Compression exam questions

15 OCR Creative iMedia R093 (J834) exam-style questions on Compression (R093 Media industry - Distribution considerations), 21 marks in all. Answer them on paper or print them, then open the mark schemes and example answers to see how each is marked.

Name
Class
Suggested time	30 minutes

1Multiple choice1 mark

Cobalt Casting is preparing a video for its website.

Which is true of lossy compression?

[1 mark]

AFile size is significantly reduced
BNo data is removed
CQuality is always kept
DText is unchanged after decompression

Mark scheme

Answer: (A) File size is significantly reduced (1)

Guidance

Correct answer only

Example answers and how they were marked

Full marks1/1

A File size is significantly reduced

Why: Correct option (1).

No marks0/1

B No data is removed

Why: Describes lossless compression, so it is not true of lossy compression.

No marks0/1

C Quality is always kept

Why: Lossy compression removes data and can reduce quality, so this is a misconception.

2Multiple choice1 mark

Kestrel Analytics is archiving a set of text documents.

Which is a reason for using lossless compression?

[1 mark]

AData must be exactly the same after decompression
BFile size is significantly reduced by removing data
CQuality can be reduced to save space
DVisible artefacts are acceptable

Mark scheme

Answer: (A) Data must be exactly the same after decompression (1)

Guidance

Correct answer only

Example answers and how they were marked

Full marks1/1

A Data must be exactly the same after decompression

Why: Correct option (1).

No marks0/1

B File size is significantly reduced by removing data

Why: This is a reason for lossy compression, not lossless compression.

No marks0/1

C Quality can be reduced to save space

Why: Lossless compression does not reduce quality, so this is a misconception.

3Multiple choice1 mark

Silverbrook Museum is reducing the size of an audio guide.

Which best describes lossy compression?

[1 mark]

AData is removed to reduce file size
BData is stored without any change
CFile size is increased to improve quality
DNo quality is lost after decompression

Mark scheme

Answer: (A) Data is removed to reduce file size (1)

Guidance

Correct answer only

Example answers and how they were marked

Full marks1/1

A Data is removed to reduce file size

Why: Correct option (1).

No marks0/1

B Data is stored without any change

Why: This describes lossless compression, not lossy compression.

No marks0/1

C File size is increased to improve quality

Why: Compression reduces file size rather than increasing it, so this is a misconception.

4Multiple choice1 mark

Elmwood Festival is compressing a high-quality photograph for its programme.

Which best describes lossless compression?

[1 mark]

AAll original data is kept when the file size is reduced
BData is removed to make the file smaller
CQuality is lost when the file is opened
DThe file cannot be decompressed

Mark scheme

Answer: (A) All original data is kept when the file size is reduced (1)

Guidance

Correct answer only

Example answers and how they were marked

Full marks1/1

A All original data is kept when the file size is reduced

Why: Correct option (1).

No marks0/1

B Data is removed to make the file smaller

Why: This describes lossy compression, not lossless compression.

No marks0/1

C Quality is lost when the file is opened

Why: Lossless compression keeps all data, so quality is not lost; this is a misconception.

5Identify1 mark

Nettleford Sound Archive stores high-quality recordings of local musicians. The recordings must keep all of their original data.

Which type of compression should the archive use?

Answer:

[1 mark]

Mark scheme

Correct answer only

Indicative content

Lossless compression/Lossless (1)

Guidance

Accept equivalent terminology

Do not accept:

Compression on its own - TV

Lossy compression

Example answers and how they were marked

Full marks1/1

Lossless compression

Why: Correctly names the type of compression that keeps all the original data (1).

No marks0/1

Compression

Why: Names compression generally but not the type needed; mark scheme says compression on its own is too vague (0).

No marks0/1

Lossy compression

Why: Lossy compression removes some data, so it is the wrong type and is not credited (0).

6Identify1 mark

Havenline Theatre records its performances and uploads the video files to its website.

What is lossy compression?

[1 mark]

Mark scheme

One from e.g.

Indicative content

Removing/losing some of the original data/information to reduce the file size (1)
Some of the quality of the file is lost (1)
Award credit for any other appropriate response

Guidance

Accept equivalent terminology

Do not accept:

Reduces the file size - TV

Keeps all the original data - TV

Example answers and how they were marked

Full marks1/1

It reduces the file size by removing some of the original data, so the quality can be lower.

Why: Credit for saying some of the original data is removed to reduce the file size (1).

No marks0/1

It reduces the size of the file.

Why: Only describes compression generally, not the loss of data that makes it lossy, so no credit.

No marks0/1

It keeps all of the original information so there is no loss of quality.

Why: This describes lossless compression, not lossy compression, so no credit.

7Identify1 mark

What is lossless compression?

[1 mark]

Mark scheme

One from e.g.

