Inverse halftoning and kernel estimation for error diffusion

Two different approaches in the inverse halftoning of error-diffused images are considered. The first approach uses linear filtering and statistical smoothing that reconstructs a gray-scale image from a given error-diffused image. The second approach can be viewed as a projection operation, where one assumes the error diffusion kernel is known, and finds a gray-scale image that will be halftoned into the same binary image. Two projection algorithms, viz., minimum mean square error (MMSE) projection and maximum a posteriori probability (MAP) projection, that differ on the way an inverse quantization step is performed, are developed. Among the filtering and the two projection algorithms, MAP projection provides the best performance for inverse halftoning. Using techniques from adaptive signal processing, we suggest a method for estimating the error diffusion kernel from the given halftone. This means that the projection algorithms can be applied in the inverse halftoning of any error-diffused image without requiring any a priori information on the error diffusion kernel. It is shown that the kernel estimation algorithm combined with MAP projection provide the same performance in inverse halftoning compared to the case where the error diffusion kernel is known.     

On computing undetected error probabilities on the Gilbert channel

Two methods for computing the probability of undetected error on the Gilbert (1960) channel are examined. First, using a method proposed by Kittel (1978), we study some standard cyclic redundancy codes and compare the results with those on the binary symmetric channel. Then we consider a general method of approximate code evaluation, proposed by Elliott, which involves P(m, n), the probability of m errors in a block of length n bits. A nonrecursive technique for computing P(m, n) on the Gilbert channel is described     

Quadtree based colour quantisation image compression

A new colour quantisation and quadtree based image compression scheme is proposed. The features of the new scheme are that colour palette ordering and requantisation of the decoded image for palette-based monitor displays are not required. Thus, fast decoding and displaying can be achieved     

A PLL clock generator with 5 to 10 MHz of lock range formicroprocessors

A microprocessor clock generator based on an analog phase-locked loop (PLL) is described for deskewing the internal logic control lock to an external system lock. This PLL is fully generated onto a 1.2-million-transistor microprocessor in 0.8-μm CMOS technology without the need for external components. It operates with a lock range from 5 to 110 MHz. The clock skew is less than 0.1 ns, with a peak-to-peak jitter of less than 0.3 ns for a 50-MHz system clock frequency     

Sequential packing algorithm for channel assignment under cochanneland adjacent-channel interference constraint

Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms     

CMOS scaling into the nanometer regime

Starting with a brief review on 0.1-μm (100 nm) CMOS status, this paper addresses the key challenges in further scaling of CMOS technology into the nanometer (sub-100 nm) regime in light of fundamental physical effects and practical considerations. Among the issues discussed are: lithography, power supply and threshold voltage, short-channel effect, gate oxide, high-field effects, dopant number fluctuations and interconnect delays. The last part of the paper discusses several alternative or unconventional device structures, including silicon-on-insulator (SOI), SiGe MOSFET's, low-temperature CMOS, and double-gate MOSFET's, which may lead to the outermost limits of silicon scaling     

波面倾斜脉冲泵浦的高效可见光飞秒光参量产生和放大器

利用脉冲波面倾斜技术补偿三波相互作用的群速度失配，建立了掺钛蓝宝石飞秒再生放大器输出倍频光泵浦共线类匹配ＢＢＯ晶体的光参量产生和放大器，其信号和空闲光输出调谐范围为０．４７～２．７μｍ，脉冲宽度为１００～１７０ｆｓ，重复率为１ｋＨｚ。脉冲最大输出能量为６．５μＪ，总能量转换效率大于１５％。     

A technique for extracting physiological parameters and therequired input function simultaneously from PET image measurements:theory and simulation study

Positron emission tomography (PET) is an important tool for enabling quantification of human brain function. However, quantitative studies using tracer kinetic modeling require the measurement of the tracer time-activity curve in plasma (PTAC) as the model input function. It is widely believed that the insertion of arterial lines and the subsequent collection and processing of the biomedical signal sampled from the arterial blood are not compatible with the practice of clinical PET, as it is invasive and exposes personnel to the risks associated with the handling of patient blood and radiation dose. Therefore, it is of interest to develop practical noninvasive measurement techniques for tracer kinetic modeling with PET. In this paper, a technique is proposed to extract the input function together with the physiological parameters from the brain dynamic images alone. The identifiability of this method is tested rigorously by using Monte Carlo simulation. The results show that the proposed method is able to quantify all the required parameters by using the information obtained from two or more regions of interest (ROIs) with very different dynamics in the PET dynamic images. There is no significant improvement in parameter estimation for the local cerebral metabolic rate of glucose (LCMRGlc) if there are more than three ROIs. The proposed method can provide very reliable estimation of LCMRGlc, which is our primary interest in this study     

Four novel quadrature overlapping modulations and their spectral efficiency analysis over band-limited non-linear channels

The power spectral density (PSD) analysis considering non-linearity is important in studying spectral efficiency of a digital modem for satellite systems. A general closed formula for numerical PSD calculation of quadrature overlapping modulations is derived in this paper. Four new quadrature overlapping modulation schemes are proposed because they have better spectral characteristics than those of conventional modulations, such as offset QPSK, MSK and staggered QORC, in both linear and nonlinear channels. The four new schemes are; overlapped minimum shift keying (OMSK), minimum shift keying triangular cosine (MSKTC), raised cosine triangular cosine (RCTC) and sinusoidal quadrature overlapped triangular cosine (SQOTC). The results show that for these new modulations, PSD side lobe regeneration caused by the channel non-linearity, is much less than that for the OQPSK, MSK and staggered QORC, a desirable feature enabling even tighter frequency band allocation in satellite communication systems. © 1997 John Wiley & Sons, Ltd.     

Highly Efficient Orange and Green Solid‐State Light‐Emitting Electrochemical Cells Based on Cationic IrIII Complexes with Enhanced Steric Hindrance

Highly efficient orange and green emission from single‐layered solid‐state light‐emitting electrochemical cells based on cationic transition‐metal complexes [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ (where ppy is 2‐phenylpyridine, dFppy is 2‐(2,4‐difluorophenyl)pyridine, and sb is 4,5‐diaza‐9,9′‐spirobifluorene) is reported. Photoluminescence measurements show highly retained quantum yields for [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂ sb]PF₆ in neat films (compared with quantum yields of these complexes dispersed in m‐bis(N‐carbazolyl)benzene films). The spiroconfigured sb ligands effectively enhance the steric hindrance of the complexes and reduce the self‐quenching effect. The devices that use single‐layered neat films of [Ir(ppy)₂sb]PF₆ and [Ir(dFppy)₂sb]PF₆ achieve high peak external quantum efficiencies and power efficiencies of 7.1 % and 22.6 lm W^–1) at 2.5 V, and 7.1 % and 26.2 lm W^–1 at 2.8 V, respectively. These efficiencies are among the highest reported for solid‐state light‐emitting electrochemical cells, and indicate that cationic transition‐metal complexes containing ligands with good steric hindrance are excellent candidates for highly efficient solid‐state electrochemical cells.