利用C#来实现基本的数字图像处理，包括彩色图像灰度化、基于像素矩阵变换的90度旋转(两个方向)、改变亮度和对比度-using C# to process digital image， including converting a color image to a gray image，90 degree rotation based on matrix of pixels(two directions)，changing brightness and contrast of the image