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Author Topic: 4K video frame grabs for photogrammetry  (Read 8452 times)

igor73

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4K video frame grabs for photogrammetry
« on: October 09, 2014, 11:05:26 PM »
I need a faster solution then a DSLR for photogrammetry.   Have been thinking of buying one of the cheaper 4K cameras that now is on the market.  Both Panasonic and Sony now have 4K cameras for under 3000 EUR.  High quality lenses can be used. 

So has anyone tried any of these cameras, Panasonic Lumix DMC-GH4 / Sony Alpha 7S ?  http://www.dpreview.com/previews/panasonic-dmc-gh4-sony-alpha-7s

Also black magic has a 4Kcamera.  Also open for other suggestions.   Any reason why i should not get good results?  The resolution on video at 4K is about 8mpix so not great but on the other hand i will have speed and be able to get great overlap. I could crank up the shutter speed to 1/100 or o to get better sharpness.   

Anyone have experience with using video for photogrammetry?  Even if just HD i would be interested in seeing some result examples. 

When i do fram grabs i guess i lose exif data?  So i have to calibrate manually or how are you dealing with this? 



emage

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Re: 4K video frame grabs for photogrammetry
« Reply #1 on: October 10, 2014, 12:49:30 AM »
The Sony a7S does not record 4K, at least not internally.
you would need an external recorded which bump up the costs and complexity considerably.

as for the GH4, it's a solid camera.
a friend of mine have one, I'll give your idea a spin on the weekend.

take into account that moving fast means rolling shutter and motion blur,
as well as a small angle between frames. you might need to drop frames.
I think that the GH4 burst mode (12 FPS for RAW & 40 (!) FPS for JPG @Full 16MP) would be a smarter move.

Cheers.
Avihay.

igor73

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Re: 4K video frame grabs for photogrammetry
« Reply #2 on: October 10, 2014, 01:58:43 PM »
"I think that the GH4 burst mode (12 FPS for RAW & 40 (!) FPS for JPG @Full 16MP) would be a smarter move."

Did not know it had that good burt mode.  That would indeed probably be a better way.  My Nikon D800 can shoot 5fps.  That is fast enough for sure but after around 20-30 images the card gets overloaded and i have to wait util it has finished writing to the card for about 30 seconds.  Can´t take pictures during the wait.  Very annoying.   Not the same problem with the GH4?

Would be great if you could test the GH4 out!! 

igor73

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Re: 4K video frame grabs for photogrammetry
« Reply #3 on: October 10, 2014, 02:01:22 PM »
I was  definitely planning to drop frames. Grab every 10 frame or so.  I would also probably use a faster shutter seed like 1/100 and i don´t need to move very fast.

But if the burst mode works without write lag to card that is better! 

ThomasVD

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Re: 4K video frame grabs for photogrammetry
« Reply #4 on: October 11, 2014, 11:46:47 AM »
Working underwater making site plans of archaeological wrecks I have used frames extracted from videos to generate 3D models because I really require a ridiculous amount of images (visibility is often only about half a meter so you have to get very close and take lots of pictures to cover the entire wreck).

I've had great results even with simple GoPro Hero 3 footage, using "Free Video to JPG Converter" to extract frames (without exif data, as you say). However it does seem like different camera models record video differently so in some cameras when you extract frames you'll just get something which looks as sharp as a picture, but in others you get image artefacts such as little jagged lines running through your image.

Good luck!

igor73

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Re: 4K video frame grabs for photogrammetry
« Reply #5 on: October 11, 2014, 07:23:00 PM »
The new Go Pro 4K version might be worth a try, 

igor73

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Re: 4K video frame grabs for photogrammetry
« Reply #6 on: October 22, 2014, 07:25:39 PM »
Emage, did you get around to testing the GH4?