Year11 - Compression Plenary Quiz

Quick recap of why we use compression, plus lossy and lossless methods.

1. Why is compression used?

To increase file quality
To reduce file size and speed up transfer
To make all files executable

Compression reduces the number of bits in a file, making it smaller and often quicker to transfer.

2. What is true of lossy compression?

Some data is permanently lost
The original file is always perfectly restored
It never changes quality

Lossy compression removes some data permanently, often reducing quality.

3. Which file type is usually suitable for lossy compression?

Executable program file
Text document
Photo/image file

Images, sound and video are common lossy targets when some quality loss is acceptable.

4. What is true of lossless compression?

It always gives the smallest possible file
No data is lost; the original can be restored
It only works on images

Lossless compression stores data differently, but keeps all data so the exact original can be recovered.

5. Which should use lossless compression?

A Python script file
A music stream preview
A social media photo

Text and executable files must not lose data, so they should use lossless compression.

6. In lossy image compression, reducing the number of colours usually...

increases quality
has no effect
reduces file size but can reduce quality

Fewer colours can reduce size, but detail/quality can drop.

7. Why are smaller files helpful online?

They use more bandwidth
They transfer or stream faster
They cannot be edited

Less data generally means quicker transfer/streaming.

8. Which statement is correct?

Lossy often compresses more, lossless preserves all data
Lossless is only for photos
Lossy and lossless always produce the same size

This captures the key trade-off from the lesson: size reduction versus data preservation.

One Thing I Learned

Write one rule you will remember about choosing lossy vs lossless compression.