Halftoning Technique Research Articles

Taming Reversible Halftoning Via Predictive Luminance.

Traditional halftoning usually drops colors when dithering images with binary dots, which makes it difficult to recover the original color information. We proposed a novel halftoning technique that converts a color image into a binary halftone with full restorability to its original version. Our novel base halftoning technique consists of two convolutional neural networks (CNNs) to produce the reversible halftone patterns, and a noise incentive block (NIB) to mitigate the flatness degradation issue of CNNs. Furthermore, to tackle the conflicts between the blue-noise quality and restoration accuracy in our novel base method, we proposed a predictor-embedded approach to offload predictable information from the network, which in our case is the luminance information resembling from the halftone pattern. Such an approach allows the network to gain more flexibility to produce halftones with better blue-noise quality without compromising the restoration quality. Detailed studies on the multiple-stage training method and loss weightings have been conducted. We have compared our predictor-embedded method and our novel method regarding spectrum analysis on halftone, halftone accuracy, restoration accuracy, and the data embedding studies. Our entropy evaluation evidences our halftone contains less encoding information than our novel base method. The experiments show our predictor-embedded method gains more flexibility to improve the blue-noise quality of halftones and maintains a comparable restoration quality with a higher tolerance for disturbances.

Utilizing the RGB Color Model and Halftone Technique for Color Segregation in Visual Cryptography

Utilizing the RGB Color Model and Halftone Technique for Color Segregation in Visual Cryptography

A survey of an inverse halftoning technique toward speech restoration of printed spectrogram images

A survey of an inverse halftoning technique toward speech restoration of printed spectrogram images

Half-Tone Visual Cryptography Scheme For RGB Color Images

Objectives: Currently used visual-cryptography methods which use binary and gray-level images have some shortcomings such as large pixel expansion, poor visual quality of the reconstructed image, etc. Further modifications in visualcryptography methods are required to provide error-free and better results. It has been observed that the use of color images is more convenient and accurate in approach. Method: This research study presents a new and optimal scheme for the visual-cryptography which is centered on RGB color images. Jarvis halftoning is applied on each decomposed color channel that is used in share generation. A special code matrix is defined for the generation of color shares and the optimal reconstruction of the original image. The method is tested with color images of different sizes, no specific dataset is required. Pixel Expansion, The Aspect Ratio, and Contrast of the method is compared with the existing method, and found more enhanced result. Findings: The scheme projected eliminates the problems of large pixel expansion and poor visual quality in the reconstructed images. The performance of the method is tested with the different statistical measures and values obtained as Mean Square Error (MSE):0, Peak- Signal-to-Noise-Ratio (PSNR): ¥, Universal Index Quality (UIQ):1, etc. This means that the original image is completely recovered with good contrast. Novelty: Color images of varied sizes and channels can be processed by applying the Jarvis half-toning technique through the codebook calculated to abolish the problems of pixel expansion and to improve the superiority of the renovated image. Keywords: Color HalfTone Images; Error Diffusion; Optimal Contrast; Secret and Secure Sharing Scheme; Expansion of Pixels

Blind Dual Watermarking Scheme Using Stucki Kernel and SPIHT for Image Self-Recovery

In this paper we propose a blind dual watermarking scheme using Set Partitioning in Hierarchical Trees (SPIHT) and Stucki Kernel halftone technique for the tamper detection and image self-recovery. The watermark consists of authentication bits for tampering area location and recovery bits for image restoration. We generate two recovery bits to ensure the high-quality recovery of the tampered image. The primary recovery bit is generated by the SPIHT encoding, and the secondary recovery bit is generated by the Stucki Kernel halftone technique. Then the authentication bit is generated based on the recovery bits. Before embedding the watermark, we shuffle the watermark bits through Arnold cat mapping and diagonal mapping to improve the security and quality of the restored image. LSB-based watermarking technique is used to embed the watermark into the original image to ensure the invisibility of the watermarked image. Experiments have been conducted on two datasets, BOW2 and USC-SIPI, and results show that the proposed scheme can achieve high restoration quality. Comparison with the existing works demonstrate the good performance and superiority of the proposed scheme.

