Color-decoupled photo response non-uniformity for digital image forensics

The last few years have seen the use of photo response non-uniformity noise (PRNU), a unique fingerprint of imaging sensors, in various digital forensic applications such as source device identification, content integrity verification and authentication. However, the use of a colour filter array for capturing only one of the three colour components per pixel introduces colour interpolation noise, while the existing methods for extracting PRNU provide no effective means for addressing this issue. Because the artificial colours obtained through the colour interpolation process is not directly acquired from the scene by physical hardware, we expect that the PRNU extracted from the physical components, which are free from interpolation noise, should be more reliable than that from the artificial channels, which carry interpolation noise. Based on this assumption we propose a Couple-Decoupled PRNU (CD-PRNU) extraction method, which first decomposes each colour channel into 4 sub-images and then extracts the PRNU noise from each sub-image. The PRNU noise patterns of the sub-images are then assembled to get the CD-PRNU. This new method can prevent the interpolation noise from propagating into the physical components, thus improving the accuracy of device identification and image content integrity verification

Laser and optical based methods for detecting and characterising microorganisms

This work investigated novel optical methods of characterizing the activity of microorganisms. Two different systems are studied in detail in this work. The possibility of using line scan speckle systems and imaging systems to understand the microbial behaviour, growth and motility was investigated. Conventionally, the growth and viability of microorganisms are determined by swabbing, plating and incubation, typically at 37degreesC for at least 24 hours. The proposed system allows real-time quantification of morphology and population changes of the microorganisms. An important aspect of the line scan system is the dynamic biospeckle. Dynamic speckle can be obtained from the movement of particles suspended in liquids. The speckle patterns show fluctuations in space and time which may be correlated with the activity of the constituents in the suspension. Initially the speckle parameters were standardized to non-motile and inert specimens such as polystyrene microspheres and suspensions of Staphylococcus aureus. The same optical systems and parameters were later tested on motile, active and live organisms of Escherichia coli. The experimental results that are presented describe the time history of the dynamic speckle pattern. A number of algorithms were used to analyse the intensity data. A 2D-FFT algorithm was used to evaluate the space and time-varying autocorrelation. Analysis of the speckle data in the Fourier domain provided insight into the motility of the organisms in broth. The mathematical analysis also gave further insight into the culture broth evaporation and its particle sedimentation characteristics at 37degreesC. These features correlated with the periodic motions associated with the organism and may therefore provide a signature for the organism and a means of monitoring. These results aided the developemnt of imaging bacterial detection systems which were discussed in the second half of the work. The second experimental system focuses on quantifying the morphology and population dynamics of Euglena gracilis under ambient conditions through image processing. Unlike many other cell systems, Euglena cells change from round to long to round cell shape and these different cell shapes were analyzed over time. In the morphological studies of single Euglena cells, image processing tools and filtering techniques were used and different parameters identified and their efficiency at determining cell shape compared. The best parameter for processing the images and its effectiveness in detecting even the interior motions of constituents within a dead cell was found. The efficiency of the measurement parameters in following sequences of shape changes of the Euglena cell was compared with the visual assessment tests from 12 volunteers and other simple measurement methods including parameters relating to the cells eccentricity, and image processing in the space and frequency domains. One of the major advantages of this system is that living cells can be examined in their natural state without being killed, fixed, and stained. As a result, the dynamics of ongoing biological processes in live cells can be observed and recorded in high contrast and sharp clarity. The population statistics of Euglena gracilis was done in liquid culture. A custom built microscopy system was employed and the laser beam was coupled with a dark field illumination system to enhance the contrast of the images. Different image filters were employed for extracting useful information on the population statistics. Similarly as with the shape study of the Euglena cell, different parameters were identified and the best parameter was selected. The population study of the Euglena cells provided a detection system that indicated the activity of the population

