This key facts covers How Lossy Compression Works 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 7 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 7 of 11
Practice
15 questions
Recall
16 flashcards
How Lossy Compression Works
Key Principle: Remove What Humans Can't Perceive
For Images (JPEG):
- Human eye limitations: More sensitive to brightness than color
- Strategy: Keep brightness detail, reduce color detail
- Averaging: Group nearby similar pixels, store average
- Discard high frequencies: Remove fine texture details
- Result: 10× smaller file, looks nearly identical to most viewers
For Audio (MP3):
- Human hearing limitations: Can't hear very high/low frequencies
- Psychoacoustic masking: Loud sounds mask quiet nearby sounds
- Strategy: Remove frequencies humans can't hear
- Remove masked sounds: Quiet sounds near loud ones = discarded
- Result: 10× smaller, sounds nearly identical to CD
Quality Levels (User Control):
- Low quality: 90% compressed - visible/audible artifacts
- Medium quality: 85% compressed - good balance (default)
- High quality: 70% compressed - minimal loss, larger file
- Trade-off: More compression = smaller file but worse quality