Towards High-Resolution Copy-Evident Ceramic Tiles: A Deep Learning Framework for Halftoning and Watermarking

Ceramic art is essential in interior design and decoration, and making exquisite ceramic tiles imposes strict requirements for inkjet printing technology. High-resolution ceramic tiles are often produced through inkjet printing, in which the input images are converted into a halftone format. However, traditional binary halftoning techniques cannot produce high-resolution images for the ensuing printing process. Given that the processes of inkjet printing and high-temperature firing of ceramic tiles are a highly complex nonlinear system, and existing halftoning methods pose intractable problems, including inconsistent textures and color deviations. Based on a modified U-Net model and a modified error diffusion algorithm, we propose a multilevel halftoning method, which is capable of converting color-separation images of ceramic tiles into high-resolution halftone images. To deter copyright infringement, we further apply an ad hoc invisible watermarking method for halftone images. In this paper, we propose a four-stage framework: (1) A self-built dataset is used to solve non-convergence and overfitting problems caused by the unbalanced samples and non-uniqueness of halftone images. (2) A modified U-Net model is trained on the self-built dataset and applied to the ceramic-tile images. (3) An improved error diffusion algorithm is used to calibrate and convert the predicted continuous-tone transition images into multilevel halftone images for inkjet printing. (4) A invisible and robust watermark is embedding algorithm towards halftone images is proposed for copyright protection. Experimental results show that our methodology is effective for performing the color-to-halftone transformation and identifying the copyright.

Computational experiment of error diffusion dithering for depth reduction in images

The halftone technique is a process that employs patterns formed by black and white dots to reduce the number of gray levels in an image. Due to the tendency of the human visual system to soften the distinction between points with different shades, the patterns of black and white dots produce a visual effect as if the image were composed of shades of gray and dark. This technique is quite old and is widely used in printing images in newspapers and magazines, in which only black (ink) and white (paper) levels are needed. There are several methods for generating halftone images. In this article we explore dithering with error diffusion and an analysis of different halftone techniques is presented using error diffusion to change the depth of the image. The results showed that the depth of the image changes 1/8 per channel, this halftone technique can be used to reduce an image weight, losing information but achieving good results, depending on the context.
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An Effective Semi-fragile Watermarking Method for Image Authentication Based on Lifting Wavelet Transform and Feed-Forward Neural Network

Digital watermarking is a significant issue in the field of information security and avoiding the misuse of images in the world of Internet and communication. This paper proposes a novel watermarking method for tamper detection and recovery using semi-fragile data hiding, based on lifting wavelet transform (LWT) and feed-forward neural network (FNN). In this work, first, the host image is decomposed up to one level using LWT, and the discrete cosine transform (DCT) is applied to each 2×2 blocks of diagonal details. Next, a random binary sequence is embedded in each block as the watermark by correlating DC coefficients. In the authentication stage, first, the geometry is analyzed by using speeded up robust features (SURF) algorithm and extract watermark bits by using FNN. Afterward, logical exclusive or operation between original and extracted watermark is applied to detect tampered region. Eventually, in the recovery stage, tampered regions are recovered using the inverse halftoning technique. The performance and efficiency of the method and its robustness against various geometric, non-geometric, and hybrid attacks are reported. From the experimental results, it can be seen that the proposed method is superior in terms of robustness and quality of the watermarked and recovered images, respectively, compared to the state-of-the-art methods. Besides, imperceptibility has been improved by using different correlation steps as the gain factor for flat (smooth) and texture (rough) blocks. Based on the advantages exhibited, the proposed method outperforms the related works, in terms of superiority, efficiency, and effectiveness for tamper detection and recovery-based applications.

Watermarking Framework for Authentication and Self-recovery of Tampered Colour Images

Methods of authentication and self-recovery of tampered information in digital images have been in constant development during the last years. These frameworks are developed by watermarking techniques, which generate an image digest, which is embedded inside the image that must be protected. In this paper, a method of authentication and self-recovery of tampered information in digital images is proposed. Our approach first generates the authentication watermarks, which are based on XOR operations on non-overlapping blocks, subsequently by using a halftoning technique the recovery watermark is generated. To have a higher performance, three copies of each watermark are embedded to have more chance to extract the recovery watermark. To evaluate the quality of the obtained images, the objective criterion of peak signal-to-noise ratio (PSNR) and Structural Similarity Index (SSIM) are used. The experimental results demonstrate the effectiveness of our method in comparisons with other schemes reported in the literature, where the quality of the watermarked images, the quality of the reconstruction images and the recovery rate of each scheme were evaluated.

Size-Invariant Visual Cryptography With Improved Perceptual Quality for Grayscale Image

The reconstructed image of the size-invariant visual cryptography (VC) is inevitably accompanied by the loss of secret image information and the degradation of perceptual quality. Here, the halftone technique comes to the forefront since it can realistically simulate the grayscale image from a discrete binary image. Thus, by combining VC sharing with grayscale image halftone technique, this paper proposes a size-invariant VC scheme for grayscale image underpinned by the efficient direct binary search (EDBS) algorithm, in which the multi-pixel encryption VC sharing is adopted into the EDBS halftone process. Through local optimizations and global iterations, the optimal reconstructed image is obtained. To further enhance the contrast of the reconstructed image with limited computational power, the image information is probabilistically extracted according to the inverse mapping in the codebook. It is theoretically proved that the proposed scheme is as secure as the traditional VC, while its effectiveness is validated through experiments and comparative analyses.

