Comprehensive Halftoning of 3D Scenes

The display of images on binary output hardware requires a halftoning step. Conventional halftoning algorithms approximate image values independently from the image content and often introduce artificial texture that obscures fine details. The objective of this research is to adapt a halftoning technique to 3D scene information and thus to enhance the display of computer generated 3D scenes. Our approach is based on the control of halftoning texture by the combination of ordered dithering and error diffusion techniques. We extend our previous work and enable a user to specify the shape, scale, direction, and contrast of the halftoning texture using an external buffer. We control texture shape by constructing a dither matrix from an arbitrary image or a procedural texture. Texture direction and scale are adapted to the external information by the mapping function. Texture contrast and the accuracy of tone reproduction are varied across the image using the error diffusion process. We halftone images of 3D scenes by using the geometry, position, and illumination information to control the halftoning texture. Thus, the texture provides visual cues and can be used to enhance the viewer's comprehension of the display.     

Dominant Texture and Diffusion Distance Manifolds

Texture synthesis techniques require nearly uniform texture samples, however identifying suitable texture samples in an image requires significant data preprocessing. To eliminate this work, we introduce a fully automatic pipeline to detect dominant texture samples based on a manifold generated using the diffusion distance. We define the characteristics of dominant texture and three different types of outliers that allow us to efficiently identify dominant texture in feature space. We demonstrate how this method enables the analysis/synthesis of a wide range of natural textures. We compare textures synthesized from a sample image, with and without dominant texture detection. We also compare our approach to that of using a texture segmentation technique alone, and to using Euclidean, rather than diffusion, distances between texture features.     

Real-time structured texture synthesis and editing using image-mesh analogies

We present a novel texture synthesis technique designed to reproduce at real-time frame-rates example texture images, with a special focus on patterns characterized by structural arrangements. Unlike current pixel-, patch- or texton-based schemes, that operate in image space, our approach is structural. We propose to assimilate texture images to corresponding 2D geometric meshes (called texture meshes). Our analysis mainly consists in generating automatically these meshes, while synthesis is then based on the creation of new vertex/polygon distributions matching some arrangement map. The output texture image is obtained by rasterizing the previously generated polygons using graphics hardware capabilities, which guarantees high speed performance. By operating in geometry space instead of image/pixel space, the proposed structural approach has a major advantage over current techniques: beyond pure texture reproduction, it allows us to define various tools, which allow users to further modify locally or globally and in real-time structural components of textures. By controlling the arrangement map, users can substitute new meshes in order to completely modify the structural appearance of input textures, yet maintaining a certain visual resemblance with the initial example image.     

Importance Driven Halftoning

Most halftoning techniques have been primarily concerned with achieving an accurate reproduction of local gray-scale intensities while avoiding the introduction of artifacts. A secondary concern in halftoning has been the preservation of edges in the halftoned image. In this paper, we will introduce a new halftoning technique that utilizes a bandpass pyramid to achieve an accurate reproduction of important attributes in the image. Ink is distributed through the bandpass pyramid primarily according to a user defined importance function. This technique has three main characteristics. First, our technique can produce results similar to many other halftoning techniques by allowing a generic importance function to be specified. If the chosen importance function is average intensity we obtain results similar to traditional halftoning. We also show how the importance function can be changed to highlight areas with high variance. Second, in addition to changing the importance function, the drawing primitives can also be changed. By using line segments instead of single pixels as drawing primitives we illustrate how edge enhancement can be achieved. Third, this technique allows the user to easily limit the number drawing primitives used. This is useful in limited resource rendering.
In addition to providing a tailorable halftoning technique our method can easily be adapted to produce two tone non-photorealistic (NPR) images. We illustrate this by showing how sketched effects can be achieved by aligning the drawing primitives according to different image attributes.     

基于最小平方差模型的改进半色调技术

基于模型的半色调技术是根据显示设备和人眼视觉系统的特性从而使图像质量达到最优,其中基于最小平方差模型的半色调技术是其中一种比较好的方法,而基于最小平方差模型的改进半色调技术则是在前者的基础上进行了改进,提出了一种新的迭代方法即取反/交换法.该技术的基本思想是对二进制图像进行打印模型和视觉模型处理,和对原始灰度图像仅进行视觉模型处理,使两者之间的输出图像之间的误差最小.实验证明该技术比传统技术具有更高的分辨率和更多的灰度级,图像更清晰.     

Halftoning of image sequences

We present an algorithm for the halftoning of greyscale image sequences. This facilitates the display of video sequences on black-and-white visual displays (e.g., high-qualityX-terminals) for multimedia applications. The main problem to be overcome when halftoning sequences is the temporal flicker between successive images.The classical problem of halftoning a static greyscale image may be posed as an optimization problem. We present an iterative algorithm for its solution. At the expense of being slower, our algorithm achieves visual results on static images better than those obtained from classic halftoning algorithms.We extend our static halftoning algorithm to image sequence halftoning. Temporal correlation between the halftoned versions of image sequences is guaranteed by using an incremental algorithm transfering information between the images. This results in binary sequences with relatively little high-frequency temporal noise, a feature that facilitates efficient no-loss compression (14) of the results.     

