After completing the parameter calibration of the projector, the projector can be regarded as another camera and integrated with the binocular cameras to form a trinocular stereovision system. Unlike the traditional calibration method that relies on high-precision planar targets, this paper only requires a simple, unmarked white paper target to obtain the world coordinates of feature points provided by the binocular system. An improved bundle adjustment method is used for the global optimal estimation of the parameters of the projector and dual cameras. The calibration verification experimental results show that the proposed improved bundle adjustment method can optimize the parameters. Comparative experiments measuring standard planes demonstrate that the proposed method can improve measurement accuracy.
Flat-top beam is widely used in laser applications such as holography, material processing, and nuclear fusion. However, it is difficult to maintain the flat-top effect over long distances due to the limitations of wavefront modulation and natural diffraction effects. This study aims to shape a circular Gaussian beam into a canonical flat-top beam and preserve its flat-top characteristics during long-distance (meter-level) transmission. Based on the principle of energy conservation, an energy mapping relationship between the incident plane and the output plane is constructed, and a circular flat-top intensity distribution is obtained at the output plane. The wavefront quality of the outgoing beam is controlled by the principle of equivalent optical length between mapping point elements. An off-axis reflective free-form surface optical shaping system is designed. The incident Gaussian beam has a spectral range of 1060±15nm, a beam waist diameter of 40mm, an energy truncation diameter of 60mm, and a beam quality β of 3. After the shaping system, a flat-top beam is shaped at the position of 5m output plane behind the mirror. The energy uniformity is more than 95% and the energy utilization rate is more than 90% within the diameter of 60mm. The flat-top effect can be maintained within 10m. The results show that this system can effectively shape and transmit a flat-top beam over long distances. This study provides a novel and practical method for flat-top beam shaping and transmission, which has potential applications in various laser fields.
Metasurfaces can overcome the shortcomings of traditional lenses, such as large volume, heavy weight and difficult aberration correction. However, based on the diffraction principle, metasurfaces have serious chromatic aberration and lower efficiency than traditional glass lenses, so they need to be used with monochromatic laser illumination. Therefore, metasurfaces are the best choice for lidar systems to realize miniaturization and lightweight design. The lidar emitting system usually uses a 905nm pulsed laser diode (PLD) as the light source, which requires two cylindrical lenses to collimate the laser beam in the X and Y directions separately. In this paper, two metasurfaces is designed in different areas of the same substrate to collimate the laser beam. By folding the light path through the right-angle prism, the beam passes through two metasurfaces successively, which are responsible for collimating the rays in the X and Y directions respectively. After collimation, the divergence angles of the rays are less than 0.3°×0.1°. By attaching a microelectro-mechanical system (MEMS) mirror behind the metasurfaces to realize scanning, we can obtain the lidar emitting system. By using metasurfaces to replace the traditional cylindrical lenses, the weight and size of the lidar emitting system can be greatly reduced. With further research on metasurface technology, metasurfaces are expected to replace the traditional lenses and even the scanning device in lidar, so as to realize highly integrated chip-level lidar.
Wavefront-based aspheric metrology techniques generally require a compensation lens to compensate for the primary aberrations. To expand the adaptability of the surface to be tested, this paper proposes and demonstrates a partial null compensator structure that can switch between the front and back mirror sides. The presented compensator comprises two sets of off-axis reflecting parts and a pre-compensation spheric lens in an integrated structure. An appropriate off-axis reflection combination mode can be selected for the range of the conic coefficient of the measured surface. With the simulation result, the presented compensator can adapt to a large-scale variation of the surface conic coefficient K from -10 to +10. The average residual wavefront aberration is no more than 1λ (PV) and 1/4 λ (RMS). The results show that the proposed structure can be efficiently applied to wavefront detection or interferometer for data post-processing.
