James K. Archibald

Review of stereo vision algorithms and their suitability for resource-limited systems

A significant amount of research in the field of stereo vision has been published in the past decade. Considerable progress has been made in improving accuracy of results as well as achieving real-time performance in obtaining those results. This work provides a comprehensive review of stereo vision algorithms with specific emphasis on real-time performance to identify those suitable for resource-limited systems. An attempt has been made to compile and present accuracy and runtime performance data for all stereo vision algorithms developed in the past decade. Algorithms are grouped into three categories: (1) those that have published results of real-time or near real-time performance on standard processors, (2) those that have real-time performance on specialized hardware (i.e. GPU, FPGA, DSP, ASIC), and (3) those that have not been shown to obtain near real-time performance. This review is intended to aid those seeking algorithms suitable for real-time implementation on resource-limited systems, and to encourage further research and development of the same by providing a snapshot of the status quo.

A cooperative multi-agent approach to free flight

The next generation of air traffic control will require automated decision support systems in order to meet safety, reliability, flexibility, and robustness demands in an environment of steadily increasing air traffic density. Automation is most readily implemented in free flight, the segment of flight between airports. In this environment, centralized control is impractical, and on-board distributed decision making is required. To be effective, such decision making must be cooperative. Satisficing game theory provides a theoretical framework in which autonomous decision makers may coordinate their decisions. The key feature of the theory is that, unlike conventional game theory which is purely egotistic in its structure, it provides a natural mechanism for decision makers to form their preferences by taking into consideration the preferences of others. In this way, a controlled form of conditional altruism is possible, such that agents are able to compromise so that every decision maker receives due consideration in a group environment. Simulations demonstrate that reliable performance can be achieved with densities on the order of 50 planes per ten thousand square miles.

A Satisficing Approach to Aircraft Conflict Resolution

Future generations of air traffic management systems may give appropriately equipped aircraft the freedom to change flight paths in real time. This would require a conflict avoidance and resolution scheme that is both decentralized and cooperative. We describe a multiagent solution to aircraft conflict resolution based on satisficing game theory. A key feature of the theory is that satisficing decision makers form their preferences by taking into consideration the preferences of others, unlike conventional game theory that models agents that maximize self-interest metrics. This makes possible situational altruism, a sophisticated form of unselfish behavior in which the preferences of another agent are accommodated provided that the other agent will actually take advantage of the sacrifice. This approach also makes possible the creation of groups in which every decision maker receives due consideration. We present simulation results from a variety of scenarios in which the aircraft are limited to constant-speed heading-change maneuvers to avoid conflicts. We show that the satisficing approach results in behavior that is attractive both in terms of safety and performance. The results underscore the applicability of satisficing game theory to multiagent problems in which self-interested participants are inclined to cooperation.

Vision Aided Stabilization and the Development of a Quad-Rotor Micro UAV

Micro Unmanned Air Vehicles are well suited for a wide variety of applications in agriculture, homeland security, military, search and rescue, and surveillance. In response to these opportunities, a quad-rotor micro UAV has been developed at the Robotic Vision Lab at Brigham Young University. The quad-rotor UAV uses a custom, low-power FPGA platform to perform computationally intensive vision processing tasks on board the vehicle, eliminating the need for wireless tethers and computational support on ground stations. Drift stabilization of the UAV has been implemented using Harris feature detection and template matching running in real-time in hardware on the on-board FPGA platform, allowing the quad-rotor to maintain a stable and almost drift-free hover without human intervention.

A cache coherence approach for large multiprocessor systems

This paper explores the architecture of high-performance large scale multiprocessors using private caches for each processor. The caches reduce the average memory access time, but they also result in the well known cache coherence problem. Multiple copies of each memory location are allowed to exist but they must be kept consistent with each other. In this paper, we present a solution to the cache coherence problem specifically for shared bus multiprocessors that adapts dynamically to the reference pattern. Simulation results are presented that demonstrate the high level of performance relative to other protocols particularly during intervals with high levels of sharing. The paper then presents a coherence solution for large multiprocessor systems organized around a hierarchy of buses. One of the first solutions of this kind, the hierarchical protocol is an extension of the adaptive shared bus approach described in this paper.

