Computer Graphics Department of Computer Science & Engineering Hamdard University Bangladesh Prepared By
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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)
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