tricky??? you have a jug of milk, and you need to measure out just one cup. how do you do this if...

Tricky???

You have a jug of milk, and you need to measure out just one cup. How do you do this if you only have a three-cup measuring container and a five-cup container?

The ages of a father and son add up to 66. The father's age is the son's age reversed. How old could they be?

You are standing in front of a room with one light bulb inside of it. You cannot see if it is on or off. Outside the room there are 3 switches in the off positions. You may turn the switches any way you want to. You stop turning the switches, enter the room and know which switch controls the light bulb. How?

Adapted from Angel: Interactive Computer Graphics 5E © Addison-

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Problem

1. A, B, C, D and E play a game of cards. A says to B, "If you give me three cards, you will have as many as E has and if I give you three cards, you will have as many as D has." A and B together had 10 cards more than what D and E together have. If B has two cards more than what C has and the total number of cards be 133, how many cards does B have?


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Problem

Count the number of squares in the given figure.


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Problem

There are some houses in a street back to back .And the house behind 10 is 23.

How many houses are there in the street?


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Problem

A batsman average was 15. At last innings he took 23 runs, then his average became16.how many runs he should have scored to make his average 18?


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Problem

A secret can be told only to 2 persons in 5 minutes .the same person tells to 2 more persons and so on . How long will it take to tell it to 768 persons ?


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Adapted from Angel: Interactive Computer Graphics 5E © Addison-Wesley 2009

7

Computer Graphics and Visualization (06 CS 65)

Dept of Computer Science and Engineering

Srinivas School of Engineering, Mukka

Chapter 1


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What is Computer Graphics?

Objectives

In this lecture, we explore what computer graphics is about and survey some application areas

We start with a historical introduction


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Computer Graphics

Computer graphics deals with all aspects of creating images with a computer– Hardware– Software– Applications


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Example

Where did this image come from?

What hardware/software did we need to produce it? Adapted from Angel: Interactive

Computer Graphics 5E © Addison-Wesley 20091

1

Preliminary Answer

Application: The object is an artist’s rendition of the sun for an animation to be shown in a domed environment (planetarium)

Software: Maya for modeling and rendering but Maya is built on top of OpenGL

Hardware: PC with graphics card for modeling and rendering


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Some interesting applications

Training pilots with simulated airplanes Generating graphical displays of virtual

environment in real time Movies! Massive multiplayer games!


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Different ways to obtain images

Handwritten Photography Computer graphics!


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Application areas of Computer Graphics

Display of information Design Simulation and animation User interfaces


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Display of information

A medium to convey info among people– More than 4000 yrs ago, babylonians displayed floor plans of buildings on

stones– More than 2000 yrs ago, Greeks conveyed their architectural ideas

graphically– Today same info generated by architects using computer-based drafting

systems Maps can be developed and manipulated in real-time over internet Detecting security threats using bio-informatics Medical imaging – CT scan, MRI scan, PET scan etc generate 3-D

data & is subjected to algorithmic manipulation to provide useful info Fluid flow, molecular biology and mathematics


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Design

Engineering and arch concerned with design– Cost effective and esthetic solution– Satisfying specifications– Iterative process

Graphic tools in Computer-Aided Design(CAD)– In mech, arch, VLSI ckts, animations

Having tools to generate different images of same objects at different stages of design process


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Simulation and animation

Sophisticated images in real time Training of pilots

– Increase safety and reduce training expenses Designing robots, planning its path, simulating its behavior

in complex environments Animation in television, motion pictures and advertising

industries– Entire animated movies using computers

Can generate photorealistic images by a computer– Difficult to distinguish computer generated or computer-altered

images from a photograph! Adapted from Angel: Interactive Computer Graphics 5E © Addison-

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Simulation and animation

Field of Virtual Reality(VR)– Human viewer equipped with a display headset that

allows to see separate images with right eye and left eye!– Body location and position tracked by the computer– Can act as part of a computer-generated scene

Can train a surgical intern to do an operation in this way! Or an astronaut might be trained to work in a weightless

environment!

