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The Travel Packing Problem
The Travel Packing Problem
You're packing for a trip. Lossless packing: You vacuum-seal clothes to remove air - they're smaller but unfold perfectly. Lossy packing: You leave your winter coat home and pack a thin jacket instead - much lighter, but not quite the same. Lossless compression is like vacuum-sealing - you can get the exact original back. Lossy compression is like leaving stuff behind - the result is good enough but some detail is permanently gone. Photos, music, videos = usually lossy (you won't notice). Documents, programs, medical scans = always lossless (need exact original)!
Deep Dive: Why Compression Matters
Remember Topic 15? An uncompressed 3-minute CD-quality song = 31.7 MB. A 4K movie uncompressed = 6,000 GB (6 TB)! Without compression:
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Exam Tips - Compression
Most common exam questions:
- "Difference between lossy and lossless?" → Lossless = perfect reconstruction; Lossy = permanent data loss
- "When to use lossy?" → Photos, music, video - for human viewing/listening
- "When to use lossless?" → Text, programs, medical images - need exact copy
- "Examples of lossy?" → JPEG, MP3, MP4
- "Examples of lossless?" → PNG, ZIP, FLAC
- "How does RLE work?" → Replace repeated values with count + value
Key comparison facts:
- Lossless: 30-70% compression, reversible, exact original
- Lossy: 80-95% compression, irreversible, "good enough" quality
- Trade-off: Quality vs file size - can't have both!
RLE exam questions:
- Always show the pattern: AAAAAABBB → 6A3B
- Count + Value format
- Works best when there are LONG runs of repeated data
- Can make files LARGER if no repetition
Common mistakes to avoid:
- Saying "lossy is always better" - NO! Depends on use case
- Confusing lossless with lossy file formats (JPEG is lossy, PNG is lossless)
- Forgetting that lossy is PERMANENT - you can't "uncompress" to perfect quality
- Not explaining WHY you'd use one over the other
Now try it yourself
Quiz · Question 1 of 16
Which statement correctly describes lossy compression?
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This topic in real past papers
Every real exam question we've found on compression, with a full worked answer.