How Lossy Compression Works
This key facts covers How Lossy Compression Works 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 7 of 12 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 12
Practice
16 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
Keep building this topic
Read this section alongside the surrounding pages in Compression. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Compression
Which statement correctly describes lossy compression?
Explain how run-length encoding (RLE) works to compress data.
Quick Recall Flashcards
16 questions on Compression — practise free
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