复合相位测量轮廓术研究

最近提出了一种只投影一幅复合光栅就可测量物体三维面形的复合相位测量轮廓术（CPMP）,其中复合光栅是由四个不同频率的载频分别调制与其方向垂直的四帧相移条纹并叠加形成的。本文对CPMP在理论及实验上进行了进一步的研究,并将之与相位测量轮廓术（PMP）进行了比较分析。结果表明对于高度连续变化的物体的动态测量,CPMP具有较大的应用前景。这对于复合相位测量轮廓术的进一步应用具有实际指导意义。     

光栅投影相位测量轮廓术在SMT锡膏三维检测中的应用研究

该文研究采用光栅投影相位测量轮廓术实现锡膏三维测量,选择合适的硬件设备搭建了锡膏三维测量实验系统,采用四步相移法进行锡膏三维测量.实验结果表明,该文所设计的锡膏三维测量实验系统采用光栅投影相位测量轮廓术能够重建锡膏三维信息,可以达到锡膏三维检测精度的要求.     

一种抑制相位测量轮廓术数字化误差的方法

在采用数字光投影仪(DLP)的相位测量轮廓术(PMP)系统中,DLP投射的光栅信号实质上是对正弦模拟光栅信号的数字化,数字化过程不可避免地影响PMP的精度,本文提出一种通过连续相移多周期的相位测量来抑制数字化过程引起的误差的新方法.实验结果表明,该方法对各种相移步数的PMP均有抑制数字化误差的能力,特别在五步相移轮廓术采用三周期相移时数字化误差抑制能力最佳.     

复合光栅投影的相位测量轮廓术

本文提出一种利用复合光栅进行相位测量轮廓术的方法,将三个有一定相移的条纹合成一个彩色光栅,用此光栅进行投影完成相位测量轮廓术.该方法具有单帧测量、无相移误差的优点.文中给出了理论分析和计算机模拟.     

DMD芯片在光栅投影三维轮廓测量技术中的应用

光栅投影成像法经常用于物体的非接触形状测量和形变测量。通过莫尔相移法,可以实时获得物体表面的等高轮廓线。但是在测量高速运动物体三维轮廓图像时误差较大,因为相移法需要拍摄几张经过相移后的变形光栅。在加入了DMD芯片后,可以在CCD的一帧图像时间内完成所有的相移后变形光栅的图像拍摄,有效地降低了高速运动物体三维轮廓成像的误差。     

基于FTP的动态相位展开方法的研究

在采用结构照明的光学三维传感方法中 ,相位展开是被测物体三维面形正确重建的关键步骤之一 ,也是一个难点。本文就动态傅里叶变换轮廓术中相位展开问题进行研究 ,对比分析了直接相位展开算法、基于相邻帧间相位差之间的相位展开算法和基于调制度排序的相位展开算法。解决了基于傅立叶变换轮廓术的动态三维测量中相位展开问题 ,特别是孤立区域的相位展开。为动态傅立叶变换轮廓术的在冲击和爆轰过程中应用 ,提供了理论基础。文中给出了详细的理论分析和计算机模拟     

三维形貌测量中基于错位条纹的解相位方法

针对光栅投影法三维测量中的相位展开问题,提出一种用四步相移法求取折叠相位的解决方案.在相移图中,提取带有90°相移的4个单周期正弦条纹,对4个单周期正弦条纹进行编码组合,生成错位条纹.测量中,摄像机获取的错位条纹图像和相移图像按灰度值相减,得到4幅条纹差图,提取各差图中灰度值为零的条纹,依此确定错位条纹图像中各个单周期...     

应用三步相移法的三维面形测量

提出一种基于三步非定步相移的三维面形测量方法。首先将投影仪投出的光栅进行预校正,保证投到参考面的条纹为标准的正弦条纹。测量时,由投影仪投影三幅等相移量的光栅到待测物体表面,CCD相机对应采集三帧变形条纹图,由相位计算模型提取相位。最后通过高度映射公式恢复待测物体的三维面形。该方法有较好的抗噪性能,在噪声较大情况下,仍能进行测量,为动态在线测量奠定了基础。模拟及初步实验均验证了该方法的可行性。     

基于“2+1”相移算法的正交复合光三维测量方法

提出一种基于"2+1"相移算法的正交复合光栅投影三维测量方法。用2帧相移量相差为π/2的正弦光栅加1帧背景光代替传统正交复合光栅相位测量轮廓术(OCGPMP)中3帧等相移正弦光栅,并将受背景项调制的载波频谱放在受2帧正弦相移光栅调制的载波频谱中间,由于背景项只有直流分量对载波的调制,与相邻调制载波交流调制成分不会发生频谱混叠,从而拓展了两相移光栅的载波频谱宽度,有效减少了频谱混叠,降低了相位测量误差。计算机仿真和实验结果表明,该方法将测量精度提高到传统OCGPMP的1.74倍。     

