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Raster Images
 Picture is made up of small cells
called pixels
 Stored in computer memory as
array of numeral values cal...
Gray scale raster images
 Pixel dept (memory required /pixel)
 n-bit memory generates 2n
color values
 Effect of pixel ...
Color Raster images
 Three numeral value for each pixel
 3-bytes true colors
Flat Panel Displays
 Emissive
 Flat screen CRT
 Plasma
 LCD with backlight
 Non-Emissive
 LCD
Display technologies
 Cathode Ray Tubes
(CRTs)
 Most common display
device today.
 Evacuated glass
bottle
 Extremely h...
CRT
Electron gun Contains a filament that, when heated, emits a stream of
electrons
 Electrons are focused with an electroma...
CRT characteristics
 What’s the largest (diagonal) CRT you’ve
seen?
 Why is that the largest?
 Evacuated tube == massiv...
Random Scan Display (Vector
Displays) Early computer displays, Control X,Y with
vertical/horizontal plate voltage
 Often...
Vector Display draws a set of lines in
any order
Vector Scanning
Vector Displays
 How to generate an image using vectors
 A line is represented by endpoints (10,10) to (90,90)
 The poi...
Raster Displays
 Raster: A rectangular array of points or dots
 Pixel: One dot or picture element of the
raster
 Scan l...
Raster Displays
 Black and white television: A fixed scan pattern: left to
right, top to bottom
 As beam sweeps across e...
Raster-scan display system
draws a discrete set of points
Line Generation on Raster Display
 How to generate a line using rasters
 A line is represented by assigning some pixels ...
Phosphers
 Fluorescence
 Light emitted while the phosphor is being struck
by electrons()
 Phosphorescence
 Light emitt...
Refresh
 Frame must be “refreshed” to draw new images
 As new pixels are struck by electron beam,
others are decaying
 ...
CRT Timing
Color CRT
 Color CRTs are much more complicated
 Requires manufacturing very precise geometry
 Uses a pattern of color ...
Color CRT
 Color CRTs have
 Three electron guns
 Beam penetration and shadow mask methods
 A metal shadow mask to diff...
CRT
 Raster CRT pros:
 Allows solids, not just wireframes
 Leverages low-cost CRT technology (i.e., TVs)
 Bright! Disp...
CRTs – A Review
 CRT technology hasn’t changed much in 50 years
 Early television technology
 high resolution
 require...
CRTs – A Review
 Raster Displays (early 70s)
 like television, scan all pixels in regular pattern
 use frame buffer (vi...
Liquid Crystal Displays (LCDs)
 LCDs: organic molecules, naturally in crystalline state, that liquefy
when excited by hea...
Polarizer
A wire-grid polarizer converts an unpolarized beam
into one with a single linear polarization. Red arrows
depict...
Liquid Crystal Display (LCD)
Liquid Crystal Displays (LCDs)
Display Technology: Plasma
 Plasma display panels
 Similar in principle to
fluorescent light tubes
 Small gas-filled ca...
Plasma Display
Thin Film
Electroluminescent Display
 Same as plasma display
 Has phosphor coating instead of gas
 High voltage applied...
Direct View Storage Tube
(DVST) Instead of refreshing screen, it Keeps information inside CRT
 Picture information is st...
Raster Scan System
 Special purpose processor called video/display
controller used to control operations of display
 Vid...
Raster Scan System
Architedure of a simple raster graphics system.
Architecture of a raster system with a fixed portion of...
Raster Scan System
intensity
Basic video-controller refresh operations
The origin of the coordinate
system for identifying...
Raster Scan System
 High quality system provides two frame buffers
 Video controller also transform screen
 Some video ...
Raster Scan Display
Processor
Architecture of a raster-graphics system with a display processor.
Raster Scan Display
ProcessorDisplay processors scan convert, lines, curves and other
objects into intensity values
Char...
Raster Scan Display
Processor Digitize/scan-conversion picture definition provided by
application program
 Display proce...
