This PDF file contains the editorial “Optics and Terrorism” for OE Vol. 40 Issue 11

A novel technique for the transmission of optical length information using a low-coherence tandem interferometer and a single-mode optical fiber is developed. The optical path length with a step gauge in the first low- coherence interferometer is transmitted through the optical fiber to the second interferometer. The interference fringes containing the length information of the gauge are generated with high accuracy by compensating the optical path difference in the second interferometer.

We propose the use of a nonlinear bacteriorhodopsin film to self-induce a Zernike-type filter in robust optical phase-contrast systems. The device requires relatively low light intensity levels (as low as 200 nW/cm2) at wavelengths around 633 nm and can contrast dynamical phase distributions.

The advancement in optical computing is impaired by a lack of development of optical computing devices leading to successful optical computing systems. In our special section published in March 1999,1 we aspired for more works in devices such that realistic optical systems might come to fruition. A similar concern was voiced recently, in the SPIE conference on Photonic Devices and Algorithms III held in San Diego.23 Therefore, this special section is a step toward addressing the needs in Optical Computing Systems, Materials, and Devices. The papers in our special section are broadly organized into three groups: (1) analysis and simulation of optical computing devices and systems; (2) implementation of optical computing systems; and (3) optical device characterization and optical materials.

A new method to analyze the influence of possible hysteresis cycles in devices employed for optical computing architectures is reported. A simple full adder structure is taken as the basis for this method. Single units, called optical programmable logic cells, previously reported by the authors, compose this structure. These cells employ, as basic devices, on-off and SEED-like components. Their hysteresis cycles have been modeled by numerical analysis. The influence of the different characteristic cycles is studied with respect to the obtained possible errors at the output. Two different approaches have been adopted. The first one shows the change in the arithmetic result output with respect to the different values and positions of the hysteresis cycle. The second one offers a similar result, but in a polar diagram where the total behavior of the system is better analyzed.

We report on the construction of a matching information terminal based on a spatially coded moiré technique, to be used as visualization equipment for genome analysis. The terminal provides the result of a string matching operation, which is achieved by overlapping of spatially coded patterns with a small intersection angle to generate moiré fringes. The fringes reveal the matching between two string sequences coded as spatial patterns. Due to its flexibility in image display, the matching information terminal is able to deal with long strings such as a gene sequence. The constructed terminal achieves string matching for 256 bases of DNA sequences and displays about 25,000 point-to-point matching results at a time.

Abstract. The theoretical storage capacity of data in the form of volume holograms is estimated to be of the order of a terabit per centimeter cube. However, the practical limit of the capacity is set by the system parameters. A model is shown that uses system parameters such as bit error rate, data access time, number of holograms, and noise to yield practical estimates of the capacity. The model calculates the impact of different system parameters on the capacity and shows the bottlenecks for this technology.

A novel optical implementation using a joint transform correlator for parallel fuzzy inference and logic processing is presented. in particular, space-variant correlation is shown to be suited for implementing the fuzzy set matching. When compared with other optical fuzzy systems, the proposed method offers the advantages of simplicity and robustness in terms of system alignment.

A fringe-adjusted joint transform correlator (JTC) based technique for improved color pattern recognition is introduced. in the proposed technique, a real-valued fringe-adjusted filter is used to reshape the joint power spectrum to yield better correlation output. A color image is processed through three channels, and fringe-adjusted filtering is applied to each of these channels to achieve excellent correlation discrimination. The correlation outputs from these channels are then fused together to make a decision on the detection of a desired color pattern. It is also shown that the fringe-adjusted filtering can be effectively applied to a multichannel single-output JTC to obtain excellent correlation discrimination between an unknown input scene target and a reference image for all color channels. The proposed techniques can be implemented in real time for practical color pattern recognition applications. Two architectures for all-optical implementation of the proposed techniques are presented.

Since the early 1960s, a major part of optical computing systems has been Fourier pattern recognition, which takes advantage of high speed filter changes to enable powerful nonlinear discrimination in "real time.'' Because filter has a task quite independent of the tasks of the other filters, they can be applied and evaluated in parallel or, in a simple approach I describe, in sequence very rapidly. Thus I use the name ITFF (independent task Fourier filter). These filters can also break very complex discrimination tasks into easily handled parts, so the wonderful space invariance properties of Fourier filtering need not be sacrificed to achieve high discrimination and good generalizability even for ultracomplex discrimination problems. The training procedure proceeds sequentially, as the task for a given filter is defined a posteriori by declaring it to be the discrimination of particular members of set A from all members of set B with sufficient margin. That is, we set the threshold to achieve the desired margin and note the A members discriminated by that threshold. Discriminating those A members from all members of B becomes the task of that filter. Those A members are then removed from the set A, so no other filter will be asked to perform that already accomplished task.

