| Can you say why images and sound files are often compressed | Reduce 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 compression | The 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 compression | The original data cannot be recovered |
| Explain what is meant by lossless compression | The original data can be fully recovered |
| State the advatages of lossly compression to lossless | The extent to which file size can be reduced is not limited for lossy |
| State the disadvatages of lossly compression to lossless | For 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 data | RLE 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 data | Patterns/ 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 compression | Not 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 on | files that contain a lot of repeated data. |
| Explain why a dictionary method may actually be neglidgible for decreasing the size of a file | Dictionary 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 |
