用opencv给一张透明图片添加背景

# -*- coding: utf-8 -*-
import cv2
import numpy as np


def add_alpha_channel(img):
    """ 为jpg图像添加alpha通道 """

    b_channel, g_channel, r_channel = cv2.split(img)  # 剥离jpg图像通道
    alpha_channel = np.ones(b_channel.shape, dtype=b_channel.dtype) * 255  # 创建Alpha通道

    img_new = cv2.merge((b_channel, g_channel, r_channel, alpha_channel))  # 融合通道
    return img_new


def merge_img(jpg_img, png_img, y1, y2, x1, x2):
    """ 将png透明图像与jpg图像叠加
        y1,y2,x1,x2为叠加位置坐标值
    """

    # 判断jpg图像是否已经为4通道
    if jpg_img.shape[2] == 3:
        jpg_img = add_alpha_channel(jpg_img)

    '''
    当叠加图像时，可能因为叠加位置设置不当，导致png图像的边界超过背景jpg图像，而程序报错
    这里设定一系列叠加位置的限制，可以满足png图像超出jpg图像范围时，依然可以正常叠加
    '''
    yy1 = 0
    yy2 = png_img.shape[0]
    xx1 = 0
    xx2 = png_img.shape[1]

    # if x1 < 0:
    #     xx1 = -x1
    #     x1 = 0
    # if y1 < 0:
    #     yy1 = - y1
    #     y1 = 0
    # if x2 > jpg_img.shape[1]:
    #     xx2 = png_img.shape[1] - (x2 - jpg_img.shape[1])
    #     x2 = jpg_img.shape[1]
    # if y2 > jpg_img.shape[0]:
    #     yy2 = png_img.shape[0] - (y2 - jpg_img.shape[0])
    #     y2 = jpg_img.shape[0]

    # 获取要覆盖图像的alpha值，将像素值除以255，使值保持在0-1之间
    alpha_png = png_img[yy1:yy2, xx1:xx2, 3] / 255.0
    alpha_jpg = 1 - alpha_png

    # 开始叠加
    for c in range(0, 3):
        jpg_img[y1:y2, x1:x2, c] = ((alpha_jpg * jpg_img[y1:y2, x1:x2, c]) + (alpha_png * png_img[yy1:yy2, xx1:xx2, c]))

    return jpg_img


if __name__ == '__main__':
    # 定义图像路径
    img_jpg_path = 'img/3.jpg'  # 读者可自行修改文件路径
    img_png_path = 'img/3.png'  # 读者可自行修改文件路径

    # 读取图像
    img_jpg = cv2.imread(img_jpg_path, cv2.IMREAD_UNCHANGED)
    img_png = cv2.imread(img_png_path, cv2.IMREAD_UNCHANGED)

    # 设置叠加位置坐标
    x1 = 0
    y1 = 0
    x2 = x1 + img_png.shape[1]
    y2 = y1 + img_png.shape[0]

    # 开始叠加
    res_img = merge_img(img_jpg, img_png, y1, y2, x1, x2)

    # 显示结果图像
    # cv2.imshow('result', res_img)

    # 保存结果图像，读者可自行修改文件路径
    cv2.imwrite('img/res.jpg', res_img)

    # 定义程序退出方式：鼠标点击显示图像的窗口后，按ESC键即可退出程序
    if cv2.waitKey(0) & 0xFF == 27:
        cv2.destroyAllWindows()