The commercialization of CD-ROM drives has clearly demonstrated the ability of optical storage devices to meet the growing demand for archival data storage. However, with the continued expansion of electronic information resources, storage capacity requirements are expected to approach the terabyte level for personal users and exceed the petabyte level for databases and data warehouse systems. Further, many data-intensive applications require real-time data access rates. Thus, designers for the next generation of archival storage systems have the challenging task of providing storage capacities several orders of magnitude larger than existing systems while maintaining current data access times. To meet this challenge, we have developed a single-chip database filter suitable for large-capacity database systems that use page-oriented optical storage devices. Based on a photonic VLSI device technology, our data filter monolithically integrates optical detectors, photoreceiver circuits, data manipulation logic, and filter control circuitry onto a single CMOS chip that can be readily fabricated using a standard VLSI fabrication facility. Thus, our device is compatible with existing electronic device manufacturing technology and shares all of the reliability, uniformity, and manufacturability benefits associated with current electronic hardware. In addition to describing the database filter concept, this paper presents design and circuit evaluation data suggesting that a 32x32-bit filter fabricated in a 1.5-?m CMOS process could have an optical page read rate of 87 Mpage/s and support 123-Mrecord/s transfer rate to a host computer. Finally, queuing theory is used to show that even with the limitation of finite queue capacity, a database filter chip could be controlled to work at near-optimal performance, where database search time is limited by the data transfer rate into the host computer. Since only valid search data are passed through to the host computer, the introduction of a database filter can dramatically reduce database search time.

We present different configurations for a compact free-space optical interconnection module by combining two radial gradient- refractive-index lenses and/or two arrays of refractive microlenses. Based on our findings with ray tracing and radiometric analysis, we discuss how we have selected the proper optical system configurations and how we have chosen the different design parameters to optimally accommodate different types of optoelectronic emitters such as LEDs, microcavity LEDs, and vertical-cavity surface-emitting lasers. We focused on maximizing optical coupling efficiencies and misalignment tolerances while minimizing interchannel crosstalk.

In binary digital computers addition is performed employing the carry propagation technique, which essentially limits the computing speed. For multiplication the speed is further reduced because of the number of shift and add operations. To alleviate this problem, a modified signed-bit (MSD) number system has already been proposed. The inherent parallel architecture of optical processors makes the best use of the carry-free features of MSD binary numbers. In this paper, we use a very large scale integration SLM and CCD detector to demonstrate truth table lookup for carry-free MSD addition.

We present, for the first time to our knowledge, a generalized lookahead logic algorithm for number conversion from signed-digit to complement representation. By properly encoding the signed-digits, all the operations are performed by binary logic, and unified logical expressions can be obtained for conversion from modified-signed-digit (MSD) to 2's complement, trinary signed-digit (TSD) to 3's complement, and quarternary signed-digit (QSD) to 4's complement. For optical implementation, a parallel logical array module using an electron-trapping device is employed and experimental results are shown. This optical module is suitable for implementing complex logic functions in the form of the sum of the product. The algorithm and architecture are compatible with a general-purpose optoelectronic computing system.

The performance of optical computers that include programmable Fourier optics depends intimately both on the physical characteristics of the particular spatial light modulator (SLM) and on the particular algorithms that map the ideal signal into the available modulation range of the SLM. Since practical affordable SLMs represent only a limited range of values in the complex plane (e.g., phase-only or quantized phase), numerous approaches have been reported to represent, approximate, encode or map complex values onto the available SLM states. The best approach depends on the space-bandwidth product (SBWP) of the signal, number of SLM pixels, computation time of encoding, the required response time of the application, and the resulting performance of the optical computer. My review of various methods, as applied to most current SLMs, which have a relatively low number of high cost pixels, leads me to recommend encoding algorithms that address the entire usable frequency plane and that emphasize the fidelity of the approximated Fourier transform over maximization of diffraction efficiency and minimization of approximation error. Frequency-dependent diffraction efficiency (due to pixel fill factor of discrete SLMs or resolution of spatially continuous SLMs) is also evaluated as a factor that can limit usable SBWP and possibly modify the choice of encoding method.

