Compression (Cambridge (CIE) IGCSE ICT): Flashcards
Exam code: 0417 & 0983
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Define compression.
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Cards in this collection (15)
Define compression.
Compression is reducing the size of a file so that it can be transmitted or stored in secondary storage.
Give two reasons why compression is needed.
Compression maximises the amount of data you can store on a device and minimises the transfer time of data being uploaded, downloaded or streamed across a network.
Other than compression, how can the file size of an image be reduced?
The file size of an image can be reduced by reducing the colour depth or the resolution.
What are the two methods of compression?
The two methods of compression are lossy and lossless.
Define lossy compression.
Lossy compression is when data is lost in order to reduce the size of a file on secondary storage. It is irreversible.
Define lossless compression.
Lossless compression is when data is encoded in order to reduce the size of a file on secondary storage. It is reversible, so the file can be returned to its original state.
What is the key difference between lossy and lossless compression?
Lossy is irreversible because data is lost, while lossless is reversible because data is encoded and the file can be returned to its original state.
True or False?
Lossless compression loses less data than lossy compression.
False.
Lossless compression does not lose any data. It encodes the data so the file can be returned to its original state, while lossy compression permanently removes data.
True or False?
Lossless compression reduces file size as dramatically as lossy compression.
False.
Lossless compression reduces the size of a file, but not as dramatically as lossy compression.
When is lossy compression suitable?
Lossy is only suitable for data where reducing quality is acceptable, for example images, video and sound.
When is lossless compression suitable?
Lossless is more suitable for data where a loss in quality is unacceptable, for example documents.
Give three file types that use lossy compression.
JPEG images, MP3 audio and MPEG-4 video all use lossy compression.
Give three file types that use lossless compression.
PNG images, ZIP files and RAR files all use lossless compression.
How does lossless compression work on a document?
Algorithms analyse the contents looking for patterns and repetition. Repeating characters are replaced with a single character and the number of occurrences, so 'EEEEE' becomes 'E5'.
How does lossy compression reduce the size of a photograph?
It groups similar colours together, reducing the number of colours in the image without compromising the overall quality.
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