Image Distortion Correction Research Articles

Quantitative Stereovision in a Scanning Electron Microscope

Accurate, 3D full-field measurements at the micron-level are of interest in a wide range of applications, including both facilitation of mechanical experiments at reduced length scales and accurate profiling of specimen surfaces. Scanning electron microscope systems (SEMs) are a natural platform for acquiring high magnification images for stereo-reconstruction. In this work, an integrated methodology for accurate three-dimensional metric reconstruction and deformation measurements using single column SEM imaging systems is described. In these studies, the specimen stage is rotated in order to obtain stereo views of the specimen as it undergoes mechanical or thermal loading. Simulations and preliminary experimental studies at 300× demonstrate that (a) spatially-varying image distortions can be removed from images using a non-parametric distortion model, (b) the system can be reliably calibrated using distortion-corrected images of a planar object and grid at various orientations and (c) specimen rotation variability during the measurement phase can be controlled so that baseline strain errors are within the range of ±150 µe. Benchmark rigid body motion experiments using calibrated SEM views demonstrate that all components of strain in the reconstructed object have a mean value around O(10−4) and a random spatial distribution with standard deviation ≈ 300 micro-strain.

Self-manifestation and universal correction of image distortion in scanning tunneling microscopy with spiral scan

We demonstrate that severe distortions may occur but hard to identify in a standard line-by-line scanned scanning tunneling microscope image, deforming the atomic lattice into a completely different structure type and leading to a wrong interpretation of the data. We also show that a spiral scan image can reveal the details of the drifting by causing the atomic rows to bend with the curvatures being closely related to the extent and direction of the drifting. By straightening the curved atomic rows, the true atomic arrangement can thus be precisely recovered.

Fully automatic stitching and distortion correction of transmission electron microscope images

In electron microscopy, a large field of view is commonly captured by taking several images of a sample region and then by stitching these images together. Non-linear lens distortions induced by the electromagnetic lenses of the microscope render a seamless stitching with linear transformations impossible. This problem is aggravated by large CCD cameras, as they are commonly in use nowadays. We propose a new calibration method based on ridge regression that compensates non-linear lens distortions, while ensuring that the geometry of the image is preserved. Our method estimates the distortion correction from overlapping image areas using automatically extracted correspondence points. Therefore, the estimation of the correction transform does not require any special calibration samples. We evaluate our method on simulated ground truth data as well as on real electron microscopy data. Our experiments demonstrate that the lens calibration robustly corrects large distortions with an average stitching error exceeding 10 pixels to sub-pixel accuracy within two iteration steps.

Model-Based Correction of Image Distortion in Scanning Electron Microscopy

A new Monte-Carlo program for simulation image formation in scanning electron microscopy for real three-dimensional use is presented; factors of image distortions are realized in the program, in respect of future photogrammetric evaluation. A first attempt for generating a 3D-analysis of simulated images is shown.

Software controlling algorithms for the system performance optimization of confocal laser scanning microscope

The relative slow scanning speed of a galvanometer commonly used in a confocal laser scanning microscopy system can dramatically limit the system performance in scanning speed and image quality, if the data collection is simply synchronized with the galvanometric scanning. Several algorithms for the optimization of the galvanometric CLSM system performance are discussed in this work, with various hardware controlling techniques for the image distortion correction such as pixel delay and interlace line switching; increasing signal-to-noise ratio with data binning; or enhancing the imaging speed with region of interest imaging. Moreover, the pixel number can be effectively increased with Acquire-On-Fly scan, which can be used for the imaging of a large field-of-view with a high resolution.

Measurement of deflections in buried flexible pipes by close range digital photogrammetry

In this study, the monitoring of the load–deflection behavior of buried flexible pipes by digital close range photogrammetry was described. Experimental investigations were performed in a test box made of steel, with a Plexiglas front wall. An online vision system with three CCD cameras was developed to measure automatically the deflections of pipes during load tests. The system can also correct image distortions caused by refraction of light rays passing through different medias. The computational approach involves first determining camera calibration parameters, then calculating of object coordinates of targets placed on pipe wall section after each load step using the results of the calibration process. In loading tests, LVDTs were also used to measure the changes in vertical diameters of the pipes. The comparison of results obtained from both measurement systems indicated that photogrammetric system is reliable and accurate to monitor deflection behavior of pipes under loading conditions.

