Lossy and Lossless (RLE) Compression

Question 1

What is compression?

Answer 1

Reducing file size while retaining the core infomation
Means fewer bits are needed to convey the original infomation. Storage and upload, download and file transfer times can be reduced.

Question 2

What is Lossy Compression?

Answer 2

• Some of the original data is removed from the file
• Not used where all data is important(E.G code), but where the only consequence is loss of quality(E.G images and video)
• After a file is decompressed the file isn’t the same as the original
• JPEG and MP3 are two lossy compression algorithms - partly work by moving sounds / colours we recognise least

Question 3

What is lossless compression?

Answer 3

• No data is removed, but it’s rearanged to become more efficient
• Can be done with Run Length Encoding(RLE)
• Replaces repeated data(“run”) with frequency/data pairs
• Works best with data likely to have lots of repeats
• If there are few repeats(E.G random text), then RLE may add to the file size. Longer the run = most compression

Question 4

Which compression type is more effective?

Answer 4

Lossy is usually more effective