Diamond Rendering

3DS MAX Mental Ray

Picture 1. This tutorial explains how to render diamonds in 3D Studio MAX.

04.08.2008 Category: 3D (Rendering)
The purpose of this tutorial is to familiarize you with the following:

• Working with Mental Ray in 3DS MAX
• Rendering diamonds with Mental Ray (picture 1)

I have prepared a simple 3DS MAX scene for this Mental Ray tutorial. In my scene there are two diamond models on a Plane object (picture 2) and a camera. 3DS MAX is on default settings and at the moment the Scanline Renderer produces picture 3.

Prepare a Scene

Picture 2. Two diamond models on a Plane object. This is the starting point for this 3DS MAX Mental Ray tutorial.

Picture 3.This is how diamond models look like when rendered with the default settings of the Scanline Renderer.

I use my diamond models but you could just use the Hedra primitive (Create > Extended Primitives > Hedra) to create some jewels in seconds. Just create two Hedra objects and place them on a Plane object to create something similar to my scene. Change the color of the Plane object to white. Create a camera and make sure that you don't see the edges of the Plane object in the view. Change the size of the Plane object when necessary.

If you would like to create a 3D diamond model I suggest the following: use Google to find diamond blueprints and model a diamond using poly modeling techniques.

Mental Ray Renderer

Let's change the renderer from Scanline Renderer to Mental Ray renderer:

• Open rendering settings (Rendering > Render...).
• Expand Assign Renderer group on Common tab.
  
• Change the Production renderer from Default Scanline renderer to mental ray renderer

You could try to render an image. At this stage the Mental Ray rendering will look almost exactly like the rendering with the Scanline renderer. Actually the Mental Ray rendering looks a little worse because of the jagged edges.

Mental Ray Material

Picture 4. Mental Ray's Arch & Design is a solid basis for rendering diamonds.

Let's start by creating Mental Ray material for the diamonds. Open material editor (Rendering > Material Editor...) and assign the first material to the diamonds. The goal is to create a material that would be suitable for a diamond. Let's make the following adjustments to the material:

Main Material Parameters

• Change the material from Standard to Arch & Design. Arch & Design is a very powerful Mental Ray material which can be applied to many different situations (For example ambient occlusion is achieved with Arch & Design material)
• Change the Transparency to 1,0 to make the material fully transparent
• Change the IOR to 2,42. This is actually a value that 3DS MAX suggests for a diamond in a tool tip
• Change the Reflectivity to 1,0 to make the material fully reflective.

BRDF

• Select: By IOR (fresnel reflections) Render the scene. The rendering should look similar to picture 4.

Mental Ray Lights

Picture 5. Diamonds rendered with Skylight and Mental Ray (Final Gather enabled).

Illumination plays a big part in diamond rendering. Luckily you can use standard 3DS MAX lights also with Mental Ray. Let's illuminate the whole scene by using Skylight:

• Create Skylight (Create > Lights > Standard Lights > Skylight)
• Change the color of the Skylight to pure white. (By default the color of the Skylight is light blue).
• In order to use Skylight with Mental Ray, you have to use Final Gather. Enable Final Gather (Rendering > Render... > Indirect Illumination > Final Gather > Enable Final Gather)

Render the scene with Mental Ray to see how your diamonds look like. The rendering should look similar to picture 5.

Diamonds look already better but there are still some problems:

• Diamonds are too black
• There are no specular highlights

Let's fix these issues to achieve more realistic Mental Ray rendering.

Background

Picture 6. Diamonds rendered in 3D Studio MAX with white background.

Change the background color to pure white (Rendering > Environment...). Render the scene with Mental Ray to see the effect of changing the background color. As a result the diamonds are brighter. The rendering should now look like in picture 6.

More Reflections

Picture 7. Black boxes are placed on top of the diamonds to produce nice reflections.

Picture 8. Reflections of black boxes can be seen in diamonds.

Now the surrounding is pure white color and therefore the diamonds look little too bright and flat. Let's create some dark objects around them to achieve more interesting reflections:

• Create a grid of 25 boxes like in picture 7 and place them on top of the diamonds.
• Change the color of the boxes to black

Render a test image. Now the rendering should look similar to picture 8. Diamonds should look more real.

Specular Highlights

Picture 9. Omni lights placed randomly around the diamonds.

Picture 10. Specular highlights are created by the Omni lights.

There are some pretty light spots in the diamonds but real specular highlights are still missing. When you see diamonds in real life there are always several light sources around that produce specular highlights. Let's add more light sources to our scene:

• Create an Omni light and make 7 instance copies of it. Now you have 8 Omni lights.
• Change the multiplier of the Omni lights to 0,2 (Omni > Intensity/Color/Attenuation > Multiplier)
• Turn the diffuse effect off so that the lights affect only the specular characteristic of the materials (Omni > Advanced effect > Affect Surfaces > Diffuse)
• Place the Omni lights randomly around the diamonds like in picture 9. Just make sure that light comes from many different directions. Avoid symmetrical arrangement.

Make a test renderings with Mental Ray and adjust the placing of the lights if necessary. The rendering should be similar to picture 10.

Mental Ray Caustics

Picture 11. By default my Mental Ray caustics effect is far too strong.

Let's increase the realism by using Mental Ray to create caustics effect with the diamonds. Caustics have to be enabled in three separate locations: lights, geometry and Mental Ray rendering settings:

• Select all Omni lights and all diamonds. Right click on them and select Object Properties... from the menu. Select mental ray tab and turn 'Generate Caustics' on.
  
• Go to Mental Ray rendering settings and enable caustics (Rendering > Render... > Indirect Illumination > Caustics and Global Illumination (GI) > Caustics > Enable).

Make a test rendering using Mental Ray to see how the caustics look like. If you can't see any effect your geometry is probably too large. Try changing the diameter of the diamond to around 0,1. (I use metric system and the diameter of my diamond is about 0,07. That's a huge diamond;) By default my caustics look like in picture 11.)

Adjusting Mental Ray Caustics

Picture 12. Diamonds rendered with Mental Ray in 3DS MAX.

At the moment the caustics effect is far too strong. Let's make a few adjustments to it:

• Change the Multiplier to 0,03. (Rendering > Render... > Indirect Illumination > Caustics and Global Illumination (GI) > Caustics > Multiplier)
• Change 'Average Caustic Photons per Light' to 40000 to make caustics more defined. (Rendering > Render... > Indirect Illumination > Caustics and Global Illumination (GI) > Light Properties > Average Caustic Photons per Light)

Render the final image. Now the Mental Ray rendering should look similar to picture 12.

If you are rendering a large picture I recommend increasing the sampling quality (Rendering > Render... > Renderer > Sampling Quality) by increasing Samples per Pixel minimum and maximum values a few steps.