A Comparison of Delta E 2000 of Brand Spot Colors with Digimarc Enhancement for Recycling

Hypothesis One

First, Hypothesis One was rejected because not all recorded Delta E 2000 values were within the range 0-3. This ideal range was set because this amount of variation is generally accepted by CPCs. Looking at Figure 1, one can see that the Spot Direct and Positive Binary measurements fell within the accepted range; however, the Black Overprint and Negative Binary did not.

Figure 1: Delta E 2000 measurement for 100 percent density patch
All data courtesy of Alice Ish

The range of Delta E 2000 values for the Black Overprint for the 100 percent patch for all spot colors except for Black and Green, which did not receive the encoding treatment, was 1.4-3.31. With these values falling partially in the accepted range, it’s probable that, with some alterations of dot size and ink density, this enhancement could produce more acceptable Delta E 2000 values. However, it should be noted that this enhancement becomes much more visible when screens of the spot color are used.

This trend can be seen in Figure 2, Figure 3 and Figure 4: the Delta E 2000 value is within or close to the target range at 100 percent solid, but as the patch reaches a 25 percent screen, the Delta E 2000 values move out of acceptable range. Figure 4 demonstrates how a darker color can decrease the impact of a lower value screen on the Black Overprint enhancement.

Figure 2: Pantone 185 Delta E 2000 measurement as patch density decreases

The Negative Binary enhancement was the least successful treatment based on the resulting Delta E 2000 values. The range of values produced was 8.51-25.72. Producing Delta E 2000 values far from the acceptable range makes this enhancement an impractical choice as it was done in this study.

Figure 3: Pantone 123 Delta E 2000 measurement as patch density decreases

Hypothesis Two

Second, Hypothesis Two was accepted as the Spot Direct technique produced a lower Delta E 2000 value than the Positive Binary and Negative Binary techniques. The range of Delta E 2000 values produced by the Spot Direct enhancement were 0.1-1.93 for the solid patch. With a calculated average value of 0.60, these values are very acceptable. The range of values produced by the Positive Binary enhancement were 0.62-0.9 or for an average value of 0.76. These data points show that while the Spot Direct enhancement produced a lower average value, the difference in range was minimal, making these enhancements comparable.

Figure 4: Pantone 286 Delta E 2000 measurement as patch density decreases

As stated previously, the Negative Binary Delta E 2000 values were not within an acceptable range. When looking at the change in Delta E 2000 values for the Spot Direct and Positive Binary techniques in Figure 2, Figure 3 and Figure 4, one can see that the values for both stayed within range across the four screen values. Interestingly, in the darkest color, Pantone 286 C, the Spot Direct saw a downward trend in Delta E 2000. This means that it produced less color difference from the L*a*b* values, as the spot color was printed with a lighter screen.

Hypothesis Three

Third, Hypothesis Three that the Black Overprint Digimarc technique will produce a lower Delta E 2000 value than the Positive Binary and Negative Binary Digimarc techniques was rejected. The Black Overprint produced lower values than the Negative Binary enhancement, but not lower than the Positive Binary enhancement. The average Delta E 2000 value for the 100 percent solid patch for the Black Overprint was 3.31. In comparison, the average Delta E 2000 value for the 100 percent density patch for the Positive Binary was 0.76. The translucency for the Pantone 9120 and the Pantone 9520 dots had much less effect on the Delta E 2000 value than the addition of black dots on top of the spot color.

It should be noted that both the Black Overprint and Positive Binary are not applicable in darker spot colors like the Pantone Black and Pantone Green used in this study. This will affect what applications these techniques can be used in. Lastly, Figure 2, Figure 3 and Figure 4 show that the Positive Binary enhancement stayed consistently lower that the Black Overprint across the four patch densities, except for Pantone 286, which saw more variation between the two.

Hypothesis Four

Fourth, Hypothesis Four that all enhancements methods will produce a robustness score greater than 60 was rejected. From examining the data, it can be concluded that most of these enhancements need additional research to improve robustness, particularly in spot direct and positive binary. I will address next steps to improve robustness.

