使用MATLAB，实现以下四个功能

一、获取图片RGB值：给定一张图片，获取点(x,y)，以及(x,y)周围8个点的R、G、B值。

二、实现rgb2gray函数：使用matlab实现rgb2gray的功能，并能计算出转换后灰度图片的方差。

三、灰度图对比度增强：分别使用灰度拉伸和直方图均衡化，增强给定图的对比度。

四、图像去噪：对给定图片加椒盐噪声，并选择两个去噪算法去除椒盐噪声。

-Using MATLAB, to achieve the following four functions

First, access to image RGB value: Given a picture, get the point (x, y), and (x, y) around 8 o clock in the R, G, B values.

Second, the realization rgb2gray function: using matlab realize rgb2gray functions, and can calculate the variance after the conversion of grayscale image.

Third, the grayscale contrast enhancement: namely, the use of gray stretch and histogram equalization, contrast enhancement given graph.

Fourth, the image denoising: for a given image add salt and pepper noise, and you know at least two　denoising algorithm to remove salt and pepper noise.