Compression

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Compression exam questions18 questions with mark schemes and example answers

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Which term describes the process of restoring compressed data to its original format?: Decompression
Which term describes a method of reducing file size that permanently removes some data, which can reduce the quality of an image or sound?: Lossy compression
What is meant by 'lossless compression'?: A method of reducing file size that keeps all of the original data so the file can be restored exactly
What is meant by a 'digital artefact' in a compressed image or video?: A small mistake, such as a block or a patch of noise, that appears after some data has been permanently removed
What is meant by 'dictionary compression'?: A lossless method that finds repeated patterns of data and stores each pattern once alongside a code
What does compression mean when it is applied to a computer file?: Reducing the size of a file using an algorithm
A file is compressed using a lossy algorithm. What happens to the data that is removed?: It is lost permanently and cannot be recovered
A company wants to make a program file smaller so it can be downloaded more quickly. Why must lossless compression be used?: Every instruction must be restored exactly as it was
A photograph is compressed with a lossy algorithm and then enlarged on screen. What is likely to be visible?: Blocks and noise where colours contrast
Why does a compressed file download faster than the uncompressed version of the same file?: Fewer packets of data need to be transferred
An MP3 music file is much smaller than the same track stored without compression. Why is this?: Sounds that listeners are unlikely to notice are not stored
Why is compression useful when a file is being sent as an email attachment?: The file is more likely to stay within the size limit
Which of these file formats uses lossy compression?: MP3
A company compresses its files before copying them onto a backup drive. What is the main benefit of compressing the files first?: More data can be stored using the same amount of space
The same sound file is compressed twice, once with a lossy algorithm and once with a lossless algorithm. How do the two compressed files compare?: The lossless file is larger but can be restored exactly
A single uncompressed frame of high definition video needs around 50 megabits of data. Why does this make compression necessary?: The video would need far too much data to store or send
A video keeps stopping and showing a buffering message while it is being streamed. What is the most likely reason?: The data is arriving more slowly than the video is being played

Compression

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