3.5.6.7 Data Compression. Flashcards
Why are images and sound files compressed?
To reduce file size as small files can be transferred faster between storage devices or over the internet.
What other files can be compressed?
Text files.
Define lossy compression.
When using lossy compression, some information is lost in the process of reducing the file’s size. This could be reducing the resolution of an image or lowering the sample resolution of a sample audio file.
Define lossless compression.
There is no information lost when using lossless. The file size can be reduces without decreasing its quality.
What are run length coding and dictionary based examples of?
Lossless compression.
Outline run length encoding,
(RLE for short) reduces the size of a file by removing repeated information and replacing it with one occurrence of the repeated information followed by the number of times it is to be repeated.
What is a disadvantage of RLE?
Not all data is suitable for compression by RLE.
Outline the Dictionary-based method.
When a file is compressed with a dictionary-based method, a dictionary containing repeated data is appended to the file.
Outline the advantages of the lossless compression
Results in a significant reduction in the file size.
No loss of information
No loss of quality
Outline a disadvantage of the lossless compression.
The dictionary used to compress the data has to be present in the file in order for the image to be
reproduced. This will increase the size of the file.
There is a limit to how much a file can be
compressed.
Outline the advantages of lossy compression.
The extent to which file size can be
reduced is not limited.
Outline the disadvantages of lossy compression.
Quality of file is reduced.
Some information is lost in the compression process.
