opencv 图像归一化

class PreprocessResizeKeepRatio(object):

    def __init__(self, width, height):
        self.width = width
        self.height = height

    def do(self, cv2_img):
        max_width = self.width
        max_height = self.height

        cur_height, cur_width = cv2_img.shape[:2]

        ratio_w = float(max_width)/float(cur_width)
        ratio_h = float(max_height)/float(cur_height)
        ratio = min(ratio_w, ratio_h)

        new_size = (min(int(cur_width*ratio), max_width),
                    min(int(cur_height*ratio), max_height))

        new_size = (max(new_size[0], 1),
                    max(new_size[1], 1),)

        resized_img = cv2.resize(cv2_img, new_size)
        return resized_img