Notes - Importance of data in vision
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Some notes after going through a few papers and 16-824 lecture slides on the different aspects of data in computer vision.
Blog posts
2018
TIL - Deconvolution
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While, I had a hand-wavy idea about deconvolution earlier, for a project I had to properly understand the concept. Hence, taking a few minutes off to write a quick note about deconvolution layers
Parallel tracking and mappping for small AR workspaces
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This is a summary of a paper i recently read. The paper can be found here: http://www.robots.ox.ac.uk/~gk/publications/KleinMurray2007ISMAR.pdf
TIL - ICP Matching
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For some class reading and a project I am pursuing, I decided to understand the iterative closed point matching algorithm. Here is a gist of my understanding.
TIL - Bayes Filters
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I am doing a course in Robot Localisation and Mapping this semester which shall hopefully trigger a bunch of posts where I try to explain concepts in the course to myself. Here is the first in that series, Bayes Filter: the foundational algorithm for state estimation.
TIL - Principal Component Analysis
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I was revising my understanding of Principal Components Analysis and I thought it might be a good idea to articulate what I understood in the form of this blog post. I intend this to serve as quick a tutorial for any future reader who has some idea about PCA and wants to brush up the concepts.
TIL - R-CNN/Fast RCNN/Faster RCNN
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Writing this post as a way to archive my notes while reading the series of papers: R-CNN, Fast R-CNN and Faster R-CNN. The last in the series is our first reading for the course 16-824: Visual Learning And Recognition at CMU. My hope is that the semester allows me enough time to write these notes for each of the readings. So far, so good, I guess.
2016
TIL - Scanning Images in openCV
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Often, we would want to scan through each and every pixel of an image in openCV. Now, if you are new to openCV (or lazy about writing code), in all probability, you will end up using the the inbuilt at function to access the pixels. This choice is understandable because all you need to do to specify the co-oridnates of the pixel and you get access to the pixel. However, this method is painfully slow and if you need to optimise your OpenCV code, this should probably the first place you should look at. If you are going to access each and every pixel in the image, in sequence, instead of relying on the at function (which was written to provide ease in random access of pixels in an image), you should go for the pointer based access. That means, get the pointer to the starting location of the image data and increment the pointer by an amount equivalent to the size of one pixel to access the next pixel. Let me explain with some code. Assume we have an image stored in Mat called imageMat. This image is an RGB image with each channel (R,G or B) of size 8 bits (1 Byte). This mean, each pixel is of size 3 bytes. In the following code, we will declare a uchar pointer (pointer pointing to a memory of 1 Byte) and increment it by 3, everytime we want to access the next pixel (simple pointer arithmetic at play here).
TIL - Include guards
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Small post to note down a small thing about programming that I learnt today because of some error I was getting.
Battling with the computer - 3 of Many
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TL;DR : My computer won’t go beyond the welcome screen in Windows 7, but it will boot properly. i removed a memory card from the memory slot to finally solve the issue
2015
Parsing command line arguments in Java
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When you have command line arguments, the beginners instinct is to resort to the basics and “parse” them by using the “args” parameter and indexing into it (like: args[0] , args[1] etc.) . Having succumbed to this instinct recently, i learnt the hard way to write better code always. Thought I must archive.
Automatically Generating Subtitles for an Audio using CMU Sphinx
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A small tutorial to generate subtitles for an audio automatically using CMU Sphinx.
Experimenting with the Goodreads API
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Goodreads.com is a website (now owned by Amazon.com) that aims to create a social network sorts for bookreaders. I recently started using the website heavily, primarily to archive the books I have been reading and also to get some good recommendations for lining up the next few books I can read. Now that I home and reading a lot more than usual I ended up spending more than I would have liked on buying the books I want to read. Since a good number of my friends have their own tiny book collections, I was wondering if some of them already own these books that I just spent so much money on. Fortunately, goodreads has an option to mark a particular book as a book you own. However, if I have to see if any of my friends own a particular book, I will have to go to each of their profile and find it out manually. Since I was a little bored anyway, I thought of writing a small script that can go through all my friends on goodreads and compile a list of books they own. Later, if I give a book id, I should simply get names of my goodreads friends who own the book.
