View Full Version : Calculating film back for matchmoving

 LOTK10-29-2009, 05:12 PMI thought this might be the right place to post this q, I'm trying to guess/calculate the CCD size for an HD camcorder. I have some footage shot with a panasonic HD camera, but not much info on the camera or the scene. After taking a look on the specs of the camera online, I found the sensor diagonal is 1/6''. Would I be correct in assuming that the sensor has dimmensions of ratio 16:9 and calculate the size by trigonometry? e.g W^2+H^2 = (1/6'')^2 and W/H = ~1.78 (16:9) Or is this totally wrong? I also know that the focal length (unzoomed) must have been 47.2mm. any help will be appreciated
LOTK
10-30-2009, 11:08 AM
I've read some threads around and it actually proves quite difficult to find this info.

The CMOS size diagonal is presumably a tube diameter that would fit this chip and the Width/Height dimensions could vary depending on how much of the chipset surface is used.

According to some a 16:9 camcorder could be using a chip with 4:3 dimensions?

If I could get my hands on this camcorder's manual, would I be able to obtain this info really?

I calculated/guessed the size with trigonometry based on my previous post at: W:36.8mm and H:20.7mm. I'm using boujou and after setting the focal length to "unknown constant", I noticed that it guessed pretty close to the focal length of the camera ~46.5mm

But the solves don't seem so accurate...

beaker
10-31-2009, 05:06 AM
Can you give the exact Panasonic Camera? You might be lucky and someone knows the sensor size. Also you might want to look around the Panasonic website and might be lucky and find a white paper or burried somewhere in the manual the actual dimensions of the chip. If you can find the name of the chip you might also be able to hunt this info down. The chips are only made by a few companies out there(often not the camera manufacturer).

The CMOS size diagonal is presumably a tube diameter that would fit this chip and the Width/Height dimensions could vary depending on how much of the chipset surface is used.the dimension of the chip is a very generic number that is usually rounded up to the closest size:2/3, 1/2, 1/3, 1/4, 1/6, etc...

According to some a 16:9 camcorder could be using a chip with 4:3 dimensions?very annoyingly yes plus many other wacky stuff depending the chip. Especially on consumer/prosumer cameras.

I calculated/guessed the size with trigonometry based on my previous post at: W:36.8mm and H:20.7mm. I'm using boujou and after setting the focal length to "unknown constant", I noticed that it guessed pretty close to the focal length of the camera ~46.5mmI doubt it since that dimension is way bigger then a 1/6" chip. A full frame of 35mm film(ie vistavision) is roughly 36x24mm and currently the only digital cameras with that size chip is a dslr camera.

LOTK
10-31-2009, 12:07 PM
beaker thanks for your reply on this, it was actually one of your past posts that enlightened me on the subject.

I'm learning more about the technicalities of this as I go along, so my assumptions were quite wrong because I didn't understand. I've done a bit more reading and certain things are much more clear now (The figures I came up with would probably belong to a Red 4K camcorder:P)

I managed to find the camcorder specs, it's a Panasonic HDC-SD5BNDL. Btw the focal length I mentioned previously is wrong.

I found an old post by "earlyworm" who after I contacted, gave me the answer. He has actually put together a pretty good trigonometrical approach to calculate the filmback, his blog and explanations here:

http://www.earlyworm.org/2008/08/filmbacks.html

very useful, also I'm writing down the values for this camcorder's filmback for others who might need it:

W: 1.678mm
H: 0.944mm

thank you ealryworm!

earlyworm
11-01-2009, 12:36 PM
I'd also recommend picking up this book if your looking to learn matchmoving... http://www.amazon.co.uk/Matchmoving-Invisible-Art-Camera-Tracking/dp/0782144039

Redsand1080
11-17-2009, 03:48 AM
@earlyworm You're blog helped me out a ton before so I just wanted to say thanks much for posting up that info. I'm actually the guy who most recently emailed you (probably about a year ago now) about explaining the process further and thanks again for actually doing that. Good to see people still finding your blog and learning from it.

Very cool! :)

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11-17-2009, 03:48 AM
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