Showing papers on "Image resolution published in 1994"

Direct recording of holograms by a CCD target and numerical reconstruction.

Abstract: The principle of recording holograms directly on a CCD target is described. A real image of the object is reconstructed from the digitally sampled hologram by means of numerical methods.

Phase gradient autofocus-a robust tool for high resolution SAR phase correction

Abstract: The phase gradient autofocus (PGA) technique for phase error correction of spotlight mode synthetic aperture radar (SAR) imagery is examined carefully in the context of four fundamental signal processing steps that constitute the algorithm. We demonstrate that excellent results over a wide variety of scene content, and phase error function structure are obtained if and only if all of these steps are included in the processing. Finally, we show that the computational demands of the fun PGA algorithm do not represent a large fraction of the total image formation problem, when mid to large size images are involved. >

The Nobeyama radioheliograph

Abstract: A new 17-GHz radio interferometer dedicated for solar observations was constructed in two years at Nobeyama, Nagano It consists of eighty-four 80-cm-diameter antennas arranged in a tee-shaped array extending 490 m in east-west and 220 m in north-south directions Since late June of 1992, radio full-disk images of the Sun have been observed for 8 h every day The spatial resolution is 10" and the temporal resolution is 1 s and also 50 ms for selected events Every 10 s correlator data are synthesized into images in real time and displayed on a monitor screen The array configuration is optimized to observe the whole Sun with high spatial and temporal resolution and a high dynamic range of images Image quality of better than 20 dB is realized by incorporation of technical advances in hardware and software, such as (1) low-loss phase-stable optical-fiber cables for local reference signal and IF signals, (2) newly developed phase-stable local oscillators, (3) custom CMOS gate-array LSTs of 1-b quadraphase correlators for 4/spl times/4 combinations, and (4) new image processing techniques to suppress large sidelobe effects due to the solar disk and extended sources >

Phase-conjugate holographic system for high-resolution particle-image velocimetry

Abstract: A novel holographic particle-image velocimeter system has been developed for the study of three-dimensional (3-D) fluid velocity fields. The recording system produces 3-D particle images with a resolution, a signal-to-noise ratio, an accuracy, and derived velocity fields that are comparable to high-quality two-dimensional photographic particle-image velocimetry (PIV). The high image resolution is accomplished through the use of low f-number optics, a fringe-stabilized processing chemistry, and a phase conjugate play-back geometry that compensates for aberrations in the imaging system. In addition, the system employs a reference multiplexed, off-axis geometry for the determination of velocity directions with the cross-correlation technique, and a stereo camera geometry for the determination of the three velocity components. The combination of the imaging and reconstruction subsystems makes the analysis of volumetric PIV domains feasible.

Wavelet based speckle reduction with application to SAR based ATD/R

Abstract: The paper introduces a novel speckle reduction method based on thresholding the wavelet coefficients of the logarithmically transformed image. The method is computational efficient and can significantly reduce the speckle while preserving the resolution of the original image. Both soft and hard thresholding schemes are studied and the results are compared. When fully polarimetric SAR images are available, the authors propose several approaches to combine the data from different polarizations to achieve even better performance. Wavelet processed imagery is shown to provide better detection performance for the synthetic-aperture radar (SAR) based automatic target detection/recognition (ATD/R) problem. >

Pinhole SPECT: An Approach to In Vivo High Resolution SPECT Imaging in Small Laboratory Animals

