Data hiding watermarking for halftone images

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.     

Oriented modulation for watermarking in direct binary search halftone images

In this paper, a halftoning-based watermarking method is presented. This method enables high pixel-depth watermark embedding, while maintaining high image quality. This technique is capable of embedding watermarks with pixel depths up to 3 bits without causing prominent degradation to the image quality. To achieve high image quality, the parallel oriented high-efficient direct binary search (DBS) halftoning is selected to be integrated with the proposed orientation modulation (OM) method. The OM method utilizes different halftone texture orientations to carry different watermark data. In the decoder, the least-mean-square-trained filters are applied for feature extraction from watermarked images in the frequency domain, and the na?ve Bayes classifier is used to analyze the extracted features and ultimately to decode the watermark data. Experimental results show that the DBS-based OM encoding method maintains a high degree of image quality and realizes the processing efficiency and robustness to be adapted in printing applications.     

A feature-based digital watermarking scheme for halftone image

It is a challenging work to design a robust halftone image watermarking scheme against desynchronization attacks. In this paper, we propose a feature-based digital watermarking method for halftone images with low computational complexity, good visual quality and reasonable resistance toward desynchronization attacks. Firstly, the feature points are extracted from host halftone image by using multi-scale Harris–Laplace detector, and the local feature regions (LFRs) are constructed according to the feature scale theory. Secondly, discrete Fourier transform (DFT) is performed on the LFRs, and the embedding positions (DFT coefficients) are selected adaptively according to the magnitude spectrum information. Finally, the digital watermark is embedded into the LFRs by quantizing the magnitudes of the selected DFT coefficients. By binding the watermark with the geometrically invariant halftone image features, the watermark detection can be done without synchronization error. Simulation results show that the proposed scheme is invisible and robust against common signals processing such as median filtering, sharpening, noise adding, and JPEG compression, etc., and desynchronization attacks such as rotation, scaling, translation (RST), cropping, local random bend, and print-scan, etc.     

植基于人类视觉系统之二色调图像信息隐藏技术

二色调图像（halftone image）是一种非常特殊的黑白图像，即在一定的距离观看它时，二色调图像仍具有灰阶图像的视觉效果。此种图像被广泛地使用在新闻报纸或杂志中。本文提出了一个利用了人类视觉特性的方法，有效地将机密信息隐藏在二色调图像中，实验结果显示此方法具有很高的实用价值。     

Multiple spatial watermarking technique in color images

This paper presents a novel multiple digital watermarking technique for the copyright protection of digital color images. In order to improve the robustness against cropping attacks, a binary watermark image is divided into four parts. Each is encrypted by a secret key and embedded into different regions of the blue component of the color image in the spatial domain. Watermark extraction is based on the comparisons between the original intensity pixel values and the corresponding watermarked intensity pixel values in blocks of size 8 × 8. The watermark-extracted bits are determined using the probabilities of detecting bit ‘1’ or bit ‘0’. The watermark can be extracted in several parts depending on the size of the host image, but only four of these are selected by a correlation coefficient detector and used to reconstruct the extracted watermark. Experimental results show that the proposed scheme successfully makes the watermark perceptually invisible and robust for a wide range of attacks, including JPEG-loss compression, median filtering, low pass filtering, rotation, rotation-scaling, rotation-crop, image cropping, image scaling, and self-similarity attacks.     

Perceptual coding of images for halftone display

The authors present a new technique for coding gray-scale images for facsimile transmission and printing on a laser printer. They use a gray-scale image encoder so that it is only at the receiver that the image is converted to a binary pattern and printed. The conventional approach is to transmit the image in halftoned form, using entropy coding (e.g., CCITT Group 3 or JBIG). The main advantages of the new approach are that one can get higher compression rates and that the receiver can tune the halftoning process to the particular printer. They use a perceptually based subband coding approach. It uses a perceptual masking model that was empirically derived for printed images using a specific printer and halftoning technique. In particular, they used a 300 dots/inch write-black laser printer and a standard halftoning scheme ("classical") for that resolution. For nearly transparent coding of gray-scale images, the proposed technique requires lower rates than the standard facsimile techniques.     

