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Chapter 24: Perception. April 20, 2004. 24.1 Introduction. Emphasis on vision Feature extraction approach Model-based approach S stimulus W world f, defined by physics and optics S = f(W) computer graphics W = f -1 (S) computer vision. 24.2 Image Formation.
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Chapter 24: Perception April 20, 2004
24.1 Introduction • Emphasis on vision • Feature extraction approach • Model-based approach • S stimulus • W world • f, defined by physics and optics • S = f(W) computer graphics • W = f-1(S) computer vision
24.2 Image Formation • Pinhole Camera (image without a lense) • Figure 24.1 • point P in scene (X, Y, Z) • point P’ in image plane (x, y, z) • f: distance from pinhole to image plane • -x / f = X / Z (similar triangles) • - y / f = Y / Z (similar triangles)
Lens Systems • A lens enables more light to enter • The pinhole camera equations are still accurate • Figure 24.2
Photometry: Study of Light • Figure 24.3 • Specular reflection: light is reflected from the outer surface of the object • Diffuse reflection: light is absorbed by the object and then re-emitted
Color • The retina has three types of cones with receptivity peaks at 650 nm, 530 nm and 430 nm • Colors can be reproduced by using linear combinations of red (700 nm), green (546 nm) and blue (436 nm)
24.3 Early Image Processing Operations • Local operations • Lack of Knowledge • Smoothing: predicting the value of a pixel, given the surrounding pixels • A weighted average can be calculated using a Gaussian filter (cancels Gaussian noise)
Edge Detection • Edges occur where there is a significant change in image brightness • Figure 24.4, kinds of edges • Figure 24.5, edges from a photograph • Figure 24.6, calculating edges • Canny edge detection
Image Segmentation • Can look at low level knowledge such as brightness, color, or texture • Can also factor in high-level knowledge.