Abstract: UNLABELLED: The performance of pinhole SPECT and the application of this technology to investigate the localization properties of radiopharmaceuticals in vivo in small laboratory animals are presented. METHODS: System sensitivity and spatial resolution measurements of a rotating scintillation camera system are made for a low-energy pinhole collimator equipped with 1.0-, 2.0- and 3.3-mm aperture pinhole inserts. The spatial detail offered by pinhole SPECT for in vivo imaging was investigated in studies of the brain and heart in Fisher 344 rats by administering 201TICI, 99mTc-HMPAO, 99mTc-DTPA and 99mTc-MIBI. Image acquisition is performed using a rotating scintillation camera equipped with a pinhole collimator; projection data are acquired in conventional step-and-shoot mode as the camera is rotated 360 degrees around the subject. Pinhole SPECT images are reconstructed using a modified cone-beam algorithm developed from a two-dimensional fanbeam filtered backprojection algorithm. RESULTS: The reconstructed transaxial resolution of 2.8 mm FWHM and system sensitivity of 0.086 c/s/kBq with the 2.0-mm pinhole collimator aperture provide excellent spatial detail and adequate sensitivity for imaging the regional uptake of the radiopharmaceuticals in tumor, organs and other tissues in small laboratory animals. CONCLUSION: The resolution properties of pinhole SPECT are superior to those which have been achieved thus far with conventional SPECT or PET imaging technologies. Pinhole SPECT provides an important approach for investigating localization properties of radiopharmaceuticals in vivo.

Spectroscopic imaging device employing imaging quality spectral filters

Abstract: Techniques for providing spectroscopic imaging integrates an acousto-optic tunable filter (AOTF), or an interferometer, and a focal plane array detector. In operation, wavelength selectivity is provided by the AOTF or the interferometer. A focal plane array detector is used as the imaging detector in both cases. Operation within the ultraviolet, visible, near-infrared (NIR) spectral regions, and into the infrared spectral region, is achieved. The techniques can be used in absorption spectroscopy and emission spectroscopy. Spectroscopic images with a spectral resolution of a few nanometers and a spatial resolution of about a micron, are collected rapidly using the AOTF. Higher spectral resolution images are recorded at lower speeds using the interferometer. The AOTF technique uses entirely solid-state components and requires no moving parts. Alternatively, the interferometer technique employs either a step-scan interferometer or a continuously modulated interferometer.

An efficient method for dynamic magnetic resonance imaging

Abstract: Many magnetic resonance imaging applications require the acquisition of a time series of images. In conventional Fourier transform based imaging methods, each of these images is acquired independently so that the temporal resolution possible is limited by the number of spatial encodings (or data points in the Fourier space) collected, or one has to sacrifice spatial resolution for temporal resolution. In this paper, a generalized series based imaging technique is proposed to address this problem. This technique makes use of the fact that, in most time-sequential imaging problems, the high-resolution image morphology does not change from one image to another, and it improves imaging efficiency (and temporal resolution) over the conventional Fourier imaging methods by eliminating the repeated encodings of this stationary information. Additional advantages of the proposed imaging technique include a reduced number of radio-frequency (RF) pulses for data collection, and thus lower RF power deposition. This method should prove useful for a variety of dynamic imaging applications, including dynamic studies of contrast agents and functional brain imaging.

Voxel similarity measures for automated image registration

Abstract: We present the concept of the feature space sequence: 2D distributions of voxel features of two images generated at registration and a sequence of misregistrations. We provide an explanation of the structure seen in these images. Feature space sequences have been generated for a pair of MR image volumes identical apart from the addition of Gaussian noise to one, MR image volumes with and without Gadolinium enhancement, MR and PET-FDG image volumes and MR and CT image volumes, all of the head. The structure seen in the feature space sequences was used to devise two new measures of similarity which in turn were used to produce plots of cost versus misregistration for the 6 degrees of freedom of rigid body motion. One of these, the third order moment of the feature space histogram, was used to register the MR image volumes with and without Gadolinium enhancement. These techniques have the potential for registration accuracy to within a small fraction of a voxel or resolution element and therefore interpolation errors in image transformation can be the dominant source of error in subtracted images. We present a method for removing these errors using sinc interpolation and show how interpolation errors can be reduced by over two orders of magnitude.