Random Scan System
Architecture of a simple random scan system.
Random Scan System
 Display processor also called display processing unit or
graphics controller
 Application program al...
Hard Copy Devices
 Purpose is to put our graphics/picture on
paper
 Quality of pictures: Dots/inch also known
as resolut...
Hard Copy Devices
Dot-matrix Printer
 Impact printer
 Dot-matrix head with rectangular array of
protruding wire pins
 N...
Hard Copy Devices
Laser Printer
 Have photoelectric,
e.g. selenium, coated
drum
 Graphics are drawn by
creating charge
d...
Hard Copy Devices
Ink-jet Printer
 Paper wrapped on a drum
 Ink is squirted horizontally across the length of paper
 In...
Hard Copy Devices
Pen Plotter
 A plotter is a vector graphics printing device to print
graphical plots
 Move pen across ...
Hard Copy Devices
Electrostatic Device
 Place negative charge on the length of paper one
row at a time
 Paper is then ex...
Hard Copy Devices
Electro-thermal Device
 Heat sensitive coated thermal paper
 Apply selective heating
 Produce output ...
Input Devices
Keyboard
 Used for entering text
 Extra features: screen coordinates, object selection,
menu selection and...
Input Devices
Mouse
 Another major input device
 Small handheld box used to reposition screen cursor
 Movement is recor...
Input Devices
Track ball and space ball
 A ball with potentiometer, produce screen
movements
 Unlike track ball, the Spa...
Input Devices
Joy Stick
 A small vertical lever which steers screen cursor
 Some record physical movement of the stick w...
Input Devices
Image scanner
 Pictures, graphs, charts, text etc can be used as bitmap in
computer memory
 They are store...
Input Devices
Touch Panels
 Select processing options, displayed
objects or screen positions with touch of
screen
 Touch...
Input Devices
Touch Panel (continued…)
 Should match the color and contour of system
 In electrical method, two transpar...
Input Devices
Light Pen
 Record screen location when electron been passes
to that point
 Don’t detect environment light
...
Voice System
 System is trained for a particular operator
 Frequencies are recorded for different words for the
operator...
Visible spectrum
(Continued)
Visible spectrum
(Continued)
Human vision system
Human vision system
 Human eye is a spherical camera with 20mm focal length
 Lens focus the image on retina
 Iris contr...
Color model
 Provide mechanism for encoding of color in
visible spectrum
 Mathematical model for describing colors as
tu...
RGB Color Model
CMY Color Model
 Cyan, Magenta, Yellow
 Subtractive color scheme (Subtract from
white, transparent inks)
 Colors which ...
CMYK Color Model
 Cyan, Magenta, Yellow, Key
(Black)
 Same as CMY
 Black is added to improve
reproduction of some dark
...
HSI or HSV Color Model
 Hue, Saturation,
Intensity or Value
HSI or HSV Color Model
 Separate Intensity from chromacy – Hue and
Saturation
 Hexagon or hexacon is formed by projectin...
2D Trasformation
 Changes in the object orientation, size and shape
is accomplished by 2D transformation
 Basic transfor...
2D Trasformation
Translation
 Object is moved along a line path from one
coordination to another
 It’s a rigid body tran...
