I recently came across a simple and easy package that can be used to create 3D reconstruction of objects. I wanted to share it and give an easy and practical explanation on how one can create visually appealing 3D models by running a few simple commands, no coding needed. I must emphasize that for keeping it simple, this post will not focus on theory as did the last few posts on binary descriptors, but instead will give an easy and practical guide to 3D reconstruction. Just to give you a taste of what can be done with the package, here’s an example of a 3D reconstruction I made (yes, that me in there):
Here you can see an original image vs. a screenshot of the 3D model:
3D reconstruction example
We’ll start by showing the following figure that shows an example of using BRISK to match between real world images with viewpoint change. Green lines are valid matches, red circles are detected keypoints.
BRISK descriptor – example of matching points using BRISK
We’ll start by showing the following figure that shows an example of using ORB to match between real world images with viewpoint change. Green lines are valid matches, red circles indicate unmatched points.
ORB descriptor – An example of keypoints matching using ORB
Following the previous posts that provided both an introduction to patch descriptors in general and specifically to binary descriptors, it’s time to talk about the individual binary descriptors in more depth. This post will talk about the BRIEF descriptor and the following post will talk about ORB, BRISK and FREAK.
Why Binary Descriptors?
Following the previous post on descriptors, we’re now familiar with histogram of gradients (HOG) based patch descriptors. SIFT, SURF and GLOH have been around since 1999 and been used successfully in various applications, including image alignment, 3D reconstruction and object recognition. On the practicle side, OpenCV includes implementations of SIFT and SURF and Matlab packages are also available (check vlfeat for SIFT and extractFeatures in Matlab computer vision toolbox for SURF).
BRISK descriptor – sampling pairs
So, if there no question about SIFT and SURF performance, why not use them in every application?
Lately, I’ve been reading a lot about BOW (Bag of Words) models  and I thought it would be nice to write a short post on the subject. The post is based on the slides from Li Fei-Fei taken from ICCV 2005 course about object detection:
As the name implies, the concept of BOW is actually taken from text analysis. The idea is to represent a document as a “bag” of important keywords, without ordering of the words (that’s why it’s a called “bag of words”, instead of a list for example).
Illustration of Bag of words model in documents
In computer vision, the idea is similar. We represent an object as a bag of visual words – patches that described by a certain descriptor:
Illustration of Bag of words model in images