Showing papers by "Norman S. Kopeika published in 2002"

Recognition of motion-blurred images by use of the method of moments.

Abstract: Image motion causes a blur that changes features of objects and therefore complicates the task of automatic recognition. In this work we develop two recognition methods for motion-blurred images. For the first method we assume that the motion function and direction during the exposure are given. We develop the relation between the blurred-image moments and the original-image moments based on the motion function only. The recognition is carried out by comparing the moments of the restored image against the moments of the image database. In the second method the motion function is not known. In this case image moments that are invariant with respect to the motion blur are identified, and only these moments are used for recognition. The advantage of the suggested methods is that no time-consuming image restoration is required prior to recognition.

Motion-blurred image restoration using modified inverse all-pole filters

Abstract: The restoration of vibration-blurred images using measured motion function is considered. Since the blurring filter is of finite impulse response type, the inverse one is of all-pole infinite impulse response type. Direct application of the inverse filter to restore images blurred by vibration is attractive because of minimal computation requirements. However, a pure inverse filter provides excessive noise amplification and is possibly unstable. The proposed technique is to construct a modified inverse filter with preserved all-pole structure and optimized noise and stability properties. An experiment testing the proposed technique was set up and the results presented here.

Possible solutions to mitigate vibration effects in laser intersatellite links

Abstract: Free space laser communication between satellites networked together can facilitate high-speed communication between different places on earth. The advantages of an optical communication system by comparison with a microwave communication system in free space are: a) smaller size and weight, b) less transmitter power, c) larger bandwidth, d) higher immunity to interference, and e) smaller transmitter beam divergence. The use of optical radiation as a carrier between the satellites engenders very narrow beam divergence angles. Due to the narrow beam divergence angle and the large distance between the satellites, the pointing from one satellite to another is complicated. The problem is further complicated due to vibrations of the pointing system caused by two fundamental mechanisms, stochastic in nature; 1) tracking nose created by the electro-optic tracker and 2) vibrations created by internal and external mechanical mechanisms. The vibrations displace the transmitted beam and the receiver field of view with respect to one another. Such movement decreases the average received signal, and increases the bit error rate (BER). In this paper we will review five methods to mitigate the effect of vibrations on laser satellite communication system. The methods are a) receiver with adaptive detector arrays, b) Bandwidth/data rate/coding rate adaptation, c) Power minimization using adaptive beam-width, d) Communication diversity within the satellite network, and e) Power control.

Influence of motion sensor error on image restoration from vibrations and motion

Abstract: We investigate the influence of motion sensor errors on the calculation of a modulation transfer function (MTF) and its implementation in image restoration. The goal of this research is to describe an automatic system for restoration of pictures blurred by vibration, and to consider its possible disadvantages. We present an analytical approach for estimating the vibration MTF from the measured system MTF according to the frequency response of motion sensors and their noise data. Our method is based on point-spread function verification by the data of motion sensor characteristics. We build an analytical model of the sensor and analyze influences of errors caused by system noise and incorrect axis direction of the restoration device. Some image restoration of degraded images is presented based on improvements using the original wiener filter. Performances of inverse and wiener filter operations are compared, and the dependence of restoration quality on the signal-to-noise ratio and angle between the restoration axis and true vibration direction is considered. We also demonstrate the axis rotation sensitivity of the system, and describe improvements over the initial method as seen from our simulation. The key to the restoration is the determination of the improved modulation transfer function unique to the image vibration and sensor characteristics.

Changes in modulation transfer function and optical resolution in helical turbulent media.

Abstract: We study the change in the behavior of the modulation transfer function and resolution with changing properties of a turbulent medium. It is shown that the form and the behavior of the functions under study undergo significant changes at the transition from Kolmogorov’s to a helical type of turbulent medium. These changes should be taken into account in developing models of electromagnetic radiation propagation through a medium as well as in interpreting experimental data.

Satellite image restoration filter comparison

Abstract: Many properties of the atmosphere affect the quality of images propagating through it by blurring it and reducing its contrast, as well as blur. Use of the standard Wiener filter for correction of atmospheric blur is often not effective because, although aerosol MTF (modulation transfer function) is rather deterministic, turbulence MTF is random. The atmospheric Wiener filter is one method for overcoming turbulence jitter. The recently developed atmospheric Wiener filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously, is implemented here in digital restoration of Landsat TM (thematic mapper) imagery over seven wavelength bands of the satellite instrumentation. Turbulence MTF is calculated from meteorological data or estimated if no meteorological data were measured. Aerosol MTF is consistent with optical depth. The product of the two yields atmospheric MTF, which is implemented in the atmospheric Wiener filter. Restoration improves both smallness of size of resolvable detail and contrast. Restorations are quite apparent even under clear weather conditions. Techniques for high resolution restoration involving more versatile filtering techniques, such as Kalman's and adaptive methods, are considered by filter comparison.

Differential sensing of vibration for high-quality restoration of motion-blurred images

Abstract: Restoration of vibrated images can be performed with or without knowledge of the motion function The algorithms based on the known motion function are more accurate However, sensing of the motion function in the real-world environment is often difficult to implement accurately We propose a differential scheme for sensing vibrations It is shown that the differential scheme permits one to obtain a true rotational motion function, which is often the main blurring factor in remote sensing systems An experiment was set up and the results are presented The proposed sensing scheme was implemented in real time and then the obtained image was restored from motion blur with a personal computer The fine accuracy of the restoration results derives from the accuracy of the proposed motion sensing scheme