Faithful Printing of Digital Source

Abstract

Faithful printing of digital source images requires simultaneous control of solid patch colors (optical density - OD), and graphic element dimensions (dot gain - DG). In Electro-Photography laser based printing, the dot-gain and the optical-density are coupled through process parameters such as toner thickness. Decreasing the DG usually decreases the OD. Since OD deviations cause color shifts, OD calibration takes precedence over DG setting, thus limiting the possible values of the attainable dot gain. The latter is determined by the writing system and by variable consumable properties such as the toner charge density. Thus, the dot gain varies in time and between printers. This causes a print fidelity problem that manifests itself in variability of graphic element dimensions and instability of highlights in halftones.We present a novel method for resolving this problem using a locally-adaptive variable laser exposure that affects only selected dots on edges of elements, thus decoupling the OD and the DG controls. The solution we present consists of a template-based algorithm combined with a novel calibration mechanism for attaining zero DG. The results show ∼50% improvement of the defacto resolution for graphics printing, and a reduced sensitivity of halftone patterns to press conditions. The new DG control, combined with existing color control, brings us significantly closer to print consistency across presses.