This key facts covers Quick Reference - Compression within Compression for GCSE Computer Science. Revise Compression in 3.3 Data Representation for GCSE Computer Science with 16 exam-style questions and 16 flashcards. This topic appears regularly enough that it should still be part of a steady revision cycle. It is section 11 of 12 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Quick Reference - Compression
Lossless Compression:
- Characteristic: Perfect reconstruction, no data loss
- Compression: 30-70% reduction
- Reversible: Yes
- Use for: Text, programs, medical images, archives
- Formats: PNG, ZIP, FLAC, GIF, RAR, 7z
- Algorithms: RLE, LZW, Huffman, DEFLATE
Lossy Compression:
- Characteristic: Data permanently removed
- Compression: 80-95% reduction
- Reversible: No
- Use for: Photos, music, video, web images
- Formats: JPEG, MP3, MP4, AAC, WebP, H.264
- Strategy: Remove what humans can't perceive
RLE Quick Guide:
- Pattern: WWWWWBBB → 5W3B
- Format: Count + Value
- Best for: Long runs of repeated data
- Worst for: Random data (can make file larger!)
The Golden Rule:
If you need the EXACT original back: use lossless. If "good enough" is fine and you need small files: use lossy.
Practice questions for Compression
Which statement correctly describes lossy compression?
Explain how run-length encoding (RLE) works to compress data.