Perceptual coding of images for halftone display

We present a new technique for coding gray-scale images for facsimile transmission and printing on a laser printer. We use a gray-scale image encoder so that it is only at the receiver that the image is converted to a binary pattern and printed. The conventional approach is to transmit the image in halftoned form, using entropy coding (e.g. CCITT Group 3 or JBIG). The main advantages of the new approach are that we can get higher compression rates and that the receiver can tune the halftoning process to the particular printer. We use a perceptually based subband coding approach. It uses a perceptual masking model that was empirically derived for printed images using a specific printer and halftoning technique. In particular, we used a 300 dots/inch write-black laser printer and a standard halftoning scheme ("classical") for that resolution. For nearly transparent coding of gray-scale images, the proposed technique requires lower rates than the standard facsimile techniques.     

Robust spatial watermarking technique for colour images via direct saturation adjustment

Most colour watermarking methods are realised by modifying the image luminance or by processing each component of colour space separately. This paper presents a novel and robust colour watermarking approach for applications in copy protection and digital archives. The proposed scheme considers chrominance information that can be utilised at information embedding. This work presents an approach for hiding the watermark into DC components of the colour image directly in the spatial domain, followed by a saturation adjustment technique performed in RGB space. The merit of the proposed approach is that it not only provides promising watermarking performance but also is computationally efficient. Experimental results demonstrate that this scheme successfully makes the watermark perceptually invisible and robust to image processing operations such as general image processing operations (JPEG2000, JPEG-loss compression, lowpass filtering, and medium filtering), image scaling and image cropping.     

Data hiding in ordered dithered halftone images

In this paper, we propose a novel method called data hiding ordered dithering (DHOD) to hide a relatively large amount of invisible watermarking data in ordered dithered halftone images while retaining good visual quality. We assume that both the original image and the ordered dithering screen are available. The proposed method includes two techniques:screen modification andthreshold selection. First, one out of everyM pseudo-random locations is selected usingthreshold selection to embed one bit of hidden data. Second, at the selected locations,screen modification is applied to change the ordered dithering screen in a local neighborhood to achieve the desired data hiding while attaining good visual quality. Some custom-made quality measures are proposed to evaluate DHOD. Simulation results suggest that DHOD can hide a large amount of data while maintaining good visual quality.This work has been supported by the Research Grants Council of the Hong Kong Special Administrative Region, China.     

数字图像水印研究综述

本文对当前数字图像水印技术的背景、现有方法、发展应用和存在的问题做了一综述,以期进一步推动我国在此前沿领域的研究工作。     

Watermarking in halftone images with parity-matched error diffusion

In this paper, a halftone watermarking technique of high watermark rate, robustness, and watermark-rate flexibility is presented. This technique, namely the parity-matched error diffusion (PMEDF) method, is capable of achieving an embedded watermark rate as high as 6.25-25% with good image quality and without the need for the original image as the reference for the decoding. The proposed PMEDF method employs the high efficient parity-matching strategy to spread a watermark bit to each pixel of a block of the host image. Thus, the majority voting mechanism can be applied for decoding to achieve an advantage of high robustness. As documented in the experimental results, this technique is capable of guarding against degradation, due to cropping, tampering, as well as print-and-scan process in error-diffused halftone images.     

灰度图像水印综述

数字水印技术作为数字媒体版权保护的重要手段之一,近年来已成为国内外研究的热点.与传统的嵌入一个无意义的一维或二维伪随机序列以及可视的二值图像相比,嵌入灰度图像水印不仅嵌入信息量大,而且更加有意义.对灰度级数字图像水印技术的最新发展情况进行了介绍,主要内容包括:空域及变换域的灰度数字图像水印技术,其中变换域水印主要讨论了DCF域和DWT域两类灰度数字水印;自适应灰度级数字水印技术;灰度数字图像水印的性能评价.最后展望了该技术的进一步研究前景及可能的研究热点.     

一种新的图像水印方案

目标区域是图像中视觉上最重要的部分。针对现有的水印算法很少考虑图像中确定的目标区域这一问题，提出了一种基于目标区域的水印方案(WIOR)。方案首先利用小波变换分析图像的目标特征，并依据图像的小波高频系数特征对其进行聚类，获得水印的嵌入域，在此嵌入域中，选择小波系数并对其进行量化调制来嵌入二值扩谱水印；同时，通过只在图像的局部区域内嵌入较少的水印信息来改善水印的隐蔽性。实验结果表明，该方案对于一类具有突出目标特征的图像具有较好的效果。嵌入的水印主要优势在于真正把水印嵌入图像的视觉重要部分，从而能有效地抵御剪切攻击，而且可以实现盲检测。     

