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Sunday, January 20, 2013

Video Compression(Spatial Redundancy).Simplified.

I want to wish you all a happy and a prosperous 2013..May it be a success professionally, personally and academically..!!.And in 2013 I hope this blog has better content, bigger reach and ofcourse be more regular..!!.

Getting straight to where we ended our previous post where I mentioned the two kinds of redundancies in a video sequence which aids in its compression namely Temporal and Spatial. The analogy for the Temporal redundancy was that of the redundancy existing between the items which go into our everyday carry bags to schools and offices. I am moving on to Spatial Redundancy and this post will be a discussion of the concept and ofcourse an analogy to help us decipher it better.

The Concept

Spatial Redundancy is the redundancy of information which exists within the same frame i.e. it is an intra frame redundancy. The numerical similarity of pixel values between frames which we discussed in the last post also exists within the space of the given frame. So, spatially a frame contains pixels which have similar/near similar values to their adjacent neighbors

Conceptually if this spatial correlation or the redundancy among pixels is exploited, then PREDICTIONS can be made about their adjacent neighbors with a reasonable/acceptable accuracy. And hence because of this correlation (leading to better predictions) we ll have lesser information/data to be encoded and transmitted which leads to video frame compression. Unless it is not a complex/complicated section of the picture frame, this redundancy can be efficiently used in compressing a video sequence. 

I ll consider the same two examples as the last post but now talk about its spatial redundancy,

  • In video telephony, the adjacent pixels in the face/eye region have similar values and have minimal (numerical) difference among them. So here there is a lot of spatial information which is redundant and 

  • In high motion sequences like a soccer match, there are enough details in a given frame which are uniform and smooth like the crowd seated. So, the prediction of the pixels from their neighbors becomes easier and efficient in these regions since it has information which is almost the same across it.  

The Analogy

We usually can infer/predict lots of information about a given population based on its geographic location. This inference is possible because of an inherent (and usually correct) assumption that people of a geographic location have similar/near similar body features, speak the same languages and have very similar food habits, possess the same shopping trends etc etc. Lets us call this Geographic Redundancy..

If the location being considered does not have a diverse or a complex (unlike a NYC or a Shanghai or a Bangalore) population, I need to only consider a small population and can rely on prediction for the rest..!!. This implies for areas like Wyoming, Nebraska, Eastern India etc, I can afford to make predictions based on neighboring population thus exploiting geographic redundancy.There might be differences/anomalies but they are very minimal when you look at it as a whole. 

  • Classic example is the famous Starbucks and the way it expands its business. It relies on the sameness/redundancy of opinions of people in a given geographic location and makes predictions for the remaining population helping it to make a quick/inexpensive decision thus compressing its time and resources invested..(The same Coffee chain studied the Indian market and consumer habits for more than an year, given its complexity..!!!!)
  • If the Indian government decides to open a Cricket Stadium (Cricket is less of a sport and more of a religion in India), it can do so with surveying a limited population..So what do you think resulted in this reduction/simplification..??...Yup you have guessed it right..They can talk to a few people and easily predict the opinion of the adjacent neighboring population..!!.
"The values of the pixels can be predicted from its neighbors assuming spatial redundancy in a video frame very similar to the way we all make predictions about people living in a certain area assuming geographic redundancy..!!! "

This attempt is to attach the entire process/knowledge of Video Compression to something all of us do and know of and comes from the real world..!!..I am hoping these couple posts and then moving onto studying Wikipedia, white/technical papers and all the other material available online might help to appreciate and digest the knowledge..I apologize if there are any mistakes or if there are any factual errors..I would be happy to make the necessary changes..

Programming is next..!!..Let's revisit the very fundamental building block of any programming language..DATATYPES..!!!

I have started a dedicated facebook page for this blog to ease the whole process of commenting and sharing stuff..

Keep Simplifying,

Thursday, September 15, 2011

Temporal Redundancy in Video Compression. For Laymen.

Video Compression is something I have been involved with since a year and a half now and in this first official post, I am discussing analogies for fundamentals of compressing a video sequence.

I want to share two basic strategies behind compressing any video sequence so that people can appreciate and acknowledge how an entire movie sequence can be stored onto a hand held device or how can it be wirelessly  transmitted to far off receivers or how live videos can be streamed anywhere and anytime on demand . 

Video compression is an area of study important but is also critical given the advent of streaming videos, storage and transmission of HD quality video sequences and the overly populated frequency spectrum and the ever increasing demand for news, blogs and entertainment, all in the form of multimedia..!!

There are two important factors governing the compression of a video sequence namely,
  1. Temporal Redundancy and
  2. Spatial Redundancy.
The Concept
Temporal Redundancy is the redundancy of information which exists between a set of frames i.e. it is an inter frame redundancy. Given the nature of any video sequence, the numerical values of the luminance/brightness and chrominance/color of all the pixels in a given frame is either exactly similar or at least near similar to those values in the previous frames. This redundancy or in simpler words the 'repetition of information between frames' is exploited by all the video compression algorithms. 
The basic idea is not to encode the similar or the near similar pixel values which have already been encoded and transmitted.

