This PDF file contains the editorial “Editorial: Retirement + 1” for OE Vol. 44 Issue 08

An all-birefringent-fiber frequency-modulated continuous-wave (FMCW) Sagnac gyroscope is described. The rotation velocity of the gyroscope is determined by measuring the phase shift of the beat signal produced by the two counter-propagating laser beams in the birefringent fiber coil. A resolution of 0.02 deg/sec with a 100-m fiber coil has been observed.

A magnetically actuated optical phase modulator is described. The phase of a reflected optical beam is modulated by deflecting a Mylar® membrane, coated with a magnetic iron/nickel film, with the field of an electromagnet. A phase change of π for light of wavelength 0.633 µm was achieved with a driving voltage of only 4 V, much smaller than the voltage required for comparable, electrostatically-actuated devices. The modulator can be scaled to micron dimensions for fabrication in arrays, scaled for even lower drive voltage, and operated at megahertz frequencies.

The use of image retrieval and classification has several applications in industrial imaging systems, which typically use large image archives. In these applications, the matter of computational efficiency is essential and therefore compact visual descriptors are necessary to describe image content. A novel approach to contour-based shape description using wavelet transform combined with Fourier transform is presented. The proposed method outperforms ordinary Fourier descriptors in the retrieval of complicated industrial shapes without increasing descriptor dimensionality.

We describe an optical displacement sensor based on optical feedback interferometry in a blue-light emitting GaN laser diode. Also presented are preliminary results from measuring variations in the optical path length (OPL) of an external cavity (EC) in the 0- to 240-nm range. These results show that, within the specified range, the sensor follows linearly the OPL variation of the EC. Moreover, the slope between a reference and the measured OPL is 1.0003, and the average deviation from the linear slope is 5 nm in this range. Finally, we also consider the stability of the interference signal in long-term measurements.

A parametric cost model for ground-based telescopes is developed using multivariable statistical analysis of both engineering and performance parameters. While diameter continues to be the dominant cost driver, diffraction-limited wavelength is found to be a secondary driver. Other parameters such as radius of curvature are examined. The model includes an explicit factor for primary mirror segmentation and/or duplication (i.e., multi-telescope phased-array systems). Additionally, single variable models based on aperture diameter are derived.

We propose an evaluation method for the reliability of the analyzed phase in a phase-shifting method using a Fourier transform (PSM/FT) for shape measurement by fringe projection method. In PSM/FT, since the initial phase information is determined only from the first frequency of the Fourier spectrum of the phase-shifted intensity values at each point of an object, and the frequency components higher than the first frequency almost depend on noise, experimental noise can almost be eliminated. The phase reliability evaluation value using a Fourier transform (PREV/FT) is, therefore, defined as the ratio of the first frequency component of the Fourier spectrum to the average of the frequency components higher than the first frequency of the Fourier spectrum. PREV/FT is useful to merge data when we change the measurement condition for shape measurement. We apply the PREV/FT to eliminate the halation effect on a metallic object. Shape measurement of an aluminum specimen that is a rotational body produced by a lathe is performed as an experiment. The results show that the halation effect is eliminated successfully by selecting the highest PREV/FT.

We describe a simple, static, fiber optic laser wavelength meter based on a Young's interferometer. In this wavelength meter, the two sources are provided by unequal-length output fibers from a single-mode 3-dB directional coupler. The cleaved ends of the output fibers are held rigidly at a fixed separation facing a linear sensor array that records the sinusoidally varying fringe pattern. Analysis of the recorded fringe pattern resolves the free-spectral-range ambiguity of the interferometer and provides a high-resolution value for the wavelength of the source. Based on our investigation, we believe that with occasional recalibration, the wavelength meter is capable of an accuracy better than one part in 10⁵.

The phase shift schlieren (PSS), an improved method of the conventional schlieren imaging technique, enables direct quantitative measurements of optical path length gradients. Like all phase-shifting imaging methods, a successive acquisition of multiple images is required, therefore limiting the PSS use to quasi-steady-state phenomena. We show that PSS can be easily modified to access real-time data. A possible implementation is disclosed, as well as experimental results that validate the method. An application on gas jet is illustrated. We present the features and limitations of the real-time phase shift schlieren (RTPSS).

The ELISA (enzyme-linked immunosorbent assay) spot assay is a method widely used by immunologists to enumerate cytokine-producing cells within a specific cell population. The ELISA results are presented in an image containing numerous colored spots. We present a method to identify the spots in the image and report on important statistics regarding them. The proposed method employs color analysis in the CIE L*u*v* color space and matched filter technique. The system is trained to obtain a standard color for the spots and calculate the color differences between the spots and background in the L*u*v* space. Matched filters are then used to remove noise and enhance the spots in the color difference map. Intensity thresholding is applied to obtain a binary image in which the pixels in the spots have a grayscale of 1 while the grayscale of the other pixels is 0. A software system is implemented, based on this method, to help immunologists analyze the results obtained from the ELISA.

In optical 3-D measurements, two steps are generally required to obtain the whole-body 3-D shapes of objects: measuring the 3-D shape from different views, and afterwards connecting them together. The multiview overlapping scanning connection technique in a cylindrical coordinate system is an effective method for measuring a surface with a rotation axis, e.g., a 360-deg shape. However, there are great difficulties in measuring a more complex surface, such as those with concavities or composed of several discontinuous patches, because a complex surface generally cannot be explicitly represented in cylindrical coordinates. To solve these problems, a novel multiview connection method based on virtual cylinders for measurement of 3-D surfaces is proposed. In a Cartesian coordinate system, the virtual cylinders are determined by least-squares fitting to the local overlapping surface patches. The error movements are obtained from a linear equation system based on the virtual cylinders. The connection of adjacent views is then performed by coordinate transformation in 3-D space. Both computer simulation and experimental results are presented to verify the effectiveness of the suggested method.

A SiGe/Si optical modulator based on the free-carrier plasma dispersion effect is presented. A SiGe/Si multilayer structure is included in a p-i-n diode and integrated in a submicrometric silicon-on-insulator (SOI) rib waveguide. A P⁺ Si layer inserted in the Si barriers provide holes that are confined in the SiGe wells at the equilibrium and can be depleted by applying a reverse bias. This structure offers high-speed phase modulation properties. Numerical simulations are used to design the optical modulator. An optimal structure is defined comprising three 10-nm-thick SiGe layers and four 5-nm-thick P⁺ Si layers. The predicted refractive index variation is 1.7×10^–4 under a –6-V bias voltage, and the associated absorption variation is 3 dB/cm. Intensity modulation is obtained by embedding the active region inside a microinterferometric structure. Using resonant cavities a few hundred micrometers long, a modulation depth larger than 60% is achieved with insertion losses of 12 dB, whereas Mach-Zehnder interferometers of a few millimeters length lead to modulation depths larger than 95% with insertion losses lower than 8 dB.

A wavelength-controlled continuous beam-steering four-element X-band (8- to 12-GHz) phased array antenna system is presented. The system is based on the continuously tunable optical true-time-delay technique. Dispersion-enhanced waveguide holograms were proposed and used to fabricate the optical true-time-delay devices. The devices are characterized both theoretically and experimentally. The wavelength of a laser was tuned within the system to get continuously tunable true time delay. The time delay was measured for a wavelength tuning range from 1537 to 1547 nm in 10-nm steps. The far-field radiation patterns of the antenna system were measured at 9 and 10.3 GHz, and they showed no beam squint. The true-time-delay formation idea presented here is suitable for not only X-band, but also for higher microwave frequencies, such as K-band.

Laser radar is increasingly used to generate high resolution spatial maps of targets. The sensitivity, and hence utility, of laser radar (and laser rangefinders) depend on the laser cross section (LCS) of the target. A significant contribution to overall LCS can be the optical cross sections (OCSs) of its optical components. Optical systems, therefore, should be analyzed to quantify their OCSs. This work develops a better understanding of OCS measurements. Specifically, the measurements of a single-lens optical system with a substrate of known reflectivity at and near focus are discussed. Current practice fails to accurately predict the OCS of this setup; diffraction-limited theory is typically used near focus, where it predicts an OCS much greater than the measured value, and ray tracing is used as the substrate is moved away from focus, where it successfully captures the general trend but fails to predict deviations caused by diffraction and interference effects. We use a wave-optics approach to account for the effects of aberrations. A model is created to accurately predict the OCS of the single-lens system. The results, along with predictions of the current theory, are compared to experimental data. In general, wave optics produces more accurate OCS predictions than ray tracing.

A chromatic performance simulation is introduced to achieve a sensitive transmission/attenuation property of aircrew laser eye protection (LEP) visors. The simulation optimizes dye selection for best visual performance during the design phase without actually manufacturing test pieces. Prototype daytime and nighttime LEP in-helmet type visors are manufactured to demonstrate that careful dye selection can realize attenuation by a factor of more than 1000 at four laser lines in the visible to near-infrared spectral range, and simultaneously realize the high visibility required for aircrew job performance. Optical measurements and several key ballistic protection tests prove that both LEP visors meet military use requirements.

A practical double-sensor multiplexed fiber optic displacement sensor is reported. The sensor is based on the principles of optical frequency-modulated continuous-wave (FMCW) interference and frequency-division multiplexing. The beat signals from the individual sensors are assigned in the frequency domain and separated with different electrical bandpass filters. The displacements of the targets can be determined simultaneously by detecting the phase shifts of the corresponding beat signals. The cross talks between the individual sensors are analyzed algebraically and with a phasor diagram. An accuracy of 0.05 µm in a dynamic range of 1000 µm is achieved.

A low-cost all-fiber Bragg grating sensing system for temperature and strain measurements is presented. Broadband interrogation and grating-based optical filtering are used to detect a strain- or temperature-induced Bragg wavelength shift with a resolution of 1 µε and 0.1°C. The passive nature of the grating demodulation enables dynamic measurements, limited only by the electronic circuitry involved in the system read out. The same system is also used for dynamic strain detection. A fiber grating is bonded to a piezoceramic actuator in different configurations. A laser-triangulation-based system is used as a reference measurements up to 10 kHz, while dynamic strain measurements by a Fiber Bragg grating (FBG) are carried out up to 50 kHz, demonstrating a dynamic resolution of ≈40 nε/(Hz)^1/2.

A method for the design of waveguide-coupled microring resonators is described based on an improved coupled mode theory (CMT) approach. Characteristic parameters including coupling efficiency and Q factor are theoretically analyzed. The effects of variations in the refractive index, waveguide width, bus-to-ring gap spacing, and ring radius are investigated. The accuracy of this model is evaluated by comparing its predicted calculation results to those of the numerical beam propagation method (BPM) and finite difference time domain (FDTD) simulations obtained using commercial software. The predictions of the model agree well with the simulation results.

The performance of code-division multiple access (CDMA) as a multiple-access technique for optical wireless communications is evaluated. The information data is modulated through dual-amplitude pulse interval modulation (DAPIM). Optical orthogonal code is used as the signature sequence. The upper bound and lower bound on the exact probability of errors per slot and per packet are derived in the presence of ambient background noise. We investigate the performance characteristics for various system parameters, including the SNR of the source information bits, receiver threshold, DAPIM order, and number of users.

A novel bandwidth- and center-wavelength-tunable interleaver structure based on birefringent materials is proposed. This device can provide network designers more flexibility in their design work and reduce system upgrading and modification costs. Since the proposed structure is a kind of finite-impulse-response filter, the interleaver can be designed to be dispersion-free. Moreover, it can be implemented without moving parts to increase reliability. These two features make the proposed device attractive for increasing design flexibility and network efficiency. Simulation and experimental results are presented to verify the fundamental idea.

A bidirectionally pumped spectrum-presliced multiwavelength fiber source is presented. Two 980-nm laser diodes are engaged to pump a section of erbium-doped fiber (EDF) in contrary directions. A double-pass Mach-Zehnder comb filter is utilized to filter and reflect the amplified spontaneous emission at one port of the EDF. An optical isolator is employed to guide out the multiwavelength outputs at the other end. The extinction ratio of the source is larger than 24.5 dB over the whole C band, and almost reaches 29 dB at 1530 nm. The integrated power of each channel is 0.58 mW at 1550 nm at 112.3-mW total pump power. The channel spacing and bandwidth are 0.81 and 0.30 nm, respectively. The ratio of the forward pump power to the total pump power is best set between 0.3 and 0.4, to obtain large extinction ratio and high output power simultaneously. The source is expected to have applications in wavelength-division-multiplexing local access networks and integrated optics.

A clock and data recovery circuit using the clock jitter reduction technique is proposed for a 622-Mbit/s burst-mode data stream. The clock jitter reduction is achieved by controlling the clock duty cycle with the phase information of the recovered clock. The proposed clock recovery circuit, based on the gated oscillator, recovers a low-jitter output clock with up to 4090 consecutive zeros.

A phase-shifting technique for full-field measurement of the strain of an object in electronic speckle-shearing interferometry is presented. The object under study is placed on a rotating platform and illuminated by an expanded laser beam. Its images are recorded at short intervals by a shearing CCD camera and stored directly into a computer. By subtracting the series of images from the first one, fringe patterns that represent the object surface strain can be obtained and shown on a computer monitor if the object is loaded. When the object is given a small angle of rotation, an additional phase will be introduced into the fringe patterns. Theoretical analysis shows that this additional phase is linear. Therefore, the electronic speckle shearing phase-shifting technique can be realized by rotating the test object. The small angle can be obtained exactly by a rotating platform controlled by a computer. The theory of the method and system as well as some experimental results is presented.

Design and experimental verification of a microscope-based circular-polarization interferometer developed for measuring the vibration of miniature specimens is detailed. This interferometer, which comes in either a two-detector or a four-detector configuration, demonstrates that the optimum operating point of a circular-polarization interferometer depends strongly on the signal detection and processing algorithms adopted. The influence of the specimen surface optical properties on the desired operating conditions is also examined. The optimum operating point of the two-detector configuration demands that the two returning light beams emitting from the specimen possess equal intensity, which matches the understanding of traditional interferometers, where two equal interference arms achieves the best interference efficiency. Surprisingly, it appears that the optimum intensity ratio for the four-detector configuration occurs if the two interference arms possess equal intensity before it hits the specimen. That is, under the constraint of a constant light source, it appears that the optimum operating point of a four-photodetector circular-polarization interferometer is independent of the surface optical properties. Both theoretical and experimental results that verify the interaction between the optoelectronic configuration and the signal-processing algorithms implemented are presented.

We propose a two-wavelength interferometric system based on a single optical element, i.e., a shear plate. The observation of beat formation phenomenon and the measurement of phase at synthetic wavelength are demonstrated for the first time using two wavelengths simultaneously in a lateral shearing interferometer. Shearing interferograms are recorded both at individual wavelength and at synthetic wavelength. The phase map at synthetic wavelength is obtained by means of subtracting the phase maps at individual wavelength as well as directly from the synthetic interferogram, and the results are found in good agreement. The validity of the principle is applied for collimation testing and reconstructing the phase map of transparent objects. The main advantages of the present system over the previous systems based on two-wavelength interferometry are high stability, nearly common path interferometry, single optical element (shear plate) requirement, compactness, and low cost.

A modified genetic algorithm is proposed for the optimization of holographic diffusers for diffuse IR wireless home networking. The novel algorithm combines the conventional genetic algorithm and the simulated annealing algorithm, in which the simulated annealing algorithm is used to maintain a better diversity of chromosomes for the genetic algorithm. A better performance in locating the global minimum is demonstrated.

We present a new technique for optical correlation using gated holographic recording by which the holograms are localized in separate slices along the recording medium. We compare the performance of localized holographic correlators (LHCs) with that of the conventional correlators using normal volume holography. Crosstalk, shift invariance, and the capacities of the LHC and of the conventional method are examined. We show that the proposed method has better performance and distinctive advantages over the conventional method. These advantages include selective recording and erasure for dynamic pattern modification, extendable capacity, and compactness.

Target acquisition tasks are often augmented by automated aids to advise human observers during the detection process. The question arises whether these automated aids, by nature imperfect, should be implemented under all conditions. This study examines the efficacy of an imperfect automated aid in human target acquisition performance under conditions of high mental workload. Human observers performed a target acquisition task aided by an automated aid (cuer) of varying accuracy concurrently with a military tracking task. Results indicate that the automated aid can improve performance over the unaided condition when it is highly reliable. Evidence of dependence on the system by the observers was found. The thesis here is that the condition of high mental workload induced greater acceptance of and reliance on the automated aid by the observers, which manifested in the highly significant cue dependence results. Another element found in the observers' interaction with the automated aid, which could be a consequence of overreliance, was a high perceived reliability of the cuer, which led observers to respond more confidently to cued targets. These results can help increase the understanding of human behavior vis-à-vis working with automated aids when under conditions of high mental workload.

Two different prototype vein contrast enhancers (VCEs) have been designed and constructed. The VCE is an instrument that makes vein access easier by capturing an infrared image of peripheral veins, enhancing the vein contrast using software image processing, and projecting the enhanced vein image back onto the skin using a video projector. The prototypes use software alignment to achieve alignment accuracy between the captured infrared image and the projected visible image better than 0.06 mm.

A test procedure is developed for an infrared laser scene projector, and applied to a projection system that we develop based on digital micromirror technology. The intended use will be for simulation and target training. Resolution and noise are significant parameters for target perception models of infrared imaging systems. System resolution is normally measured as the modulation transfer function (MTF), and its noise modeled through an appropriate signal standard deviation metric. We compare MTF measurements for both mid-wave (MWIR) and long-wave IR (LWIR) bands for an infrared laser scene projector based on the digital micromirror device (DMD). Moreover, we use two complimentary models to characterize imaging camera noise. This provides a quantitative image-quality criterion of system performance.

The images on a dot-matrix hologram consist of many 2-D grating dots with different pitches and orientations. Only some specified pitches and 256 specified orientations are usually employed. The difference between any two pitches to show different colors is more than 0.1 µm; therefore, it is possible to hide several extra pitches in a specified pitch. If all the extra pitches are almost equal to the specified pitch, grating dots with extra pitches will be of nearly the same color as the specified pitch. When a laser beam is incident on the dot-matrix hologram with hidden pitches, data for the hidden pitches will be decoded by the diffraction pattern of the grating dots of the hologram. A specified grating orientation can be used to hide extra grating orientations similarly. What's better, mixing the above two hiding techniques is possible.

Much research has been devoted to investigating the generation of stereoscopic video based on catadioptric stereo systems. These systems, which utilize a proper combination of mirrors and lens, can capture stereoscopic video using only one camera. The left and right images are usually multiplexed to generate an interlaced video where each image corresponds to one field. This field-sequential format unavoidably reduces vertical resolution of the image pair by half. We proposed a notion called stereoscopic demultiplexing (SD) to recover the original resolution of the image pairs from the field-sequential video. To increase the sharpness of the image and avoid jagged artifacts, interpolation along the edge direction is emphasized. Because the SD problem is similar to deinterlacing, several methods previously used in deinterlacing were evaluated, and a new edge adaptive interpolation (EAI) approach was proposed. This new method can estimate edge direction with higher accuracy and obtain better image quality. Several experimental results show that the proposed algorithm outperforms the other popular deinterlacing methods both visually and quantitatively. Since resolution of the display technology is higher and better than that of current catadioptric stereo systems, we believe that further improvement in the resolution of the acquisition device by software is necessary to make 3-D applications more economical and popular.

An objective measurement framework for signal-level image fusion performance, based on a direct comparison of visual information in the fused and input images, is proposed. The aim is to model and predict subjective fusion performance results otherwise obtained through extremely time- and resource-consuming perceptual evaluation procedures. The measure associates visual information with edge, or gradient, information that is initially parametrized at all locations of the inputs and the fused image. A perceptual-information preservation model is then used to quantify the success of information fusion as the accuracy with which local gradient information is transferred from the inputs to the fused image. By considering the perceptual importance of different image regions, such local fusion success estimates are integrated into a single, numerical fusion performance score between 0 (total information loss) and 1 (ideal fusion). The proposed metric is optimized and validated using extensive subjective test results and validation procedures. The results clearly indicate that the proposed metric is perceptually meaningful in that it corresponds well with the results of perceptual fusion evaluation. Finally, an application of the proposed evaluation approach to fusion algorithm selection and fusion parameter optimization demonstrates its general usefulness.

We offer a method for the a priori evaluation of the division of power among the various wavelet coefficients when they are used to reconstruct the original scene through a prioritization protocol. The method is based on applying a technique of the mathematical theory of games to social power. The analysis is fairly general and not specific to wavelet transform configurations. It is equally applicable to linearly spaced subband decompositions, and to other more general subband decompositions, such as wavelet packets and Laplacian pyramids. Here we show a prioritization protocol based on the utility-per-coding-bit optimization that is consistent with the power distribution imposed by the set partitioning sorting algorithm on the set of wavelet coefficients.

We present some development results on a system that performs mosaicking of panoramic faces. Our objective is to study the feasibility of panoramic face construction in real time. To do so, we built a simple acquisition system composed of five standard cameras, which together can take simultaneously five views of a face at different angles. Then, we chose an easily hardware-achievable algorithm, consisting of successive linear transformations, in order to compose a panoramic face from these five views. The method has been tested on a large number of faces. In order to validate our system, we also conducted a preliminary study on panoramic face recognition, based on the principal-component method. Experimental results show the feasibility and viability of our system. This allows us to envisage later a hardware implementation. We also are considering using our system for other applications, such as human expression categorization and fast 3-D face reconstruction.

A simple approach to improve the performance of JPEG is proposed. In JPEG, quantized ac coefficients at high frequency generally have zero or small energies. Thus they contribute little or nothing to the peak signal-to-noise ratio (PSNR). This implies that the bit rate can be reduced by discarding some high-frequency ac coefficients with little or no loss in PSNR. Based on this idea, we incorporate the concept of zonal coding into JPEG. This proposal is termed the zonal JPEG. In it, the coding scheme is identical to that of the traditional JPEG except that only a fixed number of coefficients are coded for each image block. Consequently, the proposed approach is totally compatible with the traditional JPEG. It has two advantages over the latter: (i) better bit-rate utilization and (ii) achievable user-defined PSNR. These advantages have been verified by simulation results.

The problem of input noise affecting the subpixel classification is examined in order to assess its relationship with the output noise. The approach followed in this study was to investigate the output noise level obtained with a least-squares subpixel classification algorithm applied to simulated spectra. The simulation of mixed pixel spectra took into account variable pixel composition and a selectable power of the superimposed noise. Noise was considered a zero-mean stochastic process over wavelength that was assumed to be jointly normal and uncorrelated. The paper outlines the structure and the mathematical properties of the performed unmixing simulations, and clearly shows the relationship between input and output noise. It is shown that a simple exponential law relates with substantial accuracy the standard deviation of input noise to that of the computed subpixel abundances for fully constrained unmixing. As expected, the cases of unconstrained and (abundances sum to one) partially constrained unmixing are controlled by a linear relationship between input and output noise amplitude. The paper also shows the dependence of unmixed abundances and output noise on the spectral similarity of end members involved in the unmixing. Three subpixel classification approaches (unconstrained, partially constrained, and fully constrained algorithms) were investigated.

We propose a fuzzy method to control the bit rate in the discrete cosine transform (DCT) domain. The method consists of a bit-rate allocation with fuzzy measures and a least-distortion bit-rate reduction. Fuzzy measures are calculated from the code length, the discontinuity ambiguity, and the neighborhood momentum in each DCT block. These measures are summed with weights and form a reduction fuzziness to indicate the degree of preferable reduction. Using the reduction fuzziness, each DCT block is filtered by the least-distortion reduction method to adjust the bit rate for the target bandwidth. In an experiment, we show that the video quality transcoded by the method is better and the bandwidth is more regular than with existing methods, both visually and quantitatively.

Aiming at the performance evaluation of image fusion, this paper discusses the existing criteria and the guidelines for choosing performance parameters, and then a new method is proposed to index the fusion algorithms on their fused images. In the method, each of the fused images is used to extract a comparative sequence. Meanwhile, a reference sequence is constructed by combining all the fused images involved. Then an overall performance index is obtained from the gray relational degrees between the two kinds of sequences. The interest of the method lies in the fact that it does not require a ground-truth or reference image in forming the reference sequence and is inexpensive in processing time and storage memory. Experimental results show that the method is effective, and its potential application includes intellichoice and intellectual control.

Digital image correlation (DIC) using a single camera has been widely used for determination of in-plane displacement. However, in order to obtain shape information on an object, one should employ stereo vision systems with multiple cameras. In this paper, a new method using digital image correlation for shape measurement is developed. In the proposed method, an object with a surface profile is given an in-plane translation, and digital image correlation is employed to measure the image displacement. Since the object has a surface height variation, the magnification at each point is different. Thus the image displacement field obtained from the DIC method contains the shape information of the object, which can be retrieved from a pinhole camera model. Principles of the proposed method are described. Experiments conducted to measure a step change and a light bulb show that the method is simple, effective, and suitable for measurement of a step change or a large object.

Arbitrary shaped coding is an important issue of MPEG-4. In this study, an efficient shaped coding method, called the boundary block-searching (BBS) algorithm, which can enhance the coding efficiency of conventional padding schemes, is proposed. The proposed BBS algorithm assumes that boundary blocks have strong correlation even though they are not connected. For an input boundary block, the most similar block (only object pixels are considered) is sought from the previously coded data. Instead of being encoded by the use of discrete cosine transform, the boundary block is encoded by a position vector, which indicates the relative position of the most similar block. Therefore, the number of bits required to denote the boundary block is greatly reduced and low bit rate can be achieved. For two video sequences under different test conditions, simulation results show that the proposed BBS algorithm can greatly improve coding efficiency.

Gears of all types and sizes are widely used in machinery and equipment. Spur gears represent the largest percentage of all gears in use, and automating their measurement has become a common goal. In this paper a new computer-assisted noncontact laser-based spur-gear measurement system is developed. The technique is based on optical obscuration and is used to measure the thickness and pitch of the test gear at a predetermined tooth height. The developed system has an inaccuracy on the order of 5 µm, and the time required to measure a whole gear is 1 min. The system can measure gears with different modules and numbers of teeth. The measured dimensions were compared with those obtained with a well-established technique and are in good agreement.