PSO vs GRACol 7

PSO (Print Standard Offset-print) and GRACol7 are industry guidelines based on the solid patch colour aims of the International Printing Process Standard ISO 12647-2:2007. In this article Yves Roussange discusses the differences and similarities between both sets of guidelines, based on the processes and methodologies used to achieve the ISO 12647-2:2007 standard.

PSO (Print Standard Offset-print) and GRACol 7 use and interpret the ISO 12647-2:2007 standard in different ways. The key is not to ask which one is better, but instead how each process, in a particular situation and to suit the specific requirements of a printing workflow, can be implemented in the optimal way.

Company culture, internal expertise, the market, the age of the press, the technology in place and of course the motivation of the people in the printing organisation are key factors when deciding which methodology to utilise.

What is Print Standard Offset-print (PSO)?
Print Standard Offset-print, or PSO, was created for BVDM (German Printing and Media Industries Federation, www.bvdm-online.de) by Fogra, the Graphic Technology Research Association based in Munich, for implementation in the German printing industry. It is based on the printing process standard ISO 12647-2:2007 specifications. PSO strictly follows the specifications defined in ISO 12647-2:2007 and complements them with some more rules, especially for digital proofing and for the priority of the mid-tone colour in cases of conflict with the colour of the solids. A detailed manual describing all PSO procedures has been published and an impressive number of supportive tools has been made available. For proofing see the free Mediastandard Print 2006 publication at www.bvdm-online.de and the Altona test form, www.eci.org.

Three years ago BVDM and Fogra started a certification programme for printers and prepress providers, where an enterprise can go through an auditing process that tests their ability to work within the procedures and tolerances of ISO 12647-2. If successful, the firm is awarded a certification label that gives its business partners some degree of confidence that the rules are understood and followed, and that there will be fewer unpleasant surprises regarding the consistency of proofs between vendors and between the proof and the production print.

This process is based on controlling and certifying a print job, in the same way that you control proofs made with the ISOcoated-v2 profile. The printer will receive a report that includes the L*a*b values of the primary and secondary colours and the dot gain.

The essential specifications of PSO/ISO 12647-2 are as follows (abridged):

L*a*b* value of primaries, secondary colours and paper white need to be within the lower tolerance of ISO 12647-2:2006. The compliance to these values is greatly facilitated if the inks conform to ISO 2846-1;

Dot gain value or TVI: 50% dot = 14% dot gain, within tolerance of ñ4% but with a tone value spread in the mid-tone not to exceed 4%. This applies to coated stock of 115gsm and conditions where it is to work in a mixed workflow with positive film/platemaking. ISO and PSO provide higher values for mixed workflows with negative film. PSO emphasises the priority of the mid-tone compliance over the solid;

Recommended grey balance for control strips: Cyan 50% - Magenta 40% - Yellow 40%.

PSO is a complete commitment to the specification of the offset process standard ISO 12647-2.

What is GRACol 7?
GRACol 7 (General Requirements and Applications for Commercial Offset Lithography, see www.gracol.org), is a trade association guideline for offset sheetfed printing.

GRACol is evolving - the latest beta-version release (release 7) was published in April, 2006. GRACol 7 defines one of several possible interpretations of the intended appearance of a press sheet, printed according to the ISO 12647-2 international printing standard.

"Neutral Print Density Curve", or NPDC, is the central concept of GRACol 7. NPDC is the relationship between measured neutral density and original cyan tone values on a grey scale, based on neutral grey of C 50, M 40, Y 40, that is specified to be equal in density to a K 55 patch.

In terms of the inks and the colours of the solids, GRACol 7 follows ISO 12647-2 exactly. Where it differs is the method used for adjusting the mid-tones. Whereas the PSO would advise to adjust the inking until the TVIs of CMY come close to their aims, GRACol 7 would request that the neutral densities of the CMY and the K grey patches should be brought close to the prescribed aim value for both, regardless of the individual TVIs that result. In practice this means each colour will have a different TVI curve to achieve the neutral grey.

However, to ensure consistent appearance between sites, it is more important that the ink solids measure on the stock as closely as possible to the solid values defined in ISO 12647-2. GRACol 7 allows for deviation of primaries in order to obtain grey balance.

The GRACol 7 specifications are as follows:

Ink specification to ISO 2846-1;

L*a*b value of primaries, secondary colours and paper white within the specification of ISO 12647-2, but allows deviation of primaries in order to obtain grey balance;

Neutral density 0.54 for both the CMY and the K grey patches, approximately equivalent to TVIs of 15% for CMY and 22% for K, both at 50% data tone value;

Grey balance: Cyan 50% - Magenta 40% - Yellow 40%.

GRACol 7 is based on printing a neutral grey by adjusting the CtP and press within an acceptable deviation of the ink.

PSO vs GRACol 7 in practice
Practical printing tests have shown that the differences between the PSO and the GRACol 7 methods are very slight. Both PSO and GRACol 7 teach that mid-tone colours are more important than those of the solids. In cases where the mid-tones are not automatically correct after the solids have been brought into compliance, the solids should be adjusted to move the mid-tones into compliance.

After having a close look at the two processes in place, as well as the position of the Australian printing industry with its cultural and climate condition, I created Print Process Standard (PPS). Print Process Standard is the optimal solution to give the Australian printer the chance to achieve the top target of PSO and still be able to achieve GRACol 7 using ISO 12647-2 process standard, including the Australian specification.

Using the expertise I have accumulated in the past when creating the SICOGIF printing standard, and to get the "best of both worlds" solution, I created Print Process Standard (PPS) as the definitive test form and process. PPS includes all PSO specifications, a base grey balance approval, a visual appreciation, complete measurement certification of the primaries, complementary colours and the dot gain compared to the ISO 12647-2:2007 standard, as well as a 3D profile definition of the press for non-standard paper.

PPS will give the printer the understanding of his press reproduction capacity in relation to the ISOCoated-v2 standard. The target will be first to achieve ISO 12647-2:2007 by the book using PSO. Even if, with the current ink set, the printer cannot achieve PSO, the press calibration will be able to achieve the neutral grey required for GRACol 7 and the tolerance to the ISO 12647-2:2007 standard.

Because PSO and GRACol 7 press processes are both within in the specification of ISO 12647-2:2007, the printer will have no problem reproducing any client supplied ISOCoated-v2 proof within the tolerance.

PSO/Fogra certification
Yves Roussange is the first Partner outside Europe of Fogra providing onsite support for the certification according to Process Standard Offset (ISO 12647-2). The certification to PSO/Fogra will be made by the BVDM and Fogra independent expert committee and is granted for two years.

PSO/Fogra certification will give printers the confidence that they are achieving the optimal quality target. Their clients and prospective clients can be guaranteed printing results of the highest quality. More and more large German firms (automotive manufacturers, banks, pharmaceutical and industrial companies) now require that all of their print suppliers be PSO/Fogra certified. For them this offers a guarantee of good practice and quality.

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