RenderMan and Katana

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RenderMan

&

Katana

Wanho Choi

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Rendering

The process of generating an image from a 2D or 3D model (or models in what collectively could be called a scene file) by means of computer program

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Physically Based Rendering (PBR)

Rendering by simulating the physical interaction of light

To generate synthetic images as close to the real as possible by calculating the steady-state distribution of light in a scene.

emission

reflection

transmission (refraction) absorption

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Ray Casting

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Ray Tracing vs Path Tracing

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Bidirectional Path Tracing (VCM)

http://www.cs.uiuc.edu/class/.../bidirectionalraytracing.ppt

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BxDF

Bidirectional x Distribution Function

x: Reflectance (BRDF), Transmitted (BTDF), Scattering (BSDF) etc.

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Super Sampling

https://en.wikipedia.org/wiki/Supersampling

Subpixel samples for each pixel

Sample numbers that are powers of two tend to give lesser image variance than other numbers -- for example, 256 is usually better than 257 or even 280.

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Incremental vs Batch Rendering

Incremental (interactive) rendering

It might make many passes over the pixels taking one sample at a time to give rapid interactive results that it refines incrementally.

Batch rendering

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Fixed vs Adaptive Sampling

Fixed sampling

• (# of samples for each pixel) = (max. number of samples per pixel) • Adaptive sampling

• (# of samples for each pixel) >= (min. number of samples per pixel) • (# of samples for each pixel) <= (max. number of samples per pixel)

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Adaptive Sampling

• As each sample is added to a pixel the renderer looks to see how much the sample changes the pixel.

• If enough samples are added without changing the pixel much, the renderer stops sampling it.

• Lower variance causes more samples and longer renders. • Higher variance causes less samples and shorter renders.

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Comparison

Fixed sampling, 2048 max samples

Adaptive sampling,

2048 max samples, 1248 actual avg.

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RenderMan RIS

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RenderMan RIS

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Integrator

• Integrators take the camera rays from the projection and return shaded results to the renderer.

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Two Types of Integrators

PxrPathTracer

A unidirectional path tracer. This combines information from the materials at the hit points with light samples to estimate direct lighting and shadowing, then

spawns additional rays to handle indirect lighting. This works well with

environment lights, and large direct light sources. It is ideal for outdoor lighting and large direct light sources

PxrVCM

A bidirectional path tracer. In addition to the paths from the camera, it traces paths from the light sources and tries to connect them. It can resolve

complicated indirect paths that may be slow to converge with PxrPathTracer. In particular, it is designed to handle specular caustics. It is ideal for interior

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Other Integrators

PxrDirectLighting PxrDefault PxrDebugShadingContext PxrValidateBxdf PxrVisualizer

• See more: https://renderman.pixar.com/resources/RenderMan_20/ risIntegrators.html

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PxrSurface

Multipurpose surface shader for RenderMan RIS : Wood, skin, plastic, glass, car paint, etc.

The same material model used in Pixar Animation Studios' feature animation • See more: https://rmanwiki.pixar.com/display/REN/PxrSurface

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PxrDomeLight

For environment lighting via image based lighting (IBL) • Scaling and translation for this light will be ignored

as it's considered nearly infinite or at least very far away.

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Materials

• Each piece of geometry has a single attached Bxdf. Roughly speaking this determines its gross material type by computing which directions it most

strongly reflects or refracts light in. The Bxdfs also provide the integrator with proposed directions for new rays to sampling indirect illumination.

• We include a general purpose, production-ready LM Material, as well as an

implementation of Disney's principled BRDF, and specialized materials for skin, glass, and hair.

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Patterns

• While material Bxdfs control the gross appearance of an object, patterns control the detail by varying the parameters of the Bxdfs across a surface. Patterns plug into Bxdfs and to each other to build up complex shading networks.

• Patterns can produce their outputs by nearly any means, from texture maps

(including atlases and Ptextures), to simple expressions, to a complete shading language like OSL.

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OSL

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OSL

• See more: http://thhube.github.io/tutorials/osl/osl.html •

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Lights

• Lighting in RIS mode is done via the geometric area light system, which

provides the integrator with relevant direct light samples to evaluate against the Bxdfs in order to shade the rays. These samples come from one of two types of sources, either emissive surfaces (with arbitrary geometry) or environment lights surrounding the scene. Whatever the sources, the system automatically

balances a sample budget across all of them.

• It also supports a wide variety of sophisticated lighting shaping effects such as gobos, blockers, and IES profiles. Lights can be turned off per-object, or just

turned off for certain types of shading, like specular highlights.

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Katana

Katana is a 3D application specifically designed for the needs of look

development and lighting in an asset-based pipeline.

Originally developed at Sony Pictures Imageworks, Katana has been their

core tool for look development and lighting for all their productions since Spider-Man 3, Beowulf, and Surf’s Up!.

• Katana provides a very general framework for efficient look development and lighting, with the goals of scalability, flexibility, and supporting an asset-based pipeline.

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Getting Started

with Katana

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But, nothing in the Viewer

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Click: MLB Then, it will appear in the VIewer.

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Where is the teapot? because this flag is off

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Q: How can I display both? A: Merge them!

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Press: P

but, nothing in the result

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Press: P

but, nothing in the result

Because no shader and light

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Click: MLB

Click: MLB Select: bxdf

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Click: MLB

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Tab → Type: gaffer

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Click: MRB

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Click: MLB Select: light

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Click: MLB

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Press: P

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Click: MRB

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Click: MLB

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Select the color.

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Click: MLB

You can choose other integrator. ex) PxrVCM

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Node Graph

Tab

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Parameters

Tab

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Scene Graph

Tab

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Viewer

Tab

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Monitor

Tab

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Catalog

Tab

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