View Full Version : Motion blur question...

11-22-2004, 02:48 PM
A long time ago someone had asked a question on motion blur and eventually someone else came along and said they wished Lightwave's motion blur was addictive. My question is is addictive better?

From what I have seen Lightwave render's motion blur by using temporal sampling (rendering more frames for a single one, then averaging them together). Should the final equation in the algorithm really be addictive?

What I am curious about is if highlights will not be attenuated. If you use the HDR capabilities of Lightwave (Full Precision/128 bits), will the averaging really damp them out? And does using an addictive (adding the samples/frames together) mode remedy this?

Thank you.

11-22-2004, 08:56 PM
Well... motion blur might be addictive for some people, but that's another story ;)

If Lightwave downsamples the images (in colorspace) before applying the motion blur, then yes, you will get artifacts, though I couldn't tell you whether it does this or not.

An additive blend wouldn't produce correct results, either. In fact, blending samples additively (i.e., without averaging/normalizing) for motion blur makes little sense in any case. For instance, you'd get brighter objects just because you were using more samples.

The way Lightwave's motion blur works is pretty cheesy in general (at least in LW7's renderer - I don't know about 8 or any future renderers). It takes samples at n discrete timesteps where n is determined by the antialiasing level ( Low = 5, Medium = 9, High = 17, and Extreme = 33 ) and weighs them with a square envelope (i.e., all samples are weighted equally). This means that you can get strobing effects for really fast moving objects, even when using "Extreme" antialiasing, not to mention that even somewhat quickly moving objects will be pretty aliased.
It would be nice if they would let you define an envelope for motion blur (to simulate different types of shutters) and sample within that distribution. Even with only a few samples, the noise resulting from the temporal distribution of samples would help with the aliasing. Of course, it's a production renderer, so I understand the motivation for the cheaper/dirtier approach. ;)

11-23-2004, 03:48 PM
This type of Motion blur has real advantages though, like being able to motion-blur your shadows for the spinning light trick. Many renderers can't do it at all. It puts LW's shadows head-and-shoulders above many high-end renderers - just look at the shadows in Episode2 Attack of the Clones, they're dead even from one end to the other - they look exactly like shadow maps.