Thẻ ghi nhớ: 1.3.3 & 1.3.4 Data Compression | Quizlet

What is data compression?

The use of algorithms to reduce file size by removing repeated or unnecessary data, helping save space and reduce transmission time.

Why is data compression useful?

It reduces file size on disk, speeds up email transfers (especially with attachment limits), and reduces bandwidth for streaming or online downloads.

What are the two main types of data compression?

Lossy compression and Lossless compression.

What is lossy compression?

Compression that permanently removes some data (like detail or resolution) to reduce file size significantly.

Examples of lossy formats?

JPG, MP3, WMV, MPG.

Advantages of lossy compression?

Smallest file sizes, least transmission time, reduces internet traffic and collisions.

Disadvantages of lossy compression?

Loss of detail, reduced resolution, colour depth, or sample rate, cannot restore original quality.

Uses of lossy compression?

Music streaming, online images and videos, cloud image libraries.

What is lossless compression?

Compression where no data is lost; the original file can be perfectly reconstructed.

Examples of lossless formats?

TIF, PDF, GIF, PNG, ZIP.

Advantages of lossless compression?

Preserves original quality, no data or information is lost.

Disadvantages of lossless compression?

Less reduction in file size compared to lossy.

Uses of lossless compression?

Text documents, e-books, high-resolution print documents.

Two advantages of using compression for online downloads?

Smaller size on server reduces download time, reduces internet traffic and saves bandwidth.

Which compression type should be used to compress software and why?

Lossless compression, because no data can be lost or the software might not run correctly.

What does RLE stand for and what type of compression is it?

RLE stands for Run Length Encoding. It is a type of lossless compression.

How does RLE (Run Length Encoding) work?

RLE works by replacing sequences of repeated data with a single value and a count. Example: Original binary: 000001110000, RLE version: 50 31 50 (5 zeros, 3 ones, 5 zeros).

What are the advantages of RLE?

Simple to implement, reduces file size when data has lots of repetition, no data is lost (lossless).

What are the disadvantages of RLE?

Not efficient for data with little repetition, can increase file size if there's lots of variation.

What is RLE commonly used for?

Simple images (e.g., black-and-white icons), graphics with many repeated pixels, barcodes, basic textures.

How does RLE relate to data compression in IGCSE CS?

RLE is an example of a lossless compression algorithm, where no data is lost. It shows how repeated patterns in data can be reduced for efficient storage and transmission.

Example of RLE for binary string 000001110000111100 → ?

RLE: 50 31 50 51 20. Means: Five 0s, three 1s, five 0s, five 1s, two 0s.

(Practice) What is the binary for RLE data: 40 31 30 21?

0000 111 000 11.

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