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Oliver Demetz
01-02-2010, 05:47 AM
Hi!

I have an image taken with an ordinary digital camera and I would like to "insert" an object into the scene in the image.

If I could compute the projection matrix that was used in the camera, then, if I rendered the object setting this as projection matrix, then the object should be shown in the correct perspective, right?

What about the point of view, the position of the camera?

Thanks for your hints in advance!

Olli

Ilian Dinev
01-02-2010, 09:57 AM
http://www.rethinkfx.com/tutorials/compositing3d

Oliver Demetz
01-04-2010, 03:21 AM
Thanks for your reply.

Shadows are not my problem, I think I can just leave them completely out of scope.

Also, I am more on a low-level technical point-of-view.

My main interest is in the configuration of the camera, to speak in 3dsmax terms.

If I could estimate the projection matrix and the general geometry of the scene, then it should be possible to insert simple items in an almost fully-automated fashion. Right?

ZbuffeR
01-04-2010, 07:07 AM
No need for fancy camera position, just leave it to 0,0,0.

Then estimate the field of view of the digital camera : take picture of a plane grid with know measurements, parallel to the lens, at a precise distance. Then in OpenGL render a virtual grid with same known dimensions, and blend it with the picture taken by real camera. Adjust fov until match is good enough.

Afterward, you "only" have to apply rotation the virtual camera, and place the objects at the correct positions.
One important step but more complex is to "undistort" the camera picture, as often straight lines are captured curved.

There is quite a lot of literature on the subject, search for "intrinsic camera parameters", "augmented reality", etc.
http://opencv.willowgarage.com/documentation/camera_calibration_and_3d_reconstruction.html
http://www.robots.ox.ac.uk/~gk/

Then there is a long list of features to attain perfect camera matching, which ones do you need ?
- manual projection/distortion match
- automatic projection/distortion match
- gl graphics can be hidden behind real objects
- gl graphics can cast shadows on real objects
- gl graphics receive cast shadows from real objects
- color match between gl/real
- add realistic color noise + bayer effects + blur on gl graphics
- add motion blur on gl
etc...

etc ...