Presented is the effect of using various cladding materials with different conductivities and dielectric constants on the applied voltage for optoelectronic (OE) devices based on nonlinear optical (NLO) polymers. Using a conductive polymer, we have demonstrated a 3 to 13 times increase in the effective electro-optic (EO) coefficient of electrode- poled NLO polymers, compared to using passive polymer claddings. We have achieved the lowest poling voltage to date for maximum EO coefficient, 300 V, for a two-layer waveguide structure consisting of a 2-?m- thick NLO polymer layer and a 2-?m-thick conductive cladding layer. The dielectric constants of both the NLO polymer core and passive polymer cladding materials used for conventional polymer-based integrated optic devices are typically very similar in magnitude. This suggests that only a small fraction of the applied modulation voltage is reaching the NLO polymer core layer, requiring 4 to 5 times higher modulation voltage than the desired V?. We have demonstrated a factor-of-2 decrease in the modulation voltage using the same conductive polymer, due to its possessing a much higher dielectric constant than the core material at the modulation frequency tested. The results show promise for shorter, lower-operating-voltage devices.

The encoding method has a considerable influence on the resolution, speed, and robustness of structured light measurement systems. A synthetic encoding method based on spatial and temporal encodings is presented. The method can achieve a spatial resolution of 231 codewords with only five projected images, which would require many more images if other binary codes were employed. The encoding and decoding processes are given, and experimental results verify the robustness and the reliability of the method. It is concluded that the combination of spatial and temporal information can further improve the efficiency of the encoding and make it more flexible in different applications of 3-D object profile measurement.

We extend our previous paper, where the focus was on error- resilient zerotree wavelet image coding on noisy channels. This concept is extended to video coding using a 3-D wavelet transform. The proposed video coding system consists primarily of a 3-D wavelet transform, coding via the 3-D set-partitioning in hierarchical trees (SPIHT) algorithm, and bit partitioning followed by bit reorganization procedure. Simulation results show that the proposed coders outperform the existing error-resilient coders from the standpoint of both noise-free channels and noisy channels. In addition, we confirm that the proposed algorithm is more error-resilient than the conventional 3-D zerotree wavelet video coding techniques for various channel-error conditions as evidenced by both objective and subjective evaluations.

We propose a digital information hiding technique in which we use a combination of a random sequence and the Hadamard matrix to hide multiple information in a digital image. Earlier work used only one random sequence multiplied by an information signal to spread the spectrum of the information signal, making it difficult for a third party to detect the information signal or jam it. But in the case of hiding multiple information in the same digital image, the use of only different random sequences that are generally not orthogonal to each other has some problems because of the cross-correlation between the sequences. Thus we present a new information hiding scheme that can be used to hide multiple information using both a random sequence that spreads the energy level of the data to be hidden and a Hadamard matrix, which results in the random sequence being uncorrelated.

The pairwise nearest neighbor (PNN) method is a simple and well-known method for codebook generation in vector quantization. In its exact form, it provides a good-quality codebook but at the cost of high run time. Afast exact algorithm was recently introduced to implement the PNN an order of magnitude faster than the original O(N3K) time algorithm. The run time, however, is still lower bounded by O(N2K), and therefore, additional speed-ups may be required in applications where time is an important factor. We consider two practical methods to reduce the amount of work caused by the distance calculations. Through experiments, we show that the run time can be reduced to 10 to 15% that of the original method for data sets in color quantization and in spatial vector quantization.

Injection locking is a useful technique for amplifying the output power of a tunable external cavity diode laser. The injection-locked output retains the spectral properties of the injected signal while offering high powers. A self-aligning injection-locked system is demonstrated that uses a chirped external cavity diode laser as the master laser. A gain of 51.8 dB is demonstrated with injection-locked output powers greater than 62 mW The amplified linear frequency chirp of 800 MHz in 4 ?s is measured and shows no deviation from the frequency chirp of the master laser. The high gain and ability of the injection-locked output to follow the rapid tuning of the injected source make it an excellent amplification technique for applications requiring higher powers with fast tuning.

Moire fringes are visually observed when two 2-D implicit grids are superposed and rotated. We introduce two innovations in the broad field of moiré. The first calls attention to hidden or implicit grids from the photocopying process that are also used to produce moire patterns. This method of moire pattern production is extended to hidden grids optoelectronically generated by digitizing TV-CCD images. Our second innovation is a proposed application of this type of moire pattern to measure distances.

