Quantum Point Cloud and its Compression

Quantum computation is becoming an important and effective tool to overcome the high real-time computational requirements of classical digital image processing. The quantum representations of two-dimensional images have been a lot of achievements. However, there are only few methods to express a three-dimensional image by quantum representation. In this paper, a three-dimensional quantum representation for digital images — quantum point cloud is proposed. Moreover, a lossy compression method is used to reduce the complexity of preparation.     

Watermarking of three-dimensional objects by digital holography

We present an optical method for information watermarking of three-dimensional (3D) objects by digital holography. A hidden image is embedded by double phase encoding in a phase-shift digital hologram of the 3D object. We decode the watermarked hologram to reconstruct the hidden image and the 3D object. We use either the entire hologram or a part of it to decode the hidden image. Experiments are presented to illustrate the ability to recover both the 3D object and the decoded hidden image. Digital holograms of the 3D object are obtained by optical experiments. The watermarking process, 3D object reconstruction, and hidden image recovery are performed digitally. To the best of our knowledge, this is the first report of 3D object watermarking by use of a phase encoding technique and digital holography.     

Calculating depth maps from digital holograms using stereo disparity

Depth extraction is an important aspect of three-dimensional (3D) image processing with digital holograms and an essential step in extended focus imaging and metrology. All available depth extraction techniques with macroscopic objects are based on variance; however, the effectiveness of this is object dependent. We propose to use disparity between corresponding points in intensity reconstructions to determine depth. Our method requires a single hologram of a scene, from which we reconstruct two different perspectives. In the reconstruction the phase information is not needed, which makes this method useful for in-line digital holography. To our knowledge disparity based 3D image processing has never been proposed before for digital holography.     

数字图像识别在混合油类三维荧光光谱分析中的应用

海上溢油已成为全球环境污染的重要问题之一,溢油严重破坏了海洋生态的平衡,并导致人类健康受到危害。因此,研究高效的溢油检测方法对保护海洋生态环境具有重要意义。三维荧光光谱技术因能获得溢油的“指纹”图谱而成为溢油鉴别领域的有效分析手段,其与平行因子分析算法相结合获得了良好的溢油鉴别效果。但平行因子算法在使用过程中需要确定不同石油产品本身所适用的浓度范围,且其对预估计组分数敏感,组分数选择是否准确直接影响最终定性定量结果,这些问题都会对油类检测造成使用上的限制。油类组分极为复杂,其中各组分间不存在统一的线性浓度范围,其相互之间还受到荧光猝灭效应的影响。直接对未经稀释的油类样本进行光谱数据采集,所获得的三维荧光光谱会因样本中组分的种类及其含量不同而存在较大差异,导致对三维荧光光谱数据进行解析的平行因子分析算法不再适用。但组分的种类及含量相近的油样其光谱特征相似度较高,并且随着特定组分及其含量的改变,其光谱形状的变化规律也较为明显。基于此,将三维荧光光谱和数字图像识别相结合,提出一种针对混合油类样本的辨识方法。首先,利用五种矿物油（汽油、柴油、航空煤油、机油和润滑油）配制三类混合油样本,其中每类混合油是用其中两种不同矿物油以不同体积比直接混合配制而成;然后利用FS920荧光光谱仪获取样本的三维荧光光谱数据,并对该数据进行求导及灰度化预处理,进而得到三维荧光导数光谱灰度图;其次提取样本三维荧光导数光谱灰度图的颜色、纹理和形状等数字图像特征;最后,通过Fisher判别分析建立样本的分类模型,采用逐步回归建立混合油样本各组分相对体积的定量模型。分类模型对三类混合油样本的分类及识别效果良好。所建立的定量模型的线性相关性R大于0.99,显著性检验p值小于0.05。研究结果表明,三维荧光光谱的数字图像特征可以被本文所述方法有效提取并用于对油类样本的定性定量分析。该研究为海面溢油检测提供了一种简单、可靠的识别方法。     

一种三维全息图的数字化实现方法

提出一种实现三维显示的新方法,从两步法彩虹全息基本原理出发,通过分区域分幅的方式对多视角图形的波前进行数字化编码,获得夫琅和费光场分布,在位相型硅基液晶空间光调制器上按视角顺序输入该信息,利用透镜的傅里叶变换特性再现多视角子图像,干涉法逐区域拼接获得完整三维图像.最后通过实验获得了三维图像样品,验证了该方法.本方法可成为三维显示的重要技术手段.     