Color recovery of black-and-white halftoned images via categorized color-embedding look-up tables

A new method of recovering the original colors of black-and-white (B&W) halftoned images with homogeneous dot patterns is proposed. The conventional inverse halftoning method, which uses a look-up table (LUT), can establish the relation between the halftoned patterns and the corresponding gray levels, while the conventional reversible color to gray conversion method can recover the original colors from a given color-embedded gray image. To accomplish our goal of original color recovery from B&W halftoned patterns, an approach of combining the conventional inverse halftoning and reversible color to gray conversion is presented in this paper. Differently from the conventional method of inverse halftoning via LUT, four LUTs categorized according to the red, green, blue, and gray reference colors are designed to more accurately map a specific B&W halftone pattern into the corresponding color-embedded gray level based on the observation that the shapes of the halftone patterns depend on input colors, thereby increasing the color recovery accuracy. Also, a color mapping method based on a linear regression which models the relation between the recovered colors and the original colors is introduced to adjust the initially recovered colors more closely to the original colors. Experimental results show that unknown original colors can be recovered from B&W halftoned images via the proposed method.     

Bit‐depth extension: Overcoming LCD‐driver limitations by using models of the equivalent input noise of the visual system

Abstract— Continuous tone, or “contone,” imagery usually has 24 bits/pixel as a minimum, with 8 bits each for the three primaries in typical displays. However, lower‐cost displays constrain this number because of various system limitations. Conversely, higher‐quality displays seek to achieve 9–10 bits/pixel/color, though there may be system bottlenecks limited to 8. The two main artifacts from reduced bit‐depth are contouring and loss of amplitude detail; these can be prevented by dithering the image prior to these bit‐depth losses. Our technique builds on Roberts's noise‐modulation idea and the subsequently influenced work in halftoning for hardcopy and dithering for displays. However, most halftoning/dithering work was primarily directed to displays at the lower end of bits/pixel (e.g., 1 bit as in halftoning) and higher ppi. We approach the problem from the higher end of bits/pixel/color, for example, 6–8, and lower spatial resolution (<100 ppi), which changes the game substantially from halftoning experience. Instead of spatial dither, it is better to use an amplitude dither. In addition, dynamic displays allow for the use of a temporal dithering component. This paper will report on techniques and observations made in achieving contone quality on ～100‐or‐less‐ppi LCDs starting from 4‐ to 8‐bit driver limits, and resulting with no visible dither patterns, noise, contours, or loss of amplitude detail at viewing distances as close as the near focus limit (～120 mm).     

基于图形硬件的纹理图像编码与实时绘制算法

真实感绘制对于细节的要求越来越高,应用程序通常采用多幅或大幅分辨率很高的纹理图像,有限的内存空间就成了一个制约的瓶颈.针对纹理图像的特点和可编程图形硬件的特殊要求,该文提出了一种新的面向绘制的编码算法--增量式纹理编码算法及相应的解压绘制算法,有效地解决了纹理存储容量和真实感之间的矛盾,并利用可编程图形硬件实现了实时解压绘制.该算法在图像压缩编码过程中,动态添加码表内容,只有当已有码表内容不能表示当前图像区域时,才增加码表内容.这种方法不仅能够对于自相似性较强的纹理图像取得很高的压缩比,而且由于码表的动态更新特性,可以对图像序列进行流式编码.在绘制纹理时,该算法充分利用了现有可编程图像硬件的特性,实现了实时解压绘制.文中分别对于静态图像和动态图像序列进行了实验,结果显示,此方法能灵活有效地对各类纹理图像进行编码.     

一种为三维物体表面添加纹理的精确方法*

针对真实物体进行三维数字化重建的工程中,物体的空间位置及色彩等特征的数据采集始终是一项困难的,同时却又是十分重要的工作,设计的三维光学数字成像系统可以同时采集物体在同一个方向的深度图像和与它精确对应的纹理图像,在深度图像合成的同时进行纹理图像的融合.在进行多视角的纹理图像融合时,对权函数的设定提出了新的准则,使融合后的纹理图像更加逼真,可以产生高真实感的物体三维数字化模型.     

半色调图像的质量评价研究

数字半色调技术是图像再现系统的核心,其算法的优劣直接影响到再现图像的视觉质量。对两类典型的数字半色调图像质量评价方法进行了简要介绍。基于Visual C#编程语言建立了数字半色调算法实验平台,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比较和分析。     

Diversifying Semantic Image Synthesis and Editing via Class- and Layer-wise VAEs

Semantic image synthesis is a process for generating photorealistic images from a single semantic mask. To enrich the diversity of multimodal image synthesis, previous methods have controlled the global appearance of an output image by learning a single latent space. However, a single latent code is often insufficient for capturing various object styles because object appearance depends on multiple factors. To handle individual factors that determine object styles, we propose a class- and layer-wise extension to the variational autoencoder (VAE) framework that allows flexible control over each object class at the local to global levels by learning multiple latent spaces. Furthermore, we demonstrate that our method generates images that are both plausible and more diverse compared to state-of-the-art methods via extensive experiments with real and synthetic datasets in three different domains. We also show that our method enables a wide range of applications in image synthesis and editing tasks.     

