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Camera Projection Problem

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Camera Projection Problem
on Aug 30, 2007 at 2:42:10 pm

My third post about motion blurring in as many days. I can't wait to get this under control. Here's the detail that's killing me.

I'm camera projecting an unblurred image sequence back onto the original scene using a surface shader. Same camera, same gate, same resolution. The trick is to render this with full motion blur. An old trick I heard about.

It works well, except for a brief 15 frame portion of the camera movement. Here, the movement is very fast and required a good deal of vertical blurring (it's a fast tilt down).

In this portion, what appears to be the top of the projection is smearing back into the bottom. It's wrapping. If I turn off the Wrap V in the place2D node (belonging to the image sequence file) the wrapping goes away, but it's replaced with plain gray-coloured smear. Very unsightly. It smears far too deep into the render to be ignored. Again, it's proportionate to the amount of motion blurring required. A 0 to 0.5 shutter cuts the problem in half, as one might expect.

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Steve Sayer
Re: Camera Projection Problem
on Sep 8, 2007 at 5:32:03 am

Sorry for the late reply--maybe this is no longer relevant.

It sounds to me like this is expected behaviour; after all, you're asking the renderer to refer to information that isn't really there (trying to blur parts of objects that were not rendered in that initial pass onto the parts that were).

In your earlier post, you mentioned that part of the technique involved rendering at 10% greater resolution than you need for the final product--perhaps this implies that you should crop the resulting footage down to the desired size, eliminating any such artifacts when the edges of the image are discarded?

If that's the case, then for your camera move you'll need to increase the resolution by more than 10%. Try rendering a tall, skinny image for those 15 frames. That should give you enough leeway that the wrapped texture isn't visible once you crop back down to the intended size.

Hope I've understood that correctly.


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