A deflectometric method for the characterization of optical systems is presented. It is based on the use of a CCD camera and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, three different algorithms for measuring the position of the deflected beam are tested and compared. Based on this comparison, an algorithm based on the calculation of the phase of the fast Fourier transform (FFT) is selected, and an accuracy of 0.024 pixels is obtained on the determination of the beam position in our setup. Using an XY scanning stage, the proposed method is completely automated and applied for the characterization of ophthalmic lenses. In this application, the gradients of the wavefront refracted by the lens are measured directly, and from them, the thickness and the local power of the lens are computed.

A simulator for the computer-aided design of holograms is developed. The direction and intensity of the reconstructed beam are calculated using the Kirchhoff diffraction integral and Kogelnik's coupled- wave theory. Grating distortions induced by physical changes in the recording medium are evaluated using the diffraction integrals, and imaging characteristics are analyzed using ray tracing. Simulator results can be used to evaluate wavefront aberrations of the reconstructed images, and holograms that compensate for aberrations can be designed by the simulator. Examples are given where recording and reconstruction wavelengths are different and where the grating is distorted by nonuniform shrinkage of the medium. Also, to illustrate practical application, a holographic optical element lens and a wavelength demultiplexer are designed and evaluated."

A hybrid holographic microscope is proposed to realize both imaging and interferometric measurement of microstructures and meet the two major challenges in micromeasurement, which are high resolution and small object size. The system is developed based on an in-line digital holographic arrangement incorporated with a long-distance microscope. Studies demonstrate that it is capable of realizing measurement of microstructures with lateral dimensions of at least 5 ?m. The application of the system in micromeasurement is experimentally investigated on a microcantilever. The load-induced deflection is obtained and validated with numerically simulated results based on a finite element model. Error analysis for displacement determination is performed.

Sampling is a necessity in minifying a digital image. In the event that the image contains spatial frequencies higher than half the sampling frequencies in any dimensions, aliasing will occur. Aliasing in minifying digital images with and without prefiltering are compared. Using the Shannon sampling theorem, the reduction of aliasing is explained based on the Fourier transform, instead of the discrete wavelet transform. It is found that one should not consider only the classical quality evaluation measures of the sampled image when selecting from the several antialiasing methods, we should also consider the particular requirements of some key local information, such as to make letters or Chinese characters more recognizable, although the degree of aliasing reduction may be lowered.

We construct a bistatic polarimetric scattering system and improve the experimental techniques to contribute to the research of a mathematical model that describes the electromagnetic waves scattering characteristics from random rough surfaces, and to serve as a tool used to better describe wave interaction with random media. To accomplish the measurement both a horn antenna operating in the far field and a parabolic-dish antenna operating in the near-field focus mode are utilized. The transmitter for the active system is a linearly polarized, helium- neon laser operating in the red light region. The receiver measures both like- and cross-polarized returns, which helps assess the scattered radiation pattern. Aflat metal plate is developed to calibrate the measuring facility. The system is automated and consists of a spherical frame over which the transmitter and receiver travel. The transmitter and receiver design, system automation, and system architecture are discussed. Experimental measurements for a target are presented to evaluate the accuracy, repeatability, and utility of the helium-neon laser measurement system.

A new iterative method for calculating the distribution of a liquid-crystal director is presented, which is based on a straightforward finite-difference approximation to the Euler-Lagrange equations. The method is applicable for various types of liquid-crystal displays, such as the twist nematic cell, nematic cell with asymmetic pretilt, or chiral supertwist nematic cell. This method is very stable and simple, and can give accurate results in a short time compared with Newton's method, the relaxation method, simulated annealing, etc.

A method to perform a predictive search for a given amplitude and phase modulation response in twisted nematic liquid crystal displays is presented. The algorithm is based on a simple physical model that we recently proposed and that considers the effect of liquid-crystal layers located in the vicinity of the edges, which are not able to tilt. This model was demonstrated to explain accurately the experimental transmittance modulation curves. Here the model is applied to perform a predictive search for an optimized modulation by changing the input and output polarization configurations. A generalized configuration to generate and detect elliptically polarized light is proposed. The method is applied for seeking two different configurations useful for optical image processors: phase-only modulation and amplitude-only modulation. The excellent agreement with the experimental measurements validates the potential of the proposed method.