消畸变、长焦距相机光学系统设计

消畸变、长焦距相机光学系统设计

A cradle-shaped gradient coil to expand the clear-bore width of an animal MRI scanner

The never ending quest for higher magnetic field strengths in MRI and MRS has led to small and medium bore scanners at 9.4 T and above for both human and animal use; however, these bore diameters restrict the size of object that can be accommodated when using a conventional gradient coil. By replacing a cylindrical gradient-coil insert with a single-sided gradient coil, the scanner's functionality can be extended to include localized imaging of wider samples. As a prototype, a three-axis, cradle-shaped gradient coil was designed, fabricated and implemented in a 9.4 T animal MRI scanner. Since gradient fields are required only to be monotonic over the desired field of view, the cradle gradient coil was designed to produce high gradient efficiencies (up to 2.25 mT m−1 A−1 over a 5 cm imaging region) at the expense of gradient linearity. A dedicated three-dimensional algorithm was developed to correct the resultant image distortion. Preliminary images of a grid phantom and a mouse demonstrated the fidelity of the algorithm in correcting image distortion of greater than 200%. Eddy currents were measured along each gradient axis. A large 65.2 (Hz mT−1 m) B0 eddy current was produced by the y-axis, suggesting potential limitations of single-sided gradient coils.

Poster - Wed Eve-50: Correcting for Fat-Shift Artifacts in Magnetic Resonance Images

The inclusion of magnetic resonance(MR)images in radiation therapytreatment planning has been hampered by inherent image distortions. As such, distortion correction algorithms have been under investigation for many years. Although distortion maps can be derived through a number of methods, a common problem arises when the resultant distortion transformation is not unique. This situation is present at the interfaces between tissues experiencing different chemical shift environments (i.e. at fat / water boundaries), and leads to hypo‐ and hyper‐intense artifacts in the distorted image. Correcting image distortion by interpolating between true and distorted coordinates cannot fully correct for the erroneous high intensity region because the distortion transformation at such locations is not unique. Thus, residual distortion artifacts remain and may hinder the accurate delineation of areas associated with fat signal, i.e. external body contours. Here we propose a series of image processing steps which are carried out prior to the standard distortion correction procedure. The method involves establishing regions of signal overlap in the distorted image (i.e. where the distortion transformation is not unique) and separating the resultant high signal into the water‐based signal component and the shifted fat‐based signal component. The fat signal is unshifted prior to the standard distortion correction technique. When the described methods are applied, the residual high‐intensity regions associated with the chemical shift artifact can be eliminated.

Estimation of mutual information objective function based on Fourier shift theorem: an application to eddy current distortion correction in diffusion tensor imaging

Diffusion tensor imaging requires correction of eddy current distortion in diffusion-weighted images. An effective retrospective correction approach is to transform a diffusion-weighted image to maximize the mutual information (MI) between the transformed diffusion-weighted image and the corresponding T2-weighted image. In the literature, either linear interpolation or partial volume interpolation is applied to estimate the MI objective function. However, these interpolation methods induce artifacts to the MI objective function, thus compromising correction results. In this work, the MI objective function is estimated based on interpolation using Fourier shift theorem. This method eliminates the artifacts incurred with the aforementioned interpolation methods. The algorithm is further improved by approximating pixel values using their nearest neighbors in the up-sampled spatial domain, resulting in dramatically increased computational efficiency without compromising the correction results. The effects of varying the number of quantization levels and using Parzen window filtering to smooth the MI objective function are also investigated to obtain optimized algorithm parameters. The diffusion tensor image quality after applying the proposed distortion correction method is significantly improved visually.

Distortion correction of diffusion tensor images using B0-field map template and its evaluation

Distortion correction of diffusion tensor images using B0-field map template and its evaluation

Automatic Reading of an Analogue Meter Using Image Processing Techniques

In this paper, we propose a system for automatic reading of an analogue meter using a digital image which is flexible and allows easy installation for various existing analogue meters. The system operates segmentation of meter area from a image, correcting image distortion and recognition of the scale on the meter in automatic setup phase. And it operates meter reading in monitoring phase. In our system, the planer projective transformation is automatically applied to a distorted image using a rectangle and a circle, to correct geometric distortion. In the automatic setup phase, the graduation marks of the scale are detected and located from a acquired image. Thereby, the meter reading can be flexibly adapted to different meter scales during the easy process. In the monitoring phase, the needle is detected and located from a new acquired image, and the meter reading is derived by comparing the relative position of the needle within the arrangement of the detected graduation marks. The experimental results show that the proposed system realizes automatic reading for various analogue meters as exactly as human observers under the controlled illuminated condition.

