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! :).
Category: programming
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.
Sharing a simple code snippet for run-length encoding with OpenCV…
So I needed to speed up / slow down an audio stream I had (speech generated with Flite TTS) and naively I thought it would suffice to simply sample it at the right intervals and interpolate.
I quickly discovered that just re-sampling won’t do because changing frequency also changes pitch proportionally. And then I discovered the world of Time Scaling in audio and it’s many algorithms and approaches to change the tempo without changing pitch.
To my surprise there were a number of ready made free libraries that do it, but the first one I tried – RubberBand – did not work out, it had too many dependencies I simply couldn’t be bothered compiling it for the Mac. But SoundTouch, well it had a Homebrew formula so it won by default.
I wrote a little simple wrapper around it, that interfaces nicely with Qt.
Let’s see what’s going on there
Categories
Simple ATTiny85 USB board
I needed to create a small, cheap USB-enabled circuit to serve as a key logger, and I’ve found some nice projects online that explain how to do this.
I found out you could use an ATTiny85 to run the V-USB software USB stack, and I only needed the one input pin to gather data (it’s going to be a USB “That was easy” button).
Since this was done so many times before, I will be brief, and try to point out problems I had instead of a regular tutorial.
¡Hola mis amigos!
I’m learning spanish, but I’m also annoyed with collaborating on LaTeX papers. That’s why I’ve created the GDoc-LaTeXifier so the syntax will be clear when I collaborate on a paper with a remote friend.
But now we both want to compile a PDF on our machines. So I’ve created the tiny shell script that downloads the paper and runs PDFLaTeX.
The problem is that this opens a new terminal window and runs the script. I’ve been able to sort it out so that it closes the terminal window when it’s done, by on my friend’s mac it doesn’t, so he ends up with a ton of open windows.
Enter – the GDoc/LaTeX compiler GUI.
Categories
Simple NURBS renderer [w/ code]
Don’t you just love scouring the web for a piece of simple code, come up short and then just write it yourself? Well that was the case with NURBS for me. These simple curvy lines, why doesn’t anyone just dish out a straightforward implementation of them? Well, now you have it. I wrote a simple renderer that reads a DXF file with NURBS (from Rhino3D) using DXFLIB, although the DXF file format is super easy to parse, and renders them to an image with OpenCV.
So I have this incredibly old and stupidly cheap AIPTEK tablet (like a Wacom, only Chinese and cheap) that is so outdated it practically has almost no existence online. Why did I bring this item across the atlantic? I have no answer, but it’s here anyways and I can’t seem to bring myself to trash it. Of course no drivers are available for it so I wrote a tiny simple driver using the great libHID library from Brandon Fosdick. It was painless, and my old tablet was saved.
There’s a fantastic way to collaborate when writing an academic paper in LaTeX – using Google Docs. LaTeX is all text anyway, so collaborating over GDocs is straightforward, but alas there is no colorization to make it like a good LaTeX editor… Fortunately there’s AppScript to help us!
I bet creating searchable PDFs has been done many times over, even so I’d like to share the way I did it recently with strictly open source tools. The pipeline is simple: GS to separate the PDF to pages, tesseract OCR to extract text, hocr2pdf to create a merged PDF and GS again to bundle everything back to unified PDF. If you’re creating a PDF from scanned books, this project may also be of help: unpaper
Edit 5/21/2014: I’ve had good experience using Scantailor, which is available on homebrew for the Mac. And also, I’ve submitted hocr2pdf to homebrew as part of the exact-image library (the name of the formula is “exact-image”).