基于边缘检测的视觉反馈误差扩散半色调算法

提出一种基于边缘检测的视觉反馈误差扩散半色调算法。首先,对原图像进行误差扩散,然后采用LOG算子提取原图像和半色调图像的边缘信息;接着计算原始图像边缘信息与半色调图像边缘信息之间的视觉差,并将该视觉差利用反馈函数传递到原图像,得到新的连续调图像;最后,对新的连续调图像进行误差扩散,得到最终的半色调图像。实验仿真结果表明,相较于标准误差扩散和快速误差扩散,所提算法在主观感受和客观评价方面都有较大提升,是一种有效的半色调图像生成方法。     

基于视觉模型和误差扩散的半色调水印算法

介绍了一种基于HVS和误差扩散的半色调图像数字水印方法.仿真结果表明:该算法具有较好的水印不可感知性,当含有水印的半色调图像遭受到扫描和去网等攻击时,仍能够检测其嵌入的水印信息.     

随机中心聚集半色调算法

目的由误差扩散半色调算法得到的二值图像存在明显的规律性纹理,针对该问题提出随机中心聚集半色调算法。方法利用蓝噪声半色调阈值矩阵算法生成随机均匀分布的种子点,采用三角网生长算法构建Delaunay三角网格,在确定三角网像素成员后,根据像素点在三角形区域内的分布位置得到该位置像素的阈值,最后通过将连续调图像与阈值矩阵的阈值比较得到半色调图像。结果同误差扩散算法相比,提出的方法可以减少半色调图像的人工纹理,图像视觉效果较好。结论文中算法可以改善半色调图像质量,实验结果证明了该方法的有效性。     

数字全息水印在印刷半色调图像中的应用

在印刷半色调图像中嵌入特定信息可用于印刷品的保护和认证。设计了一种新颖的应用于非数字形式印刷半色调图像中的信息隐藏算法,将原始水印信息制成菲涅耳全息图,以此作为水印信息,利用离散小波变换算法嵌入到宿主图像中,以实现信息隐藏。该算法利用全息图独特的不可撕毁性来增强水印的鲁棒性。实验结果表明,该算法对图像半色调化攻击具有较好的鲁棒性。     

一种改进误差扩散系数的半色调算法

目的为了解决现有半色调算法产生的半色调图像边界模糊以及视觉蠕虫等问题,获得一种人眼视觉感知较好的数字半色调图像。方法在原始经典滤波器的基础上引入α-截尾均值滤波器,得到一种新的基于邻域像素灰度值相关的误差扩散滤波器。结果所提算法相较于传统误差扩散算法能更好地再现半色调图像细节,同时其边界也得到了较好的保持,并且客观评价参数PSNR值、SSIM值均有一定幅度的提高,NSME值也得到了较为理想的结果,不仅解决了传统误差扩散算法中边界模糊现象,同时也更好地表达了半色调图像的细节纹理信息。结论依据提出的算法得到的半色调图像人眼视觉感知效果较好,并且算法简单易行效率高。     

顾及边缘信息的多尺度误差扩散半色调算法

目的为了解决传统多尺度误差扩散半色调算法会导致半色调结果图像阶调变暗和边缘模糊的问题,提出一种顾及边缘信息的多尺度误差扩散半色调算法。方法根据当前像素邻域内像素点的处理状态,设计动态非时序误差扩散滤波器;利用图像局部平均灰度与空间变化率提取图像边缘信息,结合图像边缘信息与灰度信息确定半色调处理顺序。结果半色调处理结果视觉效果均匀,阶调信息和边缘结构信息与原图像一致性良好,峰值信噪比、加权信噪比和结构相似度分别提高了0.7～1.2 d B,0.9～1.5 d B,0.11～0.18。结论该算法解决了多尺度误差扩散算法的图像阶调变暗和边缘模糊的问题,有效提高了半色调输出质量。     

一种基于动态误差扩散系数的数字半色调算法

目的为了解决现有半色调算法产生的图像边界模糊以及视觉蠕虫等问题,研究一种视觉效果较好的半色调图像。方法提出一种在半色调过程中动态分配误差扩散系数的数字半色调方法,减少由固定误差扩散系数和固定扩散方向带来的边界模糊、视觉蠕虫以及结构性纹理等现象。结果文中提出的算法相较于传统的误差扩散算法其PSNR值提高了约0.5,SSIM值提高了约0.06,NSME值下降了约0.06。不仅解决了传统误差扩散算法中的边界模糊现象,同时也更好地表达了半色调图像的细节纹理信息。结论依据提出的算法产生的半色调图像视觉效果较好,并且算法简单易行,运行效率高。     

数字加网图像的质量评价研究

介绍了两类典型的数字半色调算法以及主观评价和客观评价两种传统的半色调图像质量评价方法.基于VisualC#编程语言建立了加网算法实验平台,并根据所得图像质量参数对各算法在再现图像的质量、运行时间等方面进行了比较和分析.     

基于随机打印机模型的误差扩散半色调算法

通过把新的随机打印机模型与经典的误差扩散算法结合,以解决误差扩散算法对打印机变形敏感,造成的人工纹理和输出半色调图像质量下降的问题,并提出了一种新的基于随机打印机模型的误差扩散算法,通过实验验证获得了较好的输出质量.     