We present a novel method to measure the diameter and straightness of seamless steel pipes. A pair of line-structured lasers, which locate on different sides of the pipe but are in a common plane, cast on the pipe to create two elliptical arcs. Two CCD cameras capture these two arcs. Major and minor axis radii and spatial 3D coordinates of every corresponding elliptical cross-section center can be calculated through ellipse fitting. A pair of line-structured laser sensors, each of which includes a line-structured laser and a CCD camera, are placed at every sampling cross section of the pipe, and thus the pipe's crosssection diameter and furthermore the straightness of the pipe can be solved. We provide an on-line machine vision method for measuring a seamless steel pipe's diameter and straightness, including the design of the system, the deduction of the mathematical model, and the research of the experimental results.

Two different commercially available photoresists, specifically designed for the fabrication of charge-coupled device (CCD) microlens arrays, are compared for their effectiveness in industrial-scale array production. A method is used to characterize resist films, prepared under the same processing conditions as those for the actual lens arrays. Great differences in the transmission spectra are observed between the two resists. Similarly, the quality of the film surface, based on the interference patterns in transmission spectra, vary greatly as well. Finally, plots of absorption versus wavelength offer practical proof that power losses due to absorption vary significantly between the types of photoresist.

We describe an environment-friendly fabrication process for microretarders with a high contrast ratio and well-defined stripe boundaries. It is shown that by accurately controlling the power, spot size, and scanning speed of a CO2 laser beam, the retardation property of a polymeric film can be tailored within a localized area without altering that of the untreated areas. The measurements and analyses of the contrast ratios on the microretarders are presented. A microretarder can be used in many applications, especially in stereoscopic displays.

We propose a simple optical fiber sensor for the measurement of vibration. The sensor consists of two fiber Bragg gratings that have partially overlapped reflection spectra and are mounted on the opposite sides of a flexible beam. With this setting, the light intensity reflected by the gratings is modulated in accord with the vibration of the beam and adverse thermal effects can be largely eliminated. Experimental results are presented to demonstrate the feasibility of the sensor.

Simultaneous measurements of particle size and velocity with different media are important in the experimental study of multiphase flows. Especially, when one of the dispersed media has a relative refractive index close to unity (m? 1.0), the optical configuration requires extra consideration in phase-Doppler anemometry (PDA). Such measurements are often encountered when water flows are composed of air bubbles and glass beads with relative refractive indices of m1 = 0.75 and m2= 1.13, respectively. Large uncertainty in measurements may arise if optical parameters fall into the region of so-called "critical scattering angles.'' Furthermore, the scattering intensities from air bubbles and glass beads in water are found to have two-order-of-magnitude differences at an off-axis angle in between 60 to 85 deg, which narrows the measurable dynamic range and causes bias in the size distribution of different dispersed phases. We use a scheme based on the recently developed combined refraction-reflection model and Mie scattering theory to optimize the off-axis angle to minimize the measurement uncertainty. The variation of the critical scattering angles and scattering intensity ratios of media are quantitatively described. The predictions are validated by conducting experiments to measure glass spheres and vapor bubbles in water.

A new approach is reported for the measurement of Brewster angles in transparent biaxial crystals. The Brewster angles for potassium hydrogen phthalate (KAP) single crystal are also calculated from available refractive index data by our method. The measured values agree well with the calculated values, confirming our theory. The measured values of the Brewster angles of KAP are 60°03'± 5' and 58°30'± 5'.

This paper presents a comparative study of different thresholding methods for speckle noise reduction in electronic speckle pattern interferometry fringes using several wavelet bases. An approach based on the removal of the wavelet subbands of the transformed image is presented. The performance of this method is analyzed and compared with the results obtained with the denoising techniques that use wavelet shrinkage. It is shown that the wavelet subband removal method reduces speckle noise and maintains image features more effectively than the wavelet shrinkage techniques based on soft and hard thresholding.

When the spatial fringe analysis method based on the moire technique is applied to a noisy fringe image, problems arise in the processing with, for example, phase unwrapping, accuracy of analysis, and so on. A digital filter technique and a filter based on time series analysis are applied to the spatial fringe analysis method to solve these problems. In a simulation with a model of the fringe image, results show that the spatial fringe analysis method using digital filters is highly robust against a noise in an image, and that the method using a Kalman filter can smoothly and accurately detect the phase map of the object with a continuous phase distribution. Furthermore, the method is applied to analyze a speckle fringe image in ESPI. A new speckle interferometry based on the proposed method can analyze specklegrams with a normal ESPI system. The results show that a spatial fringe analysis method based on the moire technique can analyze accurately the phase of a speckle fringe image using only a single fringe image. The proposed method can be anticipated to accelerate the use of ESPI in industry.

