Super Simple OpenCV C++ to Python Interface

compile_and_run.md

Compile

gcc -shared -o libsimpleopencvtest.so -fPIC ./simple_opencv_test.cpp -lopencv_core -lopencv_highgui -lopencv_objdetect -lopencv_imgproc -lopencv_features2d -lopencv_ml -lopencv_calib3d -lopencv_video

Run

python simple_opencv_test.py

simple_opencv_test.cpp

#include <opencv2/opencv.hpp>

/*

 C++ program goes here as usual (put whatever you like, can use other libraries or classes etc.)

*/

cv::Mat doStuff(cv::Mat img)
{
    // Modify the image in C++ OpenCV
    img += 0.1 * 255;
    return img;
}

extern "C" void modifyImg(unsigned char *im, int width, int height)
{
    // Image gets passed in from external (e.g. Python) as ptr
    cv::Mat image = cv::Mat(width, height, CV_8UC3, im);

    image = doStuff(image);

    // Do not need to return anything because we are using pointers...
}

simple_opencv_test.py

import ctypes as C
import numpy as np

# Must put full path to the '.so' file
my_cpp_opencv_lib = C.cdll.LoadLibrary('/home/alex/opencv_test/libsimpleopencvtest.so')

res = np.ones(dtype=np.uint8, shape=(100, 100, 3))

# Pass the Numpy array in from Python
img_ptr = res.ctypes.data_as(C.POINTER(C.c_ubyte))
my_cpp_opencv_lib.modifyImg(img_ptr, res.shape[1], res.shape[0])

# See how the array has been modified
print(res)