[FIXED] Get pointer from numpy array to send image to C++

Issue

I am working on a project on which I have to deal with images between Python and C++. In order to send an image from C++ to Python, I send a pointer on the first pixel of my image (being a Mat object from OpenCV library) and in Python with two for loops I used this pointer to create a 2D numpy array.

But I don't succeed to do the same in the other way : get the memory address of the first pixel of the numpy 2D array (an image) and pass it to the C++.

Assume x is my image (2D numpy array), I tried solution like :

• x.__array_interface__['data'][0] but this give an integer, not an address
• x.data which give different values each time I call it because it gives me the address of a temporary buffer, not the image itself

Thank you in advance for any advice/help.

Solution

I found a "simple" way to do that:

In C++, the function has to take as argument a void * ptr, and like this I can create a Mat object using the pointer sent from Python :

void myCfunction(void* ptr){
    Mat matrix = Mat(sizes, CV_8UC1, (uchar*)ptr);
}

And, in Python, use __array_interface__ to get the memory address (in int type, weird) :

mydll.myFunction(myNumpyArray.__array_interface__['data'][0], ...)

Answered By - Mathieu Gauquelin