Re: Anyone have experience with PDF/A-1b?

[Henning Hraban Ramm]

Am 2014-10-16 um 01:24 schrieb Noeck <address@hidden>:

>> The only thing missing in LilyPond’s PDF files is the XMP metadata mark of 
>> PDF/A-1(b).
> 
> Would it be much work to implement that?
> LilyPond seems to write file metadata like the title. The format is
> PDF-1.4, for example.

It’s a different kind of metadata, in XMP format.

Of course LilyPond *could* embed that, but I don’t think it would make sense, 
since LilyPond can’t ensure that the PDF really complies to any standard (PDF/X 
would be another interesting one). E.g. you could embed any custom PostScript 
code or EPS pictures that totally break standards compliance. Also, LilyPond 
defines colors as device dependent, that means, black is only defined as being 
black, without a color profile or output intent. (Please read up on the basics 
of color management, if you’d like to know more.)

If you need to deliver a standard, you must be able to check on it and maybe 
enforce it, e.g. using Adobe Acrobat Pro.

I just checked a PDF from LilyPond 2.18.2:
* The color definition is device dependent. As long as you only use black, 
that’s no real problem, but violates the PDF/A (and PDF/X) requirements.
* XMP metadata is missing, but LilyPond sets an author in the „general“ 
metadata, that also violates PDF/A.
* There’s a tiny error in PDF code, a missing EOL marker. I guess that’s a 
GhostScript issue that hurts nobody, but the standard.

Acrobat can fix that automatically, you must just decide on a suitable color 
profile. If I save as PDF/A-1b, file size grows from 51 kb to 559 kB (due to 
the embedding of a color profile).


So, to support one of the standards, LilyPond would need to embed XMP metadata 
and color profiles that most of its users won’t need and that blow up the file 
size. Additionally, you’d need to decide which color profile (output intent) to 
use, any default would be wrong for some users, e.g. most office printers would 
prefer a sRGB profile, but some would make your black a grey due to conversion; 
for offset printing you probably need an „uncoated“ profile (matte paper), but 
the standards differ at least between Europe (FOGRA) and the USA (SWOP?). 
The few people who depend on a special PDF standard should be able to care for 
that themselves or employ someone who knows.


Greetlings, Hraban
---
fiëé visuëlle
Henning Hraban Ramm
http://www.fiee.net
http://angerweit.tikon.ch/lieder/
https://www.cacert.org (I'm an assurer)