CG Compositing Series – 2.2 Material AOVs (Bonus) – Cross Polarization Photography

Download the PDF here ^

Cross Polarization Photography

In this Bonus video on Material AOVs, I cover Cross Polarization photography, which is a technique that allows us to separate diffuse and specular components of everyday objects. I go into detail about the lighting concepts that allows this separation to occur, and how it’s used to gather reference and textures to recreate objects in 3D.

Electromagnetic Spectrum

  • Visible Light is a section of the Electromagnetic Spectrum
  • Light / Color is represented in 2D as a Sine Wave with a specific frequency

3D Light Wave Representation

  • The 2D representation looks a bit different in 3D space, since the light waves could be oriented in any and all directions along it’s forward axis
  • A light beam with randomly oriented Light Waves is referred to as an Unpolarized Light

Linear Polarization of Light

Linear Polarization isolates one specific angle of the light wavelength, only allowing a portion of the light waves that were oriented in the that direction, through the filter

Cross Polarization of Light

  • Cross Polarization uses 2 Polarizers that are perpendicular to each other, effectively eliminating the light wave passing through.
  • The first polarizer isolates the light wave to only one orientation
  • The second polarizer, if parallel to the first, continues to allow the polarized light through, but as it becomes more perpendicular, the light gets dimmer, and eventually blocked entirely

Polarization Upon Reflection

  • When unpolarized light hits a reflective surface (with a refractive index different than the surrounding medium, such as glass, snow, or water) the specular reflection is polarized or partially polarized to the angle perpendicular to the plane of incidence. (along the surface)
  • How polarized the Reflection depends on many factors; angle of incidence, material type, etc.

Brewster’s Angle

  • At a specific angle, the specular reflection is completely polarized to the angle perpendicular to the plane of incidence. 
  • This angle is known as Brewster’s Angle.

Unpolarized Diffuse Component

  • Only the Specular Reflection has the effect of the Brewster’s Angle Polarization 
  • The Diffuse Component is Unpolarized, because they are newly emitted photons from excited atoms
  • This phenomenon only happens when the light is reflected off dielectric materials such as water or glass.
  • When reflection occurs on a metallic surface, no Brewster Angle nor refracted light exist

Polarized Specular Reflections

  • Placing a Linear Polarizer filter in front of the observer will Cross Polarize some Specular Reflections if angled correctly.  It blocks the polarized reflection light wave from shining through it
  • This is how Polarized Sunglasses are able to eliminate harsh glares and reflections from dielectric surfaces such as glass, water, snow, etc.

Cross Polarized Photography

  • If you polarize the light source, the Specular Reflection is also polarized (because it’s a mirror reflection of the light wave).
  • The Diffuse Component is unpolarized light because it is newly created lightwaves oriented randomly.  Adding a second polarizer on the Camera, means we can block the Specular Component entirely depending on the angle of the Polarizers.  When the 2 polarizers are parallel, we see Specular + Diffuse , and when they are perpendicular we will see only Diffuse.

  • The Parallel Polarized image gives use the Specular and Partial Diffuse (only Diffuse Component of that orientation)
  • The Cross Polarized image, negates the Specular, and only shows the other half of the Diffuse Component
  • To isolate the Specular Component, take Parallel Polarized image (Specular + Partial Diffuse) and minus the Cross Polarized image (Partial Diffuse).  The Diffuse Components cancel out, and all that is left is the Specular Component

  • This Cross Polarization Photography allows CG Artists to collect photogrammetry data of everyday objects, and allows  them to recreate these objects in 3D with accurate Diffuse and Specular Maps for Physically Based Rendering
  • What seems just like theoretical Diffuse/Specular Render Pass separation in CG is actually a lighting phenomenon that can be separated into Diffuse and Specular Components in the real world

Notice that Metallic Materials have no real Diffuse Color to them, They show up as completely black in the Cross Polarized result.  Metals are entirely surface level Specular Reflections

  • Occasionally, the Diffuse Components of the Parallel Polarized and Cross Polarized Images are slightly different, (brighter or a shift in color for example)
  • In this case, when we minus the Cross Polarized result from the Parallel Polarized result, we are left with leftover color information or artifacts.  The Specular Component can be desaturated to compensate for those color artifacts
  • Remember that in Dielectric Materials the Specular Component is the same color as the light source, but Metals can sometimes tint the Specular color depending on the type of Metal

Light Stage: Cross Polarization

  • The light stage used in films is capturing evenly lit, cross polarized textures of various facial expressions.
  • This helps separate Diffuse and Specular and aids in tracking features of the face


