Reflection on Batman Tumbler - Part 1: Getting Back Reflection

Last week I did a quick Arch & Design shader test for my class. Here is the result:

First, a proper credit. The Tumbler model and textures were created by Henry Chan, a modeling student here at CG Protege.

The reason I carried out the test out was that Julien Lew, a student in the Visual Effects class I am teaching, used the model in his assignment. He worked on the shaders and could not get reflections on the model. In this post, I will share what I found.

Technical details are due. All the images were rendered using 3ds Max 2011, Mental Ray renderer. The shaders are Arch & Design.

I started off with this render.

Figure 1. Starting render. Note the lack of reflection on the body.

I used Mental Ray Daylight system and turned on the mr Photographic Exposure Control. I set Exposure Value (EV) to 10.0. To save effort of selecting a HDR map, I simply used mr Physical Sky map. I used a Photometric light for rim lighting and 8 photometric lights surrounding the Tumbler as fill lights. This way, I can get reasonably good-looking render without using Final Gather. Figure 2 shows my lighting setup.

Figure 2. Lighting setup

The first step in troubleshooting a complex shader is to understand its structure. Next, go through the structure to isolate the cause of the problem. Thanks to Julien's work, we isolated the cause of lack of reflections to the material called "Grey" assigned to the Tumbler body.

Figure 3. "Grey" material

The Reflection Glossiness map slot (highlighted in figure 3) caught my eye. Inspecting the bitmap used as glossiness map, I found that it was very dark.

Figure 4. Bitmap used as glossiness map

To verify, I rendered with the glossiness map disabled (in other words, Reflection Glossiness was constant at 0.5 throughout the surface).

Figure 5. Render with constant glossiness. Note the unnatural bumps on the metal piece near the back wheel.

Now I got reflections on the metal body. Problem solved.

However, another problem arose. One of the metal pieces near the back wheel had strange bumps (I expected it to be smooth). The next post will cover this.

Credit: The Tumbler model and textures were created by Henry Chan.