Hiccups, Poet-Unknown
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There is this poem on Hiccups that we used to recite as kids. This poem has been an all-time favourite for the pure entertainment value it provides when recited. I have recited it so many times that I think I still remember parts of it. I thought of googling the parts I remember to find out the entire poem, alas, i couldn’t find anything. So before i forget these parts as well, I am archiving it here. Hopefully, some other wandering soul on the internet might have the other parts and will help me piece it together. So here goes the poem as it is in my head:
Cycling to Work
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There had always been this itch to get back to cycling and after coming to Bangalore that yearning just became stronger when I saw so many cyclists on the roads. I remember having a similar craving for a cycle in first year of college and after a few weeks it just fizzled out. So, before actually going ahead an buying a cycle, I decided to rent one out for a couple of weeks and yesterday was Day 1 of renting that cycle. This post is just to archive experiences for these two weeks, for I believe this fancy may die too and then later when I want to get back to saddle again, the post will be a reference point for pros and cons.
Monitoring an AWS cloud using the AWS SDK
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I have now started working on a project that requires me to monitor some metrics from AWS. At first i attempted to use use the Query API provided by AWS and get the desired information by just making some REST calls, however I haven’t been able to make it run correctly yet. So now I am resorting to using the SDK which is supposed to make the process easier. (I will get back to the REST API in a while).
Finding System Statistics in Java
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Continuing on my quest to get more familiar with Java (and kill some time during this workless phase of the internship) I tried another problem to print some system statistics. The problem statement was to print the CPU utilisation, Disk Utilisation and Memory utilisation after every 2 seconds and print the average of these metrics affter ever minute. While this problem is quite straightforward in C/C++, it becomes a little interesting in Java because of JVM. The existing functions in Java would have all given the statistics for the virtual Machine and not for the actual system on which the program is running. A straight-forward google search suggested the use of SIGAR which basically made the task as simple as doing it C/C++. However, of course, it took away the flexibility of running the program on any machine as the binaries for the API were platform dependent.
Socket client-server program in Java
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A week ago I started my semester long internship in the Advanced Software Division at EMC, Bangalore. As a warm-up exercise (read: work to do till the projects are figured out), I was asked to write a basic socket client-server program in Java that allows multiple clients to connect to a server and execute the following commands:
chdir [dir] //change directory to the given directory name rmdir [dir] //remove directory mkdir [dir] //make a new directory list [ ] //list current working directory exit //close the connection
I had written a simple one server-one client socket program in C for a lab exercise in a computer network courses at the university and almost began writing a similar program in Java, when I realised the slight complexity that connection of multiple clients at the same time brings to the problem statement.
2014
Trading in the Indian Stock markets
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Now that I am about to finish my majors, one of which happens to be in economics, I have decided to finally learn some tricks of the trade - literally. ( Fun fact: OED has appended a rather controversial meaning to the word. Check here ) The idea is to start trading virtually in the Indian stock markets. I will be using icicidirect’s platform for virtual stock trading, although the UI as of now seems very discouraging. I might change to something else, with time. The big question is of course how am I goint to invest. Well, I initially intended to invest like a sensex linked fund. That means, I wanted to divide the total money I have among the same stocks and the same weights as is used to calculate the sensex. This was out of a simple observation that as of today the sensex more than doubled in the last five years and this happened while the sensex was clouded with all the negative sentiments and other things like that which financial newspapers report. These days it looks like things are hunky dory in the market and hence it’s best to invest in the market. That said, I also realised that such indices tend to follow a cycle and it looks like we are on the peaks these days and it may not be the best starting point to buy in a sensex linked manner, hence I am choosing to select my stocks in a different manner. It’s 2 in the afternoon and I had a heavy lunch, so I do not feel like doing a lot of work. I am taking the path of least resistance. I have basically selected a few stocks from the 30 in the sensex because I like the companies and more than 66% of the users of moneycontrol.com think that I should buy the stock. Simple. No brains. It’s almost like picking the stocks at random. Since this is testing the waters, I am buying one share of each company and will judge my portfolio’s performance in percentage terms only. Here are the stocks that I am buying: 1) Infosys 2) HDFC Bank 3) Tata Steel 4) ONGC 5) Unilever Now if I look at the graphs, all these stocks are doing really well right now (and hence they should fall in time to come), but I am still sticking to the (very stupid) strategy. Let the users tell me what should I do. It is almost like an experiment. I check moneycontrol for these five stocks everyday and sell only if more than 50% of the users think I should sell a stock. If they do, I sell the stock and shift to another stock that they recommend I should buy. I will sell all stocks and end the experiment, if my portfolio value increases/reduces by 20 percent of what I started with. I plan to continue on this experiment for the coming month. Setting christmas day as my deadline to evaluate the strategy.
