We used the average smoothed characterization data with the outlier removed to calculate curves for the plate using PressCal. We were not only able to create ISO curves aligning with CRPC-6, NNC (G7) curves, Optimal Method curves, and Linear SCTV curves, but also Adobe gradation curves for soft proofing our project before going to press. Characterization datasets with curves applied could be made into ICC profiles for proofing, and tone curves needed for plate making—ISO 18620:2016 Graphic Technology – Prepress Data eXchange – Tone Adjustment Curves Exchange.
We placed each of the curves on a quadrant of the plate file. Applying curves for The Optimal Method, NNC, ISO A curve and SCTV (see Figure 5).
We also added SCTV process control scales for the operators. This is a change for us. Rather than using the FIRST Printer Control Target, with printed numbers on each scale of what the results should print as, with SCTV 10 percent = 10 percent, 50 percent = 50 percent… no additional numbers were required—linear SCTV was the aim. Process control metrics used in the plate making included exposure test, relief, and micro-enlargement of the scales to assure the proper curves had been applied.
Going back to press, the operators set the press up using the FIRST Press Operating Data Sheet, and the press was run to the Fingerprint/Characterization aim points. Our findings:
- Using SCTV opens the dynamic range, giving us more levels or tone for each color, notably on the yellow and more so on the black
- Murray-Davies TVI, which most of the printing industry is currently using, shows the failures we have experienced for years
- G7 has a common appearance to multiple other printing types
- The Optimal Method combines ICC color management with smooth plate curves and seems to render the best of all workflows—but you be the judge!
Results In
Audience members polled live on site rendered the verdict:
- The Optimal Method at 81 percent—Best curves developed, closest match
- FIRST-Optimized Smoothed Press Data at 80 percent—Always optimizing gets you very close
- Near Neutral (G7) at 79 percent—The second-best appearance match
- SCTV at 77 percent—A great tool for process control and may increase our detail
- ISO TVI at 76 percent match—A poor visual match
Based off the samples, the data and visual appearance agree!
General Observations
Globally, SCTV is growing in usage for flexography and offset. Currently used for most spot colors, I believe we should be seeing new datasets using SCTV calibration as our aim from clients, several brands, as well as Graphic Technology Research Association (FOGRA) are developing that now. The ISO community is now adding CTV as a recommended method for controlling offset printing. This was added in the flexographic standard two years ago.
Throughout the testing of SCTV, during monthly calls and evaluating print samples from hundreds of tint ramps, we learned while comparing to Murray-Davies Tone Value that some of the errors we have had for 80-plus years were coming from our beloved Murray-Davies Tone Values. When densities were below a 1.10 or above a 1.40 American National Standards Institute (ANSI) T density, we were finding failures in the tone value calculation, resulting in inconsistent tone ramps (see Figure 6 and Figure 7).
As this work continued FOGRA did some testing and concluded that much of the banding we have seen in the three-quarter tones was caused by this failure.
As flexographers, this comes into play if we run densities below 1.2—meaning our yellow ink resulting in compression to the tonal scale. As we look at a standard black with an ANSI T density of 1.40 or above the banding in the black was also being compressed and showing banding where SCTV did not. After using this standard for spot colors in flexography, several colleagues tried SCTV for calibration for all colors on the fingerprint. Think about the following example—It appears we can gain 12 percent more gray levels using SCTV.
Compression Example:
- 70 percent black with Murray-Davies gains to 88 percent on press
- 70 percent with SCTV renders a 70 percent at the 70 percent
Utilizing FIRST methodology and ISO methodology, flexography is the best printing technology on the planet. We learned we can get a much better match today than we could with traditional TVI and SCTV, and it makes it easier for operators to control.
At the conclusion of Fall Conference, we asked the audience to be the judge. Responses to our polls showed they would consider using SCTV for process control and the majority preferred The Optimal Method’s results.
Going forward, we should repeat this test verifying results, we should develop a dataset using SCTV to create a flexographic reference—utilizing all levels of gray and increasing our resolution.
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