Media: Text

1
Media Text

• Words and symbols in any form, spoken or
  written, are the most common system of
  communication. unknown

2
Text - Representation

• ASCII
• 7-bit code
• 128 values in ASCII character set (English
  Alphabet)
• use of 8th bit in text editors/word processors
  creates incompatibility
• ISO character sets
• extended ASCII to support non-English text
  (symbols such as or )
• ISO Latin provides support for accented
  characters
• à, ö, ø, etc.
• ISO sets include Chinese, Japanese, Korean
  Arabic
• UNICODE
• 16 bit format (Roman vs. Western European or
  Kanji Japan)
• 65,000 different symbols
• 25 supported scripts of Version 2.0 Unicode
  Standard Arabic, Armenian, Bengali, Bopomofo,
  Cyrilic, Devanagari, Georgian, Greek, Gujarati,
  Gurmkhi, Han, Hangul, Hebrew, Hiragana, Kannada,
  Katakana, Latin, Lao, Malayalam, Oriya, Phonetic,
  Tamil, Telugu, Thai, Tibetan

3
ASCII

• All uppercase and lowercase letters
• Punctuation symbols like ! . , ? etc.
• Digits 0, , 9
• Arithmetic symbols - /
• Assorted special symbols like _at_
  ( ) etc.
• Invisible formatting characters

4
ASCII
5
Text - Representation

• Marked-up text
• nroff, troff
• LaTEX
• SGML
• HTML
• HyTime
• XML, XSL, XLL
• Structured Text
• structure of text represented in data structure,
  usually tree-based
• ODA, structure embedded in byte-stream with
  content
• Hypertext
• non-linear
• graph or web structure nodes and links
• currently subject of intensive ISO standards
  activity

6
Text - Operations

• Character operations
• basic data type with assigned value
• permits direct character comparison (a
• String operations
• comparison
• concatenation
• substring extraction and manipulation
• Editing
• perhaps the most familiar set of operations on
  text
• cut/copy/paste
• strings v. blocks, dependent on document structure

7
Text - Operations

• Formatting
• interactive or non-interactive (WYSIWYG v. LaTEX)
• formatted output
• bitmap
• page description language (Postscript, PDF)
• font management
• typeface
• point size (1 point 1/72 of an inch)
• TrueType fonts geometric description kerning
• Pattern-matching and Searching
• search and replace
• wildcards
• regular expressions
• for large bodies of text, or text databases, use
  of inverted indices, hashing techniques and
  clustering.

8
Text - Operations

• Sorting
• numerous varieties of sort, all of them
  extensively studied in basic programming
• sort complexity is a major factor in data
  handling performance
• Compression
• ASCII uses 7 bits per character, though most
  word-processors actually use the 8th bit to use
  up a byte per character
• Information theory estimates 1-2 bits per
  character to be sufficient for natural language
  text
• This redundancy can be removed by encoding
• Huffman varies the numbers of bits used to
  represent characters, shortest codes for highest
  frequency characters
• Lempel-Ziv identifies repeating strings and
  replaces them by pointers to a table
• Both techniques compress English text at a ratio
  of between 21 and 31

9
Text - Operations

• Encryption
• text encryption is widely used in electronic mail
  and networked information systems
• most widely-used techniques
• DES
• RSA public-key
• PGP
• subject of major controversy
• key escrow systems
• Clipper chip
• strong encryption now being legally outlawed in
  a number of countries
• Language-specific operations
• spell-checking
• parsing and grammar checking
• style analysis

10
About Fonts and Faces

• A typeface family of graphic character (include
  many type sizes styles)
• A font is a collection of characters of a single
  size
• Styles are boldface and italic (underlining
  outlining)
• Serif vs. Sans Serif (sans(French) without)