Fast acquisition system for digital holograms and image processing for three-dimensional display with data manipulation

A three-dimensional (3D) digital holographic display system with image processing is presented. By use of phase-shifting digital holography, we obtain the complex amplitude of a 3D object at a recording plane. Image processing techniques are introduced to improve the quality of the reconstructed 3D object or manipulate 3D objects for elimination and addition of information by modifying the complex amplitude. The results show that the information processing is effective in such manipulations of 3D objects. We also show a fast recording system of 3D objects based on phase-shifting digital holography for display with image processing. The acquisition of 3D object information at 500 Hz is demonstrated experimentally.     

Quantitative criteria for the design of dither-based quantizingsystems

This paper addresses the problem of designing quantizing systems employing dither. These are composed of a dither generator, a quantizer, a subtracting block and a low-pass digital filter. Quantitative criteria for choosing the parameters that influence the resolution and accuracy of the quantizing system are given, and the system performance is determined under worst, best, and average conditions for discrete binary, uniform, and Gaussian dither signals. The results presented also can be applied when the signal plus input-referred noise are quantized     

超声C扫描设备定量评价方法研究

超声C扫描系统在超声成像检测、缺陷识别等无损检测领域获得了广泛应用。但是,对C扫描图像的缺陷进行精确分析和表征一直是超声领域的难点之一。基于超声C扫描缺陷图像,给出了一种结合K-means聚类与Graham算法的图像特征参数定量估计方法,通过定量估计的参数能够有效地评价超声C扫描系统的检测质量。实验结果表明该方法能够有效描述标准圆形人工缺陷区域特征,有利于进一步评价超声C扫描设备。     

Application of Nonlinear Ultrasonic Measurement for Quality Assurance of Diffusion Bonds of Gamma Titanium Aluminum Alloy and Steel

A new nonlinear C-scan acoustic microscope (NCAM) has been developed and applied to inspect diffusion bonds of gamma titanium aluminum alloy–chromium molybdenum steel (γ TiAl–steel). The large mismatch of acoustic impedance gives strong ultrasonic reflection and masks a small signal from imperfections at the interface. However, NCAM detects indications of minute cracks or gaps, which are rarely observed by a conventional pulse–echo inspection method. Application of high-power ultrasound, with amplitude ten times greater than the conventional method, results in generation of second harmonic signals. All A-scope signals were stored in a computer, and frequency components were analyzed by fast Fourier transformation (FFT). As a result, no indication of fundamental frequency component was observed on a C-scan image, whereas clear indications of the second harmonic components were observed on the C-scan image. The minute cracks or gaps were confirmed at the indicated area by micrographic analysis following the inspection. Moreover, a quality assurance process for the γ TiAl–steel bond with a combination of linear and nonlinear ultrasonic responses is proposed.     

SUS304不锈钢板点焊接头超声成像及力学性能EI北大核心CSCD

利用超声波水浸聚焦入射法,对1mm厚的SUS304奥氏体不锈钢板点焊接头进行超声C扫描成像检测,研究不同焊接工艺参数下接头的C扫描图像特征,检测分析点焊的熔核直径,并对点焊接头进行拉伸-剪切实验。结果表明：超声波水浸聚焦C扫描成像法能够有效检测点焊熔核直径,为4．76～5．25mm,比金相实测值大2．6％～5．3％;随着焊接电流的增加（4-8kA）,接头的失效载荷均值从7116．8N增加到9707．1N,能量吸收均值从66．3J增加到196J,同时反映在C扫描图像上的熔核直径也从4．76mm增加到5．11mm;当焊接电流增加至9kA时,接头的失效载荷均值下降至6799．5N,能量吸收均值下降至41．3J,此时在C扫描图像上反映出飞溅、焊穿等典型的焊接缺陷。     

