OpticsReal-time Rendering of Physically Based Optical Effects in Theory and Practice

Masanori KAKIMOTOTokyo University of Technology

Table of Contents• Introduction• Basic geometrical optics• Brief overview of wave optics• Conclusion

INTRODUCTION

Real-time Rendering of Physically Based Optical Effects in Theory and Practice

Optics

Physics on Lights• Optics

– Geometrical optics – a simple, practical model– Wave optics – more physically correct and complicated

• Electromagnetism – a classical physics model• Quantum optics – a modern physics model

Optics and Computer Graphics Theories

• Computer graphics theories are based on optics

– Vast majority of the theories and techniques

upon geometrical optics

– ~1% taking wave optics into account

Photon mapping borrows a concept ‘photon’ from quantum optics and use it in a geometrical optics framework

Topics

• This course– Most topics are related with geometrical optics

– Some are wave optics related

• This talk covers:

– Basic g.o. knowledge for the rest of the course

– Brief introduction of wave-related topics for a later talk

BASIC GEOMETRICAL OPTICS

Real-time Rendering of Physically Based Optical Effects in Theory and Practice

Optics

Geometrical Optics Models for CG

• Pinhole camera model

• Thin lens approximation

• Thick lens approximation

• Full lens system

Geometrical Optics Models for CG

• Pinhole camera model

• Thin lens approximation

• Thick lens approximation

• Full lens system

+ thickness

+ aperture+ approximated refraction

+ accurate refraction+ multi-wavelengthsetc.

Geometrical Optics Models and EffectsGeometrical optics

Thin lens / Thick Lens Full simulated lensPinhole

Perspective projectionMotion blur

Bokeh (defocus)Focus breathing

Complex BokehChromatic aberration

Optical vignettingLens ghosts

+ aperture+ approximated refraction

+ accurate refraction+ multi wavelengths

Natural vignetting

Geometrical Optics Models and EffectsGeometrical optics

Thin lens / Thick Lens Full simulated lensPinhole

Bokeh (defocus)Focus breathing

Complex BokehChromatic aberration

Optical vignettingLens ghosts

+ aperture+ approximated refraction

+ accurate refraction+ multi wavelengths

Natural vignetting Today’s topics

Geometrical Optics Models and Implementations

Graphics HW(fixed pipeline)

Ray tracing

Accumulation buffer

Programmable shader techniques

Wavefront tracingPost processing

Geometrical optics

Pinhole

+ aperture + accurate refraction

Full lens systemThin lens / Thick Lens

Distribution Ray tracing

Geometrical Optics Models and Implementations

Today’s topics (geometrical optics)

Programmable shader techniques

Post processing

Geometrical optics

Pinhole

+ aperture + accurate refraction

Full lens systemThin lens / Thick Lens

Wavefront tracing

Thin Lens – Fundamentals to Understand Real-Time Special Effects

• Real-time techniques are based on thin lens theory– Many optical effects accounted for by thin lens– Some effects derived from full lens system

model• Each can be mimicked by real-time techniques

(extended thin lens theory)

Thin Lens Model

optical axis(principal axis)

focal point

f focal length

principal plane

incident light ray

center of lens(principal point)

Deffective aperture diameter

Thin Lens Approximation – Rule 1

• Incident light rays parallel to the principal axis always go through the focal point

optical axis(principal axis)

focal point

f focal length

principal plane

incident light ray

center of lens(principal point)

Thin Lens Approximation – Rule 2

• Incident light rays that passed through the focal point go parallel to the axis after exiting the lens

focal point

f focal length

incident light ray

Thin Lens Approximation – Rule 3

• Incident light rays through the center of the lens travel straight (never get refracted)

optical axis

incident light rays

center of lens

Rays Converge on a Certain Plane

• Rays from an object at distance converge on a plane at distance forming an image

odid

od

id

f f

object

image

film or sensor

focus distance

Thin Lens Equation

io ddf

111

od

id

f f

object

image

filmo

i

d

dM

Thin Lens and Closer Objects

• If the object gets closer, the converging plane (film) needs be farther from the lens

id

f f

object

image

film

od

io ddf

111

fdd io 2,

Thin Lens and Far Objects

• If the object is far, the film needs be closer to focal length

io ddf

111

id

f f

image

film

od

fdd io

Film Size and FOV for Infinite Focus

fdi

film

h

od

f

h

2tan2 1

: Field of view

for infinite focus

Film Size and FOV for Closer Focus

finite

film

h

fidod

ifinite d

h

2tan2 1

finite : Field of view

for closer focus

F-number Represents Lens Brightness

fdi

film

h

od

D

fF

D

D : diameter of the lens

Smaller f-number means brighter image

Effective F-number

film

h

fidod

Fd

d

FMD

dF

o

i

ie

1

1 D

Smaller f-number means brighter image

WAVE OPTICS OVERVIEW

Real-time Rendering of Physically Based Optical Effects in Theory and Practice

Optics

Rays travel straight

Introduction• Geometrical optics – virtually correct, simple• Wave optics – more physically correct, complicated

Geometrical optics Wave optics

Waves propagate concentrically

Wave-Related Phenomena and Effects

• Diffraction– Glare– Airy disc

• Interference– Surface coating– Thin film color effects

• Polarization– Complex reflection– Image dehazing

Can be simulated with extended ray theories[CookTorrance1981], [Gondek1994], [Wolff1999], [Schechner 2001]

Requires wave opticsCannot simulate with extended rays

Wave optics topics in this course focus on diffraction

Diffraction – A Major Cause of Glare

Geometrical optics Wave optics

Diffraction

Diffraction

Diffraction Details

• Later in this course

Wave optics based glare generation techniques

CONCLUSION

Real-time Rendering of Physically Based Optical Effects in Theory and Practice

Optics

Conclusions• Most computer graphics theories rely on

geometrical optics– Real-time techniques basically use thin lens

approximation– Effects beyond thin lens can be mimicked

(later in this course, e.g., aberrations)

• Popular wave optics effects are based on diffraction