Showing papers on "Subpixel rendering published in 1994"

A moment-based approach to registration of images with affine geometric distortion

Abstract: A new method is described for automatic control point selection and matching. First, reference and sensed images are segmented and closed-boundary regions are extracted. Each region is represented by a set of affine-invariant moment-based features. Correspondence between the regions is then established by a two-stage matching algorithm that works both in the feature space and in the image space. Centers of gravity of corresponding regions are used as control points. A practical use of the proposed method is demonstrated by registration of SPOT and Landsat TM images. It is shown that the authors' method can produce subpixel registration accuracy. >

Comparison of some techniques for the subpixel location of discrete target images

Abstract: Signalizing points of interest on the object to be measured is a reliable and common method of achieving optimum target location accuracy for many high precision measurement tasks. In photogrammetric metrology, images of the targets originate from photographs and CCD cameras. Regardless of whether the photographs are scanned or the digital images are captured directly, the overall accuracy of the technique is partly dependent on the precise and accurate location of the target images. However, it is often not clear which technique to choose for a particular task, or what are the significant sources of error. The research described in this paper describes aspects of target recognition, thresholding, and location. The results of a series of simulation experiments are used to analyze the performance of subpixel target location techniques such as: centroiding; Gaussian shape fitting; and ellipse fitting, under varying conditions.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quantifying MRI geometric distortion in tissue

Abstract: We present a method to quantify the MR field inhomogeneity geometric distortion to subpixel accuracy without using objects of known dimensions and without using an external standard such as CT. Our method may be used to quantify the geometric accuracy of MR images of anatomical structures of unknown geometry and also to test any geometry correction scheme. We have quantified the distortion in a tissue phantom and found the largest error to be approximately 2.8 pixels (1.8 mm) for Bo = 1.5 T, G = 3.13 mT/m and FOV = 160 x 160 x 70.7 mm3. We also found that our previously published correction technique reduced the largest error to 0.3 pixels (mu = 0.02 and sigma = 0.07 pixels).

Liquid crystal display with patterned retardation films

Abstract: A multi-colored pixel for a twisted nematic liquid crystal display including red, green, and blue subpixels, wherein each subpixel includes a pair of substrates, a pair of polarizers, opposing electrodes, and a color personalized retardation film which compensates for the different wavelength of each color. The personalized retardation films of the different color subpixels results in elimination of the multi-gap approach and substantially eliminates the problem of different color leakages at different viewing angles, including normal. Also, one polymer based element, preferably a polyimide, functions as both a color filter and a retardation film in certain embodiments of this invention.

Modeling edges at subpixel accuracy using the local energy approach

Abstract: In this paper we describe a new technique for ID and 2D edge feature extraction to subpixel accuracy using edge models and the local energy approach. A candidate edge is modeled as one of a number of parametric edge models, and the fit is refined by a least-squared error fitting technique. >

Detecting image cell position with subpixel accuracy

Abstract: By providing subpixel accuracy in the detection of the position of an element of a pixel data image, the invention makes possible reductions in scanner and storage resolution of the order of 65 percent or greater for two-dimensional applications. Methods use normalized gray level values to determine the extent of coverage of an image cell by individual pixels. By then applying such gray level values of a plurality of successive pixels to a preconstructed lookup table, ambiguities are resolved to determine the position of cell edges. The cell edge data can be used to determine cell position or used directly in edge-based bar code decoding techniques. Cell position data is used for construction of a virtual image of a bar code or other dataform of interest and virtual image information may then be used for purposes of decoding the bar code or other dataform. For two-dimensional applications, the gray level values of a plurality of successive pixels, as referred to, may be implemented as a sliding window of three such gray level values along successive lines in a first dimension which are applied to a lookup table, followed by repetition for successive lines in a perpendicular dimension, to derive cell edge data for both dimensions.

Antialiasing with grey masking techniques

Abstract: A method of combining antialiased edges for printing or display at a grey level reproduction device, wherein pixels have shade values determined as a function of their neighbor's shade values and mask values. Shade values are determined by processing each pixel in terms of subpixels forming the pixel. Each of a plurality of subpixels are assigned mask and shade values as a function of their position in the pixel and with respect to the nearest neighbors. The resulting values for each subpixel are averaged to determine a final output value for the pixel.