Time of flight diffraction imaging for double-probe technique

Due to rapid progress in microelectronics and computer technologies, the system evolving from analog to digital, and a programmable and flexible synthetic aperture focusing technique (SAFT) for the single-probe pulse-echo imaging technique of ultrasonic nondestructive testing (NDT) becomes feasible. The double-probe reflection technique usually is used to detect the nonhorizontal flaws in the ultrasonic NDT. Because there is an offset between the transmitter and receiver, the position and size of the flaw cannot be directly read from the image. Therefore, a digital signal processing (DSP) imaging method is proposed to process the ultrasonic image obtained by double-probe reflection technique. In the imaging, the signal is redistributed on an ellipsoid with the transmitter and receiver positions as focuses, and the traveltime sum for the echo from the ellipsoid to the focuses as the traveltime of signal. After redistributing all the signals, the useful signals can be constructively added in some point in which the reflected point is; otherwise, the signals will be destructively added. Therefore, the image resolution of the flaw can be improved and the position and size of the flaw can be estimated directly from the processed image. Based on the experimental results, the steep flaw (45°) cannot be detected by the pulse echo technique but can be detected by the double-probe method, and the double-probe B-scan image of 30° tilted crack is clearer than the pulse echo B-scan image     

航空锻件的超声成像技术

由于锻件表面不平整,且厚度不均,目前超声扫查系统普遍采用手工超声波探伤法检测锻件内部缺陷,无法应用标准的B扫描成像和C扫描成像,存在着效率低、探伤质量较差等不足之处。提出了以“厚度-灰度”超声检测为核心的基本成像过程,包括路径规划、全波采样、信号处理、波形分析和缺陷扫描成像等方法,并示例实现。该检测手段有助于促进航空锻件超声检测的智能化,提高检测的效率和可靠性。     

Imaging Hilbert-Transformed Ultrasonic Data

Automatic or semiautomatic ultrasonic nondestructive evaluation systems usually scan objects for defects by the B-scan or C-scan method. B-scan or C-scan images are used to evaluate the quality of the object. Complex ultrasonic images can be quickly and easily produced using the Hilbert transform method. Simultaneous real-time displays of the complex and C-scan images is also possible. Some characteristics of the echoes reflected from the defects do not show up clearly in C-scan images but can be easily observed in the complex ultrasonic images. Two specimens, one with a blind hole and the other with 16 blind holes, were scanned. The C-scan image and complex images were displayed simultaneously in order to compare the resolution of the images. The experimental results showed that the attributes of instantaneous amplitude can enhance the weak events, but the resolution of the image is apparently not improved. The advantage of the instantaneous phase and instantaneous frequency attributes are that they are very sensitive to the boundaries of the holes. Though the images may look noisy, they really offer an opportunity to show the holes that C-scan image cannot.     

基于掩蔽效应和抖动调制的盲水印方案

通过对信号处理领域抖动调制原理的分析,并结合人类视觉系统的掩蔽效应,提出了一个DCT 域盲水印模型。在MATLAB 仿真环境中,针对二值图像水印,实现了水印的预处理、嵌入、提取以及F 范数下水印检测。在水印嵌入过程中,通过自动调节量化步长改善了水印的透明性,水印检测时无需原始宿主图像,实现了盲检测,而且省略了反余弦变换过程,降低了算法复杂度。仿真实验表明,水印算法在JPEG 高强度压缩、剪切、各种噪声叠加以及多重水印等攻击下具有高鲁棒性。算法思想可应用于数字版权保护以及隐秘通讯等领域。     

An ultrasonic imaging system based on a new SAFT approach and a GPU beamformer

The design of newer ultrasonic imaging systems attempts to obtain low-cost, small-sized devices with reduced power consumption that are capable of reaching high frame rates with high image quality. In this regard, synthetic aperture techniques have been very useful. They reduce hardware requirements and accelerate information capture. However, the beamforming process is still very slow, limiting the overall speed of the system. Recently, general-purpose computing on graphics processing unit techniques have been proposed as a way to accelerate image composition. They provide excellent computing power with which a very large volume of data can easily and quickly be processed. This paper describes a new system architecture that merges both principles. Thus, using a minimum-redundancy synthetic aperture technique to acquire the signals (2R-SAFT), and a graphics processing unit as a beamformer, we have developed a new scanner with full dynamic focusing, both on emission and reception, that attains real-time imaging with very few resources.     

