[xep-support] PDF embedding -- parameters

Nikolai Grigoriev grig at renderx.com
Sun Feb 2 14:03:05 PST 2003


Hi Gustaf,

> I've been testing PDF embedding now and so far no big problems. I'm using
> Illustrator 10 to make illustrations. There are plenty of parameters and I
> don't know what XEP expects of prefers. So here's a list of those settings
> I'm uncertain of. Hope you can help me.
>
>   1. Color mode: ( ) CMYK  <-- these are radio buttons!
>                  (o) RGB
>
> I get accurate results with RGB, but slightly other colors with CMYK
> (yellow shifted to green). Does that mean RGB is always prefered in XEP?

XEP does not alter colors - it faithfully copies what was specified
in the source PDF. You should decide for yourself which color type
do you want in the output. If the document is for on-screen presentation
then RGB is a natural choice. CMYK only makes sense for PDFs
prepared for a 4-ink printer, and is printer-dependent; its onscreen
presentation is always approximate.

>   2. File compatibility: ( ) Acrobat 5.0
>                          (o) Acrobat 4.0
>
> I've choosen Acrobat 4. The difference I know of is that Acrobat 5 handles
> flattening, which has something to do with transparency. Does the PDF
> embedding feature in XEP support both versions?

Good point, thank you for the hint. XEP just copies objects through: if
they use features typical of PDF 1.4 (= Acrobat 5) the result will be
correctly viewable in Acrobat 5 - all objects will be preserved.
However, the PDF header produced by our generator specifies
PDF version 1.3, thus giving rise to an inconsistency. So, you are
correct to choose Acrobat 4.0.

> Afraid of unnecessary garbage, I've choosen to uncheck
> "Preserve Illustrator editing capabilities".

You are right. XEP-made PDFs have no Illustrator-specific
data; I don't see how preserving Illustrator-specific for
images could help. And they obviously eat up space -
so it is better to leave them out :-).

>   3. [x] Embed all fonts  <-- this is a check box!
>
> In illustrations containing text, this is a good thing,
> isn't it? Can I uncheck it to save file size if I use
> the same fonts for the document text?

As a rule of thumb, you should embed all fonts for PDFs
that go to prepress. For documents distributed in electronic
form, you can leave Times, Helvetica, Courier, ZapfDingbats,
and Symbol not embedded. I don't know the exact meaning
of that checkbox; if it toggles between these two behaviours,
than it is safe to uncheck for on-screen PDFs.

Important: fonts _are not shared_ between the embedded image
and the rest of the PDF file! Each embedded PDF has its own
set of resources, and cannot access fonts elsewhere in the document -
neither document's fonts nor those from a neighbour image.
(Otherwise, we should handle font merging, resubsetting,
versioning etc - it goes well beyond the resources we can
allocate for the task).

> How about subsetting fonts? There's a setting called
> "Subset fonts when less than ... % of the characters
> are used". That sounds good too, doesn't it?

Yes. As I said before, the fonts that you save in Illustrator
will be used _for that particular image only_. Different
images will not share fonts; so it is desirable to make them
as small as possible. Put a high value there: 75% or more.

>   4. [ ] Embedd ICC profile
>
> What's this?

ICC (International Color Consortium) profile is an industry-standard
format to specify color capabilities of a device. It is a means
of removing device-dependence from color specifications:
if your DeviceCMYK is accompanied by the color profile
of the target printer, the colors can be recalculated when printed
on other printers with different ink tones (using their color profiles
as a source of colorimetric information).

Internally, it's just a PDF embedded file object. If it is referenced
from the resource dictionary for the first page, XEP moves it to
the target PDF, and uses to specify colors for your image. It's up to
you to decide if you need calibrated colors in your illustration.
Naturally, this will increase file size footprint of your image.

> But there is also a check box called
>
>   5. [ ] Compress text and line art
>
> The manual says that this box "applies ZIP compression to text and line
> art". Is this compression destructive? I seek as high quality as possible.

No, it is not destructive, and has no impact on vector art quality:
it serves only to reduce image size. It is safe to leave it checked.
However, XEP recompresses all uncompressed data streams
with Flate algorithm; so additional compression in a PDF
image adds no value to the PDF that comes out of XEP.
If the size of the intermediate PDF images is not an issue,
it is better to leave this box unchecked.

(I wonder what do they mean by ZIP; it may be either Flate or LZW method.
For Flate, there are no special caveats; but if they use LZW, XEP will not
be able to repack the stream, because of Unisys patent on the algorithm.
In this case, you actually _lose_ space in the output file - Flate is more
efficient.)

Best regards,
Nikolai Grigoriev
RenderX

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