Halftone Images Research Articles

Printed Image Watermarking with Synchronization Using Direct Binary Search

In this paper, we reveal the impact of the fixed synchronization pattern on the halftone image under DBS processing; and an improved watermarking method is proposed to avoid this impact, which is extended from a previously developed DBS based watermarking method. The watermark and synchronization pattern is to be embedded into the appropriate region of the host image adaptively; and excellent image quality and decent watermark capacity is provided. The method has good resistance to a printing and scanning attack while only size of the watermark and host image is required additionally in the watermark detection. Experimental results are presented for some special host images, including a sketch and a round logo to prove the flexibility of the method.

Secure Halftone Image Steganography Based on Pixel Density Transition

Most state-of-the-art halftone image steganographic techniques only consider the flipping distortion according to the human visual system, which are not always secure when they are attacked by steganalyzers. In this paper, we propose a halftone image steganographic scheme that aims to generate stego images with good visual quality and strong statistical security of anti-steganalysis. First, the concept of pixel density is proposed and a novel construction called pixel density histogram (PDH) is proposed to design a “ $\pm 1$ ± 1 embedding” scheme for halftone images. Then, we optimize density pair selection to select density blocks that can improve visual quality. Finally, the messages are embedded through pixel density transition, where a novel pixel flipping strategy is proposed, which can maintain the structural dependence by optimizing the pixel mesh Markov transition matrix (PMMTM). The experimental results demonstrate that the proposed steganography scheme can achieve strong statistical security of anti-steganalysis with good visual quality without degrading the embedding capacity.

Applications of Algebraic Moments for Corner and Edge Detection for a Locally Angular Model

An approach to subpixel corner and edge detection in images is described. The approach is based on algebraic moments of the brightness function describing a halftone image. For an ideal two-dimensional L-corner edge, we consider a model with the following four parameters: the coordinates of the corner vertex, the orientation and the degree measure of the corner, and the brightness values from both sides of the edge. A particular case of the angular model is a linear model that describes a linear edge. To obtain all parameters of the model, six algebraic moments are used. To compute the moments rapidly, masks are used. Based on the angular model, we propose an algorithm that makes it possible to quickly refine the coordinates of the corner and edge points in the image with subpixel accuracy. The use of integral characteristics increases the resistance to various kinds of noises. We perform experiments to confirm the efficiency of the proposed approach.

Ideal Huffman Code for Lossless Image Compression for Ubiquitous Access

<p>Compression technique is adopted to solve various big data problems such as storage and transmission. The growth of cloud computing and smart phone industries has led to generation of huge volume of digital data. Digital data can be in various forms as audio, video, images and documents. These digital data are generally compressed and stored in cloud storage environment. Efficient storing and retrieval mechanism of digital data by adopting good compression technique will result in reducing cost. The compression technique is composed of lossy and lossless compression technique. Here we consider Lossless image compression technique, minimizing the number of bits for encoding will aid in improving the coding efficiency and high compression. Fixed length coding cannot assure in minimizing bit length. In order to minimize the bits variable Length codes with prefix-free codes nature are preferred. However the existing compression model presented induce high computing overhead, to address this issue, this work presents an ideal and efficient modified Huffman technique that improves compression factor up to 33.44% for Bi-level images and 32.578% for Half-tone Images. The average computation time both encoding and decoding shows an improvement of 20.73% for Bi-level images and 28.71% for Half-tone images. The proposed work has achieved overall 2% increase in coding efficiency, reduced memory usage of 0.435% for Bi-level images and 0.19% for Half-tone Images. The overall result achieved shows that the proposed model can be adopted to support ubiquitous access to digital data.</p>

Improving the Visual Quality of Size-Invariant Visual Cryptography for Grayscale Images: An Analysis-by-Synthesis (AbS) Approach.

