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level: Data compression

Questions and Answers List

level questions: Data compression

QuestionAnswer
Can you say why images and sound files are often compressedReduce file size, as they tend to be quite large, and stream more efficiently over networks
What 3 key types of files can be compressed?Images Sound Text
Whats the difference between lossless and lossy compressionThe original data cannot be recovered if lossy compression has been used The original data can be fully recovered if lossless compression has been used
Explain what is meant by lossy compressionThe original data cannot be recovered
Explain what is meant by lossless compressionThe original data can be fully recovered
State the advatages of lossly compression to losslessThe extent to which file size can be reduced is not limited for lossy
State the disadvatages of lossly compression to losslessFor lossy, the quality of file is reduced Also for lossy some information is lost in the compression process meaning a file cannot be returned to its orignal state
Is RLE and dictionary based methods lossy or lossless?Lossless
Explain the prinicple of how an RLE compresses dataRLE reduces the size of a file by removing repeated information and replacing it with one occurance of the repeated information followed by the number of times it is to be repeated
Explain the prinicple of how an dictionary based method compresses dataPatterns/ recurring bits of data are added to a dictionary This dictionary is appened to the file When diconstructing a file, the dictionary refrences can be used instead of the actual data
What are the disadvatges of Run Length Encoding compressionNot all data is suitable for comrepssion via this method I.e not all data contains lots of consecutive repeating data
What are run length encoding and dictionary-based methods are most effective onfiles that contain a lot of repeated data.
Explain why a dictionary method may actually be neglidgible for decreasing the size of a fileDictionary is appeneed to the file Meaning it actually increases the file size If there is not a lot of recuresion in the data to make the dictionary useful, it will just increase the file size