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Year 10
AQA

Lossy and lossless compression

I can compare lossy and lossless data compression.

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New
New
Year 10
AQA

Lossy and lossless compression

I can compare lossy and lossless data compression.

Download all resources
Share activities with pupils

These resources will be removed by end of Summer Term 2025.

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These resources were created for remote use during the pandemic and are not designed for classroom teaching.

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Lesson details

Key learning points

  1. Data compression is either lossy and lossless.
  2. Lossy data compression permanently removes some data to reduce file size.
  3. Lossless compression reduces file size without losing any data.

Keywords

  • Lossy - a compression method where data is permanently lost during the process

  • Lossless - a compression method where no data is permanently lost during the process

  • Quality - how good, reliable or suitable something is for its intended purpose

Common misconception

Lossy compression always results in a poor quality file that is not as usable as the original version.

Lossy compression removes data that is considered unnecessary or less noticeable, which may not impact the perceived quality of the file, especially to the human eye or ear.


To help you plan your year 10 computer science lesson on: Lossy and lossless compression, download all teaching resources for free and adapt to suit your pupils' needs...

Encourage discussion around "Would you notice the difference?" to deepen understanding of the advantages and disadvantages of lossy and lossless compression.
Teacher tip

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Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Prior knowledge starter quiz

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5 Questions

Q1.
What is the purpose of compression?
to increase file sizes
to create new file formats
Correct answer: to reduce file sizes
to delete files
Q2.
Which of the following is commonly compressed?
Correct answer: images
web browsers
passwords
operating systems
Q3.
What does bandwidth measure?
the speed of a computer
the size of a file
the type of compression used
Correct answer: the maximum amount of data that can be transferred
Q4.
What is latency?
Correct answer: the time delay between a signal being sent and received
the speed of data transfer
the size of a file
the type of compression used
Q5.
What is one advantage of compressed files?
They take up more storage.
Correct answer: They load faster on websites.
They are harder to share.
They cannot be opened.

Assessment exit quiz

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6 Questions

Q1.
Put these image formats into size order (smallest to largest):
1 - JPEG
2 - PNG
3 - BMP
Q2.
Why might lossy compression be used instead of lossless compression?
to preserve all data
Correct answer: to significantly reduce file size
to improve file quality
to make files harder to share
Q3.
What is one advantage of lossless compression?
It reduces file size significantly.
It improves file quality.
It removes unnecessary data.
Correct answer: It preserves all the original data.
Q4.
Does lossy compression always result in a poor-quality file?
Yes, because data is permanently removed.
Yes, because it reduces the file size significantly.
Correct answer: No, it removes unnecessary data that may not affect perceived quality.
No, because it increases the file size.
Q5.
Match each file type with the type of compression it commonly uses.
Correct Answer:lossy,JPEG

JPEG

Correct Answer:lossless,PNG

PNG

Correct Answer:uncompressed,BMP

BMP

Q6.
Which compression method is reversible?
lossy
Correct answer: lossless
both
neither