Document image enhancement algorithm for digital color copier
Jonghyon Yi, Sunghyun Lim · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2003
A typical document image to be copied generally consists of various types of elements, for example, texts, halftone images, line drawings, and continuous tone images printed on background. To enhance the copy quality of such a compound document image, one or more image enhancement processes can be applied. However, it is not suitable to apply an enhancement method, which is probably appropriate to a typical kind of document element, on the document image entirely. Instead, it is preferable to discriminate each document element and to apply adequate image enhancement methods on respective document elements. The proposed document image enhancement method is comprised of a segmentation phase and an enhancement phase. In the segmentation phase, it classifies each pixel of the input document image into text, continuous tone image, halftone image and background by using a state transition machine, pixel-based features and run-based features. In the enhancement phase, it applies different enhancement methods on respective document elements. In this way, the dark gray texts are converted into black texts, and the edges of texts and continuous tone images are emphasized, while prohibiting halftone image regions from inducing erroneously enhanced artifacts.