Reported by

Auradee Concepcion

Distributed Ray Tracing a stochastic sampling method

based on randomly distributed rays

over the pixel area used to reduce

aliasing effect

The random distribution of a number of rays over the pixel surface is achieved by the technique called jittering.

Distributed Ray Tracing Uses non-uniform (jittered) samples

Replacing aliasing artifacts with noise

Provides additional effects by distributing rays to sample:

Reflections and refractions

Light source area

Camera lens area

Time

Advantages DRT uses a slightly better approximation for the

illumination and reflectance integrals

The idea is based in the theory of oversampling Instead of approximating an integral by a single scalar value, the

function is point sampled and these samples are used to define a more accurate scalar value

Advantages Practical benefits:

o Gloss (fuzzy reflections)

o Translucency

o Soft shadows

o Depth of field

o Motion blur

Gloss Glossy surfaces are generated by randomly distributing

rays reflected by a surface

Instead of casting a single ray out in the reflecting direction, a packet of rays are sent out around the reflecting direction

actual value of reflectance -> statistical mean of the values returned by each of these rays

Gloss DRT can also be used to generate specular highlights

by using area light sources.

If rays that reflect off a surface hit a light source, they will add to the specular component of the surface illumination.

This can replace the specular component of the Phong model.

Translucency Achieves translucent surface by casting randomly

distributed rays in general direction of the transmitted ray from traditional ray tracing

Calculated by distributing the secondary rays about the main direction of the transmitted light

The value computed from each of these rays is then averaged to form the true translucent component.

Penumbras (Soft Shadows) Attempts to approximate soft shadows by modeling

light sources as spheres

When a point is tested to see if it is in shadow, a set of rays are cast about the projected area of the light source. The amount of light transmitted from the source to the point can be approximated by the ratio of the number of rays that hit the source to the number of rays cast.

This ratio can be used in the standard Phong lighting calculations to scale the amount of light that hits a surface.

Depth of Field Creates depth of field by placing an artificial lens in

front of the view plane

Randomly distributed rays are used to simulate the blurring of depth of field.

Depth of Field The first ray cast is assumed that the focal point of the

lens is at a fixed distance along this ray.

The rest of the rays sent out for the same pixel will be scattered about the surface of the lens. At the point of the lens they will be bent to pass through the focal point.

Points in the scene that are close to the focal point of the lens will be in sharp focus. Points closer or further away will be blurred.

Motion Blur Simulate motion blurring by distributing rays

temporally as well as spatially

Before each ray is cast, objects are translated or rotated to their correct position for that frame. The rays are then averaged afterwards to give the actual value.

Objects with the most motion will have the most blurring in the rendered image.

THE END

References http://books.google.com.ph/books?id=iJUvWG59zvkC

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