Motion Blur question

[Streetwise]

I'm doing an animation of a room that becomes populated with furniture over a 3-4 second span of time. Stuff jumps up through the floor and happens fairly quickly. Do I really need to be concerned with motion blur for something like this? I guess what I'm afraid of is that ticking the motion blur box would be similar to ticking the DOF box in the sense that it will have a severe hit on render times. As with DOF, there's a faster way using ZDepth. So is there a faster/better way to get a nice softness to things that are in motion without using the built in motion blur? My shutter speed most probably will be in the 1/30 - 1/45 range.

Thanks.

[vlado]

If you are using V-Ray 3.x, there's almost no speed penalty for turning on DOF and moblur as such. You might get noise, and cleaning it up might need more samples, but that's all there is to it.

Best regards,
Vlado

[Streetwise]

Working towards 3.x, but still on 2.4. I'd switch now, but don't really want to in the middle of a project... Sounds like there is going to be a hit to render times then with 2.4?

[vlado]

Only because it will shoot more samples per pixel, which you can control. I guess it would be best to try and see if it works. If you have stuff jumping through the floor, 2D motion blur might be tricky to get right as it doesn't work too well with intersecting objects.

Best regards,
Vlado

[Morbid Angel]

3d motion blur = will always take longer of course, not sure how dof is, but for 2d as vlado pointed out you will have problems with intersecting edges of fast moving geometry. I always look at it this way:

what is more important human time or computer time? It will take more human time to split elements out, and produce a usable motion vector, then put everything back together in comp. Or simply tick 3d motion blur check box and wait for computer to do the work for you ?

[Streetwise]

3d motion blur = will always take longer of course, not sure how dof is, but for 2d as vlado pointed out you will have problems with intersecting edges of fast moving geometry.

I see your point Dmitry, about doing the work on the frontend, vs post. But not sure I understand about 2D and intersecting edges. In the scene, the camera and set is stationary. Only the furniture is in motion. It sounds like there are some issues with how the edges blend with the background when motion blur is used?

I guess the best way will be to render out a couple of frames with and w/o and compare quality and speed.

[Morbid Angel]

Imagine this, when a renderer is blurring an image, a part of the background is visible in the motion blur's trail. This means that during motion blur both the object and the background are traced *why it takes longer also. But when you render non motion blurred image and apply a vector it literary takes the pixels in blurs them in the XY direction of the image according to where the object was moving. But because they are 2d pixels no info can ever be behind one another of the objects. So, this is where you will see artifacting.

So what people do is lets say if you had a chair moving over a floor/room, you would render the room, the chair and its shadows separately, then motion blur just the chair (which will produce motion blurred alpha) then lay that over the bg.

Oh and another thing, reflections and shadows won't motion blur so be aware of that