Here are some great websites that go into more detail about polarizations:

Reflection and Polarization of light in machine vision – Toshiba Teli Corporation

FilmicWorlds – How to Split Specular and Diffuse in Real Images

Polarization Explained: The Sony Polarized Sensor

Youtube – Cross Polarization Tutorial: Removing Specular Highlights and Reflections – Classy Dog Studios

Youtube – Cross Polarisation Explained by Grzegorz Baran

Youtube – The Key to Cleaner 3D Scans: Cross-Polarization – William Faucher

PetaPixel – Cross Polarization: What It Is and Why It Matters

optometryzone – How do Polarised glasses work?

Youtube – ScholarSwing – 16 – Class 12 – Physics – Wave Optics – Polarisation

Youtube – Khan Academy Polarization of light, linear and circular | Light waves | Physics

Youtube – xmtutor – What is Polarisation?

Youtube – xmtutor – Third Polariser

The Light Stages and Their Applications to Photoreal Digital Actors – PDF

Light Stages

CG Compositing Series – 2.1 Material AOVs – Diffuse, Specular, Emission

Material AOVs

In this post we are going to be focusing in on the Material AOVs Category.

Levels of Complexity

There are different levels of complexity to rebuilding Material AOVs into the beauty, and it all depends on how much flexibility and control you want with the cost of complexity and speed.


  • Diffuse
  • Specular
  • Emission
  • Other – Refraction / True Reflection


  • Diffuse
    • Direct Diffuse
    • Indirect Diffuse
    • Sub Surface Scattering
  • Specular
    • Direct Specular
    • Indirect Specular
    • Reflection
    • Coat
    • Sheen
  • Emission
  • Other – Refraction / True Reflection


  • Diffuse
    • Direct Diffuse
    • Indirect Diffuse
    • Sub Surface Scattering
      • Raw Diffuse
      • Albedo / Color / Texture
  • Specular
    • Direct Specular
    • Indirect Specular
    • Reflection
    • Coat
    • Sheen
      • Raw Specular
      • Albedo / Filter / Texture
  • Emission
  • Other – Refraction / True Reflection

Diffuse, Specular, and Emission are the Foundational Categories, and the complexities are subdivisions of the Diffuse and Specular Categories

So let’s first focus on the Simple category of Diffuse, Specular, and Emission and really break those down and understand them fully. This will make the future subdivisions easier, familiarise us with terms and concepts, and help us have a grounded foundation of knowledge for what we are adjusting when using these passes.

The full presentation from the video can be downloaded here in pdf format, for those who want to keep or study it offline:

Adjectives of Specular, Diffuse, and Emission


  • Reflection
  • Mirror
  • Shiny
  • Glossy
  • Wet
  • Metallic
  • Highlights
  • Pings
  • Crisp
  • Sharp
  • Polished


  • Soft
  • Flat
  • Ambient
  • Natural
  • Rough
  • Earthy
  • Organic
  • Matte
  • Weathered
  • Dull


  • Bright
  • Radiant
  • Luminescent
  • Glowing
  • Self-Illuminating
  • Incandescent
  • Electric
  • Beaming
  • Shining
  • Luminous
  • Illuminated


  • Emission is any object, material, or texture that is actively emitting light into the scene
  • This includes any Lights, Super-heated metals, or Elemental FX like fire/ sparks / lightning / magic etc
  • Neon Lights, Screens, Monitors are all examples of real life Emission objects

Diffuse vs Specular

Specular – Surface Level Reflections

Diffuse – Light passes through surface and interacts with the material at a molecular level, Scattering and Absorption allow certain colors to re-exit and scatter into scene

Let’s talk about Specular first andSurface level Reflections


Law of Reflection

  • The angles of incidence is equal to the angle of reflection

Smooth Surface – Specular Reflections

  • Light Beam = a bundle of parallel light rays
  • Light Beam remains parallel on incidence and parallel on reflection

Planar Mirror and Virtual Image

  • An Image created by planar specular reflection that does not actually exist as a physical object is referred to as a Virtual Image.
  • The Virtual Image appears to be located “behind” the mirror
  • Virtual Image distance =  Object to Mirror + Mirror to Observer.
  • Speculum is the Latin word for “mirror”, which is where “Specular” derives from

The people are witnessing a virtual image of themselves looking back, that is double the distance from them to the mirror. The light travels from them -> to the mirror, and then from the mirror -> back to their eye

Notice the reflected virtual image of the chess piece is in focus, even though the real piece (in the foreground) is out of focus. The camera lens is respecting the mirror’s virtual image distance, even though the mirror itself is out of focus.

