3d Augmented Reality code graphics opencv opengl programming qt Tracking video vision

Augmented Reality on libQGLViewer and OpenCV-OpenGL tips [w/code]

You already know I love libQGLViewer. So here a snippet on how to do AR in a QGLViewer widget. It only requires a couple of tweaks/overloads to the plain vanilla widget setup (using the matrices properly, disable the mouse binding) and it works.

The major problems I recognize with getting a working AR from OpenCV’s intrinsic and extrinsic camera parameters are their translation to OpenGL. I saw a whole lot of solutions online, and I contributed from my own experience a while back, so I want to reiterate here again in the context of libQGLViewer, with a couple extra tips.

code Mapping opencv Tracking video vision

Simplest 20-lines OpenCV video stabilizer [w/ code]

Just sharing a simple recipe for a video stabilizer in OpenCV based on goodFeaturesToTrack() and calcOpticalFlowPyrLK().
Well… it’s a bit more than 20 lines, but it is short. And it doesn’t work for every kind of video (although the results are funny anyway! :).

code Music opencv programming vision

Using Hidden Markov Models for staff line removal (in OMR) [w/code]

Screen Shot 2015-01-24 at 10.11.00 PM

So lately I’m into Optical Music Recognition (OMR), and a central part of that is doing staff line removal. That is when you get rid of the staff lines that obscure the musical symbols to make recognition much easier. There are a lot of ways to do it, but I’m going to share with you how I did it (fairly easily) with Hidden Markov Models (HMMs), which will also teach us a good lesson on this wonderfully useful approach.

OMR has been around for ages, and if you’re interested in learning about it [Fornes 2014] and [Rebelo 2012] are good summary articles.
The matter of Staff Line Removal has occupied dozens of researchers for as long as OMR exists; [Dalitz 2008] give a good overview. Basically the goal is to remove the staff lines that obscure the musical symbols, so they would be easier to recognize.

But, the staff lines are connected to the symbols, so simply removing them will cut up the symbols and make them hardly recognizable.
So let’s see how we could do this with HMMs.

code graphics opencv vision

Run length encoding in OpenCV [w/code]

RLE exampleSharing a simple code snippet for run-length encoding with OpenCV…

graphics opencv vision

Simplest Color Balance with OpenCV [w/code]

Color balanceI came across an extremely simple color balancing algorithm here. And I thought I’ll quickly transcode it to OpenCV.
Here’s the gist:

3d code graphics gui opencv programming qt vision

Moving to Qt on the SfM-Toy-Library project

Qt GUI for SfMToyLibFor those of you still interested, I’ve made the move to using Qt and QGLViewer in the SfM-Toy-Lib project. Getting rid of PCL dependency (I think it’s a bloated library), and burying FLTK long in the past, I feel much better about it now.
Get it on github:

code ffmpeg graphics opencv video vision

Extending the hand tracker with snakes and optimizations [w/ code, OpenCV]

I wish to report of a number of tweaks and additions to the hand silhouette tracker I posted a while back. First is the ability for it to “snap” to the object using a simple Active Snake method, another is a more advanced resampling technique (the older tracker always resampled after every frame), and of a number of optimizations to increase the speed (tracker now runs at real-time on a single core).

graphics opencv video vision

OpenNI 2.x and OpenCV interoperability [w/ code]

For those of you using OpenCV that are looking to upgrade from OpenNI 1.x to the new OpenNI 2.x, here’s a bit of code to make life a tiny bit easier. It simply wraps the OpenNI 2.x APIs to expose a simple frame grabber for OpenCV.

code graphics opencv programming video vision

Curve tracking with a Heap&Hogg's Particle Filters [w/ code, OpenCV]

Screen Shot 2013-03-15 at 6.18.30 PM I wanna share some code for 2D curve tracking with a particle filter, implementing the body of work of Tony Heap and David Hogg. These guys presented a relatively easy to implement method for tracking deformable curves through space and change in form using a Hierarchical Point Distribution Models (HPDM), which is another elegant way to store shape priors. Granted, it is not perfect, but for a simple 2D shape like a hand it works pretty good, and rather fast as well.
Let’s dive in then,

code graphics opencv programming video vision

Skin Detection with Probability Maps and Elliptical Boundaries [OpenCV, w/code]

maskSharing a bit of code I created for skin detection.