Nuke Tips – Matching Colour with Grade Node

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It don’t matter if you’re black or white~

So you have a live action plate and CG render and you wonder why it doesn’t mesh together?

Probably the “blackest” and “whitest” point doesn’t match for both elements. This applies to pretty much all elements during compositing of a photorealistic scene.

So for this example in celebration of “May the Fourth Be with You”, here’s a walkthrough of the process.

“You must unlearn, what you have learned”

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1) The original live action plate and CG Stormtrooper.

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2) Object ID pass since the texture on the original CG Stormtrooper doesn’t have consistent black level. This render element is also known as RGB Mask for precise selection during compositing.

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3) The raw Beauty pass rendered using Octane Render for 3ds max.

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4) The helmet with super subtle colour correction to match the body black levels.

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5) The blaster (gun) after colour correction. I also tweaked the gamma so it has a more contrasty look.

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6) After tweaking both the blaster and helmet, this is where I colour match the CG Stormtrooper with the live action plate.

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7) Noticed the funky pixels halos around the CG Stormtrooper in the previous steps? This is where I premultiply it to get rid of the halos.

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8) The colour-corrected CG Stormtrooper now sits nicely in the live action plate.

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9) This is where you apply your choice of colour grading either by yourself or by handing off to the colourist (read more on what does a colourist do over at No Film School).

The Holy Grade Node

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Tip of the day: Hold down CTRL while click drag on the viewer to colour pick in Nuke.

The function that you’re looking for is the following four parameters:

  1. Blackpoint (Usually you don’t need to adjust this but this set the the colour that you chose as the “blackest” point)
  2. Whitepoint (Vice versa as Blackpoint description. The colour that you picked will be the “whitest” point)
  3. Lift (This is where you pick the “darkest” pixels on your live action plate (or selected part of your live action plate if there is various lighting condition))
  4. Gain (Same as Lift, pick the “brightest” pixels from the live action plate to match the

Once you set the colour of your choice, play around with Multiply and Gamma for the final fine-tuning.

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Here’s the final render of the whole sequence (no sound). Enjoy!

Nuke Tips – Easy Access to Gizmo

Easy Access to Gizmo? Show me!

Lately I’ve been using gizmo a lot as I need to automate quite a number of process (read: doing things the lazy way in a quicker way).

Back then, I’ve been doing the menu.py method to add in new gizmo in Nuke. Here’s the tutorial link to said method at Nukepedia.

If you find the long wall of codes and text are intimidating, keep on reading!

The Gizmo Laundry List

  1. Firstly, make sure you have the gizmo files ready and copy to .nuke folder which are located in the Users folder in Windows (I’m unsure where it is located on OSX and Linux but look for the very same folder).
  2. Locate the Other icon on the default toolbar -> All plugins -> Update.
  3. Now press Tab to invoke the search popup for new nodes and type in the name of the gizmo to use it! Remember it is not case-sensitive.

There is tons of useful gizmo available at Nukepedia so do check it out!

ATTENTION: Using this method, you will enable every existing nodes that is available in Nuke so don’t get confuse when you are looking for the right node!

If text is boring, here’s the guide in picture format:

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Nuke Tips (of the month) – Vector Blur or 3D motion blur?

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Jingle Blur, Jingle Blur, Jingle all the way!

I’m surprised that after working full time as an FX artist at a subsidiary of a large Japanese studio, tackling motion blur in compositing stage can be problematic if the subject moves in Z axis which is where 3D motion blur triumphs.

For my personal project, I’ll analyse every shots and see if the use of 3D motion blur is necessary to improve the overall photorealism.

So in this very brief Nuke Tips, I’ll explain the difference between vector blur and 3D motion blur during compositing.

Wheels of blurry

For this demo, I’m using Octane Render for 3ds Max to generate the velocity pass. You need to look up in your preferred renderer documentation on how to output velocity pass. The default 3ds Max scanline renderer support native velocity output through the G-Buffer when saving as EXR files.

In Nuke, the Vector Blur node allows you to blur a subject either through the Transform node values or by piping in velocity pass from an external renderer

Sadly there is no way to output velocity pass together with “the motion blur” result in Octane Render so be aware that it is not a glitch or bug. Just output the velocity pass with a really high value of max velocity if your object moves really fast. I use a value of 512 for this demo and make sure to output it as 32-bit float EXR!

For the 3D motion blur, I simply enable Motion Blur in Octane Render settings as long your object has animation (which you need to enable object motion blur and moveable proxy in the object properties).

Refer to the following screenshots for the settings that I used for this demo:

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Do take note that the motion blur also blur the alpha channel so if you’re dealing with complex compositing, make sure to render the background as matte to reduce background bleeding in the beauty render.

Blurring the edges in Nuke

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Please refer to the Node Graph in the screenshot above on how to setup the Vector Blur using the Velocity pass from Octane Render. In my example, I shuffle the Velocity pass into the Forward channels but you can shuffle it into the Motion, Velocity, Distance or your preferred channels.

Also do read the official documentation on using Vector Blur at The Foundry site as I’ll not explained every single settings in this article.

Remember to set the calculation method to Forward and enable the Alpha premultiplication since the Velocity pass from Octane Render has been premultiplied. Failure to do that will create a streak/jaggy edges.

So Vector Blur or 3D Motion Blur?

Typical 3D motion blurring!

This is where things start to go awry as it rotates really fast where the motion blur failed in blurring curve motion. Also take note of the shadow on the ground where it remains crisp as there is no velocity information since it remain static in the scene.

The velocity pass in motion. A reminder that there is only two channels that will be output in velocity pass aka Red and Green channels.

Pros or Cons?

Vector Blur

  1. Flexibility in controlling the amount of blurriness during compositing.
  2. It works great… only in X and Y axis.
  3. Anything less than 32-bit Float values means less than accurate blurring process. BE WARNED. (although you can still get away with 16-bit Half Float depending on the situation)
  4. Can’t do rotational blurriness accurately (hence why the subject for this demo is a wheel!)
  5. Can be problematic when dealing with various overlapping subjects/limbs/etc. I did not prepare examples for this case but just imagine an arm crossing over the chest. Vector Blur will failed in blurring the arm edges accurately when it overlaps the chest.

3D Motion Blur

  1. Accurate because it blurs in actual 3D space!
  2. You still need to worry if the shutter angle changes during production through client/supervisor/director feedback AKA re-rendering.
  3. Depending on your choice of renderer, 3D motion blur is EXPENSIVE or nearly FREE of rendering time costs.
  4. Can be problematic when dealing with various overlapping subjects/limbs/etc too! This is more of a headache for the compositor though depending on their situation.

Nuke Tips – Flipbook Methods in Nuke

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Flipping table I mean flipbook methods in Nuke

Every major update to Nuke feature big improvement to the Viewer playback performance.

Previously, FrameCycler Pro is bundled together in Nuke as a flipbook software although one can configure other flipbook softwares such as JefeCheck or Pdplayer.

Although with Nuke 9, The Foundry develop their own flipbook integrated in Nuke which I rarely used as I prefer to rely on the Viewer to double up as my very own flipbook player.

I’ll be sharing my own approach in flipbooking a sequence for preview purpose.

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