In visual cryptography (VC) for grayscale image, size reduction leads to bad perceptual quality to the reconstructed secret image. To improve the quality, the current efforts are limited to the design of VC algorithm for binary image, and measuring the quality with metrics that are not directly related to how the human visual system (HVS) perceives halftone images. We propose an analysis-by-synthesis (AbS) framework to integrate the halftoning process and the VC encoding: the secret pixel/block is reconstructed from the shares in the encoder and the error between the reconstructed secret and the original secret images is fed back and compensated concurrently by the error diffusion process. In doing so, the error between the reconstructed secret and original secret is pushed to high frequency band, thus producing visually pleasing reconstructed secret image. This framework is simple and flexible in that it can be combined with many existing size-invariant VC algorithms, including probabilistic VC, random grid VC and vector/block VC. More importantly, it is proved that this AbS framework is as secure as the traditional VC algorithms. Experimental results demonstrate the effectiveness of the proposed AbS framework.

Efficient halftone image steganography based on dispersion degree optimization

Halftone images are usually used in facsimile and halftone image steganography can be used for facsimile channel. In recent years, real-time image processing becomes more and more important. In this paper, an efficient block-based steganographic method for halftone images is proposed. This method is based on optimal dispersion degree (DD), which can measure the complexity of the region texture. To reduce the visual distortion, the blocks with complex texture can be selected as carriers according to the dispersion degree. Finally, the secret messages are embedded by flipping the pixels that can minimize the changes of texture structure. The experiments demonstrate that the proposed scheme maintains a good image visual quality and realizes acceptable statistical security with high capacity.

Deep context-aware descreening and rescreening of halftone images

A fully automatic method for descreening halftone images is presented based on convolutional neural networks with end-to-end learning. Incorporating context level information, the proposed method not only removes halftone artifacts but also synthesizes the fine details lost during halftone. The method consists of two main stages. In the first stage, intrinsic features of the scene are extracted, the low-frequency reconstruction of the image is estimated, and halftone patterns are removed. For the intrinsic features, the edges and object-categories are estimated and fed to the next stage as strong visual and contextual cues. In the second stage, fine details are synthesized on top of the low-frequency output based on an adversarial generative model. In addition, the novel problem of rescreening is addressed, where a natural input image is halftoned so as to be similar to a separately given reference halftone image. To this end, a two-stage convolutional neural network is also presented. Both networks are trained with millions of before-and-after example image pairs of various halftone styles. Qualitative and quantitative evaluations are provided, which demonstrates the effectiveness of the proposed methods.

Автоматична сегментація напівтонових зображень методом ЦДОВ

Автоматична сегментація напівтонових зображень методом ЦДОВ

Subpixel Estimation of the Node Coordinates of Quasiperiodic Textures

An algorithm is proposed to estimate the node coordinates of deformed lattices of quasiperiodic textures with subpixel accuracy. The algorithm consists of two steps. In the first step, the frequency and initial phase vectors of a polyharmonic brightness function model are calculated from the characteristics of spectral outliers of image fragments. The obtained estimates are used to determine the coordinates of the nodes of the local lattice. In the second step, the local lattices are combined into a global lattice for the entire image of the quasi-periodic texture. Using high-accuracy estimates of model parameters from small image fragments ensures stable operation of the algorithm for significant deformations of the lattice and sub-pixel accuracy in estimating the coordinates of its nodes. Results of computer simulation and processing of real halftone images of quasiperiodic textures are given demonstrating the effectiveness of the proposed algorithm.

Separable reversible data hiding in encrypted halftone image

In this paper, new high-capacity separable reversible data hiding in an encrypted halftoned image is proposed. The proposed scheme used Hamming code to exploit embedding efficiency with a halftoned image. Our proposed scheme is meeting a condition of separable reversible data hiding in the encrypted image (SRDHEI) and can achieve a high embedding efficiency of a halftoned image with low distortion. Experimental results also show that the scheme provides a large embedding payload and reconstructs about the same original halftoned image and embedded additional information.

Two algorithms for fast 2D node generation: Application to RBF meshless discretization of diffusion problems and image halftoning

Mesh generation techniques for traditional mesh based numerical approaches such as FEM and FVM have now reached a good degree of maturity. There is no such an acknowledged background when dealing with node generation techniques for meshless numerical approaches, despite their theoretical simplicity and efficiency; furthermore node generation can be put in connection with some well-known image approximation techniques. Two node generation algorithms are here proposed and employed in the numerical solution of 2D steady state diffusion problems by means of a local Radial Basis Function (RBF) meshless method. Finally, such algorithms are also tested for grayscale image approximation through stippling.

