Circular Coding with Interleaving Phase

ABSTRACT A general two-dimensional coding method is presented that allows recovery of data based on only a cropped portion of the code, and without knowledge of the carrier image. A description of both an encoding and recovery system is provided. Our solution involves repeating a payload with a fixed number of bits, assigning one bit to every symbol in the image whether that symbol is data carrying or non-data carrying with the goal of guaranteeing recovery of all the bits in the payload. Because the technique is applied to images, for aesthetic reasons we do not use fiducials, and do not employ any end-of-payload symbols. The beginning of the payload is determined by a phase code that is interleaved between groups of payload rows. The recovery system finds the phase row by evaluating candidate rows, and ranks confidence based on the sample variance. The target application is data-bearing clustered-dot halftones, so special consideration is given to the resulting checkerboard subsampling. This particular application is examined via exhaustive simulations to quantify the likelihood of unrecoverable bits and bit redundancy as a function of offset, crop window size, and phase code spacing

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.Comment: to be published in IEEE Transactions on Visualization and Computer Graphic

ID Photograph hashing : a global approach

This thesis addresses the question of the authenticity of identity photographs, part of the documents required in controlled access. Since sophisticated means of reproduction are publicly available, new methods / techniques should prevent tampering and unauthorized reproduction of the photograph. This thesis proposes a hashing method for the authentication of the identity photographs, robust to print-and-scan. This study focuses also on the effects of digitization at hash level. The developed algorithm performs a dimension reduction, based on independent component analysis (ICA). In the learning stage, the subspace projection is obtained by applying ICA and then reduced according to an original entropic selection strategy. In the extraction stage, the coefficients obtained after projecting the identity image on the subspace are quantified and binarized to obtain the hash value. The study reveals the effects of the scanning noise on the hash values of the identity photographs and shows that the proposed method is robust to the print-and-scan attack. The approach focusing on robust hashing of a restricted class of images (identity) differs from classical approaches that address any imageCette thèse traite de la question de l’authenticité des photographies d’identité, partie intégrante des documents nécessaires lors d’un contrôle d’accès. Alors que les moyens de reproduction sophistiqués sont accessibles au grand public, de nouvelles méthodes / techniques doivent empêcher toute falsification / reproduction non autorisée de la photographie d’identité. Cette thèse propose une méthode de hachage pour l’authentification de photographies d’identité, robuste à l’impression-lecture. Ce travail met ainsi l’accent sur les effets de la numérisation au niveau de hachage. L’algorithme mis au point procède à une réduction de dimension, basée sur l’analyse en composantes indépendantes (ICA). Dans la phase d’apprentissage, le sous-espace de projection est obtenu en appliquant l’ICA puis réduit selon une stratégie de sélection entropique originale. Dans l’étape d’extraction, les coefficients obtenus après projection de l’image d’identité sur le sous-espace sont quantifiés et binarisés pour obtenir la valeur de hachage. L’étude révèle les effets du bruit de balayage intervenant lors de la numérisation des photographies d’identité sur les valeurs de hachage et montre que la méthode proposée est robuste à l’attaque d’impression-lecture. L’approche suivie en se focalisant sur le hachage robuste d’une classe restreinte d’images (d’identité) se distingue des approches classiques qui adressent une image quelconqu

Marca d'agua para documentos via modulação de luminância

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica

Printing Beyond Color: Spectral and Specular Reproduction

For accurate printing (reproduction), two important appearance attributes to consider are color and gloss. These attributes are related to two topics focused on in this dissertation: spectral reproduction and specular (gloss) printing. In the conventional printing workflow known as the metameric printing workflow, which we use mostly nowadays, high-quality prints -- in terms of colorimetric accuracy -- can be achieved only under a predefined illuminant (i.e. an illuminant that the printing pipeline is adjusted to; e.g. daylight). While this printing workflow is useful and sufficient for many everyday purposes, in some special cases, such as artwork (e.g. painting) reproduction, security printing, accurate industrial color communication and so on, in which accurate reproduction of an original image under a variety of illumination conditions (e.g. daylight, tungsten light, museum light, etc.) is required, metameric reproduction may produce satisfactory results only with luck. Therefore, in these cases, another printing workflow, known as spectral printing pipeline must be used, with the ideal aim of illuminant-invariant match between the original image and the reproduction. In this workflow, the reproduction of spectral raw data (i.e. reflectances in the visible wavelength range), rather than reproduction of colorimetric values (colors) alone (under a predefined illuminant) is taken into account. Due to the limitations of printing systems extant, the reproduction of all reflectances is not possible even with multi-channel (multi-colorant) printers. Therefore, practical strategies are required in order to map non-reproducible reflectances into reproducible spectra and to choose appropriate combinations of printer colorants for the reproduction of the mapped reflectances. For this purpose, an approach called Spatio-Spectral Gamut Mapping and Separation, SSGMS, was proposed, which results in almost artifact-free spectral reproduction under a set of various illuminants. The quality control stage is usually the last stage in any printing pipeline. Nowadays, the quality of the printout is usually controlled only in terms of colorimetric accuracy and common printing artifacts. However, some gloss-related artifacts, such as gloss-differential (inconsistent gloss appearance across an image, caused mostly by variations in deposited ink area coverage on different spots), are ignored, because no strategy to avoid them exists. In order to avoid such gloss-related artifacts and to control the glossiness of the printout locally, three printing strategies were proposed. In general, for perceptually accurate reproduction of color and gloss appearance attributes, understanding the relationship between measured values and perceived magnitudes of these attributes is essential. There has been much research into reproduction of colors within perceptually meaningful color spaces, but little research from the gloss perspective has been carried out. Most of these studies are based on simulated display-based images (mostly with neutral colors) and do not take real objects into account. In this dissertation, three psychophysical experiments were conducted in order to investigate the relationship between measured gloss values (objective quantities) and perceived gloss magnitudes (subjective quantities) using real colored samples printed by the aforementioned proposed printing strategies. These experiments revealed that the relationship mentioned can be explained by a Power function according to Stevens' Power Law, considering almost the entire gloss range. Another psychophysical experiment was also conducted in order to investigate the interrelation between perceived surface gloss and texture, using 2.5D samples printed in two different texture types and with various gloss levels and texture elevations. According to the results of this experiment, different macroscopic texture types and levels (in terms of texture elevation) were found to influence the perceived surface gloss level slightly. No noticeable influence of surface gloss on the perceived texture level was observed, indicating texture constancy regardless of the gloss level printed. The SSGMS approach proposed for the spectral reproduction, the three printing strategies presented for gloss printing, and the results of the psychophysical experiments conducted on gloss printing and appearance can be used to improve the overall print quality in terms of color and gloss reproduction

