(x,y) and e(x,y) > τ Parameters: Gaussian std. dev, window size, threshold CSE152, Spr 11 Intro Computer Vision • Segment linked edge chains into curve features (e.g., line segments). • Group unlinked or unrelated edges into lines (or curves in general). • Accurately fitting parametric curves (e.g., lines) to grouped edge points. What to do with edges? CSE152, Spr 11 Intro Computer Vision Hough Transform [ Patented 1962 ]

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2 Finding lines in an image Connection between image (x,y) and Hough (m,b) spaces A line in the image corresponds to a point in Hough space To go from image space to Hough space: – given a set of points (x,y), find all (m,b) such that y = mx + b x y m b (m 0 ,b 0 ) image space Hough space Finding lines in an image Connection between image (x,y) and Hough (m,b) spaces A line in the image corresponds to a point in Hough space To go from image space to Hough space: – given a set of points (x,y), find all (m,b) such that y = mx + b What does a point (x 0 , y 0 ) in the image space map to? x y m b image space Hough space – A: the solutions of b = -x 0 m + y 0 – this is a line in Hough space (x 0 ,y 0 ) CSE152, Spr 11 Intro Computer Vision Hough transform algorithm Typically use a different parameterization
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lec11 - Announcements Generalized Hough Transform line...

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