An improved parallel contrast-aware halftoning

Digital image halftoning is a widely used technique. However, achieving high fidelity tone reproduction and structural preservation with low computational time cost remains a challenging problem. This paper presents a highly parallel algorithm to boost real-time application of serial structure-preserving error diffusion. The contrast-aware halftoning approach is one such technique with superior structure preservation, but it offers only a limited opportunity for graphics processing unit （GPU） accel- eration. Our method integrates contrast-aware halftoning into a new parallelizable error-diffusion halftoning framework. To eliminate visually disturbing artifacts resulting from parallelization, we propose a novel multiple quantization model and space-filling curve to maintain tone consistency, blue-noise property, and structure consistency. Our GPU implementation on a commodity personal computer achieves a real-time performance for a moderately sized image. We demonstrate the high quality and performance of the proposed approach with a variety of examples, and provide comparisons with state-of-the-art methods.     

数字半色调技术中的误差扩散算法的研究

误差扩散是一种非常优秀的调频半色调技术,但这种方法在图像高光和暗调以及阶调平滑区域会产生“蠕虫”,同时噪声较多,导致半色调图像的边缘不清晰。在Floyd和Steinberg的误差扩散算法的基础上,设计一种新的基于平均阈值和改变扫描路径的误差扩散算法——阈值采用平均值法,通过优化平均阈值方法中的γ值得到最优的半色调图像,同时扫描路径采用“蛇型”路径。实验结果表明该算法可以减少“蠕虫”,增强图像的边缘,提高半色调图像的主观视觉效果。     

Line diffusion: a parallel error diffusion algorithm for digital halftoning

Floyd and Steinberg's (1976) error diffusion technique is a well-known approach to digital halftoning. The main drawback of this technique is that it is inherently serial. This paper presents a new parallelizable error-diffusion algorithm, calledline diffusion. In this method, the pixels of the original image are divided into classes line by line, and all the pixels on a line are halftoned simultaneously. Errors are distributed randomly. Experimental results show that line diffusion is comparable to error diffusion in image quality. A sequential line diffusion algorithm is also provided.     

基于K-means聚类的数字半色调算法

数字半色调是在二值设备或多色二值设备上实现图像再现的一门技术,提出将K-means聚类法应用在数字半色调技术中。算法中应用人类视觉系统模型(HVS)和印刷模型最大限度减少原始灰度连续调图像和半色调图像之间的视觉误差;利用K-means聚类法将灰度图像划分成聚类分区,在每个聚类分区应用最小平方法(least-squares)最小化二值半色调图像和原始灰度级图像之间的平方误差,所构造的半色调算法与基于模型的最小平方法(LSMB)算法相比,随着聚类分区的增加,图像平滑且边缘清晰度增加,尤其是在图像细节部位。与LSMB算法比较,该算法的均方误差值有所降低,而权重信噪比和峰值信噪比提高了0.2～2 dB,模拟实验结果验证了算法的有效性。     

基于图像极小相似度的填充曲线半色调方法

扫描路径是数字半色调技术的关键环节。针对行扫描误差扩散方法、Hilbert—Peano曲线半色调方法的不足，提出了基于图像极小相似度的填充曲线半色调方法。该方法首先定义了一个与待处理图像像素个数相等的非连通带权图及其相关的一个连通带权图；其次求出后者的最小生成树；再次根据最小生成树将非连通的原图连接成连通图，该连通图即为图像的极小相似度曲线；最后从该曲线的任意一点出发，沿此曲线深度优先处理图像的每一个像素。实验表明，用新的扫描路径处理后得到的半色调图像的整体效果较好；图像不存在与扫描路径相关的规律性纹理；图像边缘更加平滑，其边缘对比度指标比现有方法优一个数量级；图像的非边缘区域误差最小。     

基于视觉差的误差扩散半色调算法

针对传统误差扩散法在中频区域存在的结构纹理，提出了一种基于视觉差的误差扩散算法(PEB Error Diffusion)。PEB-ED借鉴了DBS中考察人类视觉误差的思想，对误差扩散结果中最容易发生误处理的中间调区域像素进行二次处理，因而明显减少了由固定的误差扩散滤波器所产生的结构性纹理，提高了图像的整体视觉效果。此外，它还可以减弱实际打印中“点增益现象”的影响。     