Revenue from video games has surpassed revenue from commercial films!


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User interfaces

Interaction with computers using a visual paradigm– Windows, icons, menus and a pointing device

X windows system, microsoft windows, Macintosh OS X etc

Internet explorers such as Firefox and IE– We often forget that we are working with computer

graphics UI for modeling geometric objects


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A graphics system

Has all components of a general-purpose computer 5 major elements

– Input devices– Processor– Memory– Frame buffer– Output devices

Although all are present in a standard computer(except frame buffer), it is the way each element is specialized for computer graphics that matters


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Basic Graphics System


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Input devices

Output device

Image formed in FB

Pixels and Frame Buffer

Almost all graphics systems are raster based Raster – an array of picture elements or pixels,

within the graphics system Collectively, the pixels are stored in a part of

memory called frame buffer Frame buffer

– Core element of a graphics system Resolution – the no of pixels in the frame buffer

– It determines the detail that you can see in the imageAdapted from Angel: Interactive


Pixels


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Image of a Cat using pixels

Detail of area around one eye showing individual pixels

Frame buffer continued..

Depth ( or precision ) of frame buffer– No of bits that are used for each pixel– Determines properties like how many colors can be

represented etc– 1 bit deep, then two colors– 8-bit deep, then 256 colors– In full color systems, there are 24( or more) bits per

pixel. Can display sufficient colors to represent most images realistically

Also called as true-color or RGB-color systemsAdapted from Angel: Interactive


Continued..

Frame buffer is implemented with special types of memory chips– Enables fast redisplay of contents of frame buffer

In a very simple system, frame buffer holds only colored pixels that are displayed on the screen

In most systems, frame buffer also holds info such as depth info needed for creating images from 3-D data– In such systems, frame buffers comprise multiple buffers


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Processor

To take specifications of graphical primitives ( lines, circles, polygons etc) generated by application programs and to assign values to the pixels in the frame buffer that best represent these entities

Conversion of geometric entities to pixel colors and locations in the frame buffer is known as rasterization or scan conversion

Now a days, special purpose graphics processing units(GPUs) are used– Custom tailored to carry out specific graphics functions– GPU can be on mother board or on a graphics cardAdapted from Angel: Interactive


Output devices

For many years dominant type of display is CRT ( Cathode Ray Tube)– When electrons strike the phosphor coating on the tube, light is

emitted– The direction of beam is controlled by two pairs of deflection plates– Output of computer is converted to voltages across x and y

deflection plates– Light appears on the surface of CRT when a sufficiently intense

beam of electrons is directed at the phosphor If the voltages steering the beam change at a constant rate,

the beam will trace a straight line, visible to a viewer– Called as random-scan, calligraphic or vector CRT


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CRT

Can be used either as a line-drawing device (calligraphic) or to display contents of frame buffer (raster mode)


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Contd…

A typical CRT will emit light only for a short time– Few millisecs

For a human to see a steady, flicker free image, the same path must be retraced or refreshed, by the beam at a sufficiently high rate, called refresh rate– Modern displays have refresh rate of about 85 Hz

Raster system – system displays them as points on the surface of display in 2 ways– Progressive display – pixels are displayed row by row at the refresh

rate– Interlaced display – odd rows and even rows are refreshed alternately


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Shadow-mask CRT – colored CRT


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Shadow mask, a metal screen with small holes, to ensure that an electron beam excites only phosphors of the proper color

Generic flat-panel display


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LEDLCDPlasma panels

Flat panel monitors

Inherently raster LEDs ( light emitting diodes )

– Middle panel contains light emitting diodes – can be turned on or off by the electrical signals sent to the grid

LCDs(liquid crystal displays)– The electrical field controls the polarization of the liquid crystals in

the middle panel Plasma panels

– Voltages on the grids energize gases embedded between the glass panels holding the grids

2 outside plates contain parallel grids of wires that are oriented perpendicular to each other– By sending electrical signals to proper wires in each grid, the

electrical field at a location, determined by the intersection of two wires, can be made strong enough to control corresponding element in the middle plate

