File Compression

Many years ago, when I was the cheapest and most inexperienced programmer in a small software house I was given a little boring job. I had to type in a program, written in a book, into a computer. The program was for file compression (LZW). The program was to be used to shrink the size of scanned documents. These were big images and they needed to be small. They needed to be small for two reasons. Firstly they needed to take up less room when stored and the also written and read from storage quickly. Strangely enough compressing and uncompressing a file is much faster than writing or reading an uncompressed file to/from a disk. The same is still true today. Most of the little gadgets in your pocket and also in your home compress and uncompress files for exactly the same reasons.

Compression works by breaking the image down to small chunks with the assumption that there will be many chunks that are identical. That chunk will be stored once and then all the places on the image where the same chunk would be, are stored too. The compressed file would simply be an instruction of how to recreate (uncompress) to a file that was an exact copy of the original. We call this ZIPPING/UNZIPPING.　 If the original file was "uncomplicated" then the compressed file would be very much smaller than the original.

We can make these files more useful by attaching information to file. For example which camera was used and the date that the photograph was taken etc... The most common type of this file is called Lossless TIFF. A Lossless TIFF file can be uncompressed to recreate a exact copy of the original saved image.

If you reduce the detail in an image, for example, the number of colours and resolution of the image then you can easily end up with a file which will compress to a much smaller size. However, you'll never be able to recreate the detail of the original file.

The most common type of this type of file is the JPG. The clever part of making a JPG is to reduce the detail without it being noticeable. This is why its the most popular image file format for the internet.

As photographers we like to use Camera RAW so we don't loose any of the detail within the picture. The problem with this is that as cameras develop and sensors get bigger we not only have to think about the size of our memory card but the amount of storage we need on our PC's! I am currently putting together a blog on storage to take this thread on a step further.

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