Representing images

• Pixels


  Tiny units that make up a digital image on a computer or mobile phone screen
• The greater the number of pixels used for a given size of display, the more detail can be displayed and the higher the quality of the image
• Representation of a 'triangle' on an 8 x 16 pixel display

  • Horizontal side is a perfect straight line
  • Other sides have a 'staircase' appearance
• When you zoom in on a digital image, each pixel expands in the display so that it is possible to see each one as a discrete square
• Binary representation


  Using just two symbols or 'states' (0 and 1) to represent information digitally
• Coding a black triangle on a white background


  Represent white pixels with 0, black pixels with 1
• Increasing the resolution (number of pixels) improves the detail and quality of a digital image
• Screens can have resolutions ranging from 2560x1600 pixels to 3840x2160 pixels
• Extending binary representation to include shades of grey or colour


  Use more bits per pixel (e.g. 2 bits for 4 colours, 3 bits for 8 colours)
• Binary word


  A set of a given number of bits used for data representation
• Bitmap


  A coding scheme that allocates a binary code to each pixel to define its colour and brightness
• Bitmap files are relatively large in size, making them less suitable for web images
• Vector graphics


  A coding approach that stores information about the different shapes in an image, rather than individual pixels
• Vector graphics can produce smaller file sizes than bitmaps, but are not effective for images like photographs or motion pictures