The University of Nebraska-Lincoln has developed an ultrawideband random noise radar operating over the 1- to 2-GHz frequency range. The system uses the technique of heterodyne correlation, and is thus phase coherent. It has therefore been used in applications such as interferometry, polarimetry, and Doppler estimation. This assesses the performance of this radar as a range-Doppler imaging system, in particular, inverse synthetic aperture radar (ISAR). By performing turntable experiments, we examine a number of issues that arise both from the wideband nature of the radar system and from the randomness of the transmit signal. Although the ultrawideband nature of the signal does yield some ambiguity as to the cross-range resolution of the system, it is seen that one may use the usual equation for cross-range resolution in narrowband systems with reasonable confidence. In addition, the random nature of the transmit waveform gives rise to variations from look to look in the ISAR images. High correlations are obtained for voltage and power amplitudes, while the complex voltage and the phase angle show low correlations from look to look. Finally, we present polarimetric color images of a complex target that captures its polarimetric scattering characteristics, which may be useful in automatic target recognition.

We prove that for gray-level or binarized synthetic aperture radar (SAR) images with enhanced scattering centers, the DC-blocked phase-only filter is the optimal, as well as the most practical, solution for SAR image recognition. Our correlation algorithm, which employs various power laws to enhance the scattering centers, was examined for images with different complexity using the moving and stationary target acquisitions and recognition (MSTAR) data base. For standard recognition problems, which represent 95% of the cases (intermediate level of noise and sufficient number of scattering centers on the target), we found that our proposed approach improves the correlation even when utilizing binary templates extracted from the region of interest and binary inputs. For more complex problems (representing nearly 5% of the cases), a further improvement in our correlation recognition approach is needed.

A new segmentation algorithm is proposed to extract a target in forward-looking IR (FLIR) images. It is based on fuzzy thresholding and edge detection. First, a region of interest (ROI) selection method is applied to the FLIR image to remove complex background and to automatically extract a small rectangular ROI including a target. Then fuzzy thresholding, which uses intensity and spatial information, is performed on the ROI. The Canny edge method is utilized to supplement the deficiency of the threshold method. As a preprocessing of edge detection, a new contrast extension method using a gray-level mathematical morphology operation is proposed to sharpen edges. The proposed segmentation algorithm is applied to many natural FLIR images and its performance is compared with conventional segmentation methods. Experimental results show that the proposed algorithm is fast and has a good segmentation performance.

The infrared (IR) seeker, mounted on the thermal tracking missile, identifies a position of the target by detecting and processing the thermal energy radiated from the target. By using the positioning information, the missile is able to track and destroy the target. To cope with the attack of the missile, the target deploys a countermeasure (CM), such as flares. Therefore, the IR seeker must have a countercountermeasure (CCM) to eliminate the effects of the flares. We analyze the radiant features of the target and the flare in the IR and ultraviolet (UV) bands, determine the spectral response ranges to distinguish the target from the flares, and present a new two-color CCM using the reference level. We simulate the IR seeker using the rosette scanning pattern to evaluate the discriminating performance of our CCM. The simulation results demonstrate that our two-color CCM can achieve an effective cancellation of the flare signal with a relatively high intensity.

The development and evaluation of texture synthesis algorithms is discussed. We present texture synthesis algorithms based on the gray-level co-occurrence (GLC) model of a texture field. These algorithms use a texture similarity metric, which is shown to have high correlation with human perception of textures. Synthesis algorithms are evaluated using extensive experimental analysis. These experiments are designed to compare various iterative algorithms for synthesizing a random texture possessing a given set of second-order probabilities as characterized by a GLC model. Three texture test cases are selected to serve as the targets for the synthesis process in the experiments. The three texture test cases are selected so as to represent three different types of primitive texture: disordered, weakly ordered, and strongly ordered. For each experiment, we judge the relative quality of the algorithms by two criteria. First, we consider the quality of the final synthesized result in terms of the visual similarity to the target texture as well as a numerical measure of the error between the GLC models of the synthesized texture and the target texture. Second, we consider the relative computational efficiency of an algorithm, in terms of how quickly the algorithm converges to the final result. We conclude that a multiresolution version of the "spin flip'' algorithm, where an individual pixel's gray level is changed to the gray level that most reduces the weighted error between the images second order probabilities and the target probabilities, performs the best for all of the texture test cases considered. Finally, with the help of psychophysical experiments, we demonstrate that the results for the texture synthesis algorithms have high correlation with the texture similarities perceived by human observers.