This research project was developed to investigate potential differences between Amplitude Modulated (AM) and Frequency Modulated (FM) screening of multicolor (CMYK) digital printing. The study examined the attributes of print contrast, dot gain, gray balance and color variation and how they may vary based on the screening method used. The experiment was conducted in a color managed digital printing workflow. Color differences were identified in print samples of AM vs. FM screening. Methods used to measure print attributes are detailed, and data was collected, graphed and analyzed.
The study shows that measurable differences do exist and that visual changes in color can occur based on the screening method employed. A custom target was printed on the Konica-Minolta C6000 bizHub digital color press using Creo's AM and FM screening technologies. A pilot test was conducted to achieve the target toner density values (+/- 0.10) according to in-house standards. During the pilot test, 200 sheets were printed. Once density values were achieved, the digital press was run continuously without operator interference and another 200 sheets were printed (100 sheets for each screening option), from which a total of 160 sheets were randomly selected (80 sheets for each screening option) for the densitometric and colorimetric analysis.
Only attributes that measured patches made up of dots or screened tint percentages were used to compare the two screening technologies. Print attributes that utilize solid patches only were not compared. The findings of this study represent specific printing or testing conditions. The findings of this research led to the conclusion that FM screening provides greater print contrast than AM screening. The findings make it difficult to draw conclusions regarding dot gain. Further study is needed to attempt greater control of variables.