Joerg Velten

FPGA-based implementation of variable sized structuring elements for 2D binary morphological operations

Binary morphological operations are an important means for real time image processing applications. While fixed size structuring elements are sufficient for usual image processing steps, more sophisticated algorithms require structuring elements of variable shape. These operations can be realized by using Boolean logic in connection with dead time elements, which leads to a straightforward implementation if using FPGAs.

Detection of Moving Objects in Image Sequences using 3D Velocity Filters

Detection of Moving Objects in Image Sequences using 3D Velocity Filters A movement analysis of objects contained in visual scenes can be performed by means of linear multidimensional filters, which have already been analyzed in the past. While the soundness of the results was convincing, interest in those systems declined due to the limited computational power of contemporary computers. Recent advances in design and implementation of integrated circuits and hardware architectures allow realizing velocity filters if the n-D system is carefully adapted to the analyzed problem. In this paper, the fundamental principles of visual scene analysis by linear multidimensional filters are examined with respect to possible sources of degradation. The extraction of movement information and its practical use are demonstrated using a wave digital filter (WDF) implementation.

Motion-Based Object Detection for Automotive Applications using Multidimensional Wave Digital Filters

Vision-based object detection is a core part of many automotive collision warning systems. Especially due to the extensive information an image can hold and the decreasing costs of computational power, it has attracted more and more interest in the last decade. In this paper we propose a motion-based approach to simplify the detection of moving objects in order to improve available methods and make them more efficient. We interpret the image sequence containing the moving object (e.g. a vehicle or a crossing pedestrian) as a three-dimensional signal, not just as a sequence of image matrices. That way we can benefit from the advanced theoretical knowledge on system description and handling from the field of signal processing. In detail, three-dimensional velocity filters implemented using wave digital filters are used to oppress every object in the image that is not moving in a certain direction at a certain velocity.

3D wave digital filter implementation on a virtex2 FPGA board with external SDRAM

Many n-D signal processing applications require realization in real time. We propose the realization of a 3-D spatio-temporal wave digital filter (WDF) in an FPGA. Optimization of the implemented hardware architecture includes evaluation of two different kinds of overflow handling, namely by saturation and a “modulo 2” type operation. The FPGA board is processing DVI signals that can be provided by usual PC hardware. The processing output is observed in real time on an LCD monitor.

Motion-based object detection using 3D wave digital filters

This paper is focused on the separation of three-dimensional signals due to different velocity or directional components, more precisely detecting moving objects in visual scenes by means of linear multidimensional filters. While soundness of results obtained by similar systems developed in the past has been convincing, interest in those systems declined to the reduced computational power of contemporary computers. Recent advances in computation speed as well as design and implementation of integrated circuits and hardware architectures allow hardware realization of the above mentioned velocity filters for real-time processing. We present wave digital filter (WDF) structures adapted to the detection of objects moving in a certain direction at a given speed. These filters have been successfully tested on sequences showing crossing pedestrians recorded by a vehicle-mounted camera.

Multidimensional velocity filters for visual scene analysis in automotive driver assistance systems

Automotive scenery often contains objects that can be classified by object speed and movement direction. These features can be extracted from video data by linear n-D filters, which have already been analyzed in the past. While soundness of results was convincing, interest in those systems declined due to the reduced computational abilities of contemporary computers. Modern hardware allows realization of velocity filters, if the n-D system is carefully adapted to the analysis problem. The present paper analyzes the premises for application of velocity filters in the domain of automotive driver assistance systems, i.e. with respect to detectability of objects and implementability in a cost effective way. Especially the influence of the frame rate and the temporal violation of the sampling theorem are analyzed. Transfer functions for n-D filters working in a vision-based blind spot collision avoidance system are presented and discussed, and promising approaches for future application fields are proposed.

Tomographical scene reconstruction in the active safety car project

Tomographical reconstruction algorithms can be applied to camera based measurements and thus reconstruct the scenery without knowledge about included objects. The latter is interesting in the domain of driver assistance systems that have to monitor the driveway independently from a priori knowledge about possibly appearing objects. The paper presents tomographical background information, the transfer from radiographing to visual light rays and its negative impacts, and some first result obtained by applying the presented algorithm to images of a from view camera.

Realization of multidimensional signal processing systems given in natural k-D state space description

The paper addresses design, analysis, and realization of linear, discrete domain k-D signal processing systems based on a natural state space description. The latter is chosen to overcome restrictions by widely known Givone-Roesser and Fornasini-Marchesini models. It is capable of describing noncausal systems as well as shift operations with respect to more than one coordinate direction. It thus provides a system description that offers better compliance with possible hardware realizations than existing models and thus allows evaluation and consideration of many realization specific effects.

Application specific stability of 2-D Roesser model realizations

Stability of multidimensional (k-D) systems is still a challenging field of work. Well known and established stability measures may lead to complex mathematical problems, while simple tests are restricted to special cases of n-D systems. A new stability test for certain discrete 2-D system realizations given in a Roesser model description is proposed. This test is suitable for signals bounded with respect to both coordinate directions, like images. The 2-D system is observed in real operation, i.e. considering a sequence of processing, which leads to a 1-D state space description. The resulting 1-D system matrix is some kind of a block Toeplitz matrix that allows definition of the test.

Multidimensional linear shift invariant velocity filters for vision-based automotive applications

Object detection and segmentation is one of the most challenging research topics in the field of active automotive safety systems. In order to warn the driver or automatically break before a potential collision, objects interfering the path of the host vehicle have to be detected and classified. Most recently developed approaches are based on two dimensional image processing, sometimes in combination with a tracking algorithm associating detections in consecutive frames to one and the same object. In contrast, the approach presented in this paper uses multidimensional velocity filters to identify moving objects, such as a pedestrian crossing the street in front of the vehicle. More precisely, movement characteristics (like velocity and direction) of objects in sight of a vehicle-mounted monochrome camera are used to enhance or suppress the corresponding pixels in the video stream. Basic considerations and example transfer functions for this application are presented and simulation results using a wave digital filter (WDF) realization thereof are presented and discussed.