Projection systems

Most of them are also raster devices Use a variety of technologies including CRTs

and DLP( Digital Light Projection )

Input Devices

Keyboard + one another input device– Like mouse, joystick or data tablet

Called as pointing devices– Allow user to indicate a particular location on the

display Game consoles – multiple buttons, joystick, dials

etc Games, CAD and virtual reality applications

– Need for 3-D location input– Laser range finders and acoustic sensors– Data gloves – sensors, computer vision systems

Objects and viewers

Object – exist in space independent of any image formation process and of any viewer– In graphics, we form objects by specifying the

positions in space of various geometric primitives (lines, points, polygons)

– In most graphic systems, a set of locations ( or vertices ) in space is sufficient to define ( or approximate) most objects. Ex., line, sphere

Imaging system

Every imaging system must provide means of forming images from objects

To form image we must have someone viewing our objects ( person, camera etc)

It is the viewer that forms the image of our objects In human visual system, image is formed at the

back of the eye, in a camera on a film plane Do not confuse objects and images

Every imaging system must provide a means of forming images from objects


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It is the viewer that forms the images of our objects

viewer can be a person, a camera or a digitizer

A camera system viewing image of a building


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Both object and viewer exist in 3-D worldBut the image that they define, on film plane, is 2-D

Light and images

If there were no light sources the objects would be dark

In the figure, we see an object, a viewer and also a light source.

Light from the source strikes various surfaces of the object, and a portion of the reflected light enters the camera through the lens

Details of interaction between light and the surfaces of the object determine how much light enters the camera


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Light source

Light is a form of EM radiation– EM energy travels as waves characterized by wavelengths or frequencies– EM spectrum includes radio waves, infrared(heat), and a portion that

causes response in our visual system Range of this visible spectrum is 350nm to 780nm

– Wavelengths in middle of the range, around 520nm are seen as green– Those near 450nm seen as blue.(shorter than blue is violet)– Those near 650 nm seen as red( wavelengths between green and red seen

as yellow) Light sources can emit light either as a set of discrete frequencies or

continuously– Laser – emits light at single frequency– Incandescent lamp – over a range of frequencies


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Contd..

Geometric optics – models light sources as emitters of light energy, each with a fixed intensity– Light travels in straight lines from sources to those

objects with which it interacts An ideal point source emits energy from a single

location at one or more frequencies equally in all directions– Sources like light bulb emits light over an area and emit

more light in one area than the other


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Image formation models

A ray is a semi infinite line that emanates from a point and travels to infinity in a particular direction– Think of rays of light emanating in all directions

from point source A portion of these infinite rays contribute to

the image on the film plane of camera or human eye


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Image formation models


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Contd…

If source is visible from camera, some of the rays go directly from the source through the lens of the camera and strike film plane

Most rays go off to infinity– Contribute nothing to the image

Rays striking objects can interact in a variety of ways– If surface is mirror, depending on orientation of the surface – enters

lens of camera and form images– Other surfaces scatter light in all directions– If surface is transparent, light ray from source can pass through it

and may interact with other objects, enter the camera, or travel to infinity without striking other surface


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Image formation techniques

Ray tracing– Not well suited for real-time computation

Photon mapping Radiosity

– Most important in computer graphics


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Imaging Systems

Two physical imaging systems– Pin hole camera– Human visual system


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Pin hole camera

A box with a small hole in the center of one side of the box– The film is placed inside the box on the side

opposite the pinhole Initially pin hole is covered

– It is uncovered for a short while to expose the film The hole is so small that only a single ray of

light, emanating from a point, can enter itAdapted from Angel: Interactive


Contd..

Side view– We can calculate the y coordinate of the image to

be Top view

– We can calculate the x co ordinate of the image to be

The z coordinate of the image will be zp = -d

This point (xp,yp,-d) is called as the projection of the point (x,y,z) Adapted from Angel: Interactive


dz

yy p /

dz

xxp /

Contd..

