Run-Length Encoding (RLE) - Simple Lossless
Part of Compression — GCSE Computer Science
This key facts covers Run-Length Encoding (RLE) - Simple Lossless within Compression for GCSE Computer Science. Revise Compression in Memory & Storage for GCSE Computer Science with 15 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 4 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 4 of 11
Practice
15 questions
Recall
16 flashcards
Run-Length Encoding (RLE) - Simple Lossless
How RLE Works:
Replace repeated values with a count + value. Instead of "AAAAAABBCC", store "6A2B2C".
Example 1: Simple Pattern
Original: WWWWWWBBBWWW (12 characters) RLE: 6W3B3W (6 characters) Saved: 50% compression ratio
Example 2: Binary Data
Original: 00000000111111110000000 (23 bits) RLE: 8×0, 8×1, 7×0 (3 pairs) Stored as: 8,0,8,1,7,0
Example 3: Image Data (Scanline)
Image row (colors): RRRRRRGGGGBBBBBB (16 pixels) RLE: 6R4G6B (3 pairs) Original: 16 pixels × 3 bytes = 48 bytes RLE: 3 pairs × (count + color) = 6 bytes Saved: 87.5%!
When RLE Works Well:
- Large blocks of same color: Simple graphics, logos, cartoons
- Black and white images: Scanned documents, faxes
- Video frames: Large unchanged areas between frames
When RLE Fails:
- No repetition: ABCDEFGH → 1A1B1C1D1E1F1G1H (BIGGER!)
- Random data: Photos, complex images - little to no repetition
- Can make file larger if there's no pattern