Stretch tasks Compression

Round 1: Quiz Blitz

1. Reducing the size of a file Smaller files use less storage and travel faster over a network.
2. It uses less storage space; It sends faster over a network Less space, faster transmission and less bandwidth.
3. Permanently removes some data It throws away detail people are least likely to notice.
4. False The removed data is gone for good.
5. PNG PNG, GIF, ZIP and FLAC are lossless. JPEG, MP3 and MP4 are lossy.
6. A program file Removing any part of a program would corrupt its instructions.
7. 6C 2D Six Cs then two Ds: 6C 2D.
8. It throws data away Lossless can only describe the data more efficiently. Lossy removes some of it.
9. True Each lossy save throws away a little more.
10. JPEG; MP3 JPEG and MP3 remove data. ZIP, PNG and FLAC keep every bit.
11. Lossless, so no quality is lost with each edit Masters must survive repeated editing without building up damage.
12. Sounds most people cannot hear Frequencies too high or too quiet for most people to hear go first.

Round 2: Quick Fire

1. • They take up less storage space
   • They are faster to send, using less bandwidth
   Model answer

   Compressed files take up less storage space, and they are faster to send over a network because there is less data.

2. • Lossy compression permanently removes data
   • Values would be missing or wrong, corrupting the spreadsheet
   Model answer

   Lossy compression permanently removes data, so some values would be missing or wrong, corrupting the spreadsheet.

3. • It records each run as a count and the character
   • Giving 8A 4B
   Model answer

   It replaces each run of the same character with a count and the character, so AAAAAAAABBBB becomes 8A 4B.

4. • Advantage: much smaller files
   • Disadvantage: quality is lost permanently, and the original cannot be restored
   Model answer

   Advantage: files become much smaller, so they load and stream faster. Disadvantage: some quality is lost permanently, and the original cannot be restored.

Round 3: Big Think

1. • Film: viewers will not notice the removed detail
   • Film: a much smaller file streams faster and uses less data
   • Contract: every word matters, so losing data could change the meaning
   • Contract: lossless restores the original perfectly
   Model answer

   The film should use lossy compression. The data it removes is detail viewers will not notice on a phone, and the much smaller file streams faster and uses less data. The legal contract must use lossless compression, because every word matters: losing data could change the meaning. Lossless lets the original be restored perfectly.

2. • Lossy permanently removes data
   • Lossy: the original cannot be recovered
   • Lossy gives a much bigger reduction in size
   • Lossy reduces the quality
   • Lossless removes no data, so the original is restored perfectly
   • Lossless gives a smaller reduction in size
   • Gives examples, such as JPEG and MP3, or ZIP and PNG
   • Lossless works by recording repetition more efficiently
   Model answer

   Lossy compression permanently removes data that people are unlikely to notice, so the original cannot be recovered. That gives a much smaller file, but the quality is reduced. It is used for JPEG photos, MP3 music and streaming video. Lossless compression removes no data: it records repeated patterns more efficiently, so the original is restored perfectly. It gives a smaller reduction in size, so files stay bigger, but it is essential for program files, documents and ZIP archives, where every byte matters.

This or That

1. JPEG JPEG throws away detail. PNG is lossless.
2. Lossy Lossy removes data, so it can make files far smaller.
3. It stays lost Lossy is irreversible: saving as PNG only stops any further loss.
4. Lossless Every byte of a program matters, so nothing can be removed.
5. 4A 3B 2C Four As, three Bs and two Cs.
6. There is less data to send Smaller files travel faster and use less bandwidth.
7. Repetition it can record compactly Lossless describes repeated data more efficiently. Lossy hunts for data people will not notice.
8. Small size and fast loading Visitors will not notice small losses, but they will notice a slow page, so lossy suits it.

Memory Match

• A 4 Lossy: Permanently removes some data
• B 3 Lossless: Original restored perfectly
• C 5 JPEG: A lossy image format
• D 6 PNG: A lossless image format
• E 2 Bandwidth: Data a connection carries per second
• F 1 Compression: Reducing the size of a file

Sort It

1. Lossy Permanently removes data people will not notice That is exactly what lossy compression does.
2. Lossy JPEG photos JPEG removes colour detail the eye barely notices.
3. Lossy Saving again and again makes it worse Each lossy save removes a little more detail.
4. Lossy Streaming video Small files matter far more than tiny details when streaming.
5. Lossless Records repetition, such as 8A 4B 8C Run-length encoding is a lossless method.
6. Lossy Gives the biggest reduction in size Throwing data away shrinks files the most.
7. Lossless FLAC audio FLAC shrinks music without losing any of it.
8. Lossless ZIP archives A ZIP must give back every file exactly.
9. Lossless PNG images PNG keeps every pixel exactly.
10. Lossless The original can be restored perfectly No data is removed, so nothing is lost.
11. Lossy MP3 music MP3 removes sounds most people cannot hear.
12. Lossless Must be used for program files Losing any part of a program would corrupt it.