Indicative content

No data/information is lost (1)
The file is exactly the same after it is uncompressed (1)
All of the original quality is kept (1)
Award credit for any other appropriate response

Guidance

Accept equivalent terminology

Do not accept:

Making the file smaller on its own - TV

It removes some of the original data (this describes lossy compression) - TV

Example answers and how they were marked

Full marks1/1

A type of compression that reduces the file size but does not lose any of the original data.

Why: Credit for saying no data/information is lost (1).

No marks0/1

It makes a file smaller.

Why: Only describes compression generally; the Do not accept line rules out making the file smaller on its own.

No marks0/1

It removes some of the original data so the file size goes down.

Why: This describes lossy compression; the Do not accept line rules it out.

8Complete the sentence1 mark

Complete the sentence. Write one word from the list in the space.

data
lossless
quality
size

Lossy compression makes a file smaller by taking out some of the original .

[1 mark]

Mark scheme

Correct answer only

Indicative content

Data (1)

Guidance

Spelling not important

Do not accept: Quality / Size

Example answers and how they were marked

Full marks1/1

data

Why: Data is the original information that lossy compression removes to reduce the file size (1).

No marks0/1

quality

Why: Near-miss: lossy compression can reduce quality, but it does so by taking out data; quality is not the original information taken out (0).

No marks0/1

size

Why: File size is what is made smaller, not what is taken out of the file (0).

9Complete the sentence1 mark

Complete the sentence. Write one word from the list in the space.

brightness
colour
contrast
quality

Lossy compression removes some of the original data from a file. As a result, the of the file is reduced.

[1 mark]

Mark scheme

Indicative content

Quality (1)

Guidance

Correct answer only

Accept: image quality / picture quality / file quality

Do not accept: Brightness / Colour / Contrast

Example answers and how they were marked

Full marks1/1

quality

Why: Quality is the correct answer: lossy compression removes original data, so the quality of the file is reduced (1).

No marks0/1

colour

Why: Near miss: colour is only one part of an image, not the overall quality of the file, so no mark is awarded.

No marks0/1

contrast

Why: Misconception: lossy compression affects the overall quality of the file, not just its contrast, so no mark is awarded.

10Identify2 marks

Nettlecombe Wildlife Trust records audio guides for its nature trails, which visitors download to their phones before setting out.

Identify two reasons why the Trust would compress the audio guide files before they are downloaded.

[2 marks]

Mark scheme

Two from e.g.

Indicative content

To reduce the file size (1)
So the files download/transfer faster (1)
To take up less storage space (1)
To reduce the amount of data sent over the internet (1)
So the guides load/play more quickly on a phone (1)
Award credit for any other appropriate response

Guidance

Accept equivalent terminology

Credit each separate reason given, even if both are written in the same sentence

Do not accept:

Improve the sound quality - TV

Example answers and how they were marked

Full marks2/2

To reduce the file size so the audio guides download faster.

Why: Two separate reasons in one sentence, both credited: reducing the file size (1) and faster download (1).

Some marks1/2

So the files take up less space on the phone.

Why: Credit for taking up less storage space (1). No second reason given.

No marks0/2

So the sound quality of the guides is better.

Why: Compression does not improve sound quality; this is a misconception and is on the Do not accept line, so no mark.

11Complete the sentence2 marks

Complete the sentences. Use a word from the list for each space. You can use each word only once or not at all.

all
large
no
small

Lossy compression is used because it gives a reduction in file size.

Lossless compression is used because original data is lost.

[2 marks]

Mark scheme

Indicative content

Space | Answer

1 | Large (1)

2 | No (1)

Guidance

Correct answers only

Spelling not important

Example answers and how they were marked

Full marks2/2

large, no

Why: Space 1 Large (1); space 2 No (1).

Some marks1/2

large, all

Why: Space 1 Large (1); space 2 'all' is not credited.

No marks0/2

small, all

Why: No marks: space 1 is not Large and space 2 is not No.

12Complete the sentence2 marks

Complete the sentences. Write a word from the list in each of the two spaces. You can use each word only once or not at all.

exactly
most
none
some

Lossless compression reduces the file size, but of the data is lost.

When the file is decompressed, it is the same as it was before compression.

[2 marks]

Mark scheme

Indicative content

Space | Answer

1 | None (1)

2 | Exactly (1)

Guidance

Correct answers only

Spelling not important

Example answers and how they were marked

Full marks2/2

none, exactly

Why: Space 1 None (1) and space 2 Exactly (1).

Some marks1/2

some, exactly

Why: Space 2 credited because the decompressed file is exactly the same as before (1); space 1 is wrong because some data being lost describes lossy compression.

No marks0/2

some, most

Why: Both spaces show the misconception that lossless compression loses some of the data, so the file is only mostly the same afterwards.

13Explain or Describe2 marks

Wexcombe Heritage is an organisation that makes podcasts about local history. Each episode is recorded in its studio and then published online for listeners.

