6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: still capture rate (still FPS)

Mon Sep 28, 2015 10:38 am

Vertigo72 wrote:But Im also a little surprised at the number of waves. Then again, Im not sure how fast a photo is taken. Shutter time doesnt mean anything, because its a rolling shutter camera. How long does it actually take from first to last line to make a full 5MP photo? Anyone know ? Im guessing its on the order of 100ms or more (10Hz) ?
32.5ns per line, 1944 lines = 63.18ms, hence how come we can get 15fps at 5MPix. (There are actually 24 padding lines after the image, so 63.96ms/frame, but those lines won't make a difference to you).
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Vertigo72
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Re: still capture rate (still FPS)

Mon Sep 28, 2015 1:20 pm

okay, so it takes ~60ms to grab a frame. My servo's have a refresh rate of 50Hz, that is 20ms between movements. Its surprising then that we count so many jello waves when theoretically, the servo could only move 3x per frame.

I replaced the bad servo and stiffened up the bracket with some carbon and expoxy, and did some more ground testing to make sure it is indeed the servo and not something else. This is with the gimbal turned off:
https://www.youtube.com/watch?v=_vCTzMkEfqM

motion blur, but no jello.
This is with the gimbal (now no longer properly configured as the servo's are different) turned on:

https://www.youtube.com/watch?v=hiyo0g4y7dY

there is clear jello, although I dont think its anywhere near the 10-15 lines we saw in the aerial stills. So there may be a secondary effect playing as well.

Vertigo72
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Re: still capture rate (still FPS)

Mon Sep 28, 2015 2:42 pm

And just did another flight test, with the gimbal stabilization turned off, so the servo's werent moving:

Image

There is still a hint of some jello I have to admit, probably from the wind and the frequency may match what we saw earlier.

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jbeale
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Re: still capture rate (still FPS)

Mon Sep 28, 2015 3:51 pm

Yep, I bet that's the resonant frequency of your camera mount, and assuming it's still external, it ought to get better if you can get it out of the turbulent airflow. Unless the vibration is driven by the propeller, of course... you could confirm that with a test if it's possible to turn the motor on and off in flight.

Vertigo72
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Re: still capture rate (still FPS)

Tue Oct 06, 2015 10:22 am

I still havent quite resolved the jello problem, despite trying without gimbal and using some foam and velcro to isolate any vibrations there might be. I think its the airflow. Anyway, this shouldnt be a problem in my next build, and meanwhile, I did get some results despite the jello. Here is a 3D reconstruction based on some aerial raspberry images:

https://www.youtube.com/watch?v=_a36Mx_fdZw

It fails in the places I had expected (the building being constructed with just thin beams, the round domes which have almost no distinguishable features), but overall looks kinda of neat.

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jbeale
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Re: still capture rate (still FPS)

Tue Oct 06, 2015 1:53 pm

Very cool 3D result! How do you generate that?

Vertigo72
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Re: still capture rate (still FPS)

Tue Oct 06, 2015 2:54 pm

I used the trial version of pix4dmapper for that. It copes better with the less than perfect images than visualfsm or photoscan, but its quite unaffordable for individuals. At least it doesnt make much sense to try and get by using a $25 camera then having to use software that costs €6500 ;) The trial version has no export functionality except 3D video's like the above, but that at least enables me to see if it could work.

BTW, if you want recreate textured 3D meshes from images, you can also try the free autodesk 123D catch. It also works quite well for objects, but is limited to 70 images.

cheezeq2
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Joined: Tue Nov 03, 2015 1:15 am

Re: still capture rate (still FPS)

Tue Nov 03, 2015 1:28 am

jamesh wrote: A mod to Raspistill would be easy to make that caches the images and writes them out later when time is not an issue.
What you're describing is exactly what I'm after:
Capture n number of images into memory... THEN save them as individual jpegs.
I've tried using camera.py with capture() and capture_sequence() but they keep saving each jpeg right after it's captured slowing the FPS down to like 4.

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