FTA’s Fall Conference 2022—themed “The Future Is Here”—included several speakers discussing optimization, trialing several ways of calibrating plate making workflows, and incorporating spot color tone values (SCTV) to manage process control.
All workflows were based off International Organization for Standardization (ISO) 10128 – Methods of Adjustment of the Color Reproduction of a Printing System to Match a Set of Characterization Data.
Using Flexographic Image Reproduction Specifications & Tolerances (FIRST) methodology for optimization, fingerprinting and characterization, the project team optimized a narrow web flexographic press. The optimization process was performed to include new anilox roll technology and required adjusting the inks to align with solid hue angles defined in ISO 15339 – Characterized Referenced Printing Conditions (CRPC)-6 and General Requirements for Applications in Commercial Offset Lithography (GRACoL 2013).
The optimization was performed to select a new anilox roll technology. Goals for the banded test were to determine the ideal volume, to align to CRPC-6. The solid inks were addressed according to CIE Lab requirements for CRPC-6. Then, to select the band providing the optimal levels of gray, SCTV (ISO 20654) was used to identify the ideal LPI and volume. Using linear SCTV for a baseline adds approximately 12 percent tone level to the total press range calibration. SCTV is very similar to Murray-Davies for cyan and magenta; but extends the levels of gray for the yellow and black. The printer selected Harper Corporation of America’s new X-CAT 1200/1.85 anilox rolls. Due to the changes in anilox roll volumes, inks were slightly adjusted, to eliminate hooking in the magenta (see Figure 1).
After optimization, we were able to combine the fingerprint and characterization target into one pressrun, printing an IT8.7/5 target and a P2P target (Figure 2). The PressCal software was used with the measured data from the IT8.7/5 chart, and we were able to develop the four sets of press curves usually calculated at the fingerprint stage, then apply them to the averaged characterization data and derive final print results.
The press form (Figure 3) developed utilizing all the methods of file conversion in ISO 10128 – Tone Value Increase (TVI), SCTV, Near Neutral Calibration (NNC – G7) and Color Management System (CMS) using curves created by The Optimal Method. We also used CMS to profile and create proofs. The images showed neutrals, high-key and low-key color area. Tonal ramps were also included, as was an Idealliance ISO 12647-7—“Process Control for the Production of Halftone Color Separations, Proof and Production Prints”—proofing control bar for measuring results.
Project Details
The aim ISO 15339 CRPC-6 dataset was adjusted to align the aim to CRPC-6 with the correct substrate for proofing and for the reference profile used in the PressCal software. CRPC-6 has a CIE Lab white point of 94, 1, -4, the Biaxially Oriented Polypropylene (BOPP) films used in this test had a white point of CIE Lab 93 ,-.77, .17. CGATS 21 Computation Spreadsheet can be downloaded here.
A Reference Dataset was created by measuring 10 of the printed IT8.7/5. sheets We tested a couple of software solutions for data smoothing: PressCal with simple median averaging, and Esko Color Pilot to smooth and remove outliers. Both methods rendered good results.
PressCal software was developed by Charles Spontelli and William Birkett, the color scientists that brought us CTV. PressCal is a coded application that runs on TextMate. PressCal can be downloaded here and TextMate can be downloaded here.
Using PressCal with the substrate corrected CRPC-6 as our reference, and the averaged data as our press sample, we created Photoshop curves for soft proofing, ISO 18620 curves for plate making, and a curve corrected IT8.7/5 for all four workflows.
FIRST plate making target, test relief, and micro-enlargement of the scales were deployed to assure the proper curves had been applied. Using the FTA plate making target in all four corners of the plate. After imaging, the first two targets were removed to verify the imaging process was under control. After plate processing, the second scales were checked to verify proper plate processing. Using the plate mounter to verify plate side-to-side measurement, per ISO 12647-6:2020 Part 6: Flexographic Printing, our fingerprint was printed to aim at flexographic hue angles and kiss impression settings. All the metrics were recorded in the Flexo Operating Data Sheet (found in the FIRST Extras download folder).
Fingerprint elements were typical—line and text thickness, highlight vignettes, tint scales, P2P51 and the new IT8.7/5. Very slight adjustments were made to the inks to match our original aims. Slight adjustments had to be made to ink densities using the new anilox roll volume, and a slight change to the magenta, as the thicker ink film in the XCAT rolls needed to be deeper blue to align to CRPC-6. All data was recorded on the FIRST Press Operator Datasheet to replicate on subsequent runs (see Figure 4).
With the optimized plate package and a characterization dataset of the press performance, we were able to calculate several workflows.
Evaluating Workflows
- ISO TVI: Murray-Davies is the method of calculating TVI we have used for over 80 years. As SCTV testing was conducted, we learned that much of the banding we have experienced in halftones was created using this method. Densities over 1.4 and under 1.1 do not show uniform tint ramps. CRPC-6 has 16 percent TVI in all four colors. Curves calculated use only 54 patches in the dataset. The TVI curves generated aligned with the 16 percent curve in the reference data
- SCTV: SCTV is recommended in ISO 12647-6 for Spot Colors and other colors if you must use a TVI curve. In this project we used SCTV in one quadrant of the verification and for all process control scales. This enabled the press operator to aim for a 50 percent at the 50 percent, and a 10 percent at the 10 percent
- Near Neutral Calibration (NNC): G7 uses 50 patches to align the neutrals on the print to match the neutrals of the reference dataset. It only affects the neutral ramp and the black ramp. All of the ISO 15339 datasets are G7 calibrated, so NNC has seemed Ideal for matching one of the CRPCs
- The Optimal Method: The Optimal Method uses ICC color management to create curves. It is an iterative process that first, eliminates noise by removing unneeded patches. Out of the 1617 patches in the IT8.7/5, we used only 988 patches. Next the Optimal Method uses triangulation to iterate the curve with the lowest Delta E to the reference dataset. For this Fall Conference’s print project, the Optimal Method did 175 iterations, to derive the optimal curves incorporating color management and rendering very smooth plate curves
- Traditional ICC Color Management: This was used to create the aim dataset, the digital proof, and for soft proofing
Our verification target also included the three-row ISO proofing control target, and a variety of images with different tonal dynamic ranges to verify visual results in our test. Process control and running scales (to be calibrated to SCTV curves) were applied to all process control elements—seems like a very simple solution to get operators to measure, with the proper SCTV curves applied, it simplifies the press operator’s job and eliminates confusion during production.
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