MED数字半色调图像中伪轮廓现象的修正方法研究

详细分析了多级误差扩散(MED)半色调数字图像中出现伪轮廓现象的原因,提出了一种二级多次半色调图像叠合成多级半色调图像的方法,并利用其结果图像对多级半色调图像进行修正补偿,最终获得的半色调图像基本消除了伪轮廓现象,并且保留了多级误差扩散的原有优点。     

Watermarking in halftone images with mixed halftone techniques

Ordered dithering and error diffusion are the two most popular processes to produce halftone results for printing industry. Ordered dithering inherently has the benefit of efficiency. On the other hand, error diffusion has high quality and reasonable complexity. In this article, we propose a watermarking that adopts the ordered dithering to produce the referenced halftone image, then applying the noise‐balanced error diffusion to embed the watermark. A low computational complexity, low memory demand, and good embedded image quality are achieved with the proposed technique. From the experimental results, this technique can guard against the cropping and print‐and‐scan two major degradation processes in halftone images. © 2008 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 303–314, 2007     

加网参数和类型不确定的小波变换逆半调研究

针对不同加网类型和参数的彩色印刷图像,提出了一种基于加网参数和类型不确定的小波变换逆半调算法。首先在RGB颜色空间中分离了颜色通道,选择了B样条小波作为小波变换基函数;然后对图像实施了二层小波分解,利用小波阈值去噪策略,去除了半色调网点噪声;最后对图像进行了小波重构,得到了逆半调图像。实验结果表明,该逆半调算法适用于调频加网和调幅加网图像,同时逆半调图像具有很好的视觉效果。     

Quality evaluation metric for greyscale error diffusion halftone images based on texture and visual characteristics

Halftone images produced by error diffusion algorithms suffer from texture structures that decrease their visual qualities, such as worm-like and stripe-like defects. An effective quality evaluation metric is needed to evaluate various error diffusion halftoning algorithms and their corresponding halftone images. A texture distortion evaluation metric (TDEM) is proposed to measure the texture distortions within the referenced halftoned greyscale images. First, the weights of different tonal regions were assigned based on the two types of visual objects available and the locations of the texture structures. Then, based on image structure correlations and human visual characteristics, a block operation was performed and TDEM values were obtained by summing the local block-weighted variances based on image information. The proposed metric was validated using objective comparison and psycho-visual experiments. Results indicate that the metric can measure texture distortions effectively, and that the results are consistent with subjective visual perception.     

Watermarking in halftone images with noise balance strategy

Two novel and robust methods for embedding watermarks into error‐diffused halftone images are presented in this study. The first method is referred to as Dither‐Referenced Error Diffusion (DREDF), where the proposed Average Ordered Dithering (AOD) is adopted to produce the referenced halftone image. The Noise‐ Balanced Error diffusion (NBEDF) is then applied to embed the watermark. The other method is referred to as Parity‐Matched Error Diffusion (PMEDF). This approach achieves good image quality and capacity as high as 6.25 to 25%. Since the two techniques are blind, the decoder does not need any priori knowledge of the original halftone image or watermark. The capacity of the two approaches is also flexible to accommodate all kinds of applications. As the experimental results demonstrated, both techniques are able to guard against degradation due to cropping, tampering, and the print‐and‐scan process in error‐diffused halftone images. Moreover, both methods have features of low computational complexity, low memory demand, and good image quality. © 2010 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 20, 202–214, 2010.     

Ranked dither for high-quality robust printing

A robust parallelized halftoning method is proposed that is insensitive to dot loss, which can be a problem with xerographic and high-resolution printing. The method uses standard clustered-dot dither for smooth image blocks but uses the rankings of dither thresholds to halftone image blocks with high spatial activity. Experiments compare the ranked dither to dither, error diffusion, and green-noise error diffusion for four-color printing using standard clustered-dot dither masks at standard angles for the cyan, magenta, yellow, and black planes, respectively.     

Digital halftoning: A model-based perspective

Model-based halftoning techniques exploit the properties of the display device and the human visual system to maximize the quality of the displayed images. They rely on accurate models of the display and human perception. The focus of this article is on printers (both black and white and color) but similar techniques can be applied to other display devices. We review two model-based techniques, the modified error diffusion algorithms and the least-squares model-based algorithm. Both algorithms produce images with high spatial resolution and visually pleasant textures. We also review the use of printer and eye models in blue-noise screening techniques, which attempt to approximate the performance of error diffusion with minimal computation. We examine the performance of these halftoning techniques using both model-based quality metrics and subjective evaluations. © 1996 John Wiley & Sons, Inc.     

融合注意力机制的多尺度深度网络的逆半调方法

目的 运用现有的逆半调方法恢复的图像存在着半色调网纹去除不够理想、图像细节恢复不够清晰等问题,为了进一步提高逆半调图像在平滑区域和纹理细节方面的质量,提出一种基于融合注意力机制的多尺度卷积神经网络的逆半调方法。方法 首先,根据半色调图像网点噪声多频分布特点,设计多尺度卷积网络为基础结构的深度学习网络,从多个不同的尺度抑制半色调网纹并恢复不同尺度的图像信息;然后,应用注意力机制重建图像信息,从而生成逆半调图像;最后,提出多任务损失函数加速网络优化,更好地实现逆半调。结果 实验结果表明,运用此方法得到的逆半调图像在视觉上与原始图像更为相近,恢复出的图像细节更好;在客观评价方面,通过与现有的最先进的方法相比,峰值信噪比平均值提高了0.562～10.095 dB,结构相似度平均值提高了0.01～0.171。结论 该方法可以实现半色调图像的高质量恢复。