python获取透明图

import cv2
import os
import numpy as np

root = "./test"
for file in os.listdir(root):
    # 读取图片
    image = cv2.imread(os.path.join(root, file), cv2.IMREAD_UNCHANGED)
    new = np.zeros((image.shape[0], image.shape[1], image.shape[2]), np.uint8)
    # 检查图片是否为RGBA格式
    print(image.shape)
    if image.shape[2] == 4:
        print("图片是RGBA格式")
        # 获取透明度通道
        new[:, :, :3] = image[:, :, :3]
    else:
        print("图片不是RGBA格式")

    # 广播机制
    new[:, :, 3] = 30
    cv2.imwrite("./test/alpha30.png", new)
    # for i in image.shape[0]:
    #     for j in image.shape[1]:
    #         new[i][j][3] = 30