tailieunhanh - Biosignal and Biomedical Image Processing phần 9

Tham khảo tài liệu 'biosignal and biomedical image processing phần 9', kỹ thuật - công nghệ, kĩ thuật viễn thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Filters Transformations and Registration 333 guides or aids the registration process. The former approach usually relies on some optimization technique to maximize the correlation between the images. In the latter approach a human operator may aid the alignment process by selecting corresponding reference points in the images to be aligned corresponding features are identified by the operator and tagged using some interactive graphics procedure. This approach is well supported in MATLAB s Image Processing Toolbox. Both of these approaches are demonstrated in the examples and problems. Unaided Image Registration Unaided image registration usually involves the application of an optimization algorithm to maximize the correlation or other measure of similarity between the images. In this strategy the appropriate transformation is applied to one of the images the input image and a comparison is made between this transformed image and the reference image also termed the base image . The optimization routine seeks to vary the transformation in some manner until the comparison is best possible. The problem with this approach is the same as with all optimization techniques the optimization process may converge on a sub-optimal solution a so-called local maximum not the optimal solution the global maximum . Often the solution achieved depends on the starting values of the transformation variables. An example of convergence to a sub-optimal solution and dependency on initial variables is found in Problem 8. Example below uses the optimization routine that is part of the basic MATLAB package fminsearch formerly fmins . This routine is based on the simplex direct search method and will adjust any number of parameters to minimize a function specified though a user routine. To maximize the correspondence between the reference image and the input image the negative of the correlation between the two images is minimized. The routine fminsearch will automatically adjust the .