Fabrication of Transmission Color Filters Using Silicon Subwavelength Gratings on Quartz Substrates

We investigate theoretically and experimentally transmission color filters using silicon subwavelength gratings on quartz substrates. Each grating area is 120$mu$m-square, which is suitable pixel size for displays and multichannel detectors. In the fabrication, electron beam lithography and fast atom beam etching are used. The grating periods are 400, 350, and 440 nm for the red, green, and blue filters, respectively. The transmission spectrum obtained from a coupling between an incident light and the submicrometer periodic grating matches with human color perception. The transmittances of 71.1%, 58.1%, and 59.3% are obtained for the red, green, and blue filters, respectively.     

Design and analysis of vector color error diffusion halftoningsystems

Traditional error diffusion halftoning is a high quality method for producing binary images from digital grayscale images. Error diffusion shapes the quantization noise power into the high frequency regions where the human eye is the least sensitive. Error diffusion may be extended to color images by using error filters with matrix-valued coefficients to take into account the correlation among color planes. For vector color error diffusion, we propose three contributions. First, we analyze vector color error diffusion based on a new matrix gain model for the quantizer, which linearizes vector error diffusion. The model predicts the key characteristics of color error diffusion, esp. image sharpening and noise shaping. The proposed model includes linear gain models for the quantizer by Ardalan and Paulos (1987) and by Kite et al. (1997) as special cases. Second, based on our model, we optimize the noise shaping behavior of color error diffusion by designing error filters that are optimum with respect to any given linear spatially-invariant model of the human visual system. Our approach allows the error filter to have matrix-valued coefficients and diffuse quantization error across color channels in an opponent color representation. Thus, the noise is shaped into frequency regions of reduced human color sensitivity. To obtain the optimal filter, we derive a matrix version of the Yule-Walker equations which we solve by using a gradient descent algorithm. Finally, we show that the vector error filter has a parallel implementation as a polyphase filterbank.     

Rejection of CW Interference in QPSK Systems Using Decision-Feedback Filters

In this paper, the performance of QPSK systems using complex transversal filters with additional decision-feedback taps, in the presence of Gaussian noise and a single CW interferer, is analyzed. Both one-sided (with lagging taps) and two-sided transversal filters with additional decision-feedback taps are considered. Analytic expressions for the tap weights and the minimum mean square errors are obtained. The effect of error propagation on the error probability is discussed and an approximate solution for the error probability is obtained. The transient behavior of the filters using the LMS adaptation algorithm is analyzed. It is shown that if the filter is used for rejecting CW interference only, the one-sided decision-feedback filter is preferred.     

Optimization of sensor response functions for colorimetry ofreflective and emissive objects

This paper describes the design of color filters for a surface color measurement device. The function of the device is to return the XYZ tristimulus vector characterizing the color of the surface. The device is designed to measure emissive as well as reflective surfaces. It uses an internal set of LEDs to illuminate reflective surfaces while characterizing their color under assumed standard illuminants. In the design of the filters, we formulate a nonlinear optimization problem with the goal of minimizing error in the uniform color space CIE L*a*b*. Our optimization criteria employs a technique to retain a linear structure while approximating the true L*a*b* error. In addition, our solution is regularized to account for system noise, filter roughness, and filter implementation errors. Experimental results indicate average and worst-case device accuracy of 0.27 L*a*b* DeltaE units and 1.56 L*a*b* DeltaE units for a "system tolerance" of 0.0005.     

彩色形态滤波器分析

形态滤波属于非线性信号变换处理,它利用信号的局部特征对信号进行修正。最近的研究表明形态滤波器能有效地滤除二值图像及灰度图像中的噪声,本文引入了建立在ＲＧＢ彩色空间上的彩色形态变换,针数字形态学理论从灰度空间扩展到彩色空间,对基本彩色形态滤波器（即彩色形态闭、开）及以它们为基础所构造出一些复杂的彩色形态滤波器进行了研究,并对它们选用不同结构元素的情况进行了分析,实验表明彩色形态滤波器能直接有效地消除     

Optimal temporal interpolation filter for motion-compensated frame rate up conversion.

Frame rate up conversion (FRUC) methods that employ motion have been proven to provide better image quality compared to nonmotion-based methods. While motion-based methods improve the quality of interpolation, artifacts are introduced in the presence of incorrect motion vectors. In this paper, we study the design problem of optimal temporal interpolation filter for motion-compensated FRUC (MC-FRUC). The optimal filter is obtained by minimizing the prediction error variance between the original frame and the interpolated frame. In FRUC applications, the original frame that is skipped is not available at the decoder, so models for the power spectral density of the original signal and prediction error are used to formulate the problem. The closed-form solution for the filter is obtained by Lagrange multipliers and statistical motion vector error modeling. The effect of motion vector errors on resulting optimal filters and prediction error is analyzed. The performance of the optimal filter is compared to nonadaptive temporal averaging filters by using two different motion vector reliability measures. The results confirm that to improve the quality of temporal interpolation in MC, the interpolation filter should be designed based on the reliability of motion vectors and the statistics of the MC prediction error.     