Infrared polarization imaging can achieve faster perception speed and higher identification accuracy, which has been widely applied in diverse areas such as space remote sensing, biomedicine, and object detection. Limited by the aperture of the lens, the single-aperture imaging system can hardly meet the needs of high-resolution and multi-polarization imaging simultaneously. Aiming at achieving the properties of high-resolution, high-integration, and multi-channel performance, a sub-aperture infrared polarization imaging system based on freeform surfaces is proposed and demonstrated. The general scheme of the polarization imaging system mainly consists of a common aperture structure, a sub-aperture imaging group, and a relay imaging group. To compress the beam aperture, a Kepler telescope configuration is employed to build up the imaging objective. The field diaphragm is set at the primary image plane to effectively eliminate stray light. Polarizers with different orientations are added to the split aperture imaging group to form four polarization state channels. To reduce the assembly errors of the sub-aperture system, a freeform surface lens is utilized to replace the lens group in the multi-channel. The freeform surface profile uses the "XY polynomial" with eight coefficients. A diaphragm array is arranged on the front surface of the sub-aperture system, which is used to avoid the intersection between the image planes of different channels. To match with the cooled detector, the relay imaging group is designed as a finite conjugate structure with a magnification of -0.44×. The structure allows for simultaneous imaging of four infrared polarization states with the same system, and the MTF of each channel at 33lp/mm is higher than 0.45. Our research satisfies both miniaturization and engineering application requirements.
With the rapid development of information technology, people's demands for large-angle coverage and high-information acquisition of optical systems are increasing in industrial production and daily life. Therefore, the requirements for imaging quality of wide-angle lenses are improving. Aiming at solving the severe aberrations in the design of the wide-angle lens, traditional optical designs often introduce complex structures. However, a complex structure will bring several drawbacks such as large volume, heavyweight and high cost. Computational imaging technology(CIT) takes information-driven as the core, breaks the imaging mode of independent optimization of optical design and image restoration, realizes global integrated optimization design, and breaks the limit of traditional imaging. Based on the CIT theory, a simple wide-angle optical system design method is proposed and demonstrated in this paper. Firstly, in the optical design process of the wideangle lens, the requirements for suppressing aberrations are relaxed, and the image quality is worse. Then, the cross-channel image restoration algorithm is used to remove the residual aberrations to obtain a high-quality image. Finally, the system is simplified. This method can not only obtain high-quality images but also reduce the complexity of a wide-angle optical system.
Optical phase correlation calculation can achieve high-speed, passive, high-signal-to-noise ratio target signal detection. This paper proposes and demonstrates a one-dimensional information parallel comparison system based on an optical correlator. The system uses 4-f optical architecture as the basic device and combines multiple optical modules such as beam shaping, wavefront phase modulation, and optical phase correlation calculation to achieve the parallel computing function with one-dimensional information as the main detection object is developed, and the feasibility of the comparison calculation is verified by simulation. The detection system based on optical correlation proposed in this paper has potential application value in the field of genetic detection.
Aiming at correcting the severe chromatic aberration of the long focal lens, the traditional optical design often requires employing complex structure, introducing special dispersive glasses or even utilizing the hybrid refractive-diffractive imaging method. However, complex structure will bring several drawbacks such as large volume and heavy weight. Special glasses and refractive-diffractive hybrid imaging will greatly increase the cost, which hardly meets the needs of miniaturization and low cost of optical imaging module. Although image restoration algorithm is commonly used to optimize the image quality to a certain extent, the optical design and image restoration process are independent of each other. Therefore, it is difficult to ensure the high resolution of the image while realizing the light weight, small volume and low cost of the optical system simultaneously. Utilizing the computational imaging theory, a simple long-focus optical system design method based on the optical/image co-design is proposed and deomonstrated in this paper. On the basis of the idea of global optimization, the reported approach considers the two independent links of optical design and image restoration as a combination. The imaging quality requirements in the optical system design are relaxed at the front end, and the image restoration algorithm is used to remove the residual aberrations in the back end. This method can not only obtain the same or even higher imaging performance, but also reduce the complexity of the optical system.
In high precision and large-scale coordinate measurement, one commonly used approach to determine the coordinate of a target point is utilizing the spatial trigonometric relationships between multiple laser transmitter stations and the target point. A light receiving device at the target point is the key element in large-scale coordinate measurement systems. To ensure high-resolution and highly sensitive spatial coordinate measurement, a high-performance and miniaturized omnidirectional single-point photodetector (OSPD) is greatly desired. We report one design of OSPD using an aspheric lens, which achieves an enhanced reception angle of −5 deg to 45 deg in vertical and 360 deg in horizontal. As the heart of our OSPD, the aspheric lens is designed in a geometric model and optimized by LightTools Software, which enables the reflection of a wide-angle incident light beam into the single-point photodiode. The performance of home-made OSPD is characterized with working distances from 1 to 13 m and further analyzed utilizing developed a geometric model. The experimental and analytic results verify that our device is highly suitable for large-scale coordinate metrology. The developed device also holds great potential in various applications such as omnidirectional vision sensor, indoor global positioning system, and optical wireless communication systems.
