No compromises
Quality Assurance: To ensure that all parties involved in a printing process can guarantee high quality, a certain degree of standardization is required—this can be summarized in five steps.
Quality assurance In order for all parties involved in a printing process to guarantee a high level of quality, a certain degree of standardization is required - this can be summarized in five stages: the increasing automation of processes in agencies, premedia/prepress, printing and processing/finishing as well as the ever closer networking of these areas require an increasing number of workflow components and procedures with which all relevant process variables can be reliably mapped and controlled. Nothing can be left to chance any more, because small errors and omissions can have a fatal effect on the final quality. Everyone must be able to rely on the quality care of the predecessor in the workflow: No compromises on quality! Don't just cut corners when it comes to price, but make a name for yourself with customers by taking care. With greater awareness, you will be able to secure the really lucrative orders. It is therefore worth investing in quality management based on consistent standardization and assurance. Ultimately, this also results in considerable time and cost savings: no unnecessary correction loops, no reworking, no quality-related complaints. And the resulting satisfaction is priceless, as it strengthens customer relationships and brings in new customers through word of mouth.
Agencies and downstream service providers in the printing and packaging industry are now striving to standardize as many processes as possible. This not only allows the work results to be repeated exactly at any time, but also makes the processes more industrialized, i.e. automated as far as possible and thus frees them from subjective assessments and operating errors.
Stage 1: CalibrationCalibration means establishing basic settings, initial states and framework conditions on devices and machines that can be reproduced at any time. This means that the calibration status of the production environment or sub-processes must be recorded and regularly checked in order to ensure the validity of
existing characterization files (level 2) and to be able to reliably characterize new constellations (e.g. other materials). In an agency, quality assurance primarily concerns color management, i.e. monitors and proof printers have to be calibrated on a daily basis. At media service providers and prepress companies, film setters plus plate copying or platesetters are also involved. And in a print shop, the technical specifications such as printing tension, standard inking and dampening, register accuracy, etc. must be met on the machines.
To check the calibration status of a monitor, a colorimeter is required - a measuring head that verifies the required white point of 5000 Kelvin in normal operating mode or under the effect of a monitor profile. There are also monitors that - like scanners and digital cameras - calibrate themselves. The calibration status of a proof printer can be easily determined on a test printout by using a spectrophotometer or spectral densitometer to measure either the indispensable Ugra/Fogra media wedge or a greyscale wedge in the four process colors. The proof printer must achieve certain solid tone densities, the grayscale wedges must reproduce a linear tonal value percentage gradation.
Stage 2: Capturing sub-processesCharacterization means capturing the process variables responsible for tonal value and colour reproduction on calibrated devices and machines. A characterization result therefore represents not only individual parameters, but entire sub-processes in which the respective devices or machines are integrated. A proof printer is always characterized in conjunction with the publishing software from which it is printed.
Depending on the measurement purpose and method, two types of characterization files are created: Tonal value transfer characteristics and ICC profiles. Characteristic curves depict the tonal value transfer behavior between two sub-processes, e.g. between the RIP platesetter configuration and the printing press. Step wedges are evaluated, which are measured most reliably with a CCD plate measuring device on the printing plate and after printing with a densitometer on the paper. ICC profiles reflect the individual color reproduction behavior of a device in the sub-process. Special software (e.g. GretagMacbeth ProfileMaker, X-Rite Monaco), which compares the measured and target values, and suitable color measurement technology are required to create them.
Stage 3: StandardizationIt is crucial that standards apply within the company and that there is agreement between the partners on the standards used. Basically, it is advisable to work according to the ISO standard-oriented guidelines Media Standard Print and Process Standard Offset Print or, in the case of other printing processes, with the corresponding ISO standards. In agencies and prepress, this means creating and processing color management profiles in accordance with the ICC specification (International Color Consortium) and generating PDF data with PDF/X-3 Distiller settings where possible, or at least always with the same optimized settings. When it comes to color management, it makes sense to use the Altona Test Suite and, for PDF issues, Enfocus Certified PDF, the application-specific PDF/X settings of the Ghent PDF Workgroup or the recommendations of the PDFX-ready association. Of course, it is also legitimate to take into account the in-house standards of customers and partners.
