1 Topic by 21000969

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I am doing my dissertation on an aspect of horse spine biomechanics to put it simply. I want to be able to video the horse cantering from a side position with markers placed along the spine. I was hoping to then upload the video and track the angles between those markers and collect this as data. I've reached a couple of questions...

1. Is an iphone appropriate to use as a camera, providing that the videos are uploaded in the correct format?
2. If not an iphone, which camera(s) would be suitable instead?
3. Is there a list of video qualities which i need to meet? (i've seen several mentions of frames per second for example)

Due to being away from wifi whilst filming, I was hoping of just uploading videos instead of real-time analysis hence wanting to use my iphone. I'm not amazingly technological however from what i've seen, kinovea is perfect for the task.

Comment your thoughts! Links to videos or other threads is also appreciated

2 Reply by petecrowe

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The iPhone is definitely usable as a camera. It has numerous high speed settings, including Super Slo-Mo (240 fps @ 720p) and Slo-Mo (120 fps @ 1080p). You can also go down to 60 fps.

When you open the files, different programs will read different fps settings, but they will all be fractionally close to 240 and 120. I prefer hooking up my iPhone directly to my Mac, thereby using ImageCapture to download any images I want via a lightning to USB wire. It's much faster. You don't get a chance to specify a format when you upload them to your Mac. They will come as .MOV files, which are playable by most video players, and importable directly into Kinovea.

You will need to figure out some way to mount the camera. I've used this (https://www.amazon.com/AILUN-Rotatable- … amp;sr=8-9) and either mount it to a tripod, if you are clever enough, you can mount it to a tripod microphone stand which would give you some elevation.

This is most likely the best solution (especially if you already have an iPhone) for non-real time analysis.

If you want to go the real time route, you will need to look into machine vision/industrial cameras, 4 brands of which Joan has written plugins to support real time operation. Read more up here: https://www.kinovea.org/help/en/capture … trial.html

They start out at affordable, then go up to over $1,000. You'll need the body, a lens, and a certain amount of technical knowledge to use and install them - thus my recommendation for using the iPhone.

High Frames per second. Shutter control. Exposure control. Lots of high quality light (make sure you check these forums for the lighting users found that work well with high frame rates. I use Hykolity lights which put out bright, non-colored light that can freeze most motion (https://www.hykolity.com/collections/le … bay-lights). Best yet, they are affordably priced.

Best of luck with your dissertation!

3 Reply by 21000969

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Thank you- that is really helpful!

I will definitely do some trials (might even do a pilot run) and play with the iphone settings. I do already own a tripod as i often use the Pivo motion sensor to record riding sessions with the horses, so i can use this (i hadn't thought about camera height so thank you again!).

I will be using a laptop running windows rather than Mac, but i'm assuming there is a way to save the videos as needed either way. Also, most of the filming will take place outside so daylight will be a lighting factor i need to consider. Failing good lighting (cloudy day for example), if i make the markers on the horse extremely visible do you think this will suffice? Im guessing this is so the software doesn't make mistakes when measuring joint angles or following a continuous point?

4 Reply by Reiner

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A concern against using the iPhone might be that the camera is a rolling shutter camera, not a global shutter.
A rolling shutter camera records one pixel line after the other from top to down until the full image is recorded, a global shutter records the full image at the same time.

Depending on the speed of movement there may be a significant distortion of the recorded frame image. The distortion does not reflect the real geometry and  may lead to wrong measurements between two points. Unfortunately, you may not correct the distortion by any equation due to the unknown movements in different directions.

For testing your approach it might be good enough but to use it in a thesis it will be difficult to explain the error in the method section.

5 Reply by petecrowe

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Great point Reiner, and you make a pertinent reference to the speed. Visual examples of rolling shutter normally include a helicopter, or fan blade - in other words, objects that are moving at a high rate of speed. In this case, the poster reports that the subject is going to be a cantering horse which a quick search will reveal it is between 10-17 mph. Do you think that's enough speed to cause rolling shutter issues? Perhaps 21000969 could use a short focal length (the iPhone max can do .5, 1.0, and 1.5x zoom) to ameliorate the effect?

6 Reply by 21000969

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I currently have an iPhone 12 which i believe is also capable of those zoom settings- do you think this will be sufficient?

After speaking with my lecturers we decided that for each horse, I should video both the left and right sides, and take several videos of the canter to create average range of motion figure for each horse. If the iphone will live up to the challenge, Ill search around for another one.

Failing that- any cheap camera suggestions which will do the job instead? Im not likely to need the cameras again, so any suggestions for affordable cameras are appreciated also smile

7 Reply by petecrowe (edited by petecrowe 2022-10-21 21:16:06)

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Sorry for the time to respond. I have an iPhone 12 Max, and yes, it has those 3 zoom levels. It also has some incremental levels (click on the zoom level number on the screen, hold it down, and it will display a zoom "wheel" which you can incrementally drag up and down. I would caution against this though as I'm pretty sure those inter-settings are not optically based zoom - just digital, and the quality will suffer.

There are lots of cameras you can buy that cost significantly less than a new iPhone. Here are some places to being your search

Daheng (supported by Kinovea)
https://www.get-cameras.com/USB3.0-Came … 160-227U3C
These are the cheapest cameras, but are well made.

Basler (supported by Kinovea)
https://www.baslerweb.com/en/products/c … meras/ace/
Basler has a very nice search interface if you scroll down, where you can dial in the exact specs of what you are looking for. USB3 interface is ideal. Then, you can set your preference for FPS, sensor size, and resolution.

IDS (supported by Kinovea)
https://www.ids-imaging.us/store_us/pro … zGEALw_wcB
Another nice camera finder.
More expensive than Daheng, approximately comparable in price to Basler.

Keep in mind supply chain disruptions mean significant lead times for ordering. Some units are in stock, but you will pay significantly more. EdmundsOptics has a good selection of most industrial cameras...https://www.edmundoptics.com/c/cameras/1012/

I'm actually in the market for a couple cameras and could possibly purchase them from you after the project.