Archive for September, 2012

Installing OpenCv in 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 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:
(‘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 */
if(argv[1] != 0)
img = cvLoadImage(argv[1], 0); // 1 for color
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
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)

$ 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
$ 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.

Some ways to check whether all lib files are installed-
1. $ apt-cache search opencv
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

If you want to install openCV from a .tar file, refer this article:
Installing opencv in linux(Ubuntu) from .tar.gz file

Programming Praxis

In their book The C Programming Language, Brian Kernigan and Dennis Ritchie say that the first program every programmer should write is a program that writes “Hello, world!” to the console. Then they give the second program that produces a fahrenheit/celsius temperature conversion table, with fahrenheit temperatures every 20 degrees from 0 to 300 and the corresponding celsius temperature to the nearest degree, each pair written on its own line with the two temperatures separated by tabs.

Your task is to write the first two programs. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.

The hello program is simple:

(define (hello)
  (display "Hello, world!")

The temperature conversion table isn’t much harder. We follow K&R by using a do-loop and calculating the celsius temperature in-line instead of in…

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