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Hough Transform. Procedure to find a shape in an image Shape can be described in parametric form Shapes in image correspond to a family of parametric solutions A voting scheme is used to determine the correct parameters. Hough Transform for Lines. Quantize space
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Hough Transform • Procedure to find a shape in an image • Shape can be described in parametric form • Shapes in image correspond to a family of parametric solutions • A voting scheme is used to determine the correct parameters
Quantize space Each bin represents a line defined by Accumulate values in bin according to edge points Each bin contains the amount of points in image that would form a line defined by Hough Transform for Lines
Hough Transform for Lines • Problem with vertical lines • Normal form
Hough Transform for Lines 2 1 -3 -2 -1 1 2 3 -1 -2
Hough Transform for Lines 4 2 -3 -2 -1 1 2 3 -2 -4
Pick in the parametric space that corresponds to the line
Hough Transform for Lines • Domain of the parametric space: Mand N image resolution Not just lines, any parametric curve! However increase of dimensions of the parametric space
Hough Transform of Circles • Circle is define by its center and radius -3D Hough parametric space
Hough Transform • Find parametric shapes in an image • Slow but robust to noise and occlusion • Quantization of the parameters controls accuracy and speed