Detection of Orientation-Modulation Embedded Data in Color Printed Natural Images

This article addresses methods for detection of orientation-modulation data embedded in color dispersed-dot-halftone images. Several state-of-the-art methods for detection of orientation-embedded data in printed halftone images have been proposed, however they have only been evaluated independently without comparing with each other. We propose an improved detection method, which is using Principal Component Analysis (PCA) components as oriented-feature extractors, and a probabilistic model for the print-and-scan channel for maximum likelihood detection. The proposed detector and four state-of-the-art detectors are compared with each other in terms of correct detection rate, using a comprehensive testing set of printed natural images captured with three different devices. The proposed detector achieves highest correct detection rate using fewer feature extractors than the other methods, and it is significantly more robust to non-calibrated devices used for capturing the printed images. This is mostly due to the improved PCA-based oriented-feature extractors that are responsive to the embedded orientations and robust and insensitive to the other visual content.

Sparsity-based inverse halftoning via semi-coupled multi-dictionary learning and structural clustering

Inverse halftoning is the restoration of a continuous-tone image from its halftone version, which is a critical process for halftone transform, digital archive management and high precision identification of halftone. In this paper, a novel inverse halftoning method based on semi-coupled multi-dictionary learning is proposed to address the cross-style image restoration from halftone images to continuous-tone images. By using semi-coupled multi-dictionary learning, multiple dictionary pairs and their corresponding mapping functions between continuous-tone image and its halftone version could be simultaneously learned. The learned multiple dictionary pairs can well represent the structure characteristics of halftone images and continuous-tone images, respectively. In addition, the mapping functions learned by semi-coupled manner can bridge the gap between the two different style images of halftone image and continuous-tone image. Unlike the existed methods, the proposed method could effectively relax the assumption of the same sparse coding coefficients in coupled dictionary learning. To obtain more accurate mapping functions, a structural clustering method for cross-style image patches is proposed by using SUSAN (smallest univalue segment assimilating nucleus) filtering and HOG (histogram of oriented gradient) features, which can capture the similar structure features from halftone images and continuous-tone images, and thus improve the classification accurate rate of halftone image patches. The experimental results demonstrate that the proposed method can restore higher quality continuous-tone images than that produced by the state-of-the-art methods, which not only reduce the screen noise in smooth regions, but also provide well fine details and clear edges.

SEGMENTATION OF IMAGES OF EYE GROUND BLOOD VESSELS INVOLVING APPLICATION OF FUZZY IMAGING

Segmentation of images is an important task while processing images. Among the most widespread methods are methods based on pixel clustering, histogram methods, morphological methods, watershed segmentation, multiscale segmentation, and others. A promising trend in image processing is the use of fuzzy logic methods and the fuzzy set theory. Their application makes it possible to improve the quality of processing by providing information in a fuzzy form. The article proposes a new method for images segmentation involving boundaries detection based on the fuzzy representation of the image and fuzzy pixels. The membership functions are proposed for describing fuzzy pixels, and the requirements for their form and type are provided. The most suitable membership functions for fuzzy imaging are the s-function and the π-function. A description of a new method for boundaries detection based on the Sobel operator and the developed fuzzy type of image is described. In this case, standard calculations of the image brightness gradient are supplemented with their fuzzy versions which are then combined to obtain the final result. The experimental verification of the developed method is carried out using the example of eyeground images. In addition to the fuzzy detection of boundaries for the detection of blood vessels, the images were subjected to pre-processing (halftone imaging, mask matching, contrasting), morphological operators (thinning of boundaries, dilatation), and an algorithm for removing small details was applied. During testing, the developed algorithm showed acceptable results in terms of segmentation of blood vessels. In the future, a fuzzy image model can be extended to use fuzzy features of the second and higher types

