← Years 9–10 Data & Information

Choosing a compression format for a task

Pick lossless (PNG, ZIP, FLAC) when every detail must be kept. Pick lossy (JPEG, MP3, MP4) when a smaller file matters more than perfect quality.

Part of: 9-10 Digital Technologies: Data compression — Module 17, IGCSE Computer Science 0478 — 1.3 Data Storage and Compression — Module 47, ACARA Digital Technologies Years 9–10 — Data Compression — Module 39

Understanding Choosing a compression format for a task in Years 9–10 Data & Information

What it does: A logo has flat colours and sharp edges, and every detail matters, so a lossless format like PNG is the best choice. Photos have lots of colour detail, and JPEG shrinks them a lot while looking fine to the eye. A PNG photo is usually much bigger. MP3 makes much smaller files, so it uses less data. Most people can't hear the difference on phone speakers or earbuds. Lossy compression permanently discards data. You can't get the original back from the smaller file. Documents must be recovered exactly. ZIP is lossless, so unzipping gives back identical files. MP4 is for video.

Common mistakes: A logo has sharp edges and flat colours that lossy JPEG would blur. It should use a lossless format, so the line should be format = "PNG". Streaming music works best with a small file, so a lossy format is the right pick. FLAC is lossless and gives bigger files. The line should be format = "MP3".

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This module's key terms are also in a printable crossword (Modules 17–51) and word search (Modules 6–132).

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Learning
Duo
You need to save a school logo with sharp edges and flat colours so it stays crisp. Which format fits best?
JPEG (lossy)PNG (lossless)
Matches
Send 20 holiday photos by email: save each as a huge lossless PNG
↓
Photos have lots of tiny colour changes, so lossless PNG files are very large. JPEG (lossy) makes them much smaller with little visible change.
Applying
Meanings
Term
Lossless vs lossy choice
Meaning
Pick lossless (PNG, ZIP, FLAC) when every detail must be kept. Pick lossy (JPEG, MP3, MP4) when a smaller file matters more than perfect quality.
Practice
logo for website -> PNG (lossless)
Testing
Gaps
use
Check Answer
Spots
2sharp_edges = true
3format = "JPEG"

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Quick Questions

1. You need to save a school logo with sharp edges and flat colours so it stays crisp. Which format fits best?
A. PNG (lossless) ✓
B. JPEG (lossy)
PNG is lossless, so sharp edges and flat colours stay perfect. JPEG can leave blurry fuzz around edges.
2. You are posting a holiday photo to a website and want a small file that loads fast. Which format fits best?
A. PNG (lossless)
B. JPEG (lossy) ✓
Photos have lots of colour detail, and JPEG shrinks them a lot while looking fine to the eye. A PNG photo is usually much bigger.
3. A band wants to keep a perfect studio master copy of their song. Which format fits best?
A. MP3 (lossy)
B. FLAC (lossless) ✓
A master copy must keep every detail. FLAC is lossless, while MP3 permanently throws away some sound data.
4. You are streaming music on a phone with limited mobile data. Which format fits best?
A. MP3 (lossy) ✓
B. FLAC (lossless)
MP3 makes much smaller files, so it uses less data. Most people can't hear the difference on phone speakers or earbuds.
5. True or false: Once a file is saved as a lossy format like JPEG, the removed detail can be fully restored.
A. False ✓
B. True
Lossy compression permanently discards data. You can't get the original back from the smaller file.

Match the Pairs

PNG → A lossless image format that keeps every pixel, so it suits logos, diagrams and screenshots with sharp edges
MP3 → A lossy audio format that throws away sounds most people can't hear to make music files much smaller
A designer must keep a school logo perfectly sharp with no quality lost, even after many edits → Save as PNG (lossless)
A streaming app needs video that loads fast on slow mobile data, and tiny quality loss is acceptable → Use MP4 (lossy)
Send 20 holiday photos by email: save each as a huge lossless PNG → Photos have lots of tiny colour changes, so lossless PNG files are very large. JPEG (lossy) makes them much smaller with little visible change.
Back up a ZIP of your assignment files using a lossy format → A lossy format permanently throws data away, so the files could be damaged or changed. Documents need lossless compression like ZIP to keep every detail.

Key Term

Lossless vs lossy choice
Pick lossless (PNG, ZIP, FLAC) when every detail must be kept. Pick lossy (JPEG, MP3, MP4) when a smaller file matters more than perfect quality.

Fill in the Blanks

1. IF image is a logo THEN use PNG ENDIF
Hint: Type the lossless image format that keeps logos sharp
2. IF photo for website THEN use JPEG ENDIF
Hint: Type the lossy image format that makes photos small
3. IF every detail must be kept THEN use lossless compression ENDIF
Hint: Type the kind of compression that loses no data
4. purpose ← "stream a video" format ← MP4
Hint: Type the lossy video format used for streaming
5. IF purpose = "archive music" THEN format ← FLAC ENDIF
Hint: Type the lossless audio format that keeps every detail

Spot the Error

Question 1
A task = "website logo"
B sharp_edges = true
C format = "JPEG"
Line C — A logo has sharp edges and flat colours that lossy JPEG would blur. It should use a lossless format, so the line should be format = "PNG".
Question 2
A task = "stream a song"
B format = "FLAC"
C reason = "smaller file"
Line B — Streaming music works best with a small file, so a lossy format is the right pick. FLAC is lossless and gives bigger files. The line should be format = "MP3".
Question 3
A task = "backup tax documents"
B needs_every_byte = true
C format = "MP3"
Line C — Documents must come back exactly as they were, so they need lossless compression. MP3 is a lossy audio format. The line should be format = "ZIP".
Question 4
A task = "email a holiday photo"
B format = "PNG"
C reason = "small file is key"
Line B — For a photo where a small file matters most, lossy JPEG is the better choice. PNG is lossless and makes photo files much bigger. The line should be format = "JPEG".
Question 5
A if quality_must_be_perfect:
B use = "lossless"
C else:
D use = "lossless"
Line D — The else branch runs when perfect quality is not needed. In that case a smaller file matters more, so the choice is lossy. The line should be use = "lossy".

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