H. Joel Trussell

Impedance of the Residential Power-Distribution Circuit

This paper presents measurements and analysis of the impedance of residential power-distribution circuits at frequencies from 5 to 20 kHz. These frequencies are used by systems such as distribution-line carriers which use the power distribution circuit as a communications medium. Residential impedances are determined by the distribution transformer secondary windings, entrance cables, house wiring, and electrical loads. Impedance measurements of these components and measurements at four residences are presented.

Measure of goodness of a set of color-scanning filters

Accurate scanning of a color image, which is absolutely essential for good color reproduction, can ensure that all relevant information about the color stimulus of a signal is obtained. The set of scanning filters is hence an important component of a color reproduction system. In this paper we introduce a measure of the goodness of a set of color-scanning filters. This measure relates the space spanned by the scanning filters to the human visual subspace. The q factor of a single color-scanning filter is shown to be a particular case of the measure. Experimental results are presented to justify the appropriateness of the measure.

Set theoretic estimation in color scanner characterization

A set theoretic approach for the spectral characterization of a color scanner is described. These devices usually employ three channels to obtain a device dependent RGB (red, green, blue) im- age. To display/print an image, the device dependent RGB values must be correctly transformed to the color space of the target de- vice. To determine accurate and efficient transformations for a num- ber of devices, knowledge of the spectral sensitivity of the scanner is essential. Direct measurement of the sensitivity requires a set of expensive narrow band reflectances and is often infeasible. Meth- ods that estimate the spectral sensitivity based on measurements with typical reflectance samples are therefore of interest. Due to the low dimensionality of the space of object reflectance spectra, this is a highly ill-conditioned problem. As a result, conventional estimation techniques that fail to take a priori knowledge into account perform rather poorly on this problem. A set theoretic approach that incorpo- rates available a priori knowledge into the estimation framework yields better results. Results are presented for a simulated scanner characterization problem and for an actual characterization to dem- onstrate the increased accuracy compared with conventional methods.

Design and realization of optimal color filters for multi-illuminant color correction

A method of selecting optimal color filters to perform accurate multi-illuminant color correction is reviewed. The transmittances for a set of filters obtained by the method were provided to a color filter manufacturer. The manufacturer used a dichroic filter modeling program to produce transmittances that satisfied the physical constraints of the manufacturing process and approximated the optimal filter transmittances. The ideal and manufacturable filters are compared through computer simulation and their accuracy assessed during the CIE Δ E L*a*b measure. The results show that the unconventional shapes of the optimal filters can be weil approximated by actual filters with slight degradation in performance.

Visual sensitivity to color-varying stimuli

We present the results of a study of the sensitivity of the human visual system (HVS) to spatially varying color stimuli. Sinusoidal grating patterns of different spatial frequencies were presented to six observers and the contrast required to just distinguish the pattern from the surrounding uniform field was determined. Tables and curves of contrast (measured in ΔELab) as a function of frequency were generated at different values of; the orientation (horizontal, vertical and diagonal) of the pattern, the average luminance, the x and y chromaticity co-ordinates, and the direction of the variation of the stimulus in color space (luminance, red-green, and blue-yellow). The results show that the HVS is more sensitive to sinusoidal gratings oriented horizontally and vertically regardless of the type of variation. Furthermore, the HVS is more sensitive to luminance variations than it is to chromatic variations. Tables and curves of the data are presented.

Mathematical method for designing a set of color scanning filters

Accurate colorimetric scanning of a color image is absolutely essential for good color reproduction. This paper formulates the design of a set of three or more color scanning filters as an optimization problem. The optimization criterion is the measure of goodness which was developed in previous work. The method can be incorporated into any scanning system for which the colorimetric responses can be defined. The total system, including the lamps, light path, and sensor characteristics, is taken into account. Simulations and results from actual hardware demonstrate the utility of the method.

Vector space approach to color imaging systems

This paper describes the color imaging system in terms of vector space notation. This includes the effects of the scanning filters and the response of the eye as defined by the CIE color matching functions. This formulation allows many image processing techniques to be generalized to include more accurate models. The problem ofimage restoration is used as an example for the vector space approach. The problem is presented in hierarchical steps. Color scanning and effect of the human observer is presented first. The problem is extended to spatial representation and spatial processing. Finally, the effects of image reproduction are considered. The assumptions at each step of the modelling process are made explicit and simplifications are noted. The choice of defining the most appropriate optimization function is considered with respect to mathematical tractability as well as subjective accuracy.

Measures of goodness of a set of color scanning filters

Abstract Accurate scanning of a colour image, which is absolutely essential for good colour reproduction, can ensure that allrelevant information about the colour stimulus of a signal is obtained. This paper introduces a measure of goodnessof a set of colour scanning filters. The q-factor of a single colour scanning filter is shown to be a particular case ofthe measure. Experimental results are presented to justify the appropriateness of the measure. 1 Introduction Most current research in colour systems assumes that the visual frequency spectrum can be adequately representedby samples taken about 10 nm apart over the range 400-700 nm. Integrals are approximated by summations, and theinfinite-dimensional Hilbert space of visible spectra with the usual 2-norm is reduced to an N-dimensional Hilbertspace, where N is the number of samples (in this case N=31). A continuous function of wavelength is representedby an N-vector of its sampled values. Hence, visual spectra will be treated as vectors in an N-dimensional Hilbertspace in this paper.The notation in this paper follows that of [1]. Let S =

Comparative study of some statistical and set-theoretic methods for image restoration

Abstract In the last decade, many researchers have devoted considerable effort to the problem of image restoration. However, no recent study has been undertaken for a comparative evaluation of these techniques under conditions where a user may have different kinds of a priori information about the ideal image. To this effect, we briefly survey some recent techniques and compare the performance of a linear space-invariant (LSI) maximum a posteriori (MAP) filter, an LSI reduced update Kalman filter (RUKF), an edge-adaptive RUKF, and an adaptive convex-type constraint-based restoration implemented via the method of projection onto convex sets (POCS). The mean square errors resulting from the LSI algorithms are compared with that of the finite impulse response Wiener filter, which is the theoretical limit in this case. We also compare the results visually in terms of their sharpness and the appearance of artifacts. As expected, the space-variant restoration methods which are adaptive to local image properties obtain the best results.

Optimal scanning filters using spectral reflectance information

The quality of color correction is dependent upon the filters used to record the image. The problem of estimating, CIE tristimulus vectors of the original image under several illuminants, from data obtained with a single imaging illuminant is discussed. Optimal filters are derived which minimize the total color correction mean square error for several viewing illuminants. The sensitivity of the filters to perturbations is investigated. Simulations are performed using real reflectance spectra.