Monday, May 5, 2014



Hi everyone!

As an advocate of open source software and freedom to share knowledge let me wish you a Happy International Day Against DRM :D

And to celebrate here is an offer from my friends at Packt Publishing: All DRM-free content at just $10 for 24 hours during May 6th!!

Here is their official press release:

Packt celebrates International Day Against DRM, May 6th 2014

Packt Publishing firmly believes that you should be able to read and interact with your content when you want, where you want, and how you want – to that end they have been advocates of DRM-free content since their very first eBook was published back in 2004.

To show their continuing support for Day Against DRM, Packt Publishing is offering all its DRM-free content at $10 for 24 hours only on May 6th – that’s all 2000+ eBooks and Videos at

Our top priority at Packt has always been to meet the evolving needs of developers in the most practical way possible, while at the same time protecting the hard work of our authors. DRM-free content continues to be instrumental in making that happen, providing the flexibility and freedom that is essential for an efficient and enhanced learning experience. That’s why we’ve been DRM-free from the beginning – we’ll never put limits on the innovation of our users.”

Dave Maclean, Managing Director

Advocates of Day Against DRM are invited to spread the word and celebrate on May 6th by exploring the full range of DRM-free content at, where all eBooks and Videos will be $10 for 24 hours.

Monday, March 24, 2014


Packt Publishing celebrates their 2000th title with an exclusive offer - We've got IT covered!

Known for their extensive range of pragmatic IT ebooks, Packt Publishing are celebrating their 2000th book title `Learning Dart’– they want their customers to celebrate too.

To mark this milestone Packt Publishing will launch a ‘Buy One Get One Free’ offer across all eBooks on March 18th – for a limited period only.

`Learning Dart’ was selected as a title and published by Packt earlier this year. As a project that aims to revolutionise a language as crucial as JavaScript, Dart is a great example of an emerging technology which aims to support the community and their requirement for constant improvement. The content itself explains how to develop apps using Dart and HTML5 in a model-driven and fast-paced approach, enabling developers to build more complex and high-performing web apps.

David Maclean, Managing Director explains `It’s not by chance that this book is our 2000th title. Our customers and community drive demand and it is our job to ensure that whatever they’re working on, Packt provides practical help and support.

At Packt we understand that sometimes our customers want to learn a new programming language pretty much from scratch, with little knowledge of similar language concepts. Other times our customers know a related language fairly well and therefore want a fast-paced primer that brings them up to a competent professional level quickly.
That’s what makes Packt different: all our books are specifically commissioned by category experts, based on intensive research of the technology and the key tasks.’

Since 2004, Packt Publishing has been providing practical IT-related information that enables everyone to learn and develop their IT knowledge, from novice to expert. 

Packt is one of the most prolific and fast-growing tech book publishers in the world. Originally focused on open source software, Packt contributes back into the community paying a royalty on relevant books directly to open source projects. These projects have received over $400,000 as part of Packt’s Open Source Royalty Scheme to date.

Their books focus on practicality, recognising that readers are ultimately concerned with getting the job done. Packt’s digitally-focused business model allows them to quickly publish up-to-date books in very specific areas across a range of key categories – web development, game development, big data, application development, and more. Their commitment to providing a comprehensive range of titles has seen Packt publish 1054% more titles in 2013 than in 2006.

Erol Staveley, Publisher, says `Recent research shows that 88% of our customers are very satisfied with the service knowing that we offer a wide breadth of titles in a timely manner, and owing to the quality of service that they receive 94% of customers are willing to recommend Packt to friends and family. It’s great that we’ve hit such a significant milestone, and we want to continue delivering this fantastic content to our customers.’
Here are some of the best titles across Packt's main categories - but Buy One, Get One Free will apply across all 2000 titles:

·        Web Development
·        Big Data & Cloud
·        Game Development
·        App Development

Monday, November 19, 2012



Finally! After so much work we released the "New Tsukuba Stereo Dataset" at ICPR2012

This dataset contains 1800 stereo pairs with ground truth disparity maps, occlusion maps and discontinuity maps that will help to further develop the state of the art of stereo matching algorithms and evaluate its performance. It has been generated using photo-realistic computer graphics techniques and modeled after the original "head and lamp" stereo scene released by University of Tsukuba in 1997. 

The dataset is a 1 minute video sequence and also contains the 3D position and orientation of the camera on each frame, so it also can be used to develop and evaluate camera tracking methods.

It can be downloaded freely from the CVLAB website

Enjoy it!

Friday, January 6, 2012



Hi everybody!

I bring you a sample of how to reconstruct a scene in 3D using OpenCV and Point Cloud Library (PCL) with a simple program and an example scene.

