Showing papers by "Norman S. Kopeika published in 2000"

Restoration of an image degraded by vibrations using only a single frame

Abstract: A recently developed method for the restoration of motion- blurred images is investigated and implemented for the special compli- cated case of image blur due to sinusoidal vibrations. Sinusoidal vibra- tions are analyzed in the context of blur identification and image restoration. The extent of the blur and the optical transfer function (OTF) are identified from the blurred image by a straightforward process with- out the use of iterative techniques. The blurred image is restored using a simple Wiener filter with the identified OTF. The main novel achievement is the use of only a single vibrated blurred image as input information, on which the restoration process is based. The various cases of blur types that depend on the imaging conditions are considered. Examples of blur identification and image restoration are presented. © 2000 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(00)01408-2)

Acquisition system for microsatellites laser communication in space

Abstract: Optical communications is a very complex task between satellites because of the small laser beam divergence and the large distance. Also, the vibrations of the satellites due to satellite internal systems and due to external sources may cause the laser beam to miss the intended satellite. In order to start the communication one of the satellites should start acquisition to compensate for possible large deviation angle between transmitter and receiver telescope lines of sight (LOS). During the communication if in the tracking process the satellite loses the connection the acquisition system should establish LOS quickly. In this paper are presented various acquisition search pattern methods such as raster and spiral, and different search methods such as scan/scan or scan/stare are analyzed. The influence of vibrations on these methods and compensation systems is discussed. Analysis of several components of the system is obtained through simulation.

Restoration and resolution enhancement of a single image from a vibration-distorted image sequence

Abstract: In many applications such as in airborne and terrestrial reconnaissance, robotics, medical imaging, and machine vision systems, the images of a video sequence are severely distorted by vibrations. Superresolution algorithms are suitable for restoring an image from a lowfrequency vibrated sequence because of high correlation between the frames and inherent interframe motion. However, we show that superresolution algorithms, which were developed for general types of blur, should be adapted to the specific characteristics of low-frequency vibration blur. We demonstrate that in the case of image sequences distorted by vibration, the images should be selected prior to processing. We find empirical selection criteria and propose a selection procedure.

Vertical profiles of aerosol and optical turbulence strength and their effects on atmospheric propagation

Abstract: On a basis of a multiple-forward-scatter propagation model the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path is estimated and compared with beam widening caused by turbulence. It is shown that the beam widening caused by atmospheric aerosols is significant, often even more significant than that caused by turbulence.

Criteria for satellite image restoration success

Abstract: Many properties of the atmosphere affect the quality of images propagating through it by blurring and reducing their contrast. The atmospheric path involves several limitations such as scattering and absorption of the light and turbulence, which degrade the image. 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 Thematic Mapper (TM) imagery over seven wavelength bands of the satellite instrumentation. Turbulence MTF (Modulation Transfer Function) is calculated from meteorological data or estimated in 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. Different restoration results are obtained by trying to restore the degraded image. A way to determine which is the best restoration result and how good is the restored image is presented here, by examining mathematical criteria such as MSE (Mean Square Error), ROH (Richness of Histogram), and SOH (Similarity of Histogram), to obtain an improved image and consequently better visual restoration results.

Influence of severe vibrations on the visual perception of video sequences

Abstract: There are two kinds of video image sequence distortions caused by vibration of the camera. The first is the vibration of the line-of-sight causing location changes of the scene in successive frames. The second effect is the blur of each frame of the sequence due to frame motion during its exposure. In this work, the relative effects of these two types of degradations on the ability of observers to recognize targets are investigated. This study is useful for evaluating the amount of effort required to compensate each effect. We found that the threshold contrast needed to recognize a target in a vibrating video sequence under certain conditions is more affected by the motion blur of each frame than the oscillation of the line-of-sight. For digital sequence restoration methods, this study determines the required precision of the deblurring and registration processes. It shows that the deblurring process should not be neglected as it often is.

Myopic Deconvolution of Adaptive Optics Images by use of Object and Point-Spread Function Power Spectra: Comment.

Abstract: It is suggested here that the lack of total image correction that is typical in adaptive optics (AO) imaging can be attributed in part to blur derived from small-angle scatter of light by aerosols, known also as the adjacency effect, especially as it is a well-established fact that such atmospheric blur is dominant in satellite imagery and the shape of the modulation transfer function after AO correction is strikingly similar to the unique shape of the aerosol modulation transfer function. Further investigation of AO systems to confirm this would aid in and improve image restoration.

Restoration of nonlinear motion-distorted composite frame

Abstract: A composite frame image is an interlaced composition of two sub-image odd and even fields. Such image type is common in many imaging systems that produce video sequences. When relative motion between the camera and the scene occurs during the imaging process, two types of distortion degrade the image: the edge 'staircase effect' due to the shifted appearances of the objects in successive fields, and blur due to the scene motion during each field exposure. This paper deals with restoration of composite frame images degraded by motion. In contrast to other previous works that dealt with only uniform velocity motion, here we consider a more general case of nonlinear motion. Since conventional motion identification techniques used in other works can not be employed in the case of nonlinear motion, a new method for identification of the motion from each field is used. Results of motion identification and image restoration for various motion types are presented.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Influence of aerosols and optical turbulence strength on laser beam widening in the atmosphere

Abstract: On a basis of a Monte Carlo simulation model, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path at various elevations is estimated and compared with beam widening caused by turbulence. It is shown that the beam widening caused by atmospheric aerosols is significant, often even more significant than that caused by turbulence.