Here you can see a ground plane mirror appearing to invert the tree in it’s virtual image

Rough Surface – Diffused Reflection

  • The uneven surface causes the Incidence Rays to hit at different angles
  • The outgoing reflection rays scatter in different directions

Here you see some examples of different CG materials along the Roughness / Glossiness spectrum

Wet Surface Reflections

When a surface is wet, the water fills the gaps and flattens the surface and causes more a specular reflection

Microscopic Surface Details

In these slides and examples we are discussing surfaces at a microscopic level. You might think a piece of paper looks smooth, but under a microscope it has quite a bit of roughness to it, which is what makes it so evenly lit and diffuse.

Metallic vs Dielectric Surfaces

The diffuse and specular terms describe two distinct effects going on.  The Light interacts with materials differently depending on if the material is a metal, or a non-metal (Dielectric)

Dielectric – Absorbs and Scatters light

Metallic – Does not Absorb light. Only Reflects

Dielectric (Non-Metal)

  • Light penetrates the surface level and the molecules of the material absorb and scatter the light within
  • The light photons excite the atoms they hit below the surface. Some of the light is absorbed, and this energy is converted to heat. Then new light rays (photons) are emitted from the excited atoms. Those might excite nearby atoms or exit the surface as new photons. These new photons are same color as our material.
  • The Base Color Texture (Albedo Map) – determines the color of the diffusely scattered photons from excited atoms.  It’s the color that is scattered back out and not absorbed by the material


  • Does not Allow light to penetrate the surface and does not Absorb light. They only Reflect light on the surface
  • Metals can be thought of as positively charged ions suspended in a “sea of electrons” or “electron gas”.  Attractions hold electrons near the ions, but not so tightly as to impede the electrons flow.  This explains many of the properties of metals, like conductivity of heat and electricity
  • The incoming photon does not excite the atoms, but bounces directly off the electron gas
  • The Base Color (Albedo) is used to describe the color tint of the specular reflection
“Electron Gas” Model

Notice the Specular Reflections are tinted a certain color depending on the metal type:

On Dielectric Plastic balls, the material color changes, but notice the specular highlights are the same color, maintaining the color of the light or surrounding environment.

Comparison of a Metallic vs Dielectric Material in CG

Chrome Sphere and Diffuse Ball

Used as a reference to see what something 100% Smooth and Metal (Specular) and 100% Rough and Dielectric (Diffuse) looks like in the scene.




The diffuse component includes light that penetrates the surface and interacts with the materials molecules. This happens in different ways in the real world


  • Light passing through the material / surface
  • Can be thought of as “transparency”


  • when light changes angles as it goes through different materials or mediums


  • When certain wavelength colors of light get absorbed by the material


  • when light is dispersed in many directions when it comes into contact with small particles or structures in the material

Simplified Diffuse Calculation

When the distance that light travels beneath the surface is insignificant and negligible, the calculation can be simplified by the renderer and just calculated at the surface point where the light hits. It uses the Base Color Texture (Albedo) as the Diffuse Color that will scatter. 

Sub Surface Scattering

When the distance the light travels beneath the surface of the material is significant, the interior scattering must be calculated. This is referred to as Sub Surface Scattering (SSS)

Physically Based Rendering Terminology


  • Base Color Texture Map
  • On Dielectrics (non-metal) refers to color of material
  • On Metals, refers to the color tint of the specular reflection
  • Texture map is without highlights, shadows, or ambient occlusion

Metalness Map

  • What area is metallic or not. (will use Albedo Color differently). Usually Black or White

Roughness (Glossiness) Map

  • How blurry or how sharp the reflection will be

Real life objects often have a diffuse and a specular component

Diffuse describes the color of the billard balls, but the specular highlights are all the same color (reflecting the color of the light above the table)


  • There is also Iridescent materials that change specular color depending on viewing angle.
  • Iridescence is a kind of structural coloration due to wave interference of light in microstructures or thin films.

Nuke – Simple Material AOV setup

We can break our fruit bowl render into the 3 simple components, Diffuse, Specular, and Emission. They layers look like this:

You can download the nuke script shown in the Tutorial. I created the mini setups for the 3 different types of renderers, Arnold, RedShift, and Octane. Dividing the Beauty render up into their 3 Diffuse, Specular, Emission Components, and Recombining them.

