COMPUTER GRAPHICS - PowerPoint

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					           COMPUTER GRAPHICS
                                CISC4/640

                   Instructor: Prof. Chandra Kambhamettu
                              TA: Mani Thomas




Intructor Office Hours:                                ppt slides credits:
Wed. 2-4pm                                             Chaitra Murthy (MS, UD)
Smith403                                               Edward Angel, UNM
                                                       Hearn and Baker, U of Illinois
INTRODUCTION
  – COMPUTER GRAPHICS

  – IMAGE PROCESSING

   – COMPUTER VISION
             >>>Graphics Timeline
COMPUTER GRAPHICS
• Computer graphics is concerned with all aspects of
       producing images using a computer

 • It concerns with the pictorial synthesis of real or
 imaginary objects from their computer based models

                     • BACK
 IMAGE PROCESSING
Image processing is the converse process of
  computer graphics. Image processing and
 Understanding areas concentrate on analysis
 and reconstruction of 2D or 3D objects from
               their pictures

                • BACK
   COMPUTER VISION

Computer vision further more extends research
      into understanding images. It is the
      construction of explicit, meaningful
  descriptions of physical objects from images.

                   • BACK
 GRAPHICS TIMELINE
• THEN
 – The field humbly began 50 years ago with
   a few lines on a cathode ray tube.
 – Until early 1980’s it was a small
   specialized field due to expensive
   hardware and software (application
   programs)
 GRAPHICS TIMELINE
Now
 – We can generate images almost
   indistinguishable from photographs

 – Interactive….highly interactive!! In
   present times user controls the contents,
   structure and appearance of objects by
   using various input devices
  GRAPHICS TIMELINE
Now (continued)
  – Direct manipulation is in heavy use
  – We can make feature-length movies
    entirely by computer
  – On the whole, the development of
    computer graphics is driven both by the
    needs of the user community and by the
    advances in hardware and software
       POPULARITY

               why is it so popular
          -A picture is worth a 10000 words!!!!!
It provides the most natural means of communicating
  with a computer, since our perception abilities are better
                with pictures than with words
  It is one of the rare fields that has many commercial
             interests as there are research interests
                 (Thanks to Hollywood!!)
             APPLICATIONS
Computer graphics is so much in demand because of its limitless variety
                            of applications

                         • Display Of Information
                     Medium to convey information
                                • Design
  Many applications exist in engineering and architecture (CAD,VLSI)
                               • Simulation
Graphical flight simulators, games, commercials and educational software
                             • User Interfaces
    Visual paradigms in user interaction: windows, icons, menus etc.
                        Virtual Reality Applications
             Wooden Mirror
             (D. Rozin, NYU)
•   Sitting
•   Movie
•   Hand-still

The wooden mirror has 830 pieces of wood each about 40 mm square
   arranged into an octagon of (170cm X 203cm X 25cm).
Each piece of wood is connected to a servo motor that can tilt it
   about 30º up and down.
The whole piece is lit from above with a few spot lights, in a way that
   when the pieces are tilted upwards they become brighter, and
   when they tilt downwards they become darker. The servo motors
   can position each piece in 255 positions theoretically yielding 255
   gray levels per piece.
In the center of the Mirror a tiny video camera is concealed.
      shinyballsmirror
• Shinyballsmirror Image
• Movie
          Animation
• Fish
• Wind
• Cloth

• Terraexplorer
       Image Creation
• Camera is used to take an image, stored on
  the film.
• Film records sample of intensity that hits
  each point
• Intensity is brightness of a point (amount
  of light reflected off the point), usually
  measured in lumens.
• Intensity is discretized to pixel values
  (continuous -> discrete)
                  Images..
CAMERA:
• Light rays come through lens in the camera and hits the
  film.
• Proportion of light that hits the film is controlled by the
  aperture (adjusted in combination with the focal length).
• Time duration (to keep the door open for light to come-in)
  is controlled by shutter speed.

Us:
• Light from the outside world excites nerves in our retina
  and brain understands the stereo images of our retina.
 Discrete vs. Continuous
         worlds
• Computers are in discrete world, so we
  break the continuous domain (time and
  space) into discrete domain.
• Animation: 24 to 30 frames per second
• Image: small dots making up a matrix for
  the display. The small dots are Gaussian,
  called pixels.
• Value given to each pixel is called
  intensity.
 Elements of Image Formation
•Objects
•Viewer
•Light source(s)

•Attributes that govern how light
 interacts with the materials in the
 scene
               Light
• Light is the part of the electromagnetic
  spectrum that causes a reaction in our
  visual systems
• Generally these are wavelengths in the
  range of about 350-750 nm (nanometers)
• Long wavelengths appear as reds and short
  wavelengths as blues
      Ray Tracing and
     Geometric Optics
One way to form an image is to
follow rays of light from a
point source finding which
rays enter the lens of the
camera. However, each
ray of light may have
multiple interactions with objects
before being absorbed or going to infinity.
     Three-Color Theory
• Human visual system has two types of sensors
   – Rods: monochromatic, night vision
   – Cones
      • Color sensitive
      • Three types of cones
      • Only three values (the tristimulus
      values) are sent to the brain
• Need only match these three values
   – Need only three primary colors
          Pinhole Camera




Use trigonometry to find projection of point at (x,y,z)

     xp= -x/z/d      yp= -y/z/d      zp = d

          These are equations of simple perspective
Synthetic Camera Model
   projector




                                p
                         image plane
                          projection of p
               center of projection
 Global vs Local Lighting
•Cannot compute color or shade of
 each object independently
 –Some objects are blocked from light
 –Light can reflect from object to object
 –Some objects might be translucent

				
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