三维面形测量中结构光场的非线性分析和校正

在基于数字投影的结构光三维面形测量中,相位测量轮廓术和傅立叶变换轮廓术是两种重要的方法,但由于受到CCD探测器光电响应的非线性、投影伽马的非线性以及环境光照等因素的影响,引起投影条纹正弦性的下降,最终导致相位和重建面形的误差.本文提出一种实用的结构光场生成方法,有效改善了结构光场的正弦性.从成像系统出发,通过理论推导,...     

一种虚条纹相移算法在结构光三维测量中的应用

相移法测量三维轮廓具有原理简单、计算速度快等优点。然而此法至少需要采集3幅以上干涉图像,且在实际操作中由于很难产生绝对的相移量而给测量带来误差。应用虚条纹相移算法只需要采集一幅图像便可恢复出物体的三维轮廓,其基本手段是先获得原始图像的基频值f0,根据此频率通过计算机生成具有π/2相位差的两虚条纹图像cos(2πf0x)和sin(2πf0x)。然后分别与原始图像进行混叠,将混叠后得到的图像进行低通滤波,再结合相移算法恢复出原始物体的三维轮廓。此法既保持了相移法本身的优点又解决了其需要采集多幅图像以及无法实现绝对相移的问题。另外低通滤波本身的去噪特性给在非陡变物体测量中高频噪声的去除带来方便。     

基于FTP的三维轮廓测量方法及实验

为了快速、高精确度地得到物体的三维轮廓信息,在此利用傅里叶变换轮廓术,将被测物体置于光栅投影下,采集变形光栅图像,根据被测物体表面的高度与相位差之间的映射关系,通过在计算机中与参考光栅原像的比较分析,以获得被测物体的三维轮廓信息。实验中搭建了由LCD投影仪、CCD摄像机、图像采集卡和光学导轨等组成的光栅投影测量系统的硬件平台,提出了用1台计算机同时控制投影和采集处理光栅图像,根据映射关系在多次实验中不断修改优化测量参数,做到既不影响视场范围,又保证较高的测量精度,并给出了由计算机重建后较好的三维轮廓图像精度及其实验的测量误差分析。     

2—D Fourier Transform Method for Optical Measurement of 3—D Surface

A emthod of 2-D Fourier transform used in 3-D surface profilometry is proposed,analyzed and compared with 1-D Fourier transform method in theory and practical measuring result.It was proved that the 2-D Fourier transform method has more advantages over 1-D Fourier transform methodd in biggest crook-rate limits,accuracy and sensitivity of measuring.Styudy on measuring object surface details with large crook-rate changing accurately used new higher-power index low-pass filter of spatial frequency domain.A new method of automatic produced reference grating image and error-correcting is proposed.One undeform row of deform grating image is used to extend a complete reference grating image,and some error-correcting method is used to process the result to get accurate surface shape and the deflection of reference surface normal line deviated from the axle of camera.By this new method,one deform rectangle grating image is only used to get the 3-D shape accurately.     

基于ADV202的遥感图像实时压缩系统设计

提出了以JPEG2000图像压缩标准作为压缩算法,采用JPEG2000专用编解码芯片ADV202来实现遥感图像实时压缩系统的方案.该方案可以满足遥感图像压缩系统对实时性、低失真以及高压缩比的要求.测试结果表明,该系统工作稳定可靠,能够满足遥感图像压缩系统实时性的要求,图像压缩效果令人满意.     

基于傅里叶变换去隔行图像的动态3维面形测量

为了解决动态面形测量中隔行扫描CCD相机记录动态物体表面变形条纹图像存在缺陷的问题,提出了傅里叶变换去隔行算法,即把隔行扫描CCD获取动态物体的错位模糊帧图像分成两个单场图像,分别对每一单场图像进行傅里叶变换去隔行处理,再利用条纹分析法重建对应时刻的3维面形。理论分析得出单场傅里叶变换去隔行图像与对应的准确满帧图像相同的结论。结果表明,该方法可以很好地恢复条纹和重建物体,且简单实用,可用于基于空间相位检测、相位测量轮廓术、傅里叶变换轮廓术等条纹分析方法的动态物体3维测量中。     