Stage 4: Industrial productionOnly the application of the objective characterization files to the calibrated production environment together with continuous metrological process control ensures that the target values are controlled or corrected within the tolerances. This enables the transition to industrial production or automation.
For example, during tonal value transfer, only regular measurements are taken to determine whether the RIP imagesetter configuration is set to linear reproduction, so that the originally determined characteristic curve can be taken into account in the tonal value reproduction curve for image processing (TRC in Photoshop or implemented in the ICC profile). This compensates for the increase in tonal value during printing. Sheet-fed offset (low), heatset web offset (high) and newspaper printing (according to ISO = 26 percent) differ significantly in the dot gain values, which must be taken into account when preparing advertisements in the various print media.
Stage 5: Quality assuranceQuality assurance not only refers to the quality control of intermediate and end products, but also ensures compliance with calibration statuses, standard specifications, tolerances and specific requirements in all sub-processes and at all workstations in stages 1 to 4. Measurement and testing is therefore carried out at all times:
1. before the production process:
(incoming inspections on substrates, printing inks and - in the form of automatic inspection routines - on data, e.g. PDF preflights);
2. during production (offline, online or inline measurement of process variables);
3. after the end of production (complete or random final inspection).
It also checks parameters that are not anchored in one of the standards mentioned, such as the precision of folding and trimming.
In general, quality is required in all sub-processes. This is why quality assurance begins in the advertising agency.
Altona Test SuiteIntegrated in the Altona Test Suite are:
- 15 PDF files, specially developed for testing proof printers as well as conventional and digital printing systems;
- 16 numbered A3 reference prints and 7 coloring standards for offset and continuous printing;
- 6 characterization data and 6 ICC profiles according to DIN ISO 12647-2;
- 1 comprehensive documentation (PDF and printed).
The ISO 1264-2 (IT8.7/3) test form replaced the European Color Initiative with ECI 2002, whose 1485 measuring patches represent the entire color space better than before. Among other things, process, duplex and spot colors, overprinting as well as gradients and resolution limits are visually evaluated. The suite's PDF and color management files can be generated into test jobs that can be used to evaluate the compatibility of a composite PDF workflow with PDF/X-3.
Further information: www.altona testsuite.com, www.ugra.ch (dk)
ISO 12647 and 2846DIN ISO 12647 "Graphic arts - Process control for the production of halftone color separations, proofs, test prints and production runs" is the central international standard for all printing processes. The European scale (DIN 16539) is no longer the standard printing ink scale, but DIN ISO 2846 "Graphic arts - Color and process control".
Transparency of printing ink sets", which uses CIELAB data to identify the process colors and composite prints. (dk)
Dieter Kleeberg
Agencies and downstream service providers in the printing and packaging industry are now striving to standardize as many processes as possible. This not only allows the work results to be repeated exactly at any time, but also makes the processes more industrialized, i.e. automated as far as possible and thus frees them from subjective assessments and operating errors.
Stage 1: CalibrationCalibration means establishing basic settings, initial states and framework conditions on devices and machines that can be reproduced at any time. This means that the calibration status of the production environment or sub-processes must be recorded and regularly checked in order to ensure the validity of
existing characterization files (level 2) and to be able to reliably characterize new constellations (e.g. other materials). In an agency, quality assurance primarily concerns color management, i.e. monitors and proof printers have to be calibrated on a daily basis. At media service providers and prepress companies, film setters plus plate copying or platesetters are also involved. And in a print shop, the technical specifications such as printing tension, standard inking and dampening, register accuracy, etc. must be met on the machines.
To check the calibration status of a monitor, a colorimeter is required - a measuring head that verifies the required white point of 5000 Kelvin in normal operating mode or under the effect of a monitor profile. There are also monitors that - like scanners and digital cameras - calibrate themselves. The calibration status of a proof printer can be easily determined on a test printout by using a spectrophotometer or spectral densitometer to measure either the indispensable Ugra/Fogra media wedge or a greyscale wedge in the four process colors. The proof printer must achieve certain solid tone densities, the grayscale wedges must reproduce a linear tonal value percentage gradation.
