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CS101 Lecture 32 Advanced Topics: Computer Graphics & Computer Vision John Magee 6 August 2013 1 Overview/Questions What are Computer Graphics? How do video games work? How are computer animation movies made? What is

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John Magee

6 August 2013

CS101 Lecture 32 Advanced Topics: Computer Graphics & Computer Vision

Overview/Questions

– What are Computer Graphics? – How do video games work? – How are computer animation movies made? – What is Computer Vision? – Video-based Human-Computer Interaction

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What are Computer Graphics?

Many uses:

– User interfaces, Applications – Design, Art – Video games – Animation – Visualization

Recall: Vector Graphics Example

A vector-graphics example in Python.

Computer graphics in general: Description of scene  Visual representation (Image)

Recall Computing: Input  processing  output

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2D Graphics

Imagine a flat world

Vector Graphics assignment by CS108 student, Spring 2008

2D Games

 Arrangement of graphic

elements on a plane.

 Can be vector graphics or

raster graphics.

 Sprite – A (small) raster

graphic that can be moved around a display.

Sprites and masks from Pac-man

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What happens in real world?

Pinhole camera

3D world is projected through a pinhole or a lens

n to a 2D plane.

3D Graphics

Description of 3D scene and viewpoint  simulated projected image

How do you describe 3D world?

Math equations – spheres,

planes, etc.

Polygon mesh – represent a

complex 3D surface with many triangles.

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Real-Time vs. Long Rendering

Rendering – The process of creating the images from the description. Usually involves Rasterization.

 Interactive graphics (GUI,

Video Games) must render the scene quickly.

 Art, Animation, etc. can

take much longer.

Ray Tracing

 Traces a path of light

from the camera through the image pixels into the scene description.

 Long rendering time.

Good for creating photorealistic images.

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Ray Tracing

– My CS680 homework assignment #4 from 2001

Ray Tracing

 Some better examples:  POV-Ray Hall of Fame

– http://hof.povray.org/ Persistence of Vision Ray Tracer http://www.povray.org/

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Other Techniques

Texture Mapping

Shading

Bump Mapping

Sphere Bump Map Result

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Graphics Accelerator

– Specialized hardware for real-time rendering (usually gaming!)

Graphics in the news recently:

WSJ: In Pixar's 'Brave,' New Software Adds Rich Detail

http://online.wsj.com/article/SB10001424052702303836404577472942036042750.html http://www.msnbc.msn.com/id/47914137/ns/technology_and_science-science/t/brave-brings-hair-raising-animation- life/#.T-flfrVrMYQ http://phys.org/news/2012-06-brave-features-hair-raising-animations.html 16

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Graphics in the news recently:

 Throwing shade: how Pixar changed the way light works

for 'Monsters University'

– Inside the studio's new Global Illumination system  http://www.theverge.com/2013/6/21/4446606/how-pixar-

changed-the-way-light-works-for-monsters-university

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Animation

How does Pixar make their movies?

– They have custom software and a large “rendering farm”

Open Movie Project:

– 2 Films made with free/open source software. – Made with Blender http://www.blender.org/ and other software. – Code for the movie is available. http://www.bigbuckbunny.org/ http://www.elephantsdream.org/

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Computer Vision

Recall: Computer graphics in general Description of scene  Visual representation (Image) Computer Vision in general: Image(s)  Some description of the scene How are Computer Graphics and Computer Vision Related? Example - Input: Image Output: Face locations

Fujifilm camera demo

Computer Vision

Many Subfields

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Some Easy Techniques

 Color Analysis  Motion Analysis  Template matching

(Ignore the extra detail on the next few slides)

Color Analysis

Skin color analyzed by lookup of 2D histogram: Histogram can be updated during operation 

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Motion Analysis

Motion analysis by frame differencing: Recall: Video compression uses frame differencing.

Template Matching

 Normalized correlation coefficient matching over

multi-resolution search space.

12 x 16 Template matching over all resolutions 

Sum of Absolute Differences

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Face Tracking

Face Detection vs. Face Recognition

Face Detection exploits the similarities between human faces. Face Recognition exploits the differences between human faces.

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Computer Vision

What can go wrong?

– You might not know anything about a scene! – Lighting could change! – People could do weird things!

Human-Computer Interaction

We’re all used to mouse and keyboard… But you could use a camera to track motion… Camera Mouse

http://www.cameramouse.org/ (Free Download)

Articles and Videos:

http://www.bu.edu/today/2009/04/10/seeing-eye-mouse http://www.bu.edu/today/2011/big-meaning-in-the- smallest-movements/ A user with severe paralysis using the Camera Mouse

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Google Similar Images

http://www.youtube.com/watch?v=6fD2t4d2Ln4

http://similar-images.googlelabs.com/

Bat Tracking

http://www.cs.bu.edu/faculty/betke/research/bats/

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Computer Vision in Games

 Playstation Eye

– http://en.wikipedia.org/wiki/PlayStation_Eye – http://www.youtube.com/watch?v=bgLN7uOj8Jg

 Xbox Kinect

– http://www.youtube.com/watch?v=oACt9R9z37U – http://www.youtube.com/watch?v=GH_gDreIdcM&feature=related