Correction of an image distorted by a wavy water surface: laboratory experiment

A laboratory-modeling installation for experimental investigations of light and image transfer through a wavy water surface was described. Measurements of the modulation transfer function of turbid media and a wavy surface have proved the reliability of laboratory image transfer modeling. An experiment to correct the image distortion caused by surface wave refraction of an underwater object was done using laboratory-modeling installation. A color digital camera was used to simultaneously obtain an image of the object and a glitter pattern on the surface. Processing the glitter pattern allows one to obtain the values of surface slopes at a limited number of points and to use these slopes for retrieval of image fragments. A totally corrected image is formed by accumulating the fragments. The accumulated image closely matches an original undistorted image. The experiment demonstrates that correction of image distortion produced by surface waves is possible, at least in special cases.

Correction of B0 susceptibility induced distortion in diffusion-weighted images using large-deformation diffeomorphic metric mapping

Geometric distortion caused by B0 inhomogeneity is one of the most important problems for diffusion-weighted images (DWI) using single-shot, echo planar imaging (SS-EPI). In this study, large-deformation, diffeomorphic metric mapping (LDDMM) algorithm has been tested for the correction of geometric distortion in diffusion tensor images (DTI). Based on data from nine normal subjects, the amount of distortion caused by B0 susceptibility in the 3-T magnet was characterized. The distortion quality was validated by manually placing landmarks in the target and DTI images before and after distortion correction. The distortion was found to be up to 15 mm in the population-averaged map and could be more than 20 mm in individual images. Both qualitative demonstration and quantitative statistical results suggest that the highly elastic geometric distortion caused by spatial inhomogeneity of the B0 field in DTI using SS-EPI can be effectively corrected by LDDMM. This postprocessing method is especially useful for correcting existent DTI data without phase maps.

Fast 3D Fluid Registration of Brain Magnetic Resonance Images.

Fluid registration is widely used in medical imaging to track anatomical changes, to correct image distortions, and to integrate multi-modality data. Fluid mappings guarantee that the template image deforms smoothly into the target, without tearing or folding, even when large deformations are required for accurate matching. Here we implemented an intensity-based fluid registration algorithm,7 accelerated by using a filter designed by Bro-Nielsen and Gramkow.3 We validated the algorithm on 2D and 3D geometric phantoms using the mean square difference between the final registered image and target as a measure of the accuracy of the registration. In tests on phantom images with different levels of overlap, varying amounts of Gaussian noise, and different intensity gradients, the fluid method outperformed a more commonly used elastic registration method, both in terms of accuracy and in avoiding topological errors during deformation. We also studied the effect of varying the viscosity coefficients in the viscous fluid equation, to optimize registration accuracy. Finally, we applied the fluid registration algorithm to a dataset of 2D binary corpus callosum images and 3D volumetric brain MRIs from 14 healthy individuals to assess its accuracy and robustness.

A practical global distortion correction method for an image intensifier based x‐ray fluoroscopy system

X-ray images acquired on systems with image intensifiers (II) exhibit characteristic distortion which is due to both external and internal factors. The distortion is dependent on the orientation of the II, a fact particularly relevant to II's mounted on C arms which have several degrees of freedom of motion. Previous descriptions of distortion correction strategies have relied on a dense sampling of the C-arm orientation space, and as such have been limited mostly to a single arc of the primary angle, alpha. We present a new method which smooths the trajectories of the segmented vertices of the grid phantom as a function of a prior to solving the two-dimensional warping problem. It also shows that the same residual errors of distortion correction could be achieved without fitting the trajectories of the grid vertices, but instead applying the previously described global method of distortion correction, followed by directly smoothing the values of the polynomial coefficients as functions of the C-arm orientation parameters. When this technique was applied to a series of test images at arbitrary alpha, the root-mean-square (RMS) residual error was 0.22 pixels. The new method was extended to three degrees of freedom of the C-arm motion: the primary angle, alpha; the secondary angle, beta; and the source-to-intensifier distance, lambda. Only 75 images were used to characterize the distortion for the following ranges: alpha, +/- 45 degrees (Deltaalpha = 22.5 degrees); beta, +/- 36 degrees (Deltabeta = 18 degrees); lambda, 98-118 cm (Deltalambda = 10 cm). When evaluated on a series of test images acquired at arbitrary (alpha, beta, lambda), the RMS residual error was 0.33 pixels. This method is targeted at applications such as guidance of catheter-based interventions and treatment planning for brachytherapy, which require distortion-corrected images over a large range of C-arm orientations.

