Circular Hough transform based on the gradient field of an image.
1. Operates on grayscale images, NOT B/W bitmaps.
2. NO loops in the implementation of Circular Hough transform, which means faster operation but at the same time larger memory consumption.
3. Detection of radii works for concentric circles as well.

包含的文件有：CircularHough_Grd.m，DrawCircle.m，Frame_0_0022_portion.jpg，TestImg_CHT_a2.bmp，TestImg_CHT_a3.bmp，TestImg_CHT_b3.bmp，TestImg_CHT_c3.bmp