一种鼻内窥镜虚拟手术仿真系统

针对传统误差扩散法在中频区域存在的结构纹理，提出了一种基于视觉差的误差扩散算法（PEB Error Diffusion）。PEB－ED借鉴了DBS中考察人类视觉误差的思想，对误差扩散结果中最容易发生误处理的中间调区域像素进行二次处理，因而明显减少了由固定的误差扩散滤波器所产生的结构性纹理，提高了图像的整体视觉效果。此外，它还可以减弱实际打印中“点增益现象”的影响。     

Multiscale rank-based ordered dither algorithm for digital halftoning

In this paper, we proposed a simple and efficient algorithm that is based on the ranking of brightness within block. It builds the cumulative intensity quadtree for each block and generates the digital halftone׳s image using its information. We did the quality assessment for the result image of the proposed algorithm. As a result of experiment, it generates the digital halftone׳s image that is a little worse than that generated by error diffusion method, but it has merits to be implemented easily in parallel hardware because of block processing and simple operations. So we can conclude that the proposed algorithm is a very practical method to apply to the hardware implementation.     

热印字机的数字半色调算法——多级多阶误差分散算法研究

文章在某军用热印字机基础上提出了一种叠代算法———多级多阶误差分散数字半色调算法,即根据图像特性有选择地分散误差,使输出图像在保持良好细节的同时有较好的对比度,结果表明有较好的视觉效果。     

A Generalization of Magic Squares with Applications to Digital Halftoning

A semimagic square of order n is an n×n matrix containing the integers 0,…,n ²−1 arranged in such a way that each row and column add up to the same value. We generalize this notion to that of a zero k×k -discrepancy matrix by replacing the requirement that the sum of each row and each column be the same by that of requiring that the sum of the entries in each k×k square contiguous submatrix be the same. We show that such matrices exist if k and n are both even, and do not if k and n are relatively prime. Further, the existence is also guaranteed whenever n=k ^m , for some integers k,m≥2. We present a space-efficient algorithm for constructing such a matrix. Another class that we call constant-gap matrices arises in this construction. We give a characterization of such matrices. An application to digital halftoning is also mentioned. A preliminary version of this paper appeared in Proceedings of International Symposium on Algorithms and Computation, Hong Kong, December, 2004. Part of the work on the paper has been carried out when B.A. was visiting JAIST. Work of B.A. on this paper was supported in part by NSF ITR Grant CCR-00-81964. Work of T.A. was partially supported by the Ministry of Education, Science, Sports and Culture, Grant-in-Aid for Scientific Research (B).     

Tone-mapping high dynamic range images by novel histogram adjustment

In this paper, we present novel histogram adjustment methods for displaying high dynamic range image. We first present a global histogram adjustment based tone mapping operator, which well reproduces global contrast for high dynamic range images. We then segment images and carry out adaptive contrast adjustment using our global tone mapping operator in the local regions to reproduce local contrast and ensure better quality. We demonstrate that our methods are fast, easy to use and a fixed set of parameter values produce good results for a wide variety of images.     

一种MSK信号的数字化解调新算法

MSK信号是一种性能优越的数字调制方式,在数字通信中得到了广泛的应用.根据MSK信号的特征,提出了一种基于DFT的MSK信号数字化解调算法.该算法是通过对MSK信号每个码元周期内的采样值分别进行两次DFT运算,计算出对应于1码和0码载波频率的幅值信息,根据幅值大小来判决,从而恢复数字信号.并对存在高斯噪声背景下,该解调算法的误码性能进行了分析.仿真结果表明了该算法计算量小、抗干扰性能好.且与传统的MSK解调算法相比,该算法对位同步不敏感.     