Subpixel contour matching using continuous dynamic programming

Abstract: This paper presents a subpixel contour matching algorithm using a novel dynamic programming scheme. Unlike classical dynamic programming methods, where a discrete path is searched for across a graph, our approach allows the optimal continuous path to be determined. The matching is obtained as a piecewise parametric function, and no discretization is involved, nor any parameterized deformation assumed. As a side result, a measure of the deformation of the matched contours is obtained, yielding information on the quality of the match. The algorithm has been tested with different types of images, demonstrating its ability to deal with chains of contour segments as well as chains of contour edges, since the discretization of the contours does not limit the precision of the matches anymore. >

Gray scale multi domain liquid crystal display panel having capacitive voltage division characteristics

Abstract: Liquid crystal is encapsulated between two transparent substrates 16, 17. Pixel electrodes 13 are formed on the inner surface of the transparent substrate 17 in the form of a matrix while a common electrode 12 is formed on the inner surface of the transparent substrate 16. Each pixel electrode 13 is divided into subpixel electrodes 13 1 , 13 2 . The subpixel electrode 13 1 is connected to the drain of a thin film transistor 21 formed adjacent the subpixel electrode to apply driving voltage to the electrode. The subpixel electrode 13 2 is supplied with capacitance-divided driving voltage through a capacitor comprising the electrode 13 1 , and a control capacitor 15 connected thereto with an insulation layer 14 interposed therebetween. Each of the subpixel electrodes 13 1 , 13 2 are divided into two domains on which are formed alignment layers 41a, 41b, 42a, 42b, in opposition to alignment layers 43a, 43b, 44a, 44b formed on the common electrode 12. One of the opposed alignment layers is adapted to impart to the liquid crystal a pretilt angle greater than the other alignment layer. One of a pair of adjacent orientating films in the same plane is adapted to impart to the liquid crystal a pretilt angle greater than the other orientating film.

Method for generating a subpixel mask for computer graphics system and apparatus thereof

Abstract: In a computer graphics system, a method for generating a subpixel mask for polygon edges directly by an operation without using a look-up table, includes the steps of forming subblocks by dividing a pixel into n subpixels depending on the slope of the polygon edge, calculating subblock coverage which is a distance from the pixel boundary to the intersection point of n subblocks and polygon edge, and generating an n×n subpixel mask depending on the calculated subblock coverage. In an apparatus using the method, edge-generated aliasing is removed.

Automated radar image matching experiment

Abstract: Stereo-parallax measurements for digital elevation excitation, matching for change detection, and creation of stacks of multi-temporal or multi-incidence angle images (“cubes”) of co-registered images all can be supported by automation via computerized image correlation. Precision parallax measurements are traditionally made by an experienced stereo-operator. Automated methods have been investigated, but have not found wide acceptance. Radar mapping, for example in NASA's Magellan mission to planet Venus, has a requirement to develop Digital Elevation Models (DEM) from stereo radar images, and to match multiple coverages from sequential image acquisition cycles. We report on an experiment to assess the quality of machine-matches for stereo-parallax detection in radar images, and find that there are often ±2 pixel differences between the experienced stereo-operator and the best image-matching method, based on a normalized cross-correlation measure. When comparing this to SPOT-images and to scanned aerial photography, we note that errors of machine matching are typically smaller in those images than in radar images, with SPOT data producing automated matches with subpixel differences to manual matches.

A method of high addressability error diffusion

Abstract: A method and system implements a high addressability characteristic into an error diffusion process. A grey level value representing a pixel is received. The grey level value has a first resolution which corresponds to an original input resolution. The grey level value is interpolated (S30) to generate subpixel grey level values which correspond to a second resolution. The second resolution is higher than the first resolution and corresponds to the high addressability characteristic. A threshold circuit thresholds the interpolated grey level value and generates (s180) an error value as a result of the threshold. The error value has a resolution corresponding to the first resolution. A portion of the error value is diffused (S190) to adjacent pixels on a next scanline.

Estimator for the random error in subpixel target location and its use in the bundle adjustment

Abstract: A CCD camera and frame store provide image data that are affected by a number of imperfect processes. However, most of these can be quantified or estimated. For instance, the quantization process of allocating integer values from 0 to 255 for the intensity level of each pixel has well-known statistical properties. This paper discusses how these can lead to an estimate of the precision of location of target image centroids. Two centroid algorithms are analyzed. The theory is tested against experimental and simulated data.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Correlation algorithm with adaptive window for aerial image in stereo vision

Abstract: Binocular stereo vision processes estimate 3D surfaces using a pair of images taken from different points of view. 3D surface characteristics are estimated by matching 2D image areas or features corresponding to the projections of same 3D points. The most classic area-based methods used cross correlation with a fixed window-size, but this technique presents a major drawback: the computation of depth is generally prone to errors close to surface discontinuities. In this paper, we present our current work on aerial stereo images of urban areas. A correlationbased algorithm, with an adaptive window-size constrained by an edge map extracted from the images, is presented. This technique is not used to refine an initial disparity map, but to create one with good discontinuities location. The algorithm follows 3 steps: first window sizes for each pixel are computed; then a disparity map is created; third, map completion is performed and a final dense disparity map with subpixel precision is produced by Kanade correction. Experimental results on real aerial images are presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Subpixel image registration using circular fiducials

Abstract: The design of fiducials for precise image registration is of major practical importance in computer vision, especially in automatic inspection applications. We analyze the sub-pixel registration accuracy that can, and cannot, be achieved by some rotation-invariant fiducials, and present and analyze efficient algorithms for the registration procedure. We rely on some old and new results from lattice geometry and number theory and efficient computational-geometric methods.