Figure 5: Verify Report Pantone 185 Positive Binary Enhancement

The most robust enhancement was the Black Overprint with a range of scores of 79-85. These scores are very promising and make the Black Overprint enhancement the only treatment with sufficient robustness to be applied to recycling scanning immediately. However, the Black Overprint was visually visible and did not produce the lowest Delta E 2000 values. The average robustness scores for the other techniques are as follows: Positive Binary – 37.5, Spot Direct – 39.9 and Negative Binary – 52.75. Figure 5, Figure 6 and Figure 7 show how many bar codes the scanner was able to pick up for Pantone 185. The greater the bar codes being recognized, the darker the blue color of the graphic. One can see that in comparison, many more bar codes were able to be seen on the Black Overprint target than either the Spot Direct or the Positive Binary targets.

Conclusion & Future Projects

For future applications, the robustness of the Spot Direct and Positive Binary techniques needs to be improved. The ink color selected in Positive Binary was likely too light. The next step for research is to add additional pigment to the Pantone 2747 and Pantone 7467 inks to increase contrast, since the Delta E 2000 impact for positive binary had sufficient room to increase contrast without going over the 3.0 target.

Figure 6: Verify Report Pantone 185 Black Overprint Enhancement

Overall, looking only at the Delta E 2000 values produced during this study, the Spot Direct enhancement produced the most promising results across all spot colors and screen tints. Another positive about this enhancement is that it was able to be used on all spot colors and does not require an additional ink on press, making it the least complex to integrate into existing CPC workflows. The Positive Binary enhancement also produced promising results for not affecting the spot color visually. This enhancement does require an additional ink and cannot be applied to dark spot colors, such as Pantone Black and Pantone Green. If these techniques were being evaluated solely on robustness, the most effective technique would be the Black Overprint Enhancement.

Figure 7: Verify Report Pantone 185 Spot Direct Enhancement

Future iterations of this project should focus on making bar codes that are robust for recycling while balancing the effect this will have on the resulting Delta E 2000 value. As the most robust technique, the Black Overprint should be altered to produce lower Delta E 2000 values. This could be done by making the black ink being overprinted less pigmented and therefore less visible. The Positive Binary Technique produced low Delta E 2000 values but was not robust enough for recycling. This could be remedied by increasing the pigmentation in the ink being overprinted. The challenge of future projects will be increasing robustness without producing Delta E 2000 values outside of the acceptable range as a result.

Acknowledgements

This project could not have been completed without the support of Rossini North America and the FFTA Rossini North America Flexographic Research Scholarship, as well as the Cal Poly Graphic Communication Department, Digimarc and MacDermid Graphics Solutions. My advisor, Malcolm Keif, devoted countless hours helping me to prepare files and operate the Mark Andy press. Digimarc lent not only its technology but also services in helping to select Digimarc Enhancement techniques, the encoding that needed to go into making the files and expertise in understanding wavelength reflection of different ink colors.

I’d like to give a special thanks to Jay Sperry and Kristyn Falkenstern. MacDermid lent its services in plate making; for this I’d like to give thanks to Becky Bunch. I’d also like to thank Multiplastics for donating a roll of film and INX International Ink Co for formulating the needed spot colors to help this project happen. Other thanks are extended to Mark Andy, Harper Corporation of America and Techkon. Everyone involved in supporting this project helped to make it possible and have given me an invaluable learning experience.

References

Reed, A., Falkenstern, K., & Hattenberger, E. (2017). Selecting Best Ink Color for Sparse Watermark. Society for Imaging Science and Technology, 130-136. https://doi.org/10.2352/ISSN.2470-1173.2017.18.COLOR-045

Reed, A., Kitanovski, V., Falkenstern, K., & Pederson, M. (2022). Using watermark visibility measurements to select an optimized pair of spot colors for use in a binary watermark. Society for Imaging Science and Technology, 197-1-197-6. https://doi.org/10.2352/ISSN.2470-1173.2020.15.COLOR-197

About the Author

Alice Ish is a fourth-year student at California Polytechnic State University, San Luis Obispo. She is a graphic communication major concentrating in Design Reproduction Technology with a minor in Packaging. She is originally from Seattle, Washington, but came to Cal Poly for its amazing hands-on learning program. She has enjoyed her time getting to work with presses as an offset lab assistant and through her FFTA Rossini North America Flexographic Research Scholarship project. Alice is excited to start working in the industry when she graduates in the spring!

Tagged California Polytechnic State University, Digimarc, Harper Corporation of America, INX International Ink Co, MacDermid Graphics Solutions, Mark Andy, Multiplastics, Procter & Gamble, Rossini North America, Techkon