A study of the feature‐based digital image stabilization system

Abstract

This article presents a digital image stabilization scheme that uses image processing techniques to compensate for undesirable image jitter due to vehicle or platform vibration to obtain a stabilized image display. The developed digital image stabilization system is based on the image combination approach combined with advanced image selection, feature detection, feature matching and pre‐rotation processing to produce crisp images. Using the Sobel edge detector, we calculate the magnitude of edge response as the judgment criteria for image transformation. To demonstrate the validity of the proposed technique, experimental results are given for some synthetic images.     

Imaging Hilbert-Transformed Ultrasonic Data

Abstract

Automatic or semiautomatic ultrasonic nondestructive evaluation systems usually scan objects for defects by the B-scan or C-scan method. B-scan or C-scan images are used to evaluate the quality of the object. Complex ultrasonic images can be quickly and easily produced using the Hilbert transform method. Simultaneous real-time displays of the complex and C-scan images is also possible. Some characteristics of the echoes reflected from the defects do not show up clearly in C-scan images but can be easily observed in the complex ultrasonic images.

Two specimens, one with a blind hole and the other with 16 blind holes, were scanned. The C-scan image and complex images were displayed simultaneously in order to compare the resolution of the images. The experimental results showed that the attributes of instantaneous amplitude can enhance the weak events, but the resolution of the image is apparently not improved. The advantage of the instantaneous phase and instantaneous frequency attributes are that they are very sensitive to the boundaries of the holes. Though the images may look noisy, they really offer an opportunity to show the holes that C-scan image cannot.     

Computer-aided speckle pattern interferometry

An on-line computer system for measuring the deformation of a diffuse object with a speckle interferometer is presented. Methods for evaluating a speckle interferogram using digital image processing techniques are also discussed. The system consists of an interferometric optical setup and a computer-TV image processing facility. A speckle interferogram is generated arithmetically between two digitized speckle patterns before and after deformation of the object. The information about the deformation is extracted by two procedures in analyzing the interferogram: (a) automatic analysis using digital image processing techniques such as gray scale modification, linear spatial filtering, thresholding, and skeletoning; (b) man-machine interactive method for simple high-speed processing of the interferogram using a light pen. The determined fringe order numbers are interpolated and differentiated spatially to give strain, slope, and bending moment of the deformed object. Some examples of processed patterns are presented.     

Dither signal effects on the resolution of nonlinear quantizers

The consequences of dithering on nonlinear quantizers are analyzed. A model of the nonlinear quantizer is considered, and a model of the same quantizer with dither is proposed. By means of this approach, relationships are given for the total quantization error in the case of discrete binary, uniform, and Gaussian dither signals     

Quantitative characterization of multiple delaminations in laminated composites using the compton backscatter technique

A Compton X-ray backscatter technique was used to supplement ultrasonic pulse-echo C-scan imaging to quantitatively assess the impact damage in quasi-isotropic laminated composites which were impacted by a drop-weight tester. A Compton backscatter imaging system with a slit-type camera was developed to obtain a cross-sectional profile of impact-damaged laminated composites from the density variation of the cross-section. A nonlinear reconstruction model is introduced to overcome distortion of the Compton backscatter image due to attenuation effects, beam hardening, and irregular distributions of the fibers and the matrix in composites. An adaptive filter is used to reduce noise from many sources including quantum noise, especially when the SNR (signal-to-noise ratio) of the image is relatively low. Delaminations masked or distorted by the first few delaminations in an ultrasonic C-scan image are detected and characterized by the Compton back-scatter technique, both in width and location.     

Thermal Wave Imaging and Ultrasonic Characterization of Defects in Plasma Sprayed Coatings

One of the primary concerns in thermal spray coatings is bond integrity, as disbonds at the coating/ substrate interface could cause premature failure of a component. Current quality control test practices use empirical destructive mechanical test methods that do not provide direct correlation between test results and coating performance. Nondestructive evaluation (NDE) techniques used for bulk materials are not readily adaptable for the evaluation and characterization of coatings. This paper reports on the use of thermal wave imaging and ultrasonic immersion C-scan to characterize artificial disbonds in plasma spray coatings on steel substrates. This work demonstrates the capability of these techniques in characterizing total disbonds and presence of ' kissing bonds ” (where the interface surfaces are in such close contact that they give a appearance of a good bond). The effects of ultrasonic frequency on the C-scan images were also studied. A critical evaluation of both thermal wave imaging and ultrasonic techniques is presented along with their relative advantages and disadvantages.     

