Data Compression

Data Compression

1. Data File Format

   • txt
     • A text file based commonly on the ASCII character set
     • DISADV
       • No formatting information
       • Can take up more storage than necessary as no compression occurs
     • ADV
       • Opened in any word processor or text editor
       • Smaller than a word processing file
       • Do not require metadata so no data Is stored
       • Easily recovered if file is corrupt
   • WAV
     • Audio file format
     • ADV
       • Lossless
       • Supports compressed audio
     • DISADV
       • Quality dependent upon sample rates + resolution
       • Large file size
   • Bitmap
     • .bmp
     • ADV
       • Store characters or graphics
       • High resolution
       • Works well with most Windows programs
   • JPEG
     • Joint Photographic Experts Group
     • ADV
       • Standard compression
       • 24-bit colour colour with 16 million colours
       • High degree of compression
   • MPEG
     • MPEG - 1 (mpg) MPEG-2 (m2v, mpg, mp2) Audio and video formats
     • ADV
       • Varying resolutions can be applied to the file at the time of storage
       • MPEG-1 produce low-resolution file formats suitable for CD storage
       • MPEG-2 records high-resolutions sequences suitable for DVD recording
     • DISADV
       • Lossy compression
   • GIF
     • .gif
     • ADV
       • Format for image files that supports animated and static images
       • GIF's are compressed
       • Lossless
       • Suitable for images with text
       • Suitable for transparency and animated images

2. Why compress?

   • Makes it easier for file transfer
   • Makes the file smaller

3. How does compression work?

   • Zipping
     • Programs like WinZip are based on lossless compression. They remove this redundant information when you compress (or “zip”) the file and restore it when you uncompress (or “unzip”). Nothing is lost. In the image world, PNG files also use lossless compression.

4. Inputting Data

   • Text
     • Keyboard
       • QWERTY keyboard most common
       • ASCII is the common character set on digital devices
     • Touch screen
       • Grid of tiny transparent electrodes
       • Uses co-ordinates and sends them from controller to the PC
   • Sound
     • Digital video cameras
   • Video
     • Recorders

5. Types

   • Lossy
   • Lossless