2D Trasformation
Translation
 Can be expressed as
 X’
= x + tx y’
= y + ty
 Can also be expressed in matrix form
2D Trasformation
Computer graphics
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Computer graphics

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Computer Graphics for Begginers

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Computer graphics

  1. 1. Raster Images  Picture is made up of small cells called pixels  Stored in computer memory as array of numeral values called pixel map or bitmap  Raster images are created suing  Hand designed images  Computed images (Mathematical model of a scene)  Scanned images (support scaling)
  2. 2. Gray scale raster images  Pixel dept (memory required /pixel)  n-bit memory generates 2n color values  Effect of pixel dept  Quality of image  Avoid color banding  Size of image
  3. 3. Color Raster images  Three numeral value for each pixel  3-bytes true colors
  4. 4. Flat Panel Displays  Emissive  Flat screen CRT  Plasma  LCD with backlight  Non-Emissive  LCD
  5. 5. Display technologies  Cathode Ray Tubes (CRTs)  Most common display device today.  Evacuated glass bottle  Extremely high voltage  Heating element (filament)  Electrons pulled towards anode focusing cylinder  Vertical and horizontal deflection plates  Beam strikes phosphor coating on front of tube
  6. 6. CRT
  7. 7. Electron gun Contains a filament that, when heated, emits a stream of electrons  Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube  The front surface of the picture tube is coated with small phosphor dots  When the beam hits a phosphor dot it glows with a brightness proportional to the strength of the beam and how long it is hit
  8. 8. CRT characteristics  What’s the largest (diagonal) CRT you’ve seen?  Why is that the largest?  Evacuated tube == massive glass  Symmetrical electron paths (corners vs. center)  How might one measure CRT capabilities?  Size of tube  Brightness of phosphers vs. darkness of tube  Speed of electron gun  Width of electron beam  Pixels?
  9. 9. Random Scan Display (Vector Displays) Early computer displays, Control X,Y with vertical/horizontal plate voltage  Often used intensity as Z (close things were brighter)  Name two disadvantages Just does wireframe Complex scenes cause visible flicker
  10. 10. Vector Display draws a set of lines in any order
  11. 11. Vector Scanning
  12. 12. Vector Displays  How to generate an image using vectors  A line is represented by endpoints (10,10) to (90,90)  The points along the line are computed using a line equation y = mx + b  If you want the image larger, no problem…
  13. 13. Raster Displays  Raster: A rectangular array of points or dots  Pixel: One dot or picture element of the raster  Scan line: A row of pixels
  14. 14. Raster Displays  Black and white television: A fixed scan pattern: left to right, top to bottom  As beam sweeps across entire face of CRT, beam intensity changes to reflect brightness  Must synchronize  Your program makes decisions about the intensity signal at the pace of the CPU…  The screen is “painted” at the pace of the electron gun scanning the raster  Solution: special memory to buffer image with scan-out synchronous to the raster. We call this the frame buffer.
  15. 15. Raster-scan display system draws a discrete set of points
  16. 16. Line Generation on Raster Display  How to generate a line using rasters  A line is represented by assigning some pixels a value of 1  The entire line is specified by the pixel values What do we do to make image larger?
  17. 17. Phosphers  Fluorescence  Light emitted while the phosphor is being struck by electrons()  Phosphorescence  Light emitted once the electron beam is removed  Persistence  The time from the removal of the excitation to the moment when phosphorescence has decayed to 10% of the initial light output
  18. 18. Refresh  Frame must be “refreshed” to draw new images  As new pixels are struck by electron beam, others are decaying  Electron beam must hit all pixels frequently to eliminate flicker  Critical fusion frequency  Typically 60 times/sec  Varies with intensity, individuals, phospher persistence, lighting...
  19. 19. CRT Timing
  20. 20. Color CRT  Color CRTs are much more complicated  Requires manufacturing very precise geometry  Uses a pattern of color phosphors on the screen:  Why red, green, and blue phosphors? Delta electron gun arrangement In-line electron gun arrangement
  21. 21. Color CRT  Color CRTs have  Three electron guns  Beam penetration and shadow mask methods  A metal shadow mask to differentiate the beams
  22. 22. CRT  Raster CRT pros:  Allows solids, not just wireframes  Leverages low-cost CRT technology (i.e., TVs)  Bright! Display emits light  Cons:  Requires screen-size memory array  Discrete sampling (pixels)  Practical limit on size (call it 40 inches)  Bulky
  23. 23. CRTs – A Review  CRT technology hasn’t changed much in 50 years  Early television technology  high resolution  requires synchronization between video signal and electron beam vertical sync pulse  Early computer displays  avoided synchronization using ‘vector’ algorithm  flicker and refresh were problematic
  24. 24. CRTs – A Review  Raster Displays (early 70s)  like television, scan all pixels in regular pattern  use frame buffer (video RAM) to eliminate sync problems  RAM  ¼ MB (256 KB) cost $2 million in 1971  Do some math… - 1280 x 1024 screen resolution = 1,310,720 pixels - Monochrome color (binary) requires 160 KB - High resolution color requires 5.2 MB
  25. 25. Liquid Crystal Displays (LCDs)  LCDs: organic molecules, naturally in crystalline state, that liquefy when excited by heat or Electric field  Crystalline state twists polarized light 90º.
