Compression zip algorithm

In order to render the compressed files, a ZIP archive holds a directory at its end that keeps the entry of the contained files and their location in the archive file. It, thus, plays the role of encoding for encapsulating information necessary to render the compressed files. The format keeps dual copies of the directory structure to provide greater protection against loss of data.

Each file in a ZIP archive is represented as an individual entry where each entry consists of a Local File Header followed by the compressed file data. The Directory at the end of archive holds the references to all these file entries.

ZIP file readers should avoid reading the local file headers and all sort of file listing should be read from the Directory. This Directory is the only source for valid file entries in the archive as files can be appended towards the end of the archive as well. That is why if a reader reads local headers of a ZIP archive from the beginning, it may read invalid deleted entries as well those are not part of the Directory being deleted from archive. The order of the file entries in the central directory need not coincide with the order of file entries in the archive.

The Local File Header of each entry represents information about the file such as comment, file size and file name. The data about an email typically about sender, receiver and domain and of course the message ,has to be processed by the systems and servers involved in the transmission. It being done for all the billion emails is a mammoth task. Sometimes it may also lead to Congestion. Hence, the email service providers use Compression as a mechanism to reduce the amount of data to be transferred.

Compression helps the email service providers to increase their productivity as the storage overhead, processing and labor spent on the maintenance of their servers is reduced. Skip to content.

Change Language. Related Articles. Table of Contents. The better the compression ratio, the more detail you lose. More information on the JPEG compression algorithm can be found on this page. If you distill a file that contains JPEG compressed images, Distiller will uncompress these and then recompress them according to your settings. This will lead to an additional loss in image quality.

Once a PDF is created, you can still alter the compression ratio. This can be handy when a file is too big for emailing or uploading it. Remember the disadvantage: when you recompress the data, there is an additional loss of detail!

If possible, redistill the original source file. This fairly new compression algorithm is supported from PDF version 1. You can find more information about the compression algorithm on this page. This basic compression can reduce the file size of a PDF to about half the size of an equivalent PostScript file. It is a lossless algorithm so it will not change the quality of your images.

More information about the algorithm can be found on this page. In Acrobat RLE compression can be used for black-and-white images. When you select ZIP compression, this does not mean that Acrobat will create a ZIPped file, it will just use the algorithm to compress grayscale or color images. It is a lossless algorithm. This means that the content of your images will not change by compressing them.

If you are still using Acrobat 3, it offers options for so-called 4-bit and 8-bit ZIP compression. This leads to an excellent compression ratio but the quality of the images suffers enormously.