mental ray Architectural and Design Visualization Shader Library

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84 3 Sun and Skyorigin 0 0 0energy 1 1 1exponent 2caustic photons 20000globillum photons 20000end lightThe shader is declared as follows:declare shader "mia_photometric_light" (boolean "on"default on,scalar "multiplier" default 1.0,color "color" default 1.0 1.0 1.0,# How to define the light intensity# 0 = using a manual peak intensity in cd# 1 = using a total amount of lumen# 2 = using the information stored in the IES fileinteger "intensity_mode",scalarscalar"manual_peak_intensity_cd","manual_flux_lm",# How to define the light distribution# 0 = Isotropic spherical distribution# 1 = Spotlight distribution# 2 = using the information stored in the IES fileinteger "distribution_mode" default 0,scalar "spotlight_cosine_bias",lightprofile "profile",# Scene and lighting unit managementscalar "units_to_meter_scale" default 1.0,scalar "cm2_factor" default 1.0)version 2apply light, emitterend declareon turns the light on or off.multiplier allows tweaking the intensity like a dimmer. Only when this is 1.0 will the intensitysettings mentioned below be accurate.color is the color of the light. Only if this is a normalized color (i.e. that the mi luminance() ofthe color is 1.0) will the intensity settings mentioned below be accurate. Fortunately, functionssuch as mib cie d and mib blackbody do return normalized colors.intensity mode guides what parameter and in what unit the light intensity is defined:
3.9 Photometric Lights 85• When intensity mode is 0, the peak intensity of the light is defined (in candela) bythe manual peak intensity cd parameter.• When intensity mode is 1, the overall flux of the light is defined (in lumen) by themaual flux lm parameter.• When intensity mode is 2, the intensity is directly derived directly from the valuesstored in the IES profile assigned to the profile parameter.distribution mode defines how the light is distributed in different directions:• When distribution mode is 0, the light is isotropic, i.e. it shines exactly the same inall directions.• When distribution mode is 1, the light is a spotlight. The light must have a spreadparameter to define the width of the beam. The distribution of light within the conefollows a cosine function, raised to the power of the spotlight cosine bias parameter.Hence, a bias below 1.0 will push light towards the edges of the cone, and a bias above1.0 will push light towards the center of the cone.• When distribution mode is 2, the intensity distribution of the light is derived fromthe values stored in the IES profile assigned to the profile parameter. Note that it islegal to combine this distribution mode with either of the manual intensity modes 0 or 1.In those cases, the IES profile is used in relative mode, trying to accomodate the desiredintensity but still accomodate the directional distribution of the IES file.Since physical lighting in real world units is highly scale dependent, the units to meter scaledefines how many scene units goes into one meter. E.g. if one scene unit is one millimeter,this would be 1000.Finally, the cm2 factor is the conversion factor between pixel values and candela persquare meter luminance values. In short, this should match the cm2 factor of themia exposure photographic shader to yield a photographically correct render, intensity wise.See also page 61.
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mental ray Architectural and Design
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Table of Contents1 Introduction 11.
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Table of Contentsix3.8.3 Examples .
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Chapter 2Architectural Material2.1
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2.2 Fundamentals 52.2.1.1 A Note on
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2.3 Features 7Hence, when using GI:
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2.3 Features 9The rules are as foll
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2.3 Features 11In the real world
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2.3 Features 13Used alone, an AO sh
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2.3 Features 152.3.7 Performance Fe
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2.4 Quick Guide to the Material Par
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2.5 Detailed Description of Materia
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Page 59 and 60: 2.6 Tips and Tricks 53There is one
Page 61 and 62: 2.6 Tips and Tricks 55• Glass-Liq
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Page 65 and 66: 2.6 Tips and Tricks 59Many small ad
Page 67 and 68: Chapter 3Sun and Sky3.1 Introductio
Page 69 and 70: 3.4 Common Parameters 633.3 Importa
Page 71 and 72: 3.5 Sun Parameters 65• saturation
Page 73 and 74: 3.6 Sky Parameters 67light"sun",# T
Page 75 and 76: 3.6 Sky Parameters 69• sun direct
Page 77 and 78: 3.8 Sky- and Environment Portals 71
Page 89: 3.9 Photometric Lights 833.9 Photom
Page 94 and 95: 88 4 Camera- and Exposure EffectsAl
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Page 111 and 112: 5.2 Environment Blur 105replaced by
Page 113 and 114: 5.2 Environment Blur 107But what is
Page 115 and 116: 5.2 Environment Blur 109Glossiness
Page 117 and 118: 5.3 Light Surface 111An example of
Page 119 and 120: 5.3 Light Surface 113the other two
Page 121 and 122: 5.3 Light Surface 115Complex geomet
Page 123: 5.3 Light Surface 117Another exampl
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