Electrostatic Halftoning

We introduce a new global approach for image dithering, stippling, screening and sampling. It is inspired by the physical principles of electrostatics. Repelling forces between equally charged particles create a homogeneous distribution in flat areas, while attracting forces from the image brightness values ensure a high approximation quality. Our model is transparent and uses only two intuitive parameters: One steers the granularity of our halftoning approach, and the other its regularity. We evaluate two versions of our algorithm: A discrete version for dithering that ties points to grid positions, as well as a continuous one which does not have this restriction, and can thus be used for stippling or sampling density functions. Our methods create very few visual artefacts, reveal favourable blue‐noise behaviour in the frequency domain, and have a lower approximation error under Gaussian convolution than state‐of‐the‐art methods.     

Halftoning colour volume datasets based on subdivision

The algorithm for halftoning 2D gray scale images based on subdivision was extended to the processing of colour volume datasets. Two main improvements were made. The first is adding a procedure to deal with cases with large errors so as to reduce the total quantizing error. The second is randomizing the directions in which errors are propagated, assuring the even distribution of the halftoned binary voxels. In addition, a method used to process large volume datasets was also proposed. The new algorithm is simple in principle, but produces good halftoning results, especially in the boundary regions. It is especially applicable in the data preparation for the rapid forming of coloured models and heterogeneous objects.     

Adaptive inverse halftoning for scanned document images through multiresolution and multiscale analysis

This paper describes an efficient algorithm for inverse halftoning of scanned document images to resolve problems with interference patterns such as moiré and graininess when the images are displayed or printed out. The algorithm is suitable for software implementation and useful for high quality printing or display of scanned document images delivered via networks from unknown scanners. A multi-resolution approach is used to achieve practical processing speed under software implementation. Through data-driven, adaptive, multi-scale processing, the algorithm can cope with a variety of input devices and requires no information on the halftoning method or properties (such as coefficients in dither matrices, filter coefficients of error diffusion kernels, screen angles, or dot frequencies). Effectiveness of the new algorithm is demonstrated through real examples of scanned document images, as well as quantitative evaluations with synthetic data.     

基于图像融合模型的矢量逆半调算法

针对矢量误差分散半调图提出了一种彩色逆半调算法。首先,分析了基于矩阵增益模型的误差分散系统,发现矢量逆半调问题可等效为相关性高频噪声的抑制问题;然后利用K-L变换去除相关性并基于Laplacian金字塔构造图像融合模型,该模型能将未知特性的高频噪声转化为易处理的脉冲噪声;最后使用维纳滤波器和中值滤波器去噪。实验表明,该算法能克服色偏,减少杂色,较准确地再现连续色调图像,逆半调图像的峰值信噪比传统算法提高2~3dB。     

印刷品水印图像的半色调算法比较

对Bayer抖动、误差扩散和绿噪声3种半色调算法进行了分析比较。利用离散小波变换将水印信息嵌入宿主图像,采用峰值信噪比对3种算法生成的半色调图像质量进行客观评价;用归一化相关系数衡量半色调图像提取的水印质量;以Matlab程序运行时间判断3种算法的计算效率;同时,结合人眼视觉对半色调图像质量进行主观评价。综合各种评价,结果表明:误差扩散是最适合小波水印图像的半色调算法。     

基于AM的误差扩散法

在打印机上输出连续色调的图像，只能依赖于数字化半色调技术。提出了一种新的基于AM的误差扩散的算法，该算法结合调幅半色调技术和调幅半色调技术中的误差扩散法，在用可调节的较小的AM模板对图像进行半色调处理的同时，将原始图像与结果二值图像间的误差扩散到周围像素，使少数像素基本上按原始图像的灰度值分布。     

一种高效的逆半调算法

论文提出了一种快速的逆半调算法,在高斯低通滤波的基础上,通过带通滤波提取边界信息,并使用界限函数和中值滤波修正边界映像,最后合成逆半调结果。实验证明该算法和现有算法相比计算速度快,输出图像信噪比高。     

基于中值金字塔变换的图像逆半调

针对误差分散半调的系统特征，构建了一种基于非线性中值算子的多分辨金字塔变换．研究了变换后各级近似、细节信号中半调噪声的分布特性和消噪方法．提出了一种用wiener滤波抑制一级细节中半调噪声，并用消噪后的细节与近似信号重构连续色调图像的逆半调算法．实验结果表明．该变换具有较好的信噪分离能力，比线性多尺度变换更适合于逆半调．新逆半调算法的时空间复杂度较低．其结果的峰值信噪比值及去噪保沿效果良好．     

基于边缘检测的动态误差分散半色调算法

针对数字半色调技术中的传统误差分散方法因误差分散系数固定而导致图像真实细节损失的问题,提出了一种基于边缘检测的动态误差分散算法。该方法沿着每个像素的误差分散方向进行边缘检测,再根据边缘检测结果动态地选择该像素各个方向的误差分散系数,减小了误差分散过程中的误差积累。实验表明,此方法可以明显改善由于误差分散系数固定而引起的图像轮廓细节损失。     

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。