I have received more reader response regarding the recommendation that "idea-type" papers be published in Optical Engineering (see my editorials in the November 1987 and March 1988 issues). I will attempt to condense this response-some of which was for and some of which was against-in the paragraphs below.

Applied Optics and Optical Engineering, Volume 10-Reviewed by Paul R. Yoder, Jr.; The Measurement of Appearance, Second Edition-Reviewed by David L. Mac Adam

The papers in this special issue are dedicated to the second part of the two special issues of Optical Engineering on Industrial Applications of Optical Signal Processing. The first eight papers appeared in the preceding issue (Vol. 27, No. 4, April 1988).

Spatial-frequency-domain Fourier-Mellin descriptors are proposed for the determination of object orientation and for object classification. The new methods require neither segmentation of the input image from the background nor an image centroid. The effect of noise is analyzed. Experimental results are shown.

Most of the defects present in manufactured glass are caused by rare explosions of hot jars and bottles on the assembly line. These explosions create particles of flying glass that may stick to the inside bottoms of other jars on the line. In this paper we present experimental results of a prototype optoelectronic inspection system that detects submillimeter stuck-glass defects. In the system described, we use a two-dimensional spatial light modulator to create in real time a unique mask for each glass jar inspected. This allows us to compensate for variations in acceptable features on the bottoms of the jars such as mold marks and lettering while detecting the presence of unacceptable features such as stuck-glass defects.

A fully engineered real-time (15 objects/s) optical Fourier transform feature space processor for product inspection is described. This unit is presently undergoing evaluation at several sites. This paper discusses the feature space techniques employed, the advantages of the Fourier transform reduced-dimensionality feature space used, and several of its properties. Emphasis is given to initial performance data obtained in many diverse applications.

In this paper recent theoretical and experimental work in the area of multiple quantum well (MQW) modulators for optical processing applications is presented. The theoretical work includes the application of the effective mass approximation to compositional MQW structures and the use of a two-band tight-binding approximation to doping-modulated nipi structures. The theoretical calculations are used to obtain electric-field-dependent absorption and refractive index in the above MQW structures. The experimental results of a 4µm thick GaAs/GaAIAs MQW modulator show an ~ 10:1 on/off ratio with an applied voltage of ~ 20 V (absorption change ~ 6000 cm-1 at E ~ 50 kV/cm) and ~0.4 rad of phase shift with an applied voltage of 10 V (~0.04 at E ~25 kV/cm). Such high electro-optical modulations have previously been reported only in the MQW optical waveguide modulator. Concepts of photoactivated, electrically addressed MQW spatial light modulators and IR-to-visible MQW spatial light modulators are presented. Finally, theoretical evaluation of quantum dot arrays and their potential use in spatial light modulators are discussed.

Recent advances in optical phase conjugation and energy coupling at optical powers as low as a few milliwatts have added a new dimension to optical image processing. Conventional image processing techniques based on convolution/correlation, matched filtering, and holographic interferometry can now be achieved with much simpler components and usually at much higher efficiency by incorporating these new features. Some of the application concepts that had been impracticable can now be realized. The basic principle and potential industrial applications of real-time image subtraction using dynamic holograms are reviewed. Optical implementations and experimental results on image subtraction, novelty filtering, and defect detection are discussed.

A real-time broadband pseudocolor image enhancement technique using a liquid crystal television spatial light modulator (LCTV SLM) is described. Three different schemes to modulate the gray-scale distribution of an input scene by an LCTV SLM through varying the orientations of its analyzer are presented. These schemes are incorporated into a compact white light optical projection system that is able to display, on a large screen, broadband pseudo-color images of real-world input scenes. Experimental results demonstrating the feasibility of the technique are reported.

An experimental procedure using one-step holographic associative memories to implement symbolic substitution is described. The proposed system as a whole is nonlinear. Experimental results of parallel half-addition are presented.

An instrument has been developed for measuring the light scattering associated with diffuse reflectance measurements. The instrument measures the sample thickness necessary to bring about diffusion of the transmitted radiation, i.e., the diffuse thickness. This quantity is inversely proportional to the light scattering coefficient as defined by the Kubelka-Munk equations. Results have shown the measurement to be independent of absorption and inversely proportional to particle density in the sample.

The optical implementation of a median filter for optical digital signal and image processing is proposed. The filter is implemented using polarization-coded symbolic substitution logic (SSL) and consists of a thresholder and a summing lens. The implementation of the median filter utilizes two properties of median filters, namely, the threshold decomposition and the stacking property. The thresholder decomposes the M-valued incoming signal into a set of M-1 binary sequences by thresholding the signal at M-1 levels. These binary sequences are then applied to a set of binary median filters, the outputs of which are added together (stacked) one sample at a time by use of the summing lens. The proposed optical implementation offers an increased throughput compared with the conventional electronic implementation by taking full advantage of the parallelism offered by SSL and the inherent massive parallelism of optics.

The objective of this research is to apply infrared sensing techniques, artificial intelligence, and robotics to improve the welding process by on-line identification and mitigation of weld plate surface contamination. A method of in-process detection of surface contaminants during the gas tungsten arc welding of steel plate has been developed, and rudimentary corrective actions have been implemented to demonstrate closed-loop control. The study employed on-line IR sensing techniques to dynamically monitor the thermal field in front of the molten pool during the welding process. Changes in thermal pattern and in the area under thermal scans taken perpendicular to the weld seam were then used by the controlling computer to identify undesirable surface contaminants. Appropriate corrective actions were generated and employed to displace the contaminants from the welding path. A computer routine was developed that recognized changes in the thermal patterns due to surface contaminants and implemented corrective procedures. The results of this study will aid in the elimination of weld defects due to surface contamination and hence will increase the reliability and productivity of the welding process.

This paper describes how a lens can be generated by starting from plane surfaces. Three different experiments, using the Los Alamos National Laboratory optimization procedure, all converged on the same stable prescriptions in the optimum minimum region. The starts were made first from an already optimized lens appearing in the literature, then from a powerless plane-surfaces configuration, and finally from a crude Super Angulon configuration. In each case the result was a double Gauss lens, which suggests that this type of lens may be the best compact six-glass solution for one imaging problem: an f/2 aperture and a moderate field of view. The procedures and results are discussed in detail.

A commercial GaAIAs diode laser is frequency locked to a Fabry-Perot interferometer. The temperature stabilization loop of this diode laser system maintains the relative frequency stability within 11 kHz. When the frequency control loop is closed, the relative frequency stability is improved to 450 Hz. A previously neglected frequency offset is also analyzed. This offset is a result of the injection current modulation technique commonly used to frequency lock diode lasers. The calculated frequency offset in our system is 150 kHz.

A turnkey optical inspection system is one for which the vendor, not the customer, assumes the responsibility for ensuring that the system satisfies the customer's needs. This paper presents some of the pitfalls that are encountered in reaching the goal of mutual satisfaction of vendor and customer, based on experience with actual turnkey inspection and measurement systems that have been developed for industrial assembly operations. A "roadmap" is presented for achieving a turnkey system that is satisfactory to both vendor and customer.