Lossy compression permanently removes data

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Date:

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Quick Questions

Shade in the A or B circle for each question.

1. A student compresses a photo using lossy compression. Can the original quality be restored from the compressed file?

A No, the removed data is gone for good

B Yes, the removed data is stored and can be put back

2. A JPEG photo has been compressed and looks blurry. The student opens it and saves it as a new file at the highest quality setting. What happens to the detail?

A The lost detail is restored

B The lost detail does not come back

3. Which is the best way to protect your photos before applying lossy compression?

A Keep a copy of the original file

B Delete the original to save space straight away

4. A song is compressed to MP3 three times in a row, each time with lossy compression. What happens to the sound quality?

A It stays the same after the first compression

B It gets lower each time it is compressed

5. Which statement about lossy compression is TRUE?

A Data removed is permanently lost

B Data removed can be rebuilt when the file is opened

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1permanent loss		AThe original cannot be rebuilt from the lossy copy because data was permanently removed. You should keep the original file.
2keep the original file		Bphoto.jpg (compressed) -> save as photo_new.png -> detail still missing
3Saving a lossy file again does not bring back the detail that was removed		Cphoto.jpg -> compress -> compress -> compress = lower quality each time
4Compressing a file with lossy compression again lowers the quality further		DSaving at a higher quality setting does not restore removed data. The lost detail is gone for good and only the original file has it.
5Open the lossy file, save it at high quality, and the lost detail returns		EStore an uncompressed copy so the full quality can be used again later
6Delete the original file after compressing it because it can be rebuilt from the lossy copy		FData removed by lossy compression is gone for good and cannot be restored

Definitions

permanent loss

Fill in the Blanks

Complete each line of code by filling in the missing parts.

Lossy compression removes data ___________

Saving again will not restore ______

Always ____ the original file

Compressing again ______ quality further

original ← "photo.bmp" backup ← ________ small ← LOSSY(backup)

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A DELETE "song.wav"

B copy ← LossyCompress(original)

C SAVE copy AS "song.mp3"

Question 2

A quality ← 100

B FOR i ← 1 TO 3

C ReSaveJPEG(photo)

D quality ← quality + 10

E NEXT i

Question 3

A photo ← LoadImage("a.jpg")

B detail_restored ← TRUE

C SAVE photo AS "a.png"

Question 4

A song ← LoadSound("track.wav")

B mp3 ← LossyCompress(song)

C original_data_lost ← FALSE

D OUTPUT original_data_lost

Question 5

A photo ← LoadImage("pic.png")

B COPY photo TO small

C LossyCompress(photo)

D SAVE small AS "small.jpg"

Answer Key

Lossy compression permanently removes data

Section A: Quick Questions

A — No, the removed data is gone for good

B — The lost detail does not come back

A — Keep a copy of the original file

B — It gets lower each time it is compressed

A — Data removed is permanently lost

Section B: Match the Pairs

permanent loss → Data removed by lossy compression is gone for good and cannot be restored

keep the original file → Store an uncompressed copy so the full quality can be used again later

Saving a lossy file again does not bring back the detail that was removed → photo.jpg (compressed) -> save as photo_new.png -> detail still missing

Compressing a file with lossy compression again lowers the quality further → photo.jpg -> compress -> compress -> compress = lower quality each time

Open the lossy file, save it at high quality, and the lost detail returns → Saving at a higher quality setting does not restore removed data. The lost detail is gone for good and only the original file has it.

Delete the original file after compressing it because it can be rebuilt from the lossy copy → The original cannot be rebuilt from the lossy copy because data was permanently removed. You should keep the original file.

Section C: Definitions

permanent loss — Data removed by lossy compression is gone for good, so the original quality cannot be restored. Keep the original file, as re-saving or compressing again only lowers quality further.

Section D: Fill in the Blanks

Lossy compression removes data permanently

Saving again will not restore detail

Always keep the original file

Compressing again lowers quality further

original ← "photo.bmp"
backup ← original
small ← LOSSY(backup)

Section E: Spot the Error

A — Lossy compression permanently removes data, so the original file must be kept. Deleting song.wav leaves only the lossy copy, which cannot be restored to full quality. The line should save the original: SAVE original AS "song.wav".

D — Each lossy re-save removes more data, so quality goes down, not up. The line should be quality ← quality - 10.

B — Saving a lossy JPEG in another format does not bring back the detail that was already removed. It is gone for good, so detail_restored must be FALSE.

C — Lossy compression removes data permanently, so the original data is lost. The line should set original_data_lost to TRUE.

C — This compresses the original, which permanently removes its data. Compress the copy so the original is kept: LossyCompress(small).