Optical non-contact measurement has many advantages, which has been widely used in the precise size measurement.
Since the precision axle hole's inner diameter is small, the measuring axis optical system cannot be placed into the axle
hole. As a result, the optical non-contact measurement is difficult to be applied in the occasion above. In this paper, a set
of optical system based on off-axis imaging principle that applied to small axle hole's inner diameter measurement is
designed. According to the Scheimpflug principle, the relationship of object plane tilt and image plane tilt is derived in
this paper. To meet the requirement of measurement accuracy, an off-axis imaging system with a suitable magnification
is presented. The off-axis imaging optical system cooperating with the fiber collimator and the PSD can attain 2μm
measurement accuracy.
A solution of the nonsymmetrical optical system to collect laser echo light is presented, which is based half on imaging
optics and half on non-imaging optics. The difficulty in the design of the large field and large aperture optical system
used to collect the laser echo is analyzed, and the influence of the aberration and cylindrical lens to the system is
illuminated. The whole system is initially designed by CODE V, and the transmittance of system is analyzed by
LightTools. The result shows that the transmittance of any interested direction is more than 80%, and the system is
feasible in practice.
Medical Electronic Endoscope (MEE) is a widely used medical instrument. Using the Field Programmable Gate Array (FPGA), we accomplish three parts of work: 1) Optical imaging system. 2) Driving of the Charged Coupled Device (CCD), the function of image data acquisition and display. 3) Based on the dot-array plate arithmetic, a real-time correction system of image distortion via hardware is designed. 4) On the basis of video-servo control method, the system achieves automatic brightness control of electronic endoscope. Finally, a medical electronic endoscope system with a real-time correction system of high-resolution color image distortion is developed.
The spatial relationship between two single plane angiograms, which is characterized by transformation in the forms of a rotation matrix and a translation vector, is important for 3D reconstruction of coronary arterial tree. The error of transformation directly reduces the precision of 3D reconstruction. In this study, we introduce the methods of 3D reconstruction, analyze the necessity of optimization of transformation, and define transformation by quaternion. Then bifurcations, vessel vectors and branch angles are employed to optimize the transformation, with Levenberg-Marquardt algorithm. The experimental results on the human angiogram data are presented. The Standard Deviation of reconstruction error reduces from 3.8573 mm to 1.0803 mm in image A and from 4.0663 mm to 1.0742 mm in image B respectively on clinical angiogram data. The results of experiments show that the technique put forward in this paper greatly improves the accuracy of 3D reconstruction.
This study investigated a bilayer gastrointestinal normal tissue (including mucosa and submucosa layers) and a cancerous tissue model (including adenoma and submucosa layers), and reconstructed their Laser-Induced Autofluorescence (LIAF) spectra by Monte-Carlo simulation. The good correlation between the reconstructed spectra and experimental spectra suggested that Monte-Carlo simulation can accurately describe the generation and transportation of fluorescence in tissue and therefore can detect cancerous tissue by revealing the real biophysical and biochemical information of tissue.
This paper focuses on obtaining the intrinsic Laser-Induced Autofluorescence (LIAF) spectra by using reflectance spectra to minimize the effect of the absorption and scattering of tissue. The correlation between fluorescence distortion coefficient (J) and reflectance spectra (R) has been studied by Monte-Carlo simulation. The results show that R represents a very good approximation of f for tissue fluorescence spectra correction. Corrected fluorescence spectra were calculated by dividing the measured LIAF spectra by the diffuse reflectance (R). The corrected fluorescence spectra for normal tissue exhibit two emission peaks at wavelength 420 nm and 475 nm, respectively, while one emission peak at 425 nm was recorded for the corrected spectra of the cancerous tissue. We proposed that the difference between spectra from normal tissue and adenoma was caused by the less NADH concentration in adenoma than that in normal tissue.
