Understanding concepts and practices in digital preservation
What is file compression? Digital files, like all other artifacts, have the potential for degradation over time if not handled properly. One way this can happen is through file compression. It is imperative to understand different compression methods to keep the artifact in its best quality possible.
The basics There are two types of file compression methods. These methods, created with special algorithms, affect the size and quality of the file. Let’s look at the two kinds of file compression methods: lossless and lossy. •
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Lossless files have very little compression. The file size is reduced, but every single bit of information within the file is preserved. These files are much larger in size than lossy files. Lossy files are compressed. Much of the data in the file has been lost to reduce file size. Uncompressed files are the raw form of the file with no compression at all.
How do I apply this? By understanding various compression methods, you will be able to know how to adequately handle the digital object in a way that will retain its quality.
Editing In a lossy digital file, the quality will degrade even more if it is edited. For example, if you receive a JPEG image and edit it in Photoshop or any other photo editing software, the image will lose more pixels per inch. If it’s in a lossless format, it will retain all of its pixels per inch as long as you continue to save it in a lossless format.
Converting Another way a file will degrade is by converting it from one lossy format to another. For example, if you convert an MP3 audio file to an AAC audio file (two lossy formats), more information will be lost. Also, bitrates are important factors in audio files. Bitrates decide how much information to keep in an audio file. The higher the number, the more information is in the file. But, the more you convert, the more you lose. If you convert an MP3 file encoded at 128 bits per second to 256 bits per second, the sound quality will actually become worse.