Stage 2: Capturing sub-processesCharacterization means capturing the process variables responsible for tonal value and colour reproduction on calibrated devices and machines. A characterization result therefore represents not only individual parameters, but entire sub-processes in which the respective devices or machines are integrated. A proof printer is always characterized in conjunction with the publishing software from which it is printed.
Depending on the measurement purpose and method, two types of characterization files are created: Tonal value transfer characteristics and ICC profiles. Characteristic curves depict the tonal value transfer behavior between two sub-processes, e.g. between the RIP platesetter configuration and the printing press. Step wedges are evaluated, which are measured most reliably with a CCD plate measuring device on the printing plate and after printing with a densitometer on the paper. ICC profiles reflect the individual color reproduction behavior of a device in the sub-process. Special software (e.g. GretagMacbeth ProfileMaker, X-Rite Monaco), which compares the measured and target values, and suitable color measurement technology are required to create them.
Stage 3: StandardizationIt is crucial that standards apply within the company and that there is agreement between the partners on the standards used. Basically, it is advisable to work according to the ISO standard-oriented guidelines Media Standard Print and Process Standard Offset Print or, in the case of other printing processes, with the corresponding ISO standards. In agencies and prepress, this means creating and processing color management profiles in accordance with the ICC specification (International Color Consortium) and generating PDF data with PDF/X-3 Distiller settings where possible, or at least always with the same optimized settings. When it comes to color management, it makes sense to use the Altona Test Suite and, for PDF issues, Enfocus Certified PDF, the application-specific PDF/X settings of the Ghent PDF Workgroup or the recommendations of the PDFX-ready association. Of course, it is also legitimate to take into account the in-house standards of customers and partners.
Stage 4: Industrial productionOnly the application of the objective characterization files to the calibrated production environment together with continuous metrological process control ensures that the target values are controlled or corrected within the tolerances. This enables the transition to industrial production or automation.
For example, during tonal value transfer, only regular measurements are taken to determine whether the RIP imagesetter configuration is set to linear reproduction, so that the originally determined characteristic curve can be taken into account in the tonal value reproduction curve for image processing (TRC in Photoshop or implemented in the ICC profile). This compensates for the increase in tonal value during printing. Sheet-fed offset (low), heatset web offset (high) and newspaper printing (according to ISO = 26 percent) differ significantly in the dot gain values, which must be taken into account when preparing advertisements in the various print media.
Stage 5: Quality assuranceQuality assurance not only refers to the quality control of intermediate and end products, but also ensures compliance with calibration statuses, standard specifications, tolerances and specific requirements in all sub-processes and at all workstations in stages 1 to 4. Measurement and testing is therefore carried out at all times:
1. before the production process:
(incoming inspections on substrates, printing inks and - in the form of automatic inspection routines - on data, e.g. PDF preflights);
2. during production (offline, online or inline measurement of process variables);
3. after the end of production (complete or random final inspection).
It also checks parameters that are not anchored in one of the standards mentioned, such as the precision of folding and trimming.
In general, quality is required in all sub-processes. This is why quality assurance begins in the advertising agency.
Altona Test SuiteIntegrated in the Altona Test Suite are:
- 15 PDF files, specially developed for testing proof printers as well as conventional and digital printing systems;
- 16 numbered A3 reference prints and 7 coloring standards for offset and continuous printing;
- 6 characterization data and 6 ICC profiles according to DIN ISO 12647-2;
- 1 comprehensive documentation (PDF and printed).
The ISO 1264-2 (IT8.7/3) test form replaced the European Color Initiative with ECI 2002, whose 1485 measuring patches represent the entire color space better than before. Among other things, process, duplex and spot colors, overprinting as well as gradients and resolution limits are visually evaluated. The suite's PDF and color management files can be generated into test jobs that can be used to evaluate the compatibility of a composite PDF workflow with PDF/X-3.
Further information: www.altona testsuite.com, www.ugra.ch (dk)
ISO 12647 and 2846DIN ISO 12647 "Graphic arts - Process control for the production of halftone color separations, proofs, test prints and production runs" is the central international standard for all printing processes. The European scale (DIN 16539) is no longer the standard printing ink scale, but DIN ISO 2846 "Graphic arts - Color and process control".
Transparency of printing ink sets", which uses CIELAB data to identify the process colors and composite prints. (dk)
Dieter Kleeberg
