图像阿尔法通道

import cv2
img=cv2.imread('C:/Users/xpp/Desktop/Lena.png')#原始图像
bgra=cv2.cvtColor(img,cv2.COLOR_BGR2BGRA)#将彩色图片转换为灰度图片
b,g,r,a=cv2.split(bgra)#拆分红、绿、蓝3个颜色通道
a[:,:]=125
bgra125=cv2.merge([b,g,r,a])#合并红、绿、蓝、alpha4个颜色通道
a[:,:]=0
bgra0=cv2.merge([b,g,r,a])#合并红、绿、蓝、alpha4个颜色通道
cv2.imshow("img",img)
cv2.imshow("bgra",bgra)
cv2.imshow("bgra125",bgra125)
cv2.imshow("bgra0",bgra0)
cv2.waitKey()
cv2.destroyAllWindows()
cv2.imwrite("bgra.png",bgra)
cv2.imwrite("bgra125.png",bgra125)
cv2.imwrite("bgra0.png",bgra0)