Explain one reason why Wexcombe Heritage would use lossy compression for an episode before it is made available online.

[2 marks]

Mark scheme

Read whole response and award

One mark for a reason for using lossy compression

AND/OR

One mark for explaining the effect of using lossy compression

e.g.

Indicative content

Significantly reduces file size
Removes some data
Faster download/streaming
Takes up less storage space
Quicker to upload/send
Uses less bandwidth/data
Loss of quality is acceptable for audio/podcasts
Award credit for any other appropriate response

Example responses

It significantly reduces the file size (1) so the episode downloads/streams more quickly for listeners (1)
It removes some of the original data (1) which makes the file much smaller than lossless compression (1)
It takes up less storage space (1) so Wexcombe can keep more episodes available on its website (1)
The small loss of quality is acceptable for a podcast (1) so the file can be compressed heavily to save space (1)
Award credit for any other appropriate response

Guidance

Do not accept

'It makes it smaller' / 'It makes it better quality' (TV)
'It keeps all of the original data' / 'No quality is lost' (this is lossless compression)

Example answers and how they were marked

Full marks2/2

It significantly reduces the file size so the episode downloads/streams more quickly for listeners.

Why: Reason (1) and effect (1): lossy compression gives a much smaller file, which leads to faster download/streaming.

Some marks1/2

It takes up less storage space.

Why: A reason for using lossy compression (1), but no explanation of the effect.

No marks0/2

It keeps all of the original data so the sound quality stays exactly the same.

Why: This describes lossless compression, not lossy compression, so no creditworthy reason or effect is given.

14Explain or Describe2 marks

Gorseway Ceramics is a pottery studio that sells its work through a website. The website shows photographs of each pot.

Explain what is meant by lossy compression.

[2 marks]

Mark scheme

Read whole response and award

One mark for saying that data/information is removed/thrown away from the file

AND/OR

One mark for the effect of this, e.g. the file size is reduced / the quality is lowered / the removed data cannot be restored

Up to two marks for an explanation of lossy compression e.g.

Indicative content

Reduces file size
Removes/throws away some data
Some quality is lost
Cannot get back the original data/quality
More data removed at higher compression
Award credit for any other appropriate response

Example responses

Some of the data is removed from the file (1) so the quality of the photograph is lowered (1)
Data is thrown away (1) so the file size is reduced (1)
It removes data that is less noticeable (1) so the file takes up less storage space (1)
Some of the data is removed (1) and it cannot be restored afterwards (1)
Award credit for any other appropriate response

Guidance

Accept equivalent terminology

Do not accept

It makes the file smaller - TV

Do not accept

It reduces the file size without losing any data/quality - this describes lossless compression

Example answers and how they were marked

Full marks2/2

Some of the data is removed from the file so the quality of the photograph is lowered.

Why: Data removed (1) and effect on quality (1).

Some marks1/2

Some of the data is removed from the photograph.

Why: Correctly says data is removed (1), but does not give an effect such as quality lowered or file size reduced.

No marks0/2

The file is made smaller without losing any of the data.

Why: Says no data is lost, which describes lossless compression, and 'made smaller' is too vague, so no credit is given.

15Explain or Describe2 marks

Woolmer House Press is a small publisher that is creating an online archive called The Woolmer Letters. Researchers will read scanned copies of the letters on the company's website, and some of the handwriting is small and needs to be clear.

Explain why lossless compression is suitable for the scanned letters in The Woolmer Letters.

[2 marks]

Mark scheme

Read whole response and award

One mark for a reason why lossless compression is suitable

AND/OR

One mark for reasoning/effect

Up to two marks for explaining why lossless compression is suitable e.g.

Indicative content

No data is removed
Quality is not lost/exact copy is kept
The handwriting stays clear/readable
Text remains accurate
Original scan can be restored exactly
File size is reduced
Award credit for any other appropriate response

Example responses

No data is removed from the scan (1) so the handwriting stays clear enough to read (1)
The quality of the scan is not lowered (1) so researchers can read the smallest letters (1)
The original scan can be restored exactly (1) so researchers can trust it is the same as the letter (1)
It keeps all of the detail in the image (1) so no detail from the original letter is lost (1)
It makes the scans take up less space (1) without losing any of the handwriting detail (1)
Award credit for any other appropriate response

Guidance

Do not accept

It removes some of the data - this is lossy compression

Example answers and how they were marked

Full marks2/2

No data is removed from the scan so the handwriting stays clear enough to read.

Why: Reason why lossless compression is suitable (1) and linked effect for the letters (1).

Some marks1/2

It keeps all of the data in the file.

Why: Correct reason about lossless compression (1), but no linked effect explaining why this matters for the scanned letters.

No marks0/2

It removes some of the image data so the letters take up less space.

Why: This describes lossy compression, not lossless compression, so no credit is given.

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