Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text...
-
Upload
charlene-kelly -
Category
Documents
-
view
221 -
download
0
Transcript of Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text...
![Page 1: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/1.jpg)
Today• More raytracing stuff
– Soft shadows and anti-aliasing
• More rendering methods– The text book is good on this
– I’ll be using images from the CDROM in the back of the book
![Page 2: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/2.jpg)
Soft Shadows• Light sources that extend over an area (area light
sources) should cast soft-edged shadows– Some points see all the light - fully illuminated– Some points see none of the light source - the umbra– Some points see part of the light source - the penumbra
• To raytrace area light sources, cast multiple shadow rays– Each one to a different point on the light source– Weigh illumination by the number that get through
![Page 3: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/3.jpg)
Soft Shadows
Umbra PenumbraPenumbra
![Page 4: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/4.jpg)
Soft Shadows
All shadow rays go through
No shadow rays go through
Some shadow rays go through
![Page 5: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/5.jpg)
Anti-Aliasing• Raytracing can alias badly
– Each ray is a single point sample
– Problem is made worse by recursive rays – the point sample depends on other point samples
• Common solutions:– Super-sampling: Cast multiple rays per pixel and average their
contribution in some way
– Jittered sampling: Frequently used with super-sampling, randomly jitters each ray within the pixel
– Adaptive sampling: Cast extra rays through the pixel if some initial sample rays indicate that they are needed
![Page 6: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/6.jpg)
Anti-Aliasing
Uniform Jittered Adaptive
![Page 7: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/7.jpg)
Distribution Raytracing• Distribution raytracing casts more than one ray for each
sample– Originally called distributed raytracing, but the name’s confusing
• Multiple rays for each pixel, distributed in time– Gives you motion blur, a strong visual clue for motion
• Cast multiple reflection rays at a reflective surface– Gives you rough, blurry reflections
• Simulate multiple paths through the camera lens system– Gives you depth of field, an important visual clue for depth
![Page 8: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/8.jpg)
Distribution RaytracingDepth of Field
Watt: \learning\Study12\
![Page 9: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/9.jpg)
Raytracing Can’t Do…• Recall light paths• Which does a raytracer capture?• Which can it not capture?
![Page 10: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/10.jpg)
Ray-traced Cornell box, due to Henrik Jensen,http://www.gk.dtu.dk/~hwj
![Page 11: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/11.jpg)
Missing Paths• Basic recursive raytracing cannot do:
– LS*D+E: Light bouncing off a shiny surface like a mirror and illuminating a diffuse surface
– LD+E: Light bouncing off one diffuse surface to illuminate others
• Basic problem: The raytracer doesn’t know where to send rays out of the diffuse surface to capture the incoming light
• Also a problem for rough specular reflection– Fuzzy reflections in rough shiny objects
![Page 12: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/12.jpg)
Bi-directional Raytracing• Cast rays from the light sources out into the scene: Light
pass– When a ray hits a diffuse surface, accumulate some light there– Surfaces record the amount of light that hits them
• Store the light in texture maps• Store the light in quadtrees• Store the light in photon maps
• Cast rays from the eye out into the scene: Eye pass– When a ray hits a diffuse surface, look up the amount of light that
hit it in the light-ray phase
• What paths does it capture?• What sort of visual effects do you see?
![Page 13: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/13.jpg)
Caustics
Watt: \learning\Study13\
Standard raytracer Bi-directional raytracer
More rays in the light pass
Note the LS*DS*E paths
![Page 14: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/14.jpg)
Refraction caustic
Henrik Jensen, http://www.gk.dtu.dk/~hwj
![Page 15: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/15.jpg)
Refraction caustics
Henrik Jensen, http://www.gk.dtu.dk/~hwj
![Page 16: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/16.jpg)
Still Missing…• LD*E paths – Diffuse-diffuse transport
– Formulated and solved with radiosity methods
• L(S|D)*E paths– Solved with Monte-Carlo renderers – very very
inefficient
– Also solvable with multi-pass methods, but also very very inefficient, and subject to aliasing
– An unsolved (unsolvable?) problem
![Page 17: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/17.jpg)
Watt: \learning\Study15\Museu4.tif
Real World LD*E Paths
![Page 18: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/18.jpg)
Radiosity Assumptions• All surfaces are perfectly diffuse
– Means that is doesn’t matter which way light hits or leaves a surface
• Illumination is constant over a patch– Can break the world up into a discrete number of pieces– Problems at sharp illumination boundaries - shadows– Ways around these problems, but less efficient and less
able to manage scene complexity
• Assumptions allow us to solve for LD*E paths
![Page 19: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/19.jpg)
Radiosity Equation
• Derived from the global illumination equation using radiosity assumptions
• Bi is the radiosity (brightness) of patch i i is the diffuse reflection coefficient• Fij is the form factor, which quantifies how much light
patch j contributes to patch i• The brightness of each patch depends on how much light it
gets from all the others, and its diffuse reflection
j
N
jijiii BFEB
1
![Page 20: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/20.jpg)
Solving the Radiosity Eqn• Radiosity algorithms use one of several methods to solve
the radiosity equation– Basically a very large linear system, so techniques can all be
mapped onto linear system solvers
• A large part of the computation is in finding form factors– Describe how much light gets from each patch to every other patch
– Geometric in nature - do not depend on the illumination, just the layout of the scene
• Another key factor is finding good meshing strategies - ways of laying out the patches
![Page 21: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/21.jpg)
Watt: \learning\Study15\Rdcb2.tif
Radiosity Example• Color bleeding is
extreme in this example
• Textures are applied after solving for illumination
• Some meshing artifacts are visible - note the banding around the pictures on the wall
![Page 22: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/22.jpg)
Watt: \learning\Study15\Rdcb1.tif
Radiosity Meshing• Each patch is colored
with its illumination
• Note the discrete nature of the solution
• The previous image was obtained by pushing color to vertices and then Gourand shading
![Page 23: Today More raytracing stuff –Soft shadows and anti-aliasing More rendering methods –The text book is good on this –I’ll be using images from the CDROM.](https://reader030.fdocuments.in/reader030/viewer/2022033101/56649e625503460f94b5da15/html5/thumbnails/23.jpg)
Next time…• We switch from rendering to animation - last
regular class