Reflection, Refraction & Transparency

A CG Integration breakdown with costume shaders.



In this project we had to create a gem material in Nuke that has a combination of subsurface scattering and transparency to it. In class, we had many options to choose from and these stones didn't necessarily had to be the references for our projects but they served as a guide how to combine materials rendered from Maya inside Nuke, using costume masks. I decided to shoot my own footage for this project as well, to have more understanding and control. I used a Cannon 5D Mark IV and had a 3 inch grey ball and chrome ball, a 4 inch cube and the reference stone with me on set.

I used a dragon Stanford model for this project becuase it has a complex geometry with a lot of cracks and cravases which helps showing the depth of the shaders. As you can see the geometry is a mess, so setting up the UVs would be a great challange...

Whenever I work on a CG integration project in Maya, I like to use render layers to give me options when it comes to compositing. These are the render layers I used :

One of the first masks we were recommnded to use was based on fresnel or IOR (Index of Refraction), which could affect the material based on the angle we are looking at the 3D model. To create such masks I used a node called samplerinfo with the facing ratio output and added a color ramp with green and red channels to determine the fallof. The main idea was that the red areas would have more of a subsurface feel rather than the green ones, which is more transmission.

I spent the majority of this project with experimenting with shaders in Maya and combining them properly. For on of the early versions I wanted to see how the dragon would look if it was only made out of a transmissive material. The inside was controlled by a 3D volume with noise and the shadow was simply merged under the dragon.

For the final version I used a more complex shader and changed some of its settings using layer overrides in render layers. These are just the settings I used in the Beauty layer.

The SSS and Transmission settings on their own seperate render layers look like this:

To have more flexibility for the inside of the shader, I created an extra render layere and called it Volume. This is basically a cloud with green and blue colors in it that gives me the abilty to add variety for the inside of the object whteher I want SSS or Transmission.

Once all elements render out, I just had to put them together in Nuke and color correct some of the passes I wasn't happy with. To make a certain part only one shader I used a merge(out) with the masks I created to remove those areas and merge(plus) something else in their position.

One of the challenges in this project was to create the caustics for the shadow. Most translusive materials create these light alterations in the shadow (might change color too) and make the composite more appealing and photorealistic. With the help of the aiFacingRatio node I could add this variety on a separate render layer and change its color. However, to utilize it I had to use the green channel of it as a mask in Nuke to get even more flexibility of the color.

Having everything rendered out and put into Nuke, here's how the final nodegraph and breakdown look like:

Overall, this project was more Maya heavy for me than Nuke. Getting the shaders ready to work was a challange but definitely a great experiment. One of the major apsects I learned is that not everything I render out from Maya has to be used as it is. Sometimes, these renders will serve as masks which is just as important as the bauty layer and creating more of thses layers will give you more flexibilty. This is something I will utilize in future projects.