python 边缘扩充方式的实现示例

import cv2
 
# big_pad=True：当目标图像高和宽均大于原图时，进行边缘填充
# big_pad=False：按照目标尺寸的最小缩放比例，先缩放，再进行边缘填充
# borderType=cv2.BORDER_CONSTANT：表示常量填充，borderValue为填充常量0~255(黑~白)
# borderType=cv2.BORDER_REPLICATE：边界复制填充
# borderType=cv2.BORDER_REFLECT：边界反射填充
# borderType=cv2.BORDER_WRAP：边框包装填充
 
def image_padding(image, target_shape, big_pad=True, 
                  borderType=cv2.BORDER_REFLECT, borderValue=(0, 0, 0)):
    # 目标尺寸大小
    ph, pw = target_shape
    # 原始图片尺寸
    h,  w, _ = image.shape
    if big_pad and ph > h and pw > w: # 以原图为中心进行边缘填充
        top = bottom = (ph - h) // 2  # 获取上、下填充尺寸
        top += (ph - h) % 2 # 为保证目标大小，无法整除则上+1
        left = right = (pw - w) // 2
        left += (pw - w) % 2 # 为保证目标大小，同理左上+1
        image_padded = cv2.copyMakeBorder(image, top, bottom, left, right,
                                          borderType=borderType, value=borderValue)
    else: # 最小比例缩放填充（大尺寸：高/宽比例变化较大的将被填充，小尺寸反之）
        # 计算缩放后图片尺寸
        scale = min(pw/w, ph/h) # 获取高/宽变化最小比例
        nw, nh = int(scale * w), int(scale * h)
        # 对原图按照目标尺寸的最小比例进行缩放
        img_resized = cv2.resize(image, (nw, nh))
        top = bottom = (ph - nh) // 2  # 获取上、下填充尺寸
        top += (ph - nh) % 2 # 为保证目标大小，无法整除则上+1
        left = right = (pw - nw) // 2
        left += (pw - nw) % 2 # 为保证目标大小，同理左上+1
        image_padded = cv2.copyMakeBorder(img_resized, top, bottom, left, right, 
                                          borderType=borderType, value=borderValue)
    return image_padded
 
 
if __name__ == "__main__":
    path = './2_2.png'
    img = cv2.imread(path)
    img_pad = image_padding(img, (640,640))
    cv2.imwrite('./1_BORDER_WRAP.png',img_pad)
    # cv2.imwrite('./1_.png',img_pad[64:576,64:576])