All points along the line between (x,y,z) and (xp,yp,-d) project to (xp,yp,-d)– We cannot go backward from a point in the image

plane to a point that produced it. Field, or angle, of view of our camera is the

angle made by the largest object that our camera can image on its film plane– If h is the height of the camera, angle of view θ is


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h

2tan2 1

Contd…

Ideal pinhole camera has an infinite depth of field– Every point within its field of view is in focus, regardless of how far it is from the

camera Disadvantages

– Pinhole is very small – admits only a single ray of light – almost no light enters the camera

– The camera cannot be adjusted to have different angle of view By replacing the pinhole with a lens, we solve the two problems of the

pinhole camera– Lens gather more light– By picking a lens with proper focal length, we can achieve any desired angle of

view upto 1800

Physical lenses do not have infinite depth of field; not all objects in front of the lens are in focus


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The human visual system

Light enters the eye through the lens and cornea, a transparent structure that protects the eye

The iris opens and closes to adjust the amount of light entering the eye

The lens forms an image on a two-dimensional structure called the retina on the back of the eye

The rods and cones are light sensors and are located on the retina– They are excited by electromagnetic energy in the range of

350 to 780 nmAdapted from Angel: Interactive


Contd..

The rods are low-level light sensors that account for our night vision and are not color sensitive– The cones are responsible for our color vision

The sizes of the rods and cones, coupled with the optical properties of the lens and cornea, determine the resolution of our visual system

Resolution is a measure of what size objects we can see– It is a measure of how close we can place two points and

still recognise that there are two distinct pointsAdapted from Angel: Interactive


Contd..

The sensors in the human eye do not react uniformly to light energy at different wavelengths

There are 3 types of cones and a single type of rod

Whereas intensity is a measure of light energy, brightness is a measure of how intense we perceive the light emitted from an object to be– We are most sensitive to green light, and least

sensitive to red and blueAdapted from Angel: Interactive


Contd…

Initial processing of light in the human visual system is based on same principles used by most optic systems– But the human visual system has a back end much more

complex that that of a camera or telescope The optic nerve is connected to the rods and cones in

an extremely complex arrangement that has many of the characteristics of a sophisticated signal processor

Final processing is done in part of brain called as visual cortex, where high level functions like object recognition are carried out


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The synthetic-camera model

We look at creating a computer-generated image as being similar to forming an image using an optical system– Called as synthetic-camera model

In the figure, we have– Objects and a viewer– Image formed on the film plane at the back of

camera


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Basic principles of image formation

The specification of the objects is independent of the specification of the viewer– So in graphics library, we need to have separate

functions for specifying the objects and viewer We can compute the image using simple

geometric calculations


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Equivalent views of image formation


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(a)Image formed on back of the camera(as in a pinhole camera)(b) Image plane moved in front of the camera

In a real camera, we flip the image to get the original orientation of the object. In our synthetic camera model, We avoid flipping by a simple trick

Imaging with the synthetic camera

We draw another plane in front of lens and work in 3-dimensions

We find image of a point on the object on the virtual image plane by drawing a line, called projector– From the point to the center of the lens, called as center of

projection– All projectors are rays emanating from the center of projection

The virtual image plane we have moved in front of the lens is called as the projection plane– The image of the point is located where the projector passes

through the projection planeAdapted from Angel: Interactive


Imaging with a synthetic camera


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Projection plane(image is formed wherever projector passes through this plane)

Clipping window

We saw not all objects can be imaged onto the pinhole camera’s film plane. – The angle of view expresses this limitation

This limitation is expressed in front by placing a clipping rectangle or clipping window, in the projection plane– This rectangle acts as a window, through which a viewer, located at

the center of projection, sees the world Given

Location of center of projection Location and orientation of projection plane Size of clipping rectangle

– We can determine which objects will appear in the imageAdapted from Angel: Interactive


The programmer’s interface

Paint program

Develop your own code– ( and we enjoy doing so!)