Hardware-accelerated algorithms in visual computing

This thesis presents new parallel algorithms which accelerate computer vision methods by the use of graphics processors (GPUs) and evaluates them with respect to their speed, scalability, and the quality of their results. It covers the fields of homogeneous and anisotropic diffusion processes, diffusion image inpainting, optic flow, and halftoning. In this turn, it compares different solvers for homogeneous diffusion and presents a novel \u27extended\u27 box filter. Moreover, it suggests to use the fast explicit diffusion scheme (FED) as an efficient and flexible solver for nonlinear and in particular for anisotropic parabolic diffusion problems on graphics hardware. For elliptic diffusion-like processes, it recommends to use cascadic FED or Fast Jacobi schemes. The presented optic flow algorithm represents one of the fastest yet very accurate techniques. Finally, it presents a novel halftoning scheme which yields state-of-the-art results for many applications in image processing and computer graphics.Diese Arbeit präsentiert neue parallele Algorithmen zur Beschleunigung von Methoden in der Bildinformatik mittels Grafikprozessoren (GPUs), und evaluiert diese im Hinblick auf Geschwindigkeit, Skalierungsverhalten, und Qualität der Resultate. Sie behandelt dabei die Gebiete der homogenen und anisotropen Diffusionsprozesse, Inpainting (Bildvervollständigung) mittels Diffusion, die Bestimmung des optischen Flusses, sowie Halbtonverfahren. Dabei werden verschiedene Löser für homogene Diffusion verglichen und ein neuer \u27erweiterter\u27 Mittelwertfilter präsentiert. Ferner wird vorgeschlagen, das schnelle explizite Diffusionsschema (FED) als effizienten und flexiblen Löser für parabolische nichtlineare und speziell anisotrope Diffusionsprozesse auf Grafikprozessoren einzusetzen. Für elliptische diffusionsartige Prozesse wird hingegen empfohlen, kaskadierte FED- oder schnelle Jacobi-Verfahren einzusetzen. Der vorgestellte Algorithmus zur Berechnung des optischen Flusses stellt eines der schnellsten und dennoch äußerst genauen Verfahren dar. Schließlich wird ein neues Halbtonverfahren präsentiert, das in vielen Bereichen der Bildverarbeitung und Computergrafik Ergebnisse produziert, die den Stand der Technik repräsentieren

Zaštita vlasništva reproducirane slike umetanjem digitalnog vodenog žiga

U ovom doktorskom radu je razvijena metoda zaštite vlasništva slike umetanjem digitalnog vodenog žiga. S obzirom da je pristup zaštite otisnutih slika digitalnim vodenim žigom nedovoljno istražen, postojala je potreba da se razvije metoda zaštite prilagođena zahtjevima grafičke reprodukcije, prvenstveno neznatnom utjecaju na kvalitetu originalne slike prilikom označavanja, i snažnoj otpornosti na proces reprodukcije i naknadne digitalizacije. Razvijena metoda zaštite vlasništva otisnutih proizvoda temeljena na digitalnom vodenom žigu predstavlja odmak od dosadašnjeg pristupa problemu zaštite. Naime, zaštita grafičkih proizvoda uglavnom se temeljila na primjeni posebnih tehnika i/ili materijala prilikom otiskivanja. Suprotno tome, korištenje digitalnog vodenog žiga ne zahtjeva posebne tehnike tiska ili posebne materijale već se metoda zaštite temelji se na manipulaciji slike u njenom digitalnom obliku, prije digitalno-analogne konverzije. U radu su definirani parametri vodenog žiga koji utječu na kvalitetu označene slike i provedeno je ispitivanje otpornosti vodenog žiga na najčešće oblike procesiranja koji se mogu pojaviti u reprodukcijskom procesu. Ispitivanje je provedeno na bazi od 1000 različitih slika. Rezultati su pokazali da je metoda prilagođena potrebama grafičke reprodukcije jer se označavanjem ne narušava kvaliteta slike, a umetnuti vodeni žig je, osim na proces grafičke reprodukcije, otporan i na cijeli niz drugih oblika procesiranja kao što su kompresija, izrezivanje, filtriranje, šum, rotacija i skaliranje