Comparing lossy and lossless compression

Name:

Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. Which type of compression lets you restore the original file exactly?

A Lossy compression

B Lossless compression

2. Which type of compression usually gives the smaller file?

A Lossy compression

B Lossless compression

3. A student reduces an image's resolution to shrink the file. Which type of compression is this?

A Lossy, because pixels are removed for good

B Lossless, because the image can be restored

4. Run-length encoding (RLE) is an example of which type of compression?

A Lossless, because no data is lost

B Lossy, because the file gets shorter

5. Which statement about data is true?

A Lossless removes some data permanently; lossy keeps all of it

B Lossy removes some data permanently; lossless keeps all of it

Match the Pairs

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

Left column		Right column
1Lossy compression		AMakes the file smaller by permanently removing some data, so the original cannot be restored exactly
2Lossless compression		BShrinks the file but keeps all the data, so the original can be restored exactly
3A lossless method: repeated values are stored as a count and a value, and every pixel can be restored		CLossy compression usually gives smaller files because it throws data away. Lossless saves less space because it must keep everything.
4A lossy method: the image has fewer pixels, so the file is smaller but the lost detail cannot return		DResolution: 1920x1080 -> 960x540
5Lossy compression: all data is kept, so the original can be restored		ERLE: WWWWBB -> 4W2B
6Lossless compression always gives a smaller file than lossy compression		FThis describes lossless compression. Lossy compression permanently removes data, so the original cannot be restored exactly.

Definitions

lossy vs lossless

Fill in the Blanks

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

method ← "RLE" type ← "________"

method ← "reduce resolution" type ← "_____"

type ← "lossy" restorable ← _____

lossySize ← 2 losslessSize ← 5 OUTPUT lossySize _ losslessSize

original ← "AAAABB" encoded ← "_A2B" decoded ← "AAAABB"

Spot the Error

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

Question 1

A method = 'lossless'

B data_removed = True

C can_restore = False

Question 2

A method = 'lossless'

B data_removed = True

C can_restore = True

Question 3

A IF method = 'lossy' THEN

B OUTPUT 'data removed'

C OUTPUT 'can restore'

D ENDIF

Question 4

A data = 'AAAABBB'

B rle = '4A3B'

C type = 'lossy'

Question 5

A image = 'photo.bmp'

B type = 'lossless'

C method = 'lower resolution'

Answer Key

Comparing lossy and lossless compression

Section A: Quick Questions

B — Lossless compression

A — Lossy compression

A — Lossy, because pixels are removed for good

A — Lossless, because no data is lost

B — Lossy removes some data permanently; lossless keeps all of it

Section B: Match the Pairs

Lossy compression → Makes the file smaller by permanently removing some data, so the original cannot be restored exactly

Lossless compression → Shrinks the file but keeps all the data, so the original can be restored exactly

A lossless method: repeated values are stored as a count and a value, and every pixel can be restored → RLE: WWWWBB -> 4W2B

A lossy method: the image has fewer pixels, so the file is smaller but the lost detail cannot return → Resolution: 1920x1080 -> 960x540

Lossy compression: all data is kept, so the original can be restored → This describes lossless compression. Lossy compression permanently removes data, so the original cannot be restored exactly.

Lossless compression always gives a smaller file than lossy compression → Lossy compression usually gives smaller files because it throws data away. Lossless saves less space because it must keep everything.

Section C: Definitions

lossy vs lossless — Lossy makes smaller files but permanently removes data; lossless keeps all data so the original can be restored, but saves less space.

Section D: Fill in the Blanks

method ← "RLE"
type ← "lossless"

method ← "reduce resolution"
type ← "lossy"

type ← "lossy"
restorable ← FALSE

lossySize ← 2
losslessSize ← 5
OUTPUT lossySize < losslessSize

original ← "AAAABB"
encoded ← "4A2B"
decoded ← "AAAABB"

Section E: Spot the Error

A — Data is removed and cannot be restored, which describes lossy compression. Line 1 should be method = 'lossy'.

B — Lossless compression keeps all the data, so no data is removed. Line 2 should be data_removed = False.

C — Lossy compression permanently removes data, so the original cannot be restored. Line 3 should output 'cannot restore'.

C — Run-length encoding keeps all the data, so the original can be rebuilt exactly. It is lossless, not lossy.

B — Reducing the resolution throws away pixel detail permanently, so this is lossy compression. Line 2 should be type = 'lossy'.