Screening is a nonlinear operation where the forward mapping is a deterministic process but the mathematical properties of the inverse solution can only be estimated. Principle motivations in the printing industry behind `inverse' halftoning or descreening are the storage costs associated with halftone film and because digital image manipulations are not possible with images in a binary format. This includes size change and rotation, two important processes for the printing industry. Clearly, it would be advantageous to be able to recapture the original gray scale from the halftone film, store it in a less expensive and easy to duplicate digital format, and perform image processing operations on the data. Initially, we introduce a metric to compare the coarseness of the screen to the image bandwidth and demonstrate how to use this metric as a predictor of the ability to descreen the screened image. Transform domain representations of the screened image are discussed as well as a sampling theory similarity in the screening process. Descreening is achieved through linear filtering and adaptations of two iterative techniques. This paper concludes that under the right conditions it is possible to recover a visually close approximation of the original image from the screened image and that the iterative techniques are robust and provide objective and subjective performance improvements compared with linear filtering.

Date Published: 8 September 1993
PDF: 1 pages
Proc. SPIE 1913, Human Vision, Visual Processing, and Digital Display IV, (8 September 1993); doi: 10.1117/12.152704

Published in SPIE Proceedings Vol. 1913:
Human Vision, Visual Processing, and Digital Display IV
Jan P. Allebach; Bernice E. Rogowitz, Editor(s)