This paper studied the LIAF transportation mechanism in tissue by a series of Monte-Carlo simulations, and investigated the effects of boundary condition, optical properties, structure, and the quantum yield of tissue chromophores on LIAF spectra. According to the layered structure of gastrointestinal tract and the penetration depth of laser beam, a bi-layer tissue model was set up for simulating the distribution of LIAF spectra obtained from normal tissue and adenoma. The results showed that an index-mismatched boundary reduced both the amount of excitation and emission that are remitted from the medium surface. In addition, the origin of fluorescence in normal and cancerous tissues was discussed. We found out that the cancerous mucosa has significant lower fluorescence efficiency compared to normal tissues. The reason is two-fold: firstly, the fluorescence quantum efficiency ofcancerous mucosa, which is the percentage of fluorescence of the cancerous tissues that get excited, is lower than that of normal mucosa., secondly, due to the higher absorption coefficient of cancerous mucosa, the amount of excitation light reaching submucosa layer is reduced, resulting in significantly lower remitted fluorescence from submucosa layer.
Coronary artery disease is greatly problematic to health in industrial countries. The information ofthe vessel diameter in angiogram is very important to detect heart vessel disease. The traditional diagnostic method suffers from inter-and intra-observer variability. Now there is no available auto-diagnosing system, our aim is to build up a objective system based on image processing technology to diagnose coronary disease.
A cost-effective autofluorescence detecting system has been developed by our research group to diagnose and localize the early gastrointestinal cancer, which is occult to the traditional means of detection, for example, biopsy. At the early stage, we utilize autofluorescence spectrum detected by OMA (Optical Multichannel Analyzer) to discriminate cancerous tissue. Although this method can effectively distinguish tumors from normal tissues, it is not suitable to be applied in clinic use due to the high cost of the- most-often used OMA-autofluorescence detector. Then we designed a novel Double PMTs (Photomultiply Tube) system, which consists of two parallel-working A/Ds with lower frequency of acquisition, to replace the OMA system, and the results of clinic experiments prove that it can effectively determine gastrointestinal cancers.
Pseudo-color coding of gray image is a typical processing in the fields of medicine, engineering and military. This paper proposed a new method of pseudo-color equi-density coding of gray image based on tri-primary colors of RGB and pixel's self-transformations. In the method, the negative Pixel f' (x,y) and the positive-negative superimposed pixel f'' (x,y) is easily obtained from the original(positive) pixel f(x,y) in an arbitrary space (x,y). Then the three signals for RGB which drive the physical display device are specified fo f(x,y), f' (x,y) and f'' (x,y) individually, and are fed separately into the red, green and blue guns of the RGB color cube of the monitor. The theoretical analysis and experimental results is also given. This method has advantages of being easy to realize and high color sensitivity for gray levels.
In this paper, a model for correction of distortion in endoscope image is proposed. The definition of optical distortion is described briefly and the theory of correction of distortion using grid consisting of solid circles is presented. Then, we address the three steps of correction, including pre-processing of grid image, correction of spatial distortion and reconstruction of gray level. Finally, the corrected results are given to demonstrate the performance and validity of correction algorithm with standard calibration grid.
To compensate for the imperfections of endoscopic mechanical structure and limitations of working space, in paper, a new approach based on recursive minimum-maximum method is proposed to enlarge images of medical electronic endoscopic. This method can be used repeatedly to realize 2n times image enlargement through optimizing the neighborhood information of the interesting pixels in adjustable windows. In order to ensure the best evaluation of the pixel, the algorithm criterion is presented to decide whether the pixel accept new value. Experimental results on applying the method to the endoscopic images are presented in this paper. The results demonstrate that the recursive minimum-maximum method for enlarging images can succeed in images blowing-up at the same time it preserves the fine details with rich edge-information.
Using JPEG standard, color still images can be compressed in high ratios while good quality can be guaranteed. The framework of the JPEG is specified, but the recommended quantization table and the Huffman table can be pruned according to the image's characteristic. In this paper, we put forward an adaptive-quantization approach which is compatible for the baseline JPEG. In our approach, we statistically calculate the image's average probability distributivity, which used as the threshold for the quantization. The quanti-table recommended by JPEG can then be justified with the characteristic of images and the average code-rate is noticeably dropped.
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