Week 4: Shadows, Part Two- Raytraced Shadows

Overview of Raytracing



Lighting Terms

  • scanline
  • raytrace
  • pathtrace
  • rays
  • bounces
  • light radius
  • ray depth
  • samples
  • XXXX




Raytrace Rendering
Raytracing is a rendering algorithm that simulates how light travels through a scene: emitted from a light source, being reflected or refracted by geometric objects with certain material properties, and finally appearing at the observer’s eye, typically on the film of a camera. In order to minimize computational costs and render just the visible parts of a scene, the algorithm works backwards: it starts at the camera and sends a ray in the direction of the current view. If this ray hits an object, then its material is evaluated, and the final color information is returned and stored. In case the material is reflective or refractive, further rays are sent into the scene to compute these contributions to the final color. This process is repeated recursively until a certain traversal depth is reached.

Both Maya Software and Mental Ray provide for raytraced renders
Scanline Rendering
When the scanline algorithm is enabled, all objects in your scene are projected onto a 2-D plane. Objects are then sorted according to their vertical and horizontal order. This technique requires less rendering time than raytracing since it does not involve repeated searching in 3D scene data to find the next contributing object.

Both Maya Software and Mental Ray provide for scanline renders
Pathtrace Rendering
Disney video- more physically accurate indirect lighting



Maya Raytrace Shadow Settings

Light Radius
A large light produces softer shadows than a small light. This controls the softness of shadow edges by setting the size (Shadow Radius or Light Radius) or angle (Light Angle) of the light.

The Shadow Radius attribute is only available for ambient lights. The Light Radius attribute is only available for point lights, volume lights and spot lights. The Light Angle attribute is only available for directional lights.


Shadow Rays
Controls the graininess of soft shadow edges. Increasing the number of Shadow Rays also increases rendering times, so set it to the lowest value that produces acceptable results. The slider range is 1 to 40. The default setting is 1. The number of rays employed to calculate the shadow edge. The higher the value, the more refined the result.


Ray Depth Limit
Ray depth specifies the maximum number of times a light ray can be reflected and, or refracted and still cause an object to cast a shadow. Transparent objects between those points in which the ray changes direction will have no affect on the light ray’s termination. This can best be visualized by example in which the ray traced shadow is visible on both the ground plane and reflection plane. If the ray depth is set to 1, the shadow will only be visible on the ground plane. If the ray depth is set to 2, the shadow will be visible on both the ground plane and the reflected plane.





Color Management in Maya 2016

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