说明：  用于ocr的预处理，主要就是去除干扰的背景，这个是专门为文本ocr预处理设计的算法，能很好的保留文本区域，并且剔除干扰
(For ocr pretreatment is to remove the interference in the background, this is specifically designed for text ocr preprocessing algorithm design, can be well retained the text area, and removing the interference)