Imagesetter requirement limits based on a simple model of visual acuity

摘要

A single spatial filter function closely replicating the contrast sensitivity of the visual system is used to predict the visual detection thresholds for narrow lines and dots and small amounts of edge blur. Both the predictions for lines and for edge blur are consistent with published data. Maximum differences with delta function lines and dots yield limits for distinguishing the actual width of lines and dots. A caution on spot size constraints based on fidelity of line width $LS approximately 20 microns is given (other constraints are mentioned). Series expansions within the mathematical definitions reveal that the detection thresholds are simply related to polynomial power integrals (i.e. moments) of both the object profile and the visual system spatial filter function. An argument is presented that a halftone screen can not be free of screen-to-raster artifacts at addressabilities $LS approximately 1200 d.p.i. if the screen is not rational tangent. Published limits on the visibility of edge raggedness suggest that stairstepping at addressabilities $GRT approximately 3700 d.p.i. should never be a concern.