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View Full Version : How to compose glass in real video footage?


frix
10-20-2007, 07:46 PM
Hi there,
I'm thinking of doing some camera tracking. I would like to use an animated 3d glass object.
The problem is how can I get the real video footage distorted correctly by the 3d glass.
Do I have to render every single video frame in my 3d package to get the wanted refraction effect?

Thanks for your help.

scrimski
10-20-2007, 08:59 PM
Generally said - yes.

more details would make it easier to make a more specific advise.

frix
10-20-2007, 09:11 PM
I don't want to track a moving objekt within the video, just the camera move. The real footage is just made with a handcam. I'm planing on using either max or maya.
So I guess there is a way to place the video (or the video's single frames) in the background of the viewport and then render just the refraction pass for example? I think this is quit painfull when it comes to rendering. One frame forward, render, change the background pic, one frame forward, render, change the background pic, and so on.

scrimski
10-20-2007, 10:16 PM
Which 3d program do you use that doesn't update the background itself when using footage or sequence files?

frix
10-20-2007, 11:29 PM
Well, I'm new to composing and never tried importing a sequenze as environment, the question was a general thought before testing it.
Reading your answer tells me that it's not too difficult. I will test that.

Thanks :)

frix
10-21-2007, 08:49 AM
Hi.
I tried to import a image sequence to the time line in 3ds max. That works fine.
I wanted to use a HDRI to light the scene. In 3ds max you have to put the HDRI in the background environment channel. The spherical HDRI as a background gets properly distored by my glass object. But the non-spherical video image sequence not at all.

The video plays just within one small scene. So I thought one hdri image of the scene is enough. And than rendering one pass with the video as a background for the refrecation.

edit: Seems like the background is just refracted when the projection method is spherical or cylindrical. With the projection method set to screen it just passes through the glass undistored. But as you can see the method cylindrical distorts the whole picture in an unwanted way :(

frix
10-21-2007, 03:33 PM
Ok did the same test with maya. Here I used the background pictures with an image plane node. This node has a checkbox for reflections and refractions. Here I got it to work without cylindrical projection. The image plane is fixed to the camera normal.
I couldn't find such an option in 3ds max.

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