Opencv - cut out mask foreground area from grayscale image

From grayscale image , According to the threshold , Cut out multiple foreground areas , Filter images with too small area .

OpenCV Of Python Logic ,clip_gray_patches：

def clip_gray_patches(img_gray, ths=32, filter_percent=0.0005):
    """  Cut out multiple foreground areas from the gray image , Threshold greater than ths, The proportion of filtering area is less than filter_percent Image  @param img_gray:  Grayscale image  @param ths:  Foreground threshold  @param filter_percent:  Filter area  @return: patches list,  Contour image  """

    #  according to thresh_val Filter mask