Part 4: Use of The ReelSmart Motion Blur Plugin to Convert Motion Vectors Into a Motion Blur
This section is where it all comes together. The sequences generated in the previous sections will now become an animation with an adjustable motion blur by applying ReelSmart Motion Blur in the compositing application.
Other Sections of This Tutorial
Step 1. Import the Sequences
Tip: As you import your frame sequence for the 2d motion vectors, make sure that color correction is not applied to the layer. It is important that the vector colors are not remapped. In After Effects you can check on this by doing the following:
“Project” window (files/assets area) -> Right Click the vector sequence -> Interpret Footage -> Color Management Tab -> Preserve RGB checkbox ON
This will ensure that whatever RGB values are in the original sequence will be preserved no matter what color space is used in your project. Thanks to Pierre at RE:Vision for bringing this to my attention.
I’m going to assume that you already know how to bring sequences into your compositor. With After Effects, it’s a little tricky using high color and .EXR, but you just need to do the following:
- Put each sequence on the time line.
- Apply the 3D Channel -> EXtractoR plugin.
- Select the correct channels in the .EXR file for that pass.
If you are confused, you can learn more about it in this post.
Here’s the only tricky and important thing about this step: If you are using the lm_2DMV shader technique, then you simply need to assign the R channel to the red channel and the G channel to the green channel. (Blue is not used.)
However, if you have used the Mental Ray 2D Normalized Motion Vector pass, then instead of R and G, you will have X, Y, and Z in your .EXR channels. Go ahead and assign X to your red channel and Y to your green channel. (Blue is still not used.)
Step 2. Apply the Matte Layer to the 2D Motion Vectors
If you are using After Effects, then you need to precompose the vector layer with the matte layer and then pick the matte layer as a luma matte for the vector layer.
Step 3. Apply the Matte Layer to the Foreground Layer
Do the same thing as above: Precomp your foreground beauty layer with its matte layer (if needed). If you have geometry that’s occluding your motion-blurred foreground (such as my yellow railing), it needs to be matted last and needs to be a separate matte on top of a precomp of everything else.
Step 4. Assemble It
Make an assemble comp and add the background, the foreground with matte precomp, and the 2D motion vectors with matte precomp. If you have made a composite render with blur from Maya for comparison, then add that too. Turn everything off except the background and foreground layers.
Step 5. Apply the ReelSmart Motion Blur Vectors Plugin to the Foreground Sequence
Go to to the foreground beauty precomp and apply:
Effect -> RE:Vision Plug-ins -> RSMB Vectors 3.x
Remember the setting you used for Normalize or Max Disp. in the Maya motion vector settings? Plug that number into the Max Displace area of RSMB. For the purpose of this tutorial, that value is either 512 or 1024, depending on which method you used to generate the vectors. The two methods of generating motion vectors deliver identical results. Now go ahead and tune the Blur Amt attribute to taste. It should probably be somewhere between 0.5 and 1 if you want to get close to the Maya motion blur with default camera settings. I chose 0.7 according to what looked good to me.
Step 7. Done!
This is a nearly identical result to the Maya motion blur, though there is a slight quality difference. Remember that one of the great things about this method is that you can now use as much motion blur as you want!
If you want to see the finished animation then click on the QuickTime icon at the top of this page.
If you have an insatiable thirst for more motion blur knowledge, there’s some additional information on these pages:
ReelSmart Motion Blur Support Page
Detailed information about using the ReelSmart plugin in different ways
la maison lm_2DMV Shader Main Page
Information about how the shader works, as well as usage instructions for XSI users
Some good info about using .EXR files with After Effects