Mathematical methods for the design of color scanning filters

The problem of the design of color scanning filters is addressed in this paper. The problem is posed within the framework of the vector space approach to color systems. The measure of the goodness of a set of color scanning filters presented in earlier work is used as an optimization criterion to design color scanning filters modeled in terms of known, smooth, nonnegative functions. The best filters are then trimmed using the gradient of the mean square DeltaE(ab) error to obtain filters with a lower value of perceptual error. The results obtained demonstrate the utility of the method.     

Mathematical methods for the analysis of color scanning filters

The problem of the sensitivity analysis of color scanning filters is addressed in this paper. The second differential of the mean square DeltaE(ab) error provides a means of calculating the sensitivity of the mean square DeltaE(ab) error to filter fabrication errors. Tolerances on the allowable change in the mean square DeltaE(ab) error are used to define bounds on the filter fabrication errors at all wavelengths and at single wavelengths.     

Fabrication and Analysis of Three-Layer All-Silicon Interference Optical Filter with Sub-Wavelength Structure toward High Performance Terahertz Optics

We propose an all-silicon multi-layer interference filter composed solely of silicon with sub-wavelength structure (SWS) in order to realize high performance optical filters operating in the THz frequency region with robustness against cryogenic thermal cycling and mechanical damage. We demonstrate fabrication of a three-layer prototype using well-established common micro-electro-mechanical systems (MEMS) technologies as a first step toward developing practical filters. The measured transmittance of the three-layer filter agrees well with the theoretical transmittances calculated by a simple thin-film calculation with effective refractive indices as well as a rigorous coupled-wave analysis simulation. We experimentally show that SWS layers can work as homogeneous thin-film interference layers with effective refractive indices even if there are multiple SWS layers in a filter.     

Nonlinear filtering of multivariate images under robust errorcriterion

A class of nonlinear filters for multivariate data is introduced. A robust error criterion is minimized. Approximate algorithms for computing the filter output are developed. A polynomial signal model is used in applications where the signal amplitude has to be retained with high fidelity. Simulated data and RGB color image data are used in experiments.     

Design of stable IIR digital filter based on least P-power error criterion

In this paper, the least p-power error criterion is presented to design digital infinite impulse response (IIR) filters to have an arbitrarily prescribed frequency response. First, an iterative quadratic programming (QP) method is used to design a stable unconstrained one-dimensional IIR filter whose optimal filter coefficients are obtained by solving the QP problem in each iteration. Then, the proposed method is extended to design constrained IIR filters and two-dimensional IIR filters with a separable denominator polynomial. Finally, design examples of the low-pass filter are demonstrated to illustrate the effectiveness of the proposed iterative QP method.     

Analysis of adaptive filters using normalized signed regressor LMSalgorithm

In this paper, adaptive filters using the normalized signed regressor LMS algorithm (NSRA) with Gaussian reference inputs are proposed and analyzed to yield difference equations for theoretically calculating expected convergence of the filters. A simple difference equation for mean squared error (MSE) is derived when the filter input is a white and Gaussian process, whereas approximate difference equations for colored Gaussian inputs are proposed and tested. Stability conditions and residual MSE after convergence are also obtained. Agreement of theoretical results with those of simulation in the experiment with some examples of filter convergence shows sufficient accuracy of the theory and assures the usefulness of the difference equations in estimating filter performances, thus facilitating the design of adaptive filters using the NSRA     

Optimal design of nonuniform multirate filter banks

The design of general nonuniform filter banks is studied. Contrary to uniform filter banks, in nonuniform filter banks, it may not be possible to achieve perfect reconstruction, but in some cases by using optimization techniques, we can design acceptable filter banks. Here, the initial finite impulse response (FIR) analysis filters are designed according to the characteristics of the input. By the design procedure, the FIR synthesis filters are found so that theH-norm of an error system is minimized over all synthesis filters that have a prespecified order. Then, the synthesis filters obtained in the previous step are fixed, and the analysis filters are found similarly. By iteration, theH-norm of the error system decreases until it converges to its final value. At each iteration, the coefficients of the analysis or synthesis filters are obtained by finding the least squares solution of a system of linear equations. If necessary, the frequency characteristics of the filters can be altered by adding penalty terms to the objective function.This research was supported by the Natural Sciences and Engineering Research Council of Canada.     

Color filters and processing alternatives for one-chip cameras

Color images can be obtained from a single solid-state sensor by covering the photosites with a repetitive pattern of color filters. This paper reviews the major issues in selecting appropriate filter patterns and compares different one-chip camera approaches. The processing used to decode the color signals and form acomposite television signal is discussed. The tradeoffs between using primary or complementary filters are considered. Checkerboard geometries are shown to be superior to stripe geometries, and the advantages of horizontally staggered sampling are explained. The constraints imposed by the sensor architecture and by the need for interlaced readout are examined.     

