text sound and images

• 1 KiloByte (KB)

  1000 bytes
• 1 MegaByte (MB)

  1 million bytes
• 1 GigaByte (GB)

  1 billion bytes
• 1 Terabyte (TB)

  1 trillion bytes
• 1 Kibibyte (KiB)

  2^10 (1024)
• 1 Mebibyte (MiB)

  2^20
• 1 Gibibyte (GiB)

  2^30
• 1 Tebibyte (TiB)

  2^40
• Bitmap image file size =

  Image resolution (in pixels) x colour depth
• Mono sound file =

  Sample rate (Hz) x sample resolution (bits) x sample length (seconds)
• Stereo sound =

  Mono sound file x 2
• What happens in lossy compression

  File compression algorithm removes unnecessary data, cannot reconstruct to original format, lost some detail of original
• What happens when lossy is used on image

  Reduce the resolution and colour depth
• What happens when lossy is used on sound file

  Reduce the sampling rate and/or resolution, e.g removes sound out of range of human ears
• Which is smaller lossy or lossless

  Lossy
• Common lossy file formats

  JPEG

  MP3s

  MP4a
• What is MP3

  -used to play music on devices

  -reduces file by 90%

  Wont match quality of sound on DVD or CS but is quality for what we need
• What is MP4s

  Allow store of multimedia files (more than sound)

  Use lossy compression (keeps acceptable quality of sound + vid)

  Movies can be streamed over internet with no real loss of quality
• JPEG

  A photograph is taken and stored as raw bitmap (very large )

  Temporary file

  Lossy compression algorithm used for bitmap images

  Once gone through algorithm, new file is produced and can not be reconstructed
• Lossless compression?

  Algorithm ensures no data is lost from original file

  E.g when transferring a large spreadsheet with financial data
• What is RLE?

  run-length encoding
• What does it do?

  Type of lossless compression

  Reduces size of a string identical pieces of data that are next to each other (repeated colour sin an image)
• How does RLE work?

  Repeating string is broken into 2 values

  -first value : number of identical data items

  -second value : code of the data item (such as ASCII code) 0r (RGB c0de for colour )

  RLE is only effective if there is a long run of repeated bits
• (E>G of RLE) aaaaafffffbbbwddd, what would the code for this be?

  5 97 5 102 3 98 1 119 3 100
• Issue of RLE?

  If we have a recurring pattern then RLE wont cope well. for this we use a flag
• What does ASCII stand for?

  American Standard Code for Inforamtion Interchange
• What does ASCII do?


  Allows us to represent all the letters, numbers and characters on a standard keyboard ( stores 32 control code)
• What is the difference in bits between capital and lower case letters?

  32 bit difference ( capital is lower number, Lowe case is higher number)
• What is extended ASCII?

  Uses 8 bits to store code, allows to store characters not in English alphabet (e.g accents on letters)
• What is ASCII disadvantage?

  Doesn't allow for representation for other characters in other languages to be represented
• What is Universal code


  A way to represent all the languages of the world it can support most operating systems and search engines and internet browsers
• Why is Universal code used

  It can use up to four bytes per character
• Five goals of Unicode?

  1) Create universal code that covers all languages and writing systems

  2)produce more efficient coding system than ACII

  3)adopt uniform encoding where each character is encoded 16-bit or 32-bit

  4)create unambiguous encoding where 16-bit or 32-bit represent same character

  5) reserve part of code for private use to enable user to adding codes for own characters
• Difference between ASCII and Unicode?

  ASCII can only use one byte to store a character, uniCode can use up to four bytes per character
• Definition of sampling rate?

  The number of samples taken per second, usually measured in Hz e.g 1Hz = 1 second
• Definition of sampling resolution?

  The number of bits per sample
• Benefits of higher sampling

  -larger dynamic range

  -Better sound quality

  -less sound distortion
• Drawbacks of higher sampling

  -larger file size

  -takes longer to send/download music

  -needs greater processing power
• How are sound waves converted?

  Using ADC
• In a bit map how many colours can you have if there are 2 bits per pixel?

  4 different colours