Installing OpenCV on Linux (Ubuntu)

Earlier i was using openCV with Microsoft Visual C++ 6.0. But let me tell you, it crashed a lot. Every time i needed to close the process from Task Manager. Then i decided to somehow install OpenCV for my ubuntu.
After searching and trying a lot for this, i was finally able to use opencv in GNU compiler(g++ or gcc).
Synaptic Package Manager has simplified the life to a great extent. OpenCV is now available in the ubuntu repositories.
Though there are some problems related to ‘ffmpeg’, i needed opencv for image processing only. So i have not mentioned here what to do about ‘ffmpeg’.

Things to know before starting installation:
i. This installation needs a C++ compiler like “g++”(which is most commonly used). So install g++ first using Synaptic or by following command at the terminal–

$ sudo apt-get install g++

ii. OpenCV requires GTK+ 2.0 or higher for displaying images. GTK is graphical user interface library. Type out the following code to know the version of GTK+ installed on ur pc.

$ dpkg -l | grep libgtk

This command should give o/p something like:

libgtk-directfb-2.0-0 2.16.1-0ubuntu2

If not, then u need to install the libraries for GTK+ 2.0 first, then start with this opencv installation.
To install GTK+ 2.0 libraries, type out the following command:

$ sudo apt-get install libgtk2.0-dev

If both g++ & GTK+ 2.0 are there then proceed as follows:

I am using Ubuntu 9.04 (Jaunty Jackalope) and i did the following steps to install & configure OpenCV(ver 1.0.0.6) successfully:

1. Go to Synaptic Package Manager (System> Administration> Synaptic Package Manager)
2. Search for “opencv” and install the main “opencv” package and the following lib files:
libcv
libcv-dev
libcvaux
libcvaux-dev
libhighgui
libhighgui-dev
opencv-doc
(‘python-opencv’ not required).
(you can also install opencv directly from the terminal by “sudo apt-get install” the above lib files
3. After installing all the packages, open a terminal & type this code:

export LD_LIBRARY_PATH=/home/opencv/lib
export PKG_CONFIG_PATH=/home/opencv/lib/pkgconfig

The above ones are default paths for the opencv libraries.
4. For testing:
Create a new folder & a file “hello.cpp” in it using any text editor & type this code in it:

#include < cv.h > /* required to use OpenCV */
#include < highgui.h > /* required to use OpenCV's highgui */
#include < stdio.h >

int main(int argc, char *argv[]) {
IplImage* img=0; /* pointer to an image */
printf("Hello\n");
if(argv[1] != 0)
img = cvLoadImage(argv[1], 0); // 1 for color
else
printf("Enter filename\n");
if(img != 0) {
cvNamedWindow("Display", CV_WINDOW_AUTOSIZE); // create a window
cvShowImage("Display", img); // show image in window
cvWaitKey(0); // wait until user hits a key
cvDestroyWindow("Display");
}
else
printf("File not found\n");
return 0;
}

5. To check the path where opencv & other lib files are stored, do:

$ pkg-config --cflags opencv

(output will come as)
-I/usr/include/opencv

$ pkg-config --libs opencv

(output will come as)
-lcxcore -lcv -lhighgui -lcvaux -lml

These paths are needed to compile your opencv programs, as given in the next step.

6. To compile & run:

$ g++ -I/usr/include/opencv -lcxcore -lhighgui -lm hello.cpp
./a.out img


where “img” is the name of any image within the same folder with extension.
You should be able to see “Hello” and the image in a different window.

-> If this runs, Congrats! now you can run any C/C++ program with opencv lib.
Else, try

$ export PATH=$HOME/usr/bin/:$PATH

and go to step3 again.

7. Now lets simplify the above big command by making a shortcut for it:
go to your local home directory(cd /home/) and open the .bashrc file using gedit(the file will be hidden). Append the following to the file:

alias gcv="g++ -I/usr/include/opencv -lcv -lcxcore -lcvaux -lhighgui -lm"

and save. Close the terminal and open it again.(as this process requires relogin of the terminal)

8.Now, go to directory containing a sample program & do

$ gcv filename.c && ./a.out
or
$ gcv filename.c
$ ./a.out input_img.jpg

As you can see the commands now become similar to $cc filename.c, $./a.out which are used normally for compiling and executing C programs.

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Some ways to check whether all lib files are installed-
1. $ apt-cache search opencv
returns:
libcv-dev - development files for libcv
libcv0.9-0c2 - computer vision library
libcvaux-dev - development files for libcvaux
libcvaux0.9-0c2a - computer vision extension library
libhighgui-dev - development files for libhighgui
libhighgui0.9-0c2 - computer vision GUI library
opencv-doc - OpenCV documentation and examples

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If you want to install openCV from a .tar file, refer this article:
Installing opencv in linux(Ubuntu) from .tar.gz file
Other helpful links on this topic:
http://ivkin.net/2009/11/installing-opencv-2-0-on-ubuntu-9-10-karmic-koala/