  26. 26. Polarizer A wire-grid polarizer converts an unpolarized beam into one with a single linear polarization. Red arrows depict the electric field vector.
  27. 27. Liquid Crystal Display (LCD)
  28. 28. Liquid Crystal Displays (LCDs)
  29. 29. Display Technology: Plasma  Plasma display panels  Similar in principle to fluorescent light tubes  Small gas-filled capsules are excited by electric field, emits UV light  UV excites phosphor  Phosphor relaxes, emits some other color
  30. 30. Plasma Display
  31. 31. Thin Film Electroluminescent Display  Same as plasma display  Has phosphor coating instead of gas  High voltage applied on phosphor  Require more power  Good colors are hard to generate  Another emissive display is LED
  32. 32. Direct View Storage Tube (DVST) Instead of refreshing screen, it Keeps information inside CRT  Picture information is stored as charge distribution behind the phosphorous screen  Two electron guns are used in DVST, the primary gun and flood gun  Primary helps is storing picture patterns and flood gun maintain picture display  No refresh requires, can display complex high resolution picture without flicker  Usually doesn’t display colors  Part of a picture can’t be refreshed (redrawn)  Erasing old picture and redrawing modified picture could take seconds  No replaced by raster displays
  33. 33. Raster Scan System  Special purpose processor called video/display controller used to control operations of display  Video controller accesses frame buffer from system memory  Some systems also use graphics/display processor to relieve CPU of core graphic activities  Frame buffer locations and corresponding screen positions are referenced in Cartesian coordinates  Coordinate origin is decided
  34. 34. Raster Scan System Architedure of a simple raster graphics system. Architecture of a raster system with a fixed portion of the system memory reserved for the frame buffer.
  35. 35. Raster Scan System intensity Basic video-controller refresh operations The origin of the coordinate system for identifying screen positions is usually specified in the lower-left corner.
  36. 36. Raster Scan System  High quality system provides two frame buffers  Video controller also transform screen  Some video controllers use lookup tables (color palets) and frame buffer values are indexed into it to retrieve intensities  Some controllers allows mixing frame buffer’s image with camera picture
  37. 37. Raster Scan Display Processor Architecture of a raster-graphics system with a display processor.
  38. 38. Raster Scan Display ProcessorDisplay processors scan convert, lines, curves and other objects into intensity values Characters are specified by rectangular grid or curved lines Character grid can be 5 by 7 or 9 by 12 or more in high quality displays Character grid is superimposed and character curves are scan converted
  39. 39. Raster Scan Display Processor Digitize/scan-conversion picture definition provided by application program  Display processor also performs additional tasks e.g. changing line styles, coloring areas, transformation on objects etc  Efforts are made to shorten frame buffer  One way is to store intensity information as link list and apply run- length encoding  Similar method applies when intensities change linearly  Short runs can increase storage requirements  Short runs bring difficulty in processing  Another approach encode raster as set of rectangular areas, called cell encoding
  40. 40. Random Scan System Architecture of a simple random scan system.
