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I have been struggling with this for a few days, so I thought I'd ask for help here...

Basically, I'm trying to use ps2pdf (version 9.10) to create correct PDF/X-1 and PDF/X-3 documents. Yes, I know that ps2pdf is said to only support PDF/X-3 (see this thread and this thread and this thread). However, as PDF/X-1 is basically a subset of PDF/X-3, I guess such a conversion should be possible. Also, using the command...

gs -sDEVICE=pdfwrite -dPDFX -dBATCH -dNOPAUSE -dNOOUTERSAVE -sProcessColorModel=DeviceCMYK -sOutputFile=out.pdf PDFX_def.ps in.pdf

I noticed that the colors of the PDF/X-3 files that I'm creating are converted to CMYK, instead of leaving them in RGB (which should be the case with PDF/X-3). So, technically, the files are now PDF/X-1: Which I can confirm by adding "/GTS_PDFXVersion (PDF/X-1a:2003)" to PDFX_def.ps and running the file through Adobe's Preflight.

Which brings me to the first part of the question: How can I prevent the RGB colors that are defined in the original PDF document to be converted to CMYK? The switch "-dColorConversionStrategy=/LeaveColorUnchanged" doesn't seem to have any effect. (Actually, I read here that such a conversion isn't even possible. So, why is it happening? Or is this outdated information?)

Secondly, why does the documentation say that "RGB is not allowed" in combination with "-dPDFX"? Isn't this what PDF/X-3 is all about?

Thirdly, is it possible to also create PDF/X-4 documents that pass Adobe's preflight?

By the way, here's my PDFX_def.ps file:

%!
% $Id$
% This is a sample prefix file for creating a PDF/X-3 document.
% Feel free to modify entries marked with "Customize".

% This assumes an ICC profile to reside in the file (Blurb_ICC_Profile.icc),
% unless the user modifies the corresponding line below.

systemdict /ProcessColorModel known {
  systemdict /ProcessColorModel get dup /DeviceGray ne exch /DeviceCMYK ne and
} {
  true
} ifelse
{ (ERROR: ProcessColorModel must be /DeviceGray or DeviceCMYK.)=
  /ProcessColorModel cvx /rangecheck signalerror
} if

% Define entries to the document Info dictionary :

/ICCProfile (ISOcoated_v2_300_eci.icc) def  % Customize or remove.

[ /GTS_PDFXVersion (PDF/X-3:2002) % Must be so (the standard requires).
  /Title (Title)                  % Customize.
  /Trapped /False                 % Must be so (Ghostscript doesn't provide other).
  /DOCINFO pdfmark

% Define an ICC profile :

currentdict /ICCProfile known {
  [/_objdef {icc_PDFX} /type /stream /OBJ pdfmark
  [{icc_PDFX} <</N systemdict /ProcessColorModel get /DeviceGray eq {1} {4} ifelse >> /PUT pdfmark
  [{icc_PDFX} ICCProfile (r) file /PUT pdfmark
} if

% Define the output intent dictionary :

[/_objdef {OutputIntent_PDFX} /type /dict /OBJ pdfmark
[{OutputIntent_PDFX} <<
  /Type /OutputIntent              % Must be so (the standard requires).
  /S /GTS_PDFX                     % Must be so (the standard requires).
  /OutputCondition (ISOcoated_v2_300_eci.icc) % Customize
  /Info (Info)                     % Customize
  /OutputConditionIdentifier (Custom)      % Customize
  /RegistryName (http://www.color.org)   % Must be so (the standard requires).
  currentdict /ICCProfile known {
    /DestOutputProfile {icc_PDFX}  % Must be so (see above).
  } if
>> /PUT pdfmark
[{Catalog} <</OutputIntents [ {OutputIntent_PDFX} ]>> /PUT pdfmark

Thanks in advance!

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2 Answers 2

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OK first off you can't produce PDF/X-1 using pdfwrite currently, because of limitations with the colour support in PDF/X-1. It is actually almost possible to do now, but Separation and DeviceN colour spaces are not converted to device spaces, and need to be.

Secondly, you should really use the current version of Ghostscript (9.16).

As you noted yourself later in your answer, the documentation states that you can't use /RGB. So the reason your RGB colours are converted to CMYK is because you can't use RGB (see later).

The Ghostscript bug report you reference is 5 years old, what was true 5 years ago isn't true any longer (and wasn't true when 9.10 was released nearly 2 years ago). However as I Noted above you still can't produce PDF/X-1, which is why the bug is still open. Some work has been done, more remains to do.

Setting ColorConversionStrategy in conjunction with PDFX has no effect, because the colour conversion requirements of PDFX supercede the ColorConversion from the command line.