Composite-Component Transformation and Predictive Coding of the Component Color TV Signal

Component coding of the NTSC color TV signal is investigated. This coding involves digital demodulation of the composite signal sampled at three times the color subcarrier frequency, the implementation of the compression algorithms on the subsampled component signal, and digital reconstruction of the processed NTSC color signal. The comb filter, bandpass filter, and Hilbert transformer are used for the demodulation of the luminance and theIandQchrominance signals. The reconstructed components at the receiver are interpolated and modulated to obtain the composite signal. Different combinations of comb filters, bandpass filters and Hilbert transformers are used to investigate their effect on compositecomponent separation and reconstruction. Because of their reduced bandwidths, the chrominance signals are subsampled both horizontally and vertically. Several intrafield and intraline predictors are simulated. Of these, three predictors with small variances of the prediction error are combined with 4 and 3 bit Max quantizers for further processing and transmission in a TDM format. The data compression algorithms have been applied to color test pictures and their effectiveness is compared on the basis of quantitative criteria. The bandwidth reduction technique results in digital transmission of a single color TV signal at 32-43 Mbits/s.     

On the phase response of the error diffusion filter for imagehalftoning

Conventional error diffusion halftoning uses a causal error filter. We propose the iterative error diffusion algorithm by extending the error diffusion to accommodate noncausal error filters. We realize the importance of the phase response of the error filter in the error diffusion halftoning method, and demonstrate it using examples. Iterative error diffusion is able to realize a zero phase error filter. We also trace a drawback of error diffusion to the shape of the error filter, and provide a remedy. The results obtained using a zero phase error filter in the iterative error diffusion algorithm are, in our opinion, superior to the error diffusion halftones.     

Subpixel rendering for diamond-shaped PenTile displays using patch-based adaptive filters

We propose a novel subpixel rendering algorithm for diamond-shaped PenTile displays, which reduces color distortions while improving apparent resolutions. We develop two types of subpixel rendering filters: main filter and color distortion reduction (CDR) filters. To derive the filters, we formulate a quadratic program to minimize the difference between an original input image and a virtual image that the human visual system perceives. By imposing two constraints for filter size and coefficients, we obtain the main filter, which has a suitable size and is normalized. Then, we design the CDR filters based on the analysis of various patch patterns for image areas. We define the patch patterns to classify local areas with possible color distortions. By imposing additional constraints according to the patch patterns, we derive the CDR filters. Lastly, by matching local areas in the input image into the pre-defined patch patterns, we render the image using the main filter and the CDR filters, which are applied adaptively to the local areas. Experimental results demonstrate that the proposed subpixel rendering algorithm improves apparent resolutions and suppresses color distortions effectively, thereby outperforming conventional algorithms.     

基于加权平均值的汽车车牌监控图像过滤技术研究

车牌监控图像由于照明、天气、运动目标位置和运动目标速度的不同,图像质量差异很大,从而不利于车牌监控的定位和识别。本文采用最大值法、平均值法和加权平均值法三种方法对车牌监控图像进行过滤,结果表明：采用加权平均值法进行车牌图像颜色过滤能够保留绝大部分的汽车车牌信息,使得目标和背景之间边界清晰,是一种较好的车牌图像彩色过滤方法。     

Generalized multichannel image-filtering structures

Recent works in multispectral image processing advocate the employment of vector approaches for this class of signals. Vector processing operators that involve the minimization of a suitable error criterion have been proposed and shown appropriate for this task. In this framework, two main classes of vector processing filters have been reported in the literature. Astola et al. (1990) introduce the well-known class of vector median filters (VMF), which are derived as maximum likelihood (ML) estimates from exponential distributions. Trahanias et al. (see ibid., vol.2, no.4, p.528-34, 1993 and vol.5, no.6, p.868-80, 1996) study the processing of color image data using directional information, considering the class of vector directional filters (VDF). We introduce a new filter structure, the directional-distance filters (DDF), which combine both VDF and VMF in a novel way. We show that DDF are robust signal estimators under various noise distributions, they have the property of chromaticity preservation and, finally, compare favorably to other multichannel image processing filters.     

Image coding using wavelet transforms and entropy-constrainedtrellis-coded quantization

The discrete wavelet transform has recently emerged as a powerful technique for decomposing images into various multi-resolution approximations. Multi-resolution decomposition schemes have proven to be very effective for high-quality, low bit-rate image coding. In this work, we investigate the use of entropy-constrained trellis-coded quantization (ECTCQ) for encoding the wavelet coefficients of both monochrome and color images. ECTCQ is known as an effective scheme for quantizing memoryless sources with low to moderate complexity, The ECTCQ approach to data compression has led to some of the most effective source codes found to date for memoryless sources. Performance comparisons are made using the classical quadrature mirror filter bank of Johnston and nine-tap spline filters that were built from biorthogonal wavelet bases. We conclude that the encoded images obtained from the system employing nine-tap spline filters are marginally superior although at the expense of additional computational burden. Excellent peak-signal-to-noise ratios are obtained for encoding monochrome and color versions of the 512x512 "Lenna" image. Comparisons with other results from the literature reveal that the proposed wavelet coder is quite competitive.