Spatial filter

About: Spatial filter is a research topic. Over the lifetime, 6170 publications have been published within this topic receiving 100451 citations.

Phase-space beam summation for time-dependent radiation from large apertures: continuous parameterization

Abstract: We extend the study of alternative phase-space formulations of time-harmonic radiation from extended but truncated aperture source distributions to the time domain. Included are nonwindowed continuous forms spanning the space–time (configuration) domains, wave-number-frequency (spectrum) domains, and windowed (local beam-type) continuous forms. Synthesized in the frequency domain by nonwindowed or windowed Fourier transforms, field synthesis in the time domain involves nonwindowed or windowed radon transforms combined with the theory of analytic signals. Because the properties of suitable wave objects used in the analysis and synthesis of the field are strongly tied to relevant configurational and spectral parameters, the incorporation of these aspects into the various formats is referred to as phase-space parameterization. In the continuous parameterization the resulting time-dependent field radiated from the aperture is expressed as a superposition of pulsed beams whose phase-space parameters are their initiation time, initiation location, and initial direction. The properties of these formulations are discussed in detail, within a rigorous format and also with more physically transparent asymptotic approximations. As in the time-harmonic case, major stress is placed on localization in the phase space, which is achievable with various alternatives, and on the corresponding implications. Specific examples include analytic δ windows that yield as propagators complex-source pulsed beams, and numerical implementation of field synthesis for nonfocused and focused pulsed aperture distributions.

Character Recognition by Incoherent Spatial Filtering

Abstract: The character recognition method described here is based on the principle of incoherent spatial matched filtering. The input to this matched filter is not the unknown character itself, but its Fraunhofer diffraction pattern. The intensity distribution in this diffraction pattern is insensitive against shifting of the unknown character, avoiding the need for character registration. The incoherent matched filter is easier to implement than the coherent matched filter, since only binary rather than continuous-tone masks are required. The theory and some experiments will be discussed and compared with other optical character recognition methods.

Image gathering and processing for enhanced resolution

Abstract: Traditional approaches to optical resolution enhancement have involved either the design of appropriate image-formation systems or some type of postprocessing of an image that has already been formed. Results presented in this paper suggest that improved images can be obtained if the image-gathering system is designed specifically to enhance the performance of the image-restoration algorithm to be used. We consider a class of problems in which the total available spatial bandwidth is fixed but the location of this bandwidth along the spatial-frequency axis is to some extent under our control. For example, we might consider either a low-pass system or a bandpass system of the same total bandwidth. We show that system performance can be substantially improved by proper allocation of the available bandwidth in the spatial-frequency domain. The optimum allocation is shown to be a function of the signal-to-noise ratio. We also describe coherent and incoherent optical image-gathering systems that can achieve the desired spatial-frequency passbands.

Apparatus for ophthalmic operation using photocoagulation by a laser beam

Abstract: An apparatus for performing an ophthalmic operation on an eye by photocoagulation using a laser beam while allowing continuous observation of the eye to be treated, includes a light source for producing the laser beam, an observing system having a first inherent optical path including a slit-lamp microscope, a laser optical system having a second inherent optical path, means for transmitting the laser beam from the light source to the laser optical system, means for introducing the laser beam from the second optical path of the laser optical system to the first optical path of the observing system, a contact lens having predetermined characteristics positioned in front of and contacting the eye to be treated, first optical means provided in the first inherent optical path of the observing system for adjusting an objective plane observable from the slit-lamp microscope, means for shifting the objective plane to a desired position along the optical path while observing the objective plane, and second optical means provided in the second inherent optical path of the laser optical system for adjusting a focal point, the laser beam being controlled while adjusting the focal point along the second optical path of the laser optical system, wherein the first optical means controls the movement of the objective plane observed from the observing system according to the predetermined characteristics of the contact lens and the second optical means adjusts the focal point to direct the laser beam on the objective plane.

Combined wavelet domain and temporal video denoising

Abstract: We develop a new filter which combines spatially adaptive noise filtering in the wavelet domain and temporal filtering in the signal domain. For spatial filtering, we propose a new wavelet shrinkage method, which estimates how probable it is that a wavelet coefficient represents a "signal of interest" given its value, given the locally averaged coefficient magnitude and given the global subband statistics. The temporal filter combines a motion detector and recursive time-averaging. The results show that this combination outperforms single resolution spatio-temporal filters in terms of quantitative performance measures as well as in terms of visual quality. Even though our current implementation of the new filter does not allow real-time processing, we believe that its optimized software implementation could be used for real- or near real-time filtering.