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Prespective problem for live action matching

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Miguel Marinheiro
Prespective problem for live action matching
on Oct 16, 2011 at 6:24:35 pm

Hi everyone I have recentely started doing some live action and matchmoving experiences but I always have a lot of problems setting up the camera properly, namely because of prespective distortion problems. I tried to play with all the camera's settings but could not get a decent result.. I include a frame of the footage i am working on, any help would be greately apreciated! Thx for the attention



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Ben van Hamelen
Re: Prespective problem for live action matching
on Oct 17, 2011 at 8:42:48 pm

I have quite some experience with matchmoving. If I do it right, I pretty much have no remaining tasks in Maya regarding camera setup. I use PFTrack. Here are some tips that might help you:

- Before tracking, un-distort your footage. Ideally you'd have shot a distortion grid on location, but you can do without. Render the undistorted footage and use this in the rest of your pipeline. Your last step should be to re-distort.

- Always gather as much info as possible during the shoot. Most important factors: sensor size, focal length, framerate and crop factor, if applicable.

- I strongly prefer working with manual tracking points for added accuracy and clean scenes. Only if I really lack proper tracking points I resort to automatic tracking. It takes longer and is not the most fun thing to do, but for me, it always pays off.

Last note: my copy of Maya has a habit of setting the framerate to 23,976. Always. A lot of footage, however, is shot in 25 or 30 fps. Adjust it accordingly.

Does that about cover your question or are you still facing problems?

Regards,

Ben van H.

http://www.fireinthesole.com/


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Miguel Marinheiro
Re: Prespective problem for live action matching
on Oct 18, 2011 at 12:16:34 pm

Hello Ben van H. and thank you for your helpful reply.

I used Boujou to track my footage but my issue here was not about the cleanness of the camera solve but rather the perspective construction of the scene, for which a single frame would suffice, and so the relationship between the real camera values you mentioned and the virtual camera parameters in Maya.

Following recomendations I got from another forum I did manage to get the result I wanted, basically by matching the side of a cube to the vertical left wall and tweaking the focal lengh downwards from there so I didn't need to go through the undistort-pipeline-distort process.

I think that is more crucial when there are curved distortions due to rolling shutter issues or so right? As I don't have much camera movement in my shot I have no big issues with that so i just neglected them, but I would like to know which software do you use for the undistorting-distorting process. I guess I could use photoshop but it would be nice to be able to process the footage and not the image sequence..

Anyway thank you very much for your feedback and your help!

Best,

Miguel Marinheiro


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Ben van Hamelen
Re: Prespective problem for live action matching
on Oct 18, 2011 at 7:46:37 pm

Ah, then I indeed misunderstood. Glad you got it fixed.

To answer your question: PFTrack does undistortion. PFTrack gives you the option to export the undistorted footage and gives you the distortion value (which you can later use to re-distort).

That said, I'm absolutely sure that Boujou can all that as well, no problem. My experience in Boujou, however, is too limited to go in detail.

http://www.fireinthesole.com/


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