  41. 41. Random Scan System  Display processor also called display processing unit or graphics controller  Application program along with graphic package stored in memory  Graphics commands of application are transformed by graphic package into display file, stored in memory  Display processor goes through each line in display file in a refresh cycle  Lines are specified by end points  Scene is drawn one line at a time and deflection voltages are directed to fill region b/w end points
  42. 42. Hard Copy Devices  Purpose is to put our graphics/picture on paper  Quality of pictures: Dots/inch also known as resolution  High quality printing: Adjacent dots overlaps  Two type of printers: Impact and non- impact  Impact: press formed character faces against ink ribbon  Non-impact: Use laser technique, inkjet spay, xerographic process, electrostatic or electro-thermal methods
  43. 43. Hard Copy Devices Dot-matrix Printer  Impact printer  Dot-matrix head with rectangular array of protruding wire pins  Number of pins depends on quality of printer  Character face or graphic patterns drawn by retracting certain pins  Single column vs multi column printing head
  44. 44. Hard Copy Devices Laser Printer  Have photoelectric, e.g. selenium, coated drum  Graphics are drawn by creating charge distribution on drum using laser beam  Toner is applied to the drum  Toner then applied to paper to draw graphics Xerographic Process
  45. 45. Hard Copy Devices Ink-jet Printer  Paper wrapped on a drum  Ink is squirted horizontally across the length of paper  Ink-stream is deflected by electric field  Produce dot-matrix patterns  Three types: Thermal ink-jet, Piezoelectric ink-jet and continuous ink-jet  Thermal inkjet send current through heating element in heating chamber and make steam explosion  Current send to piezoelectric material in ink-filled chamber which changes shape & size and produce pressure  High-pressure pumps direct ink through a gunbody, microscopic nozzle, piezoelectric crystal produce accoustic waves which breaks ink stream into droplets at continuous intervals  Heating element contract on cooling and suck further ink from reserviors
  46. 46. Hard Copy Devices Pen Plotter  A plotter is a vector graphics printing device to print graphical plots  Move pen across the piece of paper  Can draw complex line art and text but very slowly  Can draw filled regions by complex closed lines  Printer control languages created to send more detailed command for text  Paper placed over a roller which moves paper back & forth for x motion and pen moved back & forth for y motion  Fast computing, inexpensive memory and quality raster graphics with laser and inkjet have replaced pen-plotters
  47. 47. Hard Copy Devices Electrostatic Device  Place negative charge on the length of paper one row at a time  Paper is then exposed to toner  Toner is positively charged  Negative and positive charge produce adhesion
  48. 48. Hard Copy Devices Electro-thermal Device  Heat sensitive coated thermal paper  Apply selective heating  Produce output patterns using dotmatrix printing head  Image is produced in the area where it is heated  Two color direct thermal printer produce black and red color images when heated on two different temperatures
  49. 49. Input Devices Keyboard  Used for entering text  Extra features: screen coordinates, object selection, menu selection and graphic functions  Function keys used to activate frequently used operations  Cursor control keys used to relocate screen cursor  Can accompany track ball or joy stick  Additional numeric keyboard used for fast entry of numeric data  Specialized application: buttons, switches and dials
  50. 50. Input Devices Mouse  Another major input device  Small handheld box used to reposition screen cursor  Movement is recorded using wheel or roller in bottom  Movement is also detected with optical sensor with special mouse pad having horizontal and vertical line grid  Not fixed, Used for relative changes in screen cursor  Also accompany two or three buttons to activate certain function  Also Z mouse for 3D application
  51. 51. Input Devices Track ball and space ball  A ball with potentiometer, produce screen movements  Unlike track ball, the Space ball doesn’t actually move  Strain gauges measure the amount of pressure and the direction of pressure  Used for three dimensional positioning in virtual reality, animation and CAD
  52. 52. Input Devices Joy Stick  A small vertical lever which steers screen cursor  Some record physical movement of the stick while others record only pressure on the stick  In first movement and direction and in second pressure and direction is gauged (strain gauge)  Potentiometer is used  Might be mounted on the keyboard  Can also use one or more buttons
