Basic Compression Techniques
By knowing how to compress a PDF file, we reduce storage space, increase transmission speed and portability of the PDF document. Basic functions that can be performed by a user include the usage of black and white pictures rather than colored ones, usage of simple small sized fonts, grey scaling of the document, and using `save as' to save the document rather than just plainly saving it to append the changes. Further, more complex approaches involve the employment of multiple algorithms, which contribute to the condensing of the file in small ways of their own areas of competency. They are classified into two kinds - lossy and lossless algorithms.
How to Compress a PDF - Algorithms
Lossy algorithms lose partial information content permanently, and hence yield a smaller size PDF file, whereas lossless techniques revolve on no compromise on quality, yet shrinking the PDF size considerably. To compress a PDF, the algorithms analyze the kind of images in the file, and accordingly put to use the respective algorithms. Compressing PDF is literally compressing images and the lossless algorithms are - CCITT (group 3 and 4), Flate, LZW, ZIP and RLE compressions. RLE (run length encoding) works best on large areas of black and white patches on images, and compresses them. LZW compression is based on a table look up mechanism, creating shorter codes for a pattern of characters and entering them in a table format. Flate method uses Huffman coding techniques for compression. JPEG is the most flexible compression; it can reduce the image size to one twentieth its size, with almost no change in quality change, however by losing information. Yes, this implies that it is a lossy technique and it is efficient for photographic pictures as it uses the human eye sensory engine's ability to detect changes in brightness rather than contrasts.
PDF Compression Features
While we compress a PDF, not only does the file become smaller in size, but also the format allows text searchable options, for easy access of users. Optimized PDF files are sometimes obtained by the PDF software itself, which may have in-built compression technology. We can compress a PDF batch of files as well, to save more time and space in the work area. The quality of the original images should not be sacrificed whatsoever, when compressions take place and this lies in the character of the compression algorithms.