mental ray Architectural and Design Visualization Shader Library

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92 4 Camera- and Exposure Effects1, a strong “toe” region is added to the transfer curve so that low intensities gets pushed moretowards black, but in a gentle (soft) fashion.Compressing bright color components inherently moves them towards a less saturated color.Sometimes, very strong compressions can make the image in an unappealingly de-saturatedstate. The saturation parameter allows an artistic control over the final image saturation.1.0 is the standard “unmodified” saturation, higher increases and lower decreases saturation.The gamma parameter applies a display gamma correction. Be careful not to apply gammatwice in the image pipeline. This is discussed in more detail on page 4.The side channel and side channel mode is intended for OEM integrations of the shader,to support “interactive” tweaking as well as for the case where one wants to insert an outputshader prior to the conversion to “display pixel values”.This is accomplished by applying two copies of the shader, one as lens shader, the other asoutput shader. The two shaders communicate via the “side channel”, which is a separatefloating point frame buffer that needs to be set up prior to rendering.Valid values for side channel mode are:• 0 - the shader is run normally as either lens- or output-shader.• 1 - the lens shader will save the un-tonemapped value in the side channel frame buffer.The output shader will re-execute the tone mapping based on the data in the sidechannel, not the pixels in the main frame buffer.• 2 - the lens shader works as for option 1, the output shader will read the pixels from theside channel frame buffer back into the main frame buffer. This is useful when onewant to run third party output shaders on it that only support working on the mainframe buffer.One may wonder, if one wants to apply the tone mapping as a post process, why not skipapplying the lens shader completely? The answer is twofold: First, by applying the lens shader(even though it’s output is never used), one can see something while rendering, which is alwayshelpful. Second, the mental ray over-sampling is guided by the pixels in the main frame buffer.If these are left in full dynamic range, mental ray may needlessly shoot thousands of extrasamples in areas of “high contrast” that will all be tone mapped down to white in the finalstage.The use preview and preview work exactly like in the mia exposure simple shader describedabove.4.1.2.2 ExamplesLets walk through a practical example of tuning the photographic tone mapper. We have ascene showing both an indoor and outdoor area, using the sun and sky, mia material, and a
4.1 Tone Mapping 93portal light in the window. The units are set up such that the raw pixels are in candela persquare meter.The raw render, with no tone mapping, looks something like this:No tone mappingThis is the typical look of a Gamma=1 un-tonemapped image. Bright areas blow out in avery unpleasing way, shadows are unrealistically harsh and dark, and the colors are extremelyover-saturated.Applying mia exposure photographic with the following settings:"cm2_factor" 1.0,"whitepoint" 1 1 1,"film_iso" 100,"camera_shutter" 100.0,"f_number" 16.0,"vignetting" 0.0,"burn_highlights" 1.0,"crush_blacks" 0.0,"saturation" 1.0,"gamma" 2.2,...gives the following image as a result 4 :4 For speedy results in trying out settings for the tone mapping shaders, try the workflow with the “preview”parameter described on page 89.
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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 55 and 56: 2.6 Tips and Tricks 49• For extre
Page 57 and 58: 2.6 Tips and Tricks 51Diagram for g
Page 59 and 60: 2.6 Tips and Tricks 53There is one
Page 61 and 62: 2.6 Tips and Tricks 55• Glass-Liq
Page 63 and 64: 2.6 Tips and Tricks 57Enjoy the tro
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 and 90: 3.9 Photometric Lights 833.9 Photom
Page 91: 3.9 Photometric Lights 85• When i
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Page 109 and 110: Chapter 5General Utility Shaders5.1
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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mental ray Architectural and Design Visualization Shader Library

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