Method and system for locating objects with subpixel precision

Abstract: A method of locating an object which has a straight edge is disclosed. An illustrative embodiment of the invention orients the object's edge so that it is at an oblique angle to the axis of the coordinate system of the sampling plane of the input device scanning the object. A subset of the pixels associated with the object's edge are identified and used to estimate the location of the object or edge.

Evaluation of subpixel feature localization methods for precision measurement

Abstract: This paper provides a review of a number of subpixel estimators classified as moment based, local modelling and reconstruction. Three algorithms are described in detail, one from each class. In the first, the basic centroid method is generalized so that it is applicable to a wider class of problems and the general formulation is applied to develop a subpixel ridge estimator. The second algorithm is a restricted polynomial model and is developed based on the assumption that an edge profile remains invariant in a local neighborhood. The third algorithm uses Gaussian interpolation to perform local image reconstruction. Simulations are performed to measure the performance of these three algorithms under ideal and noisy conditions.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

High‐resolution restoration of dynamic image sequences

Abstract: We investigated an approach to reconstructing high-resolution images from dynamic image sequences using local spectral analysis. High-resolution reconstruction from linearly shifted multiple static image frames has previously been studied, in which the aliasing relationship between the spectrum of the original signal and the DFTs of shifted and sampled signals is exploited. In the high-resolution reconstruction of dynamic image sequences, difficulties occur as a result of nonuniform shifts in the frames. We use loca spectral analysis to achieve high-resolution reconstruction by overlapped block decomposition and motion compensation. For each block image in a reference frame in the sequence, motion estimation and subpixel registrations are performed against adjacent frames. High resolution reconstruction is performed on such motion-compensated block-image sequences. For some blocks containing motion boundaries, high resolution reconstruction is difficult; a new scene emerges or disappears producing inconsistent information. An interpolation technique is used in such blocks to generate the number of pixels consistent with other high-resolution blocks. The flower-garden image sequence is used for the computer simulations. The quality of the restored images are very encouraging; the aliasing effects in the original frames are significantly reduced and sharper edges are produced. The overall procedure to generate such higher-resolution images from a dynamic image sequence is described in detail. The result can be applied to various image sequence restoration applications including up-conversion of conventional video signals.©1994 John Wiley & Sons Inc

Precise visual inspection for LSI wafer patterns using subpixel image alignment

Abstract: This paper reports on an image processing algorithm and hardware for fast, precise inspection of LSI wafer patterns. In order to detect deep sub-micron defects such as 0.2 /spl mu/m at high speed by grayscale image comparison, we must overcome the sampling errors that inevitably occur between two images during detection. For this purpose, we have developed a subpixel image alignment algorithm that infers the correct sampling position and creates the two resampled images with subpixel accuracy. We have also developed an 8-channel pipelined processor with gate arrays. It has 8/spl times/19,000 gates and can operate at 8/spl times/15 MHz. Evaluation of the system confirmed that the accuracy of the subpixel image alignment was 0.16 pixels or less and that the inspection system could detect 0.18 /spl mu/m defects at a pixel size of 0.25 /spl mu/m for half-micron LSI wafer patterns with an inspection speed of 25 s/cm/sup 2/. >

Method and apparatus for rendering visual images employing area calculation and blending of fractional pixel lists for anti-aliasing and transparency

Abstract: A system for rendering visual images that combines sophisticated anti-aliasing and pixel blending techniques with control pipelining in hardware embodiment. A highly-parallel rendering pipeline performs sophisticated polygon edge interpolation, pixel blending and anti-aliasing rendering operations in hardware. Primitive polygons are transformed to subpixel coordinates and then sliced and diced to create "pixlink" elements mapped to each pixel. An oversized frame buffer memory allows the storage of many pixlinks for each pixel. Z-sorting is avoided through the use of a linked-list data object for each pixlink vector in a pixel stack. Because all image data values for X, Y, Z, R, G, B and pixel coverage A are maintained in the pixlink data object, sophisticated blending operations are possible for anti-aliasing and transparency. Data parallelism in the rendering pipeline overcomes the processor efficiency problem arising from the computation-intensive rendering algorithms used in the system of this invention. Single state machine control is made possible through linked data/control pipelining.

