Understanding the Portable Document Format (PDF): Part 2

We covered a bit of the PDF specification in the previous article Understanding the Portable Document Format (PDF). One of the areas that I had purposely failed to cover was Filters. Filters are an interesting topic altogether. My technical knowledge about filters again is very minimal but I will try to explain what they do with whatever info I have.

What are Filters?

Filters in simple terms are algorithms that convert encoded data back to their original form.

For instance, when creating a new PDF file that contains some text, I might have encoded (changed) my data to a bunch of characters that make no sense but save a lot of space and overall reduce the size of my PDF file. When I send this file to a friend and he/she tries to open it using say PDFBox, the program will have to use a specific filter to decode (change back to the original form) my data to its original form - with no loss whatsoever - In fact, there are some algorithms that result in data loss but these algorithms are for images and not for text. These filters are called Decompression filters.