基于KL与小波联合变换的多光谱图像压缩

鉴于卫星拍摄的遥感图像的空间分辨率和光谱分辨率越来越高,在一些应用中,常会对多光谱图像进行压缩。为了提高多光谱图像的压缩质量,提出了联合相位相关和仿射变换的图像配准方法,有效提高了图像谱段之间的相关性。针对多光谱图像压缩,提出了结合Karhunen-Love,KL变换去除谱间相关和嵌入式二维小波编码方法。相比JPEG2000谱段图像独立压缩方法,提出方法解压图像的Peak Signal to Noise Ratio,PSNR值平均提高2.1 dB。实验结果表明:所提出的方法能在相同的压缩率下获得比JPEG2000谱段图像独立压缩方法更好的图像质量。     

Artifact reduction in JPEG2000 compressed images at low bit-rate using mathematical morphology filtering

JPEG2000 is known as an efficient standard to encode images. However, at very low bit-rates, artifacts or distortions can be observed in decoded images. In order to improve the visual quality of decoded images and make them perceptually acceptable, we propose in this work a new preprocessing scheme. This scheme consists in preprocessing the image to be encoded using a nonlinear filtering, considered as a prior phase to JPEG 2000 compression. More specifically, the input image is decomposed into low- and high-frequency sub-images using morphological filtering. Afterward, each sub-image is compressed using JPEG2000, by assigning different bit-rates to each sub-image. To evaluate the quality of the reconstructed image, two different metrics have been used, namely (a) peak signal to noise ratio, to evaluate the visual quality of the low-frequency sub-image, and (b) structural similarity index measure, to evaluate the visual quality of the high-frequency sub-image. Based on the reconstructed images, experimental results show that, at low bit-rates, the proposed scheme provides better visual quality compared to a direct use of JPEG2000 (excluding any preprocessing).     

An effective and efficient compression algorithm for ECG signals with irregular periods

This paper presents an effective and efficient preprocessing algorithm for two-dimensional (2-D) electrocardiogram (ECG) compression to better compress irregular ECG signals by exploiting their inter- and intra-beat correlations. To better reveal the correlation structure, we first convert the ECG signal into a proper 2-D representation, or image. This involves a few steps including QRS detection and alignment, period sorting, and length equalization. The resulting 2-D ECG representation is then ready to be compressed by an appropriate image compression algorithm. We choose the state-of-the-art JPEG2000 for its high efficiency and flexibility. In this way, the proposed algorithm is shown to outperform some existing arts in the literature by simultaneously achieving high compression ratio (CR), low percent root mean squared difference (PRD), low maximum error (MaxErr), and low standard derivation of errors (StdErr). In particular, because the proposed period sorting method rearranges the detected heartbeats into a smoother image that is easier to compress, this algorithm is insensitive to irregular ECG periods. Thus either the irregular ECG signals or the QRS false-detection cases can be better compressed. This is a significant improvement over existing 2-D ECG compression methods. Moreover, this algorithm is not tied exclusively to JPEG2000. It can also be combined with other 2-D preprocessing methods or appropriate codecs to enhance the compression performance in irregular ECG cases.     

Ultrasound beamforming using compressed data

The rapid advancements in electronics technologies have made software-based beamformers for ultrasound array imaging feasible, thus facilitating the rapid development of high-performance and potentially low-cost systems. However, one challenge to realizing a fully software-based system is transferring data from the analog front end to the software back end at rates of up to a few gigabits per second. This study investigated the use of data compression to reduce the data transfer requirements and optimize the associated trade-off with beamforming quality. JPEG and JPEG2000 compression techniques were adopted. The acoustic data of a line phantom were acquired with a 128-channel array transducer at a center frequency of 3.5 MHz, and the acoustic data of a cyst phantom were acquired with a 64-channel array transducer at a center frequency of 3.33 MHz. The receive-channel data associated with each transmit event are separated into 8 × 8 blocks and several tiles before JPEG and JPEG2000 data compression is applied, respectively. In one scheme, the compression was applied to raw RF data, while in another only the amplitude of baseband data was compressed. The maximum compression ratio of RF data compression to produce an average error of lower than 5 dB was 15 with JPEG compression and 20 with JPEG2000 compression. The image quality is higher with baseband amplitude data compression than with RF data compression; although the maximum overall compression ratio (compared with the original RF data size), which was limited by the data size of uncompressed phase data, was lower than 12, the average error in this case was lower than 1 dB when the compression ratio was lower than 8.     

A new phase calculation method in 3D optical phase measurement by combining PSP with IFTP

The improved Fourier transform profilometry(IFTP) and phase-shifting profilometry(PSP) are typical phase calculation methods in 3D optical phase measurement.The PSP has a high ability of anti-noise,but the projective grating needs a spatial frequency as high as possible,so that the wrapped phase results in superposition due to undersampling.IFTP expands measuring range,but the loss of high frequency component in the wrapped phase would cause a fast change of phase.Considering the advantages and disadvantage...