H331: Computer Graphics

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H331 Computer Graphics

• http//www.cs.kuleuven.ac.be/graphics/H331/Phili
  p Dutré
• Department of Computer Science
• Wednesday, April 30

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Production Rendering

• Making movies
• Images portray and accent the story
• Cheating physics to make images less boring
• Image will be seen very large by millions of
  people
• No artifacts please
• Deadlines cannot be broken
• Better be fast, robust, predictable

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Live action movies

• They are NOT photographs of real scenes
• Have to combine virtual and real

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Issues in image synthesis

• Efficiency
• How much does it take for the machine?
• Control
• How hard is it to render the image for a person?
• Fidelity
• How faithful is the picture to what I have in
  mind?

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Production requirements

• Large amount of high quality geometry
• Arbitrary programmable shading
• Limited time memory
• No artifacts (aliasing, tesselation, noise,
  cracks, numerical instability)
• Mixed rendering algorithms (scanline, raytracing,
  volume rendering)
• Robustness

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Some numbers

• 2000x1800 _at_ 36-100 samples/pixels
• 120,000 frames
• Not counting trials, mistakes, multiple elements
• Input geometry per frame 1 GB
• Input texture per frame 1-10 GB
• Average cost 4 hours, 256-512 Mb
• Roughly 50 visibility, 50 shading

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Numbers and money

• Renderfarm
• 100 Sun boxes with 14GB memory
• Approximate cost 10M (12 of a movie)
• Cannot afford slow rendering!

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PIXAR PRMan

• Strenght
• Really good antialiasing
• Really good motion blur
• High level surface primitives
• Cheap displacement maps
• Flexibility/Robustness
• Physical light transport?

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Ray tracing

• Yes, they do it moderately
• Glad they do it only occasionally
• Normally raytrace only hand-simplified versions
  of the scenes

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Ray tracing
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Control
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The typical problem
Make this side less satured
Make this corner pinker
Make this shadow sharper
Make this shadow blurrier
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Hollywood solution ? light props

• Light props, light tricks

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Hollywood solution ? compositing
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Hollywood solution ? compositing
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The CG solution ? fake lights
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The CG solution ? bend light
Physical light
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The CG solution ? bend light
Physical light
Movie light
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Light tells a story
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Hard issues with Rendering

• Production requirement
• Flexibility
• Robustness
• Control
• Mixing with live action footage
• Cant afford to change the WORKFLOW!!!

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True production problems

• Modeling
• Animating
• Lighting

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What would they pay you for?

• Time/memory requirements
• Automation/Control
• Skilled lighters do better than GI
• Too many lighters need better tools
• Quality issues
• Raytracing is VERY artifact prone, but simple
• Cheating physics better

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Reality is nice, but the art director wants the
shadow to be blue and the motion blur streak to
be longer and the wagon wheals to strobe like an
old movie. Every aspect of the image must be
adjustable for artistic interpretation, even when
doing so violates physics, mathematics and common
sense. Larry Gritz