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Gaurav Sharma - One of the best experts on this subject based on the ideXlab platform.
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per separation clustered dot color Halftone watermarks separation estimation based on spatial frequency content
Journal of Electronic Imaging, 2010Co-Authors: Basak Oztan, Gaurav SharmaAbstract:A framework for clustered-dot color Halftone watermarking is considered, wherein watermark patterns are embedded in individ- ual colorant Halftones prior to printing and embedded watermarks are detected from scans of the printed images after obtaining esti- mates of the individual Halftone separations. The principal challenge in this methodology arises in the watermark detection phase. Typical three-channel RGB scanner systems do not directly provide good es- timates of the four CMYK colorant Halftones that are commonly used in color printing systems. To address this challenge, we propose an estimation method that, when used with suitably selected Halftone periodicities, jointly exploits the differences in the spatial periodicities and the color (spectra) of the Halftone separations to obtain good estimates of the individual Halftones from conventional RGB scans. We demonstrate the efficacy of this methodology experimentally us- ing continuous phase modulation for the embedding of independent visual watermark patterns in the individual Halftone separations. Wa- termarks detected from the estimates of Halftone separations ob- tained using the proposed estimation method have a much higher contrast than those detected directly. We also evaluate the accuracy of the estimated Halftones through simulations and demonstrate that the proposed estimation method offers high accuracy. © 2010 SPIE
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orientation modulation for data hiding in clustered dot Halftone prints
IEEE Transactions on Image Processing, 2010Co-Authors: Orhan Bulan, Gaurav Sharma, Vishal MongaAbstract:We present a new framework for data hiding in images printed with clustered dot Halftones. Our application scenario, like other hardcopy embedding methods, encounters fundamental challenges due to extreme bilevel quantization inherent in halftoning, the stringent requirements of image fidelity, and other unavoidable printing and scanning distortions. To overcome these challenges, while still allowing for automated extraction of the embedded data and a high embedding capacity, we propose a number of innovations. First, we perform the embedding jointly with the halftoning by employing an analytical Halftone threshold function that allows steering of the Halftone spot orientation within each Halftone cell based upon embedded data. In this process, image fidelity is emphasized and, if necessary, the capability to recover individual data values is sacrificed resulting in unavoidable erasures and errors. To overcome these and other sources of errors, we propose a suitable data detection and error control methodology based upon a statistical representation for the print-scan channel that effectively models the channel dependence upon the cover image gray-level. To combat the geometric distortion inherent in the print-scan process, we exploit the periodic Halftone structure to recover from global scaling and rotation and propose a novel decision directed synchronization technique that counters locally varying printing distortion. Experimental results demonstrate the power of the proposed framework: we achieve high operational rates while preserving Halftone image quality.
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data embedding in hardcopy images via Halftone dot orientation modulation
electronic imaging, 2008Co-Authors: Orhan Bulan, Gaurav Sharma, Vishal Monga, Basak OztanAbstract:The principal challenge in hardcopy data hiding is achieving robustness to the print-scan process. Conventional robust hiding schemes are not well-suited because they do not adapt to the print-scan distortion channel, and hence are fundamentally limited in a detection theoretic sense. We consider data embedding in images printed with clustered dot Halftones. The input to the print-scan channel in this scenario is a binary Halftone image, and hence the distortions are also intimately tied to the nature of the halftoning algorithm employed. We propose a new framework for hardcopy data hiding based on Halftone dot orientation modulation. We develop analytic Halftone threshold functions that generate elliptically shaped Halftone dots in any desired orientation. Our hiding strategy then embeds a binary symbol as a particular choice of the orientation. The orientation is identified at the decoder via statistically motivated moments following appropriate global and local synchronization to adress the geometric distortion introduced by the print scan channel. A probabilistic model of the print-scan process, which conditions received moments on input orientation, allows for Maximum Likelihood (ML) optimal decoding. Our method bears similarities to the paradigms of informed coding and QIM, but also makes departures from classical results in that constant and smooth image areas are better suited for embedding via our scheme as opposed to busy or "high entropy" regions. Data extraction is automatically done from a scanned hardcopy, and results indicate significantly higher embedding rate than existing methods, a majority of which rely on visual or manual detection.
