1 Why is compression needed?
To reduce the storage size of a file, for example you might want to reduce the download times for a webpage, or to allow an email to be sent with a large attachment where otherwise it might be too large to send.
* Note: If you just say reduce file size you could get 0 marks because you might be referring to file size in terms of 200 pixels x 400 pixels but it is about the STORAGE size.
Lossy
Compression
What is it?
: Lossy reduces the storage size of a file.
With lossy, the decompressed file is not identical to the original because some data has been
permanently removed…the difference is unlikely to be noticed by humans
Advantages
- Reduces the storage size or a file.
Achieves higher compression ratio / smaller file size / therefore faster streaming than lossless - The image/video/sound can still be viewed at lower quality.
Disadvantages
- The image/video/sound is lower quality once it has been decompressed because some data was permanently removed.
Suitable for - Images on a website, sound, video because the difference is unlikely to be noticed by humans
Lossless
Compression
What is it?
* Lossless reduces the storage size of a file.
* With Lossless, the decompressed file is identical to the original
Advantages
* No data is lost - after decompression the file is identical to it was before compression.
Disadvantages
* Lower compression ratio so the file size won’t be as small in storage space as it would be if it was lossy compressed.
not Suitable for
* Text or very high quality images, because if data was removed from text files it would not be readable! Also a professional photographer may need all the data kept for printing large prints etc.
