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Wednesday, July 17, 2013

Visual Perception

    There are events in nature that are very fast ,there are events that are very slow while there are others that can be perceived as neither too fast or too slow what we call in common terms normal pace.


         While we have 5 senses to perceive things and events around us viz. touch, see,hear,taste and smell there is also one more sense known as the sixth sense that let us know things that may happen it is used highly but in scientific terms very little is known about it. However this post will focus on visual perception.


         For our eye to see some event in continuous motion on a video screen it has to have at least 24 frames displayed one after another at continuous time intervals ,now there are events that are too fast to see like in sports a ball hitting a bat or what happens when a boxer lands a punch on his opponents face. With the help of high speed cameras this problem is solved however the term high speed may confuse people. Actually High Speed cameras are nothing but cameras that can record a very high number of frames per second in order of 2000 fps. Once this recording is done the video can be played back at normal 24 fps thus a one second video would now be played in 83.33 seconds so an event that occurred at 1/100th of a second can be seen easily and this has lead to many new findings in the field of sport.


        In cricket it can be seen that when a ball hits the bat at high velocity the bat moves at the point of impact for a very short span of time this fact was totally unknown to everyone before the advent of high speed cameras. In the same sport there was a rule that if at the point of delivery a bowler's hand straightens  by a certain angle that particular delivery would be considered illegal and the bowler would be warned for chucking. It was 5 degrees for spinners,10 degrees for medium pacers and 15 degrees for fast bowlers. When biomechanics study was done with the help of modern high speed cameras it was found that almost every bowler subconsciously ends up straightening  his arm at the point of delivery there was a famous chucking incident involving ace Sri Lankan spinner Muttaiah Muralidharan where he was called by the umpire for chucking. Thankfully his team-mates,his captain  and board backed him and when video analysis were done on all bowlers it showed that Murali straightened the arm as much as other bowlers did although at normal pace the videos tell a different story even a bowler with copybook action like Glenn McGrath was found to be straightening his arm by more than 15 degrees at times. Had it not been for high speed cameras the racist umpire could have ended up ending Murali's carrear right there and after that Muralidharan went on to become a great bowler picking up 800 wickets in his entire carrear.


          Also high speed cameras are used to by various authorities to ascertain whether a person is speaking the truth or not while questioning him/her taking the high speed images of their subconscious facial reactions and then watching it at normal speed.


          Now talking about events that are slow in nature like the growth of a tree in that case a normal camera may be used and programmed and installed in such a way that it would take 1 photograph an hour and stay in the very same position focused on a plant now after a certain point of time when the plant has grown to a certain extent the images and then taken and played at normal 24 fps the view of the video one would get is that as if he is able to see the plant grow slowly in a matter of minutes. Such cameras are also installed at construction site the rate of taking photographs maybe varied as per necessity but again when the video is played one can see how the construction of a building or stadium is done in a matter of minutes without any focus on unnecessary parts.

Rakesh

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