More than ever, the growing amount of exchanged digital content calls for efficient and practical techniques to protect intellectual property rights. During the past two decades, watermarking techniques have been proposed to embed and detect information within these contents, with four key requirements at hand: robustness, security, capacity, and invisibility. So far, researchers mostly focused on the first three, but seldom addressed the invisibility from a perceptual perspective and instead mostly relied on objective quality metrics. In this paper, a novel DFT watermarking scheme featuring perceptually optimal visibility versus robustness is proposed. The watermark, a noise-like square patch of coefficients, is embedded by substitution within the Fourier domain; the amplitude component adjusts the watermark strength, and the phase component holds the information. A perceptual model of the human visual system (HVS) based on the contrast sensitivity function (CSF) and a local contrast pooling is used to determine the optimal strength at which the mark reaches the visibility threshold. A novel blind detection method is proposed to assess the presence of the watermark. The proposed approach exhibits high robustness to various kinds of attacks, including geometrical distortions. Experimental results show that the robustness of the proposed method is globally slightly better than state-of-the-art. A comparative study was conducted at the visibility threshold (from subjective data) and showed that the obtained performances are more stable across various kinds of content.

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Perceptual DFT Watermarking With Improved Detection and Robustness to Geometrical Distortions

Based on quaternion Hadamard transform (QHT) and Schur decomposition, a novel color image watermarking scheme is presented. To consider the correlation between different color channels and the significant color information, a new color image processing tool termed as the quaternion Hadamard transform is proposed. Then an efficient method is designed to calculate the QHT of a color image which is represented by quaternion algebra, and the QHT is analyzed for color image watermarking subsequently. With QHT, the host color image is processed in a holistic manner. By use of Schur decomposition, the watermark is embedded into the host color image by modifying the Q matrix. To make the watermarking scheme resistant to geometric attacks, a geometric distortion detection method based upon quaternion Zernike moment is introduced. Thus, all the watermark embedding, the watermark extraction and the geometric distortion parameter estimation employ the color image holistically in the proposed watermarking scheme. By using the detection method, the watermark can be extracted from the geometric distorted color images. Experimental results show that the proposed color image watermarking is not only invisible but also robust against a wide variety of attacks, especially for color attacks and geometric distortions.

Color image watermarking scheme based on quaternion Hadamard transform and Schur decomposition

Semi-fragile watermarking for image authentication with sensitive tamper localization in the wavelet domain

Digital image authentication is an extremely significant concern for the digital revolution, as it is easy to tamper with any image. In the last few decades, it has been an urgent concern for researchers to ensure the authenticity of digital images. Based on the desired applications, several suitable watermarking techniques have been developed to mitigate this concern. However, it is tough to achieve a watermarking system that is simultaneously robust and secure. This paper gives details of standard watermarking system frameworks and lists some standard requirements that are used in designing watermarking techniques for several distinct applications. The current trends of digital image watermarking techniques are also reviewed in order to find the state-of-the-art methods and their limitations. Some conventional attacks are discussed, and future research directions are given.

https://www.mdpi.com/2078-2489/11/2/110/pdf

Digital Image Watermarking Techniques: A Review

This paper proposes a novel fractional transform, denoted as the fractional Krawtchouk transform (FrKT), a generalization of the Krawtchouk transform. The derivation of the FrKT uses the eigenvalue decomposition method. We determine the eigenvalues and the corresponding multiplicity of the Krawtchouk transform matrix. Moreover, the orthonormal eigenvectors of the transform matrix are derived. For validation purpose only and as a first illustration of the interest of FrKT, a watermarking example was chosen. Experimental results show that better watermark robustness and imperceptibility are achieved by adjusting the fractional orders in the FrKT.

Fractional Krawtchouk Transform With an Application to Image Watermarking

In this paper, we evaluate the degradation of an image due to the implementation of a watermark in the frequency domain of the image. As a result, a watermarking method, which minimizes the impact of the watermark implementation on the overall quality of an image, is developed. The watermark is embedded in magnitudes of the Fourier transform. A peak signal-to-noise ratio is used to evaluate quality degradation. The obtained results were used to develop a watermarking strategy that chooses the optimal radius of the implementation to minimize quality degradation. The robustness of the proposed method was evaluated on the dataset of 1000 images. Detection rates and receiver operating characteristic performance showed considerable robustness against the print-scan process, print-cam process, amplitude modulated, halftoning, and attacks from the StirMark benchmark software.