Efficient, image-based appearance acquisition of real-world objects

Two ingredients are necessary to synthesize realistic images: an accurate rendering algorithm and, equally important, high-quality models in terms of geometry and reflection properties. In this dissertation we focus on capturing the appearance of real world objects. The acquired model must represent both the geometry and the reflection properties of the object in order to create new views of the object with novel illumination. Starting from scanned 3D geometry, we measure the reflection properties (BRDF) of the object from images taken under known viewing and lighting conditions. The BRDF measurement require only a small number of input images and is made even more efficient by a view planning algorithm. In particular, we propose algorithms for efficient image-to-geometry registration, and an image-based measurement technique to reconstruct spatially varying materials from a sparse set of images using a point light source. Moreover, we present a view planning algorithm that calculates camera and light source positions for optimal quality and efficiency of the measurement process. Relightable models of real-world objects are requested in various fields such as movie production, e-commerce, digital libraries, and virtual heritage.Zur Synthetisierung realistischer Bilder ist zweierlei nötig: ein akkurates Verfahren zur Beleuchtungsberechnung und, ebenso wichtig, qualitativ hochwertige Modelle, die Geometrie und Reflexionseigenschaften der Szene repräsentieren. Die Aufnahme des Erscheinungbildes realer Gegenstände steht im Mittelpunkt dieser Dissertation. Um beliebige Ansichten eines Gegenstandes unter neuer Beleuchtung zu berechnen, müssen die aufgenommenen Modelle sowohl die Geometrie als auch die Reflexionseigenschaften beinhalten. Ausgehend von einem eingescannten 3D-Geometriemodell, werden die Reflexionseigenschaften (BRDF) anhand von Bildern des Objekts gemessen, die unter kontrollierten Lichtverhältnissen aus verschiedenen Perspektiven aufgenommen wurden. Für die Messungen der BRDF sind nur wenige Eingabebilder erforderlich. Im Speziellen werden Methoden vorgestellt für die Registrierung von Bildern und Geometrie sowie für die bildbasierte Messung von variierenden Materialien. Zur zusätzlichen Steigerung der Effizienz der Aufnahme wie der Qualität des Modells, wurde ein Planungsalgorithmus entwickelt, der optimale Kamera- und Lichtquellenpositionen berechnet. Anwendung finden virtuelle 3D-Modelle bespielsweise in der Filmproduktion, im E-Commerce, in digitalen Bibliotheken wie auch bei der Bewahrung von kulturhistorischem Erbe

Festschrift zum 60. Geburtstag von Wolfgang Strasser

Die vorliegende Festschrift ist Prof. Dr.-Ing. Dr.-Ing. E.h. Wolfgang Straßer zu seinem 60. Geburtstag gewidmet. Eine Reihe von Wissenschaftlern auf dem Gebiet der Computergraphik, die alle aus der "Tübinger Schule" stammen, haben - zum Teil zusammen mit ihren Schülern - Aufsätze zu dieser Schrift beigetragen. Die Beiträge reichen von der Objektrekonstruktion aus Bildmerkmalen über die physikalische Simulation bis hin zum Rendering und der Visualisierung, vom theoretisch ausgerichteten Aufsatz bis zur praktischen gegenwärtigen und zukünftigen Anwendung. Diese thematische Buntheit verdeutlicht auf anschauliche Weise die Breite und Vielfalt der Wissenschaft von der Computergraphik, wie sie am Lehrstuhl Straßer in Tübingen betrieben wird. Schon allein an der Tatsache, daß im Bereich der Computergraphik zehn Professoren an Universitäten und Fachhochschulen aus Tübingen kommen, zeigt sich der prägende Einfluß Professor Straßers auf die Computergraphiklandschaft in Deutschland. Daß sich darunter mehrere Physiker und Mathematiker befinden, die in Tübingen für dieses Fach gewonnen werden konnten, ist vor allem seinem Engagement und seiner Ausstrahlung zu verdanken. Neben der Hochachtung vor den wissenschaftlichen Leistungen von Professor Straßer hat sicherlich seine Persönlichkeit einen entscheidenden Anteil an der spontanten Bereischaft der Autoren, zu dieser Festschrift beizutragen. Mit außergewöhnlich großem persönlichen Einsatz fördert er Studenten, Doktoranden und Habilitanden, vermittelt aus seinen reichen internationalen Beziehungen Forschungskontakte und schafft so außerordentlich gute Voraussetzungen für selbständige wissenschafliche Arbeit. Die Autoren wollen mit ihrem Beitrag Wolfgang Straßer eine Freude bereiten und verbinden mit ihrem Dank den Wunsch, auch weiterhin an seinem fachlich wie menschlich reichen und bereichernden Wirken teilhaben zu dürfen

Entropy-Based Dark Frame Subtraction

Noise due to dark current is a serious limitation for taking long exposure time images with a CCD digital camera. Current solutions have serious drawbacks: interpolation of pixels with high dark current leads to smoothing effects or other artifacts -- especially if a large number of pixels are corrupted. Due to the exponential temperature dependence of the dark current, dark frame subtraction works best for temperature controlled high end CCD imaging systems. On the physical level, two independent signals (charge generated by photons hitting the CCD and by the dark current) are added. Due to its random distribution, adding (or subtracting) the dark current noise signal increases the entropy of the resulting image. The entropy is minimal if the dark current signal is not present at all. A dark frame is a good representation of the dark current noise. As the generated dark current depends on the temperature equally for all pixels, a noisy image can be cleaned by the subtraction of a scaled dark frame. The scaling factor can be determined in an optimization step which tries to minimize the entropy of the cleaned image. We implemented a software system that effectively removes dark current noise even from highly corrupted images. The resulting images contain almost no visible artifacts since only the noise signal is removed. This extends the range of usable exposure times of digital cameras without temperature control systems by about one to two orders of magnitude