Reconstruction of a high-resolution image on a compound-eye image-capturing system

The authors have proposed an architecture for a compact image-capturing system called TOMBO (thin observation module by bound optics), which uses compound-eye imaging for a compact hardware configuration [Appl. Opt. 40, 1806 (2001)]. The captured compound image is decomposed into a set of unit images, then the pixels in the unit images are processed with digital processing to retrieve the target image. A new method for high-resolution image reconstruction, called a pixel rearrange method, is proposed. The relation between the target object and the captured signals is estimated and utilized to rearrange the original pixel information. Experimental results show the effectiveness of the proposed method. In the experimental TOMBO system, the resolution obtained is four times higher than that of the unit image that did not undergo reconstruction processing.     

Real-Time Hand-Held Ultrasound Medical-Imaging Device Based on a New Digital Quadrature Demodulation Processor

A fully hardware-based real-time digital wideband quadrature demodulation processor based on the Hilbert transform is proposed to process ultrasound radio frequency signals. The presented architecture combines 2 finite impulse response (FIR) filters to process in-phase and quadrature signals and includes a piecewise linear approximation architecture that performs the required square root operations. The proposed implementation enables flexibility to support different transducers with its ability to load on-the-fly different FIR filter coefficient sets. The complexity and accuracy of the demodulator processor are analyzed with simulated RF data; a normalized residual sum-of-squares cost function is used for comparison with the Matlab Hilbert function. Three implementations are integrated into a hand-held ultrasound system for experimental accuracy and performance evaluation. Real-time images were acquired from a reference phantom, demonstrating the feasibility of using the presented architecture to perform real-time digital quadrature demodulation of ultrasonic signal echoes. Experimental results show that the implementation, using only 2942 slices and 3 dedicated digital multipliers of a low-cost and low-power field-programmable gate array (FPGA) is accurate relative to a comparable software- based system; axial and lateral resolution of 1 mm and 2 mm, respectively, were obtained with a 12-mm piezoelectric transducer without postprocessing. Because the processing and sampling rates are the same, high-frequency ultrasound signals can be processed as well. For a 15-frame-per-second display, the hand-held ultrasonic imaging-processing core (FPGA, memory) requires only 45 mW (dynamic) when using a 5-MHz single-element piezoelectric transducer.     

A signal processing technique for measurement of multimode waveguide signals: An application to monitoring of reaction bonding in silicon nitride

A system that uses ultrasonic techniques to monitor the reaction bonding of silicon nitride is described. Reaction bonding of silicon nitride takes place in a nitrogen atmosphere at temperatures up to 1400°C. As with many sensors used in hostile environments, it is difficult to design the ultrasonic sensor in a way that provides optimal clarity of the signal. The sensing system must be designed within the physical limitations on access to the furnace. Ultrasonic probes that accommodate limited access to the silicon nitride sample have been designed and ultrasonic signals acquired during processing, albeit with significant noise and complexity in the signal. Signal processing techniques are used which make it possible to measure changes in phase velocity and attenuation during reaction bonding. Because of variability in the measured velocity and attenuation, the method of signal processing presented is applicable to those cases where it is not possible to redesign the probe for optimal clarity of the ultrasonic signal. This technique demonstrates the potential to perform measurements using signals that would have been considered intractable in the past. Data obtained from ultrasonic monitoring are suitable for use as input to a manufacturing process control feedback loop.     

用于堤坝检测的剖面声纳系统实验研究

针对水下堤坝安全检测，提出并设计实现了适合水下机器人等小平台为载体的可用于堤坝安全检测的高分辨率剖面声纳，系统通过获取被测堤坝内部的回波信号，由DSP构成的水下处理单元进行实时信号处理，从而可获得坝体内介质不连续的信息，并由水上分机进行堤坝内部剖面图像的重建及显示。通过水池和外场堤坝工程检测等应用实例，取得了良好的效果，验证了系统技术路线的可行性和性能的稳健性。