A comparison of conventional and spiral CT : an experimental study on the detection of spherical lesions

Abstract: Objective It is accepted that spiral CT scanning may offer significant advantages in a number of clinical applications. There is still some concern with respect to image quality, however, since slice sensitivity profiles are slightly broadened due to the table motion. We carried out theoretical analysis, phantom measurements, and computer simulations to evaluate and to compare contrast and spatial resolution for conventional and for spiral scanning. Special emphasis was put on the task of detecting spherical lesions. Materials and methods For standard test objects that measure only resolution in the scan plane, no significant difference between conventional and spiral scanning was observed. We therefore designed a phantom setup that allowed us to place spheres of arbitrary diameter and contrast in arbitrary positions to test three-dimensional (3D) resolution. Results For conventional CT, both lesion contrast and the degree of spatial separation of lesions observed depend on the relation of the start position of the scan series to the random location of a sphere or lesion. Spiral CT offers space-invariant resolution due to its continuous scanning. Small lesion contrast may be improved by up to a factor of 1.8 when compared with conventional CT since slices can be centered retrospectively. Measurements and simulations were in excellent agreement. Conclusion We conclude that spiral CT can offer improved 3D contrast and spatial resolution. To exploit these advantages, images should be reconstructed in spiral CT at increments of less than half the distance traveled during one 360 degrees tube rotation. With four to five images per such interval, usually equal to the slice width, results very close to the theoretical optimum are achieved. Many of the presented considerations and results apply to other slice imaging modalities like MRI in analogous fashion.

Optical system for a head mounted display combining high and low resolution images

Abstract: A display system includes a relatively higher resolution display for presenting visual information, and a relatively lower resolution display for presenting visual information, the displays being positioned to present the visual information images therefrom in substantially side-by-side relation, the lower resolution image being provided by the cooperation of focusing optics which form a real image at a retro-reflector, which reflects light along an optical path conjugate with light incident thereon to provide an image for viewing, and the higher resolution image being provided without passing through the focusing optics. A method of display includes forming a relatively lower resolution real image, reflecting the image to the eye of an observer, forming a relatively higher resolution image, and directing the relatively higher resolution image to the eye of the observer such that at least a portion of the relatively lower resolution image circumscribes at least a portion of the relatively higher resolution image.

Ultrasound synthetic aperture imaging: monostatic approach

Abstract: An ultrasound synthetic aperture imaging method based on a monostatic approach was studied experimentally. The proposed synthetic aperture method offers good dynamical resolution along with fast numerical reconstruction. In this study complex object data were recorded coherently in a two-dimensional hologram using a 3.5 MHz single transducer with a fairly wide-angle beam. Image reconstruction which applies the wavefront backward propagation method and the near-field curvature compensation was performed numerically in a microcomputer using the spatial frequency domain. This approach allows an efficient use of the FFT-algorithms. Because of the simple and fast scanning scheme and the efficient reconstruction algorithms the method can be made real-time. The image quality of the proposed method was studied by evaluating the spatial and dynamical resolution in a waterbath and in a typical tissue-mimicking phantom. The lateral as well as the range resolution (-6 dB) were approximately 1 mm in the depth range of 30-100 mm. The dynamical resolution could be improved considerably when the beam width was made narrower. Although it resulted in a slightly reduced spatial resolution this compromise has to be done for better resolution of low-contrast targets such as cysts. The study showed that cysts as small as 2 mm by diameter could be resolved. >

Image compression via improved quadtree decomposition algorithms

Abstract: Quadtree decomposition is a simple technique used to obtain an image representation at different resolution levels. This representation can be useful for a variety of image processing and image compression algorithms. This paper presents a simple way to get better compression performances (in MSE sense) via quadtree decomposition, by using near to optimal choice of the threshold for quadtree decomposition; and bit allocation procedure based on the equations derived from rate-distortion theory. The rate-distortion performance of the improved algorithm is calculated for some Gaussian field, and it is examined vie simulation over benchmark gray-level images. In both these cases, significant improvement in the compression performances is shown. >

Efficient multiscale regularization with applications to the computation of optical flow

