36682359
Ultrasound speckle reduction by directional median filtering
This paper presents a novel adaptation of the median filter to the problem of boundary-preserving speckle reduction in ultrasonic imaging. The technique involves applying a bank of oriented one-dimensional median filters to the image, and retaining at each point the largest value among all the filter bank outputs. The result is an operator which suppresses speckle noise while retaining the structure of the image, particularly the thin bright streaks, which tend to occur along boundaries between tissue layers. The technique is compared to a block median filter and an algorithm discussed by Loupas et al. (1989), and is shown to be far superior to the median filter, and noticeably better than the Loupas filter at enhancing thin lines.
6177362
Line and boundary detection in speckle images
This paper considers the problem of detecting lines in speckle imagery, such as that produced by synthetic aperture radar (SAR) or ultrasound techniques. Using the physical principles that account for the speckle phenomenon, we derive the optimal detector for lines in fully developed speckle, and we compare the optimal detector to several suboptimal detection rules that are more computationally efficient. We show that when the noise is uncorrelated, a very simple suboptimal detection rule is nearly optimal, and that even in colored speckle, a related class of detectors can approach optimal performance. Finally, we also discuss the application of this technique to medical ultrasonic images, where the detection of tissue boundaries is considered as a problem of line detection.
1963957
Fast and efficient searches for effective optimization-phase sequences
It has long been known that a fixed ordering of optimization phases will not produce the best code for every application. One approach for addressing this phase-ordering problem is to use an evolutionary algorithm to search for a specific sequence of phases for each module or function. While such searches have been shown to produce more efficient code, the approach can be extremely slow because the application is compiled and possibly executed to evaluate each sequence's effectiveness. Consequently, evolutionary or iterative compilation schemes have been promoted for compilation systems targeting embedded applications where meeting strict constraints on execution time, code size, and power consumption is paramount and longer compilation times may be tolerated in the final stage of development, when an application is compiled one last time and embedded in a product. Unfortunately, even for small embedded applications, the search process can take many hours or even days making the approach less attractive to developers. In this paper, we describe two complementary general approaches for achieving faster searches for effective optimization sequences when using a genetic algorithm. The first approach reduces the search time by avoiding unnecessary executions of the application when possible. Results indicate search time reductions of 62%, on average, often reducing searches from hours to minutes. The second approach modifies the search so fewer generations are required to achieve the same results. Measurements show this approach decreases the average number of required generations by 59%. These improvements have the potential for making evolutionary compilation a viable choice for tuning embedded applications.
9647930
Cross-layer adaptive video coding to reduce energy on general-purpose processors
Traditionally, video encoders have been designed assuming that the more redundancy is removed, the better the encoder. However, on current laptops, reducing the compression efficiency of the video encoder by reducing the number of instructions used to perform compression can actually reduce the total energy used to encode and transmit a sequence. The correct balance between computation and compression efficiency may change dynamically, motivating adaptive encoders. At the same time, recent general-purpose processors also employ energy-driven adaptations. For best gains, the adaptations in the hardware and application layers must be coordinated. From a system design viewpoint, this coordination must happen through minimal, well-defined interfaces. This paper develops (1) an adaptive video encoder for general-purpose processors that trades computational complexity for compression efficiency to minimize total system energy, and (2) a method for determining the best configuration for such an encoder when running on a processor that is also adaptive. Our adaptive processor employs recent energy saving techniques of dynamic voltage and frequency scaling and architectural adaptation. Using a detailed simulator, we show that our cross-layer adaptive application algorithm reduces energy significantly, when employed on a fixed or adaptive processor.
2859083
A general joint source-channel matching method for wireless video transmission
With the rapid growth of multimedia content in wireless communication, there is an increasing demand for efficient image and video transmission systems. We present a joint source-channel matching scheme for wireless video transmission which jointly optimizes the source and channel coder to yield the optimal transmission quality while satisfying real-time delay and buffer constraints. We utilize a parametric model approach which avoids the necessity of having detailed a priori knowledge of the coders, thus making the scheme applicable to a wide variety of source and channel coder pairs. Simulations show that the scheme yields excellent results and works for several different types of source and channel coders.
