Computer Graphics

Department of Computer Science & Engineering

Hamdard University Bangladesh

Prepared By

The definition of computer graphics is the technology that deals with designs and pictures on computers.

Computer graphics

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• Recognize how a visual image can be an effective means of communication

• Distinguish and interpret various types of typography.

• Utilize a broad range of type styles in combination with visual images.

• Use a computer to create and manipulate images and text for use in various

print and digital mediums.

Goals of Computer Graphics

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Applications of Computer Graphics

o Computational biologyo Computational physicso Computer-aided designo Digital arto Educationo Graphic designo Information visualizationo Scientific visualizationo Special Effects for cinemao Video Gameso Web designo Design

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Overview of Graphics Systems

• Images• Hardware

– Input Systems – Output Systems

• Software– OpenGL

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Two Dimensional Images

• Images (at least the ones in this class) are two dimensional shapes.

• The two axes we will label as X (horizontal), and Y (vertical). X Axis

Y

Axis

(0,0) +X

+Y

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Three Dimensional Images

• The three axis: X (horizontal), Y (vertical) and Z (middle).

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Color Model

RGB Color cube (what we use in computer graphics)

Other color spaces include HSV, CMY, and YIQ

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Hardware Pipeline

Input OutputComputation

We want to draw a rectangle, how do we describe it to a computer?

Model (n) - object description that a computer understands.

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Record every position

Bitmap - a rectangular array of bits mapped one-to-one with pixels.

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Position relative

Vector display system - graphical output system that was based on strokes (as opposed to pixels). Also known as: random, calligraphic, or stroke displays.

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Representing Objects

• Most common method is the VERTEX method. Define the object as a set of points with connectivity information.

• Why is connectivity important?

Connectivity - information that defines which vertices are connected to which other vertices via edges.

Edge - connects two vertices

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Input Devices

• Locator Devices• Keyboard• Scanner

– Images– Laser

• Cameras

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Locator DevicesWhen queried, locator

devices return a position and/or orientation.

• Tablet• Joystick• Virtual Reality Trackers

– Data Gloves– Digitizers

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Keyboard

• Text input– List boxes, GUI– CAD– Modeling

• Hard coded– Vertex locations are inserted into code

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Computation Stage

• Now that we have a model of what we want to draw, what goes on inside the computer to generate the output?

Input OutputComputation

Computation

Transformations Rasterization

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Computation Stage

Computation

Transformations Rasterization

Model

Transformed

Model

Output

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Store process in memory

We would like to allocate memory to hold the results of the computation stage.

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Frame buffer

Frame buffer – The picture definition is stored in a memory is called refresh or frame buffer.

Pixel - one element of the framebuffer

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Basic architecture of raster graphics of frame buffer

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Frame buffer in Memory

• If we want a frame buffer of 640 pixels by 480 pixels, we should allocate:

Frame buffer = 640*480 bits=307200 bits=38400 bytes

=38.4 kilobytes

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Output

• Hardcopy• Display

– Vector or random scan– Raster Scan

Input OutputComputation

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Image Quality Issues

• Screen resolution• Color• Blank space between the

pixels• Intentional image

degradation

• Brightness• Contrast• Refresh rate• Sensitivity of display to

viewing angle

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Pixels

Pixel - The pixel (a word invented from "picture element") is the basic unit of programmable color on a computer display or in a computer image.

CRT - Color triad (RGB phosphor dots) LCD - Single color element

• Screen Resolution - measure of number of pixels on a screen (m by n) m - Horizontal screen resolution n - Vertical screen resolution

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Raster Displays• Cathode Ray Tubes (CRTs),

most “tube” monitors. Very common, but big.

• Liquid Crystal Displays (LCDs), there are two types transmissive (laptops, new flat panel monitors) and reflective (wrist watches).

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Cathode Ray Tube

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CRT color monitor

1. Beam Penetration Method (Red & Green)2. Shadow Mask Method (RGB)

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CRTs

• Strong electrical fields and high voltage• Very good resolution • Heavy, not flat

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Liquid Crystal Displays (LCDs)

• Also divided into pixels, but without an electron gun firing at a screen, LCDs have cells that either allow light to flow through, or block it.

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Advantages of LCDs

• Flat • Lightweight• Low power consumption

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Projection Displays

• Use bright CRT or LCD screens to generate an image which is sent through an optical system to focus on a (usually) large screen.

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Basic Projector Designs

                                                                                     

                                                            Reflective Projection System Transmittive Projection

System

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Graphics Software

• Special purpose software– Excel– AutoCAD– Medical Visualization

• Programming API

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Computer animation is a general term for a kind of visual digital display technology that simulates moving objects on-screen.

Computer animation

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Displaying animation sequences

• Movies work by fooling our eyes

• A sequence of static images presented in a quick succession appears as continuous flow

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Displaying animation sequences

• To achieve smooth animation, a sequence of images (frames) have to be presented on a screen with the speed of at least 30 per second

• Animations frames can be – pre-computed in advance and pre-loaded in memory

– computed in real time (e.g. movement of the cursor)