Overview of Computer Graphics

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 biology
o Computational physics
o Computer-aided design
o Digital art
o Education
o Graphic design
o Information visualization
o Scientific visualization
o Special Effects for cinema
o Video Games
o Web design
o 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 Devices
When 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?
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
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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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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)
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Overview of Computer Graphics

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