An Optimized Halftone Visual Cryptography Scheme Using Error Diffusion

Halftone Visual Cryptography (HVC) is an encryption technique that encodes the secret image into halftone images in order to produce secure meaningful shares. Many methods have been proposed for developing HVC to protect the security of the images. Yet, these methods still have some problems such as poor visual quality of shares, large pixel expansion, interference of secret image on shared images, and interference shared images on retrieved image. To solve such problems, an optimized HVC scheme (OHVCS) using Error Diffusion (ED) is proposed in this paper. The proposed scheme eliminates the explicit requirement of codebook and reduces the random patterns of the shared images, as it encodes only the black pixels of the secret image, taking into account that the pixel expansion is the smallest size to be used. Moreover, it performs the basic concept of Visual Cryptography (VC); therefore, the security of the construction scheme is assured. The experimental results, performance evaluation through statistical analysis, and comparison with some existing schemes in various aspects of HVC show the effectiveness of the proposed scheme.

Color CLU-DBS Halftoning based on Neugebauer Primary Area Coverage: Improving the Breed

Though a color aperiodic, clustered-dot, halftoning (NPACMS-MP-CLU-DBS) algorithm can overcome the visible moire and rosette artifacts in conventional color halftoning methods, it still has some disadvantages, such as the color mismatch caused by the initial stage color management method, and texture artifacts caused by the concentric-ring cluster structure. In this paper, first, a new color gamut mapping method is used during the color management process, that is an image-dependent mapping method, which can make the most use of the printer color gamut, in order to reduce the color mismatch between the continuous-tone original and printed halftone images. Secondly, a new color, clustered-DBS halftoning algorithm with separated-cluster structure is developed. As a color halftoning method based on the clustered-DBS algorithm, not only it can overcome the visible moire and rosette artifacts, but also the separated-cluster structure is more stable, compared with the concentric-ring cluster structure. It can also reduce the texture artifacts significantly.

High Quality Data Hiding in Halftone Image Based on Block Conjugate

This paper proposes a High quality data hiding in halftone image based on block conjugate (HQDHBC). We construct Least mean square filters (LMSF), and using LMSFs to evaluate the quality of halftone images. This paper proposes block conjugate property, and this property can be applied to hide a secret pattern. Therefore a data hiding method based on block conjugate can be proposed, and in this method two images should be divided into multiple blocks of M × N pixels, and in the corresponding block if the first M × N −1 pixels are conjugate or identical, the last pixel can implement normal halftone method instead of date hiding methods. Experimental results show that the proposed HQDHBC can be applied in gray-scale and color error diffused halftone images, and through implementing this method, not only the quality of halftone images can be improved, but also the Correct decoding rate (CDR) of revealed pattern can be guaranteed.

The Dancing Lares and the Serpent in the Garden: Religion at the Roman Street Corner by Harriet I. Flower