  • In video telephony there are fine movements of the face and hands yet the background information from frame to frame remains the same throughout the sequence.

  • In a live steaming of a tennis match, the motion is represented by the players and the ball while the remaining information that of the stadium and the audience remains similar all through the video.

The Analogy
People travel everyday to office, school or research labs and the weight/size of the bag we carry each day remains important irrespective of our mode of transport. Hence, we make all efforts to minimize/compress the size of the same and remain intelligent in selection of the items which go into the bag. We should be clever enough to reduce the redundancy in the items which exists between days by not carrying rather not repeating the stuff which we would need the immediate day. 
Hence a bit of knowledge about what we carried the previous day, what we have got today and the prediction for the next day combined with some intelligent and wise choices saves us a lot of weight..!!

  • There are items like laptop and phone chargers, water bottles and clothes for gym which need not to be carried back everyday from office and
  • In case of students going to schools, we need not repeat carrying all our books, pens and other stationary back to home (by using a locker at school), reduce the redundancy and hence the keep the size of the bag smaller.
All of us reduce redundancy of items between days to wisely carry our bags everyday and this is similar to how a video gets compressed by exploiting redundancy between frames..!!. 

"Do not carry already encoded information in case of video compression and do not carry items back and forth if you need them the immediate day and you end up compressing  your bag..!!!."

So, this is how analogies work for me, they might not be entirely convincing or not every time do they provide insight into a technical concept. But yes, if they are related to real world examples from our daily lives, things/concepts seem simpler, creates trigger/interest for further reading and understanding, serves as a quick tool for revision too and sometimes just helps me appreciate a concept, I might never get an opportunity to learn or read about in detail.

I would be grateful for all the honest feedback and suggestions from all my well wishers so that I have a fair idea about the acceptance of this IDEA and the scope for its improvement and of course I ll come back with more analogies..Spatial Redundancy is next..:)    

Keep Simplifying,

PS - Belated "Engineers Day" to all the engineers around the world and it is celebrated in India on Sep 15 on the august occasion of the birthday of Sir M Visvesvaraya, the greatest engineer India has seen and a greater human being..!!  
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Friday, August 12, 2011


Thanks for the amazing support, guidance and suggestions to this effort of ours..!!!.I sincerely thank people for the interest, all the suggestions, all the well wishers, people who visited my blog, people who gave me cues  as to how to keep this going,all of these gestures have helped me and my confidence and I am back after a hiatus to start contributing stuff..:)..

So, for people joining us now in this attempt, I request you to visit my First Post for the introduction..:)

My personal writing would be discussion of what I have learnt, rather how I have digested few of the topics which might be of interest to a layman..And I am considering the way of connecting real life scenarios/ examples to the concepts i.e. creating ANALOGIES..just for the take off..for that trigger and to keep us moving..

This habit of mine, creating an analogy for understanding a concept, with time and repeated usage has become a strong way of my preparation..And, by the grace of God during my stint at the prestigious Indian Institute of Science, I had discussed the coarser version of this attempt with Dr.Krishnaswami Kasturirangan, the renowned scientist of the Indian Space Program. He was convinced and even gave me his approval and suggested me to come up with a CD or a tutorial online..But for me it was a student project and things did not take off then..may be I was not thinking BIG....And here we, thanks to the social media and the platform/audience it provides to voice your opinion and discuss your ideas..

I have picked up the same cause with a renewed interest and spirit and with a will to make it big..!!..Life is long enough to have extraordinary dreams, yet short if you have want to achieve it all by yourself..Hence, I am gathering ideas..I am gathering people..I am gathering support..I am putting together my dream..See u soon with my first post on a layman's take about the buzz word which dominates the present mobile phone industry..

Keep Simplifying,


Tuesday, May 10, 2011

Knowledge to Layman.

Finally after saving this draft for almost an year, I have gathered courage to go ahead and publish this as my first blog. It has been quite a while since I have been living with this idea, and this quote by H. Jackson Brown, "When you look back on your life, you'll regret the things you didn't do more than the ones you did.", and the eagerness to gift something special to my Mother on Mother's Day has eventually motivated me to get started with this..They say it is all about starting off but you and I know how difficult these beginnings are when it comes to any task..!.

So, then the immediate question was regarding the content of my blog as to what do I write and how do I make use of the attention of the audience (if I have any.. :))?.How do I efficiently utilize the platform and what do I convey?

I personally feel (after reading quite a few blogs...esp of my friends who write extremely well and have been instrumental in this effort of mine to take up blogging..) that writing something to express yourself is the most genuine way of communicating because you are not conscious of the onlookers and you are not biased according your listeners either. Hence, I decided to blog for a cause and try contributing for solving an inherent, almost eternal problem of getting people to study and sustain their interests.

After a lot of research online (for people who are really interested, just Google for "Why do kids drop out from schools?"), most of the school drop outs and the rural kids unwilling to go to schools IS NOT ENTIRELY BECAUSE OF FINANCIAL REASONS.And this is  true, with respect to any country in the world whether developed or developing. These are just a couple of links to back up the above claim,

No family/father prevents his child from getting elementary education due to lack of money if the child shows genuine interest and confidence to learn/study. But the reason is, the way the students see knowledge/science and education from outside. They are made to feel it is not their cup of tea. They back off with a burden in their mind thinking that the material is too complex for them to digest. The sample of education they get is extremely complex and not so convincing.