/pdf/discrete-fourier-transform-based-watermarking-method-with-an-564qh4dycx.pdf

Discrete Fourier transform-based watermarking method with an optimal implementation radius

For separation purposes image information is usually defined as RGB record, what will be converted in CMY, CMYK or some other suitable image processing procedure, for reproduction purposes. Applying specific and dedicated NIR separation we developed, secondary achieved image is hidden and secured. NIR image is based on absorption diversities of used basic inks as well other inks that should be separated. On that way we achieved optimal instrumental determining of secondary image. Basic postulate for effective CMYKIR separation and double image are twin dyes, theirs imposing and reflection differentiation of inks, that has to be carried out in in extended area. If differentiation is not managed properly, secondary image is not secured, and could appear incorrectly. Present photographic and printing options facilitate responsible and stable adjusting for steady double image recognition. We presented relevant NIR separation and twins principles at prepress/press stages for extended experience, and some considerable implementation of technological and scientific aspects.

/pdf/importance-of-extended-separation-in-nir-technology-for-4bzjlkgdtn.pdf

Importance of extended separation in NIR technology for secure secondary image identification, a survey

In this paper the robustness of a Discrete Fourier Transform (DFT) based image watermarking scheme to amplitude modulation (AM) halftoning is evaluated. Halftoning is used for reproduction of continuous images. Thus, it is important that a watermarking method is robust to halftoning. Three different shapes of clustered dots of AM (Amplitude Modulation) halftones are used (round, ellipse and line) with five different halftone frequencies (10, 13, 15, 40, and 60 line/cm). The tests where done on a dataset of 1000 images. As the metric of robustness, watermark detection rate, distribution of detection values, and ROC (Receiver Operation Characteristic) curves were used. The results showed that the watermarking scheme is robust to halftoning for halftone frequencies greater than 15 line/cm. Also, the type of AM halftone used has almost no effect on a detection rate.

Robustness of a dft based image watermarking method against am halftoning

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Blizanci bojila za proširenje infra informacijske tehnoligije

U radu se razmatra toplinski utjecaj na odabranoj karakteristicnoj skupini tekstilnih materijala na kojima su tehnikom digitalnog ink-jet tiska nacinjeni otisci. U teorijskom razmatranju analizirane su kljucne postavke relevantnih istraživanja vezanih za kontrolu kakvoce otisaka, a odnosi se na razliku u boji otisaka dobivenim na razlicitim tekstilnim podlogama koje su podvrgnute toplinskoj obradi. Analizirani su pristupi izracunavanju razlike u boji i modeli koji se pri tome koriste. Da bi se karakterizirale teorijske postavke napravljena su ispitivanja na cetiri referentna materijala. Na materijalima su napravljeni otisci digitalnom ink-jet tehnikom tiska. Za svaku vrstu materijala određivani su parametri hrapavosti, ICC profili spektrofotometrijskim mjerenjima. Materijali su toplinski obrađeni u karakteristicnom temperaturnom intervalu, a toplinsko polje analizirano je termovizijskom (IR) kamerom kako bi se dobile raspodjele temperatura promatrane povrsine uzoraka. Za karakteristicne temperature određivane su razlike boja u odabranom standardnom modelu mjerenja boja (CMC 2:1), a nakon toplinske obrade otisnutih materijala analizirane su promjene opsega boja. SEM analizom pracene su nastale promjene na povrsini tekstilnog materijala prije i poslije tiska, te nakon termicke obrade otisnutih uzoraka. Analizom su potvrđene određene teorijske postavke.

Darko Agić

Papers

Discrete Fourier transform-based watermarking method with an optimal implementation radius

Importance of extended separation in NIR technology for secure secondary image identification, a survey

Robustness of a dft based image watermarking method against am halftoning

Blizanci bojila za proširenje infra informacijske tehnoligije

Thermographic analysis of thermal effects on the change of colour differences on the digitally printed textile materials