Radiometry Sung-Eui Yoon ( ) ( ) C Course URL: URL - - PowerPoint PPT Presentation

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Radiometry Sung-Eui Yoon ( ) ( ) C Course URL: URL - - PowerPoint PPT Presentation

Apr 03, 2023 128 likes •533 views

CS680: CS680: Radiometry Sung-Eui Yoon ( ) ( ) C Course URL: URL http://jupiter.kaist.ac.kr/~sungeui/SGA/ Announcements Announcements 2 papers for each student 2 papers for each student Choose 4 papers from the

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CS680: CS680:

Radiometry

Sung-Eui Yoon (윤성의) (윤성의)

C URL Course URL: http://jupiter.kaist.ac.kr/~sungeui/SGA/

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Announcements Announcements

2 papers for each student

  • 2 papers for each student
  • Choose 4 papers from the paper list
  • Send them (titles of 4 papers) to TA (Bochang
  • Send them (titles of 4 papers) to TA (Bochang

Moon) by Oct-11 (Mon)

  • Look at videos and talk files (captured talk

Look at videos and talk files (captured talk video or presentation files)

  • Schedule of student presentations
  • Will be decided on Oct-12 (Tue)

( )

  • Presentations will start after the mid-term

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Motivation Motivation

Eye ???

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SLIDE 4

Light and Material Interactions Light and Material Interactions

Physics of light

  • Physics of light
  • Radiometry
  • Material properties

From kavita’s slides

  • Rendering equation

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Models of Light Models of Light

Quantum optics

  • Quantum optics
  • Fundamental model of the light
  • Explain the dual wave particle nature of light
  • Explain the dual wave-particle nature of light
  • Wave model
  • Simplified quantum optics
  • Simplified quantum optics
  • Explains diffraction, interference, and

polarization polarization

  • Geometric optics

Geometric optics

  • Most commonly used model in CG
  • Size of objects >> wavelength of light

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j g g

  • Light is emitted, reflected, and transmitted
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SLIDE 6

Radiometry Radiometry

Measurement of light energy

  • Measurement of light energy
  • Critical component for photo-realistic rendering
  • Light energy flows through space
  • Varies with time position and direction
  • Varies with time, position, and direction
  • Radiometric quantities
  • Radiometric quantities
  • Densities of energy at particular places in time,

space, and direction space, and direction

  • Photometry

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Photometry

  • Quantify the perception of light energy
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SLIDE 7

Hemispheres Hemispheres

Hemisphere

  • Hemisphere
  • Two-dimensional surfaces

Direction

  • Direction
  • Point on (unit) sphere

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From kavita’s slides

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SLIDE 8

Solid Angles Solid Angles

2D 3D 2D 3D Full circle F ll h Full circle = 2pi radians Full sphere = 4pi steradians

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SLIDE 9

Solid Angles Solid Angles

2D 3D 2D 3D Full circle = 2pi radians Full sphere = 4pi steradians

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2pi radians = 4pi steradians

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SLIDE 10

Hemispherical Coordinates Hemispherical Coordinates

Direction 

  • Direction,
  • Point on (unit) sphere

From kavita’s slides

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Hemispherical Coordinates Hemispherical Coordinates

Differential solid angle

  • Differential solid angle

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Hemispherical Integration Hemispherical Integration

Area of hemispehre:

  • Area of hemispehre:

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SLIDE 13

Energy Energy

Symbol: Q

  • Symbol: Q
  • # of photons in this context
  • Unit: Joules
  • Unit: Joules

From Steve Marschner’s talk

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SLIDE 14

Power (or Flux) Power (or Flux)

Symbol P or Φ

  • Symbol, P or Φ
  • Total amount of energy through a surface per

unit time dQ/dt unit time, dQ/dt

  • Radiant flux in this context
  • Unit: Watts (=Joules / sec.)

Unit: Watts ( Joules / sec.)

  • Other quantities are derivatives of P
  • Example
  • A light source emits 50
  • A light source emits 50

watts of radiant power

  • 20 watts of radiant power is

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p incident on a table

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SLIDE 15

Irradiance Irradiance

Incident radiant power per unit

  • Incident radiant power per unit

area (dP/dA)

  • Area density of power
  • Area density of power
  • Symbol: E unit: W/ m2
  • Symbol: E, unit: W/ m
  • Area power density existing a

surface is called radiance exitance (M) or radiosity (B)

  • For example
  • A light source emitting 100 W of

0 1

2

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area 0.1 m2

  • Its radiant exitance is 1000 W/ m2
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SLIDE 16

Irradiance Example Irradiance Example

Uniform point source illuminates a small

  • Uniform point source illuminates a small

surface dA from a distance r

  • Power P is uniformly spread over the area of
  • Power P is uniformly spread over the area of

the sphere

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SLIDE 17

Irradiance Example Irradiance Example

Uniform point source illuminates a small

  • Uniform point source illuminates a small

surface dA from a distance r

  • Power P is uniformly spread over the area of
  • Power P is uniformly spread over the area of

the sphere θ

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SLIDE 18

Radiance Radiance

Radiant power at x in direction θ

  • Radiant power at x in direction θ
  • : 5D function
  • Per unit area

) (   x L

  • Per unit area
  • Per unit solid angle
  • Important quantity for rendering

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SLIDE 19

Radiance Radiance

Radiant power at x in direction θ

  • Radiant power at x in direction θ
  • : 5D function
  • Per unit area

) (   x L

  • Per unit area
  • Per unit solid angle
  • Units: Watt / (m2 sr)
  • Irradiance per unit solid angle
  • 2nd derivative of P

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  • Most commonly used term
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SLIDE 20

Radiance: Projected Area Radiance: Projected Area

  cos

2

dA d P d 

  • Why per unit projected surface area

  cos dA d

y p p j

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SLIDE 21

Properties of Radiance Properties of Radiance

Invariant along a straight line (in vacuum)

  • Invariant along a straight line (in vacuum)

From kavita’s slides

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SLIDE 22

Invariance of Radiance Invariance of Radiance

W it b d We can prove it based

  • n the assumption the

conservation of energy conservation of energy.

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Sensitivity to Radiance Sensitivity to Radiance

Responses of sensors (camera human eye)

  • Responses of sensors (camera, human eye)

is proportional to radiance

From kavita’s slides

  • Pixel values in image proportional to

di i d f h di i radiance received from that direction

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SLIDE 24

Relationships Relationships

Radiance is the fundamental quantity

  • Radiance is the fundamental quantity
  • Power:
  • Radiosity:
  • Radiosity:

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SLIDE 32

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SLIDE 33

Light and Material Interactions Light and Material Interactions

Physics of light

  • Physics of light
  • Radiometry
  • Material properties

From kavita’s slides

  • Rendering equation

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SLIDE 34

Materials Materials

Ideal diffuse (Lambertian) Ideal specular Glossy Glossy

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From kavita’s slides

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SLIDE 35

Bidirectional Reflectance Distribution Function (BRDF) Distribution Function (BRDF)

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SLIDE 36

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SLIDE 38

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SLIDE 39

Homework Homework

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SLIDE 40

Next Time Next Time

Rendering equation

  • Rendering equation

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