6351001 Procedural Animation Introduction to Procedural Methods in 3D Computer Animation Dr Midori Kitagawa In class Pay attention Take notes Learn Be ready for a pop quiz Week 10 Rendering ID: 484184
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Slide1
Procedural Animation
Introduction
to Procedural Methods in 3D Computer
Animation
Dr. Midori KitagawaSlide2
In class
Pay attention
Take notes
Learn
Be ready for a pop quizSlide3
Week 10: Rendering
Rendering
Scan-line
Ray-tracing
Photon mapping
Physically based rendering
Assignment 14 review
Assignment 16Slide4
Rendering
The
process of converting the abstract representations of geometric entities into the appropriate color values in
an image.Slide5
Rendering algorithms
Scan-line
Ray-tracing
Photon mapping
Physically based renderingSlide6
Scan-line algorithm
Most
commonly used rendering
algorithm, especially in real-time.
Fast
E.g. Micro-polygon rendering in HoudiniSlide7
Scan lines and pixels
Any
digital image is composed of a 2D grid of
pixels
.
Scan line
is each row of pixels.
Scan lineSlide8
Scan-line algorithm
looks
at each pixel, one after the other, scan line by scan line, and calculates the color that pixel should be rendered. Slide9
Scan-line algorithm
The
color of each pixel is computed
using:
the
color and other
surface characteristics
of the surface visible from the camera (i.e, the surface closest to the camera
),
the
lights
in the scene, and
the
position of the
camera. Slide10
Scan-line algorithm
If
the surface closest to the camera is transparent, the color of the pixel is computed using the surface characteristics of the next closest surface as well.
With
the scan-line algorithm, light is never refracted.Slide11
Ray-tracing
traces the origins of the imaginary light ray that arrives the camera through each pixel in the image plane. Slide12
Ray-tracing
To
achieve this, a ray is cast back into the object space to determine whether the ray was
absorbed
or
reflected
by
a surface
,
refracted
by a transmissive medium,
or
originated
directly from a light source. Slide13
Ray-tracing
The path of a ray may be divided into two when part of light is reflected by a surface while another part travels through the surface. Slide14
Ray-tracing
good at reflection, refraction and shadows.
more
time-
consuming than
scan-line
rendering.
Ray-tracing
Scan-lineSlide15
Direct vs. indirectillumination
Direct illumination
occurs when a light source directly illuminates objects in a scene.
Indirect
illumination
occurs when the light that is reflected or transmitted by objects illuminates other objects
.Slide16
Global illumination
Global Illumination
is
the technique used to simulate
indirect illumination
.
Photon mapping
is one of global Illumination methods
.
Photon mapping is
a
two-pass rendering algorithm
that deals with both diffuse and specular reflections. Slide17
Photon mapping: 1st pass
In
the first pass
, photons are shot from the light into the
scene.
Photons
are bounced around interacting with all surfaces that they encounter. Slide18
Photon mapping: 1st pass
Photons
are stored in
a
photon
map
for later
use.
The resolution
of the photon map is independent from the resolution of the geometry.
Only
a few thousands to a million photons are sparsely stored and the rest is statistically estimated from the density of the stored photons.
After
all the photons have been stored in the map, an estimate of the illumination at each photon is statistically computed.Slide19
Photon mapping: 2nd pass
In the second pass
, the direct illumination is computed like ray-tracing and the indirect illumination is computed from querying the stored photons in the photon map. Slide20
Photon mapping
In
short, photon mapping shoots photons from the light and tracks their distribution in the scene.
It
is fast but not as accurate as final gatherSlide21
Physically based rendering (PBR)
follows the physical behavior of light and surfaces as closely as possible.
incorporates ray-tracing, photon-mapping, and other methods.Slide22
Physically based rendering (PBR)
Fresnel
Energy conservation Slide23
PBR: Fresnel
describes
the
behavior of light reflected by a surface having differing
reflectivity that occurs at different angles.Slide24
PBR: Fresnel
brighter reflections near the edges
.Slide25
PBR: Energy conservation
The outgoing
energy cannot be greater than the incoming
energy.
Diffuse reflection + specular reflection <= incoming lightSlide26
in other rendering algorithms
Diffuse reflection and specular reflection are independently controlled.
Diffuse
reflection + specular
reflection >
incoming
light is possible.Slide27
PBR: Energy conservation
In PBR, the energy conservation law is enforced.