Download nuke script project file

If you haven’t downloaded the FruitBowl Renders already yet, you can do so now:

You can Choose to either download all 3 FruitBowls at once: (1.61 GB)

Or Each FruitBowl Render Individually for faster downloads: (569.1 MB) (562.8 MB) (515.4 MB)

The project files and the Renders are separate downloads, so if you have already downloaded 1.1 What and Why files or the Fruitbowl Renders, there are a couple ways to combine them to work.

  1. Either add the .nk script to the previous package (in the folder above SourceImages, with the other .nk scripts)
  2. Or simply drop the Render files into the SourceImages folder of the new 1.2 project folder

This will help the Read nodes auto-reconnect to the sourceImages for you.


  • Emission / Illumination materials emit light
  • Specular and Diffuse can be separated by Surface Level Reflections and below surface Material Interactions
  • Each individual light ray follows the Law of Reflection.
  • The smoother a surface is, the more mirror-like the specular reflection will be.
  • The roughness of a surface will cause the reflected rays to scatter, and reflection to be blurred.
  • Metallic materials do not allow light to enter the surface.  They only reflect light
  • Dielectric materials allow light to enter the surface.  Light rays are refracted, absorbed, scattered by the materials molecules. Certain color wavelengths re-exit the surface in random directions, which is what we perceive as the materials color
  • Albedo – Base Color Texture. On Dielectrics – color of material | On Metals – color tint of the specular reflection.
  • Sub Surface Scattering is when light below the surface travels a significant distance before re-exiting
  • Iridescent materials tint the color of the specular reflection depending on viewing angle.

References, Resources, Credits

Firstly, Thanks to Pexels for providing such a good resource for stock reference images

I did a hell of a lot of research on this topic before creating the video, I really encourage you to dig a little further and explore the topics more using these great resources:

Naty Hoffman

Youtube – 2015 Siggraph Presentation – Naty Hoffman – Physics and Math of Shading | SIGGRAPH Courses

2015 Siggraph Presentation – Naty Hoffman PDF Paper:

Khan Academy

Video – Specular and diffuse reflection

Video – Specular and diffuse reflection 2

Video – Virtual Mirror

Scientific websites:

Website – The Physics Classroom – Specular vs Diffuse Reflection

Youtube – The Physics Classroom – Specular vs Diffuse Reflection

Website – Olympus LS – Interactive Explanation of Diffuse and Specular

Youtube – Specular vs. Diffuse Reflection, Incident and Reflected Angles | Geometric Optics | Doc Physics

Website – Erika Jame Site – Reflection of Light

Youtube – Specular vs Diffuse Reflection | Physics with Professor Matt Anderson | M27-05

Youtube – Physics with Professor Matt Anderson | Physics with Professor Matt Anderson

Youtube – Reflection of Light Explained Clearly – MooMooMath and Science

CGI Blog Posts

Master of Light – Vector Perez Mindmap

Website – CG Learn – Physically Based Shading

Website – PBR Texture Conversion – Marmoset

Website – Basic Theory of Physically-Based Rendering – Marmoset

Website – JORGEN HDRI Explained

Website – THE PBR GUIDE – PART 1 – Adobe Substance 3D

Website – Material physics in context of PBR texturing – HandlesPixels


Website – Tutorial: Blender – Quixel/Substance – Sketchfab: A Proper PBR Workflow

Website – Omniverse MDL Materials

Website – What is an Albedo Map and How to use it ? by Alex Glawion

Website – to buy chrome sphere and diffuse balls – VFX Super Store

Wesbite – Physics Stack Exchange – Why don’t dielectric materials have coloured reflections like conductors?

As always thank you for watching, hope you learned something. More videos to come.

CG Compositing Series – 1.2 Categories of Passes

Download the project files for this video here to follow along:

1.2 Categories of Passes Files – Nuke scripts and slides only (2.8 MB)

If you haven’t downloaded the FruitBowl Renders already yet, you can do so now:

You can Choose to either download all 3 FruitBowls at once: (1.61 GB)

Or Each FruitBowl Render Individually for faster downloads: (569.1 MB) (562.8 MB) (515.4 MB)

The project files and the Renders are separate downloads, so if you have already downloaded 1.1 What and Why files or the Fruitbowl Renders, there are a couple ways to combine them to work.

  1. Either add the .nk script to the previous package (in the folder above SourceImages, with the other .nk scripts)
  2. Or simply drop the Render files into the SourceImages folder of the new 1.2 project folder

This will help the Read nodes auto-reconnect to the sourceImages for you.

