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Canon PowerShot TX1 HD video feature brain3Dhack

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Canon PowerShot TX1 HD video feature brain3Dhack
« on: 25 / January / 2009, 10:28:26 »
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Hi everyone,

I wonder, where to start to hack videos to be in synch with double hacked Canon PowerShot TX1.

I read out there is no way to access video genlock directly in this DIGIC models and start thinking on how to hack it on other way.

Here are some ideas, crossing my mind:

- we could observe two video signals comparing sync pulses

- what we need is kind of script to make delay on one camera

- posibility that the script will switch ON OFF circuits partialy -like on off for short periods of video processor, switching between video - photo, overdrive shutter, etc..

- is someone familiar with access to firmware parts where this would be possible??

- the result will be simply shown with LED, when the cameras are synched enough.


Just wonder what could be done..

brgds, Johan


Re: Canon PowerShot TX1 HD video feature brain3Dhack
« Reply #1 on: 26 / January / 2009, 02:43:08 »
Firstly read: http://forums.powershot-tx1.com/index.php?topic=12.0 - ask Cybercom on the TX-1 forum about his experiences - he may even give you his example footage using 4 TX-1s (stereo-squared) if you ask nicely.

Given that http://stereo.jpn.org/eng/sdm/index.htm talks about normal stereo shots with less than 1ms difference in timing between left and right cameras, I suspect that the same technique could be used for getting the cameras properly synchronised starting video too. Cybercom said he was getting consistent 1 frame start differences on his videos between the left and right cameras - but that can probably be solved.

Lets presume that Canon have implemented the 30fps based on crystal clocks i.e. no drift in video timebase *except* due to crystal drift (testable - although very difficult IMHO - by taking videos under different conditions and measuring scatter of drift rates over time). Two crystals on any two TX-1s should have less than 100ppm difference between them, which over 5 minutes video works out to 3ms which is about 1/10th of a frame. You don't freefall&parachute for longer than 5 minutes eh?

If you really want to be a perfectionist then if you can find a friendly supplier with multiple TX-1s, you can very likely find two with very well matched crystal speeds - although measuring if they were well matched would take a bit of effort (and could drift out of sync over years).

You don't need CHDK to do this:

* Set up a reference subject you can video which allows you to measure frame to less than say 1/10th of a frame (e.g. well lit marked rotating disk with digital clock behind it?)

* Make sure all cameras are same temperature, same battery condition, same new SD cards.

* Take simultaneous video of subject with all cameras for say 15 minutes. Don't run them individually at any time, as crystal drift is temperature dependant, which is dependant on how long each camera has been running for, and the current room temp. More importantly this way your reference doesn't have to be accurate since you are only interested in measuring drift.

* measure time drift over time for each of the cameras. e.g. Take avi files and chop off start frames until all files start within 1 frame of each other, then split out all frames using http://forums.powershot-tx1.com/index.php?topic=147.0 and then look for the cameras that best stay synchronised during the video.

* You would probably want to do more than one run and make sure everything is repeatable. It won't detect systematic errors (hopefully most can be ignored) but separate runs would detect random errors (due to unforseen factors!).

I hope that helps!
« Last Edit: 26 / January / 2009, 02:55:45 by robocat »

Re: Canon PowerShot TX1 HD video feature brain3Dhack
« Reply #2 on: 26 / January / 2009, 04:51:05 »
ask Cybercom on the TX-1 forum about his experiences - he may even give you his example footage


His video, made with SDM, is showing here http://www.hd3dvdo.com/

For video shooting, see bottom of this page http://stereo.jpn.org/eng/sdm/capture.htm.

Re: Canon PowerShot TX1 HD video feature brain3Dhack
« Reply #3 on: 26 / January / 2009, 22:44:12 »
If you are near NYC on the 3rd, Cybercom has an open invite to see his "8.5-minute HiDef, 3d video of last year's Mermaid Parade shot with four TX-1's".

Cheers


Re: Canon PowerShot TX1 HD video feature brain3Dhack
« Reply #4 on: 08 / February / 2009, 11:51:08 »
Thanks guys,

seams it should works in sync already, no need of any upgrading. From your typing to the ears of god.

Sure I will test it as soon as I get my cameras - still waiting, the delivery 4 to 6 weeks to EU...

I ll let you know the results,

brgds Johan

Re: Canon PowerShot TX1 HD video feature brain3Dhack
« Reply #5 on: 09 / February / 2009, 21:16:08 »
I've had no problems with video synch between two cameras as long as they were started with the remote. Sometimes, in the heat of the moment, it was too easy to start them both just by pressing the video record buttons "simultaneously." That was the only time when there were problems that could be seen as one camera might be about a 1/2-frame different from the other. For much of what I shot at the "Mermaid Parade," I kept shooting for extended periods of time and there was no noticeable drift.

FWIW, our 3D screening at The Kettle of Fish on Feb 3rd was a great success with over 250 attendees braving a cold and snowy night to see the show. We had to run it four separate times to accommodate everyone!

The overwhelming consensus was that TX-1 HiDef, 3D video rocks!!!

Many thanks to Microfunguy and all those here at CHDK who helped make it possible. 8)
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