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Thread: Using my video camera as a speed gun

  1. #1

    Default Using my video camera as a speed gun

    Hi,

    Am brand new to this forum. I have recorded my bowling action (the english game of cricket, where you throw/bowl the ball the the batsmen). It was recorded side on to my run up. I wanted to measure my speed, so I thought, using 2 consecutive frames from movie maker, giving a time of 0.04 sec. Then using Pixlr(free photoshop), overlap the two frames, and measure the pixel distance the ball has traveled. Then I use the diameter of the ball (known) to measure how much distance each pixel is in real life. Then I calculate speed.

    This should be accurate, with the only uncertainty coming from the pixel measurements. The results so far have me questioning if there are other factors I have missed, I got most of readings at 40mph, this is very slow, spinners bowl at this speed, I have been told I am faster, then I have one reading at 75mph. The fast one showed really good technique, so is why is that fast, but the slower ones shouldn't be that slow.

    Thanks so much for the help.

    Jay

  2. #2

    Default

    Would the results be more accurate if you compare frames which are further apart?

  3. #3

    Default

    Quote Originally Posted by TimAndrews View Post
    Would the results be more accurate if you compare frames which are further apart?
    Yep, I would. However, I would then need to set the camera further back, maybe harder to take the measurments. As it is, the ball diameter is several pixels long, while it travels 100 of pixels between the two frames, so I think it should be OK. I have posted this on other forums, and they talk about progressive interlaced stuff, etc. Kinda have an idea about that stuff, but not sure. Is it that progressive causes the ball to not be were it actually should be. Something like that, but a bit confused.

  4. #4

    Default

    You don't mention anything about not being able to see the edge of the ball which is the important thing so I wouldn't worry about things like progressive and interlaced. So long as you know the frame rate of the camera it's about as good as you will get. I would have thought shutter speed may have a baring on how clear the ball can be seen.

    I'm not sure this is the best way to accurately measure the ball speed as missing one pixel will through out your calculations. Wouldn't something like THIS be better. OR even better these guys. OR even THIS
    Last edited by Midnight Blue; 09-20-2012 at 05:47 PM.

  5. #5

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    Quote Originally Posted by Midnight Blue View Post
    You don't mention anything about not being able to see the edge of the ball which is the important thing so I wouldn't worry about things like progressive and interlaced. So long as you know the frame rate of the camera it's about as good as you will get. I would have thought shutter speed may have a baring on how clear the ball can be seen.

    I'm not sure this is the best way to accurately measure the ball speed as missing one pixel will through out your calculations. Wouldn't something like THIS be better. OR even better these guys. OR even THIS
    Oh right, The edge of the ball, I can see it, and would estimate I could be out by around 1 pixel. So would this be accurate then. Not an expert, but seems like others of differenet forum talked about issues of progressive. Thanks for the links btw, I needed something which I can use regularly, and the ball, I have heard its totally unreliable.

    Thanks

  6. #6

    Default

    Try a faster shutter speed to reduce blur
    A TV frame is 1/25s
    set the camera up and then measure the distance of the frame (from where the bowl is bowled) so you know how far the ball will travel, then use one edge of the frame as the start point and the others as the end, measure the amount of frames it take the ball to travel as it enters the frame to when it leaves and get you speed from that.
    The further you are form the bowler the more accurate your reading will be , but the ball will be smaller, try using a negative plugin on the NLE to see if that helps see the ball better.

    You could also use the sound, so if you can see the ball leaving the hand and then hear the noise of the ball on the bat, you could try timing that

  7. #7
    Join Date
    Mar 2011
    Location
    London, England
    Posts
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    Default

    I wonder that you can't do the job better with audio (on camera?) - when you relaese the ball shout! Then, when the ball reaches the batsman you hear a Thwack! - distance time speed QED.
    Some adjustment may be needed for the distances to camera, but that won't be too much.
    +Best to have the camera in a defined position - aligned with the stumps (at the bowling end)....and keep the distance sensible . . the Boundary may be too far?

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