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continuous phase modulated Halftones and their application to Halftone data embedding
International Conference on Acoustics Speech and Signal Processing, 2006Co-Authors: Basak Oztan, Gaurav SharmaAbstract:We propose a generalization of periodic clustered-dot Halftones, wherein the phase of the Halftones is modulated using a secondary signal. The process is accomplished using an analytic Halftone threshold function and allows Halftones to be generated with different phase variation in different regions of the printed page. We demonstrate that ensuring continuity of the phase assures that the resulting Halftone images are free from visible artifacts despite the modulation in phase. We present, applications of the proposed method to Halftone data embedding, wherein the changes in phase or in frequency encode the embedded information. For the frequency embedding, using continuous phase modulation, we also consider the limitations on signals that are embedded within our framework. For both applications, we demonstrate how the embedded signals may be recovered from the printed Halftones either using the image as a self-reference which reveals the watermark when it is shifted and overlaid with itself or by employing a separate transparency mask.
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ICIP - Self-Modulated Halftones
2006 International Conference on Image Processing, 2006Co-Authors: Basak Oztan, Gaurav SharmaAbstract:We propose an analytic method to overcome the trade-off between the spatial and tonal resolution of traditional clustered dot Halftones. Continuous phase modulated Halftones that allow variations in screen frequency in different regions of the printed image are employed and Halftone screen frequency is varied according to the frequency content of the image to be Halftoned. The method, which we term self-modulated halftoning, has a computational complexity similar to screening and is significantly lower than that of other adaptive methods that have previously been used to address the same problem. We demonstrate the experimental performance of self-modulated Halftones and discuss its capabilities and limitations.
Basak Oztan - One of the best experts on this subject based on the ideXlab platform.
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Clustered-dot periodic Halftones : modeling, modulation, and applications
University of Rochester, 2020Co-Authors: Basak Oztan, Sharma GauravAbstract:Thesis (Ph. D.)--University of Rochester. Dept. of Electrical and Computer Engineering, 2010.This thesis addresses analyses and applications of periodic clustered-dot Halftones that are widely utilized in electrophotographic (laser) and lithographic (offset) printing. Within this broad setting, we address three specific problems: 1) the modeling and analysis of the color shifts induced by inter-separation misregistration, 2) phase and frequency modulation in clustered-dot Halftones for watermark embedding and content adaptive halftoning, and 3) per-separation color Halftone watermarking by exploiting differences in spatial periodicity and colorant spectra of the individual colorant Halftones. The work and contributions in each of these areas are summarized in the following. Misregistration-induced color shifts for periodic clustered-dot color Halftones are characterized by combining the Neugebauer model with a periodic lattice representation for the individual Halftones to obtain a spatio-spectral model for the color print. Conditions for color misregistration invariance are identified by using the model in terms of colorant spectra, periodicity of the individual separation Halftones, dot shapes, and misregistration displacements. Furthermore, quantitative estimates of the color shifts induced by interseparation misregistration are obtained via a hybrid analytical-numerical simulation model that allows assessment of the impact of different Halftone parameters such as Halftone periodicities, spot functions, inter-separation misregistration displacements, and optical dot gain on the color shift. Our simulation results show good qualitative agreement with the experimental data. We introduce continuous phase-modulated Halftones as a general class of clustereddot Halftones, wherein the phase of the Halftone spots is modulated using a secondary signal. The process is accomplished by using an analytic Halftone threshold function that allows Halftones to be generated with controlled phase variation in different regions of the printed page. The method can also be used to modulate the screen frequency, albeit with additional constraints. Visible artifacts are minimized/eliminated by ensuring the continuity of the modulation in phase. Limitations and capabilities of the method are analyzed through a quantitative model. We exploited this technique for: a) embedding watermarks in the Halftone image by encoding information in phase or in frequency, and b) modulating the screen frequency according to the frequency content of the continuous tone image in order to improve spatial and tonal rendering. Experimental performance is demonstrated for both applications. Finally, we propose a framework for clustered-dot color Halftone watermarking, wherein watermark patterns are embedded in individual colorant Halftones prior to printing and embedded watermarks are detected, from scans of the printed images, after obtaining estimates of the individual Halftone separations. The principal challenge in this methodology arises in the watermark detection phase. Typical three channel RGB scanner