opencv - How to load png images with 4 channels?

Question

I have been trying to load .png files with transparency channel (RGB and Alph) with no luck. It appears that openCV strips the 4th channel out of the image. Is there any method to load the image with the complete 4 channels including the alpha channel even if I had to modify the OpenCV source code and rebuild it?

Answer 1

If you are using OpenCV 2 or OpenCV 3 you should use IMREAD_* flags (as mentioned at here).

C++

using namespace cv;
Mat image = imread("image.png", IMREAD_UNCHANGED);

Python

import cv2
im = cv2.imread("image.png", cv2.IMREAD_UNCHANGED)