共查询到20条相似文献,搜索用时 15 毫秒
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Imaging by two concentric spheres is studied by geometrical method. As the system is symmetric with respect to the common center of curvature, peripheral aberrations, namely coma, astigmatism, and distortion, do not appear. The imaging surface is a sphere that shares the center of curvature with two mirrors. As we solve the zero spherical aberration condition for imaging of an object at infinite distance, the golden section number appears as the ratio of the distance between two mirrors and the radius of the primary mirror. For imaging of an object at finite distance, we have to increase the radius of the second mirror. This system also has no peripheral aberrations. Making the object surface spherical, we can obtain a flat image surface. As the spherical aberration is zero in the original system, spherical aberration, coma, and astigmatism remain zero when the object surface is curved. 相似文献
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莫尔测量法被广泛用于各类流场的结构显示和关键参量测量中,关于相位物体在光路中的放置位置已有不同的报道,针对该问题进行了理论和实验研究。理论分析表明,当相位物体放置于2个光栅前时,偏移量和相位主要取决于2个光栅之间的距离,偏折角取决于相位物体引起的相位扰动与2个光栅之间的间距的比值;而当相位物体放置于2个光栅之间时,偏移量和相位主要取决于相位物体到后面一个光栅之间的距离,偏折角则取决于相位物体引起的相位扰动与其到后面一个光栅之间的距离的比值。为了验证理论结果的正确性和合理性,实验中选取燃烧蜡烛火焰作为对象,对比发现在两种情况下,只要相应的距离选取适当,则相位物体的位置并不影响实验中重建的相位和偏折角等结果。相关研究成果可为莫尔测量法更好地用于各类流场的检测提供一定的参考。 相似文献
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Shih-Heng TungMing-Hsiang Shih 《Optics and Lasers in Engineering》2011,49(7):937-945
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. 相似文献
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Fast Computation of Fresnel Holograms Employing Difference 总被引:1,自引:0,他引:1
Hiroshi Yoshikawa 《Optical Review》2001,8(5):331-335
We propose an approximation method that can calculate the Fresnel hologram 16 times faster than the conventional method. To compute the hologram, an object is assumed to be a collection of self-illuminated points and the fringes from each object point are superposed. The distance between object point and sampling point on the hologram is used to obtain the phase of the light. Since a sampled hologram usually has small pixel intervals, the difference of the distance values between adjacent pixels is also small and its n-th order difference can be assumed to be constant. Therefore, the distance value at a certain pixel can be obtained from its neighbor with simple additions. The distance error can be reduced less that one wavelength with practical parameters. A hologram, which has a horizontal parallax only, 1.3 Mega-pixels and 1,000 object points, can be calculated in less than one second with a personal computer. 相似文献
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While an object is approaching a particular location, we can make an estimate of the time when the object will arrive at that
location. A geometric model predicts that the estimate of time-to-contact (TTC) is greatly improved by using the rate of change
of visual direction of the object when the object is moving with a slow velocity toward a point of nearest approach at a distance
far from the observer. It has been shown that pursuit eye movements provide the rate of change of visual direction of an approaching
object. We conducted psychophysical experiments, and compared TTC estimates during pursuit eye movements to those during fixation.
We found that the differences in TTC estimates between fixation and pursuit show a qualitatively similar pattern to the geometric
model prediction. However, the results also show that the magnitudes of the TTC estimation errors are greater than the theoretical
values from the geometric model, indicating that the human visual system has a perceptual bias in estimating TTC. These results
suggest that the human visual system estimates TTC during pursuit eye movements in a different way from the geometric model,
although the effect of these eye movements on TTC estimates in human performance is qualitatively consistent with the model
prediction. 相似文献
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Stephen S. WelshJohannes Courtial 《Optics Communications》2012,285(24):4802-4806
Pairs of planar ray-rotating windows can rotate the view through different angles. The angle by which an object appears rotated is independent of the distance of the object behind the windows. The observer distance has to be chosen such that the observer is in a principal plane of this combination of windows. 相似文献
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相对于传统水下光电成像,水下激光扫描成像系统可以获得更远的作用距离和更好的图像质量.基于激光同步扫描技术,提出了水下运动目标的测距方法,并对测距误差进行了定量分析,为水下目标测距提供了一个新的途径.其中单探测头水下激光扫描测距方法能对合作目标进行测距,在近距离时具有较高的测距精度,双探测头水下激光扫描测距方法能对非合作... 相似文献
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运用光学系统的近轴成像公式,推导出微分形式的物面位于任意位置时热补偿的通用条件,包括薄单透镜、密接薄透镜组和分离薄透镜组等不同情况。推导过程中假设物面位置不随温度发生变化,并且忽略分离薄透镜组中各组分上光线入射高度随温度的变化。利用推导的条件建立了像距的归一化温度变化率与各透镜光热膨胀系数之间的关系,指出所得到的条件具有更加普遍的意义,能够指导机械和伺服控制系统的工程设计,并且在物面位于无穷远时与目前普遍采用的热补偿条件相吻合,即光学系统的光热膨胀系数等于壳体的热膨胀系数。 相似文献
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A self-consistent problem of interaction of two dipole atoms separated by an unrestricted distance with the field of a quasi-resonance
light wave was solved on the assumption that the investigated atoms are Lorentz linear oscillators and the polarizing fields
inside the system consist of the Coulomb and the retarded parts. The solution obtained was investigated for the case where
the atoms have the same polarizability and the distance between them is much smaller than the length of the external light
wave. Formulas for the electric fields inside a small object and outside it have been obtained. It is shown that inside a
small two-atom object there can take place longitudinal and transverse optical vibrations accompanied by corresponding dispersion
effects depending on the interatomic distance and the angle between the axis of the system and the direction of propagation
of the external light wave. The field outside the small object in the wave zone is linearly polarized when the external wave
has linear polarization. However, the direction of polarization of the corresponding waves is largely determined by their
frequency. It is also shown that the amplitude of the field outside the small object in the wave zone depends greatly on the
frequency of the external field and the interatomic distance. The effects observed are considered as a near-field effect in
optics of small objects. This phenomena makes it possible to investigate the structure of small objects with the use of optical
radiation.
