Due to environmental illumination and other factors, actual shearing interference image used to measure the rotation angle contains high-frequency speckle noises. According to the characteristics of shearing interference images, a low-pass filter based on homomorphic filtering principle is selected to filter these images. The desired filtering result can be achieved by adjusting the filter parameters such as the cutoff frequency radius and the order of the filter. The Hilditch thinning algorithm is applied to extract the center of the fringes to calculate the spacing between neighbor fringes. The accuracy of the algorithm is verified by the actual and simulation experiments with the error of fringe spacing detection less than 0.01%.
Advanced low frequency vibration calibration is imperative required as the wide applications of low frequency accelerometers. Low frequency calibration is commonly realized by the Earth’s gravity method or the laser interferometry. However, affected by the limited stroke of the standard vibration shaker, the calibration precision of laser interferometry at very low frequency is usually not ideal. Although the Earth’s gravity method can avoid this low calibration precision at very low frequency, its calibration frequency usually <5 Hz due to the influence of rotator centripetal acceleration. In this paper, the Earth’s gravity method mentioned in ISO 16063-16 is improved by using an effective image feature detection method. This method detects the angel between Earth’s gravity field direction and acceleration sensitivity axis direction to improve the Earth’s gravity static calibration accuracy.
Each band image contains the most obvious tissue feature according to the optical characteristics of different tissues in different specific bands for multispectral medical images. In this paper, the tissues were segmented by their spectral information at each multispectral medical images. Four Local Binary Patter descriptors were constructed to extract blood vessels based on the gray difference between the blood vessels and their neighbors. The segmented tissue in each band image was merged to a clear image.
Phase response is an essential parameter of vibration sensors in primary vibration calibration, heterodyne interferometer was usually used to obtain this parameter. To reduce sampling rate of heterodyne interferometer signal and sampling number, analog mixer and lowpass filter are used to down-convert the interferometer signal. However, the using of analog devices will introduce additional phase delay for the measurement of the phase response, it leads to the measurement by the calibration is unreliable. A novel correction of phase delay method was proposed to precisely measure the phase response of the vibration sensors. Experiment results show the performance of the proposed correction method.