Compression

Question 1

What is compression

Answer 1

Compression is reducing the amount of data.

Question 2

What kind of compression is there?

Answer 2

Lossy and lossless

Question 3

What is lossy compression?

Answer 3

Compressing a file by deleting some of the data that is not very crucial.
• Some data is permanently lost when compressed
• Good for compressing things where some quality can be sacrificed – e.g. a photo or a song

Question 4

What is lossless compression?

Answer 4

Lossless compression works by recording patterns in the data rather than the data itself.
• No data is lost through compression
• Good for compressing things such as code files where data cannot be removed

Question 5

What is RLE?

Answer 5

• Patterns stored – e.g. 10 blue pixels, 5 green pixels etc.
• Compresses the file without loss of data
• Has to be patterns or lots of repetition otherwise it is not very effective

Question 6

What is the dictionary?

Answer 6

• Repeated data is assigned a specific binary code – e.g. the word “cat” might be assigned 00110101
• Compresses the file without loss of data
• Binary codes take up less space in memory than the ASCII values for each individual letter/character
• Has to be a lot of repetition otherwise it is not very effective
• Have to also store the dictionary (list of codes) so final file size may not be as small