Bernd Jähne

Wind/Wave-Tunnel Experiment on the Schmidt Number — and Wave Field Dependence of Air/Water Gas Exchange

Gas exchange experiments have been carried out in the Heidelberg circular wind tunnels and the large linear I.M.S.T. wind/wave facility in order to study the wave field and Schmidt number dependence of gas exchange. With a smooth water surface the experimental results agree well with the model treating the water surface as a rigid wall both in the Sc−2/3 dependence and the absolute rates. Gas exchange rates with a rough wavy surface are 3–5 times higher than in the smooth case and the Schmidt number dependence is lower (Sc−n, n = 0.55 ± 0.05). The total square wave slope seems to be a more appropriate parameter to describe the enhanced rates than the capillary wave slope.

Computer vision and applications: a guide for students and practitioners

Preface. Contributors. B. Jahne, Introduction. Sensors and Imaging. H. Haubecker,Radiation and Illumination. P. Geibler,Imaging Optics. H. Haubecker,Radiometry of Imaging. P. Seitz,Solid-State Image Sensing. R. Godding, Geometric Calibration of Digital Imaging Systems. R. Schwarte, G. Hausler, R.W. Malz, Three-Dimensional Imaging Techniques. Signal Processing and Pattern Recognition. B. Jahne, Representation of Multidimensional Signals. B. Jahne, Neighborhood Operators. H. Haubecker, H. Spies, Motion. P. Geibler, T. Dierig, H.A. Mallot, Three-Dimensional Imaging Algorithms. J. Weickert, Design of Nonlinear Diffusion Filters. C. Schnorr, Variational Adaptive Smoothing and Segmentation. P. Soille, Morphological Operators. J. Hornegger, D. Paulus, H. Niemann,Probabilistic Modeling in Computer Vision. H. Haubecker, H.R. Tizhoosh, Fuzzy Image Processing. A. Meyer-Base, Neural Net Computing for Image Processing. Application Gallery. Index.

Imaging of short ocean wind waves: a critical theoretical review

Optical techniques to measure the small-scale shape of the ocean surface, i.e., the short wind waves, are theoretically reviewed. The well-known shape-from-shading and shape-from-stereo paradigms from computer vision are applied to a specular reflecting surface such as the ocean surface and are used to study a variety of techniques. The analysis shows that most techniques for the imaging of short wind waves, such as Stilwell photography and various stereo techniques, have significant deficiencies. Stereophotography is plagued by insufficient height resolution for small waves and by the problem that, because of the specular nature of reflection at the water surface, features seen in one image are not necessarily found in the other (correspondence problem). Techniques based on light reflection (shape from reflection) are useful only for deriving wave-slope statistics, and techniques based on light refraction (shape from refraction) are found to be most suitable for wave slope imaging.

Theoretical and experimental error analysis of continuous-wave time-of-flight range cameras

We offer a formal investigation of the measurement principle of time-of-flight 3-D cameras using correlation of amplitude-modulated continuous-wave signals. These sensors can provide both depth maps and IR intensity pictures simultaneously and in real time. We examine the theory of the data acquisition in detail. The variance of the range measurements is derived in a concise way and we show that the computed range follows an offset normal distribution. The impact of quantization of that distribution is discussed. All theoretically investigated errors like the behavior of the variance, depth bias, saturation and quantization effects are supported by experimental results.

Range Flow Estimation

Abstract We discuss the computation of the instantaneous 3D displacement vector fields of deformable surfaces from sequences of range data. We give a novel version of the basic motion constraint equation that can be evaluated directly on the sensor grid. The various forms of the aperture problem encountered are investigated and the derived constraint solutions are solved in a total least squares (TLS) framework. We propose a regularization scheme to compute dense full flow fields from the sparse TLS solutions. The performance of the algorithm is analyzed quantitatively for both synthetic and real data. Finally we apply the method to compute the 3D motion field of living plant leaves.

