Blind removal of lens distortion

Use of Digital Image Correlation Method to Measure Bio-Tissue Deformation

Traditionally, strain gauge, extensometer, and reflection tracking markers have been used to measure the deformation of materials under loading. However, the anisotropy and inhomogeneity of most biological materials restricted the accessibility of the real strain field. Compared to the video extensometer, digital image correlation has the advantage of providing full-field displacement as well as strain information. In this study, a digital image correlation method (DIC) measurement system was employed for chicken breast bio-tissue deformation measurement. To increase the contrast for better correlation, a mixture of ground black pepper and white sesame was sprayed on the surface of samples. The first step was to correct the distorted image caused by the lens using the inverse distorted calibration method and then the influence of subset size and correlation criteria, sum of squared differences (SSD), and zero-normalized sum of squared differences (ZNSSD) were investigated experimentally for accurate measurement. Test results of the sample was translated along the horizontal direction from 0 mm to 3 mm, with an increment of 0.1 mm and the measurement result was compared, and the displacement set on the translation stage. The result shows that the error is less than 3%, and accurate measurement can be achieved with proper surface preparation, subset size, correlation criterion, and image correction. Detailed examination of the strain values show that the strain εx is proportional to the displacement of crosshead, but the strain εy indicates the viscoelastic behavior of tested bio-tissue. In addition, the tested bio-tissue’s linear birefringence extracted by a Mueller matrix polarimetry is for comparison and is in good agreement. As noted above, the integration of the optical parameter measurement system and the digital image correlation method is proposed in this paper to analyze the relationship between the strain changes and optical parameters of biological tissue, and thus the relative optic-stress coefficient can be significantly characterized if Young’s modulus of biological tissue is known.

Driver's Preview Modeling Based on Visual Characteristics through Actual Vehicle Tests

This paper proposes a method for obtaining driver's fixation points and establishing a preview model based on actual vehicle tests. Firstly, eight drivers were recruited to carry out the actual vehicle test on the actual straight and curved roads. The curvature radii of test curved roads were selected to be 200, 800, and 1500 m. Subjects were required to drive at a speed of 50, 70 and 90 km/h, respectively. During the driving process, eye movement data of drivers were collected using a head-mounted eye tracker, and road front scene images and vehicle statuses were collected simultaneously. An image-world coordinate mapping model of the visual information of drivers was constructed by performing an image distortion correction and matching the images from the driving recorder. Then, fixation point data for drivers were accordingly obtained using the Identification-Deviation Threshold (I-DT) algorithm. In addition, the Jarque-Bera test was used to verify the normal distribution characteristics of these data and to fit the distribution parameters of the normal function. Furthermore, the preview points were extracted accordingly and projected into the world coordinate. At last, the preview data obtained under these conditions are fit to build general preview time probability density maps for different driving speeds and road curvatures. This study extracts the preview characteristics of drivers through actual vehicle tests, which provides a visual behavior reference for the humanized vehicle control of an intelligent vehicle.

Doublet metalens design for high numerical aperture and simultaneous correction of chromatic and monochromatic aberrations

Metalens is one of the most prominent applications among metasurfaces since it gives possibilities to replace the conventional lenses for compactness and multi-functionalities. Recently, many studies have been demonstrated to overcome the aberrations of the metalenses for high performance practical applications. Previous studies have used the methods that control the dispersion of meta-atoms for correcting chromatic aberrations and use doublet platform for correcting monochromatic aberrations. Despite these studies and the large demands for simultaneous correction of the aberrations in high numerical aperture metalens, the simultaneous correction has not been demonstrated yet. In this paper, we report the doublet metalens design with high numerical aperture which corrects longitudinal chromatic aberration and four monochromatic aberrations including spherical aberration, coma, astigmatism, and field curvature simultaneously for the three primary visible colors. Based on the novel doublet platform, the multi-wavelength targeted correction lens and geometric phase lens with color filtering functionality are utilized. Our doublet metalens has numerical apertures of 0.33, 0.38, and 0.47 for 445 nm, 532 nm, and 660 nm, respectively. The back focal length of our doublet metalens remains nearly 360 µm for target wavelengths and incident angles up to 30 degrees.

Smartphone-based spectral imaging otoscope: System development and preliminary study for evaluation of its potential as a mobile diagnostic tool

We develop a novel smartphone-based spectral imaging otoscope for telemedicine and examine its capability for the mobile diagnosis of middle ear diseases. The device was applied to perform spectral imaging and analysis of an ear-mimicking phantom and a normal and abnormal tympanic membrane for evaluation of its potential for the mobile diagnosis. Spectral classified images were obtained via online spectral analysis in a remote server. The phantom experimental results showed that it allowed us to distinguish four different fluids located behind a semitransparent membrane. Also, in the spectral classified images of normal ears (n = 3) and an ear with chronic otitis media (n = 1), the normal and abnormal regions in each ear could be quantitatively distinguished with high contrast. These preliminary results thus suggested that it might have the potentials for providing quantitative information for the mobile diagnosis of various middle ear diseases.

