HP INCFollow


In some scanning printers one possible image quality issues is dark light zone banding, where regions whose intended tone is constant smoothly (rather than abruptly) oscillate in lightness, with a period equal to the media advance. The causes behind it can differ and depend on the type of ink and substrate. For some types of inks, drying can also play a crucial role. The printing process must be robust against dot-placement variations, including those due to variations in media advance, and ink-media interactions. The ink on media interaction in particular can also be correlated to the drying performance, to have homogeneity in optical density the ink must be deposited on the media under similar conditions of drying time. Minimizing variations in drying time and amount of ink makes the system more robust against dark light zone banding. The solution presented in this paper is a way to reduce the drying differences across the paper (vertical) axis, paying attention to the layering of different passes (the stack) and how it evolves across printing passes. The print ramps method, which is commonly used for media advance robustness and in which use of nozzles at the extremes of the print head is minimal and increases gradually toward the middle part, has a problem of inhomogeneous drying behavior: the edges of the ramps have a different density stack than their center (though the accumulated density is the same everywhere). Due to this difference in ink layering, some positions dry faster than others. When layering a ramp and its complement, at the edges we have a distribution 100% - 0 %, while at the centre it is 50% - 50%. Stack control masking deals with the problem by extending the ramp towards the neighbouring stack and ensuring that the condition of 100% - 0% does never take place. The solution has two parameters that must be set according to the drying behavior, Slope and Bias. The slope of the ramp would be the new interaction of the edges, and then the bias is how far goes the penetration of the next stack. Example could be Slope of 30% - 70%, and a bias of a half of the media advance. The slope reduction must be compensated by the Bias.

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Creative Commons License
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