Optical diffraction tomography (ODT) is an effective label-free technique for quantitatively refractive index imaging, which enables long-term monitoring of the internal three-dimensional (3D) structures and molecular composition of biological cells with minimal perturbation. However, existing optical tomographic methods generally rely on interferometric configuration for phase measurement and sophisticated mechanical systems for sample rotation or beam scanning. Thereby, the measurement is suspect to phase error coming from the coherent speckle, environmental vibrations, and mechanical error during data acquisition process. To overcome these limitations, we present a new ODT technique based on non-interferometric phase retrieval and programmable illumination emitting from a light-emitting diode (LED) array. The experimental system is built based on a traditional bright field microscope, with the light source replaced by a programmable LED array, which provides angle-variable quasi-monochromatic illumination with an angular coverage of ±37 degrees in both x and y directions (corresponding to an illumination numerical aperture of ∼0.6). Transport of intensity equation (TIE) is utilized to recover the phase at different illumination angles, and the refractive index distribution is reconstructed based on the ODT framework under first Rytov approximation. The missing-cone problem in ODT is addressed by using the iterative non-negative constraint algorithm, and the misalignment of the LED array is further numerically corrected to improve the accuracy of refractive index quantification. Experiments on polystyrene beads and thick biological specimens show that the proposed approach allows accurate refractive index reconstruction while greatly reduced the system complexity and environmental sensitivity compared to conventional interferometric ODT approaches. 相似文献
We present a region of interest (ROI) generation method specialized for nighttime pedestrian detection using far-infrared (FIR) images. Because pedestrians typically appear brighter than background in FIR images, previous research efforts primarily attempted to extract ROIs based on the intensity threshold. However this approach has problems resulting from the intensity variances of pedestrians due to their clothing and, especially in urban scenarios, and other heat sources that emit more heat than the pedestrians. In this paper, we propose a novel ROI generation method that is based on combining image segments instead of using the intensity threshold. In order to minimize dependence on brightness, we utilize the low-frequency characteristics of FIR images. As a result, our proposed method generates a small number of ROIs at an acceptable miss rate and the generated ROIs provide advantages for classification because the pedestrians are satisfactorily arranged within a bounding box. Experiments conducted indicate that our proposed method performs reliably in urban scenarios. 相似文献
The determination of film thickness is of prime importance in the quality assurance of coated pharmaceutical preparations. The rapid measurement of this parameter is problematic for multi-particulate pellet systems. The aim of this study was to apply the Raman spectroscopic method for the determination of the thickness of polymer coating on pellets. The change of Raman intensity was compared with measured film thickness, which was calculated from the change of the geometric parameters of the pellets, measured with an image-analyzing system. The results revealed that despite some difficulties Raman spectroscopy is a suitable method for the fast and accurate determination of film thickness on multi-particulate systems. 相似文献
Although many models have been put forward to realize static infrared scene, they could not generate dynamic infrared scene real time in interactive way. In this paper a new method is proposed to solve the problem. We first model the targets and background of infrared scene based on the hybrid way of geometry and multi-spectral texture images. Then considering the attenuation effect of atmosphere and the noise mechanic of infrared image sensor, we present an infrared depth image model to generate dynamic images of the objects in the scene from different viewpoint. The complexity of infrared dynamic scene is thus reduced greatly and the reality of infrared scene is improved. Finally, real-time walkthrough for infrared scene is successfully realized and the average walkthrough speed is larger than 25 frames per second. 相似文献
Knowledge of the structure of biological specimens is critical to understanding their function. Electron crystallography is
an electron microscopy (EM) approach that derives the 3D structure of specimens at high-resolution, even at atomic detail.
Prior to the tomographic reconstruction, the images taken from the microscope have to be properly aligned. Traditional alignment
methods in electron crystallography are based on a phase residual function to be minimized by inefficient exhaustive search
procedures. This work addresses this minimization problem from an evolutionary perspective. Universal Evolutionary Global
Optimizer (UEGO), an evolutionary multimodal optimization algorithm, has been applied and evaluated for the task of image
alignment in this field. UEGO has turned out to be a promising technique alternative to the standard methodology. The alignments
found out by UEGO show high levels of accuracy, while reducing the number of function evaluations by a significant factor
with respect to the standard method. 相似文献
Microelectronics packaging has been developing rapidly due to the demands for faster, lighter and smaller products. Printed circuit boards (PCBs) provide mechanical support and electrical interconnection for electronic devices. Many types of composite PCBs have been developed to meet various needs. Recent trends in reliability analysis of PCBs have involved development of the structural integrity models for predicting lifetime under thermal environmental exposure; however the theoretical models need verification by the experiment.
The objective of the current work is the development of an optical system and testing procedure for evaluation of the thermal deformation of PCBs in the wide temperature range. Due to the special requirements of the specimen and test condition, the existing technologies and setups were updated and modified. The discussions on optical methods, thermal loading chambers, and image data processing are presented. The proposed technique and specially designed test bench were employed successfully to measure the thermal deformations of PCB in the −40°C to +160°C temperature range. The video-based moiré interferometry was used for generating, capturing and analysis of the fringe patterns. The obtained information yields the needed coefficients of thermal expansion (CTE) for tested PCBs. 相似文献