图像求反，黑变白，白变黑，对图像求反：黑变白，白变黑,将灰度级是[0 L-1]的图像变换为[L-1 0]-Inverted image, black and white, white black, negate the image: black and white, white to black, the gray scale is [0 L-1] of the image is transformed into [L-1 0]