Post motion blur effect comparison

I have results from 3 different post motion blur effects.

1. Furnace motionBlur in Nuke with no motion vector.

2. Reel Smart Motion Blur using la maison 2d motion vector shader.

3. Nuke's built-in vector Blur effect using Maya's 2d motion vector render pass (normalized one).

Here's the comparison in color channels. 

 Apparently, they all look very similar and showing a reasonable quality.

But in alpha channel, there are some differences.

The first one, Furnace motionBlur shows some artifacts. For example, you can find some smudging around the ball especially when the ball is being released from the hand.

This not-so-clean alpha is not desirable for compositing. Since the Furnace motionBlur was not helped by any motion vector source, this kind of artifact should be unavoidable.

The other two effects are done with a proper motion vector source provided and did generate a relatively clean and smooth alpha.

RSMB still produced a better alpha than Nuke's vectorBlur.
While the ball is exiting the frame, the edge of the ball looks better in RSMB's case ( the center )than Nuke's vectorBlur ( the right ).

Overall, the winner is... Reel Smart Motion Blur (imho).

How to use Maya's 2d motion vector pass for Nuke's vectorBlur. (2of2)

In Nuke, you need to use VectorBlur node. ( under Filter menu )

The VectorBlur node has just one single input. This means the input source image must carry its own motion data, in this case, the separately rendered out 2d motion vector pass.

To do this, you need a ShuffleCopy node ( under channel ). 

Check out the connection.

And set up the node like it's seen in Pic_2. Notice that the R and G channel of the 2d Motion vector image feed the u and v motion channel of the Masterbeauty pass.

 

 

How to use Maya's 2d motion vector pass for Nuke's vectorBlur. (1of2)

We all know that motion blur is one of the essential effects to accomplish better realism but it generally requires a long rendering time, especially when using full 3d motion blur of Mental ray renderer.

As an alternative,  2d motion vector methods are widely used since it is a cheaper and still very effective and flexible solution.

There are some good articles and tutorials that you can find in the internet about 2d motion vector methods but I will focus on a more specific issue in this article which is a sync problem.  

First, let's take a look at what really happens when motion blur is on, in terms of moving objects' position.

Here's a very simple five-frame animation.

Pic 1. Master beauty

Click the image to see the moving stick.
The animated stick moves by one notch at a time so the moving stick is perfectly aligned with the sticks at the bottom at each frame.

Now you turn on 3d motion blur in Render Settings and you'll get this motion-blurred animation.

Pic 2. Master beauty 3d motion-blurred