1.2.5 Compression

What is data compression?

The process of reducing the file size of digital data, often to save storage space or speed up transmission.

What is lossy compression?

Compression that removes some data permanently, significantly reducing file size but lowering the quality. It is not reversible (e.g., JPEG, MP3).

What is lossless compression?

Compression that finds patterns to reduce redundancy without losing any data, allowing the original file to be perfectly reconstructed. File size is smaller than original but larger than lossy (e.g., PNG, ZIP).

Which compression type is best for code or text files?

Lossless, because losing a single character of code or text would make the file unusable or corrupt.

Which compression type is better for streaming music or video where a small loss in quality is acceptable?

Lossy, because the significant file size reduction allows for faster transfer speeds and less buffering, and the quality loss is often unnoticeable (especially when streaming).

What is the main reason for the need for compression?

To save storage space on devices with limited capacity (e.g., memory card) and to enable quicker transfer/streaming of files (less bandwidth/time).

Give a common scenario where compression is needed for images.

Storing a large number of photos on a digital camera's memory card or uploading images to a web server/social media for quick loading.

Give a common scenario where compression is needed for audio.

Streaming music/video or downloading audio files (like MP3s) where file size needs to be small for faster transfer.

What is the main advantage of Lossy Compression?

It results in the greatest reduction in file size (e.g., JPEG can reduce file size to about 10% of the original).

What is the main disadvantage of Lossy Compression?

It is a destructive process; data is permanently lost and the original file cannot be exactly reconstructed. Repeated compression worsens the quality.

What is the main advantage of Lossless Compression?

No data is lost; the decompressed file is an identical copy of the original (perfect reconstruction).

What is the main disadvantage of Lossless Compression?

The resulting file size is larger than that achieved with lossy compression, and the reduction is less significant.

For which files is Lossy Compression suitable?

Files where minor quality loss is unnoticeable and file size is critical, such as photos (JPEG) and streaming audio/video (MP3, MPEG).

For which files is Lossless Compression suitable?

Files where the exact content must be preserved, such as text documents/code, archived files (ZIP), and images requiring high quality (PNG, GIF).

What effect does compression have on file properties like image resolution or sound duration?

Compression does not change the fundamental properties like resolution, colour depth, or the duration of an audio file. It only changes the number of bits used to represent the data.