The interface between an application program and a graphics system can be specified through a set of functions that resides in a graphics library– These specifications are called the application programmer’s

interface Following fig shows application programmer’s model of the

systemAdapted from Angel: Interactive


Application programmer’s model of graphics system

He sees only API– Shielded from details of both hardware and software

implementation of graphics library Software drivers are responsible for interpreting

the output of API and converting these data to a form that is understood by particular hardware

The functions available through the API should match the conceptual model that the user wishes to employ to specify images


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The pen-plotter model

Most early graphics systems were 2-D systems– Images were formed by using a pen-plotter

A pen-plotter produces images by moving a pen held by a gantry, a structure that can move the pen in 2 orthogonal directions across the paper– Plotter can raise and lower the pen as required to create the

desired image Still used for applications like blueprints etc

Some APIs have origins in this model– Process of creating image is similar to process of drawing on

a pad of paper Adapted from Angel: Interactive Computer Graphics 5E © Addison-

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Contd…

We can describe such graphics systems with following drawing functions– moveto(x,y) – moves the pen to location (x,y) on paper

without leaving a mark– lineto(x,y) – moves the pen to location (x,y) and draws a

line from the old to the new location of the pen Add a few more options like initiation/termination

procedures and ability to change pens ( to alter drawing color or line thickness) – and we get a simple but complete graphics system


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Fragment of a program to draw a square in pen-plotter based APIs

moveto(0,0); lineto(1,0); lineto(1,1); lineto(0,1); lineto(0,0);


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What is the image obtained by below program segment?

moveto(0,0); lineto(1,0); lineto(1,1); lineto(0,1); lineto(0,0); moveto(0,1); Lineto(0.5,1.866); lineto(1.5,1.866); lineto(1.5,0.866); lineto(1,0); moveto(1,1); lineto(1.5,1.866);


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Answer


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A raster-based approach for 2-D model

Write pixels directly into frame buffer We can use a single function of the following

form– write_pixel(x,y,color);– x,y is the location of the pixel in the frame buffer– color gives the color to be written there

Such models used while writing algorithms for rasterization and processing of digital images


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Limitations of pen-plotter model in 3-D world

We need to produce the image of a 3-D object on our 2-D pad– Need to figure out where to place 2-D points corresponding to points on our

3-D object. These 2-D points are the projections of points in 3-D space

– Need to apply trigonometry to determine projections Its preferable to use an API, that allows users to work directly in the

domain of the problems and use computer to carry out details of the projection process automatically ( without users having to make trigonometric calculations)

Users can rely on hardware and software implementations of projections within the implementation of the API ( far more better than any possible implementation of projections within their programs!)


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Three-Dimensional APIs

The synthetic camera model is the basis for all popular APIs, including OpenGL, Direct3D, and Open Scene Graph

We need functions in API to specify the following– Objects– A viewer– Light sources– Material properties Adapted from Angel: Interactive


Defining Objects

Objects are defined by sets of vertices– For simple geometric objects(line segment,

rectangle, polygons etc), there is a simple relationship between list of vertices and the object

For complex objects, multiple ways of defining object from set of vertices– Circle defined by 3 points on its circumference or

by its center and one point on its circumference.


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Objects in OpenGL

OpenGL programs define primitives through list of vertices– Ex., triangular polygon– glBegin(GL_POLYGON);– glVertex3f(0.0, 0.0, 0.0); /* vertex A*/– glVertex3f(0.0, 1.0, 0.0); /* vertex B*/– glVertex3f(0.0, 0.0, 1.0); /* vertex C*/– glEnd();

Function glBegin specifies the type of primitive that the vertices define Function glVertex3f specifies x,y,z coordinates of a location in space Function glEnd ends the list of vertices Can also have GL_LINE_STRIP and GL_POINTS


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Specifying viewer

Position Orientation Focal length Film plane


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Viewer or camera

Available APIs differ in both how much flexibility they provide in camera selection, and in how many different methods they allow.

1. Position: The camera location usually is given by the position of the center of the lens (the center of projection).

2. Orientation: Once the camera is positioned, a camera coordinate system can be placed with its origin at the center of projection. Then the camera can be rotated independently around the three axes of this system.

3. Focal length: The focal length of the lens determines the size of the image on the film plane or, equivalently, the portion of the world the camera sees.

