You have no idea how long I have been sitting on this one. I made some videos like a billion years ago, and still no post. Why? Oh well, here it is.
I like video analysis of motion. I like looking at stuff on youtube or other video sites. But sometimes, you need to make the video yourself. What should you use? My personal favorite is a Flip Mino HD. It is small and quick. Are there other options? Sure. In this post, I will do the video analysis with the following cameras:
- Flip Mino HD
- A Canon PowerShot A470
- Panasonic DMC-FZ18
- Canon HV10 HD miniDV camcorder (you know, the kind that uses miniDV tapes)
- LG Shine phone camera
- Built in iSight camera in a Macbook Pro
For this test, I set up all the cameras together and had them record the same event. This is me in my garage throwing an oversized tennis ball I stole from my dog. At the time of the test, I couldn’t find a silly meter stick, so I used a yard stick.
Flip Mino HD
Here is a shot from Tracker Video:
You can see it gives an acceleration of about 9.8 m/s2. Good for me. There is some interlacing issues – I will show a comparison frame for each camera at the end.
Canon HV10 HD miniDV
I imported and exported this through iMovie, so it is not raw. However, it does give a very good, clear and crisp image. Here is the data from Tracker.
Notice that this one gives an acceleration closer to 10.2 m/s^2. I suspect this depends on the scaling of the video (but I didn’t do an error estimate calculation).
Built in iSight
Here you can see a difference from the other cameras. The image quality is not very good, it is difficult to see exactly where the ball is in each frame. Also, there seems to be a problem with the frame rate. A couple of times there would be duplicate frames. You can see this in the plot from Tracker.
Even though the plot doesn’t look like a pretty parabola, it still gives a reasonable acceleration.
LG Shine Phone
First, the format of this movie was not compatible with Tracker Video. I used MPEG StreamClip to convert it to a .mov format. Honestly, I could barely see the ball in each frame. I felt like I had the blast shield down and was stretching out with the force to find the location of the ball. Here is what I got.
I must be strong in the force.
This one made pretty good videos despite being still shot camera.
Canon PowerShot A470
Really, all of these worked to some degree – even the stupid cell phone. The question comes down to speed. Warning: I am not a video expert, so what I am saying might be completely made up stuff. Ok, you have been warned. Many video cameras use interlaced video. This means that it takes every odd line of scanning and then every even line. If things are moving slow, there is not much change between the time it takes these two partial pictures. If things are moving fast, there is a difference. However, for normal video usage, viewing fast moving objects looks ok. The problem comes about when you look at one frame. Here is an example from my videos:
Here the only ones that clearly show the ball are the Flip and the HV-10. I think the panasonic would have looked better, but for some reason the white ceiling light made everything very bright. These videos show a point where the ball is moving fast. At the highest point of the trajectory, the ball is moving slow and looks much better in all the videos. I am not sure if the Canon HV-10 is progressive scan, but that means that it scans both fields at the same time. Progressive scan = good.
There is a way to fix some of these videos. You can have program “average” the two interlaced frames. This is (unsurprisingly) called “deinterlaced” video. I use MPEG StreamClip to do this. Sometimes it can make a big difference. I tried this with the video from the powershot and it looked about the same.
I think the moral of this post is that a better camera is better. However, you can still find useful things to do with even a cell phone camera. In fact, I have a video from the fair that has been sitting in my “to do list” for quite some time. Sometimes though, you need a good camera to get anything useful. In fact, I had another set of videos that I shot outside. The ball was not very visible in the background though. For that situation, only the HV-10 or the Flip could get useful data.