You can't use DeviceRGB space in a PDF/X-1 document unless you specify a DefautlRGB colour space which is not itself a DeviceRGB or DeviceN space. As I recall there is currently no provision in pdfwrite for specifying a DefaultRGB space, which is why you can't use DeviceRGB.

Finally; no you can't yet produce PDF/X-4 file using the pdfwrite device.

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12 Comments

Thanks, @KenS, for this helpful reply. May I ask a few more questions: (1) What do you mean by saying pdfwrite can't produce PDF/X-1 files? As I see it, the PDF/X-3 files produced really seem to be PDF/X-1. They even pass Adobe's PDF/X-1 preflight. If they were X-3, there would be no need to convert RGB to CMYK? (I'm not using DeviceN spaces.) (2) For me, the main advantage of using PDF/X-3 lies in being able to include RGB colors and have the printer handle the conversion. So, if what you're saying is true (and I assume it to be), it seems to me that I really can't produce PDF/X-3 files!?
The code, as it stands, cannot take arbitrary input and reliably produce a PDF/X-1 output. There are possible inputs which will not be converted to an acceptable device space. Therefore it cannot produce PDF/X-1 (there may be cases in which specific kinds of input will result in a PDF file which would pass PDF/X-1 validation, but it is not reliable). You can produce a PDF/X-3 file because it has wider support for colour spaces. Using RGB and 'letting the printer handle the conversion' will lead to poor quality results, unless you have a carefully colour calibrated workflow.
@KenS: please write "PDF/X-1a", not "PDF/X-1". There technically is a difference between the two and the only thing used today is PDF/X-1a
@KenS: also, why do you say "Separation and DeviceN colour spaces are not converted to device spaces, and need to be"? That is not the case, PDF/X-1a fully supports separation and DeviceN color spaces (not N-Channel) as long as their alternate color spaces as acceptable by the PDF/X-1a standard.
I'm currently the Executive Officer of the Ghent Workgroup (www.gwg.org) which is a standards organisation widely recognised primarily in Europe. All of the standards used in different countries are based on PDF/X-1a. That 's not to say there aren't PDF/X-3 based standards, but the ones used are almost exclusively built on PDF/X-1a. The only exception that I know of is Switzerland. You're right about printers knowing their machines better, but with conversion from RGB to CMYK comes responsibility and most printers dislike that :)
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OK, KenS's answer should be accepted as the correct one for this question, but having been heavily involved with standards work for a couple of years (about fifteen now :)), I wanted to add some more general statements.

PDF/X-1a
Please refer to PDF/X-1a, not PDF/X-1. Those are two different things and while nobody uses PDF/X-1 at the moment it would be good to use the correct name of the standard, which includes the "a".

PDF/X-3 and RGB
The statement in the original question "instead of leaving them in RGB (which should be the case with PDF/X-3)" is incorrect or at least misleading (though the intent is correct I think).

The difference between PDF/X-1a and PDF/X-3 is indeed that PDF/X-3 supports color spaces other than CMYK. But that doesn't mean that CMYK is not allowed or that you can't perfectly well use PDF/X-3 for CMYK only files. In fact, most implementations that use "PDF/X-3" that I know of are simply using CMYK only files.

And yes, if you have a PDF/X-3 file that contains only CMYK and/or spot color, and you change the standard metadata fields to PDF/X-1a, you'll end up with a valid PDF/X-1a file; there is very little difference between those standards.

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Thanks, @David, for the clarification regarding PDF/X-1a. Indeed, I keep forgetting the letter "a" all the time. :) As to RGB vs. CMYK: Yes, I'm aware of the fact that it is perfectly fine to use CMYK spaces in PDF/X-3. As I see it, however, the possibility to use CIELAB and (managed) RGB is one of the main advantages of PDF/X-3, which is why I asked if that was possible.
Also, thanks, @David, for the confirmation regarding PDF/X-1a: So, am I correct in assuming that the files that are produced by the above procedure indeed are valid PDF/X-1a files? They seem to pass the validation... but is there anything that I need to pay attention to, when letting ghostscript handle the conversion?
Yes, as I said there are potential input colour spaces which will not be converted to a valid PDF/X-1a colour space but instead will be preserved unchanged. This will leave the file as a valid PDF/X-3 file, but not a valid PDF/X-1a file.
Unless you have a method that guaranteed produces PDF/X files or throws an error if it can't, or unless you have ironclad control over the PDF generation process, you're really only sure that a PDF file is PDF/X compliant if it passes a preflight check (such as the one you've already done using the Acrobat Preflight plug-in).
@DavidvanDriessche: So it is important to add the letter a to the digit 1 when talking about a certain standard. But you can even skip the digit after the /X- with impunity?!? [Never mind, David -- just kidding...] :-)
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