4. Film plane: The back of the camera has a height and a width. On the bellows camera, and in some APIs, the orientation of the back of the camera can be adjusted independently of the orientation of the lens.


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Contd…

Developing the specifications for the camera location and orientation uses a series of coordinate system transformations. – These transformations convert object positions represented

in the coordinate system that specifies object vertices to object positions in a coordinate system centered at the center of projection.

The synthetic-camera model emphasizes object is independent of the view. But, the classical viewing techniques, stress the relationship between the object and the viewer.


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Viewer specification in OpenGL

In OpenGL API, all transformations can be set with complete freedom. In addition to that, OpenGL also provides helpful extra functions.

E.g. Function call gluLookAt(cop_x, cop_y, cop_z,

at_x, at_y, at_z, ...); points the camera from a center of projection toward a desired point.

Function call glPerspective(field_of_view, ...); selects a lens for a perspective view.


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Light sources

Light sources can be defined by their location, strength, color, and directionality. APIs provide a set of functions to specify these parameters for each source


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Material Properties

Material properties are characteristics, or attributes, of the objects,

Such properties are usually specified through a series of function calls at the time that each object is defined.

Both light sources and material properties depend on the models of light-material interactions supported by the API.


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Graphics Architectures

Early graphics systems Display processors Pipeline architectures


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Early graphics systems

Used general purpose computers with the standard architecture – single processing unit that processes a single instruction at a time

Host computer to run application program– Send info to the display at a rate high enough to avoid

flicker on the display Simple displays using A/D converters to go from

computer to calligraphic CRT Cost of refresh for CRT too high

– Computers slow, expensive, unreliableAdapted from Angel: Interactive


1

Computer Graphics: 1960-1970

Wireframe graphics– Draw only lines

Display Processors


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wireframe representationof sun object

Display Processors

Rather than have the host computer try to refresh display use a special purpose computer called a display processor (DPU)

Graphics stored in display list (display file) on display processor

Host compiles display list and sends to DPUAdapted from Angel: Interactive


4

Contd…

The display processor would execute repetitively the program in the display list– At a rate sufficient to avoid flicker– Independent of the host– Freeing the host for other tasks


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Pipeline architecture

Pipelining– Similar to an assembly line in car plant– Higher throughput

An arithmetic pipeline– Same computation a+(b*c) with many values of

a,b,c– Throughput doubled

Need to balance latency against throughputAdapted from Angel: Interactive


Graphics pipeline

Set of objects– Each object comprises of a set of graphical

primitives– Each primitive comprises of a set of vertices

In a complex scene, there may be millions of vertices that define the objects

Need to process all these vertices in same manner to form an image in frame buffer


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Four major steps in imaging process

Vertex processing Clipping and primitive assembly Rasterization Fragment processing


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Vertex processing

Each vertex is processed independently This block includes two major functions:

– Transformation– Assignment of Vertex Color


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Clipping and primitive Assembly

Clipping is done because of the limitation that no imaging system can see the whole world at once.– Cameras have film of limited size and their fields of view can be

adjusted by selecting different lenses. Equivalent property can be obtained in the synthetic camera

model, by considering a clipping volume, such as the pyramid in front of the lens– The projections of objects in this volume appear in the image.

Those that are outside do not and are said to be clipped out.– Objects that straddle the edges of the clipping volume are partly

visible in the image.Adapted from Angel: Interactive


Clipping and primitive Assembly

Clipping must be done on a primitive by primitive basis rather than on a vertex by vertex basis. – sets of vertices must be assembled in to primitives,

such as line segments and polygons before clipping can take place within this stage of the pipeline

the output of this stage is a set of primitives whose projections can appear in the image.

Clipping can even be subdivided further into a sequence of pipelined clippers.


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Rasterization

The primitives that emerge from the clipper are still represented in terms of their vertices and must be further processed to generate pixels in the frame buffer. – E.g. if three vertices specify a triangle filled with a solid color, the rasterizer

must determine which pixels in the frame buffer are inside the polygon. The output of the rasterizer is a set of fragments for each primitive A fragment can be thought of as a potential pixel that carries with it

information, including its color and location, that is used to update the corresponding pixel in the frame buffer.

