computer graphics/and multimedia cmm472/cit773 what is cg ?, history of cg, course overview

Computer Graphics/and MultimediaCMM472/CIT773

What is CG ?, History of CG, Course

Overview

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Introduction

• Story of CG– Producing image using computer– 40 years ago : display a few line on CRT– Now generated images are indistinguishable

from photographs

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Application of CG

• Depends on the user community need • Advance of hardware and software• Area of CG

– Display information – Design– Simulation– User interface

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Display Information

• Classical using spoken and written language• Drawing field

– Babylonians (4000 years ago) use stone for floor plan– Greek (2000 years ago) till Renaissance

• Has idea of architecture graphically

– Before today use manual drafting and drawing – Today : computer based system

• Able to develop and manipulated in real-time

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CG Applications

• Statistic– 100 years : explored the techniques for plotting

data– Now, computer plotting package provided

variety of technique, color tools etc.

• Medicine– Interested in data-analysis problems– Image technology, CT, MRI, Ultrasound, PET

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Design

• Engineer, architecture using CAD– Iterative process for best or optimize solution– Ex. Mechanical parts, VLSI etc.

• CAD package has interactive tools ex. menu, tool bar– interactive interface and analyze etc.– Able to generate different image, different view

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Simulation

• Refer to capable of generating images in real-time• Applied with advance hardware • Ex. Training Pilot, Flight simulator• Some special VLSI chip able to generate

sophisticate game• Photo realistic movie • Together with headset led her has stereoscopic

effect by different view for each eye

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User Interface

• GUI from OS like MS windows, X windows, Macintosh OS

• Use of menu and icon, mouse• Different only in detail

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Graphical System• 5 major elements

– Processor, memory, frame buffer, output devices and input devices

• General for every system

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Pixel and Frame buffer

• Picture is produced as array of pixel (raster)• Pixel are stored in Frame buffer memory :

VRAM for fast redisplay• Depth : number of bits for each pixel

– 24 bit has true color system : RGB system

• Resolution : number of pixel in frame buffer

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Detail of area around one eye showing individual pixel.

Pixels. Image of Yeti the cat

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Output Device

• Domain type : CRT display• Computer convert display signal from digital to analog to

control plate• Refresh rate : rate for retrace the screen at least 50 times

per second

The cathode-ray tube (CRT)

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2 systems for refresh rate

• In order to avoid flicker of display• Interlace display :

– Odd row and even row are refresh alternately

• Noninterlace display– Display scan in one time row by row

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Color display system

Shadow-mask CRT

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Images

• Computer generate synthetic images• Lighting , shading and properties involve

many aspect of image formation

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Object and Viewers in CG

• Object references – Shape referred by object point to reference coordinate

system– Position– Geometric primitives : eg. point, line etc.

• Viewer• One who observe object ( man, camera etc.)• The same object different image for different place

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A’s view

B’s view C’s view

Image seen by three different viewers

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Image forming in real camera

Viewer and object are both in 3D system but the formed image is 2D

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Light and Images

• Make an image more realistic• Light from source strike and reflect from object

enter the camera give some surface detail to the viewer

A camera system with a light source

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Ray tracing

• The strike and illuminate ray that interact the object surface is the ray that make an image to viewer

Scene with single point source

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Ray tracing

A

B

C

D

E

F

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Source of light

• Light travels in straight line to object• Point source

– Light from single location emit equally in all direction

• Light bulb– Emitting over an area, more in one direction

• More sources can be modeled by a number of point sources

• Monochromatic light : source of single frequency

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Receptor: Human Visual system

• Extremely complex • Response to 350 nm to 780 nm light• Sensor :3 type cone cell and 1 type of rod cell

The human visual system

• Resolution : how large object size that can see• Intensity: the measure of light energy• Brightness : how perceive intense light that

emitted form object• Eyes do not have the same response like

monochromatic– Red light and green light with same intensity have

different to us

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CIE standard observer curve

Cone sensitivity

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Pinhole Camera: How image build on projection plane

• Simple geometric model to understand how image contribute

Pinhole camera Side view of pinhole camera

• Properties– Infinite depth of field

• Disadvantage– Admits only single ray– Unable to adjust to different angle of view

q : view angle

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The synthetic camera model

• Learn to understand that the specification of the object is different from the viewer

Imaging system

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Equivalent views of image formation

(a) With image formed on the back of camera

(b) With image plane move in front of the camera

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Imaging with the synthetic camera

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Image Clipping

Clipping (a) with window in initial position, and (b) with window shifted.

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Application Programmer Interface

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Application model for programmer

Application programmer’s model of software

• Set of function reside in a graphics library• API should match the conceptual model that the user

wish to employ to the specific images• Available API: OpenGL, PHIGS, Direct3D, VRML

and JAVA-3D• Specification of the synthetic camera model

– Objects– Viewer– Light source– Material Properties

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Modeling - Rendering

• Renderer duty– Adding light source – Material properties– Other detail effect

The modeling-rendering pipeline

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Graphic Architecture

• Information had to be sent with high enough rate to avoid flicker

Early graphics system

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Display Processor

Display-processor architecture

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Pipeline: arithmetic processing pipeline

Arithmetic pipeline

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Object processed geometry

Geometric pipeline

Convert the object coordinate system to display system

Limit the image part on display

Project 3D object into 2D on display

2D image converted to pixel and store at frame buffer

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Performance characteristic

• Pipeline architecture• Floating point VLSI chip : able to do 4*4

matrix