systems do not directly provide good estimates of the four CMYK colorant Halftones. To address this challenge, we propose an estimation method that, when used with suitably selected Halftone periodicities, jointly exploits the differences in the spatial periodicities and the color (spectra) of the Halftone separations to obtain good estimates of the individual Halftones from conventional RGB scans. We demonstrate the efficacy of this methodology experimentally by embedding independent visual watermark patterns via continuous phase modulation in the individual Halftone separations. Watermarks detected from the estimates of Halftone separations obtained using the proposed estimation method have a much higher contrast then those detected directly. The accuracy of the estimated Halftones is also evaluated through simulations and is seen to be higher than other alternatives
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per separation clustered dot color Halftone watermarks separation estimation based on spatial frequency content
Journal of Electronic Imaging, 2010Co-Authors: Basak Oztan, Gaurav SharmaAbstract:A framework for clustered-dot color Halftone watermarking is considered, wherein watermark patterns are embedded in individ- ual colorant Halftones prior to printing and embedded watermarks are detected from scans of the printed images after obtaining esti- mates of the individual Halftone separations. The principal challenge in this methodology arises in the watermark detection phase. Typical three-channel RGB scanner systems do not directly provide good es- timates of the four CMYK colorant Halftones that are commonly used in color printing systems. To address this challenge, we propose an estimation method that, when used with suitably selected Halftone periodicities, jointly exploits the differences in the spatial periodicities and the color (spectra) of the Halftone separations to obtain good estimates of the individual Halftones from conventional RGB scans. We demonstrate the efficacy of this methodology experimentally us- ing continuous phase modulation for the embedding of independent visual watermark patterns in the individual Halftone separations. Wa- termarks detected from the estimates of Halftone separations ob- tained using the proposed estimation method have a much higher contrast than those detected directly. We also evaluate the accuracy of the estimated Halftones through simulations and demonstrate that the proposed estimation method offers high accuracy. © 2010 SPIE
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Continuous Phase-Modulated Halftones
IEEE Transactions on Image Processing, 2009Co-Authors: Basak OztanAbstract:A generalization of periodic clustered-dot Halftones is proposed, wherein the phase of the Halftone spots is modulated using a secondary signal. The process is accomplished by using an analytic Halftone threshold function that allows Halftones to be generated with controlled phase variation in different regions of the printed page. The method can also be used to modulate the screen frequency, albeit with additional constraints. Visible artifacts are minimized/eliminated by ensuring the continuity of the modulation in phase. Limitations and capabilities of the method are analyzed through a quantitative model. The technique can be exploited for two applications that are presented in this paper: (a) embedding watermarks in the Halftone image by encoding information in phase or in frequency and (b) modulating the screen frequency according to the frequency content of the continuous tone image in order to improve spatial and tonal rendering. Experimental performance is demonstrated for both applications.
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data embedding in hardcopy images via Halftone dot orientation modulation
electronic imaging, 2008Co-Authors: Orhan Bulan, Gaurav Sharma, Vishal Monga, Basak OztanAbstract:The principal challenge in hardcopy data hiding is achieving robustness to the print-scan process. Conventional robust hiding schemes are not well-suited because they do not adapt to the print-scan distortion channel, and hence are fundamentally limited in a detection theoretic sense. We consider data embedding in images printed with clustered dot Halftones. The input to the print-scan channel in this scenario is a binary Halftone image, and hence the distortions are also intimately tied to the nature of the halftoning algorithm employed. We propose a new framework for hardcopy data hiding based on Halftone dot orientation modulation. We develop analytic Halftone threshold functions that generate elliptically shaped Halftone dots in any desired orientation. Our hiding strategy then embeds a binary symbol as a particular choice of the orientation. The orientation is identified at the decoder via statistically motivated moments following appropriate global and local synchronization to adress the geometric distortion introduced by the print scan channel. A probabilistic model of the print-scan process, which conditions received moments on input orientation, allows for Maximum Likelihood (ML) optimal decoding. Our method bears similarities to the paradigms of informed coding and QIM, but also makes departures from classical results in that constant and smooth image areas are better suited for embedding via our scheme as opposed to busy or "high entropy" regions. Data extraction is automatically done from a scanned hardcopy, and results indicate significantly higher embedding rate than existing methods, a majority of which rely on visual or manual detection.
