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Camera Lens Blur - doesn't accurately blur objects in front of in-focus objects

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Brian Murphy
Camera Lens Blur - doesn't accurately blur objects in front of in-focus objects
on Oct 26, 2011 at 9:46:02 pm

I have a depth map animation from Cinema 4D along with the real animation. The depth map file certainly renders correct with the 256 grays but in using the Lens Blur with it, it won't blur objects like it should. I have front and rear blurs set and if anything falls in the out of focus range but visually goes in front of the in focus objects, the out of focus objects have sharp edges and they should be blurred....what the?

Does anyone know how to make this work?

Thank you for any help!



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Roland R. Kahlenberg
Re: Camera Lens Blur - doesn't accurately blur objects in front of in-focus objects
on Oct 27, 2011 at 2:04:38 am

This is indeed strange. Which version of AE are you using? In the meantime, give Compound Blur a try.

Cheers
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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ben g unguren
Re: Camera Lens Blur - doesn't accurately blur objects in front of in-focus objects
on Oct 27, 2011 at 4:25:01 am

Can you post a screenshot? That would help troubleshoot the problem.

One thing to keep in mind is that DOF maps have an inherent limitation where edges are concerned.

The inherent limitation: you can't [or shouldn't] anti-alias depth maps

The reason for this is pretty evident once you go through the logic. If white is close, black is distant, imagine a very-close (white) plane in front of a very distant (black) plane. Imagine that they intersect visually -- white edge over black background.

Now examine the depth map in this imaginary situation. If you want that white/black depth-map edge to look smooth, you'd have to anti-alias it, which involves "blending" the white edge to the black, creating... (wait for it) ... GREYS! Which, technically, suggest little bits and pieces floating in z-space from the edge of the white plane to where it intersects with the black plane.

So you have an aliased DOF image, and are using it with an anti-aliased render. And sometimes it doesn't work that well.

Usually this doesn't matter, especially with more organic 3D objects. But if you have really strong, contrasty edges in your render (a red box against a green background) or dramatic changes in DOF, you will begin to notice that the edges don't look right.... For the reason above.

The best solution I've found is to render your DOF blur in your 3D program of choice using the "Full Sample" option (C4D has this option, I believe...). Full Sample usually takes a bit longer to render, but when crazy DOF is involved, it looks sooooooooo much better than doing it in AE. In my opinion.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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