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