Fourier single-pixel imaging based on edge attenuation technique

Fourier single-pixel imaging has been widely concerned with its real-time and high quality. However, DMD (Digital Micromirror Array) as an illumination source cannot produce a continuous gray level of the Fourier basis pattern. Therefore, the inevitable error is produced. This paper proposes a halftone technique based on edge attenuation, which can be applied to the Fourier basis pattern generation method on DMD without loss of resolution, and compared with the traditional methods, the invention solves the problem that the traditional methods has a single scanning direction and accumulated errors, finally; we improve the image quality.

Developing a visual method to characterize displays

The goal is to develop a display characterization model to include the personal vision characteristics. A two-step model for visually characterizing displays was developed. It was based on the concept of half-toning technique for obtaining gamma factor for each colour channel, and unique hue concept for achieving 3x3 matrix coefficients, respectively. The variation can be presented by the optimized RGB primaries for each observer. The typical difference between the individual and the measured ground truth is 2.2 in terms of CIEDE2000 units.

Optimized Inverse Halftoning Technique Based on Bilateral Filter

Halftoning and inverse-halftoning processes are tools that have been widely used in the last few years, which are used in scientific research for the development of visual cryptography, steganography, reconstruction of tampered images, authentication systems, among others. In this paper, a technique of inverse-halftoning, which generates grayscale images from halftone images, is proposed. This method obtains a high quality in the generated grayscale images. Our approach first uses a low-complexity low-pass filter to obtain an approximation to the desired grayscale image, and then a bilateral filter is applied in order to eliminate regions with noise without affecting the edges of the image. To evaluate the quality of the obtained images, the objective criterion of peak signal-to-noise ratio (PSNR) is used. The experimental results demonstrate the effectiveness of our method in comparisons with other schemes reported in the literature, additionally, the average processing time for the proposed system maintains a good performance against the reported schemes.

Hatching for 3D prints: Line-based halftoning for dual extrusion fused deposition modeling

This work presents a halftoning technique to manufacture 3D objects with the appearance of continuous grayscale imagery for Fused Deposition Modeling (FDM) printers. While droplet-based dithering is a common halftoning technique, this is not applicable to FDM printing, since FDM builds up objects by extruding material in semi-continuous paths. The line-based halftoning principle called ‘hatching’ is applied to the line patterns naturally occurring in FDM prints, which are built up in a layer-by-layer fashion. The proposed halftoning technique is not limited by the challenges existing techniques face; existing FDM coloring techniques greatly influence the surface geometry and deteriorate with surface slopes deviating from vertical or greatly influence the basic parameters of the printing process and thereby the structural properties of the resulting product. Furthermore, the proposed technique has little effect on printing time. Experiments on a dual-nozzle FDM printer show promising results. Future work is required to calibrate the perceived tone.

Digital surface model applied to unmanned aerial vehicle based photogrammetry to assess potential biotic or abiotic effects on grapevine canopies

Abstract: Accurate data acquisition and analysis to obtain crop canopy information are critical steps to understand plant growth dynamics and to assess the potential impacts of biotic or abiotic stresses on plant development. A versatile and easy to use monitoring system will allow researchers and growers to improve the follow-up management strategies within farms once potential problems have been detected. This study reviewed existing remote sensing platforms and relevant information applied to crops and specifically grapevines to equip a simple Unmanned Aerial Vehicle (UAV) using a visible high definition RGB camera. The objective of the proposed Unmanned Aerial System (UAS) was to implement a Digital Surface Model (DSM) in order to obtain accurate information about the affected or missing grapevines that can be attributed to potential biotic or abiotic stress effects. The analysis process started with a three-dimensional (3D) reconstruction from the RGB images collected from grapevines using the UAS and the Structure from Motion (SfM) technique to obtain the DSM applied on a per-plant basis. Then, the DSM was expressed as greyscale images according to the halftone technique to finally extract the information of affected and missing grapevines using computer vision algorithms based on canopy cover measurement and classification. To validate the automated method proposed, each grapevine row was visually inspected within the study area. The inspection was then compared to the digital assessment using the proposed UAS in order to validate calculations of affected and missing grapevines for the whole studied vineyard. Results showed that the percentage of affected and missing grapevines was 9.5% and 7.3%, respectively from the area studied. Therefore, for this specific study, the abiotic stress that affected the experimental vineyard (frost) impacted a total of 16.8 % of plants. This study provided a new method for automatically surveying affected or missing grapevines in the field and an evaluation tool for plant growth conditions, which can be implemented for other uses such as canopy management, irrigation scheduling and other precision agricultural applications. Keywords: remote sensing, canopy cover, viticultural management, frost damage, digital surface model DOI: 10.3965/j.ijabe.20160906.2908 Citation: Su B F, Xue J R, Xie C Y, Fang Y L, Song Y Y, Fuentes S. Digital surface model applied to unmanned aerial vehicle based photogrammetry to assess potential biotic or abiotic effects on grapevine canopies. Int J Agric & Biol Eng, 2016; 9(6): 119－130.