Often there are a lot of renders passes to sort, and it’s useful to divide them into categories based on their functions. We can divide up all the render passes by how they are used.

There are 2 Overarching Types of CG Passes:

  1. Beauty Rebuild Passes – Will recreate the Beauty Render
  2. Data Passes – Helper passes

There are 4 Main Categories of CG Render Passes

  1. Material AOVs
  2. Light Groups
  3. Utilities
  4. IDs

Material AOVs

  • Used to adjust the Material Attributes (Shader) of objects in the scene


  • Diffuse, Specular, Reflection, Sub-Surface Scattering, Refraction, Texture/Color, Emission, Raw Lighting, etc.

The passes in this category should add up to recreate the beauty render, as demonstrated in the previous video

From now on in the series, if I only say “AOVs”, I am referring to this category here. I will try my best to say Material AOVs, but I am so used to it being in my terminology and don’t find the AOV “all render pass” definition very useful.

Material AOVs are passes related to the shader or material from the 3D application. When we use these passes, we are wanting to manipulate the material or the shader of the object

Extra Research on Materials:

Material Attributes & Properties | 3D Wombat

Textures, Shaders, and Materials | Working with Models, Materials, and Textures in Unity Game Development | InformIT

Sources for Material images:

Everyday Material Collection for C4D – Greyscalegorilla

Realistic Vray Materials I by AlexCom | 3DOcean

Light Groups

  • Used to adjust the Individual lights in the scene


  • Key, Rim, Fill, HDRI, Light-Emitting Objects, etc.

You can separate your lights however you like. Usually you see things like the 3 point lighting set up broken out into different lights. Along with HDRI and light emitting objects separated.

We are usually adjusting light attributes such as temperature and intensity

3 point lighting reference:

Types of Film Lights (and How to Use Them)

Color temperature – Wikipedia

In the fruitbowl renders, I have just named the lights LG01, LG02, etc

References, extra reading material on lights and light groups:

Setting Up Proper AOV’s and LightGroups With Arnold – Lesterbanks

The Basics of Three Point Lighting for Portraits

Three Point Lighting – Morgan Adams Next Gen Blog


  • Used in combination with tools to achieve various effects like defocus, motion blur, re-lighting, etc


  • Depth, Motion Vectors, Normals, Position, Ambient Occlusion, UVs, etc

These do not add up to the Beauty Render


Render Elements – V-Ray 5 for 3ds Max – Chaos Help

VRayNormals – V-Ray 5 for 3ds Max – Chaos Help


  • Used to create alphas or mattes for different areas of the render


  • RGB IDs, Object IDs, Texture IDs, Cryptomattes, etc

The ID category could probably live under the Utilities Category, but I do think the separation of these 2 categories is useful.

ID’s sole purpose is to pull out an alpha or matte channel, whereas Utilities can have many use cases beyond just that.

Many times a texture artist working on characters will make custom texture matte passes that can be rendered out as Texture RGB IDs to help isolate those important parts of the texture for adjustment in comp.

These also do not add up to the Beauty Render

Nuke Script: Breaking out Categories of the Renderers

Nuke script is a node graph representation of the slides table we looked at and I’ve broken out the passes in the categories for each of the 3 render engines.

In order for the LayerContactSheet node to display just the passes for each category, I am removing all layers from the other categories.

Useful Unlimited Remove tool:
K_Remove – Nicolas Gauthier

I’ve also broken out all of the Category’s Layers into shuffles when a text of the layer name into a contact sheet. The main difference would be that this contact sheet would be renderable, and the UI text on the layerContactSheet is not.

In the Beauty Rebuild Passes Section, underneath we have a Material AOV rebuild and a Light Group Rebuild, showing that these passes add up to equal the Beauty.

Please look through the different categories and different Render Engines to familiarise yourself.

Tips and Tricks for making contact sheets

Split Layers

Here are some links to some various Split out layers / shuffle layers python scripts found on nukepedia:

Display Postage Stamps in node Graph

You can turn on the Shuffle Node’s postage stamp in the node graph with
alt + P for a more visual overview

Make a Text node auto display a Shuffle’s layer name

If you use a Text Node, you can display the layer name of the Shuffle it is connected to by entering the following:

For Old Shuffle Nodes:


For New Shuffle Nodes:

[value input.in1]

Multi-Paste to Selection

Paste to Selection python script by Frank Rueter on Nukepedia:

W_Hotbox by Wouter Gilsing – which also contains paste to selection button:

Nicer Contact Sheet

ContactSheetAuto tool by Tony Lyons on Nukepedia:

Multi-connect inputs

To multi-connect inputs on the contactSheetAuto node:

  1. Select the contactSheetAuto node first
  2. Next select the inputs in exactly which order you want the inputs to appear
  3. click the Y key and nuke will connect the inputs

Also works on a Merge node, or any node in nuke.

