OpenCV - Computer Vision Library

OpenCV is an open source computer vision library developed by Intel. This library is written in C/C++ and it has lot of very powerful image processing features.

I got to know about this library few months back when I was doing researches for our final year project. Our project "Sign2Voice" interprets signs of sign language to voice in real time using a video captured using simple webcam.

OpenCV has rich image processing API that that provides wide range of functionally ranging from simple image processing tasks to machine learning algorithms.  In our project we uses OpenCV library to detect and identify sign language hand gestures. We uses Haar-Cascade classifier provided with OpenCV to detect hand. After training the classifier with set of positive and negative images we can use the classifier to detect objects. OpenCV has a good trained classifier for face detection.

Training of Haar-classifier is not an easy task. This became especially difficult because there is nor proper documentation for this process. Their are few web sites that give instructions on how to train, but they are not that comprehensive.

We had to do lot of experiments and learn through trail and error to find out how to do the training properly. After lot of failures we managed to achieve good results in had detection. 

hand_detect hand_detect1


I'm planning to do some posts regarding how to train haar-classifier share the knowledge I gained with you in future. So keep you figures crossed. :)


Reader Comments

Wuts so special abt OpenCV???

How were you able to identify different sign languages? Did you use the classifiers of your trained haar or you used another algorithm for the recognition part? Thanks

How were you able to identify different sign languages? Did you use the classifiers from the haar training or you used another algorithm? Thanks!

Yes, Yann. We used Haar classifier to detect the hand and then cropped it and use HMM algorithm to identify the sign.

Ok thanks! Can I have another favor? Can I ask for some links for HMM. We are trying to recognize 5 hand gestures and we also used haar for detecting the hand. We are also considering HMM for recognition but I can not find any links that would help. Thank you so much!

We used the HMM implementation found at
It gives all the instructions on how to use it as well. It will be agood starting point.

Ok thanks a lot! I'll check this site

hi.. simple question does it really take 5 days to generate the haar classifier???

can i ask you for a favour can u give me the initially implementation of detecting the hand only,
we are implementing a hand gesture recognition system, so if you could help us out a bit here, it would be awesome, thanks....

Good job!
Is it possible to get the Hand Classifier?


Great job. Did you guys write a paper or report about it?. I am interested in reading about using Haar for hand detection as well. Any info, is well appreciated.


i found your work about the hand detector very interesting; i would like to try it with my tracker algorithm developed for my thesis.

This is my site ( ) where i put my projects; you can take a look at my tracking algorithm for faces (with pose estimation) and for pedestrians. It's a real time "plugin" algorithm able to track several kind of objects.

Nowadays my site it's mostly in italian, the english translation it's a bit out of date, but u can watch the videoclip and contact me if u want.


Hey, i am working on a project in which we are developing a language for cameras. This project is total researchy.. We are using opencv for this purpose. We do not want to get to much into the problems of vision and make some thing on basis of what people have already developed. Is it possible that you can give me your xml file of haarcascade as making one on thousands positive and negative images is a very long process.

Did you ever post a follow-up to this post regarding your training experiences? I'd be very interested.

With coincidence I along with my team are doing the same project using OpenCV and Visual C++ for our final year project... But we are resorting to a different approach and we r having some troubles in understanding the concept... We wud appreciate any kind guidance from ur side if its possible... At first we resorted not to use HAAR cascades but in shortage of time and resources we r looking for alternative methods.... Please may i know ur e-mail address so that i can contact u as soon as possible... b'coz our team is running out of time....

Thanking you.

- Ashutosh Mukherjee

Ashutosh- A possible alternative to using Haar cascades and classifiers is to compare histograms to detect objects or ROIs. Do you have O'Rielys book "Learning OpenCV?" It is quite insightful.

We r implying histogram only.... wish i cud post screen shots of my project here.... but how to do the recognition part we r getting histograms but we r not able to generate pattern from it... need some assistance in pattern recognition from histogram... we have devised our own logic but we r not sure that they work for various cases....

We did this project more than a year ago and after that I've not read much about OpenCV.
Think good place for you to get some guidance is OpenCV yahoo group.

we are doing hand gesture recognition but i am facing lots of difficulty in implementing haar classifier.

Please help me!!!Can u post your sample code for hand detection using haar classifier??

Your help/guidance will be much appreciated

Can the gesture recognition be done by Artificial neural networks after detection by haar classifier instead of HMM

Hi! i hope your still there.. i just wanted to know what are the steps in recognizing different sign on my thesis now. i just wanted to know how HMM algorithm works.thanks!!!

Hi!! wonderful project! I'm planning on creating something similar, so im just curious as to why you chose to use a HMM algorithm? I read that HMM can be costly in resources??

u r great sandarenu....... thanx thanx a lot... u have done a fabulous job by providing these resources for haar training.... u r a life saviour.... :)

Hello! This is an awesome idea and I want to do something similar in University as a project. Would it be possible to get the classifier? My Email address is:

I couldn't find your contact info, so I wrote here. Please respond asap.


We used the HMM implementation found at
It gives all the instructions on how to use it as well. It will be agood starting point.

-> This link didn't work


I am also trying to recognize hand signs. Can you please tell me does haar classification is enough for static hand sign classification and recognition. I am new to this area of study can you please send me some info including steps I should follow.
my email address is

Please help me.



I am also trying to recognize hand signs. Does haar classification is enough for static hand sign recognition. I am very new to this study. Can you please send me some info including the steps I should follow.
My email address is

Please help me.

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