Improving user assessment of error implications in digital elevation models

A digital representation of a terrain surface is an approximation of reality and is inherently prone to some degree of error and uncertainty. Research in uncertainty analysis has produced a vast range of methods for investigating error and its propagation. However, the complex and varied methods proposed by researchers and academics create ambiguity for the dataset user. In this study, existing methods are combined and simplified to present a prototype tool to enable any digital elevation model (DEM) user to access and apply uncertainty analysis. The effect of correlated gridded DEM error is investigated, using stochastic conditional simulation to generate multiple equally likely representations of an actual terrain surface. Propagation of data uncertainty to the slope derivative, and the impact on a landslide susceptibility model are assessed. Two frameworks are developed to examine the probable and possible uncertainties in classifying the landslide hazard: probabilistic and fuzzy. The entire procedure is automated using publicly available software and user requirements are minimised. A case study example shows the resultant code can be used to quantify, visualise and demonstrate the propagation of error in a DEM. As a tool for uncertainty analysis the method can improve user assessment of error and its implications.     

基于FPGA的改进误差扩散加网算法实现

传统的误差扩散算法内存占用率高,加网速度慢。通过结合传统算法和并行优化算法,提出一种基于FPGA的算法改进方案并加以实现,大大减少了资源占用率并提高了加网速度。以FS误差扩散算法为例对加网结果进行分析表明,优化后的算法效果良好,基于可编程器件的数字加网不再依赖大容量存储,并使得实时加网成为可能。     

用TMS320实现数字控制系统的几个问题

本文讨论了用TMS 320实现数字控制系统的几个具体问题,并着重研究由于定点运算和有限字长效应引起的量化误差、舍入和溢出,以及对这些问题的处理方法.     

基于误差扩散模型的图像复制色彩管理分析

本文从误差扩散角度分析了图像复制过程中存在色彩复制管理的机制原理,色彩误差是不可避免的,但通过建立色彩误差扩散模型进行色彩复制传递的校正管理,可以客观正确反映了彩色图像印刷的颜色视觉质量效果。     

基于差错控制编码的数字图像水印方法

数字水印是近年来出现的一种新的数字媒体产品版权保护技术,其过程可看作干扰信道的通信,不可见性和鲁棒性是数字水印最基本的要求。文章根据通信中的差错控制编码(ECC)原理提出了一种提高数字水印鲁棒性方法,水印的嵌入在DCT域进行,为保证水印不可见,嵌入算法结合图像特征和人眼视觉掩蔽特性自适地将水印信号嵌入到DCT系数中。实验结果表明该方法能大大提高水印的鲁棒性。     

可逆变长编码差错复原技术在数字视频传输中的应用

在无线移动信道和因特网等环境下的压缩视频传输业务,信道传输差错不但严重影响业务质量,甚至会导致整个视频通信完全失效。采用变长编码时,变长编码虽然提高了编码效率,但也使得编码后的视频数据对抗差错的能力十分脆弱。而采用可逆变长编码可以对码流进行双向解码,在差错发生后,解码器可分别由两个重同步点进行解码,并可更精确地确定差错发生的位置,恢复部分本应丢弃的数据。文章将可逆变长编码差错复原技术应用在数字视频传输中,采用可逆变长编码,对应用了数据分割技术的压缩视频传输码流中的宏块头信息和运动矢量等重要信息进行编码,从而提高视频流的抗差错能力和解码端的差错复原能力。并利用第三代移动通信系统的信道模型进行了差错复原技术的实验。结果表明,在应用了可逆变长编码差错复原技术后,重建图像的主客观质量得到了明显的改善。     

Sharing a verifiable secret image using two shadows

In this paper, we propose a novel (2,2) verifiable secret sharing (VSS) scheme, which not only protects a secret image but also allows users to verify the restored secret image in the revealing and verifying phase, for all binary, grayscale and color images. Error diffusion and image clustering techniques are adopted to achieve our objective. Experimental results and discussions show that the proposed scheme, with its smaller shadow size and lower computational complexity, obviously outperforms previous VSS schemes designed either with or without the cheating prevention mechanism. Moreover, the use of a halftone logo gives an efficient solution to verifying whether the restored secret image is correct by using a halftone logo.