Ul'yanovsk Branch of the Institute of Radio Engineering and Electronics, Russian Academy of Sciences, 48 Goncharov Str., Ul'yanovsk,
432700, Russia; e-mail: gadomsky@quant.univ.simbirsk.su. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 6,
pp. 765–770, November–December, 1999. 相似文献
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Mean shift is an efficient pattern match algorithm. It is widely used in visual tracking fields since it need not perform
whole search in the image space. It employs gradient optimization method to reduce the time of feature matching and realize
rapid object localization, and uses Bhattacharyya coefficient as the similarity measure between object template and candidate
template. This thesis presents a mean shift algorithm based on coarse-to-fine search for the best kernel matching. This paper
researches for object tracking with large motion area based on mean shift. To realize efficient tracking of such an object,
we present a kernel matching method from coarseness to fine. If the motion areas of the object between two frames are very
large and they are not overlapped in image space, then the traditional mean shift method can only obtain local optimal value
by iterative computing in the old object window area, so the real tracking position cannot be obtained and the object tracking
will be disabled. Our proposed algorithm can efficiently use a similarity measure function to realize the rough location of
motion object, then use mean shift method to obtain the accurate local optimal value by iterative computing, which successfully
realizes object tracking with large motion. Experimental results show its good performance in accuracy and speed when compared
with background-weighted histogram algorithm in the literature. 相似文献
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Laplacian differential reconstruction of in-line holograms recorded at two different distances 总被引:1,自引:0,他引:1
We analyze the diffraction of the picture obtained by the subtraction of two in-line holograms recorded in two planes at distances of z and z+Deltaz apart from the object plane. Our theoretical analysis reveals that the reconstructed field at the object plane is approximately equal to the Laplacian second-order differentiation of the object wave in transverse direction when Deltaz is much smaller than the distance z, that is, the reconstructed image presents a high quality of edge enhancement. We further investigate the dependence of the edge-enhancement quality on the longitudinal differential distance Deltaz and find that the reconstructed images have the sharpest edge-enhancement and high signal-to-noise ratio at the same time only when the value of Deltaz/z lies between 0.7% and 0.9% under our experimental condition. We also construct a criteria function, named the entropy of the image, to automatically focus the edge-enhanced image and demonstrate its adaptability in experiments. 相似文献
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Interaction between auditory and visual perceptions on distance estimations in a virtual environment
Navigation in virtual environments relies on an accurate spatial rendering. A virtual object is localized according to its position in the environment, which is usually defined by the following three coordinates: azimuth, elevation and distance. Even though several studies investigated the perception of auditory and visual cues in azimuth and elevation, little has been made on the distance dimension. This study aims at investigating the way humans estimate visual and auditory egocentric distances of virtual objects. Subjects were asked to estimate the egocentric distance of 2–20 m distant objects in three contexts: auditory perception alone, visual one alone, combination of both perceptions (with coherent and incoherent visual and auditory cues). Even though egocentric distance was under-estimated in all contexts, the results showed a higher influence of visual information than auditory information on the perceived distance. Specifically, the bimodal incoherent condition gave perceived distances equivalent to those in the visual-only condition only when the visual target was closer to the subject than the auditory target. 相似文献
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为实现书籍扫描图像的畸变自动校正,提出用多项式来描述各像素的理论灰度g(zi)与页面上对应点到扫描仪工作平面距离zi二者之间的关系。为确立该多项式,在畸变参数已知条件下扫描一幅图像,根据已知畸变参数求出zi,即可按最小二乘法原理由各像素灰度的实际值求出多项式的各个系数。实验证明,采用4阶多项式已能满足一般要求,并求出了各系数。对任意扫描图像,自动计算畸变参数的方法为:首先利用扫描图像上页边空白处各像素的灰度,对畸变参数进行估计,并求出zi的估计值;然后代入所确立的多项式,可求得g(zi);通过调整各畸变参数的估计值,直到g(zi)与gi最为接近,即得最佳畸变参数。用于图像校正实验,获得了较好的校正效果,最大误差由不校正时的41%下降到了6.9%。这使得无需用户测量并输入有关畸变参数即可进行自动校正。 相似文献
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A process of granularity growth in partially developed speckle patterns produced in the near field of wavy object surfaces illuminated using a laser has been experimentally studied by investigating the probability density function and average contrast of their intensity variations. These parameters have been measured as a function of the distance from the object surface to the detector for four typical sample objects having different surface qualities. It has been found that the variation in average speckle contrast with receiving distance is strongly dependent on the surface quality of the objects. The saturated value of the speckle contrast, found from the graph of its dependence on receiving distance, is also related to the maximum height of irregularities in the surface. 相似文献
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基于差分交集的视频对象分割与跟踪算法 总被引:3,自引:0,他引:3
视频对象分割算法的性能好坏将直接影响MPEG 4编码产品的质量。连续两次差分后自适应处理,对差分图像取交集获得运动对象的边界,形态学处理后最终获取运动目标。基于改进的Hausdorff距离度量法对后续帧中视频对象进行跟踪。实验结果证明,该方法能够从背景不变的图像序列中较好的提取出运动对象,具有较强的鲁棒性。 相似文献