12684339
Frequency-shift-invariant orthonormal wavelet packet representations
It is commonly known that wavelet expansions are very sensitive to translation of an input signal due to their dyadic structure. Without proper time alignment of the signal to the decomposition basis vectors, a compact expansion may be unattainable. Recently, work has been done to combat translation sensitivity by determining the best translation-invariant expansion of a signal with respect to a set of bases. However, the dyadic structure of wavelet expansions also results in frequency alignment sensitivity. In this work, we introduce a frequency-shifted wavelet packet library as well as an efficient best basis algorithm for determining the best signal representation among all frequency shifts of a signal.
14721450
Implementation of a block based neural branch predictor
This paper contributes to a dynamic branch predictor algorithm based on a perceptron in two directions: Firstly, a new block form of computation is introduced that reduces theoretically by half the combinational critical path for computing a prediction. Secondly, implementation in FPGA hardware is fully developed for quantitative comparison purposes. FPGA circuits for a one-cycle block predictor produces 1.7 faster clock rates than a direct implementation of the original perceptron predictor. This faster clock allows to realize predictions with longer history lengths for the same hardware budget.
18506033
Evaluation of voting systems
T he recent spate of security issues and allegations of " lost votes " in the U.S. demonstrates the inadequacy of the standards used to evaluate our election systems. The current standards (the FEC Voting Systems Standards) along with the revision being developed by IEEE 1583 (see the article by Deutsch and Berger in last month's Communications) are poor from another perspective: they establish a single pass/fail threshold for all systems, thereby eliminating incentives for existing suppliers to improve their products and rendering the market unattractive to new entrants. Moreover, they fail to precisely define the properties that should be required of a voting system. Instead, the standards rely on specific designs that are more than 15 years old. These legacy designs handicap promising new approaches, such as the various voter-verified printing schemes. New systems are unnecessarily burdened, while their substantial advantages go unrecognized. A set of well-defined properties would encourage the development and commercialization of better voting systems, especially when combined with objective ways to measure performance with respect to those properties. The overall result would then resemble the quantitative federal ratings for automobiles , where features such as vehicle safety and fuel efficiency form a basis for Consumer Reports-style comparative tables. Similarly, specific performance rating guidelines for different aspects of voting systems would provide meaningful metrics upon which system developers could compete. Decision makers, both regulatory and purchasing, would then be free to establish their own minimums for these metrics. Such a rating system can thus cleanly disentangle the development of the technical evaluation process from the various political and regulatory processes. asked the technical community for assistance in determining a new standard. This community is no stranger to the area of voting system properties and standards: a number of authors have tried to characterize requirements , and, in 2002, the Workshop on Election Standards and Technology addressed similar issues. The performance properties for voting systems might include the following: integrity of the votes (both voter verification, " I can check that my vote was captured correctly " and public verification, " anyone can check that all recorded votes were counted correctly "); ballot secrecy (both voter privacy and resistance to vote selling and coercion); robustness (including resistance to denial of service attacks); usability and accuracy (including access for the disabled); and transparency (both of mechanism and election data). The inherent differences in system architectures can be characterized …
38666741
On Matchings in Graphs
14105636
Experience with concurrent simulation
We have successfully implemented a concurrent simulator and we report initial speedup measurements for this technique. Our algorithm requires a shared-memory multiprocessor and is appropriate to any discrete-event simulation model. In addition, our algorithm places no constraints on minimum service times or the presence of cycles in the simulation model. Our experimental simulator runs on an Encore Multimax computer and is applicable to closed product-form queueing networks. We have observed speedups of 2.3 for a central-server queueing model using our simulator.
17285109
Concurrent operations on priority queues
Among the fastest priority queue implementations, skew heaps have properties that make them particularly suited to concurrent manipulation of shared queues. A concurrent version of the top down implementation of skew heaps can be produced from previously published sequential versions using almost mechanical transformations. This implementation requires O(log n) time to enqueue or dequeue an item, but it allows new operations to begin after only O(1) time on a MIMD machine. Thus, there is potential for significant concurrency when multiple processes share a queue. Applications to problems in graph theory and simulation are discussed in this article.