Secure self-recovery watermarking scheme for error concealment and tampering detection

In this paper, we present a method for protecting and restoring lost or tampered information in images or videos using secure watermarks. The proposed method consists of a combination of techniques that are able to detect image and video manipulations. Contrary to most existing watermarking schemes, the method can identify the exact position of the tampered region. Furthermore, the method is capable of restoring the manipulated information and retrieve the original content. This set of capabilities make it possible to use the proposed method in error concealment and digital tampering applications. The proposed method is employed as both an error concealment algorithm and a tampering detection algorithm. The proposed method is divided into two stages. At the encoder side, the method generates a binary version (watermark) of the original picture (image or video frame) using a halftoning technique. Then, a quantization index modulation technique is used to embed this watermark into the protected picture. At the decoder side, after the lost or tampered regions are identified, the original content is recovered by extracting the watermark corresponding to the affected areas. An inverse halftoning algorithm is used to convert the dithered version of the picture into a good-quality multi-level approximation of the original content. First, we test the method in error concealment applications, using a set of still images and H.264 videos. Then, we test the proposed method for tampering detection and content retrieval applications, again considering both images and videos. We compare the proposed method with several other several state-of-the-art algorithms. The results show that the proposed method is fast, robust, and accurate. Our results show that we can use a single approach to tackle both error concealment and tampering detection problems. The proposed method provides high levels of security, high detection accuracy, and recovery capability, and it is robust to several types of attacks.

Implementation of TiOISSS with meaningful shadows and with an additional authentication image

Visual Cryptography Scheme (VCS) is a cryptographic technique for protecting secret images. The advantage of using VCS is that decoding can be done without use of any computations. Nevertheless, the reconstructed image has poor visual quality. Therefore, Two in One Image Secret Sharing Scheme (TiOISSS) was proposed which takes the advantage of VCS and provides good quality decoded images. However, the existing TiOISSS has security limitations as it is implemented only for noisy shadows. Hence, in this paper, modified TiOISSS is proposed and implemented for meaningful shadows. To enhance the security of the shares and prevent fake shares that may be introduced by hackers, an authentication image is shared along with the secret image. The quality of the reconstructed image is improved by using adaptive halftoning technique. Experimental results demonstrate the improved security and quality by the proposed scheme.

Grayscale performance enhancement for time-multiplexing light field rendering.

One of the common approaches to compensate for the grayscale performance limitation in time-multiplexing light field displays is to employ a halftone technique. We propose an ordered-dithering halftone algorithm based on a 3-dimension super-mask to increase the gray levels of the time-multiplexing light field display. Our method makes full use of the overlapping perceived pixels which are caused by the time-multiplexing design, such that effectively trading-off the spatial resolution and color performance. A real-time rendering time-multiplexing display prototype is built to validate the proposed halftone algorithm. We conducted a user study to evaluate the quality of display scenes dithered by different super-mask configuration, which showed the consistency with the parameters we pre-calculated. The 3D ordered-dithering algorithm is able to present better visual perception than the conventional halftone algorithms with respect to grayscale representation, and flexible to be applied in different time-multiplexing light field display systems.

Spatially modulated laser pulses for printing electronics

The use of a digital micromirror device (DMD) in laser-induced forward transfer (LIFT) is reviewed. Combining this technique with high-viscosity donor ink (silver nanopaste) results in laser-printed features that are highly congruent in shape and size to the incident laser beam spatial profile. The DMD empowers LIFT to become a highly parallel, rapidly reconfigurable direct-write technology. By adapting half-toning techniques to the DMD bitmap image, the laser transfer threshold fluence for 10 μm features can be reduced using an edge-enhanced beam profile. The integration of LIFT with this beam-shaping technique allows the printing of complex large-area patterns with a single laser pulse.

Integration of Lenticular Displays with Image Switching and Infrared Watermark

The objective of this paper is to integrate lenticular lens with switching images and embedding the infrared watermark to provide value-added and anti-counterfeiting features. Digital halftoning technique has been used to compose animated graphics and the infrared watermark. The infrared watermark consists of halftone dots in cyan, magenta, yellow, and black inks. The carbon material in black ink absorbs the infrared light and the watermark could be displayed under infrared detection. By using the lenticular lens, image-switching effect can be observed from different viewing angles. The results show that it is successful to implement a lenticular display with both image-switching feature and hidden watermark which can be decoded under infrared detection. The proposed method has many potential applications to anti-counterfeiting and brand protection.