Information Representation: Characters and Images

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Information Representation Characters
and Images
Department of Computer and Information
Science,School of Science, IUPUI
CSCI 230
Dale Roberts, Lecturer IUPUI droberts_at_cs.iupui.edu
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Information Representation Review

• All information must be rendered into binary in
  order to be stored on a computer.
• Prior example of binary information
  representations include positive integers,
  negative integers, and floating point.
• Besides numbers, almost all applications must
  store characters and string information.
• Images are pervasive in todays internet world
  and must be rendered in binary to be handled by
  internet browsers.
• Crucial to make general purpose computers,
  computers that can easily perform many different
  tasks, is the idea that the program is just data.
  Like any other information, programs must be
  rendered into binary in order to be stored within
  a computer.

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Character Representations

• ASCII PC workstations
• EBCDIC IBM Mainframes
• Unicode International Character sets

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ASCII

• ASCII
• Expanded name American Standard Code for
  Information Interchange
• Area covered 7-bit coded character set for
  information interchange
• Sponsoring body American National Standards
  Institute (ANSI)
• Source documents Information Systems Coded
  Character Sets 7-Bit American National Standard
  Code for Information Interchange (7-Bit ASCII)
• Characteristics/description Specifies coding of
  space and a set of 94 characters (letters, digits
  and punctuation or mathematical symbols) suitable
  for the interchange of basic English language
  documents. Forms the basis for most computer code
  sets and is the American National Version of
  ISO/IEC 646.
• Usage Used as the basic US code set for personal
  and workstation computers.
• Further details available from ANSI, 25 West
  43rd Street, New York, NY 10036, USA
• Other references A list of ASCII codes can be
  obtained from http//www.dkuug.dk/i18n/charmaps/AN
  SI_X3.4-1968.

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ASCII Code Set
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EBCDIC

• EBCDIC
• Expanded name Extended Binary Coded Decimal
  Interchange Code
• Area covered 8-bit coded character set for
  information interchange between IBM computers
• Sponsoring body Proprietary specification
  developed by IBM
• Characteristics/description A set of national
  character sets for interchange of documents
  between IBM mainframes. Most EBCDIC character
  sets do not contain all of the characters defined
  in the ASCII code set but there is a special
  International Reference Version (IRV) code set
  that contains all of the characters in ISO/IEC
  646 (and, therefore, ASCII). Several national
  versions have been updated to support the
  encoding of the euro sign (in lieu of the
  currency sign).
• Usage Not much used outside of IBM and similar
  mainframe environments. When transmitting EBCDIC
  files between systems care needs to be taken to
  ensure that the systems are set up for the
  relevant national code set.
• Further details available from Your local IBM
  office.
• Other references Details of the most commonly
  used sets of EBCDIC codes can be obtained from
  http//www.dkuug.dk/i18n/charmaps which, however,
  has not necessarily been updated to cover the new
  code pages that also support the euro sign..

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EBCDIC Code Table
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Unicode

• From MSDN Unicode can represent all of the
  world's characters in modern computer use,
  including technical symbols and special
  characters used in publishing. Because each
  Unicode code value is 16 bits wide, it is
  possible to have separate values for up to 65,536
  characters. Unicode-enabled functions are often
  referred to as "wide-character" functions. Note
  that the implementation of Unicode in 16-bit
  values is referred to as UTF-16. For
  compatibility with 8- and 7-bit environments,
  UTF-8 and UTF-7 are two transformations of 16-bit
  Unicode values. For more information, see The
  Unicode Standard, Version 2.0.

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Unicode The Wide-Character Set

• From VB Online Help
• A wide character is a 2-byte multilingual
  character code. Any character in use in modern
  computing worldwide, including technical symbols
  and special publishing characters, can be
  represented according to the Unicode
  specification as a wide character. Developed and
  maintained by a large consortium that includes
  Microsoft, the Unicode standard is now widely
  accepted. Because every wide character is always
  represented in a fixed size of 16 bits, using
  wide characters simplifies programming with
  international character sets.
• A wide character is of type wchar_t. A
  wide-character string is represented as a
  wchar_t array and is pointed to by a wchar_t
  pointer. You can represent any ASCII character as
  a wide character by prefixing the letter L to the
  character. For example, L'\0' is the terminating
  wide (16-bit) NULL character. Similarly, you can
  represent any ASCII string literal as a
  wide-character string literal simply by prefixing
  the letter L to the ASCII literal (L"Hello").
• Generally, wide characters take up more space in
  memory than multibyte characters but are faster
  to process. In addition, only one locale can be
  represented at a time in multibyte encoding,
  whereas all character sets in the world are
  represented simultaneously by the Unicode
  representation.