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continuous phase modulated Halftones and their application to Halftone data embedding
International Conference on Acoustics Speech and Signal Processing, 2006Co-Authors: Basak Oztan, Gaurav SharmaAbstract:We propose a generalization of periodic clustered-dot Halftones, wherein the phase of the Halftones is modulated using a secondary signal. The process is accomplished using an analytic Halftone threshold function and allows Halftones to be generated with different phase variation in different regions of the printed page. We demonstrate that ensuring continuity of the phase assures that the resulting Halftone images are free from visible artifacts despite the modulation in phase. We present, applications of the proposed method to Halftone data embedding, wherein the changes in phase or in frequency encode the embedded information. For the frequency embedding, using continuous phase modulation, we also consider the limitations on signals that are embedded within our framework. For both applications, we demonstrate how the embedded signals may be recovered from the printed Halftones either using the image as a self-reference which reveals the watermark when it is shifted and overlaid with itself or by employing a separate transparency mask.
Ping Wah Wong - One of the best experts on this subject based on the ideXlab platform.
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Image processing for Halftones
IEEE Signal Processing Magazine, 2003Co-Authors: Ping Wah Wong, N.d. MemonAbstract:Compression is routinely used in printing pipelines. While both lossless and lossy compression methods exist for compressing Halftones, dispersed types of Halftones remain difficult to compress given their very nature. In recent years researchers have started looking at the problem of designing Halftoners that generate both good quality and compressible Halftones. We believe that the problem of optimizing halftoning for compression is a very interesting and useful area. Watermarking and steganography for Halftone images arc relatively new areas that are motivated by the proliferation of networking and the exchange of digital data. We have described a number of approaches in watermarking Halftones and embedding Halftones into each other. Certainly many more aspects of this problem can and will be considered in the future.
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embedded multilevel error diffusion
IEEE Transactions on Image Processing, 1997Co-Authors: J R Goldschneider, Eve A Riskin, Ping Wah WongAbstract:We present an algorithm for image browsing systems that embeds the output of binary Floyd-Steinberg (1975) error diffusion, or a low bit-depth gray-scale or color error diffused image into higher bit-depth gray-scale or color error diffused images. The benefits of this algorithm are that a low bit-depth Halftoned image can be directly obtained from a higher bit-depth Halftone for printing or progressive transmission simply by masking one or more bits off of the higher bit-depth image. The embedding can be done in any bits of the output, although the most significant or the least significant bits are most convenient. Due to constraints on the palette introduced by embedding, the image quality for the higher bit-depth Halftone may be reduced. To preserve the image quality, we present algorithms for color palette organization, or binary index assignment, to be used as a preprocessing step to the embedding algorithm.
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Entropy-constrained halftoning using multipath tree coding
IEEE Transactions on Image Processing, 1997Co-Authors: Ping Wah WongAbstract:We suggest an optimization-based method for halftoning that involves looking ahead before a decision for each binary output pixel is made. We first define a mixture distortion criterion that is a combination of a frequency-weighted mean square error (MSE) and a measure depending on the distances between minority pixels in the Halftone. A tree-coding approach with the ML-algorithm is used for minimizing the distortion criterion to generate a Halftone. While this approach generates Halftones of high quality, these Halftones are not very amenable to lossless compression. We introduce an entropy constraint into the cost function of the tree-coding algorithm that optimally trades off between image quality and compression performance in the output Halftones.
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Error diffusion with delayed decision
Human Vision Visual Processing and Digital Display VI, 1995Co-Authors: Ping Wah WongAbstract:A new halftoning algorithm is proposed that incorporates the concept of delayed decision in error diffusion. This algorithm is similar to a recently proposed tree coding Halftoner in that both examine at each pixel location a neighborhood of future (with respect to the scanning direction) pixels before deciding the value of the current output pixel. Because of the feedback in the error diffusion process, one can reduce the size of the 'look ahead' window compared to a typical tree-coding Halftoner, resulting in a relatively low complexity. It is shown that this algorithm improves the quality of Halftone images compared to those generated by traditional error diffusion.
