1.灰度变换之imadjust函数（实现图像灰度的反转）
>> a = imread('view.jpg');
>> b = imadjust(a, [0,1], [1, 0]);
>> figure;
>> subplot(211);
>> imshow(a)
>> title('原图');
>> subplot(212)
>> imshow(b)
>> title('调整后')
>> b = imadjust(a, [0,1], [1, 0]);
>> figure;
>> subplot(211);
>> imshow(a)
>> title('原图');
>> subplot(212)
>> imshow(b)
>> title('调整后')