Concept Of Spatial Filtering Research Articles

Sparkle measurement revisited: A closer look at the details

Four years after introduction of the first instrument for measurement of sparkle, the foundations have been reconsidered, and the pool of practical experience has been analyzed to provide a more detailed and complete picture of the subject matter. The following aspects are introduced and discussed: observation conditions and resulting requirements for imaging (sampling) and filtering, analysis of spatial periods and frequencies as a basis for filtering, spatial filtering concepts, sparkle in the frequency domain, sparkle evaluation based on analysis of single images and difference images, origins of unwanted sparkle components, scaling and offset in sparkle evaluation, and verification of the method.

42.4: Sparkle Measurement Revisited: A Closer Look at the Details

AbstractThree years after introduction of the first instrument for measurement of sparkle the foundations have been reconsidered and the pool of practical experience has been analyzed to provide a more detailed and complete picture of the subject matter. The following aspects are introduced and discussed: observation conditions and resulting requirements for the imaging optics, imaging of the display under test (2‐dimensional sampling), analysis of spatial periods and frequencies as basis for separation of periodic and statistic intensity modulations, sparkle evaluation based on analysis of single images and difference images, spatial filtering concepts, sparkle in the frequency domain, pseudo‐sparkle, scaling and bias in sparkle evaluation, verification of the method.

Spatial filtering through elementary examples

The spatial filtering features of resistive grids have become important in microelectronics in the last two decades, in particular because of the current interest in the design of ‘vision chips.’ However, these features of the grids are unexpected for many who received a basic physics or electrical engineering education. The author's opinion is that the concept of spatial filtering is important in itself, and should be introduced and separately considered at an early educational stage. We thus discuss some simple examples, of both continuous and discrete systems in which spatial filtering may be observed, using only basic physics concepts.

Measurement and sensors

The fundamental function of a measuring system is discussed, and the importance of achieving selectivity for the quantity to be measured is pointed out. Next, three main methods of realizing this selectivity in sensor technology are described, and it is pointed out that cooperation and task sharing between them are necessary to simplify the hardware construction of a superior sensor. Finally, the spatial filtering method is considered as an example of such task sharing. The concept of spatial filtering and the basic structure of a spatial filter detector are explained, and applications to linear speed measurement, two-dimensional velocity measurement and macro-measurement of random movement are presented.

Spatial and temporal filtering of scintillation in remote sensing

The concept of spatial filtering as applied to remote sensing of the transverse flow velocity and refractive-index spectrum along a line-of-sight propagation path was first outlined in 1974. The technique was applied to optical propagation through the turbulent atmosphere. Random fluctuations in the field were produced by irregularities advected across the optical path by a mean flow. We extend and modify this earlier work to include source and receiver motion, temporal filtering, and dispersion of the refractive index structure. The technique described in this study can be applied to the remote probing of random atmospheric, ionospheric, and oceanic flows using either electromagnetic or acoustic sources. It can also be used for the remote sensing of rough surfaces such as the sea surface. The analysis indicates that this technique is a new, powerful tool with a unique capability for probing the spatial and temporal structure, and evolution of geophysical flows.

Measurement of ion beam parameters with electrostatic induction electrodes

One source of information concerning ion beam parameters is the electromagnetic field which can be sensed in a non-destructive manner by means of electrostatic induction electrodes. It is shown that the response of an electrode system is a solution of the Laplace equation with boundary conditions specified by the weighting function of the system. Electrode systems as integral devices can provide information on the beam intensity, transverse beam coordinates, and some coefficients associated with the beam profile. A new class of electrode systems based on the Walsh weighting functions is introduced. Methods are studied for computing the response of electrode systems of a circular as well as of a rectangular cross section. A lower bound, known as the Cramer-Rao bound, on the performance of a measuring system using an electrode system is presented. A concept of spatial filtering is discussed and a novel closed-loop scan generator is proposed. Finally, a brief discussion on the applications of electrode systems indicates that the systems meet requirements for non-destructive sensors suitable for automated equipment employing continuous ion beams.

Transfer Function of an Elliptical Annular Aperture

The normalized transfer function of an elliptical annular aperture for incoherent illumination is derived. The relationship between the formulation developed here and a problem occurring in the diffraction from apertures illuminated with partially coherent radiation is shown. Results are discussed in terms of spatial-filtering concepts, with emphasis on the behavior of the cutoff frequency and the passband characteristics in the spatial-frequency plane.The effect of the aperture ellipticity for arbitrary annulus width is to introduce an asymmetry in the behavior of the cutoff frequency. The presence of a central obstruction, for arbitrary ellipticity, emphasizes the high-frequency transmission, with the region of emphasis dependent upon the angular orientation in the frequency plane.