Multimedia Information Processing Group


Claudius Zelenka, Reinhard Koch (2017): 
Improved wavefront correction for coherent image restoration 
Opt. Express 25, 18797-18816 (2017) 
original publication at

Abstract: Coherent imaging has a wide range of applications in, for example, microscopy, astronomy, and radar imaging. Particularly interesting is the field of microscopy, where the optical quality of the lens is the main limiting factor. In this article, novel algorithms for the restoration of blurred images in a system with known optical aberrations are presented. Physically motivated by the scalar diffraction theory, the new algorithms are based on Haugazeau POCS and FISTA, and are faster and more robust than methods presented earlier. With the new approach the level of restoration quality on real images is very high, thereby blurring and ringing caused by defocus can be effectively removed. In classical microscopy, lenses with very low aberration must be used, which puts a practical limit on their size and numerical aperture. A coherent microscope using the novel restoration method overcomes this limitation. In contrast to incoherent microscopy, severe optical aberrations including defocus can be removed, hence the requirements on the quality of the optics are lower. This can be exploited for an essential price reduction of the optical system. It can be also used to achieve higher resolution than in classical microscopy, using lenses with high numerical aperture and high aberration. All this makes the coherent microscopy superior to the traditional incoherent in suited applications.


Claudius Zelenka, Reinhard Koch (2016): 
Restoration of images with wavefront aberrations 
2016 23rd International Conference on Pattern Recognition (ICPR), (IEEE 2016) 
original publication at

Abstract: This contribution deals with image restoration in optical systems with coherent illumination, which is an important topic in astronomy, coherent microscopy and radar imaging. Such optical systems suffer from wavefront distortions, which are caused by imperfect imaging components and conditions. Known image restoration algorithms work well for incoherent imaging, they fail in case of coherent images. In this paper a novel wavefront correction algorithm is presented, which allows image restoration under coherent conditions. In most coherent imaging systems, especially in astronomy, the wavefront deformation is known. Using this information, the proposed algorithm allows a high quality restoration even in case of severe wavefront distortions. We present two versions of this algorithm, which are an evolution of the Gerchberg-Saxton and the Hybrid-Input-Output algorithm. The algorithm is verified on simulated and real microscopic images.


Anne Jordt, Claudius Zelenka, Jens Schneider von Deimling, Reinhard Koch, Kevin Köser (2015):
The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites
Sensors 2015, 15, 30716-30735.
original publication at Sensors Journal bibtex

Abstract: Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information.


Claudius Zelenka, Reinhard Koch (2015):
Blind Deconvolution on Underwater Images for Gas Bubble Measurement
Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci., XL-5/W5, 239-244, 2015
original publication at Archives of ISPRS bibtex

Abstract: Marine gas seeps, such as in the Panarea area near Sicily (McGinnis et al., 2011), emit large amounts of methane and carbon-dioxide, greenhouse gases. Better understanding their impact on the climate and the marine environment requires precise measurements of the gas flux. Camera based bubble measurement systems suffer from defocus blur caused by a combination of small depth of field, insufficient lighting and from motion blur due to rapid bubble movement. These adverse conditions are typical for open sea underwater bubble images. As a consequence so called ’bubble boxes’ have been built, which use elaborate setups, specialized cameras and high power illumination. A typical value of light power used is 1000W (Leifer et al., 2003).
In this paper we propose the compensation of defocus and motion blur in underwater images by using blind deconvolution techniques. The quality of the images can be greatly improved, which will relax requirements on bubble boxes, reduce their energy consumption and widen their usability.


Claudius Zelenka (2014):
Gas Bubble Shape Measurement and Analysis
in Pattern Recognition, Volume 8753 of LNCS, pp. 743-749. Springer Berlin / Heidelberg
original publication at bibtex

Abstract: This work focuses on the precise quantification of bubble streams from underwater gas seeps. The performance of the snake based method and of ellipse fitting with the CMA-ES non-linear optimization algorithm is evaluated. A novel improved snake based method is presented and the optimal choice of snake parameters is studied. A Kalman filter is used for bubble tracking. The deviation between the measured flux and a calibrated flux meter is 4 % for small and 9 % for larger bubbles. This work will allow a better data gathering on marine gas seeps for future climatology and marine research.


Master's thesis on
Underwater Bubble Shape Measurement and Analysis
Supervised by Reihard Koch and Anne Jordt
awarded the Fokusfinder 2014 price by the Initiative Bildverarbeitung




WS 2015 - Computer Graphics - Teaching Assistant
WS 2015 - Computer Systems - Teaching Assistant
SS 2015 - Computer Science for Engineers - Teaching Assistant
WS 2014/2015 - Introduction to Image Processing - Teaching Assistant
SS 2014 - Computer Graphics - Teaching Assistant