An Objectively-Measured Index of Banding

The incidence of banding in printed vignettes was observed to be a common defect with prints generated from computer-to-plate (CTP) systems. The evaluation of banding has traditionally been a subjective visual assessment. This study compares subjective assessments of banding with an objectively derived index in a controlled experiment. Eleven printed samples from CTP systems were evaluated by nine judges, who identified the locations and severity of bands in the prints. The samples were then measured with a scanning densitometer to record the variations in reflectance. This data was subjected to non-linear regression analysis to identify a best-fitting third-order equation to model the changes in density. Differences between the predicted and measured densities were calculated (Y values). Next the changes in the Y ((Y), along with the density level involved, were used to formulate a predictive equation that was found to correlate with the subjective values for banding.