Downing a day in Delhi
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So, yesterday I went to Delhi because I have a bunch of friends living there and a lot of free time. One of them (manickam), has suddenly become a meticulous planner and we ended up going on a food trip. Since I liked most of the places we went to, I am writing this down so that next time I have a handy reference when someone asks what should they do in Delhi. I wish I had bought one of those cameras I have been obsessing about for the last few days (more on that in some other blogpost) by now. Owing to the lack of discounts on cameras in India, please bear with lots of text and no pictures (modern day blog readers’ nightmare?)
Battling with the Computer - 2 of many
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Another extremely trivial battle I used to have with my computer everyday until I decided to do something about it, finally.
Battling with the Computer - 1 of many
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My epic plans of self-training myself into a Data Scientist, failed as miserably as the first few models I made for the problem sets on Kaggle. Meanwhile, I was being humbled by more simpler problems in the world of Computers, namely ‘battery plugged in and not charging’. The problem has been solved for now, without a penny being spent; taking it down for future reference.
2013
Kaggle – Data Science London + Scikit-learn (Using k-nn in R)
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This post won't make much sense unless you have seen this post as well: http://siddhantj.wordpress.com/2013/12/31/kaggle-data-science-london-scikit-learn-using-svm-in-r/
Alright, so moving on.
I implemented the k-nearest neighbour model next and there was a significant improvement in my leader-board ranking (16 positions!) and a 2.5% increment in my accuracy. I tried two different values for k: 5 and 15. For k=15, my accuracy dropped slightly(0.3%) and hence k=5 seems to be a giving a decent value. I am left with just one more allowed submission in the next 6 hours and I am tempted to try another value of k (12, no sound logical reasoning behind the number. Just a hunch.)
I ended up spending a lot of time in order to figure out how to use KNN in R. Have little or no idea about the data types in R which is where I got stuck. So far, I have been floating by looking at examples and learning. Hoping, that I will eventually learn about R as well. Most of my time went in solving a trivial error that was there because my variable that stored the labels of the training set was not of the type - Factor. The problem and the solution that I ended up using are almost exactly explained here
Again, appending the commands that worked:
#assuming train,test and trainLabels are as defined in the previous post
cl=trainLabels[,1]
answer<- knn(train,test,cl, k=5)
write.csv <-(answer,"answer2.csv")
PS: I did try that k=12 hunch and failed. Must learn how to do cross-validation next.
Kaggle - Data Science London + Scikit-learn (Using SVM in R)
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I finished a course on machine learning last semester and came across kaggle some time around then. I immediately pushed it in my winter-break-to-do list and lucky kaggle got selected as the only thing that actually happened from that list.
Eidetic Memory and the lack of it
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Eidetic Memory, more commonly known as photographic memory is basically the ability to remember everything you perceive through most of your senses. I just took a test here, and well the predictable happened - I failed. Obviously, I do not have a photographic memory, hence this blog to archive things I want to recollect.