Analog versus Digital

1
Analog versus Digital

• Norman White

2
Analog

• Analog means that information is represented in a
  continuous manner, as in a time varying
  electrical voltage, sound level, water level,
  etc.
• Examples
• Electrical current

3
Digital

• We need a way to represent analog information in
  a computer
• Digitization converts analog format to digital
• Sample signal every time period and generate a
  time series of data representing the signal
• Time Value
• .1 0
• .2 243
• .3 128
• As we sample more frequently, we have a closer
  and closer representation of the original signal

4
Common examples

• Scanned images scanner looks at image as a
  sequence of dots, each having a color value. The
  scanner converts the picture into a sequence of
  numbers, each number is the color value for 1
  pixel
• For instance, faxes have only 2 color values,
  black and white (0white, 1 black)
• At 300 dpi (dots per inch) 1 line of pixels on an
  8 inch page would take 3008 bits 2400 bits or
  300 bytes. An 8 x 10 black and white image would
  take 8 300 10300 bits 720,000 bits
• What happens with color?

5
Color

• Color is also continuous (light spectrum etc) and
  needs to be represented as a discrete value.
• There are several different color models (RGB
  Red, Green, Blue) Hue, saturation etc.
• Each pixel has to have color information added. 8
  bit color 256 colors, 16 bit color 32768
  colors etc.
• Color 8 x 10 image 16 bits 16720000 bits 11
  Mbits or over 1 MB (megabyte)

6
Audio

• Audio sampling rates
• Voice 64000 bits per second
• 8000 8 bit samples
• High quality stereo 187KB / sec
• 44000 16 bit samples per second/ channel

7
Video

• Video audio and images together
• Total bitrates can be enormous
• Much of the course will focus on this problem