cuda_opencv_simple_test.cpp

// https://forums.developer.nvidia.com/t/eliminate-upload-download-for-opencv-cuda-gpumat-using-shared-memory/83090/3
//  SimpleTest.cpp
//  Loads an image, calls a GPU enabled function that uses opencv GPUMat upload/download
//

#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <iostream>
#include <stdio.h>

// cuda stuff
#include <opencv2/cudaarithm.hpp>
// Nvidia cuda api
#include <cuda_runtime.h>

using namespace std;

cv::Mat testfunction(cv::Mat& h_original) {
    // receives a CPU/host based image, converts it to GPU/device based image
    // manipulates it, then converts back to CPU/host based result.
    cv::Mat h_result (h_original.size(), h_original.type());
    
    // create GPU/device images, same size and type as original host image
    cv::cuda::GpuMat d_original(h_original.size(), h_original.type());
    cv::cuda::GpuMat d_result(h_original.size(), h_original.type());
    
    // upload the original image from host to device
    d_original.upload(h_original);
    
    // perform a GPU operation of some sort.  Using threshold for simple placeholder
    cv::cuda::threshold(d_original, d_result, 128.0, 255.0, cv::THRESH_BINARY);

    // download the result image from device to host
    d_result.download(h_result);

    return h_result;
}

int main(int argc, char *argv[]) {
    
    cv::namedWindow("original image", cv::WINDOW_AUTOSIZE);
    cv::namedWindow("modified image", cv::WINDOW_AUTOSIZE );
    cv::String filename = "./lena.jpg";
    cv::Mat image, newimage;
    image = cv::imread(filename);
    if (image.empty()) {
        cout << "could not open or find the image" << endl;
        return -1;]
    }

    newimage = testfunction(image);
    
    cv::imshow("original image", image);
    cv::imshow("modified image", newimage);
    cv::waitKey(0);
    cv::destroyAllWindows();
    
    return 0;
}