Fragments can also carry along depth information that allows later stages to determine if a particular fragment lies behind other previously rasterized fragments for a given pixel.


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Fragment processing

It updates the pixels in the frame buffer for the fragments generated by the rasterizer.

If the application generated 3-D data, some fragments may not be visible because the surfaces that they define are behind other surfaces.

The color of a fragment may be altered by texture mapping or bump mapping.

The color of the pixel that corresponds to a fragment can also be read from the frame buffer and blended with the fragment's color to create translucent effects.


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Performance Characteristics

Two types of processing in graphics architecture– Front end geometric processing– Back end direct manipulation of bits in the frame buffer

Front end geometric processing, based on processing vertices through the various clippers and transformers. – This processing is ideally-suited tor pipelining– usually involves floating-point calculations.


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Front end geometric processing

The geometry engine developed by Silicon Graphics was a VLSI implementation for many of these operations in a special-purpose chip that became the basis for a series of fast graphics workstations.

Later, floating-point accelerator chips, such as the Intel i860, put 4 x 4 matrix-transformation units on the chip, reducing a matrix multiplication to a single instruction.

Graphics workstations and add-on graphics boards use Application Specific Integrated Circuits (ASICS) that perform many of the graphics operations at the chip level.


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Contd…

Pipeline architectures are the dominant type of high-performance system.

As more boxes are added to the pipeline, however, it takes more time for a single datum to pass through the system.

This time is called the latency of the system Latency must be balanced against increased

throughput in evaluating the performance of a pipeline.


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Back end direct manipulation of bits in the frame buffer

Beginning with rasterization including many other features

process directly the bits in the frame buffer. It is fundamentally different from front-end

processing, and can be implemented most effectively using architectures that have the ability to move blocks of bits quickly.


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Performance

The overall performance of a system is characterized by – how fast the geometric entities are moved through the pipeline– how many pixels per second can be altered in the frame buffer.

The fastest graphics workstations are characterized by – pipelines at the front ends– parallel bit processors at the back ends.

Pipeline architectures dominate the graphics field, especially where real-time performance is of importance.

Pipelining architecture can be implemented not only in hardware but also in a software system implementation of an API. – The power of the synthetic-camera paradigm is that the pipelining works

well in both casesAdapted from Angel: Interactive


Continued in slides on Chapter 2


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Raster Graphics Beginning of graphics standards

– IFIPS GKS: European effort

– Becomes ISO 2D standard Core: North American effort

– 3D but fails to become ISO standard

Workstations and PCs


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Raster Graphics

Image produced as an array (the raster) of picture elements (pixels) in the frame buffer


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Raster Graphics

Allows us to go from lines and wire frame images to filled polygons


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PCs and Workstations

Although we no longer make the distinction between workstations and PCs, historically they evolved from different roots– Early workstations characterized by

Networked connection: client-server model High-level of interactivity

– Early PCs included frame buffer as part of user memory

Easy to change contents and create imagesAdapted from Angel: Interactive


04


Realism comes to computer graphics


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smooth shading environment mapping

bump mapping


Special purpose hardware– Silicon Graphics geometry engine

VLSI implementation of graphics pipeline

Industry-based standards– PHIGS– RenderMan

Networked graphics: X Window System Human-Computer Interface (HCI)


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OpenGL API Completely computer-generated feature-

length movies (Toy Story) are successful New hardware capabilities

– Texture mapping– Blending– Accumulation, stencil buffers


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Computer Graphics: 2000-

Photorealism Graphics cards for PCs dominate market

– Nvidia, ATI Game boxes and game players determine

direction of market Computer graphics routine in movie industry:

Maya, Lightwave Programmable pipelines


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tricky??? you have a jug of milk, and you need to measure out just one cup. how do you do this if...

Documents

interactive computer

e addison wesley

graphics card

mukka slide

dept of computer science

game of cards

total number of cards

cup container