Image processing with cat brains - Gabor Filters

When building panoramas or capturing depth using multiview geometry or structure from motion techniques, temporal decorrelation often makes things harder. One of the confusing elements typically is cloud. Hugin had a nice addition during one of the previous GSoC's to identify match points found on clouds - Celeste. So I decided to attach it to the SFM solution while I figured out how the cloudy_photos option in Bundler actually worked.

So this is how I initially came across the fabled Gabor filter. The Hugin cloud detection implementation classifies matchpoints using the local texture estimated with -- a system similar to that in the mammalian visual cortex. Here is a nice OpenCV Gabor filter which can be conveniently glued together in Python to the osm-bundler scripts.  The cat brain research and the biological basis of the Gabor filter is quite interesting :

In 1946, Gabor suggested representing signals over space and time called Information diagrams. He showed that a Gaussian occupies minimal area in such diagrams.  Time and Frequency analysis are the two extremes of such an analysis.  Gabor filters  became popular in vision partly because J.G Daugman (1980, ‘88, ‘90) showed that the receptive fields of most orientation receptive neurons in the (cat’s) brain looked very much like Gabor functions.
As with Gabor filters, the brain often makes use of over complete, non-orthogonal functions.

- Stanforn Robotics.

I tend to get excited whenever a new library sprouts Python bindings. For point cloud processing, a lot of effort is going into the Point Cloud Library (PCL), it is nice to see Python bindings among the projects for GSoC 2012. There is a pass through filter in PCL which can be used perform simple colour-range based filters on the bundle adjustment outputs. The statistical outlier detection can then be used to clean up any straggling garbage points.

Last days in Hobart - Keeping little momentos

I had an exciting last week in Hobart. I made a necklace from things found in the IXL courtyard just to take things from Hobart with me, it forms a grungy addition to the Ethiopian coptic cross.

Checked out of the nicest house I have ever lived in , Derek and Cate have been the nicest landlords imaginable. They helped me shift the high amounts of entropy that had accumulated in my apartment to the Hobart tip. Whatever I have left behind is not sufficient compensation for the amount of consideration they have shown me.

My precious bike and surfboards went to interesting new owners. Somebody planning to ride the bike around Tasmania is a worthy new owner at any time.

The last week was spent at the backpackers and strangely enough people from the recent past reappeared. I also met some nice new people , particularly Roscoe. I spent time dividing attention between the grunting coming from the screen (just tennis) and people drawing, cooking, reading and planning their trips. My old acquaintances let me capitalise on the trike ride David, a local tourist operator, had promised. It was quite a bit of fun.

On the 27th plenty of my friends turned up for my farewell, from various circles I have drifted around in the city - Salsa, CSIRO, arts and people I had met by chance at the bar like Mr. Leigh. Just a note to self - he has my "Small Antennas" book which I need to return to the library. Thanks a lot for signing my Frida Kahlo book guys and all the great times.

Last day of taking the MONA pill - learning to be Limitless

The greatest deception that men suffer from is from their own opinions. - Leonardo da Vinci.

Last saturday was my last day at MONA. I have been taking the MONA pill for a year now and the course has made me realise a lot about myself that was latent. Drugs are inherently replicants or cocktails of natural neurotransmitters. External non-chemical stimuli like music or visual arts can have a drug like effect by triggering secretion of certain neurotransmitters. You do not have to take a pill to go to sleep, put on the sound of a water fall or your mother's heart beat and your body will learn that it is now safe to stop defending its existence and renew - sleep. Like the drug in the movie Limitless, the MONA drug works best on people who are already quite smart.

Without going into details of how things work I will recount my only verbal encounter with David Walsh, apparently formerly called Glenn. I was hanging out with a couple I had met at the museum, Perth town planner and his Fiancée - an artist and an air hostess with Qantas. We managed to miss the last boat while chatting at the wine bar and called a cab. Eventually a cab arrived, it was the wrong company in retrospect. We hopped in the back seat, it was apparently a cab David had called. He walked in, graciously let us ride in the back seat and cab share. He said - "You were visiting my place" , and realisation dawned. A lot of babbling ensued, I don't recall the exact details, but I do remember David saying - "I am a Mathematician". That explains everything.

Let no man who is not a Mathematician read the elements of my work. - Leonardo da Vinci.