初步完成第二道题

test/2024,9,10/set_alpha.py

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+import cv2 as cv
+
+# read image
+img=cv.imread("opencv_logo.png",cv.IMREAD_UNCHANGED)
+# concert to rgba
+img_rgba=cv.cvtColor(img,cv.COLOR_BGR2BGRA)
+# split alpha channel
+blue,green,red,alpha = cv.split(img_rgba)
+#set alpha channel
+alpha[int(alpha.shape[0]/2):alpha.shape[0],int(alpha.shape[1]/2):alpha.shape[1]]=0
+# remix alpha to img_rgba
+img_rgba=cv.merge((blue,green,red,alpha))
+# show
+cv.imshow("changed",img_rgba)
+cv.waitKey(0)
+cv.destroyAllWindows()