CW激光辐照薄板热力响应全场测量

实验研究了CW激光辐照铝合金薄板的热力响应过程,利用三维数字图像相关技术(3D-DIC)结合红外测温系统对整个过程的变形场和温度场实现了全场实时测量。分析了入射激光功率对变形场和温度场的影响,发现变形和温度均随入射激光功率线性增长。建立了三维有限元模型对实验过程进行模拟,模拟结果与实验结果吻合较好,验证了有限元模型的可靠性。3D-DIC结合红外测温系统可以很好地对激光破坏试验中的靶体变形场和温度场进行实时测量,是一种很有效的实验测量手段。     

Precision verification of a simplified three-dimensional DIC method

The traditional three-dimensional (3D) digital image measurement technique uses at least two images captured from different positions to determine the 3D coordinate of an object. One disadvantage of this method is that the mechanical and optical properties of the image capture devices are not fully identical, and the calibration procedure is quite complicated. This paper introduces a simplified 3D digital image correlation (DIC) method, in which only one image capture device is used. The theoretical measurement error equation is derived and experimentally verified. Experimental results show that distortion correction plays an important role in the improvement of measurement precision. After a radial distortion correction, the measurement precision of the object distance can reach 0.0043%. The optimal camera spacing should be set from 1/50 to 1/30 of the object distance, to obtain a satisfactory precision.     

Digital particle holographic system for measurements of spray field characteristics

A digital particle holographic system for measurements of spray fields is presented. A double exposure hologram recording system with a synchronization system for time control is established, resulting in digital holograms that can be quickly recorded. To process recorded holograms, the correlation coefficient method is used for focal plane determination of particles. To remove noise and improve the quality of holograms and reconstructed images, a Wiener filter is adopted. The two-threshold and image segmentation methods are used for binary image transformation. For particle pairing, the match probability method is adopted. The proposed system is applied to a spray field, and three-dimensional velocities and sizes of spray droplets are measured. Measurement results from the digital holographic system are compared to those made by laser instruments, which prove the feasibility of the proposed in-line digital particle holographic system as a good measurement tool for spray droplets.     

数字全息显微术中重建物场波前的相位校正

数字全息显微术克服了传统光学显微术无法直接提取样品相位信息的缺点,可以对活体细胞组织等相位型生物样品进行定量测量和有效观察。但在数字全息显微成像过程中,像场弯曲会对再现像相位分布的测量和观察产生影响。提出一种采用相位相减来校正数字全息再现像像场弯曲的方法。通过在样品加入前后两次拍摄全息图,并对数值重建像分别进行去包裹运算再令其相减,即可实现对像场弯曲的有效校正,对蝉翼和大蒜表皮细胞等相位型物体进行测量,并采用数值校正和相位相减两种方法对像场弯曲进行校正。与现有的数值校正方法相比,利用相位相减获得样品三维相位信息的方法更为简单、可靠,是校正像数字全息再现场弯曲的有效方法。     

Three-dimensional image fusion by use of multiwavelength digital holography

We present three-dimensional (3D) image fusion by use of digital holography. We demonstrate experimentally that, through the image fusion technique with multiresolution wavelet decomposition, it is possible to increase the details and contrast of 3D reconstructed images obtained by multiwavelength digital holography. Although there is substantial activity in the fields of image fusion and holography, to the best of our knowledge, this is the first report of 3D image fusion by use of digital holography.     

多光束数字全息的研究

提出了一种多光束数字全息技术来解决当利用菲涅耳数字全息对全息图进行再现时,物体的多个表面无法同时再现得明亮、清晰.该方法是记录时采用多光束照明同一物体的多个表面,增强CCD上接收到的物体侧表面散射光的强度.实验成功地同时再现了物体的多个表面.同时,为了减弱再现像的散斑噪声,采用双线性插值和中值滤波处理图像,获得了质量高的三维物体的再现图像.     

Effect of intensity quantization level in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) enables the instantaneous recording of three-dimensional fields. The three-dimensional field can be reconstructed using a computer by numerical scalar wave propagation. In PPSDH, we record a space-division multiplexed hologram that includes the required phase retardation in the spatial distribution of the reference wave and then interpolate the data at blanked pixels for each phase retardation to obtain the complex amplitude distribution of an object wave. The recorded quality of the multiplexed hologram influences the reconstruction quality. In this study, we investigate the effect of the intensity quantization of a multiplexed hologram on the reconstruction quality. We compare the influence of intensity quantization in PPSDH with that in the conventional phase-shifting method. Random noise is also added to the multiplexed hologram. The required intensity quantization level is helpful for selecting a digital image sensor.     

Securing complex and multi-plane data in a lens-less digital holographic information system that uses position-phase-shifting geometry

A digital holographic information system can process complex three-dimensional (3-D) object information. We demonstrate a scheme for securing complex and 3-D information in the context of in-line digital holography. Double random phase encoding in the free-space propagation domain of light is used to secure the complex information. Encrypted in-line digital holograms are recorded using the position-phase-shifting method. The encrypted complex image at the CCD recording plane is retrieved from the real-valued digital holograms, and is used for decryption. The robustness of the method has also been studied for various securing keys used in the method against blind decryption. A layer-by-layer information retrieval from the encrypted digital hologram is also discussed. The method can also be used to secure digital complex information in a virtual optics modality using holographic principles.     

