Extended Range for Black-White Halftones Using Combination of Negatives.

A technique employing combination of negatives is described for expanding tonal range and thus compensating for the normal tone distortion in the highlight and shadow areas of printed reproductions. Data are presented showing how this technique can extend the tonal range without a loss of highlight and shadow contrast by use of a combination of two halftone dots in the deep shadows. The resulting tone reproductions are analyzed in terms of densities and by mathematical analysis using quality domain criteria. The latter method offers a means to measure the change in halftone print quality and can be used to define attribute tolerances for halftone reproduction quality. The validity of this technique was tested on four reproductions and found to be quite good.