数字图像处理-冈萨雷斯-课件(英文)Chapter11 表示与描述.ppt

Fourier Approach for Texture Descriptor (Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition. Original image 2D Spectrum (Fourier Tr.) S(r) S(q) Another image Another S(q) Moments of Two-D Functions The moment of order p + q The central moments of order p + q Invariant Moments of Two-D Functions where The normalized central moments of order p + q Invariant moments: independent of rotation, translation, scaling, and reflection Example: Invariant Moments of Two-D Functions (Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition. 1. Original image 2. Half size 3. Mirrored 4. Rotated 2 degree 5. Rotated 45 degree * Digital Image Processing Chapter 11: Image Description and Representation 12 September 2007 Image Representation and Description? Objective: To represent and describe information embedded in an image in other forms that are more suitable than the image itself. Benefits: - Easier to understand - Require fewer memory, faster to be processed - More “ready to be used” What kind of information we can use? - Boundary, shape - Region - Texture - Relation between regions Shape Representation by Using Chain Codes Chain codes: represent an object boundary by a connected sequence of straight line segments of specified length and direction. 4-directional chain code 8-directional chain code Why we focus on a boundary? The boundary is a good representation of an object shape and also requires a few memory. (Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition. Examples of Chain Codes Object boundary (resampling) Boundary vertices 4-directional chain code 8-directional chain code (Images from Rafael C. Gonzalez and Richard E. Wood, Digital Image Processing, 2nd Edition. The First Difference of a Chain Codes Problem of a chain code: a chain code sequence depends on a starting point. Solution: