所有PDF文件是否压缩？ [英] Are all PDF files compressed?

问题描述

因此，在这里有一些线程在PDF压缩说，有一些，但不是很多，在压缩PDF的增益，因为PDF已经压缩。

So there are some threads here on PDF compression saying that there is some, but not a lot of, gain in compressing PDFs as PDFs are already compressed.

我的问题是：对于所有的PDF，包括旧版本的格式，这是真的吗？

My question is: Is this true for all PDFs including older version of the format?

确保它可能为某人（一个白痴可能）将位图放置在PDF而不是JPEG等。我们公司有很多PDF在其DB（一些较旧的格式可能）。我们正在考虑在传输过程中使用gzip压缩，但不知道是否值得一试。

Also I'm sure its possible for someone (an idiot maybe) to place bitmaps into the PDF rather than JPEG etc. Our company has a lot of PDFs in its DBs (some older formats maybe). We are considering using gzip to compress during transmission but don't know if its worth the hassle

推荐答案

对其包含的对象使用内部压缩。但是，根据文件格式规范，这种压缩决不是强制性的。所有（或某些）对象可能完全未压缩，它们仍会生成有效的PDF。

PDFs in general use internal compression for the objects they contain. But this compression is by no means compulsory according to the file format specifications. All (or some) objects may appear completely uncompressed, and they would still make a valid PDF.

有些命令行工具可以解压缩大部分所有）内部对象流（即使是最现代的PDF版本），并且文件的新的未压缩版本将在屏幕或纸张（如果打印）上呈现完全相同。

There are commandline tools out there which are able to decompress most (if not all) of the internal object streams (even of the most modern versions of PDFs) -- and the new, uncompressed version of the file will render exactly the same on screen or on paper (if printed).

所以回答你的问题：不，你不能假设一个gzip压缩只添加麻烦，没有好处。你必须用你的文件的代表性示例集来测试它。

So to answer your question: No, you cannot assume that a gzip compression is adding only hassle and no benefit. You have to test it with a representative sample set of your files. Just gzip them and take note of the time used and of the space saved.

这也取决于使用的PDF生成软件的类型...

It also depends on the type of PDF producing software which was used...

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