CG Compositing Series – 1.1 What And Why

Download the project files here to follow along:

1.1 What and Why Project Files – Nuke scripts and slides only (1.2 MB)

You can Choose to either download all 3 FruitBowls at once: (1.61 GB)

Or Each FruitBowl Render Individually for faster downloads: (569.1 MB) (562.8 MB) (515.4 MB)

Place the FruitBowl renders files into the /SourceImages/ folder of the project files and nuke will reconnect the read nodes.

What is a CG multi-pass Render?

A CG Render with multiple extra layers or passes that are to be used to recreate the Beauty Render and to aid in further manipulation while Compositing.

Why do we need it?

  • Renders are Expensive, and Changes are often necessary.  It can take too long to make tweaks and hit notes if you have to re-render the image.  
  • Sometimes it’s faster to find the “look” you are going for in Comp, rather than waiting for the Render results. 
  • Some effects are better achieved in Comp and need additional passes to help achieve the effect in Compositing.

Terms and Definitions

Here are some useful Terms and Definitions that I will be using in this series. They are commonly used in the industry, but sometimes they can be confusing or interchangeable, so I will try and define them for us to help while discussing CG Compositing

  1. Render – The output image or final result of the export calculation from the CG software.
  2. Renderer – The Render Engine or algorithm used to produce the render.
  3. Render Passes – A general term for additional layers exported by the CG renderer meant to be used alongside the main render. These might come contained within a multi-pass EXR or be rendered as separate images.

SourceImages and Stamps

  • All of the read nodes and source images in the nuke scripts will be located at the top of each nuke script under a “Source Images” Backdrop
  • You will need to re-link the files in this area if you are following along

We will be using Adrian Pueyo’s “Stamps” add-on to nuke in order to populate our nuke script with the files in the source image folder.

You can download Adrian Pueyo’s Stamps from Nukepedia:

or from GitHub:

Here is a direct link to the Stamps Online Documentation:

Different Types of Renderers

Common Renderers

  1. Arnold
  2. Redshift
  3. Octane
  4. V-Ray
  5. Cycles/Eevee
  6. Mantra
  7. Renderman
  8. Maxwell

Reference Websites

Tool Farm | In Depth: Which 3D Renderer is best?

Render Pool | 10 Best Rendering Software by Price

Blender Guru | Render Engine Comparison: Cycles vs The Rest

ActionVFX | Which 3D Render Engine Should I Use for VFX?

Radar Render | Redshift vs Octane Comparison

Ace5 Studios | Render engine comparison – Redshift, Arnold, Octane, Cycles 4D

Thesis Paper:
Konstantin Holl | A Comparison of Render Engines in Nuke – Thesis

Art Cafe | Grant Warwick about Bias and Differences of 3D Rendering Engines – Youtube

Andrey Lebrov | About RENDER ENGINES – Youtube

Default Application Renderers

  1. AutoDesk Maya – Arnold
  2. Cinema4D – Redshift
  3. Blender – Cycles / Eevee
  4. Houdini – Mantra

Third party plugins

  1. Octane
  2. V-Ray
  3. Renderman
  4. Maxwell

Most Common Renderers in 2021

  1. Arnold
  2. Redshift
  3. Octane
  4. V-Ray
  5. Cycles / Eevee

Renderers used and provided in this series

Rendered from Cinema4D

  1. Arnold
  2. Redshift
  3. Octane

Credits and Inspiration

Inspiration for FruitBowl render:

El Profesor | Research: Blender 2.83 CYCLES vs Maya 2020.2 ARNOLD

The still life scene was originally set up in Blender 2.79 with photogrammetry models by Oliver Harries:

ArtStation – Oliver Harries

Oliver Harries Portfolio

GumRoad | Free FruitBowl Photogrammetry Model Collection

Chase Bickel provided us with our Fruitbowl Render Scene and AOV renders for Redshift, Arnold, and Octane

Chase Bickel’s Portfolio

Additional Downloadable Renders

  1. V-Ray Architectural Scene:

Chaos Group | Cryptomattes post with render

Download link:

  1. The Foundry Toolset Examples – Renderman Example Render

Link to the 2GB download package for nukes toolsets content, there you can find the Renderman Example file