182 PHOENIX The Dancing Lares and the Serpent in the Garden: Religion at the Roman Street Corner. By Harriet I. Flower. Princeton, New Jersey: Princeton University Press. 2017. Pp. xiii, 394, 24 color and 70 b/w illustrations. In the mid-1800s King Ludwig i of Bavaria had a splendid Roman house, loosely modeled on the House of the Dioscuri in Pompeii, built in the city of Aschaffenburg. Hidden in the corners of the Pompejanum are references to Roman domestic religion: a winged snake decorates a kitchen wall, an altar is tucked away to the side of the atrium, and a small room acts as a lararium. The gods of the lararium, the Lares, are the focus of Harriet Flower’s rich and beautifully illustrated book. By surveying a wide range of evidence, it offers a compelling and coherent picture of how the Lares can fit into our wider picture of Roman society. This is the first comprehensive book-length investigation of the Lares, the (usually twin) deities that were worshipped in Roman households, at crossroads, and on property boundaries in the countryside. Unlike the major Roman gods, the Lares do not have a rich mythology associated with them and no detailed literary treatment survives. While the material remains of their worship have received attention from archaeologists, works on Roman religion tend to have little to say about the Lares.1 It may therefore seem surprising that a book would focus only on the Lares. At first glance the geographical and chronological focus also seem narrow: the book primarily concerns itself with the city of Rome with excursions to Pompeii, and, on one occasion, Delos.2 Many of the sources under discussion date to the late republic and the Augustan period. But, as Flower shows, if we look hard enough, the twin gods are everywhere: from fragments of material evidence to short references in inscriptions and literary texts, there are glimpses of the Romans interacting with these gods in settings ranging from private worship to shrines that served as rallying points during political disputes. The book looks at all these pieces of evidence and asks why the Lares were so popular. The study is divided into four parts, each grouping together several chapters of varying lengths. A preface summarizes the structure of the book and its intellectual aims, an epilogue considers the fate of the Lares in the Christian empire and three appendices provide, among other things, a list of all mentions of the Lares in Roman authors. The text is copiously illustrated throughout with both halftone images and color plates. Part One provides an overview of the various topics and approaches of the work. As stated in the preface, the book aims to show “how far we as modern researchers can rediscover and understand traditional Roman religion independent of pervasive comparisons and contrasts with various monotheisms” (ix). At the start of Part One, it is 1 Scholars tend to focus on either the domestic worship of the gods or their role in more public cults. So the Lares Compitales and the Lares Augusti receive a brief discussion in M. Beard, J. North, and S. Price, Religions of Rome (Cambridge 1998), but there is no significant reference to the Lares in domestic religion. R. Parker and K. Bowes in R. Raja and J. Rüpke (eds.), A Companion to the Archaeology of Religion in the Ancient World (Malden, MA 2015), on the other hand, focus on domestic worship. J. Bodel, “Cicero’s Minerva, Penates, and the Mother of the Lares: An Outline of Roman Domestic Religion,” in J. Bodel and S. M. Olyan (eds.), Household and Family Religion in Antiquity (Oxford 2008) 248–275, takes a broader approach to the various manifestations of the Lares and is thereby an intellectual precursor to the book under review, if on a different scale. 2 Those interested in provincial Lares will therefore have to start with case studies, for example, M. I. Portela Filgueiras, “Los dioses lares en la Hispania romana,” Lucentum 3 (1984) 153–180; A. Kaufmann-Heinimann, Götter und Lararien aus Augusta Raurica (Augst 1998). BOOK REVIEWS/COMPTES RENDUS 183 not only the Christianizing lens that is cast aside: republican...

Comparative study of description algorithms for complex-valued gradient fields of digital images using linear dimensionality reduction methods

The paper presents an analysis of various approaches to constructing descriptions for the gradient fields of digital images. The analyzed approaches are based on the well-known methods for data dimensionality reduction, such as Principal (PCA) and Independent (ICA) Component Analysis, Linear Discriminant Analysis (LDA). We apply these methods not to the original image, represented as a two-dimensional field of brightness (a halftone image), but to its secondary representation in the form of a two-dimensional gradient field, that is, a complex-valued image. In this case, approaches based on using both the entire gradient field and only its phase component are considered. In addition, two independent ways of forming the final description of the original object are considered: using expansion coefficients of the gradient field in a derived basis and using an original authors' design that is called model-oriented descriptors. With the latter, the number of real coefficients used in the description of the original object can be halved. The studies are conducted via solving a face recognition problem. The effectiveness of the analyzed methods is demonstrated by applying them to images from Extended Yale Face Database B. The comparison is made using a nearest neighbor's classifier.

PERANCANGAN APLIKASI PENYISIPAN CITRA BERWARNA PADA QR CODE DENGAN METODE HALFTONE

The project is made in the form of a software application that accepts input color image to be processed into Halftone QR-Code. Halftone QR-Code is a composite image of the QR-Code and halftone image that can be recognized by QR-Code Scanner. QR-Code image generated using the Library Massagingtoolkit-QRCode with alphanumeric text input degan various versions QR-Code in accordance with a lot of character input. The input image is processed into a halftone image with methods Ordered Dithering variation dither matrix 4 x 4 and 8 x 8. The image of the QR-Code and halftone images will be processed into QR-Code Halftone Pattern Assignment method. Output generated by the application Halftone QR-Code tested with QR-Code ZXing Library and QRAFTER application on Iphone 6s Plus and QR. The average rate of overall success with the test scenario ZXing QR-Code Library by 94%. The average rate of overall success with the test scenario QRAFTER application on Iphone 6s Plus from the laptop screen and hardcopy respectively by 100%.