Showing papers on "Subpixel rendering published in 1990"

Three-dimensional displacement measurements using digital image correlation and photogrammic analysis

Abstract: The application of digital image correlation and stereoscopic principles is used to determine three-dimensional displacements. Two pairs of stereo images of a speckled surface before and after deformation are digitized and correlated to determine the three-dimensional displacements. The images are interpolated so as to account for subpixel displacements. A sequential decision technique and a coarsefine search are employed to increase computer efficiency and decrease run time. Very accurate results are obtained, expecially when the magnification is increased. The effect of camera tilt is shown to be negligible. Theory and experimental verification are presented.

Estimation of subpixel vegetation cover using red-infrared scattergrams

Abstract: The bulk properties of discontinuous vegetation canopies are estimated at subpixel scales by applying the method of moments to a linear stochastic geometric model of canopy-soil reflectance and one set of multispectral observations without ground truth. The procedure involves the formulation of conditional moments for subsets of pixels that possess similar properties and can be identified through their common orientation in red-infrared scattergrams. The analysis is facilitated by assuming geometric similarity among the canopy elements and by formulating a sampling scale ratio in terms of the bulk geometric scales of the canopy and the pixel. Three versions of the method are demonstrated using two simulated scenes and an actual forested watershed for which aerial radiometric data and corresponding ground truth were obtained. >

Apparatus and method for providing a gray scale in liquid crystal flat panel displays

Abstract: A liquid crystal display is described that includes gray scale capability Each pixel of the display is subdivided into a plurality of subpixels Each subpixel has coupled thereto a thin film transistor, the thin film transistor coupled to the effective subpixel capacitor The liquid crystal material is contained between the effective capacitor plates The voltage applied to the effective capacitor resulting from current flowing through the thin film transistor controls the optical activity of the subpixel By controlling parameters associated with the thin transistor and by controlling the voltage applied to the pixel (and the subpixel thin film transistors), the optical properties of the subpixel can be controlled as a result of the charge applied across the effective capacitor to provide an angular independent gray scale for the pixel

Liquid crystal display with sub-pixels

Abstract: A half-tone pixel having subpixels and control capacitor constituting a 100 percent optically active pixel. The subpixel design results in no reductions in the maximum pixel aperture ratio, brightness or contrast, as a pixel with no subpixels would have. Various subpixel layouts including differing numbers of subpixels and subpixel-turn-on sequences may be implemented and still result in the entire pixel being optically active.

A survey and examination of subpixel measurement techniques

Abstract: There is increasing use of electronic sensors and digital signal processing for measurements of optically acquired data. Applications include automatic inspection, surveying, remote sensing and photogrammetry. Sensors, at the present time, require subpixel methods to improve the resolution above that available given the spacing of sensing elements and the analogue to digital conversion resolution. This paper reviews proposed subpixel methods in the context of an increasingly important application, namely, the determination of the position of a laser spot on a sensing array for triangulation. A number of techniques are chosen and analysed experimentally. Their performances are compared and contrasted with respect to spatial resolution, quantisation accuracy and noise. For the comparison, use is made of simulated data, and real data obtained from a triangulation system9.

Predicting and estimating the accuracy of a subpixel registration algorithm

Abstract: It is shown that an efficient practical registration algorithm previously described by H.G. Barrow et al. (1977) can provide high-accuracy registration. Experiments with a quantized video image of a solid triangle yielded registration that was accurate to 3% of the interpixel spacing (i.e. accurate to 0.5 mils) in the x and y directions and 0.015 degrees in rotation. It may also be important to predict the accuracy in advance, to see whether specifications can be met and to estimate accuracy during registration, in order to control quality. The authors provide practical formulas for both purposes for two kinds of image point data: edge detection (ED) data and direct measurement (DM) data. In two experiments using ED data, the predicted, estimated, and observed accuracies are all in agreement. The prediction theory developed suggests five precautions to avoid loss of registration accuracy. Perhaps most important is Precaution c, the necessity of the ED case not to have a large fraction of the total segment length of the model aligned with the horizontal or vertical directions of the pixel grid. When the model consists largely of horizontal and vertical segments, a good way to observe this precaution is to tilt the pixel grid a few degrees away from perfect alignment, e.g. by tilting the video camera. A third experiment verifies that violating Precaution c can seriously degrade accuracy. >

