opencv中drawing line时报错

error: (-215) size.width>0 && size.height>0 in function imshow

1         img2 = cv2.rectangle(frame, (x,y), (x+w,y+h), 255,2)
2         cv2.imshow(‘img2‘,img2)

调试时可发现img2的类型为NoneType.即img2为empty

改为如下

1       cv2.rectangle(frame, (x,y), (x+w,y+h), 255,2)
2
3       cv2.imshow(‘img2‘,frame)