Automated subpixel image registration of remotely sensed imagery

Abstract: An algorithm is described for the automated registration of remotely sensed imagery that registers 6000 × 6000-pixel images in 8–18 minutes on an IBM RISC System/6000® workstation. The resulting registration is accurate to the subpixel level even in the presence of noise and large areas of change in the images. It is shown that the registration- mapping function for parallel projections has the form F(x,y) = A(x,y) + h(x,y)e, where A(x,y) is an affine transformation, h(x,y) is a function that depends on the topographic heights, and e is a vector that defines the epipolar lines. The algorithm determines the parameters of this equation using only the image data, without knowledge of the viewing orientations or scene point coordinates. The search for match points is then a one-dimensional search along the epipolar lines, which greatly increases the speed and accuracy of the registration.

Adaptive window algorithm for aerial image stereo

Abstract: Binocular stereo vision processes estimate 3D surfaces using a pair of images taken from different points of view. Three-dimensional surface characteristics are estimated by matching 2D image areas or features corresponding to the projections of the same 3D points. The most classic area-based methods used cross correlation with a fixed window-size, but this technique presents a major drawback: the computation of depth is generally prone to errors close to surface discontinuities. In this paper, we present our current work on aerial stereo images of urban areas. A correlation-based algorithm, with an adaptive window-size constrained by an edge map extracted from the images, is presented. This technique is not used to refine an initial disparity map but to create one with good discontinuities location. The algorithm follows three steps: first, window sizes for each pixel are computed; second, a disparity map is created; third, map completion is performed and a final dense disparity map with subpixel precision is produced by Kanade correction. Experimental results on real aerial images are presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Adaptive spatial/spectral detection of subpixel targets with unknown spectral characteristics

Abstract: This paper extends the maximum likelihood concept as applied to the adaptive detection of sub-pixel targets with unknown spectral signatures. The clutter is modeled stochastically with a spatial-spectral covariance matrix. The target model is primarily stochastic and partially deterministic. Within any given spectral band the spatial target signature is deterministic. For the sub-pixel target application, a system point spread function (PSF) is used. The PSF is allowed to vary spectrally, due to the dependency of a sensor's diffractive PSF on the spectral wavelength. The spectral target signature is completely stochastic and must be determined at each pixel using maximum likelihood estimation techniques. Based on these assumptions, an optimal maximum likelihood processor is derived. Encouraging performance results are presented from real IR data. Detection probabilities are shown in many cases to improve significantly when compared to spatial-only detection processes.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Precision of subpixel measurements in videometry

Abstract: Investigations have been carried out on the precision of target location in digital images to determine the influence of spatial and intensity quantization and threshold levels. Circular targets and centroiding methods are used in the study, and deviations from ideal images of the targets cause considerable loss of precision. Under favorable conditions, the precision of location was found to be better than 0.02 pixel size in both the x and y directions. The precision varies with several hundred percent according to the choice of the quantization parameters.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Robust and fast computation of edge characteristics in image sequences

Abstract: In this paper we consider a non-parametric analytical model of the intensity for a curved edge, and derive the relations between the image data and some local characteristics of the edge, in the discrete case. In order to identify this model we also study how to develop high order non-biased spatial derivative operators, with subpixel accuracy. In fact, this discrete approach corresponds to the notion of spatio-temporal surfaces in the continuous case, and provides a way to obtain some of the spatio-temporal parameters from an image sequence. An implementation is proposed, and experimental data are provided. Computed characteristics are subpixel localization, normal displacement between two frames, orientation and curvature, but the method is easy to extend to other geometrical or dynamical parameters of the edge. Results derived in this paper are always valid for step-like edges, but computation of orientation and curvature are also valid for edges with more general profiles.

Subpixel edge estimation using geometrical edge models with noise miniaturization

Abstract: The significant disadvantage for traditional contour representation is as the resolution is reduced the effort of undersampling is proportional enlarged. The goal of this study is to improve edge detection results, especially for those corner points in low resolution. This study describes a method, which is based on 4-connected pixel-wise linearization, for finding contours from low resolution video images. This allows a more accurate inspection and identification of objects from image data. In practice, geometrical models are used to manipulate this linearization. A method is employed for examining the corner points as well. >

Subpixel Resolution from Multiple Images

Abstract: Multiple images taken from similar locations and under similar lighting conditions contain similar, but not identical, information. Slight differences in instrument orientation and position produces mismatches between the projected pixel grids. These mismatches ensure that any point on the ground is sampled differently in each image. If all the images can be registered with respect to each other to a small fraction of a pixel accuracy, then the information from the multiple images can be combined to increase linear resolution by roughly the square root of the number of images. In addition, the gray-scale resolution of the composite image is also improved. We describe methods for multiple image registration and combination, and discuss some of the problems encountered in developing and extending them. We display test results with 8:1 resolution enhancement, and Viking Orbiter imagery with 2:1 and 4:1 enhancements.