Accurate rendering by subpixel addressing

Abstract: A simple method is presented for eliminating most pixel-positioning errors when rendering lines and polygons with J.E. Bresenham's algorithm (see IBM Syst. J., vol.4, no.1, p.25-30 (1965)). The method affects only the calculation of the initial values for Bresenham's vector-generating algorithm. It does not alter the actual vector-generating algorithm, requiring only inter arithmetic to find the next pixel in a vector. The method eliminates all dropouts and virtually all overlaps between adjacent polygons whose edges lie on the same line. This eliminates the need to grow polygons to avoid dropout and opens the possibility of drawing surfaces composed of adjacent polygons with read modify/write pixel operations such as add or alpha buffering. It is shown that most rendering artifacts of today's display controllers ultimately result from pixel-positioning errors, not insufficient z-buffer resolution. >

Transputer-based image photon-counting detector

Abstract: A prototype microprocessor-based electronic processing system is described which performs the on-line data processing in an image photon-counting detector. The detector head consists of a microchannel-plate intersifier optically coupled to a CCD with rapid-scanned readout. The digitized data are passed to a group of transputers which separate out the events, calculate the event centers to subpixel accuracy and accumulate the results in an image buffer. In the prototype, all processing is done in software for evaluation purposes. This paper discusses the basic design of the system, the centroiding algorithm and fixed patterning correction, and the implications of the results for future systems.

Functional relation among subpixel canopy cover, ground shadow, and illuminated ground at large sampling scales

Abstract: The functional relation among subpixel canopy cover, illuminated soil, and shadowed soil, which progressively develops with increasing pixel size, is investigated for Poisson distributed plants using a geometric canopy simulation model An analytical relation among cover components is shown to be applicable when the scale of the pixel is much larger than the scale of the plant and ground shadow The analysis is facilitated through the use of a nondimensional solar-geometric similarity parameter, eta, equal to the ratio of the area of one plant canopy to its associated ground shadow area, as viewed from nadir A sampling scale ratio, defined as the ratio of the area of the pixel to the mean area of a single plant shadow, is tested as a quantitative criterion to evaluate when the functional relation among subpixel components occurs The results of a remote sensing experiment over a natural conifer landscape provide preliminary confirmation of the theoretical analysis

Detection of weak, subpixel targets using mesh-connected cellular automata

Abstract: Effective use of military cellular automata such as military data array processor (MilDAP) and geometric arithmetic parallel processor (GAPP), in weak, subpixel target detection is shown to be possible by using new signal processing regimes based on binary ranking filter theory By using binary ranking filters, the MilDAP can furnish 6 dB of processing gain against white Gaussian noise while monitoring from one to four million potential target tracks at 10-40 frames/s GAPP is shown to be capable of monitoring 37 million tracks over 216*384 detectors at 14000 frames/s and, in a time sharing mode, 15 million tracks over 432*768 detectors at 24 frames/s The special case of threatening targets is discussed, as well as alternate cellular architectures which use multidimensional binary ranking filters in multidimensional coordinate systems >

An adaptive algorithm for edge detection with subpixel accuracy in noisy images

Abstract: There is a tradeoff between noise insensitivity and accurate position in edge detection. This paper suggests an adaptive algorithm which takes advantage of both LOG and NonLL filters. Several masks of different size cover a wide band of frequencies under the supervision of the nonlinear Laplace filter. Calculation is dramatically reduced by thresholding. Zero-crossings are tested simultaneously with convolution and interpolated with subpixel accuracy.

A priori information in image analysis: assessment of intensity distribution for definition of shape and size of small vessels

Abstract: A method for incorporating prior information in computer-based image analysis is described and critically evaluated. The specific application improves pixel resolution (spot size) and shape estimation of small vessel cross sections in exchange for dynamic range information. The potential subpixel spot size sensitivity for a 16-bit gray scale is better than one part in 32000. The performance of shape recovery is assessed in relation to signal-to-noise ratio, acquired image resolution, vessel shape complexity and aspect ratio. The process is shown to be effective and stable when the signal-to-noise ratio exceeds 10, when the number of pixels across the vessel is two or more, when the vessel contour has as many as six lobes, and when the aspect ratio is in the range 0.2-5.0. >

Analysis of SILEX tracking sensor performance

Abstract: Two tracking sensor breadbroads have been developed for the European SILEX program. Critical requirements to be met by these sensors include the determination of the 1-sigma position of the focused laser spot on the detector surface to accuracies of less than 100 nm, with update frequencies as high as 8 kHz, and the minimum optical power level of 110 pW. The design is based on the use of a 14 x 14 pixel CCD array, where the spot position is determined to small subpixel accuracies over the central 2 x 2 pixel area via a centroiding algorithm executed in a microprocessor. Coarse position measurements are also made over the full area at rates up to 2 kHz.