  53. 53. Input Devices Image scanner  Pictures, graphs, charts, text etc can be used as bitmap in computer memory  They are stored as color or grayscale grades  Purpose is to process image objects  Transform objects  Crop different areas (Picture editing)  Image processing  Extract text  Available in variety of sizes, from hand held to huge
  54. 54. Input Devices Touch Panels  Select processing options, displayed objects or screen positions with touch of screen  Touch inputs are devised with optical, electrical or acoustic methods  In optical method, infrared LEDs are fixed along vertical and horizontal edges of the frame (light detectors on opposite sides)  Detector detects which horiz and vert beams are interrupted  In case of closed LEDs, Avg is taken when two or more beams are interrupted
  55. 55. Input Devices Touch Panel (continued…)  Should match the color and contour of system  In electrical method, two transparent plats, one conductor and second resister, placed on small distance  Both plates touches when pressure is applied  Voltage drop in resister plates is recorded as screen coordinates  In acoustic method, acoustic waves are generated across horiz and vertical directions  Interruption causes reflection of waves  Time interval is calculated to find screen coordinates
  56. 56. Input Devices Light Pen  Record screen location when electron been passes to that point  Don’t detect environment light  Can’t detect black spots  Application must keep non-zero intensity for black screen position  Few other disadvantages
  57. 57. Voice System  System is trained for a particular operator  Frequencies are recorded for different words for the operator  System record word and operation performed on those words  On use, operator voice is searched in dictionary and operation for that word is performed  User don’t have to switch among devices
  58. 58. Visible spectrum (Continued)
  59. 59. Visible spectrum (Continued)
  60. 60. Human vision system
  61. 61. Human vision system  Human eye is a spherical camera with 20mm focal length  Lens focus the image on retina  Iris control the amount of light passing through pupil  Each eye is populated unevenly with 100m receptor cells  Near the fovea dense concentration of color receptor called cons  Density of black & white receptors, called rods, increases away from the center and cons decreases  Three different types of cons (with different chemical properties) are sensitive to light of three different wavelengths  human is tri-chromate
  62. 62. Color model  Provide mechanism for encoding of color in visible spectrum  Mathematical model for describing colors as tuple of numbers  Numbers are usually three or four  Gives precise definition of how components are interpreted  Usually define some primary colors
  63. 63. RGB Color Model
  64. 64. CMY Color Model  Cyan, Magenta, Yellow  Subtractive color scheme (Subtract from white, transparent inks)  Colors which are not absorbed, determine color  Cyan absorb red, magenta absorb green and yellow absorbs blue  White(0,0,0): No component of light is absorbed  Black(255,255,255): ???
  65. 65. CMYK Color Model  Cyan, Magenta, Yellow, Key (Black)  Same as CMY  Black is added to improve reproduction of some dark colors  To save money on ink, and to produce deeper black tones, unsaturated and dark colors are produced by substituting black ink for the combination of cyan, magenta and yellow
  66. 66. HSI or HSV Color Model  Hue, Saturation, Intensity or Value
  67. 67. HSI or HSV Color Model  Separate Intensity from chromacy – Hue and Saturation  Hexagon or hexacon is formed by projecting RGB color cube along its major diagonal  Vertical intensity axes  H is defined angle between 0 and 2Π relative to a-axes (0 angle mean pure red)  S is defined as color purity (1 pure i.e. saturated and 0 for unsaturated i.e. some shades of gray)  Convenient for graphics designers, provide direct control over hue and brightness
  68. 68. 2D Trasformation  Changes in the object orientation, size and shape is accomplished by 2D transformation  Basic transformations  Translation  Rotation and  Scaling
  69. 69. 2D Trasformation Translation  Object is moved along a line path from one coordination to another  It’s a rigid body transformation (no deformation)  (x, y) Original coordinate location  (tx, ty) translation distance, also called the translation vector or shift vector  (x’ ,y’ ) new coordinate location
  70. 70. 2D Trasformation Translation  Can be expressed as  X’ = x + tx y’ = y + ty  Can also be expressed in matrix form
  71. 71. 2D Trasformation

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