Integrator
#Introduction#
What is an integrator?
In simple terms, the integrator is responsible for solving the way light travels through the scene, which is the first stage in turning a virtual 3D scene into a 2D image. Because light is capable of many complex effects, most rendering integrators only look for a subset of these effects in order to keep rendering times reasonable. RenderMan RIS has several available raytracing integrators, and each one is tuned for different uses and lighting situations.
A brief summary of each integrator is listed below. If you are looking for detailed information on the settings for each integrator, links into the main Renderman documentation are also provided.
Helpful Tip: The Path Tracer and the VCM integrator are the only two options designed to create realistic images. All of the other integrators are designed for troubleshooting or debugging.
Helpful Tip 2: While this is not a hard and fast rule, in many cases the Path Tracer excels at outdoor scenes or scenes lit with Image Based Lighting (IBL). The VCM integrator is more useful for interior scenes or other situations with complex indirect lighting.
####Available Integrators####
####Wordlist####
Path Tracing: Path Tracing is the main method PRMan's RIS mode uses to render a scene. A virtual light ray is sent into the scene from the camera. That light ray then strikes an object in the scene. Depending on the BXDF assigned to the object, the light ray will either be reflected, absorbed, or transmitted. The ray will continue to bounce around until it either runs out of energy or reaches a 'bounce' limit set by the user. To aid in rendering the direct illumination, at each bounce point the renderer will also attempt to fire a ray from that point directly to one of the light sources in the scene. This source is picked through a sophisticated procedure that looks at a lights intensity, its distance to the object, and its distance to the camera.
Bi-Directional Path Tracing: BDPT is a more complex version of Path Tracing. In addition to the light rays traced from the camera, rays are also sent into the scene from the light sources. Once both of these rays have reached their maximum bounces, the renderer then attempts to connect the bounce points of each path together.
BXDF: An acronym for bi-directional scattering distribution function. A BXDF is assigned to an object surface and tells the renderer how light is scattered when it hits that object.
Vertex Merging: An advanced method for solving difficult specular and caustic light paths. Based on a variation of progressive photon mapping and usually combined with a bi-directional path tracer.
Properties > Render > Sampling > Integrator
####Visualizer####
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####VCM####
Features: Bi-Directional path tracing with additional vertex merging.
Strengths: Good at rendering images with caustic effects or 'difficult' lighting, for example an indoor scene with recessed light sources.
Weaknesses: Less control over sampling. Takes longer per sample than the Path Tracer, so should not be used in scenarios where PathTracer excels, such as outdoor or otherwise 'easy' lighting without caustics.
####ValidateBxdf####
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####PathTracer####
Features: Unidirectional path tracer with direct light sampling.
Strengths: Produces realistically lit scenes without having to spend time manually adding in phenomena such as bounce lighting or reflections.
Weaknesses: Does not handle scenes with high amounts of indirect illumination well. Also does not do well with caustic effects, although they can be enabled if desired. If your scenes have either of these, the VCM integrator is often more efficient.
####DirectLighting####
Features: Direct lighting engine. A ray is sent from the camera into the scene. When the ray hits an object, the integrator will send a new ray in the direction of a light source to determine if the point will be visible to the source.
Strengths: Quick results. Creates images with less noise than the PathTracer or VCM integrators. Good for preview images. Very simple controls.
Weaknesses: Does not account for indirect lighting, volumetric, reflection or refraction effects.
####Default####
Features: Shadeless lighting engine. Places a light in the scene at the same location as the camera and then uses a raytracing method similar to DirectLighting.
Strengths: Very fast. Useful for tracking down the source of image issues by removing the lighting element.
Weaknesses: Highly unrealistic lighting. Not only ignores all light sources in the scene, but also ignores shadow, indirect lighting, volumetric, reflection and refraction effects.
####DebugShadingContext####
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