Compiling error cv::gpu - c++

Question

I'm using OpenCV master branch (3.0.0. dev) with CUDA on Ubuntu 12.04, and trying to compile the following opencv with gpu code:
#include <iostream>
#include "opencv2/opencv.hpp"
#include "opencv2/core.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/gpu/gpu.hpp"
using namespace cv;
int main (int argc, char* argv[])
{
try
{
cv::Mat src_host = cv::imread("file.png", CV_LOAD_IMAGE_GRAYSCALE);
cv::gpu::GpuMat dst, src;
src.upload(src_host);
cv::gpu::threshold(src, dst, 128.0, 255.0, CV_THRESH_BINARY);
cv::Mat result_host = dst;
cv::imshow("Result", result_host);
cv::waitKey();
}
catch(const cv::Exception& ex)
{
std::cout << "Error: " << ex.what() << std::endl;
}
return 0;
}
The compiling command is:
g++ testgpu.cpp -o test `pkg-config --cflags --libs opencv` -lopencv_gpu
It has the following compiling errors:
testgpu.cpp: In function ‘int main(int, char**)’:
testgpu.cpp:13:51: error: ‘CV_LOAD_IMAGE_GRAYSCALE’ was not declared in this scope
cv::Mat src_host = cv::imread("file.png", CV_LOAD_IMAGE_GRAYSCALE);
^
testgpu.cpp:17:52: error: ‘CV_THRESH_BINARY’ was not declared in this scope
cv::gpu::threshold(src, dst, 128.0, 255.0, CV_THRESH_BINARY);
^
testgpu.cpp:19:31: error: conversion from ‘cv::gpu::GpuMat’ to non-scalar type ‘cv::Mat’ requested
cv::Mat result_host = dst;
^
It is something wrong with the installation of OpenCV, or the API change in Opencv 3.0.0?

Answer 1

The gpu module was redesigned in OpenCV 3.0. It was splitted onto several modules, it was renamed to cuda and gpu:: namespace was renamed to cuda::. The correct code for OpenCV 3.0:
#include <iostream>
#include "opencv2/opencv.hpp"
#include "opencv2/core.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/cudaarithm.hpp"
using namespace cv;
int main (int argc, char* argv[])
{
try
{
cv::Mat src_host = cv::imread("file.png", cv::IMREAD_GRAYSCALE);
cv::cuda::GpuMat dst, src;
src.upload(src_host);
cv::cuda::threshold(src, dst, 128.0, 255.0, cv::THRESH_BINARY);
cv::Mat result_host(dst);
cv::imshow("Result", result_host);
cv::waitKey();
}
catch(const cv::Exception& ex)
{
std::cout << "Error: " << ex.what() << std::endl;
}
return 0;
}

Answer 2

Ah, they've been playing with the constants in master. Expect the CV_* prefix removed almost anywhere ( except the types, CV_8U and such are still alive).
So it's cv::THRESH_BINARY, cv::LOAD_IMAGE_GRAYSCALE, but .... cv::COLOR_BGR2GRAY (you didn't use it now, but i'll spare you the searching ;) )
Sorry, I've no experience with GPU stuff, so i can't solve the last riddle there.