Abstract: A new approach to regularization methods for image processing is introduced and developed using as a vehicle the problem of computing dense optical flow fields in an image sequence. The solution of the new problem formulation is computed with an efficient multiscale algorithm. Experiments on several image sequences demonstrate the substantial computational savings that can be achieved due to the fact that the algorithm is noniterative and in fact has a per pixel computational complexity that is independent of image size. The new approach also has a number of other important advantages. Specifically, multiresolution flow field estimates are available, allowing great flexibility in dealing with the tradeoff between resolution and accuracy. Multiscale error covariance information is also available, which is of considerable use in assessing the accuracy of the estimates. In particular, these error statistics can be used as the basis for a rational procedure for determining the spatially-varying optimal reconstruction resolution. Furthermore, if there are compelling reasons to insist upon a standard smoothness constraint, the new algorithm provides an excellent initialization for the iterative algorithms associated with the smoothness constraint problem formulation. Finally, the usefulness of the approach should extend to a wide variety of ill-posed inverse problems in which variational techniques seeking a "smooth" solution are generally used. >

Combined distributed temperature and strain sensor based on Brillouin loss in an optical fiber

Abstract: We present a novel distributed sensor that utilizes the temperature and strain dependence of the frequency at which the Brillouin loss is maximized in the interaction between a cw laser and a pulsed laser. With a 22-km sensing length, a strain resolution of 20 µ? and a temperature resolution of 2°C have been achieved with a spatial resolution of 5 m.

Recovery of ego-motion using image stabilization

Abstract: A method for computing the 3D camera motion (the ego-motion) in a static scene is introduced, which is based on computing the 2D image motion of a single image region directly from image intensities. The computed image motion of this image region is used to register the images so that the detected image region appears stationary. The resulting displacement field for the entire scene between the registered frames is affected only by the 3D translation of the camera. After canceling the effects of the camera rotation by using such 2D image registration, the 3D camera translation is computed by finding the focus-of-expansion in the translation-only set of registered frames. This step is followed by computing the camera rotation to complete the computation of the ego-motion. The presented method avoids the inherent problems in the computation of optical flow and of feature matching, and does not assume any prior feature detection or feature correspondence. >

Design and analysis of an image transfer system using microlens arrays

Abstract: Efficient large-aperture lens elements are required for 3-D integral imaging and display systems. A systematic evaluation of the spatial resolution capabilities of microlens optical combinations and the synthesis of a large-aperture objective lens by a segmented lens form is reported. It is shown that by employing an optical combination comprising macrolens arrays in conjunction with microlens focusing screens a suitable transmission element, which retains the required angular and lateral resolution, can be constructed. The advantage of using segmented lenses is their capacity to produce spatially inverted, scaled images suitable for direct orthoscopic capture. The analysis of spatial resolution presented by various authors is examined and evaluated by comparison with collated evidence.

Two generations of laser-guide-star adaptive-optics experiments at the Starfire Optical Range

Abstract: We report results that were obtained with two generations (Generation I and Generation II) of a laser-guide-star adaptive-optics system that is capable of continuous compensation at 65-Hz (Generation I) and 130-Hz (Generation II) closed-loop bandwidths on a 1.5-m telescope. We used a copper-vapor laser that was focused at a 10-km range as the laser guide star and a range-gated Shack–Hartmann sensor to operate a continuous-facesheet deformable mirror that controlled either 149 or 241 actuators. We used a separate full-aperture sensor and a steering mirror to remove overall tilt. System performance was measured by imaging stars with a high-resolution CCD camera in a narrow spectral band that was centered at 0.88 μm, from which we computed point-spread functions, optical transfer functions, and Strehl ratios. Using the laser guide star, we achieved a FWHM image resolution of 0.13 arcsec and a Strehl ratio of 0.48. Using a natural guide star, we achieved a Strehl ratio of 0.64 at 0.13 arcsec FWHM resolution. We also obtained compensated images of the Trapezium region in Orion in H-α light, using only the laser guide star.

CFA compatible resolution reduction in a single sensor electronic camera

Abstract: An electronic camera is adapted for processing images of different resolution to provide a user selectable image record size. A buffer memory is provided for storing color image pixels from a sensor corresponding to at least one image. Processing responsive to a resolution mode switch controls the order in which color image pixels are selected for output storage in both vertical and horizontal directions. The order selected by the resolution switch includes a full resolution mode, and at least one reduced resolution mode in which the low resolution color image pixels are calculated to exactly replicate the pixel geometry of the original CFA image. This simplifies the image processing for the rest of the imaging chain because the same algorithms can be used regardless of the selected image resolution.