Ways to View Render Passes

LayerContactSheet node

  • Shows a grid of all the layers in the input
  • LayerContactSheet is the easiest, fastest, and most convenient way to get a visual overview of all the passes contained in your render.
  • Turn on Show Layer Names to get UI labels of each pass name. This is only a GUI overlay, so you cannot render it out, it’s just for viewing purposes, but it’s great for identifying the pass names we are looking at

The Viewer

  • The Viewer shows an alphabetical dropdown list of channels of the stream where the viewer is plugged into.
  • Remember to set the viewer back to RBGA when you are done viewing that layer
  • You can use the PageUp PageDown hotkeys to cycle through layers in the Viewer
  • Along the bottom left of the viewer, it also lists all the channels separated by commas. It’s good to occasionally look at this part of the viewer to keep track of if you’ve lost your layers from the stream, or you are accidentally carrying layers that you do not need anymore in the stream.

Shuffle node

  • The Old Shuffle node will show a list of all layers in the stream which it is plugged into if you use the “in 1” dropdown
  • Good way to quickly check what layers are in your stream, but not as visual as layerContactSheet

ShuffleCycleLayers python script:

I wrote a tool called “ShuffleCycleLayers” which you can use hotkeys like Page Up, Page Down or + , – to cycle through the layers of the selected shuffle node, just like the viewer layer cycler. Maybe some people will find this handy if they don’t like to changed the viewer channel dropdown and would prefer to cycle through Shuffle node layers

Difference between Old Shuffle and New Shuffle:

  1. Old shuffle only displays list of layers within the stream the input is plugged into
  2. New shuffle displays list of every layer in the nuke script

If you’d like to exclusively use the old shuffle node instead of the new shuffle node, you can add this line of code to your in your User/.nuke/ folder

nuke.toolbar(‘Nodes’).addCommand(‘Channel/Shuffle’, ‘nuke.createNode(“Shuffle”)’, icon=‘Shuffle.png’)

Or, simply type X in the nodegraph and type


hit enter to get the old shuffle

Splitting or Shuffling out Layers

  • Split Layers is a python script that shuffles out all available layers from a selected node
  • This will make 1 shuffle per layer all connected to the source.
  • You can then just view and toggle between all the layers in the nodegraph
  • selecting all and hitting the hotkey alt + p will toggle on the postage stamp feature in all the shuffles, and if you visual thumbnails for all the passes. This can be useful for grouping and organising the passes.

Here are some links to some various Split out layers / shuffle layers python scripts found on nukepedia:

Layers vs Channels

  • Channels are the individual pieces that make up a Layer, or Channel Set. The most common example is red, green, blue and alpha, channels that make up the rgba layer
  • A layer must contain at least 1 channel, but often has multiple channels.
  • Nuke prefers layers to have a maximum of 4 Channels per layer, any more and it has difficulty displaying them in the GUI interface
  • It becomes significantly more difficult to see the channels beyond 4 that are in 1 layer. Nuke’s interface is built around displaying 4 channels.
  • An individual channel in nuke is written as LayerName.ChannelName, to let you know what layer it belongs to
  • Depth.Z for example, in which Depth is the LayerName, and Z is the ChannelName
  • Whenever there is only 1 Channel, this displays in the viewer as the red channel, since it’s the first channel visible in rgba
  • There are also many cases where someone will just refer to it as “The Depth Channel”, where they are recalling referring to the Layer, but since it commonly has only 1 Channel, they are talking about the same thing.
  • Some nodes in nuke deal with layers and channel differently, or prefer to deal with one vs the other
  • A shuffle dropdown displays LayerNames for example whereas a Copy node displays Channels, and therefore the list is much bigger since it is displaying the individual pieces of the layer
  • Blur node “channels” dropdown actually lists layers, and then you can toggle the channels of that layer on/off
  • Basically any node with a mask input is dealing with channels since it only needs 1 channel to function
  • The first 4 channels of a layer are mapped to, and will display as Red, Green, Blue, and Alpha in the viewer, regardless the actual name of the layer. Any more than 4 channels in a layer and nuke has a hard time displaying them
  • A motion pass for example, is describing motion in XY directions. Left-Right and Up-Down. So only 2 channels are needed in the Layer and they display as Red and Green
  • A position pass, for example, is usually describing XYZ – 3D space coordinates, and sometimes the channels are actually named x, y, and z. So Position.x, Position.y, Position.z
  • Since X, Y, and Z are taking up the first 3 channels in this layer, they will display as red, green, blue


  • AOVs stand for Arbitrary Output Variables
  • Arbitrary output variables (AOVs) allow data from a shader or renderer to be output during render calculations to provide additional options during compositing. This is usually data that is being calculated as part of the beauty pass, so comes with very little extra processing cost.