Gaussian process modeling for image distortion correction in echo planar imaging

An enhanced method for correction of image distortion due to B(0)-field inhomogeneities in echo planar imaging (EPI) is presented. The algorithm is based on the measurement of the point spread function (PSF) associated with each image voxel using a reference scan. The expected distortion map in the phase encode direction is then estimated using a nonparametric inference algorithm known as Gaussian process modeling. The algorithm is shown to be robust to the presence of regions of low signal-to-noise in the image and large inhomogeneities.

A precise method for correcting stereo pairs collected by a new binocular device

PurposeThe paper seeks to develop a stereo vision system based on a new binocular device. It aims to present an explicit‐implicit correction method to correct radial and tangential distortion of image synchronously. It also aims to propose a step‐rotation rectification method to rectify epipolar error between stereo pairs.Design/methodology/approachLeast squares technique was used in solving the explicit‐implicit correction model. When the step‐rotation rectification method was implemented, the technology of rotating image space was used.FindingsThe paper finds that the stereo vision system based on a new binocular device can be used in different circumstances, and it can obtain more eyeshot of cameras. The explicit‐implicit correction method can eliminate radial and tangential distortion of images, and the solution to this method is so easy that it can be solved by least squares technique. The theory of step‐rotation rectification is simple, and it is effective for rectifying epipolar error.Practical implicationsThe explicit‐implicit correction method and step‐rotation rectification method can be used in correcting image distortion and epipolar error in stereo pairs collected by a stereo vision system. The new binocular device can be used in building a stereo vision system.Originality/valueA new binocular device is developed in the paper. Explicit distortion method and implicit distortion method are united to correct image distortion. A step‐rotation rectification method is proposed to rectify epipolar error.

A method based on moving least squares for XRII image distortion correction

This paper presents a novel integrated method to correct geometric distortions of XRII (x-ray image intensifier) images. The method has been compared, in terms of mean-squared residual error measured at control and intermediate points, with two traditional local methods and a traditional global methods. The proposed method is based on the methods of moving least squares (MLS) and polynomial fitting. Extensive experiments were performed on simulated and real XRII images. In simulation, the effect of pincushion distortion, sigmoidal distortion, local distortion, noise, and the number of control points was tested. The traditional local methods were sensitive to pincushion and sigmoidal distortion. The traditional global method was only sensitive to sigmoidal distortion. The proposed method was found neither sensitive to pincushion distortion nor sensitive to sigmoidal distortion. The sensitivity of the proposed method to local distortion was lower than or comparable with that of the traditional global method. The sensitivity of the proposed method to noise was higher than that of all three traditional methods. Nevertheless, provided the standard deviation of noise was not greater than 0.1 pixels, accuracy of the proposed method is still higher than the traditional methods. The sensitivity of the proposed method to the number of control points was greatly lower than that of the traditional methods. Provided that a proper cutoff radius is chosen, accuracy of the proposed method is higher than that of the traditional methods. Experiments on real images, carried out by using a 9 in. XRII, showed that residual error of the proposed method (0.2544 +/- 0.2479 pixels) is lower than that of the traditional global method (0.4223 +/- 0.3879 pixels) and local methods (0.4555 +/- 0.3518 pixels and 0.3696 +/- 0.4019 pixels, respectively).

Simultaneous Acquisition and Image Synthesis of Gamma Cameras and Optical Cameras for Sentinel Lymph Node Identification During Radioguided Surgery

We have developed a method that combines a small semiconductor gamma camera with an optical camera to synthesize the two respective kinds of images and help surgeons to easily identify sentinel lymph nodes in various cancer surgery. The proposed method includes some key techniques such as distortion correction of the optical camera image, distance estimation between the camera head and the object surface using a laser and the optical camera, and perspective transformation of the gamma camera image to fuse with the optical camera image. The method, along with preliminary experimental results with a prototype setup are presented here.