Precise localization of geometrically known image edges in noisy environment

Abstract: A method based on random samples least variance geometric form determination in precision measurement using computer vision is presented. The method is designed to extract the geometrically known image edges in a digital image with subpixel precision. The advantages of such a method are that the localization precision is unaffected by the noisy environment, and for many elementary geometrical forms it does not need traditional edge-following but only vertical and/or horizontal scannings of images. The precise localization and the elimination of the noise effect are achieved by iterative form determination from randomly chosen image points and the selection of points according to the measurement of the distance between image points and the reference primitive. The application of this technique to the measurement of ellipse and polygonal family forms is presented. >

Registration of digital subtraction peripheral angiography images

Abstract: Computer algorithms for automatic translational registration are investigated. Sometimes patient movement is not simply translational (this often occurs in the foot, for example) requiring the mask frame to be warped. Two methods of warping are investigated: (1) segmented registration where the mask frame is segmented and each segment is registered; (2) subpixel warp where, for each pixel in the contrast frame, the nearest neighbors in the mask frame are searched for the best subpixel match. The study indicates that automatic registration is feasible for angiography images of the legs and can probably be done in a reasonable amount of time if special hardware is utilized. In all cases, results match those obtained by a human operator. >

Calculation of analytical elements in space using a contour algorithm

Abstract: The parameters p of analytical elements in space (straight lines, circles, spheres, cylinders, etc) are determined by minimizing the distance between the rays related to a contour of an element in the images and the element in space itself The coordinates of a contour assigned to an element are determined with subpixel accuracy using a complex filter algorithm, which automatically follows a line The proposed method does not need marks on the object to calculate the desired parameters Hence it is especially suited for quality control in industrial applications

Improved resolution of medical 3-D x-ray computed-tomographic images

Abstract: Many applications require the acquisition of 3D CT images made of a stack of 2D Xray slices. The different slices are obtained by the displacement of the patient table which sets the resolution in the z direction perpendicularly to the slice plane. This resolution is physically limited by the detector width on which the X-ray radiation is integrated. Those detectors inherently carry out a low pass filtering process and aliasing effects. As a consequence the reconstruction of a slice in any direction can present artefacts. Then we propose to apply a superresolution technique based on a deconvolution method associated to oversampling using subpixel motion in order to improve the resolution in the z-direction. This method requires the acquisition of overlapping slices which are later processed directly in the spatial domain what is particularly interesting for computer time. Its application provides thinner and accurate new slices. After the presentation of the method the results obtained on experimental images coming from a conventional CT scanner are presented.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Determination of ground control points to subpixel accuracies for rectification of spot imagery

Abstract: This study focused on the issue of how to obtain subpixel image coordinates of ground control points (GCP) by using image processing techniques. Objects with well-defined geometric shapes, such as an elliptic disk-shaped disk, and an intersection of two straight roads, may be identified on a SPOT image. Their centers can be processed as GCPs with subpixel accuracies if the background appears homogeneous. In many cases, such conditions can be satisfied. Algorithms MATSEL (Median Axis Transformation by Subpixel Edge Location), MATGAUS (Median Axis Transformation by GAUSsian fitting), and EDCA (Elliptic Disk Center Algorithm) were developed to derive GCPs with subpixel accuracies from SPOT images. MATSEL and EDCA are based on finding edge locations according to the moment preservation principle, while MATGAUS is based on fitting a set of raw data to a Gaussian distribution function. EDCA was developed several years ago, and was used in an automated coordinate measuring system. MATSEL and MATGAUS can be used to determine the center of a bright cross on a dark background. All three algorithms were tested with simulation data, and achieved an accuracy of 0.02-0.10 pixel. SPOT panchromatic data for Jacksonville, Florida were chosen for the study. The image coordinates of GCPs from two subscenes, Hilliard NE Florida and Gross Florida-Georgia, were calculated by the image processing algorithms. The ground coordinates of the GCPs were digitized from USGS 7.5' quadrangles. The subscenes were then rectified to a UTM coordinate system by a simple rectification method. Rectification of the Hilliard NE area using 10 GCPs achieved a RMSE of two meters along both x- and y-directions, which exceeded Interim Accuracy Standards for Large-Scale Maps (IASLSM) for maps at scale 1:12,000. The results from the Gross area with more relief were within one meter to meet IASLSM for maps at scales of 1:24,000 when 29 GCPs were used. More accurate results can be achieved if the ground coordinates of GCPs can be provided through a field survey. The methodology developed in this research allows a less skilled operator to determine accurately the image coordinates of a GCP. The further improvement of the algorithms will provide important means for automated/ semiautomated rectification.