  • They can be considered ”checkpoints” or “steps” in the rendering process. The render engine splits up many calculations while making the final image (Beauty) and is exporting these smaller steps out to disk so we can combine them and manipulate them in Comp.
  • The important thing to take away is the renderer takes these “pieces, these AOVs, and combines them together to form the final Beauty render. We are essentially trying to recreate this process with our CG rebuild, while retaining control over the individual pieces.
  • One of the best things about AOVs is we get them “for free” since the renderer was going to calculate them anyway.
  • AOVs can sometimes be just a “catch all term” for all layers/passes you will render out
  • “What AOVs are you exporting” is a common question, and many 3D applications will use the term AOVs to define any render passes (even though some of them require extra work to get, like ID’s or custom passes)

Differences in the Render AOVs

  • All the renderers are essentially doing the same thing. They are crunching the numbers, using different algorithms, and coming up with the math needed to produce the final renders.
  • Since all the renders are basically doing the same steps / calculations, you just have to get used to what that renderer chooses to name these AOVs or lighting passes. All the passes will combine together and add up to the final Beauty output.
  • There are certain similarities or patterns between all the renderers.
  • Sometimes we’ll be looking at 1 renderer while explaining concepts, but they often translate over to the other renderers in some way. So keep an eye out for the patterns described and apply what is being taught to your renderer’s output.
  • Our renders have differences in amount of AOVs exported and differences in naming conventions for the AOVs

Rebuild Equations per Renderer

  1. Arnold AOV Rebuild:
Beauty = diffuse_direct, diffuse_indirect, specular_direct, specular_indirect, coat, sheen, sss, transmission, emission

  1. Redshift AOV Rebuild:
Beauty = DiffuseLighting, GI, SpecularLighting, Reflections, SSS, Refractions, Emission

  1. Octane AOV Rebuild:
Beauty = Diffuse_direct, Diffuse_indirect, Reflection_direct, Reflection_indirect, Subsurface_scattering, Refraction, Emitters

CG Compositing Series – 1.0 Introduction

For a long time I wanted to release a CG compositing series. Many things stopped me in the past:

  1. Time constraints
  2. Access to good Render examples to work with
  3. Not thinking I had too much to contribute to the subject matter

This series will be focused on answering the following question

How do I best rebuild my CG passes, for the most flexibility as a Compositor?

Download the FruitBowl Renders for the Series

My Friend and fellow artist, Chase Bickel, has kindly provided us with some high quality renders of a FruitBowl to download for free and play around with.

Download the FruitBowl renders now, or I will always post the links at the top of each video and blog post for you to download later:

You can Choose to either download all 3 FruitBowls at once: (1.61 GB)

Or Each FruitBowl Render Individually for faster downloads: (569.1 MB) (562.8 MB) (515.4 MB)

You can place the FruitBowl renders files into the /SourceImages/ folder of the project files folder accompanying each video and nuke will reconnect the read nodes.

For Example:

These Renders are full of common passes you would find in production, including:

  1. AOVs
  2. Lightgroups
  3. IDs
  4. Utility


Start with the Basics –> Build our way to more advanced topics –> End with a proposed template for your CG Rebuild

I will go through different types of AOV passes you would typically find at a studio, what they are, how they are used, and how should think about them in relationship to one another. We will categorise and group different AOVs in order to define them better, and help us find the commonality and patterns between renderers.

This series aims to be useful no matter what renderer your CG comes from, as the principles are the same.

Topics Covered

  1. Differences between Additive and Subtractive Workflows, and the pros and cons of both
  2. Explaining the difference between Material AOVs and LightGroups and how to work with them together seamlessly
  3. This includes an elegant solution to the infamous AOV – Lightgroup paradox
  4. I will cover the importance of making Mattes and alphas, to help us isolate, and automate our CG manipulation. We will go over common utility passes and IDs and show how to do some cool things with them

Using Full CG Render

  • Will not cover how to integrate CG renders into a live-action plate
  • Will focus on the CG rebuild and various methods of manipulation to get the most out of your CG renders

Something for everyone

  • Juniors, Mids, Seniors, TDs, Comp Supervisors
  • There will be knowledge to be learned across all levels
  • Perhaps this will one day be a pre-requisite for a full CG Compositing into live-action plate course

This series will take some time to release all episodes, so please have patience

Thank you!