用matlab实现自编直方图程序并与matlab自带直方图函数进行比较，以及实现直方图均衡- Histogram Equalization

　 (a) Write a computer program for computing the histogram of an image.

　 (b) Implement the histogram equalization technique discussed in Section 3.3.1.

　 (c) Download Fig. 3.8(a) and perform histogram equalization on it.

　 As a minimum, your report should include the original image, a plot of its histogram, a plot of the histogram-equalization transformation function, the enhanced image, and a plot of its histogram. Use this information to explain why the resulting image was enhanced as it was.