Multiple prefetch adaptive disk caching

A new disk caching algorithm is presented that uses an adaptive prefetching scheme to reduce the average service time for disk references. Unlike schemes which simply prefetch the next sector or group of sectors, this method maintains information about the order of past disk accesses which is used to accurately predict future access sequences. The range of parameters of this scheme is explored, and its performance is evaluated through trace-driven simulation, using traces obtained from three different UNIX minicomputers. Unlike disk trace data previously described in the literature, the traces used include time stamps for each reference. With this timing information-essential for evaluating any prefetching scheme-it is shown that a cache with the adaptive prefetching mechanism can reduce the average time to service a disk request by a factor of up to three, relative to an identical disk cache without prefetching. >

Rapid Color Grading for Fruit Quality Evaluation Using Direct Color Mapping

Color grading is a crucial step in the processing of fruits and vegetables that directly affects profitability, because the quality of agricultural products is often associated with their color. Most existing automatic color grading systems determine color quality either by directly comparing product color against a predefined and fixed set of reference colors or by using a set of color separating parameters, often in three-dimensional color spaces. Using these methods, it is not convenient for the user to adjust color preferences or grading parameters. In this paper, we present an effective and user-friendly color mapping concept for automated color grading that is well suited for commercial production. User friendliness is often viewed by the industry as a very important factor to the acceptance and success of automation equipment. This color mapping method uses preselected colors of interest specific to a given application to calculate a unique set of coefficients for color space conversion. The three-dimensional RGB color space is converted into a small set of color indices unique to the application. In contrast with more complex color grading techniques, the proposed method makes it easy for a human operator to specify and adjust color-preference settings Tomato and date maturity evaluation and date surface defect detection are used to demonstrate the performance of this novel color mapping concept.

BACH: a hardware monitor for tracing microprocessor-based systems

Abstract This paper describes the design and operation of the BACH system, a hardware monitor that can be used to obtain run-time information about a variety of microprocessor-based systems. BACH (BYU Address Collection Hardware) operates by monitoring CPU pins directly and can be used to trace any workload under any operating environment supported by the target platform. A modification to hardware monitoring techniques allows the collection of accurate, yet long and contiguous traces. The traces collected by BACH contain all references made by the processor including kernel references, interrupt routines, multiple user tasks, and data references. BACH traces also include detailed timing. BACH has been functional since December 1991 and its operation has been verified extensively; traces of over a billion references have been captured. Interfaces to three hardware platforms have been built: the Intel i80486DX, the Motorola MC68030 and the SPARC processor. To date traces have been collected under a number of operating environments, including: MS-DOS, UNIX SysVR3.2, UNIX SysVR4, Mach 2.6, MACH 3.0, SUN OS and HP-UX.

A feature construction method for general object recognition

This paper presents a novel approach for object detection using a feature construction method called Evolution-COnstructed (ECO) features. Most other object recognition approaches rely on human experts to construct features. ECO features are automatically constructed by uniquely employing a standard genetic algorithm to discover series of transforms that are highly discriminative. Using ECO features provides several advantages over other object detection algorithms including: no need for a human expert to build feature sets or tune their parameters, ability to generate specialized feature sets for different objects, and no limitations to certain types of image sources. We show in our experiments that ECO features perform better or comparable with hand-crafted state-of-the-art object recognition algorithms. An analysis is given of ECO features which includes a visualization of ECO features and improvements made to the algorithm.

Improved Census Transforms for Resource-Optimized Stereo Vision

Real-time stereo vision has proven to be a useful technology with many applications. However, the computationally intensive nature of stereo vision algorithms makes real-time implementation difficult in resource-limited systems. The field-programmable gate array (FPGA) has proven to be very useful in the implementation of local stereo methods, yet the resource requirements can still be a significant challenge. This paper proposes a variety of sparse census transforms that dramatically reduce the resource requirements of census-based stereo systems while maintaining stereo correlation accuracy. This paper also proposes and analyzes a new class of census-like transforms, called the generalized census transforms. This new transform allows a variety of very sparse census-like stereo correlation algorithms to be implemented while demonstrating increased robustness and flexibility. The resource savings and performance of these transforms is demonstrated by the design and implementation of a parameterizable stereo system that can implement stereo correlation using any census transform. Several optimizations for typical FPGA-based correlation systems are also proposed. The resulting system is capable of running at over 500 MHz on a modern FPGA, resulting in a throughput of over 500 million input pixel pairs per second.