Returning A Opencv Mat Type From My Python Code

I tried to return the (c++ opencv Mat) from my opencv python code Steps i done: A. Generated .so file for my opencv C++ program by using SWIG B. Wrote a sample Opencv Python Progr

Solution 1:

Posting just in case someone will face the same issue:

Using SWIG and https://github.com/renatoGarcia/opencv-swig to deal with passing cv::Mat I ended up with

my_lib.hpp

#include<opencv2/core.hpp>#include<iostream>cv::Mat getImage(cv::Mat& image){
    std::cout << "image size " << image.rows << " " << image.cols << std::endl;
    return image;
}

my_lib.i

%module my_lib
%include <opencv.i>
%cv_instantiate_all_defaults

%{
    #include"my_lib.hpp"#include<opencv2/core.hpp>#include<iostream>
%}

%include "my_lib.hpp"

test.py (with opencv-swig library placed at the same folder as script)

import my_lib
import cv2
import numpy as np
import sys
sys.path.append('./opencv-swig-master/test/build/')
import mat

img = cv2.imread("test.jpg")
new_img = my_lib.getImage(mat.Mat.from_array(img))
new_img = np.asarray(new_img)
cv2.imwrite("test_out.jpg", new_img)

And these commands

swig -I<path to opencv-swig-master/lib/> -I<path to opencv2 include folder> -c++ -python my_lib.i
g++ -shared -fpic my_lib_wrap.cxx $(pkg-config--cflags --libs python3) $(pkg-config --libs opencv) -o _my_lib.so

Solution 2:

In the c++ code you are using a cv::Mat datatype. As in python you also use openCV, I can imagine that you also expect to get the same datatype. But in python openCV uses an numpy array as image format.

In the following link, they speak about a numpy dataformat under c++. I can imagine that you use this dataformat to communicate between python and C++. In C++ you need to do the conversion from numpy to cv::Mat then.

https://scipy-lectures.github.io/advanced/interfacing_with_c/interfacing_with_c.html