武汉理工大学数字图像处理英文课件 Chapter8（3）.pptVIP

Translation Only (1:1) Image Reduction (many:1) Image Enlargement (1:many) Image Reduction by Pixel Averaging Image Reduction by Subsampling Image Enlargement by Pixel Replication Matlab Function imresize Example Using imresize Image Rotation Matlab Function imrotate Example Using imrotate * Each new (black) pixel incorporates at most four source (blue) pixels. The diagram suggests that simple area of overlap may be sufficient. Each new (black) pixel incorporates at most four source (blue) pixels. The diagram suggests that simple area of overlap may be sufficient. Each new (black) pixel incorporates at many source (blue) pixels. The diagram suggests that summing the contributions over the source pixels is required, ideally with weights proportional to the area of overlap. Each new (black) pixel typically samples a small portion of a single source (blue) pixel. The diagram suggests that a subpixel interpolation scheme is required. original 4x4 pixel average pixel averaging subsampling Sampling reduces the size of an image by extracting pixels on a periodic sample grid, every 3th pixel in every 3th row, for example. Sampling produces a different reduced image than averaging, especially in patterned regions. Compare the hat and hair in the examples above. original 4x4 pixel replication B = imresize(A,m,method) returns an image matrix that is m times larger (or smaller) than the image A. The image B is computed by interpolating using the method in the string method. Possible methods are nearest (nearest neighbor), bilinear (bilinear interpolation) bicubic (bicubic interpolation). B = imresize(A,[mrows ncols],method) returns an image of size [mrows ncols]. B = imresize(A,m) uses nearest as the default interpolation scheme. When the specified output size is smaller than the size of the input image, and method is bilinear or bicubic, imresize applies a lowpass filter before interpolation to reduce aliasing. The default filter size is 11-by-11. You can specify a di