Computer graphics

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Graphics & Graphical
Programming

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Computer Graphics
The experimentation of cathode rays is largely accredited to J.J.
Thomson, an English physicist who, in his three famous
experiments, was able to deflect cathode rays, a fundamental
function of the modern CRT. The earliest version of the CRT was
invented by the German physicist Ferdinand Braun in 1897 and is
also known as the Braun tube

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Computer Graphics is about animation (films)
Major driving force now

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Games are very important in Computer Graphics

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Medical Imaging is another driving force
Much financial support
Promotes linking of graphics with video, scans, etc.

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Computer Aided Design too

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Scientific Visualisation
To view below and
above our visual range

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Graphics Pipelines
• Graphics processes generally execute
sequentially
• Typical ‘pipeline’ model
• There are two ‘graphics’ pipelines
– The Geometry or 3D pipeline
– The Imaging or 2D pipeline

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Geometry Pipeline
Animation/Interaction : time
Modeling: shapes
Shading: reflection and lighting
Transformation: viewing
Hidden Surface Elimination Imaging
Pipeline

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Imaging Pipeline
Rasterization and Sampling
Texture Mapping
Image Composition
Intensity and Colour Quantization
Geometry
Framebuffer/Display
Pipeline

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An example through the pipeline…
The scene we are trying to represent:
Images courtesy of Picture Inc.

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Wireframe model – Orthographic views

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Perspective View

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Depth Cue

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Hidden Line Removal – add colour

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Constant Shading - Ambient

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Faceted Shading - Flat

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Gouraud shading, no specular highlights

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Specular highlights added

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Phong shading

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Texture mapping

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Texture mapping

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Reflections, shadows & Bump mapping

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Computer Graphics
A cathode ray tube is a vacuum tube which consists of one or more
electron guns, possibly internal electrostatic deflection plates, and
a phosphor target.
An image is produced by controlling the intensity of each of the
three electron beams, one for each additive primary color (red,
green, and blue).
In all modern CRT monitors and televisions, the beams are bent
by magnetic deflection, a varying magnetic field generated by coils
and driven by electronic circuits around the neck of the tube,
although electrostatic deflection is commonly used in
oscilloscopes, a type of diagnostic instrument.

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Graphics Definitions
• Point
– a location in space, 2D or 3D
– sometimes denotes one pixel
• Line
– straight path connecting two points
– infinitesimal width, consistent density
– beginning and end on points

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Graphics Definitions
• Vertex
– point in 3D
• Edge
– line in 3D connecting two vertices
• Polygon/Face/Facet
– arbitrary shape formed by connected vertices
– fundamental unit of 3D computer graphics

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Graphics Definitions
• Raster
– derived from TV systems for a row of pixels
– commonly referred to as a scanline
– does influence algorithms – reducing memory
requirements, parallelism, etc.
– is the derivation of rasterization, scan-line
algorithms

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Raster interlaced scanning

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Raster pros and cons
•Disadvantages
•Requires screen-sized memory array
•Discrete spatial sampling (pixels)
•Moire patterns result when shadow-mask and
dot-pitch frequencies are mismatched
•Convergence (varying angles of approach
distance of e-beam across CRT face)
•Limit on practical size (< 40 inches)
•Spurious X-ray radiation
•Occupies a large volume
•Advantages
•Allows solids to be displayed
•Uses low-cost CRT H/W (TVs)
•Whole Screen is constantly updated
•Bright light-emitting display technology

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Summary
• The course is about algorithms, not application
packages
• Graphics execution is a pipelined approach
• Most of the steps introduced with an example
• Basic definitions presented
• Some support resources indicated
• www.massey.ac.nz/~kahawick/159235
• Acknowledgements - Thanks to Eric McKenzie,
Edinburgh, from whose Graphics Course some of
these slides are based.