pdf settings, need help

[behzad]

Just wanted to know what they mean?

Native
None
Flate

Oh and Unicode

[Odat]

I'm not sure what "Native" means for bitmap compression, but the Flate method is the same compression method that is used by zip programs (like WinZip).

Flate is a lossless compression method, which means that when uncompressed your image will look exactly as it did when it was compressed. This is in comparison to JPEG, which is a lossy compression method that essentially makes your image smaller by throwing some of the information away entirely.

Flate by a different name is also the compression method that is used in PNG files. It is also related to (but different than) the compression method used in GIF and some TIFF files.

"None" as a compression method would mean exactly that; the image would be inserted into the file in more or less the same way that it would be represented in memory while you're looking at it. The advantage of this is that your PDF file will be readable by people whose PDF reader can't handle compressed data (either really old, or perhaps special purpose). The disadvantage is that your PDF file would be huge.

The amount of memory it takes to hold a bitmap varies based on the number of colors that are possible, but for our purposes here, the bare minimum would be width in pixels * height in pixels. More likely, the value would be 2, 3 or even 4 times this value (again, based on the color depth of the image). So for example an image that was 640x480 could take between 307,200 (300kb) to 1,228,800 (1.2Mb) to store.

"Unicode" is a way of storing textual information that makes sure that the information is fully readable by anyone. One of the properties of Unicode is that the representation for normal "Western" text (for example, english text) is the same in Unicode as in the non-unicode method. When using characters that are accented (like in french or spanish), or expressing languages that use their own character set (like chinese), Unicode makes sure that everyone sees your text the same way that you do.

The tradeoff there is that the space required to store Unicode text is twice as big as it would be without Unicode.

Just some quick and (kinda) brief explanations, hope they help!

[behzad]

Odat, thank you. would you use flate at all?

[Odat]

Which one to use is generally a judgement call based on the kind of graphics the file is going to contain.

For a lot of photographs, or pictures without a lot of fine detail, JPEG will get you better compression than flate will.

On the other hand, if there is a lot of fine detail in the images, they might end up looking fuzzy if you use JPEG, and so Flate would probably be a better choice.

The only circumstance I can come up with in which you would want to select None would be if you are giving the file to someone whose PDF reader can't handle Flate compression at all. Otherwise, at a bare minimum Flate would be a better default choice.

Most of the PDF's that I make are for my own local use, so the size of the files doesn't really concern me that much, so I normally use Flate compression.

In the rare cases where I'm sending the file off to someone else or posting it on the web, etc, I usually create one with Flate and one with JPeg and compare the sizes and quality of PDF's and try to make a determination that way.

[behzad]

Thanks Odat, your the best