What about kids coming from uneducated families who want to start off.. kids who took up labor because of poverty and now want to get back. Are we bothered as a society to this class, have we made any efforts to make this transition easy for these students? So many just give up because no one in their family is an engineer/graduate or because they have do not have the required IQ to go ahead with the present education system, and they just get back to their previous lives, and the shine in their eyes to study and progress just fades away..

So quickly coming to the point, there is an immediate need to SIMPLIFY KNOWLEDGE. There are numerous tutorials online, millions of video lectures, lots of e-books, online courses, academic websites and organizations like IEEE who regularly come up with articles and journals covering the cutting edge technology and keeping us updated about the same. I would be foolish if I do not appreciate their contribution to all our lives including mine. People/ Students have enough access to material of ever increasing complexity and this is true with every branch of education. May it be a high school Science project or material for IAS preparations! The standard of any material available somehow is judged by how "complex" it is, and it again caters to the elite group which is already well equipped with the required knowledge. 

But sources which are trying exactly the opposite are very minimal. The opposite effort refers to a more easier and diluted version of the material just for students to get going, just to trigger some interest and get them excited about education system and make them believe, anyone from any part of the world can learn anything.

Through this blog, I am looking for a platform to gather all the great ideas/resources/videos/links/advice and guidance to make it easy/attractive/simple for a common man who wants to LEARN. Yes, the idea might sound familiar and over ambitious. Yet this problem persists globally in so many different forms. We cannot ignore it only because we have elected a government which would take care of it, only because it refers to an extremely minute population in the society, or feel such students just do not have what it takes to study and make a living out of it.

Broadly classifying the problems facing any education system,
1) Lack of money
2) Lack of facilities
3) Lack of support (personal and academic)
4) Lack of interest

The government has devised a lot of schemes to overcome all of the above issues and its progress is outside the scope of this writing. This blog will all be about the fourth cause i.e. the Lack of Interest and in particular for students (from economically and academically backward community) who do not find the present education system simple/easy enough. Owing to the immense/rapid growth of the social networking platform, the ability to generate interest amidst the lesser privileged class of the society is very much in our reach.

From next post onwards, I ll start doing my bit and write about means/methods which made my understanding (related to my area of study) better and easier . I would also wait for people to post any kind of information relating to but not limited to,

1)Videos/Block Diagrams/Analogies/Tutorials which simplify academic content.
2)Websites which make understanding better and easier.
3)Contacts of people thinking on similar lines.
4)Personal understanding of a certain topic/subject (any subject is acceptable).

People can just write about any subject (I mean any damn subject on this planet earth) and discuss the way they understand it or may be post links which they used for learning the material. Once we have enough of such content, we can think getting all of this together into a piece of material which makes sense. I ll start posting on topics and subjects which I am aware of, the way I learnt them and with a hope that a common man will be able to relate to it and appreciate the content. But this is OUR space, not mine. We are building this for the future and I humbly request you all to join hands in SHARING THE MEANS of easing up the academics! What worked for me and you might work for someone else...!!
Apart from my parents and friends back home in India and even here, there have been quite a few role models I follow and worship and these couple of links just show how a common man can start creating a difference in the society if he wants to.. :)

1) Salman Khan, I love the actor too..but this Sal Khan, as he is fondly called is a MIT graduate who quit his job to make 10 -12 minute video tutorials on almost any subject, on a full time basis.

2) Narayan Krishnan, quit his job offer from a restaurant in Switzerland just to start Akshaya Trust and serve the poor.

I am not very sure of the future posts and the future prospects for this blog or the format of the whole attempt. The one thing I am sure about is that we need to "share our means of learning" to let more people progress/prosper. But, I am glad it has started. I am hoping people will pitch in with their ideas, suggestions and contributions. People who know the content might use this along with other material for better retaining of the same knowledge. People rushing for interviews might go through this as a revision material, student drop outs might get convinced with this SIMPLIFIED CONTENT and go ahead and decide to study further. 

Even if a single kid/drop out gets attracted/influenced/interested with this material and decides to get back to school or decides to give it one more shot...We win..:) 

The intention is not to sell this content as a replacement for all the correct yet difficult material available elsewhere (books/online/schools) but to make this accessible as a PRECURSOR, may be a quick learning tool or that which would create interest for further studies.  

My long term goal is to see this attempt by all of us grow into a database/website where any user/student can type in his query on any subject/topic in a search box and get back a easy/simplified explanation  with which he can proceed further in the direction of gaining knowledge. 
If, as a reader you have made it till here, I thank you for your patience and apologize for the length of this blog. I promise my future posts would be concise.

I might have erred, made a point which is not valid or might not have been convincing enough, hence I would be more than happy to listen to any unbiased suggestions/contributions and comments/crticisms from my friends/seniors/colleagues and well wishers.

Keep Simplifying,