Digital Image Processing, 5th revised and extended edition

This is the fifth edition of this popular handbook. As was the case in previous editions the book is well presented over 500+ pages with nearly 250 figures, clear exposition of mathematical equations and high quality greyscale images. The book is in four main parts. The first lays the foundations of the subject and gives a good introduction to the basic tools used in image processing such as random variables, probability density functions and a very sound section on image representation. The basics of digital filtering by convolution are also explained in this section of the book. The second part of the book deals with image formation and preprocessing. As well as the more conventional material on image formation, e.g. detectors, basic optics etc, this section interestingly includes material on 3D imaging from structured light and tomography. The author is to be congratulated for including this important, but sadly often neglected, aspect of imaging. Section three deals with feature extraction in a very competent, if rather conventional, fashion. All of the major techniques are covered including filtering, gradient methods, neighborhood processes etc. The inclusion of both motion extraction and texture analysis make this section more worthwhile. The books final part deals with the problems of image analysis. This includes interesting and useful treatments of inversion problems, morphological operations, shape descriptors etc. In all there are some 20 chapters in the book. Each chapter concludes with a useful list of further reading. Overall the references given in the book are accessible and reasonably up to date. The supporting CD offers the complete text of the book in electronic form and a copy of a general-purpose image processing package, which makes a useful tool. An overall evaluation would be that this is an excellent and comprehensive review of digital image processing. While not an elementary text - the book requires a reasonably accomplished level of mathematical knowledge - it would be a excellent text for a final-year degree or Masters level module in the subject. It would also be a first-class introductory text for anybody new to research in this field. Finally the book would also be of value as a reference text for established workers in the field; its comprehensive nature and high quality references mean that it would be an excellent starting point for information on areas outside ones immediate specialty. David BurtonThis is the fifth edition of this popular handbook. As was the case in previous editions the book is well presented over 500+ pages with nearly 250 figures, clear exposition of mathematical equations and high quality greyscale images. The book is in four main parts. The first lays the foundations of the subject and gives a good introduction to the basic tools used in image processing such as random variables, probability density functions and a very sound section on image representation. The basics of digital filtering by convolution are also explained in this section of the book. The second part of the book deals with image formation and preprocessing. As well as the more conventional material on image formation, e.g. detectors, basic optics etc, this section interestingly includes material on 3D imaging from structured light and tomography. The author is to be congratulated for including this important, but sadly often neglected, aspect of imaging. Section three deals with feature extraction in a very competent, if rather conventional, fashion. All of the major techniques are covered including filtering, gradient methods, neighborhood processes etc. The inclusion of both motion extraction and texture analysis make this section more worthwhile. The books final part deals with the problems of image analysis. This includes interesting and useful treatments of inversion problems, morphological operations, shape descriptors etc. In all there are some 20 chapters in the book. Each chapter concludes with a useful list of further reading. Overall the references given in the book are accessible and reasonably up to date. The supporting CD offers the complete text of the book in electronic form and a copy of a general-purpose image processing package, which makes a useful tool. An overall evaluation would be that this is an excellent and comprehensive review of digital image processing. While not an elementary text - the book requires a reasonably accomplished level of mathematical knowledge - it would be a excellent text for a final-year degree or Masters level module in the subject. It would also be a first-class introductory text for anybody new to research in this field. Finally the book would also be of value as a reference text for established workers in the field; its comprehensive nature and high quality references mean that it would be an excellent starting point for information on areas outside ones immediate specialty. David Burton

Study of Dynamical Processes with Tensor-Based Spatiotemporal Image Processing Techniques

Image sequence processing techniques are used to study exchange, growth, and transport processes and to tackle key questions in environmental physics and biology. These applications require high accuracy for the estimation of the motion field since the most interesting parameters of the dynamical processes studied are contained in first-order derivatives of the motion field or in dynamical changes of the moving objects. Therefore the performance and optimization of low-level motion estimators is discussed. A tensor method tuned with carefully optimized derivative filters yields reliable and dense displacement vector fields (DVF) with an accuracy of up to a few hundredth pixels/frame for real-world images. The accuracy of the tensor method is verified with computer-generated sequences and a calibrated image sequence. With the improvements in accuracy the motion estimation is now rather limited by imperfections in the CCD sensors, especially the spatial nonuniformity in the responsivity. With a simple two-point calibration, these effects can efficiently be suppressed. The application of the techniques to the analysis of plant growth, to ocean surface microturbulence in IR image sequences, and to sediment transport is demonstrated.

Outdoor Stereo Camera System for the Generation of Real-World Benchmark Data Sets

We describe a high-performance stereo camera system to capture image sequences with high temporal and spatial resolution for the evaluation of various image processing tasks. The system was primarily designed for complex outdoor and traffic scenes that frequently occur in the automotive industry, but is also suited for other applications. For this task the system is equipped with a very accurate inertial measurement unit and global positioning system, which provides exact camera movement and position data. The system is already in active use and has produced several terabytes of challenging image sequences which are partly available for download.

Estimation of Surface Flow and Net Heat Flux from Infrared Image Sequences

The study of dynamical processes at the sea surface interface using infrared image sequence analysis has gained tremendous popularity in recent years. Heat is transferred by similar transport mechanisms as gases relevant to global climatic changes. These similarities lead to the use of infrared cameras to remotely visualize and quantitatively estimate parameters of the underlying processes. Relevant parameters that provide important evidence about the models of air-sea gas transfer are the temperature difference across the thermal sub layer, the probability density function of surface renewal and the flow field at the surface. Being a driving force in air sea interactions, it is of equal importance to measure heat fluxes. In this paper we will present algorithms to measure the above parameters of air-sea gas transfer during night-time and show how to combine physical modeling and quantitative digital image processing algorithms to identify transport models. The image processing routines rely on an extension of optical flow computations to incorporate brightness changes in a total least squares (TLS) framework. Statistical methods are employed to support a model of gas transfer and estimate its parameters. Measurements in a laboratory environment were conducted and results verified with ground truth data gained from traditional measurement techniques.

A theoretical and experimental investigation of the systematic errors and statistical uncertainties of Time-Of-Flight-cameras

The following paper presents a model to predict the systematic errors and statistical uncertainties of Time-Of-Flight (TOF) 3D imaging systems. The experimental data obtained with a custom build test setup show that the SD of the depth signal rises approximately quadratically with the depth. The most significant systematic depth error is periodic with an amplitude of around 50mm. It is provoked by the inharmonic correlation function. The inhomogeneity in each pixel (fixed pattern) accounts for a depth error of about 20mm, while illumination and reflectivity variations cause depth errors of less than 10mm, provided that no overflows occur.