Krontalk
General => General highspeed discussion => Topic started by: wally_x on July 14, 2019, 06:28:39 PM

Hello, I was wondering if someone could help me with the math on calculating the speed of a moving object that I record with my Chronos.
I've built what I call a "speed chart" (black and whiteboard behind the moving object like on Mythbusters) and I know my capture frame rate and my playback frame rate, but not sure what the equation is. Especially with the capture speed vs the save or "playback speed".
Any help would be much appreciated!

The playback speed doesn't matter.
What you want to do is to count the number of frames the object takes to move from the start point to the end point you chose on your speed chart.
Then as you know the framerate of the capture you can know the time (frames number / fps = time in seconds) and you have the distance (let's say it's a foot) so you just have to do distance / time to have the speed in ft/s (or whatever distance you chose on your reference chart, per second) ;)

So basically if my object moves 2 ft on my chart in 10 frames and I was shooting at 2000fps then the math is something like:
10 divided by 2000 = .005 seconds. That divided by 2 gives me .0025 ft/sec, which I can convert to mph or anything else. This sound right?

Here you've done time over distance, not distance over time, so that's not good. The speed is actually 400 ft/s (2 / 0.005). Everything else is right ;)

Awesome! Thanks again for you help!!

For the calculation of the speed accurately. First, take two successive images from your video. you can use "free video to jpg converter" to extract every frame. Second, download imageJ software and open the two images. you supposed to know the time interval between them. Then use the scale feature and draw a line for a known distance in the image. this stage determines how accurate your measurement is. it will give you how many pixels per inch/mm depends on your known distance. Finally, find the delta x and delta y of the moving object in pixels (you can easily get the pixel position by hovering the mouse in the image).
For example:
delta t between the two images is 0.001 second
delta x is 114 pixels
delta y is 0 >> object is moving horizontally.
scale: 228 pixels/mm
to find the distance: delta x / scale = 114/228 = 2 mm in 0.001 second
the speed then is distance/delta t = 2/0.001 = 2,000 mm/s or 2 m/s

For the calculation of the speed accurately. First, take two successive images from your video. you can use "free video to jpg converter" to extract every frame.
The Chronos can already safe individual frames, no need for external tools here. However a firmware upgrade might be required to do this.

For the calculation of the speed accurately. First, take two successive images from your video. you can use "free video to jpg converter" to extract every frame.
The Chronos can already safe individual frames, no need for external tools here. However a firmware upgrade might be required to do this.
Yes. Also as a TIFF Format, but I found it less quality than h.254

For the calculation of the speed accurately. First, take two successive images from your video. you can use "free video to jpg converter" to extract every frame.
The Chronos can already safe individual frames, no need for external tools here. However a firmware upgrade might be required to do this.
Yes. Also as a TIFF Format, but I found it less quality than h.254
[/quote
In what way was the quality lower for TIFF? The TIFF images are uncompressed, so they should be higher quality.