Walk-Through Illustrations: Frame-Coherent Pen-and-Ink Style in a Game Engine

In this paper we show how a game engine designed to generate photorealistic images can be extended to produce non-photorealistic and hybrid renditions. We introduce new hardware-based methods to accomplish pen-and-ink illustrations. The combination of the highly optimized processing of a game engine and the use of hardware for NPR algorithms yields real-time animation of pen-and-ink illustrations.
The particular advance of this method is that it yields the first real-time, frame-coherent pen-and-ink animations which maintain both tone and texture.     

图像逆半调及其质量评价综述

数字半调是数字印刷乃至现代印刷的核心技术之一。半调可使连续色调图像转换为二值图像。如需对半调图像作分类识别、图像压缩、图像增强等处理,就应先让半调图像重建为连续色调图像,即进行逆半调处理。首先介绍了半调图像的不同发展阶段;然后对已有的逆半调方法根据不同的图像恢复依据进行了分类介绍,并对重建的逆半调图像的质量进行了客观评价;最后总结了已有逆半调方法的不足,并指出了未来可改进的关键方向。     

一种新的图像纹理表示方法

该文基于纹理元直方图导出了纹理的新表示方法,并根据正交镜像滤波器的小波变换能量的转换和量化来定义纹理元。此种,给出了数种小波纹理特征集的实验评价,此方法具有将Brodatz纹理分类的极好性能。同时还研究了数种考虑近似旋转不变性或比例不变性的变换。最后,引入了生成纹理直方图和形成二进制纹理集的特征空间的过程,而且纹理直方图和二进制纹理集的特征空间与颜色直方图是对称的。获得纹理的这些表示旨在为度量纹理的相似性和从图像中抽取纹理区域。     

Photorealistic Material Editing Through Direct Image Manipulation

Creating photorealistic materials for light transport algorithms requires carefully fine-tuning a set of material properties to achieve a desired artistic effect. This is typically a lengthy process that involves a trained artist with specialized knowledge. In this work, we present a technique that aims to empower novice and intermediate-level users to synthesize high-quality photorealistic materials by only requiring basic image processing knowledge. In the proposed workflow, the user starts with an input image and applies a few intuitive transforms (e.g., colorization, image inpainting) within a 2D image editor of their choice, and in the next step, our technique produces a photorealistic result that approximates this target image. Our method combines the advantages of a neural network-augmented optimizer and an encoder neural network to produce high-quality output results within 30 seconds. We also demonstrate that it is resilient against poorly-edited target images and propose a simple extension to predict image sequences with a strict time budget of 1–2 seconds per image.     

Halftone Visual Cryptography Via Error Diffusion

Halftone visual cryptography (HVC) enlarges the area of visual cryptography by the addition of digital halftoning techniques. In particular, in visual secret sharing schemes, a secret image can be encoded into halftone shares taking meaningful visual information. In this paper, HVC construction methods based on error diffusion are proposed. The secret image is concurrently embedded into binary valued shares while these shares are halftoned by error diffusion—the workhorse standard of halftoning algorithms. Error diffusion has low complexity and provides halftone shares with good image quality. A reconstructed secret image, obtained by stacking qualified shares together, does not suffer from cross interference of share images. Factors affecting the share image quality and the contrast of the reconstructed image are discussed. Simulation results show several illustrative examples.      

基于纹理和草图的图像铅笔画绘制

针对目前铅笔画生成方法中的线条不够灵活、纹理缺少方向感的问题,提出了一种基于带方向的纹理和线条草图将一幅图像转换为铅笔画风格的方法。首先,对输入图像进行直方图匹配得到图像的色调图,并将图像分割为多个区域,对每个区域,根据其颜色和形状计算其色调和方向,以此决定铅笔纹理的色调和方向;然后,通过可调整的线性卷积方法得到铅笔画的线条草图;最后,将纹理和草图结合得到铅笔画效果。运用提出的方法对不同类型的自然图像进行了铅笔画的转换,并与已有的线卷积积分方法和基于色调的方法进行了对比。实验结果表明带方向的区域纹理能更好地模拟手工铅笔画纹理的方向,可调整的线条能够更好地模拟手工铅笔画的线条的随意性和灵活性。     

Neural network based method for image halftoning and inverse halftoning

A hybrid neural network based method for halftoning and inverse halftoning of digital images is presented. The halftone image is performed by single-layer perceptron neural network (SLPNN), and its corresponding continuous-tone image is reconstructed by radial-basis function neural network (RBFNN). The combined training procedure produces halftone images and the corresponding continuous tone images at the same time. The PSNR performance and visual image quality of these contone images achieved is comparable to the well-known inverse halftoning methods. The resultant halftone images compared with the error diffusion halftone are visually good, too. Furthermore, we apply different kinds of halftone images to a bi-level image compression method, called Block Arithmetic Coding for Image Compression (BACIC), which is better than the current facsimile methods.