Arkadiusz Hulewicz

Application of a Multi-sensor Set for Comparative Evaluation of the Photoplethysmographic Waveforms

In this work, we present the structure of a system based on several optoelectronic sensors used for noninvasive monitoring of local changes in the arterial blood pulse waveform. The phenomena accompanying the acquisition of optical signals from biological objects were analyzed. Reflectance optoelectronic sensors, photoplethysmographic signal conditioning and acquisition system were designed and constructed. Sample time curves of the signals obtained have been presented. The presented set expands the possibilities of the analysis based on the measuring data from several sensors placed in various points of human body.

Computer-Assisted Acquisition and Statistical Evaluation of Multifocal Visual Evoked Potentials

The subject of this paper concerns the electro-physiological examination of the visual organ, the acquisition and statistical evaluation of the multifocal visual evoked potentials (M-VEP), in particular. The results presented are related to the real multifocal VEP waveforms, obtained during the examination of numerous patients in clinical conditions. The statistical evaluation of the results obtained during the examination of numerous healthy eyes enables the determination of electrical potential tolerance intervals and latency in the scope of the entire visual path of a healthy eye. Due to the lack of standardized values of the M-VEP test, the intervals may represent reference data in the valuation of various visual tract diseases. The data included therein, upon being exported to Microsoft Excel, enable the calculation of the average and standard deviation, and the tolerance intervals based on them

Utilization of human-computer interaction in wireless transmission of arterial pulse waveforms

The shape of the arterial pulsations depends upon the thickness of the blood vessels and contractility of the heart as well as the state of the vascular smooth muscle in the vessel wall. Photoplethysmography (PPG) is by definition an optoelectronic method for measuring and recording changes in volume of a body part. The shape and stability of the PPG waveform can be used as an indication of possible motion artifacts or low perfusion conditions. Furthermore, the photoplethysmogram reveals circulatory depression and arrhythmia. In the paper, we propose a system that allows wireless transmitting of peripheral arterial pulse waveforms with use of a GPRS network. Selected examples of results, which were obtained during investigations made on a number of real PPG signals, are presented.

A New Approach to Objective Evaluation of Human Visual Acuity

The paper presents the way that colour can serve solving the problem of calibration points indexing in a camera geometrical calibration process. We propose a technique in which indexes of calibration points in a black-and-white chessboard are represented as sets of colour regions in the neighbourhood of calibration points. We provide some general rules for designing a colour calibration chessboard and provide a method of calibration image analysis. We show that this approach leads to obtaining better results than in the case of widely used methods employing information about already indexed points to compute indexes. We also report constraints concerning the technique. Nowadays we are witnessing an increasing need for camera geometrical calibration systems. They are vital for such applications as 3D modelling, 3D reconstruction, assembly control systems, etc. Wherever possible, calibration objects placed in the scene are used in a camera geometrical calibration process. This approach significantly increases accuracy of calibration results and makes the calibration data extraction process easier and universal. There are many geometrical camera calibration techniques for a known calibration scene [1]. A great number of them use as an input calibration points which are localised and indexed in the scene. In this paper we propose the technique of calibration points indexing which uses a colour chessboard. The presented technique was developed by solving problems we encountered during experiments with our earlier methods of camera calibration scene analysis [2]-[3]. In particular, the proposed technique increases the number of indexed points points in case of local lack of calibration points detection. At the beginning of the paper we present a way of designing a chessboard pattern. Then we describe a calibration point indexing method, and finally we show experimental results. A black-and-white chessboard is widely used in order to obtain sub-pixel accuracy of calibration points localisation [1]. Calibration points are defined as corners of chessboard squares. Assuming the availability of rough localisation of these points, the points can be indexed. Noting that differences in distances between neighbouring points in calibration scene images differ slightly, one of the local searching methods can be employed (e.g. [2]). Methods of this type search for a calibration point to be indexed, using a window of a certain size. The position of the window is determined by a vector representing the distance between two previously indexed points in the same row or column. However, experiments show that this approach has its disadvantages, as described below. * E-mail: A.Nowakowski@ire.pw.edu.pl Firstly, there is a danger of omitting some points during indexing in case of local lack of calibration points detection in a neighbourhood (e.g. caused by the presence of non-homogeneous light in the calibration scene). A particularly unfavourable situation is when the local lack of detection effects in the appearance of separated regions of detected calibration points. It is worth saying that such situations are likely to happen for calibration points situated near image borders. Such points are very important for the analysis of optical nonlinearities, and a lack of them can significantly influence the accuracy of distortion modelling. Secondly, such methods may give wrong results in the case of optical distortion with strong nonlinearities when getting information about the neighbouring index is not an easy task. Beside this, the methods are very sensitive to a single false localisation of a calibration point. Such a single false localisation can even result in false indexing of a big set of calibration points. To avoid the above-mentioned problems, we propose using a black-and-white chessboard which contains the coded index of a calibration point in the form of colour squares situated in the nearest neighbourhood of each point. The index of a certain calibration point is determined by colours of four nearest neighbouring squares (Fig.1). An order of squares in such foursome is important. Because the size of a colour square is determined only by the possibility of correct colour detection, the size of a colour square can be smaller than the size of a black or white square. The larger size of a black or white square is determined by the requirements of the exact localisation step which follows the indexing of calibration points [3]. In this step, edge information is extracted from a blackand-white chessboard. This edge information needs larger Artur Nowakowski, Wladyslaw Skarbek Institute of Radioelectronics, Warsaw University of Technology, Nowowiejska 15/19, 00-665 Warszawa, A.Nowakowski@ire.pw.edu.pl Received February 10, 2009; accepted March 27, 2009; published March 31, 2009 http://www.photonics.pl/PLP