水印图像读取与制作，三通道图转为4通道，制作透明图

def watermark_handle(watermark_path):
    '''
    水印图像读取与制作，三通道图转为4通道，制作透明图
    :param watermark_path: 水印图像路径
    :return: 图像数据，图像高度，图像宽度
    '''
    im = cv2.imread(watermark_path)
    h, w = im.shape[:2]
    # 转换为灰度图
    gray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY)
    # 像素翻转
    thresh = cv2.threshold(gray, 225, 255, cv2.THRESH_BINARY_INV)[1]
    img = np.stack((thresh,) * 3, axis=-1)
    image = np.dstack([img, np.ones((h, w), dtype="uint8") * 255])
    return image, h, w

def watermark_merge(frame, watermark, xmin, ymin):
    frame_h, frame_w = frame.shape[:2]
    wm_h, wm_w = watermark.shape[:2]
    # 转为四通道图像数据
    im = np.dstack([frame, np.ones((frame_h, frame_w), dtype="uint8") * 255])

    overlay = np.zeros((frame_h, frame_w, 4), dtype="uint8")
    overlay[ymin:ymin + wm_h, xmin:xmin+wm_w] = watermark
    alpha = 0.25
    cv2.addWeighted(overlay, alpha, im, 1.0, 0, im)
    return im