1.3 Compression

Compression is the process that reduces file size while maintaining acceptable quality. Two types: Lossless and Lossy

Reasons for compressing:

• Less Bandwidth Required
• Less Storage Space Required
• Shorter Transmission Time

Lossless Compression

• A method that allows data to be perfectly reconstructed from the compressed file
• E.g. bitmap (.bmp), vector graphic (.svg) and .png images, text file compression, database records

Run-length Encoding (RLE)

• A form of lossless compression
• Used for text files and bitmap images.
• Encodes consecutive identical elements using two values: run count and run value.
• E.g. RLE of bitmap image
  • We can represent the first row as a sequence of pixels: “WBBWWWBBBBW” | W: white and B: black
  • After applying RLE: “W 2B 3W 4B W”
  • The process is repeated for other rows.

Lossy Compression

• A method that permanently removes redundant data to achieve higher compression rates
• While the file size is significantly reduced, some quality is lost
• E.g. Sound files (.mp3), .jpeg images
• Sound files compression (.mp3) utilizes Perceptual Coding to remove certain parts of sound that are less audible to human hearing.