At the recently concluded PIA Color Management Conference in Scottsdale AZ, Dov Isaacs, Principal Scientist with Adobe Systems, reviewed where we are and where we've been with PDF workflows…
A Brief History Lesson in PostScript
It started all the way back to 1984 with the introduction of PostScript. PostScript V1 had an opaque imaging model with no support for any color management. Device RGB to device CMYK conversions were problematic. But PostScript was the first real industry standard vs. vendor specific page description language, and was the first real step towards device independence.
Adobe PostScript Level 2 was developed in 1990. It featured official CMYK support, but RGB to CMYK conversions were still a problem. It provided CIE-based color space support with device Color Rendering Dictionaries.
Adobe PostScript Level 3 was developed in 1997 with products shipping in 1998. While it included more color features like color rendering intent support for ICC color management compatibility, it had very poor application print driver and OEM support. It was doomed by emerging ICC color management standards, and became increasingly irrelevant for color managed workflows.
"The Father of PostScript" as he is known, John Warnock founded Adobe with Charles Geschke in 1982.
In the spring of 1991, Dr. John Warnock, co-founder of Adobe Systems (Adobe was named after the creek that ran past Warnock's garden in Los Altos California), recognized that the strengths of PostScript for publishing were in fact a weakness of PostScript as a medium for communicating visual material between different computer systems and rapidly accessing, displaying, and printing on any typical desktop system. So he published a paper called The Camelot Project which described a new language he called "Interchange Postscript". The Camelot Project became The Carousel Project that eventually yielded PDF and Acrobat in 1993.
The Camelot Project, published in 1991 by Adobe co founder Dr. John Warnock, would serve as the original concept behind Acrobat and the PDF standard we know today.
Each release of Acrobat and PDF included more support for color. By late 2000, Acrobat, Illustrator, InDesign and Photoshop supported full ICC color management and live transparency per PDF 1.4.
With the release of Adobe PDF 1.7 in 2008, the PDF specification became an ISO standard - ISO PDF 32000-1. Implementation began with Acrobat 9 and some third party applications.
Currently under development is ISO PDF 32000-2, which is expected to be approved and published in late 2013 as PDF 2.0. Features of PDF 2.0 are to include:
- Formal support for extensions already being incorporated into PDF/UA and PDF/VT standards
- Spot color enhancements
- Per-page output intents
- Overprint handling
- Black point compensation
What is PDF/X?
PDF/X is a family of graphic technology standards that standardize the use of the PDF for eXchange of print-ready material.
- PDF/X identifies a subset of PDF objects that may be used with restrictions to the use, or form of use, of those objects and/or keys within those objects.
- Goal - If a sender and receiver of data file use applications that conform to the same PDF/X specification, then the received file will print exactly ad the sender intended - No surprises!
- PDF/X was developed by ANSI CGATS (Committee for Graphic Arts Technologies Standards) and ISO/TC 130
- Complete exchange of CMYK and spot color data - no live transparency
- Provides for either embedding of output intent ICC profile or naming an output condition
- Supported by Adobe CS applications and Acrobat, and virtually all PDF workflow and prepress software
- Very reliable when the generator of the PDF file knows the exact final printing conditions
- Considered to be the de facto professional printing standard
Problems with PDF/X-1a
- If the original content uses live transparency
- If the generator of the PDF file does not know the exact final printing conditions
- If the print service provider needs the ability to retarget the PDF file for differing print conditions
PDF/X-1a:2003 is an updated version of PDF/X-1a-2001 based on PDF 1.4 but without any support for live transparency. It was virtually ignored by the printing industry.
- Complete exchange (blind exchange) of CMYK, spot color and color managed data
- Adds support for live transparency
- Improved compression" JPEG2000 and compressed XRefs and Streams
- Adds support for PDF layers
- Requires the embedding of an output intent ICC profile
- The next generation de facto professional printing standard
PDF/X-4:2010 with support for additional features via three conformance levels:
- PDF/X-5n:2010 provides n-color output support
- PDF/X-5g-2010 provides support of external graphics via use of Reference XObjects
- PDF/X-5pg:2010 adds a URL which is used to point to the output intent of an ICC profile
The Adobe chart above lists the different flavors of PostScript and PDF/X along with the different features of each.
The Ghent PDF Workgroup was founded in 2002 by European print associations under Enfocus' sponsorship. It has been expanded to include participation of worldwide vendors, publishers, and academic institutions. Their primary focus is on the development of PDF/X standards, application and preflight settings; product certification, and education.
- Adobe Acrobat XI Pro fully supports the latest GWG 2012 PDF/X Plus standard within its preflight profiles
- Adobe is a member and active participant in the Ghent PDF Workgroup, however they do not endorse the use of current Ghent PDF Workgroup standards due to the total lack of support of color management (i.e., support of only DeviceCMYK and spot colors)
Adobe Summary and Recommendations:
- Due to lack of support for ICC color management and live transparency, PostScript is strongly not recommended for graphic arts workflows
- For low-end PostScript devices and RIPs that do not have true direct PDF consumption, print PDF/X-4 files from Acrobat Pro, carefully selecting "advance options" associated with flattening and spot colors
PDF 1.4 is the minimal PDF version that supports ICC color management and live transparency
- PDF/X-4 is recommended for reliable PDF print publishing workflows with blind exchange (exchange of a PDF file with little or no technical discussion)
- PDF/X-4p and the PDF/X-5 variants are recommended of reliable PDF print publishing workflows with "special needs"
Maintain content at it's highest level of abstraction until rendering (late binding workflow)
- Maintain original color spaces with profiles; don't prematurely convert
- Don't flatten transparency
- Don't outline text
- Don't rasterize either text or vector objects
PDF File Creation
- Avoid PDF creation via distillation of PostScript when at all possible
- Use "PDF Export" or Save as PDF" with Adobe InDesign or Adobe Illustrator using the PDF/X-4:2010 job options
- Do not do any color conversions or transparency flattening as part of the PDF creation process