Global Illumination CS5502 Fall 2006 (c) Chun-Fa Chang Can you get - - PDF document

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Global Illumination CS5502 Fall 2006 (c) Chun-Fa Chang Can you get - - PDF document

Dec 13, 2023 117 likes •233 views

Global Illumination CS5502 Fall 2006 (c) Chun-Fa Chang Can you get this with ray tracing? CS5502 Fall 2006 (c) Chun-Fa Chang Rendering Equation = + I ( x , x ) g (

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SLIDE 1

CS5502 Fall 2006 (c) Chun-Fa Chang

Global Illumination

CS5502 Fall 2006 (c) Chun-Fa Chang

Can you get this with ray tracing?

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SLIDE 2

CS5502 Fall 2006 (c) Chun-Fa Chang

Rendering Equation

  • g() is the “visibility” function
  • ρ() is related to BRDF:

] ) , ( ) , , ( ) , ( )[ , ( ) , ( x d x x I x x x x x x x g x x I

s

′ ′ ′ ′ ′ ′ ′ ′ ρ + ′ ε ′ = ′

∫

ref ref ref in in

x x x θ′ θ φ′ θ′ φ′ θ′ ρ = ′ ′ ′ ρ cos cos ) , , , ( ) , , (

From Watt’s p.277

CS5502 Fall 2006 (c) Chun-Fa Chang

How to Solve It?

  • We must have:

– ε(): model of the light emitted

– ρ(): BRDF for each surface – g(): method to evaluate visibility

  • Integral evaluation !Monte Carlo
  • Recursive equation ! Ray Tracing
  • The problem is view independent
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SLIDE 3

CS5502 Fall 2006 (c) Chun-Fa Chang

Ray Tracing Revisited

  • The reflected intensity (or color) at a

surface point is computed by:

– Local reflection model (no interaction with

  • ther objects): ambient, diffuse, and

specular. – Global model: perfect reflection and refraction.

  • What if we spawn many reflected rays?

CS5502 Fall 2006 (c) Chun-Fa Chang

Global Illumination Algorithms

  • Radiosity (topic of the next lecture).
  • Distributed Ray Tracing.
  • RADIANCE
  • Photon Map
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SLIDE 4

CS5502 Fall 2006 (c) Chun-Fa Chang

Distributed Ray Tracing

  • Distribute a group of rays at a hit point to

sample the “reflection lobe” (similar to a 2D slice of BRDF).

  • May also distribute rays

along camera aperture, time, and pixel region to produce effects of depth of fields, motion blur, and anti- aliasing.

CS5502 Fall 2006 (c) Chun-Fa Chang

Why Distributed Ray Tracing?

  • Anti-Aliasing
  • Features

– Gloss (fuzzy reflections) – Fuzzy translucency – Penumbras (soft shadows) – Depth of field – Motion blur

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SLIDE 5

CS5502 Fall 2006 (c) Chun-Fa Chang

Anti-Aliasing

  • Supersampling
  • Jittering – Stochastic Method

1 4 9 5 11 7 15 8 12 14 3 13 2 10 6

eye

CS5502 Fall 2006 (c) Chun-Fa Chang

Gloss

surface surface normal normal

I R I R

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SLIDE 6

CS5502 Fall 2006 (c) Chun-Fa Chang

Fuzzy Reflection

4 rays, 37 seconds 64 rays, 956 seconds

CS5502 Fall 2006 (c) Chun-Fa Chang

Translucent

surface surface normal normal

I T T I

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SLIDE 7

CS5502 Fall 2006 (c) Chun-Fa Chang

4 rays 16 rays

CS5502 Fall 2006 (c) Chun-Fa Chang

Penumbra (Soft Shadow)

surface surface

Hard Shadow Soft Shadow

eye eye

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SLIDE 8

CS5502 Fall 2006 (c) Chun-Fa Chang

Soft shadow - cube

Without penumbra With penumbra

CS5502 Fall 2006 (c) Chun-Fa Chang

Depth of Field

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SLIDE 9

CS5502 Fall 2006 (c) Chun-Fa Chang

Depth of Field

CS5502 Fall 2006 (c) Chun-Fa Chang

Depth of Field

F-Stop = 5.8 F-Stop = 2.8

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SLIDE 10

CS5502 Fall 2006 (c) Chun-Fa Chang

Depth of Field

Focal Distance = 13 Focal Distance = 11

CS5502 Fall 2006 (c) Chun-Fa Chang

Motion Blur

  • Sampling in time
  • Each element in the cell stands for a

time slice

  • Jitter time slice to the current time
  • Move object via the current time slice

1 4 9 5 11 7 15 8 12 14 3 13 2 10 6

Current time = Time Slice + Jitter Time e.g. time slice at left-upper = 6 + rand()

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SLIDE 11

CS5502 Fall 2006 (c) Chun-Fa Chang

Motion Blur

CS5502 Fall 2006 (c) Chun-Fa Chang

Typical Distributed Ray Path