Glass: Match to Live

- All Elements, Glass blown by Shawn Fortner

Some of the most difficult materials to match to reality are sub-surface scattering and glass. In this piece I tackled a man made - small glass candle holder. This came with many challenges as I tried to mimic it’s imperfections and unique elements. I've included some information below about how I set up my scene, and sent out my renders to make this end image.

Collecting Data to Perform the Match

Before I could match my object, I had to first take a picture of the object in the environment I wanted. Done and Done. But! There is so much more that you should do to get a proper match.

Your Camera - After you have all the necessary data and you have your digital model built, you can then go on to match the camera. First, make sure that you have the correct focal length and camera back info into the maya camera. Then insert a stand in ground plane. Ideally you would want to take an image with a box in it, or any object that you can get precise xyz lengths for. In my case I measured the width of the floor planks and the height of the baseboard.

The Image Map - Since my Object is highly reflective and refractive I needed an spherical map to project the real objects environment. To clean up where the the ball shadowed I took a top down photograph for editing.

The Object itself - To Guarantee that the 3D object has the same proportions as the original, it's best to try scanning the original object if possible.

Making the Digital Copy

Digital Camera Setup- Be sure that when you shot your back plate that you also wrote down your Focal Length, this will be very important for when you try to match your camera.

Key Light Setup - If you disregard my environment, my lighting setup is pretty simple. I have one direct source, the Sun. To align the light source it was easiest to open up an IPR render window and manipulate the light until the shadows matched. Another more technical way to get this information is by recording the time and date of your image, and then looking up the azimuth of the sun.

Environment R&D- Since the realism of my object heavily depended on my reflections and refractions, I put extra time and care into making sure my scene, specifically my ground, was correctly textured. To do this I combined a project of my back plate, two spherical maps, and a top down view of my floor.

Material R&D- Once my environment was properly setup, it was but a matter of dialing in the Glass Shader and painting a couple maps. One of the most interesting challenges though was getting the paint inside the glass looking correct. To achieve my final look I ended up having a separate piece of geometry with a transparency inside the glass with maps to give it a translucent feel.

Render Passes, Layers & Comp

RL1| Basic Color Passes
- Diffuse
- Specular
- Reflectivity
- Refraction
RL2| Soft Shadow
- Ambient Occlusion
RL3| Hard Shadow
- Direct Light Source Shadow
RL4| Caustics
- Caustic Refraction on Surface

To make sure I could tweak all aspects of the glass I sent out quite a few render passes. Once I had my images rendered I followed a 2 stream system where I added the color passes on one side, and built the environment and shadow passes on the other.

Final Image

Probably the best advice I can give someone whose working with glass is to keep working at it. If your stuck with high render times, be sure to lower your ray depth and sampling. If that doesn't help, try applying your shader to a ball and see how that responds. There is so much to learn about glass, but the only way your going to learn it is by continuing to work with it.