I recently had the pleasure of teaming up with Josh Parks and Adrian Pueyo in a Foundry Live Panel event on YouTube Live. We talk about advice for people starting in the industry, getting into teaching, how to keep learning, and the importance of networking and community.
Josh, Adrian, and I are friends and former colleagues. I couldn’t be more proud and excited to see them evolve in their careers and see their various contributions to the VFX Compositing Community over the years. It was an honor to talk alongside them in what felt like a typical chat we might have if we all met up in person over lunch.
Back in December we decided to create a space on LinkedIn to be a place for folks to share cool nuke and compositing posts. The LinkedIn news feed can be a little bit of a fire hose of information, and if you don’t save something, it can quickly disappear into the ether. If you’d like to be part of the nuke community there, for articles, tutorials, news, and questions, we’d be happy to have you.
I had an absolute blast speaking alongside Adrian and Josh, and in my opinion, it went by too fast! I hope you enjoy the talk and maybe get a little inspiration out of it. I really hope to chat with them again in the future.
If you’re interested in checking out Josh or Adrian’s websites and courses, here are some links:
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
References:
Here are some great websites that go into more detail about polarizations:
Compositing Mentor 
