OpenCV: Using OpenCV with gcc and CMake

| OpenCV 3.4.2 Open Source Computer Vision

Using OpenCV with gcc and CMake

Note
  We assume that you have successfully installed OpenCV in your workstation.

- The easiest way of using OpenCV in your code is to use CMake. A few advantages (taken from the Wiki):
  1. No need to change anything when porting between Linux and Windows
  2. Can easily be combined with other tools by CMake( i.e. Qt, ITK and VTK )
- If you are not familiar with CMake, checkout the tutorial on its website.

## Steps

### Create a program using OpenCV

Let's use a simple program such as DisplayImage.cpp shown below.

#include <stdio.h>
#include <opencv2/opencv.hpp>
using namespace cv;
int main(int argc, char** argv )
{
if ( argc != 2 )
{
printf("usage: DisplayImage.out <Image_Path>\n");
return -1;
}
Mat image;
image = imread( argv[1], 1 );
if ( !image.data )
{
printf("No image data \n");
return -1;
}
namedWindow("Display Image", WINDOW_AUTOSIZE );
imshow("Display Image", image);
waitKey(0);
return 0;
}

### Create a CMake file

Now you have to create your CMakeLists.txt file. It should look like this:

cmake_minimum_required(VERSION 2.8)
project( DisplayImage )
find_package( OpenCV REQUIRED )
include_directories( ${OpenCV_INCLUDE_DIRS} )
add_executable( DisplayImage DisplayImage.cpp )
target_link_libraries( DisplayImage ${OpenCV_LIBS} )

### Generate the executable

This part is easy, just proceed as with any other project using CMake:

cd <DisplayImage_directory>
cmake .
make

### Result

By now you should have an executable (called DisplayImage in this case). You just have to run it giving an image location as an argument, i.e.:

./DisplayImage lena.jpg

You should get a nice window as the one shown below: