This PDF file contains the editorial “Changing the Way We Read” for OE Vol. 48 Issue 01

A new motion vector coding method with optimal predictive motion vector selection is proposed. To improve compression performance, the proposed encoder selects an optimal predictive motion vector that produces minimum bits for motion vector coding. The proposed decoder estimates the optimal predictive motion vector without additional information for indicating which predictor is to be used at the encoder side. Experimental results show that compared to the H.264/AVC standard, the proposed scheme improves coding efficiency for various video sequences.

A continuously tunable, coherence-free microwave photonic notch filter is proposed and demonstrated experimentally. This filter is based on two polarization beamsplitters with a high-birefringence linearly chirped fiber Bragg grating used as the tunable component. High stability is obtained. The polarization-maintaining structure is free from the random optical interference problem. By adjusting the operating wavelength, more than 5 GHz free-spectral-range tunability with 40-dB notch rejection is achieved.

In the control system of a CCD-based tracking loop for a fast steering mirror (FSM), the most effective method often employed to improve pointing performance is to increase high gain of the control system for a high bandwidth, which, however, usually suffers a great deal from a low CCD sampling rate and the mechanics of the FSM. Moreover, the amount of time delay engendered by sampling and data processing can significantly reduce the performance of a closed-loop system. Therefore, a tentative approach to the implementation of a CCD-based tracking control system with acceleration feedback is proposed. In theory, the position open loop is made of double integrators with a high bandwidth of the acceleration feedback loop; in fact, however, the acceleration open loop of the FSM response includes a quadratic differential, and it is very difficult to compensate a quadratic differential with an integral algorithm. To solve this problem, a novel acceleration closed system such as a bandpass filter is proposed. The position is reconstructed into a simple first-order filter instead of a third-order control system. In addition experimental results show that the acceleration feedback proposed here can effectively enhance the bandwidth of the closed-loop system and its trajectory tracking and pointing performance.

The linear sizing technique is used to evaluate the accuracy of a new correction strategy to limit scattering matters. The ratio of the elastic scattered light with fluorescence emission over monodispersed microspheres homogenously mixed in water is measured. Three cells filled with different concentrations of these fluorescent particles are illuminated with a thin laser beam that is moved inside the cell from the front to the back. A comparison of the linear sizing technique with and without correction is presented and shows that the correction enables the measurement of higher concentrations; the limits of the correction method are also shown. These results could be a potential step to apply this technique to sprays.

We offer a formal investigation of the measurement principle of time-of-flight 3-D cameras using correlation of amplitude-modulated continuous-wave signals. These sensors can provide both depth maps and IR intensity pictures simultaneously and in real time. We examine the theory of the data acquisition in detail. The variance of the range measurements is derived in a concise way and we show that the computed range follows an offset normal distribution. The impact of quantization of that distribution is discussed. All theoretically investigated errors like the behavior of the variance, depth bias, saturation and quantization effects are supported by experimental results.

Camera calibration is a fundamental task in computer vision and photogrammetry. This paper presents an approach for automatic estimation of intrinsic parameters from images by using vanishing points with orthogonal directions. Firstly, image lines are extracted and are clustered into groups corresponding to three dominant vanishing points. Second, camera parameters including the radial distortion are estimated by adjusting linear parameters locating the images. Finally, the rotation matrix of the projection matrix is computed from the vanishing points, and the image edges and the translation matrix are obtained with the help of additional translation motion between the viewpoints. Our approach does not need any a priori information about the cameras being used. Experiments to evaluate the performance of this approach on synthetic and real data are reported.

We present a new method for testing an optical surface. It uses the Ronchi test with variable-frequency rulings and a liquid-crystal display. The rulings can be formed by substructuring the spacing of a Ronchi ruling or combining several classical Ronchi rulings in a single variable-frequency ruling. This change allows us to observe smaller defects on the surface, because it enlarges the spatial-frequency domain of the ruling, and a larger dynamic range of detection of the Ronchi test can be obtained instead of increasing the resolution of the detection of the Ronchi test by iteratively changing classical Ronchi rulings with higher line density. As a result, we have found that it is possible to measure defects on a optical surface that are of size ≥ 57 nm (λ/11).

A novel method is provided in conventional TE CO₂ laser configuration by utilizing a specially designed small capacitance in the UV preionization scheme and a carefully optimized pulser/sustainer discharge circuitry so that the initial spike energy in the laser pulse profile induced by gain-switch effect can be greatly reduced. An experimental illustration is given in which the initial spike energy in the laser pulse is suppressed to less than 3.5% of the total pulse energy while stable laser performance is maintained.

A robust, miniaturized, diode-pumped high-energy neodymium doped yttrium aluminium garnet (Nd:YAG) laser with passive Q-switch generating 25 mJ at 3 ns has been demonstrated at repetition rates of up to 150 Hz. The device is designed for ignition of fuel air mixtures in internal combustion engines. The pump diodes and Peltier cooling are integrated in the laser head, giving a compact design with a small number of optical components for easy assembly. The laser was successfully operated as an optical spark plug on a test engine at high temperature and vibration levels.

We present an efficient and highly alignment-tolerant light coupling and distribution system for a multichannel Si₃N₄/SiO₂ single-mode photonics sensing chip. The design of the input and output couplers and the distribution splitters is discussed. Examples of multichannel data obtained with the system are given.

A new triplexing filter based on a silica direction coupler and an arrayed waveguide grating is presented. Using a combination of a direction coupler and an arrayed waveguide grating, a 1310-nm channel is multiplexed and 1490- and 1550-nm channels are demultiplexed for fiber-to-the-home. The direction coupler is used to coarsely separate the 1310-nm channel from the 1490- and 1550-nm channels. Subsequently, an arrayed waveguide grating is used to demultiplex the 1490- from 1550-nm channel. The simulated spectra show the 1-dB bandwidth of 110 nm for the 1310-nm channel and 20 and 20.5 nm for the 1490- and 1550-nm channels. The insertion loss is only 0.15 dB for 1310 nm and 5 dB for 1490 and 1550 nm. The crosstalk between the 1490- and 1550-nm channels was less than -35 dB.

A resonant cavity waveguide device structure is reported which uses a grating structure to couple the vertical incident light into the waveguide. A thin, high-refractive-index waveguide is used to attain high sensor sensitivity for the surface refractive index variation measurement.

We measure the stimulated Raman scattering (SRS)-induced tilt in spectral-amplitude-coding optical code-division multiple-access (SAC–OCDMA) systems as a function of system main parameters (transmission distance, power per chip, and number of users) via computer simulations. The results show that SRS-induced tilt significantly increases as transmission distance, power per chip, or number of users grows.

We propose a new system of signal security using nonlinear micro ring resonators for optical communication system. When a soliton pulse is input into the system, the chaotic signal is generated and multiplexed into the optical link. The chaotic waveform can be canceled using an add/drop device connected into the transmission link. Using the appropriate ring parameters, the original signal can be retrieved. An other application results from the fact that the fast and slow light behaviors can be presented, and can be seen using the add/drop multiplexers. In some cases, we can generate signal to obtain the two identical "signal" and "ghost" signals, which are observed in a different time frame. In this application, communication security can be performed when the required information is multiplexed and performs the link using the chaotic signal, fast and slow light, and signal and ghost signals, where the original signal can be retrieved by the known clients.

A time- and wavelength-interleaved optical pulse source, which is based on spectral slicing and dispersion management, is proposed and experimentally demonstrated. The pulse source has a simple configuration, and both the repetition rate and the wavelength channels can be tuned easily.

A rigid flexible optical electrical printed circuit board (RFOE-PCB) with both electrical layers and an optical layer was fabricated using a conventional PCB manufacture process. The RFOE-PCB is applicable to fold-type mobile devices such as mobile phones and laptop computers. The RFOE-PCB was designed to be embedded with a flexible 45-deg-ended optical waveguide, which was made using a polymeric material. The precise lamination between an electrical layer and an optical layer was achieved by a passive alignment method. We carried out the repetitive folding test and an environment test for physical and optical reliability suitable for mobile devices. Data transmission of 2.5 Gb/s was demonstrated with a clear eye diagram using the fabricated RFOE-PCB.

Rotation-invariant texture classification is one of the most challenging problems in computer vision. We present a new and effective method for rotation-invariant texture classification based on circular Gabor wavelets. Two group features can be constructed by the mean and variance of the circular Gabor filtered images and rotation invariants. Using the two group features, a discriminant can be found to classify rotated images. The proposed method is evaluated on three public texture databases: Brodatz, CUReT, and UIUCTex. The experimental results, based on different testing data sets, show that the proposed method has comparatively high correct classification rates not only for the rotated images, but also for the images under different illuminations and viewing directions. The proposed method is robust to additive white noise.

Scalable video coding, which is an extension of H.264/AVC, provides efficient methods for merging 8-bits/pixel sequences and higher bits per pixel sequences into one scalable bitstream. In this work, two types of prediction approaches are supported. One is based on interlayer intraprediction, by which texture residuals between the base layer and the enhancement layer are removed. The interlayer intraprediction is restricted to the enhancement macroblock whose collocated macroblock is intracoded. In this prediction structure, a global look-up table, obtained from an arithmetic average or scale offset pairs of each macroblock, is chosen as an inverse tone-mapping process, depending on rate distortion (RD) performance. The other is based on interlayer motion prediction, where motion compensation is performed in the enhancement layer as well as in the base layer. But motion parameters in the enhancement layer are inferred from the corresponding blocks in the base layer, which minimizes the complexity increase. A coding gain of 0.14 dB or 1.2% reduction in bit rate is obtained for 10 bits/pixel test sequences, while a coding gain of 12 bits/pixel test sequences reaches up to 4.2 dB or 48% reduction in bit rate.

The problem of estimating optical flow fields corresponding to multiple moving objects in a spatiotemporal image sequence is addressed. A modified version of the neural gas (NG) unsupervised learning algorithm is used to implement a nonlinear interpolation strategy to overcome the aperture problem encountered during local motion estimation. Local motion constraints are formulated, and the best information over four point pairs is used to produce a single motion estimate. Wherever the aperture problem is encountered the minimum-norm estimate is produced. These local estimates are then refined using the modified NG. NG provides a framework for the fusion of local incomplete motion information into complete global estimates. Due to the self-organizing nature of NG the number of motion classes need not be specified a priori. The technique leads to generation of an optical flow field without the smearing of flow fields encountered in regularization-based techniques. Motion estimation results obtained on synthetic natural image sequences are shown.

Image matching is a critical issue in many image processing applications. It is very likely that the real-time sensed image and the reference image have significant differences in terms of brightness, contrast, and angle due to the changing parameters of imaging devices, the illumination conditions, and the view angles. This has greatly affected the precision and the efficiency of the target recognition tasks in remote sensing. We construct a novel moment invariant as a confidence measure for the image matching task. Using the distance between template and local region in a real-time image in the feature space of moment invariant, a target detection algorithm is implemented that does not rely on either the imaging angles or the illumination conditions. Based on the phases of complex moments, the direction of each matching region in relation to the template can also be obtained. The experiments show that the algorithm can be used in target identification with changing conditions of the brightness, contrast, and the rotation angles in relation to the template.

Locality preserving projections (LPP) is a recently developed linear-feature extraction algorithm that has been frequently used in the task of face recognition and other applications. However, LPP does not satisfy the shift-invariance property, which should be satisfied by a linear-feature extraction algorithm. In this paper, we analyze the reason and derive the shift-invariant LPP algorithm. Based on the analysis of the geometrical meaning of the shift-invariant LPP algorithm, we propose two algorithms to minimize the locality and maximize the globality under an orthogonal projection matrix. Experimental results on face recognition are presented to demonstrate the effectiveness of the proposed algorithms.

This study investigates the use of simple, low-cost infrared sensors for the recognition of geometry and surface type of commonly encountered features or targets in indoor environments, such as planes, corners, and edges. The intensity measurements obtained from such sensors are highly dependent on the location, geometry, and surface properties of the reflecting target in a way that cannot be represented by a simple analytical relationship, therefore complicating the localization and recognition process. We employ artificial neural networks to determine the geometry and the surface type of targets and provide experimental verification with three different geometries and three different surface types. The networks are trained with the Levenberg–Marquardt algorithm and pruned with the optimal brain surgeon technique. The geometry and the surface type of targets can be correctly classified with rates of 99 and 78.4%, respectively. An average correct classification rate of 78% is achieved when both geometry and surface type are differentiated. This indicates that the geometrical properties of the targets are more distinctive than their surface properties, and surface determination is the limiting factor in recognizing the patterns. The results demonstrate that processing the data from simple infrared sensors through suitable techniques can help us exploit their full potential and extend their usage beyond well-known applications.

The object tracking method using the scale-invariant feature transform (SIFT) is applicable to rotated or scaled targets, and also maintains good performance in occluded or intensity-changed images. However, the SIFT algorithm has high computational complexity. In addition, the template size has to be sufficiently large to extract enough features to match. This paper proposes a scale-invariant object tracking method using strong corner points in the scale domain. The proposed method makes it possible to track a smaller object than the SIFT tracker by extracting relatively more features from a target image. In the proposed method, strong features of the template image, which correspond to strong corner points in the scale domain, are selected. The strong features of the template image are then matched with all features of the target image. The matched features are used to find relations between the template and target images. In experimental results, the proposed method shows better performance than the existing SIFT tracker.