Digital Image Compression

• Digital image


  Made up of multiple small elements known as pixels
• Resolution


  Number of pixels per unit area of the image
• Solutions to reduce memory required for digital images

  • Reduce number of pixels (reduce resolution)
  • Compress data using compression software
• JPEG


  One of the most important standards for photo image coding, also used in MPEG video
• JPEG compression


  1. Divide picture into small blocks of pixels

  2. Perform complex calculations to arrive at a reasonably accurate but concise description of the block

  3. Remove or reduce some components that are not important for human vision
• JPEG compression


  Lossy method, original data cannot be recovered exactly
• JPEG compression can achieve high compression ratios with no visible loss of quality
• Other common image formats


  • GIF (Graphics Interchange Format)
  • PNG (Portable Network Graphics)
• GIF and PNG


  Use lossless compression methods
• Increasing compression ratio


  Creates images of lower quality
• Human perception is less sensitive to colour than it is to brightness
• Information about colour and brightness can be coded and recorded separately
• If human perception is less sensitive to colour than brightness

  Use fewer bits to code colour information than are used to code the brightness