Subnanometer localization accuracy in widefield optical microscopy

The common assumption that precision is the limit of accuracy in localization microscopy and the typical absence of comprehensive calibration of optical microscopes lead to a widespread issue-overconfidence in measurement results with nanoscale statistical uncertainties that can be invalid due to microscale systematic errors. In this article, we report a comprehensive solution to this underappreciated problem. We develop arrays of subresolution apertures into the first reference materials that enable localization errors approaching the atomic scale across a submillimeter field. We present novel methods for calibrating our microscope system using aperture arrays and develop aberration corrections that reach the precision limit of our reference materials. We correct and register localization data from multiple colors and test different sources of light emission with equal accuracy, indicating the general applicability of our reference materials and calibration methods. In a first application of our new measurement capability, we introduce the concept of critical-dimension localization microscopy, facilitating tests of nanofabrication processes and quality control of aperture arrays. In a second application, we apply these stable reference materials to answer open questions about the apparent instability of fluorescent nanoparticles that commonly serve as fiducial markers. Our study establishes a foundation for subnanometer localization accuracy in widefield optical microscopy.

Phase wavefront aberration modeling using Zernike and pseudo-Zernike polynomials

Orthogonal polynomials can be used for representing complex surfaces on a specific domain. In optics, Zernike polynomials have widespread applications in testing optical instruments, measuring wavefront distributions, and aberration theory. This orthogonal set on the unit circle has an appropriate matching with the shape of optical system components, such as entrance and exit pupils. The existence of noise in the process of representation estimation of optical surfaces causes a reduction of precision in the process of estimation. Different strategies are developed to manage unwanted noise effects and to preserve the quality of the estimation. This article studies the modeling of phase wavefront aberrations in third-order optics by using a combination of Zernike and pseudo-Zernike polynomials and shows how this combination may increase the robustness of the estimation process of phase wavefront aberration distribution.

Estimation of phase wave-front aberration distribution function using wavelet transform profilometry

Reduction of image quality under the effects of wavefront aberration of the optical system has a direct impact on the vision system's performance. This paper tries to estimate the amount of aberration with the use of wavelet transform profilometry. The basic idea is based on the principle that under aberration effects, the position of the fringes' image on the image plane will change, and this change correlates with the amount of aberration. So the distribution of aberration function can directly be extracted through measuring the amount of changes in the fringes' image on the image plane. Experimental results and the empirical validity of this idea are evaluated.

Foveated endoscopic lens

We present a foveated miniature endoscopic lens implemented by amplifying the optical distortion of the lens. The resulting system provides a high-resolution region in the central field of view and low resolution in the outer fields, such that a standard imaging fiber bundle can provide both the high resolution needed to determine tissue health and the wide field of view needed to determine the location within the inspected organ. Our proof of concept device achieves 7 ≈ 8 μm resolution in the fovea and an overall field of view of 4.6 mm. Example images and videos show the foveated lens' capabilities.

Lens distortion models evaluation

Many lens distortion models exist with several variations, and each distortion model is calibrated by using a different technique. If someone wants to correct lens distortion, choosing the right model could represent a very difficult task. Calibration depends on the chosen model, and some methods have unstable results. Normally, the distortion model containing radial, tangential, and prism distortion is used, but it does not represent high distortion accurately. The aim of this paper is to compare different lens distortion models to define the one that obtains better results under some conditions and to explore if some model can represent high and low distortion adequately. Also, we propose a calibration technique to calibrate several models under stable conditions. Since performance is hard conditioned with the calibration technique, the metric lens distortion calibration method is used to calibrate all the evaluated models.

Prototype of video endoscopic capsule with 3-d imaging capabilities

Wireless video capsules can now carry out gastroenterological examinations. The images make it possible to analyze some diseases during postexamination, but the gastroenterologist could make a direct diagnosis if the video capsule integrated vision algorithms. The first step toward in situ diagnosis is the implementation of 3-D imaging techniques in the video capsule. By transmitting only the diagnosis instead of the images, the video capsule autonomy is increased. This paper focuses on the Cyclope project, an embedded active vision system that is able to provide 3-D and texture data in real time. The challenge is to realize this integrated sensor with constraints on size, consumption, and processing, which are inherent limitations of the video capsule. We present the hardware and software development of a wireless multispectral vision sensor which enables the transmission of the 3-D reconstruction of a scene in real time. An FPGA-based prototype has been designed to show the proof of concept. Experiments in the laboratory, in vitro, and in vivo on a pig have been performed to determine the performance of the 3-D vision system. A roadmap towardthe integrated system is set out.

Estimating planar surface orientation using bispectral analysis

In this correspondence, we propose a direct method for estimating the orientation of a plane from a single view under perspective projection. Assuming that the underlying planar texture has random phase, we show that the nonlinearities introduced by perspective projection lead to higher order correlations in the frequency domain. We also empirically show that these correlations are proportional to the orientation of the plane. Minimization of these correlations, using tools from polyspectral analysis, yields the orientation of the plane. We show the efficacy of this technique on synthetic and natural images.

Three-dimensional optical high-resolution profiler with a large observation field: foot arch behavior under low static charge studies

Our aim is to describe a method for detecting small deformations from a three-dimensional (3D) shape of large lateral dimensions. For this purpose the measurement method is based on the simultaneous utilization of several 3D optical systems and the phase-shifting technique. In this way, the following problems appear: optical distortion due to the large field observed, nonlinear phase-to-height conversion, conversion of image coordinates into object coordinates for each 3D optical system, and coordinate unification of all optical systems. The resolution is 50 microm with a field of view of 320 mm x 150 mm. We used this system to study the 3D human foot arch deformation under low loads in vivo. First results indicate the hysteresis behavior of the human foot under a low load (50 to 450 N).