Shape of Asteroid 4769 Castalia (1989 PB) from Inversion of Radar Images.

Abstract: The inversion of previously reported, delay-Doppler images of Castalia yields a 167-parameter, three-dimensional shape model that is bifurcated into two distinct, irregular, kilometer-sized lobes. The crevice that separates the lobes has an average depth of between 100 and 150 meters and is oriented roughly perpendicular to the asteroid's longest dimension. The constrained least-squares reconstruction method introduced here can be used to determine the shape, spin vector, and radar-scattering properties of any asteroid or comet for which delay-Doppler images provide sufficient signal-to-noise ratio, orientational coverage, and spatial resolution.

Diffraction-specific fringe computation for electro-holography

Abstract: Diffraction-specific fringe computation is a novel system for the generation of holographic fringe patterns for real-time display. This thesis describes the development, implementation, and analysis of diffraction-specific computation, an approach that considers the reconstruction process rather than the interference process in optical holography. The primary goal is to increase the speed of holographic computation for real-time three-dimensional electro-holographic (holovideo) displays. Diffraction-specific fringe computation is based on the discretization of space and spatial frequency in the fringe pattern. Two holographic fringe encoding techniques are developed from diffraction-specific fringe computation and applied to make most efficient use of hologram channel capacity. A "hogel-vector encoding" technique is based on undersampling the fringe spectra. A "fringelet encoding" technique is designed to increase the speed and simplicity of decoding. The analysis of diffraction-specific computation focuses on the trade-offs between compression ratio, image fidelity, and image depth. The decreased image resolution (increased point spread) that is introduced into holographic images due to encoding is imperceptible to the human visual system under certain conditions. A compression ratio of 16 is achieved (using either encoding method) with an acceptably small loss in image resolution. Total computation time is reduced by a factor of over 100 to less than 7.0 seconds per 36-MB holographic fringe using the fringelet encoding method. Diffraction-specific computation more efficiently matches the information content of holographic fringes to the human visual system. Diffraction-specific holographic encoding allows for "visual-bandwidth holography," i.e., holographic imaging that requires a bandwidth commensurate with the usable visual information contained in an image. Diffraction-specific holographic encoding enables the integration of holographic information with other digital media, and is therefore vital to applications of holovideo in the areas of visualization, entertainment, and information, including education, telepresence, medical imaging, interactive design, and scientific visualization. Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.

Image data compression having minimum perceptual error

Abstract: A method for performing image compression that eliminates redundant and invisible image components. The image compression uses a Discrete Cosine Transform (DCT) and each DCT coefficient yielded by the transform is quantized by an entry in a quantization matrix which determines the perceived image quality and the bit rate of the image being compressed. The present invention adapts or customizes the quantization matrix to the image being compressed. The quantization matrix comprises visual masking by luminance and contrast techniques and by an error pooling technique all resulting in a minimum perceptual error for any given bit rate, or minimum bit rate for a given perceptual error.

Resolution in surface plasmon microscopy

Abstract: In this article we demonstrate how to obtain the ultimate lateral resolution in surface plasmon microscopy (SPM) (diffraction limited by the objective). Surface plasmon decay lengths are determined theoretically and experimentally, for wavelengths ranging from 531 to 676 nm, and are in good agreement. Using these values we can determine for each particular situation which wavelength should be used to obtain an optimal lateral resolution, i.e., where the plasmon decay length does not limit the resolution anymore. However, there is a trade‐off between thickness resolution and lateral resolution in SPM. Because of the non‐optimal thickness resolution, we use several techniques to enhance the image acquisition and processing. Without these techniques the use of short wavelengths results in images where the contrast has vanished almost completely. In an example given, a 2.5 nm SiO2 layer on a gold layer is imaged with a lateral resolution of 2 μm, and local reflectance curves are measured to determine the laye...

Multiple Coulomb scattering and spatial resolution in proton radiography.

