File Compression

There are few technologies in the IT world which are just so helpful that once you’ve got used to using them you will find them simply indispensable; file compression is just one of those things that you may not have yet given any thought to and it just so happens to be the subject of this weeks article.

To give you an example of how file compression would reflect the real world; Could you imagine how useful it would be that when you wanted to go onto holiday you simply put everything you needed into one huge suitcase which could then be shrunk to a quarter of the size whilst travelling and then made the correct size again when you reached your hotel room?

For the IT professional being able to do a similar thing with PC files is almost as useful; file compression allows them to collect many files and compact them all into one easy to manage package for transportation, either using a floppy disk, CD-ROM or more commonly the Internet.The recipient would then simply uncompress the package and use the files exactly as normal – The advantages of this are numerous.Most obvious is that instead of sending 2 Megabytes over the Internet you are able to compress it into 1 Megabyte, halving the time that you have to spend online.In addition you are able to send for example, 20 files all compressed into the same package and so it would be easier to manage for both yourself and the recipient.

Generally, the way most compression techniques work is to remove duplicate data from a file and then put it back again when the file is uncompressed.Let’s assume we compressed a text file which contained “Ask not what your country can do for you — ask what you can do for your country”.Now, as you can see, half of the words in this phrase are repeated so it would be possible for the computer to remove them and reinsert them at the point of uncompression.Since there are so many different uses for compression, the methods for making files smaller varies from type to type and so below are details of the most standards and their most common uses in real life:

“Zip Files” – As explained above, by using a program such as WinZip (www.winzip.com) you are able to compress a number of files into one easy to manage archive; these files are perfect for downloading a piece of software onto your computer as all the program files can be transferred in one go and at a greater speed than if the files were uncompressed.

WinZip is a free to use program and since the majority of software off the Internet comes ‘Zipped up’, it is definitely worth the download.

“MP3 Files” – These are very tightly compressed music files meaning that an average track can be compressed from around 50 Megabytes down to approximately 5 Megabytes which means they should be able to download in around a tenth of the time.The possibilities for abuse in terms of copyright are obvious, which is why MP3’s have been in the news so much recently especially in relation to Napster (www.napster.com) which allows you to search for and download them freely.

The main technique which is used to compress MP3’s down so much is that the top and bottom sections (upper treble and low base) of the sound wave are removed.This can lead to a reduced sound quality of the music but generally speaking the difference is minimal since most people can’t distinguish these extreme pitches on both sides of the sound wave anyway.

“Jpeg Files” – These graphic files are very commonly used on the Internet webpages as they are very small in size in comparison to an uncompressed graphic file and so download in much faster times.

They work on the same principle of removing irreverent data as explained above but in a slightly different way; let’s assume that we have a picture of Berry Head which we’d like to compress so that people on our Internet site don’t have to wait a long time for it to download.The compression program would look for areas of the picture which look very similar, for example, in reality the sky would be a great number of millions of different tones of blue but the program would see the similarities between the colours and decrease this value to something a bit more manageable such as 256 colours.This way the program would find repeating areas of the picture, where for example 1500 pixels all of the same colour converge next to one another meaning the program could make a note of this instead of having to store the colour and positioning of each individual pixel.

Obviously, reducing the number of colours in this way would have a detrimental effect on the image but if done well, it is hardly noticeable and the reduction in file size is incredible.

About the Author – Chris Holgate works for Refresh Cartridges who supply a wide range of printer cartridges at the UK’s lowest prices.

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