mental ray Architectural and Design Visualization Shader Library

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6 2 Architectural Materialone can end up with washed out gamma due to it being applied twice. Make sure to keep aneye on the gamma workflow so it is applied in one place.2.2.2 Use Final Gathering and Global IlluminationThe material is designed to be used in a realistic lighting environment, i.e. using full directand indirect illumination.In mental ray there are two basic methods to generate indirect light: Final Gathering andGlobal Illumination. For best results at least one of these methods should be used.At the very least one should enable Final Gathering, or use Final Gathering combined withGlobal Illumination (photons) for quality results. Performance tips for using Final Gatherand Global Illumination can be found on page 48 of this document.If you are using an environment for your reflections, make sure the same environment (or ablurred copy of it) is used to light the scene through Final Gathering.2.2.3 Use Physically Correct LightsTraditional computer graphics light sources live in a cartoon universe where the intensity of thelight doesn’t change with the distance. The real world doesn’t agree with that simplification.Light decays when leaving a light source due to the fact that light rays diverge from theirsource and the “density” of the light rays change over distance. This decay of a point lightsource is 1/d 2 , i.e. light intensity is proportional to the inverse of the square of the distanceto the source.One of the reasons for this traditional oversimplification is actually the fact that in the earlydays of computer graphics tone mapping was not used and problems of colors “blowing out”to white in the most undesirable ways 3 was rampant.However, as long as only Final Gathering (FG) is used as indirect illumination method, suchtraditional simplifications still work. Even light sources with no decay still create reasonablerenderings! This is because FG is only concerned with the transport of light from one surfaceto the next, not with the transport of light from the light source to the surface.It’s when working with Global Illumination (GI) (i.e. with photons) the troubles arise.When GI is enabled, light sources shoot photons. It is imperative for the mia material (orany other mental ray material) to work properly for the energy of these photons to match thedirect light cast by that same light! And since photons model light in a physical manner, decayis “built in”.3 Raw clipping in sRGB color space is very displeasing to the eye, especially if one color channel clips earlierthan the others. Tone mapping generally solves this by “soft clipping” in a more suitable color space thansRGB.
2.3 Features 7Hence, when using GI:• Light sources must be emitting photons at the correct energy• The direct light must decay in a physically correct way to match the decay of the photons.Therefore it is important to make sure the light shader and the photon emission shader of thelights work well together.To solve this, the mia photometric light shader (see page 83) is included, which automaticallybalances photons and direct light in the correct way.2.3 Features2.3.1 The Shading ModelFrom a usage perspective, the shading model consists of three components:• Diffuse - diffuse channel (including Oren Nayar “roughness”).• Reflections - glossy anisotropic reflections (and highlights).• Refractions - glossy anisotropic transparency (and translucency).The mia material shading model
Page 1 and 2: mental ray Architectural and Design
Page 3 and 4: Table of Contents1 Introduction 11.
Page 5: Table of Contentsix3.8.3 Examples .
Page 9 and 10: Chapter 2Architectural Material2.1
Page 11: 2.2 Fundamentals 52.2.1.1 A Note on
Page 15 and 16: 2.3 Features 9The rules are as foll
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Page 19 and 20: 2.3 Features 13Used alone, an AO sh
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Page 59 and 60: 2.6 Tips and Tricks 53There is one
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2.6 Tips and Tricks 57Enjoy the tro
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2.6 Tips and Tricks 59Many small ad
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Chapter 3Sun and Sky3.1 Introductio
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3.4 Common Parameters 633.3 Importa
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3.5 Sun Parameters 65• saturation
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3.6 Sky Parameters 67light"sun",# T
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3.6 Sky Parameters 69• sun direct
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3.8 Sky- and Environment Portals 71
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90 4 Camera- and Exposure Effects4.
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Chapter 5General Utility Shaders5.1
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5.2 Environment Blur 105replaced by
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5.2 Environment Blur 107But what is
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5.2 Environment Blur 109Glossiness
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5.3 Light Surface 111An example of
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5.3 Light Surface 113the other two
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5.3 Light Surface 115Complex geomet
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5.3 Light Surface 117Another exampl
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mental ray Architectural and Design Visualization Shader Library

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