1 by dr. hany elsalamony. 2 3 computer graphics generally means creation, storage and manipulation...

1By Dr. Hany Elsalamony

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Computer graphics generally means creation, storage and manipulation of models and images

Such models come from diverse and expanding set of fields including physical, mathematical, artistic, biological, and even conceptual (abstract) structures

Frame from animation by William Latham, shown at SIGGRAPH 1992. Latham uses rules that govern patterns of natural forms to create his artwork.

By Dr. Hany Elsalamony

Examples: OpenGL™, DirectX™, Windows Presentation Foundation™ (WPF), RenderMan™

Primitives (chars, lines, polygons, meshes,…) Attributes

• color• line style• material properties for 3D

Lights Transformations Immediate mode vs. retained mode

• immediate mode: no stored representation, package holds only attribute state, and application must completely draw each frame

• retained mode: library compiles and displays from scene graph that it maintains, a complex DAG. It is a display-centered extract of the Application Model


Computer graphics – process of producing a picture or image using the computer

Computer interfaces popular on personal computers

Desktop publishing Realistic images generated using

mathematical and physical methods


Creating a model Perform necessary transformation Lighting and rendering the object The goal is the creation of an image

by writing a program instead of taking a picture with a camera

There exists an analogy between writing graphical programs and taking pictures by a camera


Pixel or “Picture element” is the simplest element in computer graphics

Single location on the computer screen or printout

Value of each pixel is the range from white to black or range of intensities of red, green, blue (RGB) colors.


The pixels of an image are organized into two dimensional grid – frame buffer

Multiple frame buffers can be stored in computer memory

Double buffering – first image is drawn into frame buffer and sent to display. While the user is looking on the display, the next picture is drawing to the second buffer.


Image don’t fill the entire screen but is drawn into a window

Pixels are adressed within the window based on their location

Relative position of each pixel enables moving the window and change its size


Calculating pixel values to create impression of a realistic picture

Simulation of objects from the real word

Approximation of physical properties of objects

Limitations given by computing time and memory space


Modeling – creates an internal representation of the objects in the scene

Rendering – converts the screen description into image

Display – shows the image on the output device


Object Specification

Model

TransformationScene Description

Scene Description Model

TransformationView and Light Specification

Clipping and Hidden Surface Removal

Shading Image


Display TransformationImage Output


1. Display of information2. Design3. Simulation and animation4. User interfaces


Display of information• Maps • GIS (geographic information system)• CT (computer tomography)• MRI (magnetic resonance imaging) • PET (positron-emission tomography)• Fluid flow, molecular biology,

mathematics…


Design• CAD (computer-aided design):

VLSI (very-large-scale integrated) circuits• Together with other tools:

architecture or interior design


Simulation and animation• Flight simulation – pilot training• Games and educational software• Benefits:

Less cost Less danger, e.g. combination with the VR

(virtual reality) techniques can help surgical interns and astronauts


User interfaces• Friendly working environment:

windows, icons, menus, pointing devices

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Interface for a painting program


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Specifications of the functions in the graphics library

•The OpenGL graphics system is an Application Programming Interface (API) to graphics hardware.


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Objects Viewers Light sources Material properties


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Position (COP)

Orientation Focal length Film plane


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Wireframe Flat shading

• HSR (Hidden surface removal) Smooth shading Curves and surfaces

• NURBS, Bezier curves/surfaces Texture mapping

• Bump mapping, environmental maps, antialiasing…


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High-end systems: VRAM or DRAM Simpler systems: part of memory Depth: the number of bits per pixel True color: depth=24 Resolution: the number of pixels in

the frame buffer


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Conversion of geometric entities to pixels in the frame buffer

• High-end systems Special-purpose processors

• Simpler systems A single and shared processor


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CRT (Cathode-ray tube)By Dr. Hany Elsalamony

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CRT• Refresh: at least 50 times per second• Interlace and non-interlace systems• Color CRTs have three colored phosphors

and a shadow mask Other raster devices:

• LCD (liquid-crystal displays)• Plasma panels and digital projection

systems• Non-refreshable: printers and plotters


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Mouse Joystick Data tablet Anything else?

Hand Foot Voice Mind?


Image formation• Lighting• Shading• Properties of materials


Object: formed from geometric primitives• Points, lines, polygons• Vertex (pl. Vertices) is the most primitive

one Viewer:

• Locations• Viewing angles


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3D world 2D image


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Synthetic-camera Model

Film Plane

Projection Plane


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Penetrating transparent surfaces

Reflected by

Mirrors

Diffuse surfaces

Refracted

AbsorbedBy Dr. Hany Elsalamony

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Visual system does not have the same response to each color.We are most sensitive to green light


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dz

xx

dz

yy

p

p

/

/

d

h

2tan2 1

(xp, yp, -d) is the projection of (x, y, z)


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Bellows Camera Projector


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COP(Center of Projection)

Focal Length


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Clipping Window


Wireframe Flat shading

• HSR (Hidden surface removal) Smooth shading Curves and surfaces

• NURBS, Bezier curves/surfaces Texture mapping

• Bump mapping, environmental maps, antialiasing…


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Example: Scene graph


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Early graphics system

Computeline segments

Drawline segments

Very high rate to avoid flickering


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Display-processor architectureBy Dr. Hany Elsalamony

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Arithmetic pipeline: doubling the throughput!

Pipeline Architecture: Geometric pipeline


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Arithmetic pipeline: doubling the throughput!

Pipeline Architecture: Geometric pipeline


Transformation• Conversion between coordinate systems• Translation, rotation, scaling• Aggregate transforms by matrix

multiplications Clipping

• Could be further pipelined


Projection• Remaining 3D objects are projected into 2D

objects• Parallel or perspective projections

Rasterization• Convert 2D objects into pixels


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Latency Throughput:

• How fast we can move geometric entities through the pipeline

• How many pixels per second we can alter in the frame buffer

Pipeline architecture is not a must• Ray tracing or radiosity for better quality


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Application of computer graphics A graphics system Human visual system Pinhole and synthetic camera models Image formation Geometric pipeline Realistic images may require

resolution of up to 40006000


1 by dr. hany elsalamony. 2 3 computer graphics generally means creation, storage and manipulation...

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