All we need is the left image of our stereo camera:

(You can implement your own cheap stereo webcam following this post: OpenCV Stereo Webcam)

Google ads, probably not very well related to the audience of this blog...
The disparity map generated with your preferred Stereo Matching algorithm:

(For example you can use OpenCV's stereoBM algorithm: OpenCV StereoBM)

And the reprojection matrix (Q) obtained at calibration time:

<?xml version="1.0"?>
<Q type_id="opencv-matrix">
    1. 0. 0. -2.9615028381347656e+02
    0. 1. 0. -2.3373317337036133e+02
    0. 0. 0. 5.6446880931501073e+02
    0. 0. -1.1340974198400260e-01 4.1658568844268817e+00
(You can get the matrix Q for your own stereo camera following the instructions in this post: OpenCV Camera Calibration)

Now download the source code (I highly recommend to read the source code to understand what is going on, don't worry there is comments :P):

[NOTE]: You will need to have installed OpenCV Library (you can get it here) and Point Cloud Library (you can get it here). Also you will need CMake to generate the Makefiles.

Once you have downloaded the source code and installed the dependencies, just run:

tar xzvf OpenCVReprojectImageToPointCloud-1.0.tgz
cd OpenCVReprojectImageToPointCloud
cmake .
./OpenCVReprojectImageToPointCloud rgb-image.ppm disparity-image.pgm Q.xml

You should see something similar to the following video:

I hope you enjoy it!
[UPDATE: 04/02/2012] I have released a bug-fix. Thanks to Chris for pointing it out.

Monday, November 14, 2011



Today, an easy one :) A small program in OpenCV to implement a cheap stereo webcam and visualize the left and right images. The only thing you need are two USB webcams plugged in your computer (better if both are same brand and model):

Google ads, probably not very well related to the audience of this blog...

 Download the source code:

Compile it:

tar xzvf OpenCVStereoWebcam-1.0.tgz
cd OpenCVStereoWebcam

And there you go, your cheap USB stereo webcam.

Have fun!

Sunday, October 30, 2011



Cleverbot is an Artificial Intelligence conversation system specially designed to learn from the conversations that it has with other people trying to mimic the human behavior in a conversation.

To find out the level of intelligence of this kind of artificial entities the archi-famous mathematician Alan Turing proposed in 1950 the Turing Test .  Basically, a human judge engages in a natural language conversation with a human and a machine designed to generate performance indistinguishable from that of a human being. All participants are separated from one another. If the judge cannot reliably tell the machine from the human, the machine is said to have passed the test.

Google ads, probably not very well related to the audience of this blog...

Every year the Turing Test  takes place, this year was celebrated on September 3rd at Techniche 2011, IIT Guwahati, India. In this scenario, several human judges had 5 minutes conversations with another entity (they ignored whether the entity was human or not). Some people believe that if 50% of the judges classify the entity they are talking to as human when in reality it is a machine, then the machine has passed the test. 

This year Cleverbot was classified as human 59% of the times and people might say it passed the Turing Test, but we humans still have hope... humans where classified as humans 63% of the time. I will start getting scared when Cleverbot is classified more often as a human than real humans xD

Anyway, it is fun to talk to Cleverbot, you really have to try it! How? You can do it right here! Just enter some text in the text bar above and hit the "Think About It!" button. Have fun!!

EDIT [2011/11/14]: I removed the widget to talk to Cleverbot directly because it was causing undesired behavior on the website. You can still talk to it by clicking on its logo and visiting Cleverbot's homepage.

Monday, October 10, 2011



Today I would like to publish the answer to another question in the comments of a previous post that might be worth its own post:

Hi Martin,

You gave such an informative article. Good Job Martin:-)

I'll explain steps that I performed in calculating distance of object.

1. Calibrated stereo camera with chessboard 8x6 cm with 2.8cm square size.

2. My calibration was success with rms error 0.206 and rectified images was good.

3. I found my interest point on left-right image. I tried to determine distance of object using method you specified. There is an error in distance measured from 3cm for closer object to 12cm or more for distant object.
Say, actual - 27cm ; measured - 24cm.
actual - 60cm ; measured - 48cm.

My queries are,
- why does there comes this much big varition is distance measurement?
- What may be reason/solution for this error?

Is there any mistake in my procedure or do i miss parameters?

Sathya Kumar

Dear Sathya,

First of all, thank you very much for your kind comment. Regarding your queries, I am afraid that what you describe is quite normal. The steps that you followed are correct, so I don't think that you did any mistake in your procedure or missed any parameters.

The thing is, that the relation between the disparity and the depth is non-linear.

Google ads, probably not very well related to the audience of this blog...

For this reason there is such a big variation in the distance measurement error, for close objects a small variation in disparity means a small variation on depth. But, for far objects a small variation in disparity means a big variation in depth.

So, there is no easy solution, it is unavoidable to get bigger error for distant objects, but you can try to mitigate the effects and reduce the error by getting a calibration as good as possible. And to do that you should take captures of the calibration pattern in as many different positions and orientations as possible, far, near, inclined, etc... Also increasing a bit the size of the chessboard could help you to get better accuracy for distant objects.

I hope this solved your doubts.

Best regards,