In this paper, we propose a method to hide invisible patterns in color error diffused halftone images. The hidden pattern is embedded in different color components. The hidden patterns would be revealed when the watermarked color halftone images are under Boolean operation or overlaid. Simulation results show that the watermarked color halftone images have good visual quality and the hidden pattern is visible clearly.

In this paper, we discuss how to use the watermarking technique for visual cryptography. Both halftone watermarking and visual cryptography involve a hidden secret image. However, their concepts are different. For visual cryptography, a set of shared binary images is used to protect the content of the hidden image. The hidden image can only be revealed when enough shared images are obtained. For watermarking, the hidden image is usually embedded in a single halftone image while preserving the quality of the watermarked halftone image. In this paper, we propose a joint visual-cryptography and watermarking (JVW) algorithm that has the merits of both visual cryptography and watermarking

In many printer and publishing applications, it is desirable to embed data in halftone images for copyright control and authentication purposes. While intentional attacks on printed matters may not be likely, unintentional attacks such as cropping and distortion due to dirt or human writing/marking are likely. In this paper, we proposed a novel halftone image watermarking method called watermarking error diffusion (WED) to embed a watermark in the parity domain of halftone images with symmetric key during halftoning while introducing minimal distortion.

In this paper, we propose a novel way called DHCED to hide invisible patterns in two or more visually different halftone images (e.g. Lena and Harbor) such that the hidden patterns would appear on the halftone images when they are overlaid. Conjugate error diffusion is used to embed the binary visual pattern in the two distinct halftone images. Simulation results show that the two halftone images have good visual quality, and the hidden pattern is visible when the two distinct halftone images are overlaid.

In this paper, we propose a method called, modified stochastic error diffusion (MSED), to hide an invisible binary visual pattern in a set of error diffused halftone images. MSED can embed a dithered watermark in multiple halftone images while preserving the visual quality of each halftone image. When any of these images overlapping with any others, the watermark will appear. In case that many of these image overlapped together, the contrast of watermark becomes clearer.

In many printer and publishing applications, it is desirable to embed data in halftone images for copyright control and authentication purposes. While intentional attacks on printed matters may not be likely, unintentional attacks such as cropping and distortion due to dirt or human writing/marking are likely. In this paper, we proposed a novel halftone image watermarking method to embed a robust, invisible, multi-bit watermark in the halftone images during halftoning while introducing minimal distortion.

In this paper, we propose a novel way called DHCED to hide invisible patterns in two or more visually different halftone images (e.g. Lena and Harbor) such that the hidden patterns would appear on the halftone images when they are overlaid. Conjugate error diffusion is used to embed the binary visual pattern in the two distinct halftone images. Simulation results show that the two halftone images have good visual quality, and the hidden pattern is visible when the two distinct halftone images are overlaid.

In many printer and publishing applications, it is desirable to embed data in halftone images. We proposed some novel data hiding methods for halftone images. For the situation in which only the halftone image is available, we propose data hiding smart pair toggling (DHSPT) to hide data by forced complementary toggling at pseudo-random locations within a halftone image. The complementary pixels are chosen to minimize the chance of forming visually undesirable clusters. Our experimental results suggest that DHSPT can hide a large amount of hidden data while maintaining good visual quality. For the situation in which the original multitone image is available and the halftoning method is error diffusion, we propose the modified data hiding error diffusion (MDHED) that integrates the data hiding operation into the error diffusion process. In MDHED, the error due to the data hiding is diffused effectively to both past and future pixels. Our experimental results suggest that MDHED can give better visual quality than DHSPT. Both DHSPT and MDHED are computationally inexpensive.

We propose a novel method called DHSED (data hiding stochastic error diffusion) to hide binary visual patterns in two error diffused halftone images. While one halftone image is only a regular error diffused image, stochastic error diffusion is applied to the other image to generate special stochastic characteristics with respect to the first image such that the visual pattern would appear when the two halftone images are overlaid Simulation results show that the two halftone images have good visual quality, and the hidden pattern appears with "normal" and "lower-than-normal" intensity when the two halftone images are overlaid.

There is growing interest in hiding data for authentication and copyright control in halftone images printed in books, newspapers and by computer printers. A previous data hiding method, the data hiding by pair-toggling (DHPT), is reasonably good but introduce considerable visual artifacts. In this paper, we analyze the sources of the artifacts in DHPT and propose an improvement by using smart pair toggling. Simulation results suggest that the proposed data hiding by smart pair-toggling (DHSPT) algorithm can hide the same amount of data while generating halftone images with considerably better visual quality than DHPT.