← IGCSE Computer Science Paper 1

Choosing settings: quality versus file size

Balancing quality against file size: pick the lowest sample rate, resolution or colour depth that still looks or sounds good enough, so the file stays small enough to store or send.

Part of: IGCSE Computer Science 0478 — 1.2 Text, Sound and Images — Module 22, ACARA Digital Technologies Years 7–8 — Representing Text, Images and Sound — Module 57

Understanding Choosing settings: quality versus file size in IGCSE Computer Science Paper 1

What it does: A thumbnail is viewed small on screen, so few pixels and fewer colours keep the file small without a visible loss in quality. Speech does not need high fidelity, so a lower sample rate keeps the file small and quick to send while the voice is still clear. Music has many frequencies and needs detail, so higher quality settings are worth the larger file size. A large print shows every pixel, so low resolution looks blocky. Here quality matters more than saving space. Good exam answers state the setting, explain its effect on file size, and link it to the scenario.

Common mistakes: A single = assigns a value. To compare use with the text you need ==, so the line should be if use == "voice message":. An if statement must end with a colon. The line should be if use == "music": so the indented line belongs to it.

Class: _____________________ · Name: _____________________ · Date: _________

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Learning

Duo

A student records a voice message to send on a chat app. Which setting is the better choice?

A very high sample rate, because voice messages must be studio qualityA low sample rate, because speech stays clear and the file stays small

Matches

Answer: Use the highest settings for every file because quality is all that matters.

↓

This ignores the trade-off: higher settings give bigger files that use more storage and take longer to send, so the choice should fit the scenario.

Applying

Meanings

Term

trade-off

Meaning

Balancing quality against file size: pick the lowest sample rate, resolution or colour depth that still looks or sounds good enough, so the file stays small enough to store or send.

Practice

IF purpose = "voice message" THEN

Testing

Gaps

sampleRate ←

Check Answer

Spots

1use = "voice message"

2if use = "voice message":

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Quick Questions

1. A student records a voice message to send on a chat app. Which setting is the better choice?

A. A very high sample rate, because voice messages must be studio quality

B. A low sample rate, because speech stays clear and the file stays small ✓

Speech does not need high fidelity, so a lower sample rate keeps the file small and quick to send while the voice is still clear.

2. A band wants to release a song for streaming. Which choice fits best?

A. A high sample rate and sample resolution, because listeners expect accurate, detailed sound ✓

B. The lowest sample rate possible, because a small file is always the top priority

Music has many frequencies and needs detail, so higher quality settings are worth the larger file size.

3. A web designer is making a small thumbnail for a web page. Which image settings suit it?

A. Very high resolution and a large colour depth, so it matches a print photo

B. Low resolution and a small colour depth, so the page loads quickly ✓

A thumbnail is shown small on screen, so extra pixels and colours are not noticed but still make the file larger and slower to load.

4. A photographer wants a poster-sized print of a holiday photo. Which is the better choice?

A. A high resolution and a high colour depth, because the image is enlarged and detail matters ✓

B. A low resolution to save storage, because print size does not affect the pixels needed

A large print shows every pixel, so low resolution looks blocky. Here quality matters more than saving space.

5. Which statement describes the trade-off when choosing media settings?

A. Higher quality settings give a larger file, so you pick the lowest setting that is good enough ✓

B. Higher quality settings give a smaller file, so you should always pick the highest setting

More samples, pixels or bits per sample means more data to store. The trade-off is quality against file size.

Match the Pairs

sample_rate = 8000 → A low sample rate that is good enough for a voice message and keeps the file small

sample_rate = 44100 → A high sample rate that suits music because it captures more detail, but makes the file bigger

A small web thumbnail only needs a low image resolution and a small colour depth to load fast → resolution = 150 x 100, colour_depth = 8 bits

A print photo needs a high image resolution and a large colour depth so it looks sharp and realistic → resolution = 4000 x 3000, colour_depth = 24 bits

Answer: Use the highest settings for every file because quality is all that matters. → This ignores the trade-off: higher settings give bigger files that use more storage and take longer to send, so the choice should fit the scenario.

Answer: Use a low sample rate for the music file because it makes the file smaller. → The answer gives the effect on size but does not justify it: a low rate would make music sound poor, so quality is lost and the scenario is not considered.

Key Term

trade-off

Balancing quality against file size: pick the lowest sample rate, resolution or colour depth that still looks or sounds good enough, so the file stays small enough to store or send.

Fill in the Blanks

1. IF clip = "voice" THEN sampleRate ← LOW ENDIF

Hint: Type the setting level that is good enough for speech and keeps the file small.

2. IF use = "print" THEN imageResolution ← HIGH ENDIF

Hint: Type the setting level needed so a printed photo stays sharp, even though the file is larger.

3. IF fileSize > spaceAvailable THEN sampleRate ← LOW ENDIF

Hint: Type the comparison operator that checks whether the file is bigger than the storage space.

4. IF type = "music" THEN sampleRate ← HIGH ELSE sampleRate ← LOW

Hint: Type the keyword that starts the alternative branch for every other type of sound.

5. fileSize ← rate * resolution * seconds

Hint: Type the variable for the number of bits stored per sample. Reducing it shrinks the file.

Spot the Error

Question 1

A use = "voice message"

B if use = "voice message":

C rate = 8000

D else:

E rate = 44100

Line B — A single = assigns a value. To compare use with the text you need ==, so the line should be if use == "voice message":.

Question 2

A use = "music"

B if use == "music"

C rate = 44100

Line B — An if statement must end with a colon. The line should be if use == "music": so the indented line belongs to it.

Question 3

A use = "web thumbnail"

B if use == "web thumbnail":

C depth == 8

D else:

E depth = 24

Line C — == compares values and does not store anything. To set a small colour depth for the thumbnail you need the assignment depth = 8.

Question 4

A depth = 8

B colours = 2 * depth

C print(colours)

Line B — The number of colours is 2 to the power of the colour depth, so it needs ** and not *. 8 bits gives 256 colours, not 16.

Question 5

A define count_colours(depth):

B return 2 ** depth

C print(count_colours(8))

Line A — A function is created with the keyword def, not define. The line should be def count_colours(depth):.

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