Lidija Mandić

Bio: Lidija Mandić is an academic researcher from University of Zagreb. The author has contributed to research in topics: Digital watermarking & Color balance. The author has an hindex of 6, co-authored 48 publications receiving 258 citations. Previous affiliations of Lidija Mandić include Vienna University of Technology.

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

Abstract: 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.

Comparison of Color Difference Equations

Abstract: Advanced color difference equations still do not necessarily predict accurately the color differences for complex stimuli such as photographic images. The CIELAB color-difference formula has been used extensively for quality control in industry but its application is limited because CIELAB space is still far from being perceptually perfectly uniform. The consequence of this is that for equal perceptual color differences, the values of CIELAB color differences can vary by an order of magnitude. The aim of this work is to compare accuracy of three color difference equations that are recently used.

Location-based smartwatch application for people with complex communication needs

Abstract: One of the important elements of successful parenting is care for children's safety, which includes parental knowledge about children's whereabouts, especially when a child has complex communication needs. In this context smartwatch may become a new aid not only for children but for all persons with complex communication needs, primary due to location and communication functions which can be efficiently deployed within smartwatch application, combined with everyday habit of wearing a watch on the wrist. Innovative functions and applications may put the smartwatch in the category of safety products within assistive technology, but there is a lot to investigate since the smartwatch technology is advancing very quickly. The paper presents multidisciplinary research performed in the area of information and communication technology, focusing on a smartwatch application as the assistive technology for locating persons with complex communication needs. Developed software application is described, that is based on the concept of predefined and ad hoc safety zones, enabling smartphone mobile application and web application users to define the zones for safe movement of smartwatch wearer. Also the graphical issues related to the smartwatch user interface design and other smartwatch performances that were faced during the research are presented.

The impact of different navigation speeds on cybersickness and stress level in VR

Abstract: Navigation (or locomotion) techniques refer to the way in which users move within Virtual Reality (VR) environments. A well-known negative side effect of movement in VR is known as cybersickness, which is manifested as a physical feeling of nausea, headache, dizziness and sweating (Rebenitsch & Owen, 2016). This nauseogenic state can be explained as a mismatch between vestibular and oculomotor sensors, meaning that a person perceives movement even though he or she is not actually moving in real space (Golding, 2006). This sensation of illusory movement is known as vection (Keshavarz et al., 2015b; McCauley & Sharkey, 1992). A common example is that of a person sitting on a train and another train starts to move, causing the person to become confused as to which train is actually moving.

Functional measurements of human ventral occipital cortex: retinotopy and colour.

Abstract: Human colour vision originates in the cone photoreceptors, whose spatial density peaks in the fovea and declines rapidly into the periphery. For this reason, one expects to find a large representation of the cone–rich fovea in those cortical locations that support colour perception. Human occipital cortex contains several distinct foveal representations including at least two that extend onto the ventral surface: a region thought to be critical for colour vision. To learn more about these ventral signals, we used functional magnetic resonance imaging to identify visual field maps and colour responsivity on the ventral surface. We found a visual map of the complete contralateral hemifield in a 4 cm2 region adjacent to ventral V3; the foveal representation of this map is confluent with that of areas V1/2/3. Additionally, a distinct foveal representation is present on the ventral surface situated 3–5 cm anterior from the confluent V1/2/3 foveal representations. This organization is not consistent with the definition of area V8, which assumes the presence of a quarter field representation adjacent to V3v. Comparisons of responses to luminance–matched coloured and achromatic patterns show increased activity to the coloured stimuli beginning in area V1 and extending through the new hemifield representation and further anterior in the ventral occipital lobe.

Introduction to Color Imaging Science

Abstract: Colour imaging technology has become almost ubiquitous in modern life in the form of monitors, liquid crystal screens, colour printers, scanners, and digital cameras. This book is a comprehensive guide to the scientific and engineering principles of colour imaging. It covers the physics of light and colour, how the eye and physical devices capture colour images, how colour is measured and calibrated, and how images are processed. It stresses physical principles and includes a wealth of real-world examples. The book will be of value to scientists and engineers in the colour imaging industry and, with homework problems, can also be used as a text for graduate courses on colour imaging.

Perceptual DFT Watermarking With Improved Detection and Robustness to Geometrical Distortions

Abstract: 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.