Facsimile Compression - PowerPoint PPT Presentation

Title: Facsimile Compression


1
Facsimile Compression

• Michael Hollander
• Doug Woodgate
• Francois Yang

2
Introduction

• Definition of Facsimile
• Background of Facsimile
• One Dimensional Coding
• Two Dimensional Coding
• Future / New technology in Facsimile

3
Facsimile

• The word Facsimile comes from the Latin Fac
  simile which means make it the same.
• It represents the faithful rendition of originals.

4
Facsimile Theory

• Facsimile or Fax machine was invented in 1842 by
  a Scottish electrical engineer Alexander Bain.
• This was about 5 years after Morse invented the
  telegraph.
• Fax machine break up a document into pixels and
  send them one by one to another fax using phone
  line.

5
Types of Facsimiles

• Group 1 old FM transmission time - Approx. 6
  min. Standard fax machines.Slow communication
  with no compression.
• Group 2 Transmission time - Approx. 3 min.
  Changed the modulation method to amplitude
  modulation and suppressed the sideband to
  compress bandwith.
• Group 3 Transmission time - Less than 1 min.
  Most use over standard phone line. Combination of
  amplitude and phase modulation.
• Group 4 Transmission time - Approx. 10 sec. Use
  with Primary Data Networks, required group 3.

6
Basic Process
7
Future / New technology in Facsimile

• Technology now exists that permits the
  transmission and reception of facsimile data to
  or from a computer without requiring hard copy at
  either end.

8
Examples
Examples of hard copy include teletypewriter
pages, continuous printed tapes, facsimile pages,
computer printouts, and radiophoto prints.
Magnetic tapes, diskettes, and nonprinted punched
paper tapes are not hard copy.
9
Two-Dimensional Encoding

• How is two-dimensional encoding different than
  one-dimensional?
• What types of fax machines support it?
• What are the benefits of two dimensional
  encoding?
• What are some drawbacks of this method?
• Short example.

10
Two-Dimensional vs. One-Dimensional

• Two dimensional encoding switches between three
  different modes.
• Pass mode
• Vertical mode
• Horizontal mode

11
How it works.

• Compares current scan line(coding line) to the
  previous line(reference line)
• Assumes an all white reference line above the
  first line of the page.
• Once the coding line is encoded, it becomes the
  reference line, and the next line is the coding
  line.

12
What machines use it?

• Some Group 3 machines have Two-Dimensional
  encoding as an option.
• At most K 1 lines will be encoded with 2
  Dimensional. (K 2 std res. K 4 high res.)
• Then it encodes the next with 1 Dimension.
• All Group 4 machines strictly use Two-
  Dimensional encoding.

13
Benefits and Drawbacks

• Produces better results than one dimensional for
  encoding gray areas. (High entropy areas)
• Less reliable than one dimensional.
• Error in one line propagates to all succeding
  lines.

14
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a0
a1
a2
a1 b1 1, Vertical Mode
010
15
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a0
a1
a2
a1 b1 0, Vertical Mode
010
1
16
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a0
a1
a2
a1 b1 gt 3, Horizontal Mode
3 White, 4 Black
010
1
001
1000
011
17
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a1
a2
a0
B2 to the left of a1, Pass
Mode b1b2 (2 white)
010
1
001
1000
011
0001
0111
18
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a1
a2
a0
a1 b1 -2, Vertical Mode
010
1
001
1000
011
0001
0111
000011
19
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a1
a2
a0
a1 b1 2, Vertical Mode
010
1
001
1000
011
0001
0111
000011
000010
20
Short example
Beginning of Line
Edge of page
b1
b2
Reference Line
Coding Line
a1
a2
a0
a1 b1 gt 3, Horizontal Mode
4 White, 7 Black
010
1
001
1000
011
0001
0111
000011
000010
001
1011
00011