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Author Topic: blue shift in PDF/X-3  (Read 4117 times)

mbod

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blue shift in PDF/X-3
« on: October 06, 2011, 08:25:18 am »
Hello,

I am using Scribus 1.4.0rc3 on Debian Linux. When I export to PDF/X-3 the resulting PDF document is a little too blue. The monitor view in Scribus with sRGB profile shows correct colors. In fact, the colors look the same in different applications (scribus, gwenview, rawtherapee)

I export to PDF/X-3 with profile "ISO Coated v2 300%". In the PDF the blue color is a little too enhanced (see attachment as example). I can see it in the PDF viewer and when printing the photobook via www.viaprinto.de I see the same blue shift in the print.

How can I correct this slight blue shift? I tried almost all available PDF/X-3 export profiles but it makes absolutly no difference. The PDF always looks exactly(!) the same.

Thank you for your help,
Matthias

Nermander

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Re: blue shift in PDF/X-3
« Reply #1 on: October 06, 2011, 08:51:47 am »
That is kind of the point with PDF/X-3: It does NOT convert colors, it just includes the profiles and leaves the color management to the printer.

So, i'd say that it is your computer (or more likely monitor) that lacks correct color calibration.

mbod

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Re: blue shift in PDF/X-3
« Reply #2 on: October 06, 2011, 08:57:49 am »
and why does the PDF on the montior show the same colors as the printed PDF? If the monitor colors would be off, I would see a difference to the printed PDF. Right?

But in my case: monitor PDF = printed PDF

That tells me, that the color calibration of the monitor is not the problem.

And in any case I would expect  that the PDF viewed on the same monitor looks the same as the Scribus original document. But that is not the case. Why do I see a color shift going from SLA to PDF?

Matthias
« Last Edit: October 06, 2011, 09:12:23 am by mbod »

mbod

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Re: blue shift in PDF/X-3
« Reply #3 on: October 06, 2011, 09:03:10 am »
And I want to add one more:

If I turn off color management and export as PDF 1.3 or 1.5, the resulting PDF shows the correct colors.
See screenshot.

Why is that?

Matthias

Nermander

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Re: blue shift in PDF/X-3
« Reply #4 on: October 06, 2011, 10:09:01 am »
Color management is a very complex thing, if you don't understand what is happening then you don't understand color management.

And if you don't understand color management, don't use PDF/X-3, because it genereally assumes that you have set color profiles for your images and have a correct output profile.

I don't use PDF/X-3 because I know enough about color management to understand that I know to little about color management...

mbod

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Re: blue shift in PDF/X-3
« Reply #5 on: October 06, 2011, 11:04:50 am »
Hi Nermander,

I am surprised about the tone in your reply. What is wrong with my question?
And, yes, I do not understand the color management in scribus and PDF/X-3, PDF 1.5. Thats why I am asking the question in the first place. This is what this forum is all about, right? Why do you reply if you do not want to give an answer? That makes no sense.

By the way, I am using PDF/X-3 because that is the recommended format from www. viaprinto.de.

Is anybody else in this forum who can explain my findings and tell me how to best solve the issue?

Matthias

Nermander

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Re: blue shift in PDF/X-3
« Reply #6 on: October 06, 2011, 01:10:05 pm »
The point is that if you don't know color management you shall not use PDF/X-3.

If PDF 1.5 gives you the correct colors, why don't you use it?

If your printer requires you to use PDF/X-3 you will have to learn color management and calibrate your workflow. Expect to spend a few weeks to learn it. I have spent maybe 20-30 hours trying to learn it and know enough to know I shouldn't be using it:)


You can not expect to get a 200+ pages explanation on color management in a forum.

Here are a few links to start with (found by googling for "color management introduction"). Scribus does not work differently to other applications, color management is always color management.

http://www.normankoren.com/color_management.html
http://www.drycreekphoto.com/Learn/color_management.htm
http://www.northlight-images.co.uk/article_pages/CM_intro.html
http://www.blurb.com/guides/color_management/intro
http://www.booksmartstudio.com/color_tutorial/


a.l.e

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Re: blue shift in PDF/X-3
« Reply #7 on: October 06, 2011, 02:33:20 pm »
matthias,

i think that you should carefully read what nermander is telling you.

personally, what i understand is:
- while you're working in scribus you're using color management
- while you're viewing a pdf 1.5 you're using color management (if you have created the PDF with CMS enabled and use a PDF viewer which supports it)
- while you're viewing a PDF/X-3 you're viewing the PDF without color management (and this per definition of PDF/X-3) except if you do everything 100% correct
- it's hard to do everything correctly with PDF/X-3 and you need to invest much time to understand it

this imo explains why you're seeing a blue shift.

mbod

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Re: blue shift in PDF/X-3
« Reply #8 on: October 06, 2011, 03:31:15 pm »
I understand all your and Nermanders points. Color Management is difficult. And I should not use it or even ask until I have a deep understanding of everything. Well, I thought it is part of the exercise of learning to ask questions ;-)

Anyhow, just three quick question you might be able to answer:

In Scribus I create PDF 1.5 without Color Management and I create PDF/X-3 with Color Management (sRGB for Monitor and pictures, ISO Coated v2 300% for printer.

1) The PDF/X-3 looks blue-ish on the screen, the PDF 1.5 does not and has the correct colors. Why if Color Management in Scribus for PDF 1.5 was disabled?

2) If the blue tilt of the PDF/X-3 is a result of Color Management, why is it not affected by different output profiles?

3) From Nermander I understand that the output profile does not change the colors. He says: "It does NOT convert colors". But why is the PDF blue-ish then while PDF 1.5 is correct?

Matthias

« Last Edit: October 06, 2011, 08:17:10 pm by mbod »

a.l.e

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Re: blue shift in PDF/X-3
« Reply #9 on: October 06, 2011, 09:12:03 pm »
because with 1.5 the colors are corrected by your computer and with pdf/x-3 not.

please, you've been told to acquire a deep understanding of CMS *before* you can even think about solve this issue.

you've got a list of link by nermander: go through them. go further. and then you will be ready to ask new questions.

until now, all people in here can tell you is: it's correct that way.

and i tell you this, without knowing anything about CMS! (or very little...). i just explain you what you have been told to do until now!

ciao
a.l.e

Nermander

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Re: blue shift in PDF/X-3
« Reply #10 on: October 07, 2011, 08:48:32 am »
1) The PDF/X-3 looks blue-ish on the screen, the PDF 1.5 does not and has the correct colors. Why if Color Management in Scribus for PDF 1.5 was disabled?
This is really easy to explain: Your images don't have any colors. The pixels in your images just have numbers. It is up to your application, operating system and graphics or printer driver to "decide" what color you will see on screen/paper.

Color management is about mapping those numbers to acheive the correct colors. For a monitor it is done by adjusting the amounts of red, green and blue in each pixel, but note that if the image has a pixel with RGB value 127,127,127 your graphics driver and monitor might NOT use "half of each color". There is still a conversion done by the graphics card.

That is where profiling comes in, when you create a profile for your monitor you find out what color a given number results in. Then you will ba able to know what number to use for a certain color.

Quote
2) If the blue tilt of the PDF/X-3 is a result of Color Management, why is it not affected by different output profiles?
It would be, if you did not use PDF/X-3. The point with X-3 is that it does no conversion, it includes the profile instead.

You can enable color management for PDF 1.5 and export "for Printer", then you will get a CMYK PDF using the target profile. Changing profile will change the PDF.

I think that also answers your question number 3. The profile changes the color when it is used. For PDF/X-3 it is not used but embedded.