Mikel J. Stanich

Digital watermarking and steganography via overlays of halftone images

Recently, several watermarking schemes have been proposed that embed a watermark into two halftone images such that the watermark can be extracted by overlaying these halftone images. The watermark images in these schemes are binary images and the pixels in the two halftone images are correlated or not depending on whether the corresponding pixel in the watermark is on or off. In these schemes, the watermark is binary and does not contain detailed features. Furthermore, the extracted watermark contains residual patterns from the two images which reduces the fidelity of the extracted watermark image. This paper proposes a watermarking algorithm that addresses these problems. In addition, the proposed scheme admits more general watermark extraction functions and allows embedding of multiple watermark images.

Print-quality enhancement in electrophotographic printers

Print-quality enhancement (PQE) is a sophisticated form of image enhancement that is used to improve print quality. The benefits of PQE include reduced edge raggedness, control over boldness, stroke-imbalance correction, and improvements to the appearance of patterns that are difficult to print. Use of PQE permits one to obtain high-quality printing while using printers with lower resolution than would be required otherwise. Data bandwidth and storage requirements are therefore reduced. PQE relies on an imaging system with multiple exposure levels. A PQE algorithm generates an exposure value for each picture element (pel) based on neighboring bilevel pels. Since the exposure value is generated algorithmically, there is no need to store or internally transmit multiple bits per pel. This paper describes the capabilities of PQE and illustrates the level of print-quality improvements that can be obtained. Imaging-system requirements are presented, with attention to the modulator technology. The major focus is a PQE model that includes the PQE algorithm from the bitmap algorithm through the image-writing process.

Testing of nonimpact optical printheads.

A multipurpose optical-printhead evaluation device was designed that is capable of quantifying the performance of an optical printhead. A charge-coupled device (CCD) linear array measures the energy distribution produced by the printhead at the surface normally occupied by a photoconductive drum. From these measurements various mathematical entities, such as the modulation transfer function and image fidelity, are calculated to help evaluate the printhead. Measurements are reported that were performed on a laser printhead.