Peter Kubinec

Localization of moving edge with sub-pixel accuracy in 1-D images and its FPGA implementation

Contour detection is often utilized algorithm in picture processing. Sometimes is useful to localize edges with sub-pixel accuracy. In this paper we discuss about precise position of edge which is moving during the exposure time. To localize moving edge we define accumulative function and then we use three edge detection algorithms with sub-pixel accuracy in 1-D images: algorithm based on approximation of image function with function erf, method based on statistical moments and technique using spatial moments of the 1-D image. Our article presents results of simulations with noisy images, as accuracy criterion we choose the upper and lower 5% quantiles.

Improvement of short-term frequency stability of the Chip Scale Atomic Clock

Utilization of the Chip Scale Atomic Clock (CSAC) today gives great potential for wide range of strategic systems requiring superior long-term frequency stability. Compared to CSAC, an OCXO has many drawbacks, e.g. it has larger long-term frequency instabilities (aging rate), longer warm-up time and higher power consumption. On the other hand, the main disadvantage of the CSAC is the higher phase noise. In this paper we describe a method of improvement of the CSAC SA.45s short-term frequency stability (phase-noise) using an external OCXO (MTI 230-0827) syntonized to the CSAC. In the low power mode, the CSAC SA.45s consumes less than 20 mW of power; however it operates as simple TCXO and over a full operating temperature range, the frequency stability is limited to ±1 ppm. In the last part of the paper we introduce combined low power clock system that can achieve frequency stability ±0.01 ppm over a wide temperature range, while consuming similar power.

Sub-pixel localization of edges in JPEG images

Many methods for edge detection have been proposed in the last two-three decades. Sometimes is desirable to increase resolution of system for edge detection. There are two ways how to deal with this problem. Either a sensor with a greater number of pixels is used or method for edge detection with sub-pixel accuracy is applied. In some cases, only JPEG pictures are used as incoming data. In this paper we analyze how JPEG compression of picture changes the accuracy of edge localization. JPEG pictures with different compression quality were used to test three methods for edge localization in 1-D images with sub-pixel accuracy: method that approximates real 1-D picture with function erf (EFA) and edge detectors based on statistical moments (STM) or spatial moments (SPM) of the image function. This paper presents results of simulations of noiseless pictures and pictures with Gaussian noise. Lower and upper 5% quantiles are chosen as the accuracy criterion.

Dynamic phase shifting method utilized in the enhanced frequency controlled clock system

In this paper, we describe low-noise clock system based on combination of the chip-scale atomic clock CSAC SA.45s and the low-noise OCXO. We introduce here a new approach of frequency comparison resolution enhancement, which is based on continuous dynamic phase shifting of the evaluated signal. We have efficiently utilized fine-resolution phase shifter, which is embedded in DCM (Digital Clock Manager) blocks within widely used FPGAs from XILINX, Inc. The maximum residual frequency instabilities of the developed clock system were measured below ±0.02 ppb.

Detecting edges with sub-pixel precision in JPEG images

Edge localization is one of the mostly used procedures in image processing. In some applications it is desirable to improve edge detector precision to sub-pixel values. The input data for precise edge detector are usually in the form of uncompressed image. Sometimes, only JPEG images are available for processing. In our paper we deal with this situation, we focus on the question how lossy JPEG compression of image can change the precision of edge detection. We used JPEG images with different quality to test three methods for edge localization with accuracy at the sub-pixel level for 1-D images. First two algorithms are based on spatial and gray level moments of the image function. Third method used in our experiments approximates samples of real image with erf function. To compare these three methods we used noiseless and noisy JPEG images, two types of noise were used: Gaussian noise and ‘salt & pepper’. The standard deviation of edge position error was chosen as the precision criterion.

The critical radius of stimulation electrode related to heart activation

This article examines the dependence of stimulation current threshold on stimulation electrode radius and other cardiac tissue parameters. The dependence was evaluated on a homogeneous slab model of the heart wall, with local membrane properties determined by modified FitzHugh-Nagumo model. Simulation results reveal that stimulation current density threshold depends proportionally on diffusivity related to tissue conductivity and on membrane excitation threshold. It is also inversely proportional to stimulation electrode radius. The critical radius of the stimulation electrode for the given model parameters estimated to be 0.8 mm was compared with simulation results. Stimulation electrodes with smaller radius are ineffective in eliciting excitation in the cardiac tissue.

Enhanced clock based on the Chip Scale Atomic Clock and Dual-Mode Crystal Oscillator

In this paper we introduce enhanced low power clock system that is able to achieve frequency stability ±0.01 ppm over a wide temperature range, which is approximately 100 times better than the stability achievable with typical Temperature Compensated Crystal Oscillator (TCXO). The proposed clock system is based on Dual-Mode Crystal Oscillator (DMXO) and the Chip Scale Atomic Clock (CSAC). Power consumption of the clock system is comparable with the power consumption of the CSAC (Symmetricom SA.45s) in the low power mode. Typical power consumption of the CSAC is approximately 120 mW in a normal full accuracy mode (±0.01 ppb). In the low power mode, the CSAC operates as simple TCXO and consumes less than 20 mW of power; however over a wide temperature range, the frequency stability is limited to ±1 ppm.