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Paper 2 - Computer Science > Data Compression > Flashcards

Flashcards in Data Compression Deck (11)
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What is compression?

Compression reduces files sizes to allow download speeds and file storage requirements to be reduced.


What is lossless compression?

Compression where no data is lost, so the original can be perfectly reconstructed


What is lossy compression?

Compression where data is discarded so the original copy cannot be reconstructed


What are the advantages of lossless compression?

- Different resolutions are accessible
- Has the ability to be compressed for downloading then expanded before it runs
- No data is lost so higher image quality retained


What are the advantages of lossy compression?

Produces smaller sized files than lossless compression


What is RLE and how is it achieved?

Achieved by replacing all the repeated values with the quantity of repeated values, then what the repeated value is.


What is Dictionary based compression?

- Strings (i.e words) are encoded as single symbols
- The symbol is used as the index for a look up table
- Compression is used where symbols are smaller than the original strings.


Why is a symbol less storage than a word

The symbol is usually less bits than the original string which uses a byte per character


What type of compression is dictionary based compression?

Dictionary based compression is lossless compression.


What type of compression is RLE?

RLE is lossless compression.


What type of compression is used on sounds?

Lossy compression, it removes frequencies that are too high for humans to hear, reducing the file size