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Universal Character Set (Unicode)

• ISO/IEC 10646
• Expanded name ISO/IEC 10646 Universal
  Multiple-Octet Coded Character Set (UCS)
• Area covered Multilingual, multi-octet character
  set covering all major trading languages. The
  intent is to provide coding for all the
  characters of all the scripts of the world.
• Sponsoring body ISO/IEC JTC1/SC2 and ISO/IEC
  JTC1/SC22 WG20
• Source documents
• ISO/IEC 10646-1 Information technology --
  Universal Multiple-Octet Coded Character Set
  (UCS)
• Part 1 Architecture and Basic Multilingual Plane
  
• Part 2 Supplementary Planes
• ISO/IEC DIS 14651  International string ordering
  and comparison -- Method for comparing character
  strings and description of the common template
  tailorable ordering
• ISO/IEC PRF TR 14652 Information technology --
  Specification method for cultural conventions
• ISO/IEC 147551997 Information technology --
  Input methods to enter characters from the
  repertoire of ISO/IEC 10646 with a keyboard or
  other input devices
• Unicode 3.2
• RFC 2279 UTF-8, a transformation format of ISO
  10646
• Characteristics/description Integrates previous
  internationally/nationally agreed character sets
  into a single code set together with additional
  characters to previously encoded scripts and new,
  both current and ancient scripts. ISO/IEC 10646
  is based on 4 octet (32-bit) coding scheme known
  as the "canonical form" (UCS-4), but a 2-octet
  (16-bit) form (UCS-2) is used for the Basic
  Multilingual Plane (BMP), where the missing two
  high order octets are assumed to be 00 00. The
  code set is split into 128 "groups" of 256
  "planes", each containing 256 "rows" with 256
  "cells" for characters. Each character is given a
  code position using multiple octets, the third
  (first) of which identifies the row containing
  the character and the fourth (second) its cell
  number.
• Usage This standard has become the basic coding
  form for all 16 and 32-bit computer systems.
  Users of Internet Explorer 5, and XLink-aware XML
  browsers, can obtain more details about
  applications of ISO 10646 from our Diffuse Topic
  Map service.
• Further details available from ISO and national
  standards bodies.
• Other references Details of the Unicode
  standard, the repertoire and coding of which are
  identical to those of the ISO/IEC 10646 code set
  can be obtained from http//www.unicode.org.

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Unicode Latin Set
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Additional Unicode Pages
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Comparing Characters Collating Sequence

• If you look at the ASCII Character Code Table the
  ASCII binary number for A is 1000001, which is
  65 decimal. The ASCII binary number for a is
  1100001, which is 97 decimal. Therefore, A is
  less than a. A blank is stored as 0100000, or
  32 decimal. The blank has the smallest value of
  the digits or characters.
• Rules
• Upper case lt lower case
• Space lt any other character

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Comparing Strings

• A useful operation is the comparison of two
  strings. Two strings are related in the same
  three basic ways as number values. One string is
  either less than, equal to, or greater than the
  other. String comparison is usually based on the
  positions of the characters in the character set.
  
• Scanning along both strings and comparing
  corresponding characters establish the
  relationship between two strings. The strings
  are equal as long as corresponding characters are
  equal. If two characters are different, the
  comparisons are based on their relative order in
  the character set. The character whose code is
  less belongs to the lesser string.
• Ex. abcd lt abcz
• If the two strings are of different length, but
  identical up to the end of the shorter one, then
  the shorter string is the lesser of the two
• Ex. abc lt abcd
• If the two strings are of different length and
  consist of Upper and lowercase letters, Upper
  case letters come before lower case letter and a
  blank has a lower value than all other letters.
• Ex. AZZZ lt Aaaah
• Below is an example of a comparison of strings
  that contain blanks. Scanning along both strings
  and comparing corresponding characters, you see
  the strings are equal for the first two
  characters. You then compare the blank and the
  t you then reach the conclusion below.
• Ex. hi there lt hit a ball

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Image Data

• Image Data
• Because of the number of different shapes,
  colors, textures, sizes and shadings of images,
  there is no standard representational format and
  there is with alphanumeric codes.
• There are 2 ways of representing images
• 1 Bit map or raster images
• 2 Object or vector images are made up of simple
  geometrical elements. Each element is specified
  by its geometric parameters, its location in the
  picture and other details.
• Common Graphics Formats

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Rastor Images

• Bit map or raster images consist of an array of
  pixel values (pixel stands for 'picture
  element'). Each pixel represents the sampling of
  a small area of the picture.In its simplest form
  an image is represented as a long string of bits
  representing the rows of pixels in the image,
  where each bit is either 1 or 0 depending on
  whether the corresponding pixel is black or
  white.
• Color images are only slightly more complicated,
  since each pixel can be represented by a
  combination of bits indicating the color of that
  pixel. It is common to record the color of each
  pixel as three components
• red
• green
• blue
• One byte is typically used to represent the
  intensity of each color component

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Acknowledgements

• A list of character standard was obtained from
  www.diffuse.org.
• A portion of the discussion regarding character
  and string comparisons was obtained from Emad
  Hayajneh.
• A portion of the discussion regarding images was
  obtained from Dr. Robert Stephens.