说明：  顶帽变换是指原始图像减去其开运算的图像 而开运算可用于补偿不均匀的背景亮度，所以用一个大的结构元素做开运算后 然后用原图像减去这个开运算，就得到了背景均衡的图像，这也叫做是图像的顶帽运算
(Top hat transformation refers to the image of the original image minus its opening operation. The open operation can be used to compensate for the uneven background brightness, so a large structural element is used to calculate the opening. Then the original image is subtracted from the opening operation and the background equalizing image is obtained, which is also called the top hat operation of the image.)