Compression | Computer for GCSE/IGCSE - Year 11 PDF Download

Compression

Compression involves reducing the size of a file to save storage space or decrease bandwidth usage during file transmission. There are two primary types of compression:

Lossless Compression

• A compression algorithm minimizes file size while retaining all data.
• It identifies and indexes recurring patterns within the file.
• Data is substituted with the respective index and stored positions.
• The frequency of pattern occurrences is also recorded.
• Methods like run-length encoding (RLE) and Huffman encoding are employed.
• RLE substitutes repeated character sequences with a code denoting the character and its repetition count.
• Huffman encoding assigns shorter codes to commonly used characters and longer codes to less frequent ones.

Lossy Compression

• Lossy compression decreases file size by permanently discarding portions of data.
• It's commonly employed for images and audio files, where minor details can be sacrificed without noticeable quality loss.
• Downsampling, resolution or color depth reduction, and lowering sample rate or resolution are typical techniques for lossy compression.
• The degree of compression chosen determines the extent of data removal, which can affect the file's overall quality.

Overall

• Compression is essential for shrinking large files, facilitating storage, transmission, and quicker processing.
• Selecting between lossy and lossless compression techniques hinges on the file type and its intended application.
• Lossy compression is typically applied to media files, tolerating minor data loss, whereas lossless compression is favored for text, code, and archival purposes.