Joint trellis-coded quantization watermarking for JPEG2000 images

Watermarking in the Joint Photographic Experts Group (JPEG)2000 coding pipeline is investigated in this paper. A joint quantization and watermarking method based on trellis-coded quantization (TCQ) is proposed to reliably embed data during the quantization stage of the JPEG2000 part 2 codec. The central contribution of this work is the use of a single quantization module to jointly perform quantization and watermark embedding at the same time. The TCQ-based watermarking technique allows embedding the watermark in the detail sub-bands of one or more resolution levels except the first one. Watermark recovery is performed after image decompression. The performance of this joint scheme in terms of image quality and robustness against common image attacks was estimated on real images.     

Wavelet-based watermarking for color images through visual masking

In this paper, a wavelet-based watermarking scheme for color images is proposed. The watermarking scheme is based on the design of a color visual model that is the modification of a perceptual model used in the image coding of gray scale images. The model is to estimate the noise detection threshold of each wavelet coefficient in luminance and chrominance components of color images in order to satisfy transparency and robustness required by the color image watermarking technique. The noise detection thresholds of coefficients in each color component are derived in a locally adaptive fashion based on the wavelet decomposition, by which perceptually significant coefficients are selected and a perceptually lossless quantization matrix is constructed for embedding watermarks. Performance in terms of robustness and transparency is obtained by embedding the maximum strength watermark while maintaining the perceptually lossless quality of the watermarked color image. Simulation results show that the proposed scheme is more robust than the existing scheme while retaining the watermark transparency.     

一种鲁棒的彩色图像多功能水印算法

首先转换彩色图像的颜色空间抽取相应的灰度图像,再对灰度图像进行提升小波分解,在分解过程中利用图像压缩操作,引起近半数的小波系数增大,另一半系数减小,基于系数增减特征实现版权水印和消费者数字指纹的同时嵌入,从而获得版权认证和盗版追踪的双重功能。仿真实验表明该算法具有良好的鲁棒性和不可感知性。     

Filters involving derivatives with application to reconstructionfrom scanned halftone images

This paper presents a method for designing finite impulse response (FIR) filters for samples of a 2-D signal, e.g., an image, and its gradient. The filters, which are called blended filters, are decomposable in three filters, each separable in 1-D filters on subsets of the data set. Optimality in the minimum mean square error sense (MMSE) of blended filtering is shown for signals with separable autocorrelation function. Relations between correlation functions for signals and their gradients are derived. Blended filters may be composed from FIR Wiener filters using these relations. Simple blended filters are developed and applied to the problem of gray value image reconstruction from bilevel (scanned) clustered-dot halftone images, which is an application useful in the graphic arts. Reconstruction results are given, showing that reconstruction with higher resolution than the halftone grid is achievable with blended filters.     

A wavelet-based watermarking algorithm for ownership verificationof digital images

Access to multimedia data has become much easier due to the rapid growth of the Internet. While this is usually considered an improvement of everyday life, it also makes unauthorized copying and distributing of multimedia data much easier, therefore presenting a challenge in the field of copyright protection. Digital watermarking, which is inserting copyright information into the data, has been proposed to solve the problem. In this paper, we first discuss the features that a practical digital watermarking system for ownership verification requires. Besides perceptual invisibility and robustness, we claim that the private control of the watermark is also very important. Second, we present a novel wavelet-based watermarking algorithm. Experimental results and analysis are then given to demonstrate that the proposed algorithm is effective and can be used in a practical system.     

Digital fragile watermarking scheme for authentication of JPEG images

It is a common practice in transform-domain fragile watermarking schemes for authentication purposes to watermark some selected transform coefficients so as to minimise embedding distortion. The author points out that leaving most of the coefficients unmarked results in a wide-open security gap for attacks to be mounted on them. A fragile watermarking scheme is proposed to implicitly watermark all the coefficients by registering the zero-valued coefficients with a key-generated binary sequence to create the watermark and involving the unwatermarkable coefficients during the embedding process of the embeddable ones. Non-deterministic dependence is established by involving some of the unwatermarkable coefficients selected according to the watermark from a nine-neighbourhood system in order to thwart different attacks, such as cover-up, vector quantisation and transplantation. No hashing is needed in establishing the non-deterministic dependence.