计算机视觉课件(5).ppt
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1、Course 3 Binary Image,Course 3 Binary Image,Binary Images have only two gray levels: “1” and “0”, i.e., black / white. save memory fast processing many features of an intensity image appear in binary form, e.g. edge, contour, human can understand binary line drawings.,1. Neighbors/path/connectivity
2、(1) Neighbors of a pixel a. 4-neighbors: the upper, lower, left and right neighbor pixels of a pixel. b. 8-neighbors: the 4-neighbors pixels plus the diagonal neighbors. 4-neighbor 8-neighbor,(2) Path A path form pixel to the pixel is a sequence of pixel indices: where the pixel is a neighbor of pix
3、el for all . 4 path if 4-neighbor is used 8 path if 8-neighbor is used,(3) Connectivity: A pixel is said to be connected to if there is a path from to consisting of pixels of . Connected component: A set of pixels in which each pixel is connected to all other pixels of the set.,4-connected 8-connect
4、ed,2. Geometric attributes of a binary image/component: (1) size (area): for all B.,. = 1 pixels. (2) position: the position of a binary image component is defined by its mass center.,Orientation: The orientation of binary image component is defined by a straight line that the distance sum from all
5、the pixels to the line is minimized,i.e., where is the distance from pixel i, j to the line. Let the line in polar coordinates be: Then: So:,Set , and We get: where is the center of the component, and where,Note: may minimize or maximize . The has two values; the corresponding lines are called maxim
6、um axis and minimum axis of the image component.,(4) Foreground / Background : Foreground: the set f all “1” pixels in an image. Background: the set of all connected components of that have points on the border of the image. Hole: the connected component in but it does not have border points. Note:
7、foreground and background must use different connectivities. Hole or not?,(1) Boundary: boundary of S is a set of pixels in S that has 4-neighbours in , denoted by . (2) Interior (pixels in S but not in ) Surrounds: if any 4-path from any point of S to image border must intersect region T, we say re
8、gion T surrounds region S.,(7) Perimeter Def.1: The total length of lines that separate pixels of S from . Def.2: The number of boundary pixels. (8) Compactness Where P perimeter, A area. The smallest value of c is . If c = , S is a circular region. When c is larger, S is elongated when , S is a lin
9、e segment.,3. Binary Processing: (1) Thresholding: Thresholding converts an intensity image into a binary image, partitioning the original image to regions. Let image has gray level ranged in 0,L , T be threshold, 0TL Then, If you are interested in image information of certain range of gray level, y
10、ou can choose double thresholds,Then,Original image Image by threshold double threshold (L=64) T=48 T1 = 2, T2 = 48,(2) Run-length encode: Run-length code is a compact way to represent a binary image. Run-length encoding is a row-based operation. Method 1: only encode “1” pixels. Using start positio
11、n and length of runs of “1” to represent the runs. Method 2: encode “1” runs and “0” runs alternatively. Using only one number to indicate the length of the run. If an image row starts with a “0” run, put a “0” as the header of the code of the row, otherwise the header will not appear.,Method1: (1,3
12、), (7,2), (12,4), (17,2), (20,3) (5,13), (19,4) (1,3), (17,6) Method 2: 3, 3, 2, 3, 4, 1, 2, 1, 3; 0, 4 ,13 ,1, 4; 3, 13, 6,(3) Boundary-following: Track boundary pixels of a region in a particular order (chain sequence),Algorithm: a) Use systematic scan (from left to right, and from top to bottom)
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