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.
Continue reading "Augmented Reality on libQGLViewer and OpenCV-OpenGL tips [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! :).
Continue reading "Simplest 20-lines OpenCV video stabilizer [w/ code]"
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.
Continue reading "Using Hidden Markov Models for staff line removal (in OMR) [w/code]"
Sharing a simple code snippet for run-length encoding with OpenCV...
Continue reading "Run length encoding in OpenCV [w/code]"
I came across an extremely simple color balancing algorithm here. And I thought I'll quickly transcode it to OpenCV.
Here's the gist:
Continue reading "Simplest Color Balance with OpenCV [w/code]"
For 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: https://github.com/royshil/SfM-Toy-Library
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).
Continue reading "Extending the hand tracker with snakes and optimizations [w/ code, OpenCV]"
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.
Continue reading "OpenNI 2.x and OpenCV interoperability [w/ code]"
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,
Continue reading "Curve tracking with a Heap&Hogg's Particle Filters [w/ code, OpenCV]"