Fast algebra algorithm of shape-from-shading with specular reflectance

Shape-from-shading (SFS) is to reconstruct three-dimensional (3D) shape from a single gray image, which is an important problem in computer vision. We propose a novel SFS method based on hybrid reflection model which contains both diffuse reflectance and specular reflectance. The intensity gradient of image is in the direction that the shape of urface changes most, so we use directional derivative of the reflectance map as parts of objective function. When discrete characteristic of digital images is considered, finite difference approximates differential operator. So the reflectance map equation described by a partial differential equation (PDE) turns into an algebra equation about the nknown surface height correspondingly. Using iterative numeric computation, a new SFS method is gained. Experiments on synthesis and real images show that the proposed SFS method is accurate and fast.     

Optical-path-length-shifting color digital holography

We propose an in-line color digital holography that can suppress a 0th-order diffraction image and a conjugate image. This technique reconstructs the image of an object from two holograms that are formed at two different distances from the object for each primary color. We numerically simulated the proposed technique and confirmed that it enabled the reconstruction of higher-quality images of an object than the Fresnel transform alone, which is the simplest reconstruction algorithm in digital holography. The effectiveness of the proposed technique was also quantitatively shown by evaluating the reconstructed images using root-mean-square errors. Thus, it was confirmed that the proposed technique was capable of recording and reconstructing both three-dimensional information and color information of an object.     

Cross-talk free image encryption and watermarking by digital holography and random composition

In previous image watermarking methods an encoded host image and a watermark image are usually directly added, consequently the two images have cross-talk in the decryption step. To eliminate this effect, we propose a novel method based on digital holography, in which all the image pixels of the two sets of holograms resulted from two hidden images are rearranged and integrated into one set of composite holograms with a random scattering matrix (RSM). In decryption the use of this matrix can ensure the exact retrieval of each hologram, and then the perfect reconstruction of each image without cross-talk noise can be achieved. The feasibility of this method and its robustness against occlusion and additional noise are verified by computer simulations with phase-shifting interferometry and double random-phase encoding technique. This approach is suitable for both two- and three-dimensional images, and the additional RSM as a key provides a much higher level of security.     

Projection-type moiré topography with frequency modulation technique using liquid crystal digital gratings

A projection-type moiré topography that uses a frequency modulation technique with two liquid crystal digital gratings (LCDGs) is proposed. In this method, moiré contours are filtered to remove the image of the original grating from the moiré contours by moving the image created by the LCDGs. The frequency modulation technique can be used to analyze the fringe of step heights or other separate areas by modulating the fringe interval. The experimental results showed the possibility of measuring three-dimensional shapes and step heights.     

微细铣刀位姿同轴全息重建方法

微细铣刀在主轴上存在装夹偏角时,会加剧刀刃磨损,降低刀具使用寿命.为了精确观测微细铣刀在机倾斜状态,提出了基于景深的微细铣刀三维位姿重建方法.利用激光同轴数字全息实验装置得到微细铣刀全息图,并通过菲涅尔再现算法获得再现像.在再现像中提取刀具边缘点作为关键点,采用小波变换局部方差算子求出关键点的聚焦程度,确定铣刀对应的轴...     

Laser-based volumetric colour-coded three-dimensional particle velocimetry

We present a method of three-dimensional particle velocimetry with a single digital colour camera using multiple colour illumination to encode image depth over a large volume. A copper vapour laser operating at 511 nm is used to pump an optical fibre producing a multiple-wavelength beam via multiple order stimulated Raman scattering. The beam is dispersed and formed into a stack of thin sheets to illuminate a volume of space. The spatial co-ordinates of particles imaged within the illuminated volume are obtained from their imaged x,y positions with depth discerned from particle hue (set by the wavelength of illumination). The method exhibits an RMS depth error of 3% in relation to the thickness of the illuminated region. This paper reports a proof-of-principle of three-dimensional particle imaging using a multi-wavelength laser source with a view to 3D-3C particle velocimetry.     

Three-dimensional integral imaging with large depth of focus by use of real and virtual image fields

We present an integral imaging method to enhance the depth of a three-dimensional image by displaying it throughout real and virtual image fields. When the product of depth and resolution square of the displayed three-dimensional image is used as a figure of merit in integral imaging systems, our method can maximize this merit especially when three-dimensional images with large depth of focus are displayed. The feasibility of our method is experimentally demonstrated by generation of elemental images by a computer.