View Full Version : Mental Ray HDR motion blur

05 May 2007, 10:56 AM
Hi, I'm using Maya 7, and I started to experiment with HDR image-based lighting, and going through possible problem scenarios I found I can't get motion blur to work correctly. I tested with an object reflecting a hard highlight (blown-out window in this case), and having a camera pan quickly sweep past that. The expected result would be for the blurred highlight to remain blown out, but instead I get a light gray blur. Is there anything I can do to make motion blur behave more realistically?

05 May 2007, 11:49 AM
Maya 7?

Switch to a floating point frame buffer.

In that old version of mr, the logic was "if non-floating point frame buffer, clip each sample to 0-1 range". But this happened *prior* to motion blur, which cause the result you see.

In newer versions of mental ray we actually changed so clipping happens afters after temporal blur (but before spatial blur). If the frame buffer is floating point, naturally, no clipping is performed at all.


05 May 2007, 12:15 PM
Not quite sure how your problem looks like, maybe Master Zap answered your question already and I'm just talking crap now.. anyways.

That motion blurred things look less 'opaque' is a natural behavior, caused by the fact that although they reflect the same amount of light, they do this seemingly strechted over time - imagine their total amount of radiance, or luminance (which doesnt change in motion, at least usually not too significant) being smeared over 'more space' on your image. So your highlight would indeed appear less intense.
Of course this is not meant to be a physical explanation.

If you still want to have your objects keeping their luminance, try 2d motion blur, it usually does not take the 'exposure' thing into account, instead it only streaks the pixels regardless.

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05 May 2007, 12:15 PM
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