Extracting color halftones from printed documents using texture analysis

Abstract

Printed documents often contain text and halftones on the same page. When processing these documents electronically, it is important to separate halftones from text and other illustrations, since their processing requirements differ. We present an algorithm that extracts both grayscale and color halftones from other information on a page. Halftones are commonly produced as a pattern of dots on a uniform lattice. The halftone dot pattern forms an “invisible texture”, producing a spectral component distinct from other information on the page. We show that a single circularly symmetric bandpass filter, tuned to this spectral component, can be used to segment halftones having arbitrary shape and size, even in the presence of image rotations.