← ACARA Digital Technologies Years 9–10

Common compressed file formats and what they are used for

A file type that stores data compressed: ZIP, PNG, FLAC are lossless; JPEG, MP3, MP4 are lossy. Each suits its content, such as photos, logos, music, video or documents.

Part of: ACARA Digital Technologies Years 9–10 — Data Compression — Module 37

Understanding Common compressed file formats and what they are used for in ACARA Digital Technologies Years 9–10

What it does: PNG is lossless, so the sharp edges and flat colours of logos and screenshots stay clean with no blurry artefacts. MP3 is a lossy audio format that removes sounds we are least likely to hear, making songs small enough to store in large numbers. JPEG uses lossy compression, which suits photos. Small changes in colour are hard to notice, so the file gets much smaller. ZIP is for bundling files such as documents. PNG compresses without losing any data. The original image can be rebuilt exactly. Documents must be restored exactly. Losing even one character could change the meaning, so lossless compression is needed.

Common mistakes: JPEG is a lossy format because it permanently throws away some detail to make photos smaller. Line 4 should print "Lossy". A function definition must end with a colon. Line 1 should be def best_for_logo():.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

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This module's key terms are also in a printable crossword (Modules 226–254) and word search (Modules 226–329).

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Learning
Duo
Which format is the better choice for a holiday photo you want to share online with a small file size?
JPEGZIP
Matches
Save the school logo as JPEG because JPEG is lossless
↓
JPEG is lossy, not lossless. It can blur the sharp edges of a logo, so PNG is the better choice.
Applying
Meanings
Term
Compressed file format
Meaning
A file type that stores data compressed: ZIP, PNG, FLAC are lossless; JPEG, MP3, MP4 are lossy. Each suits its content, such as photos, logos, music, video or documents.
Practice
Photo -> JPEG (lossy)
Testing
Gaps
photoFormat = ""
Check Answer
Spots
3 print("Photo format")
4 print("Lossless")

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Quick Questions

1. Which format is the better choice for a holiday photo you want to share online with a small file size?
A. ZIP
B. JPEG ✓
JPEG uses lossy compression, which suits photos. Small changes in colour are hard to notice, so the file gets much smaller. ZIP is for bundling files such as documents.
2. Which format suits a school logo with sharp edges and flat colours?
A. PNG ✓
B. JPEG
PNG is lossless, so the edges stay crisp. JPEG can blur sharp edges and leave fuzzy marks around text and lines.
3. Which statement is true?
A. PNG is lossless, so no image data is lost ✓
B. PNG is lossy, so some image data is lost
PNG compresses without losing any data. The original image can be rebuilt exactly.
4. You want to save a screenshot of an error message with readable text. Which format should you pick?
A. PNG ✓
B. MP3
PNG keeps screenshots sharp and the text readable. MP3 is an audio format and can't store images.
5. Which file type is a lossy format for music?
A. ZIP
B. MP3 ✓
MP3 removes sounds that are hard to hear to make music files smaller. ZIP is lossless and is used to bundle and shrink files.

Match the Pairs

photo.jpg → A JPEG photo: lossy compression gives a much smaller file by dropping detail the eye barely notices
report.zip → A ZIP archive: lossless compression that shrinks documents and can be unzipped to the exact original
A logo or screenshot with sharp edges and flat colours should be saved in a lossless format so it stays crisp → school_logo.png
Music for a phone is often saved in a lossy format so the song takes up far less storage → song.mp3
Save the school logo as JPEG because JPEG is lossless → JPEG is lossy, not lossless. It can blur the sharp edges of a logo, so PNG is the better choice.
movie.mp4 can be restored exactly to the original video → MP4 video is lossy, so the discarded data cannot be restored. Only lossless formats like ZIP or FLAC restore the original.

Key Term

Compressed file format
A file type that stores data compressed: ZIP, PNG, FLAC are lossless; JPEG, MP3, MP4 are lossy. Each suits its content, such as photos, logos, music, video or documents.

Fill in the Blanks

1. photoFormat = "JPEG" compression = "lossy"
Hint: Type the name of the lossy image format commonly used for photos, where small colour changes are hard to notice.
2. logoFormat = "PNG" compression = "lossless"
Hint: Type the name of the lossless image format used for logos and screenshots that need sharp edges.
3. musicFormat = "MP3" compression = "lossy"
Hint: Type the name of the common lossy audio format used for music files.
4. videoFormat = "MP4" compression = "lossy"
Hint: Type the kind of compression that permanently discards some data so video is small enough to stream.
5. documentFormat = "ZIP" compression = "lossless"
Hint: Type the name of the lossless format used to bundle and shrink documents so they can be restored exactly.

Spot the Error

Question 1
A file = "beach.jpg"
B if file.endswith(".jpg"):
C print("Photo format")
D print("Lossless")
Line D — JPEG is a lossy format because it permanently throws away some detail to make photos smaller. Line 4 should print "Lossy".
Question 2
A def best_for_logo()
B fmt = "PNG"
C print(fmt, "is lossless")
D best_for_logo()
Line A — A function definition must end with a colon. Line 1 should be def best_for_logo():
Question 3
A music = song.mp3
B lossy = True
C if lossy:
D print("Smaller file")
Line A — The file name is text, so it needs quotes. Without them Python treats song.mp3 as a variable. It should be music = "song.mp3".
Question 4
A docs = "essay.docx"
B method = "lossy"
C archive = "ZIP"
D print(archive, method)
Line B — ZIP is used for documents because it is lossless and every character must come back exactly. Line 2 should be method = "lossless".
Question 5
A video = "clip.mp4"
B lossy = True
C print("MP4 is lossless")
D print("Good for video")
Line C — MP4 video uses lossy compression to get small files that can be streamed. Line 3 should say MP4 is lossy.

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