Fundamentals of Data Representation

Fundamentals of Data Representation

1. Representing images

   • Pixel: Picture Element; a single point in a graphical image
     • VDUs display pictures by dividing the dispaly screen into thousands of pixels, arranged into rows and columns
   • Bitmaps
     • image resolution = width x hight
     • Colour depth
       • Number of bits used to represent each pixel
     • File size= width x height x colour depth

2. Representing Sound

   • sound is analogue
     • must be converted to a digital form for storage and processing in a computer
   • Sampling
     • Sample: measure of amplitude at a point in time
       • Sound waves are sampled to create the digital version of sound
   • Digital representation of sound
     • sampling rate
       • number of samples taken in a second - measured in hertz
     • Sample resolution
       • the number of bits per sample
     • Sound File
       • rate x resolution x seconds

3. Data Compression

   • used to reduce file sizes
   • Lossless compressioon
     • reduces the size of a file without any damage to the file or reduction in quality
     • Examples
       • Huffman coding
       • Run length encoding
   • Lossy compression
     • permanently removes data from the file that the computer believes you can do without
     • Examples
       • MP3, MP4 and JPG