Digital Imaging (PowerPoint download)

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					CS 1308 Computer Literacy and the Internet

DIGITAL IMAGES
  Creating Digital Pictures

 A traditional photograph is an analog
  representation of an image.
 Digitizing a picture is the act of creating picture
  elements (pixels) to represent the image.
 The process is similar to the sampling of analog
  audio
   The more pixels, the better the quality
   The more bits for each pixel, the closer the
    approximation
   The human eye can be tricked into filling in the
    missing pieces
    A 15x12 picture




One Pixel


             15x12 = 170 total pixels
Resolution

 The number of pixels
   The higher the resolution, the clearer the picture
   Increased resolution allows you to zoom in and
    see more detail
   Higher resolution increases the size of the file in
    memory
Aliasing
           Zoomed in 5 times




           Notice the Pixelation
Colors

 RGB (Red, Green, Blue)
   How many bits for one color in this cube?
Image Colors




   45,000 Colors   256 Colors
Image Colors




   45,000 Colors   16 Colors
Image Colors




   45,000 Colors   2 Colors
Image Colors




   45,000 Colors   250 Grey scale tones
Pixel Densities

 Resolution Example
How much space?

 For each pixel you have to store a color or
  grey scale.
 Resolution 300x200 = 60,000 pixels
   8 bit greyscale (256 tones) – 60KB
   24 bit true color – 180KB (3 bytes per pixel)
Graphics File Formats

 Raster Graphics
   Stores information on a pixel-by-pixel basis
   BMP, GIF, JPEG, PNG
 Vector Graphics
   Stores a description of shapes in the picture
   Scalable Vector Graphics (SVG)
  JPEG vs GIF

 JPEG
   Joint Photographic Experts Group
     Forgent Networks claims patent on key algorithm
   24 bit color
   Lossy compression
     Cleverly removes portions of picture that humans won’t see
   Very good for pictures, “realistic” scenes
   Allows use to select amount of compression
 GIF (Graphics Interchange Format)
     Patented by Compuserve
     256 colors
     Lossless compression
     Good for line drawings, clip art
Digital Cameras

 Much like a normal
  camera in terms of
  optics
 Has advantage of
  knowing what a picture
  looks like immediately
Digital Pictures

 Image is acquired by
  absorbing reflected light
  and recording the
  wavelengths (very similar
  to sampling audio)
 The sensor takes the place
  of the film
 Stored in proprietary RAW
  format before download to
  computer
 Sensor sends digital signals
  to be processed and stored
  in non-volatile memory
Megapixels?

 What does it mean?
   Amount of sensor information
   Allows for more pixels at maximum resolution
 Why is 5 megapixels better than 3 or 4?
 Can they really zoom in on pictures like on
  CSI?
Displaying Images
 Display types
   CRT                       15”
   LCD
   Gas Plasma
 Typical resolutions
     800x600
     1024x768          12”
     1152x864
                                    19”
     1280x1024
 4 to 3 ratio
   Movies are 16:9
 Refresh rate
   Interlacing
 Graphics Card
Graphics Cards

 Hardware that connects monitors to your PC
    Have processors, memory, clocks
    Almost sub-computers
    Controls resolution and refresh rate
 Drivers
    Software that allows graphics cards to interface with monitors
    Specific to Operating Systems
      Linux often has worse support because fewer people use it
 Some card include “tuners” for television
    NTSC
  MPEG Compression
 MPEG-1
     video resolution of 352-by-240 at 30 frames per second (fps)
     quality slightly below the quality of conventional VCR videos
 MPEG-2
   offers resolutions of 720x480 and 1280x720 at 60 fps
   full CD-quality audio
   sufficient for all the major TV standards, including NTSC, and even HDTV
   MPEG-2 is used by DVD-ROMs. MPEG-2 can compress a 2 hour video into a
    few gigabytes
   decompressing an MPEG-2 data stream requires only modest computing
    power, encoding video in MPEG-2 format requires significantly more
    processing power
 MPEG-4
   graphics and video compression algorithm standard that is based on MPEG-1
    and MPEG-2 and Apple QuickTime technology
   Wavelet-based MPEG-4 files are smaller than JPEG or QuickTime files
   designed to transmit video and images over a narrower bandwidth and can
    mix video with text, graphics and 2-D and 3-D animation layers
Digital Animation

 Programs used to describe
  desired output
   Maya
 Images are “rendered” one
  screen at a time
   24 fps
   More for slow motion
   Takes a lot of computer time
 Graphics machines need A
  LOT of memory, processor
  speed, and secondary
  storage

				
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