Lately I had the opportunity to test Mental Ray. In MR 3.4 I found “Ambiant Occlusion”, a shading tool that is becoming a true alternative to Global Illumination. Amb. Occ. is nothing new to CG, but it last implementation in Mental Ray comes with a lot of handy parameters :

• sampling rate : quite obvious, will determine the amount of rays cast by the shader
• spread angle : will make the probing from narrow to wide angle, thus more or less sensitive to the details around
• distance : a critical parameter that define the probing range from near to far

Among them, Distance is a real breakthru against Global Illumination. Small probing distance make shorter render times (more than 200% in some cases). And it gives subtles areas of shadow.

Of course, it doesn’t take account of the “boucing energy” phenomenon. Fortunately that’s the funniest part of the lighting job : adding pointlights here & there to mimic the bouncing of light. That what I did in this scene.

In the end, hires render time came under 2 minutes (VS 8 minutes for a full GI solution with LW)

Here’s how it works, in pseudo-code :

 amb_occ = ambiant_occlusion("cone=wide","distance=small","fallof=high"); C = diffuse() * noise("grey","orange") * amb_occ; C += specular() * noise() * amb_occ ; C += reflect("blur") * amb_occ ;

Quite simple, eh ? 😀

1. Despite the very low amount of polygons, it is always possible for a model to catch the play of light
2. Darker areas sometime claims to be colored. This can be observed with traditional medias, especially on sensitive color films
3. Depth of field will blur the unwanted details, as long as the shapes remains readable, and will enable you to composite a texture layer

This scene uses a strong backlight, as a tribute to the earlier sci-fi movies. The first step was to setup dark silhouetes on a light background, then add a backlight so that shadows will be running accross the camera, and eventualy recreate the bouncing of light to emphasize the characters’ features.

The modeling of this scene was very quick, for I wanted to focus on lighting, as always . It simply consists of some poles in a field, around a roughly shaped tank.

1. The funniest is : there’s only one light on this scene that suggests a raising sun and casts rather long shadows. The blue backlight seen on the tank and the robot is pure reflexion of the blue environment. Eventually, I used a strong blue fog to give the scene its overall color and to strenghten the tank agains the background.
2. Adding grass was an obvious choice to me, for it really catch the play of light.
3. As the final render seemed too blue, color corrections on high colors proved very useful to achieve a warmer lighting.

Testing Max 7SP1 = Mental Ray 3.4 + Shave & Haircut, I just found a lot of nice features :

• generate geometry, thus can be combined with ambiant occlusion
• conform fur along a spline, reminds me Worley-Sasquatch, with more feedback
• tickness spinners are locked to max = 100% but it can be overrid with a texture slot
• physics enabled (didn’t tested it)

‘Tried it with ambiant occlusion & baking. Damn ! It rocks.

This scene was primarily designed for a realtime toon rendering. Thus the modeling is very simple, with few polygons and square-looking shapes. Later on, I decided to render it as if it was a realistic scenery, featuring little toys.

First of all, I played with depth of field to suggest the small scale. Most of camera lenses can hardly shoot a sharp image of the whole scene, so the foreground and the background are often out of focus.

Secondly, I used the same texture basis on each material of the scene, to have a coherent overall look :

Figure above shows the process :

• Flat shaded geometry is usually dull. I needed something to texture the shadows : a hand-painted layer was camera-mapped onto the scene, with a slightly different angle than the viewpoint
• It’s very powerful because it’s more than a simple 2D layer and you can move freely around the viewpoint without too much distortion. But this layer is hoverwhelming if you don’t modulate it with the luminance of the initial render.
• Eventually, I just did some levels tweaking to get colored shadows and obtain a far more interesting result.

These are the techniques involved in the creation of this scene. Everything in this process is done with animation in mind, so that I could easily redo it on an image sequence.

1. Textured scene + shadow map spotlight
2. HDRI-based skydome
3. Composite of the 2 previous passes
4. Color corrections