Installing OpenCV in Ubuntu and Other Linux Flavours

OpenCV is a library package that is commonly used for Image Processing in C/C++. Here I have mentioned the installation process of OpenCV in Ubuntu. Just altering the installation commands can make it work for other Linux flavours.


Step-1:

Prerequisites for Installations of OpenCV:


1. A C++ compiler like g++.
       You can install it by using the command:
                     $ sudo apt-get install g++
2. GTK+ 2.0
        It is a graphical user interface library. Install it by:
                     $ sudo apt-get install libgtk2.0-dev


Step-2:

Now we can install the OpenCV packages.
You can use the Package Manager or can use the commands from terminal to install the packages.
OpenCV consists of:
1. libcv-dev
2.libcvaux-dev
3.libhighgui-dev
4.opencv-doc


Search in the Package Manager or Use the Command : 
    $ sudo apt-get install <package-name>
Now the Installation is complete.


Step-3:
Let us write a small program to test it.

////////////////////////////////////////////////////////////////////////
//
// hello-world.cpp
//
// This is a simple, introductory OpenCV program. The program reads an
// image from a file, inverts it, and displays the result. 
//
////////////////////////////////////////////////////////////////////////
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <cv.h>
#include <highgui.h>

int main(int argc, char *argv[])
{
  IplImage* img = 0; 
  int height,width,step,channels;
  uchar *data;
  int i,j,k;

  if(argc<2){
    printf("Usage: main <image-file-name>\n\7");
    exit(0);
  }

  // load an image  
  img=cvLoadImage(argv[1]);
  if(!img){
    printf("Could not load image file: %s\n",argv[1]);
    exit(0);
  }

  // get the image data
  height    = img->height;
  width     = img->width;
  step      = img->widthStep;
  channels  = img->nChannels;
  data      = (uchar *)img->imageData;
  printf("Processing a %dx%d image with %d channels\n",height,width,channels); 

  // create a window
  cvNamedWindow("mainWin", CV_WINDOW_AUTOSIZE); 
  cvMoveWindow("mainWin", 100, 100);

  // invert the image
  for(i=0;i<height;i++) for(j=0;j<width;j++) for(k=0;k<channels;k++)
    data[i*step+j*channels+k]=255-data[i*step+j*channels+k];

  // show the image
  cvShowImage("mainWin", img );

  // wait for a key
  cvWaitKey(0);

  // release the image
  cvReleaseImage(&img );
  return 0;
}

Step-4:

Now let us compile it.

We use the command:
   $ g++ -I/usr/include/opencv -lcxcore -lhighgui -lm hello-world.cpp

 
Step-5:
Execute it:
  $ ./a.out <image-name>
Voila!!!! Here runs your first IP program.
 

Step-6:
But every time you have to compile you have to write a long command. So, we can have an alias defined for it.
Open the file /etc/bash.bashrc in super-user mode.
You can use:
     $ sudo gedit /etc/bash.bashrc
Now append the following line to the file to have an alias named "ipt".
   alias ipt="$ g++ -I/usr/include/opencv -lcxcore -lhighgui -lm"
Close the terminal and open it to make the changes effective.
Now to compile you can use:
   $ ipt hello-world.cpp
 
 
Thats all with the installation. In my upcoming posts, I will focus on basic programming concepts.