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inverse halftoning and kernel estimation for error diffusion
IEEE Transactions on Image Processing, 1995Co-Authors: Ping Wah WongAbstract:Two different approaches in the inverse halftoning of error-diffused images are considered. The first approach uses linear filtering and statistical smoothing that reconstructs a gray-scale image from a given error-diffused image. The second approach can be viewed as a projection operation, where one assumes the error diffusion kernel is known, and finds a gray-scale image that will be Halftoned into the same binary image. Two projection algorithms, viz., minimum mean square error (MMSE) projection and maximum a posteriori probability (MAP) projection, that differ on the way an inverse quantization step is performed, are developed. Among the filtering and the two projection algorithms, MAP projection provides the best performance for inverse halftoning. Using techniques from adaptive signal processing, we suggest a method for estimating the error diffusion kernel from the given Halftone. This means that the projection algorithms can be applied in the inverse halftoning of any error-diffused image without requiring any a priori information on the error diffusion kernel. It is shown that the kernel estimation algorithm combined with MAP projection provide the same performance in inverse halftoning compared to the case where the error diffusion kernel is known. >
Gonzalo R. Arce - One of the best experts on this subject based on the ideXlab platform.
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ICASSP - Halftone visual cryptography by iterative halftoning
2010 IEEE International Conference on Acoustics Speech and Signal Processing, 2010Co-Authors: Zhongmin Wang, Gonzalo R. ArceAbstract:Halftone visual cryptography (HVC) is a visual sharing scheme where a secret image is encoded into Halftone shares taking meaningful visual information. In this paper, novel construction method of HVC based on an iterative halftoning method is proposed. The secret image is concurrently embedded into binary valued shares while these shares are Halftoned by constrained iterative halftoning. The proposed method is able to generate Halftone shares showing natural images with high image quality. Reconstructed secret images, obtained by stacking qualified shares together, does not suffer from cross interference of share images. Simulations are provided to show the effectiveness of our proposed method.
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Halftone visual cryptography via error diffusion
IEEE Transactions on Information Forensics and Security, 2009Co-Authors: Zhongmin Wang, Gonzalo R. Arce, Giovanni Di CrescenzoAbstract: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.
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Halftone visual cryptography
International Conference on Image Processing, 2003Co-Authors: Zhi Zhou, Gonzalo R. Arce, Giovanni Di CrescenzoAbstract:Visual cryptography encodes a secret image SI into n shares of random patterns. If the shares are xeroxed onto transparencies, we can visually decode the secret image by superimposing a qualified subset of transparencies, but no secret information can be obtained from the superposition of a forbidden subset. Such a scheme is mathematically secure, however, it produces random patterns which have no visual meaning, raising the suspicion of data encryption. In this paper, to achieve a higher level of security, we propose Halftone visual cryptography, where all shares are Halftones of grey level images carrying significant visual information. The proposed methods utilize blue-noise dithering principles to construct Halftone shares having visually pleasing attributes.
Zhongmin Wang - One of the best experts on this subject based on the ideXlab platform.
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GrC - Halftone visual cryptography with color shares
2012 IEEE International Conference on Granular Computing, 2012Co-Authors: Yuanfeng Liu, Zhongmin WangAbstract:Halftone visual cryptography (HVC) is a visual sharing scheme where a secret image is encoded into Halftone shares taking meaningful visual information. In this paper, a HVC construction method is proposed that can encode a secret Halftone image into color Halftone shares. The secret image is concurrently embedded into color Halftone shares while these shares are Halftoned by constrained vector error diffusion. The proposed method is able to generate Halftone shares showing natural color images with high image quality.
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ICASSP - Halftone visual cryptography by iterative halftoning
2010 IEEE International Conference on Acoustics Speech and Signal Processing, 2010Co-Authors: Zhongmin Wang, Gonzalo R. ArceAbstract:Halftone visual cryptography (HVC) is a visual sharing scheme where a secret image is encoded into Halftone shares taking meaningful visual information. In this paper, novel construction method of HVC based on an iterative halftoning method is proposed. The secret image is concurrently embedded into binary valued shares while these shares are Halftoned by constrained iterative halftoning. The proposed method is able to generate Halftone shares showing natural images with high image quality. Reconstructed secret images, obtained by stacking qualified shares together, does not suffer from cross interference of share images. Simulations are provided to show the effectiveness of our proposed method.
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Halftone visual cryptography via error diffusion
IEEE Transactions on Information Forensics and Security, 2009Co-Authors: Zhongmin Wang, Gonzalo R. Arce, Giovanni Di CrescenzoAbstract: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.