Abstract: A simple formula for the spatial resolution of transmission proton radiography is derived for two different methods of measuring the proton coordinates. The effect of multiple Coulomb scattering and energy loss are taken into account. Experimental measurements of the spatial resolution have been done and are compared with the calculations. The technique of measuring entrance and exit coordinates in coincidence for each single proton improves the spatial resolution by a factor of 8 compared to a single coordinate measurement.

Method and apparatus for visual communications in a scalable network environment

Abstract: A method and apparatus for providing a flexible and scalable videoconferencing system for use in connection with a network provides for scalably encoding an image sequence for transmission onto the network. The encoding enables the encoded image sequence to be decoded at any one of at least two spatial resolutions and any one of at least two frame rates. The decoder, depending upon the computing platform, its resources, speed, and efficiencies, can select to decode the received image at any of the available spatial resolutions and at any of the available frame rates. A lower spatial resolution and/or a lower frame rate require less computing resources. Multiple received image sequences can be decoded simultaneously, at, for example, a lowest resolution. The decoded images can be displayed for viewing on the computer monitor at the desired spatial resolution level and frame rate.

Design and engineering aspects of a high resolution positron tomograph for small animal imaging

Abstract: Describes the Sherbrooke positron emission tomograph, a very high resolution device dedicated to dynamic imaging of small laboratory animals. Its distinctive features are: small discrete scintillation detectors based on avalanche photodiodes (APD) to achieve uniform, isotropic, very high spatial resolution; parallel processing for low deadtime and high count rate capability; multispectral data acquisition hardware to improve sensitivity and scatter correction; modularity to allow design flexibility and upgradability. The system implements the "clam-shell" sampling scheme and a rotating rod transmission source. All acquisition parameters can be adjusted under computer control. Temperature stability at the detector site is ensured by the use of thermoelectric modules. The initial system consists of one layer of 256 modules (two rings of detectors) defining 3 image slices in a 118 mm diameter by 10.5 mm thick field. The axial field can be extended to 50 mm using 4 layers of modules (8 rings of detectors). The design constraints and engineering aspects of an APD-based PET scanner are reviewed and preliminary results are reported. >

Resolution limits for optical transillumination of abnormalities deeply embedded in tissues

Abstract: Random walk theory is used to calculate the line spread function (LSF) of photons as they cross the midplane of a slab of finite thickness. The relationship between the LSF and the photon transit time in transillumination time-resolved experiments is investigated. It is found that the LSF is approximately Gaussian distributed, with a standard deviation, sigma, which can be used as a criterion of the spatial resolution of the imaging system. Results are substantiated by comparison with actual data in the literature. Any given resolution can be improved by reducing the excess transit time delta t, but heterogeneity of the scattering medium and low levels of detected light enormously complicate the achievement of subcentimeter spatial resolution. The latter point is discussed by using optical parameters of breast tissues for visible and near-infrared radiation (NIR) light.

High-resolution image reconstruction from a low-resolution image sequence in the presence of time-varying motion blur

Abstract: We address the problem of reconstruction of a high-resolution image from a sequence of low-resolution images containing arbitrary relative motion, excluding occlusion effects. We develop a formulation that simultaneously takes into account blurring due to relative sensor-object motion, sensor integration, and additive noise. We propose a POCS-based algorithm for performing the high-resolution reconstruction, and provide experimental results. >

Method and apparatus for dynamically selecting an image compression process based on image size and color resolution

Abstract: A method and apparatus which dynamically selects an image compression process for an image to be transferred from a first agent to a second agent. The image being compressed has a particular size associated with it, which indicates the amount of storage space required to store the image, such as in the system memory or a mass storage device. The image also has a particular color resolution associated with it, which indicates the number of different colors which the image may contain. A particular image compression process is selected for the image based on its size and color resolution. In one embodiment, the present invention produces one of three possible outcomes. First, the image may remain uncompressed. Second, the image may be compressed using a lossless compression process, which reduces the size of the image while retaining all data for the image. Third, the image may be compressed using a lossy compression process, which reduces the size of the image by losing a small amount of data for the image.