Nuke Tips – Kronos, MotionBlur, Oflow, or VectorBlur?

The last draft for this article dated back to Jan 25, 2016… time to revive it!

Kronos, MotionBlur, Oflow, or Vector Blur? I’m blur…

The great thing with Nuke is that we have many ways to skin a cat problem.

I’ll be focusing on adding motion blur to CGI FX elements like fire, blood and debris. Yes you can abuse I mean use Kronos and Oflow for adding motion blur instead of slowing down footage!

Time to explore the various methods and see which one make or break depending on the situation.

Do not get confused with MotionBlur2D and MotionBlur3D which are not designed to generate motion blur by analysing the image sequences. MotionBlur2D uses the Transform animation while MotionBlur3D uses the camera animation to generate motion blur.

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Houdini Tips – Matching Mantra Motion Blur with Vray Motion Blur (3ds Max)

Matching Mantra Motion Blur with Vray Motion Blur? That’s wicked!

So I’ve been working across two 3D package for my upcoming demoreel and one of the issue is to find the right settings for Mantra to match as closely as possible with the motion blur from Vray in 3ds Max.

Since I’m doing all my FX works in Houdini, I did impose a rule to not transfer any of the FX caches from Houdini into Max for the final render.

Actually that is a lie as I did render one FX shot (fracture) as I need to reuse the Vray material in 3ds Max. The rest though are rendered using Mantra and composited over the Vray renders in Nuke.

What’s the magic chant to match the motion blur?

If the camera and Vray motion blur in Max are at default value, proceed as usual.

If not… maybe look at the following steps and see if you can figure out the right value to use for Mantra.

First, make sure the imported Alembic from Max are unpacked.

Don’t forget to put a Trail SOP set to Compute Velocity and also enabling Compute Angular Velocity like in the screenshot above.

This assume you import the camera from Max (and the Alembic geometry and camera are correctly scaled as covered in my prior Houdini Tips)!

Configure Mantra Renderer with the following settings:

  • Allow Motion Blur: On
  • Geo Time Samples: 2
  • Shutter Offset: -2

As usual, do a test render and compare with the Vray render!

The following animated GIFs are self-explanatory.

OK it is not exactly 100% match. Maybe 97-99%?

The rest can be fix in compositing stage if required.

Any reasons for doing this thingamajig instead of round tripping from Houdini to Max?

Basically if I were to render in Max using Vray, I need to match the look of the Pyro FX shader aka spending a long time tweaking the Vray VolumeGrid shader…

Unless you already prepared presets for both Pyro FX and Vray VolumeGrid shader that achieved the same look, I say working directly in Houdini and adjusting in compositing stage is faster and flexible.

Exception for situation that requires interaction with elements in Max only (like Fume FX or BiFrost) but a workaround for it is to convert the caches to VDB and use your preferred renderer.

So it is up to you (or your team) to figure out the best solution to a problem!

Further Reading

Matching Mantra motion blur with Vray motion blur ? – https://www.sidefx.com/forum/topic/34051/

http://www.sidefx.com/docs/houdini/render/blur.html

https://docs.chaosgroup.com/display/VRAY3MAX/Volumetric+Grid+%7C+VRayVolumeGrid

Nuke Tips – Hide Node Input

Hide Node Input or Node Hide Input or Input Node Hide

When your Nuke script start to grow bigger and complicated, it is time to start to organise the node graph flow for better readability and remove redundancy.

I don’t feel like writing a lengthy explanation on when or why to use it but here’s a bullet list on the usefulness of hiding node input:

  • Reduce redundancy by avoiding duplicates “copy” of the same node
  • Ensuring a cleaner and easier to read Node Graph (if only I can keep my personal belongings as tidy as the node graph–)
  • Avoid potential Nuke script corruption when cloning a node which can happen if you’re not lucky

Potential Nuke Script Corruption?!! Eeeepssss

To further explain on the last point, there are situation where you want to clone a node so you can use it on another part of the comp and prefer the ease of manipulating either of the clone nodes to propagate the same changes.

BUT

It comes with the risk of Nuke potentially screwing up the actual render and one of the way to fix it is to have a copy of it (think Clone Nodes is like Duplicate Special in Maya or Instance in 3ds Max) or linking the master node directly to where you want to use it.

This is where the Hide Node Input comes in handy!

Quick GIF Demonstration