Showing papers on "Subpixel rendering published in 2001"

Hyperspectral subpixel target detection using the linear mixing model

Abstract: Relative to multispectral sensing, hyperspectral sensing can increase the detectability of pixel and subpixel size targets by exploiting finer detail in the spectral signatures of targets and natural backgrounds. Over the past several years, different algorithms for the detection of full-pixel or subpixel targets with known spectral signature have been developed. The authors take a closer and more in-depth look at the class of subpixel target detection algorithms that explore the linear mixing model (LMM) to characterize the targets and the interfering background. Sensor noise is modeled as a Gaussian random vector with uncorrelated components of equal variance. The paper makes three key contributions. First, it provides a complete and self-contained theoretical derivation of a subpixel target detector using the generalized likelihood ratio test (GLRT) approach and the LMM. Some other widely used algorithms are obtained as byproducts. The performance of the resulting detector, under the postulated model, is discussed in great detail to illustrate the effects of the various operational factors. Second, it introduces a systematic approach to investigate how well the adopted model characterizes the data, and how robust the detection algorithm is to model-data mismatches. Finally, it compares the derived algorithms with regard to two desirable properties: capacity to operate in constant false alarm rate mode and ability to increase the separation between target and background.

A fast direct Fourier-based algorithm for subpixel registration of images

Abstract: This paper presents a new direct Fourier-based algorithm for performing image-to-image registration to subpixel accuracy, where the image differences are restricted to translations and uniform changes of illumination. The algorithm detects the Fourier components that have become unreliable estimators of shift due to aliasing, and removes them from the shift-estimate computation. In the presence of aliasing, the average precision of the registration is a few hundredths of a pixel. Experimental data presented here show that the new algorithm yields superior registration precision in the presence of aliasing when compared to several earlier methods and has comparable precision to the iterative method of P. Thevenaz et al. (1998).

Method and apparatus for adjusting subpixel intensity values based upon luminance characteristics of the subpixels for improved viewing angle characteristics of liquid crystal displays

Abstract: Viewing angle characteristics of a liquid crystal display (LCD) are improved by reducing the number of subpixels in an image with mid-tone luminance values. In a preferred embodiment, a first table of entries associating subpixel intensity values and subpixel luminance values for a LCD in at least one viewing angle direction is provided. A target intensity value is determined from the first table, corresponding to the average subpixel luminance over a small number of adjacent subpixels. A second table of entries associates the target intensity values with intensity values above and below the target. The adjacent subpixel intensity values are modified according to the second table, thereby reducing the number of subpixels with mid-tone luminance values. The subpixel data is preferably processed within a portion of an application-specific integrated circuit (ASIC), contained within the display module.

Automated detection of subpixel hyperspectral targets with continuous and discrete wavelet transforms

Abstract: A major step toward the use of hyperspectral sensors to detect subpixel targets is the ability to detect constituent absorption bands within a pixel's hyperspectral curve. This paper introduces the use of multiresolution analysis, specifically wavelet transforms, for the automated detection of low amplitude and overlapping constituent bands in hyperspectral curves. The wavelet approach is evaluated by incorporating it into an automated statistical classification system, where wavelet coefficients' scalar energies are used as features, linear discriminant analysis is used for feature reduction, and maximum likelihood (ML) decisions are used for classification. The system is tested using the leave-one-out procedure on a database of 1000 HYDICE signals where half contain a subpixel target or additive Gaussian absorption band. Test results show that the continuous and discrete wavelet transforms are extremely powerful tools in the detection of constituent bands, even when the amplitude of the band is only 1% of the amplitude of the background signal.

Liquid crystal display device, electroluminescent display device, method of driving the devices, and method of evaluating subpixel arrangement patterns

Abstract: An active matrix liquid crystal display device has a plurality of unit pixels being arranged in a matrix configuration, each unit pixel being divided into a plurality of subpixels. Each of the subpixels has a subpixel electrode, a pixel transistor connected to the subpixel electrode, and a voltage controlling capacitor connected to the subpixel electrode. A voltage controlling capacitor line for supplying a compensation voltage signal is connected to the voltage controlling capacitor so that after the writing to the subpixel has been completed, the potential of the compensation voltage signal is varied to modulate the potential of the subpixel electrode to be a predetermined voltage, using the voltage controlling capacitor. Such combining of spatial dithering attained by a pixel-dividing technique and a capacitively-coupled driving method eliminates the need for digital-to-analog converter circuits, attains gray scale display based on a digital image signal, and achieves a reduction in power consumption.

Advances in superresolution using L-curve

Abstract: Subsequent to the work of Kim, Bose, and Valenzuela in 1990 on the simultaneous filtering and interpolation of a registered sequence of undersampled noisy and shift-invariant blur degraded images, Bose and Boo tackled in 1998 the problem of reconstructing a high-resolution image from multiple undersampled, shifted, degraded frames with subpixel displacement errors. This led to a formulation involving a periodically shift-variant system model. Lertrattanapanich and Bose advanced in 1999 a procedure for construction of a high-resolution video mosaic following the estimation of motion parameters between successive frames in a video sequence generated from a video camera. Current research is focused on simultaneous blur identification and robust superresolution. The blur is not restricted to be linear shift-invariant and could not only be of the linear shift-variant type but also some nonlinear blurs could be accommodated. The optimal tuning parameter may, if desired, be calculated analytically and not by trial-and-error.

Trinocular stereo: a real-time algorithm and its evaluation

Abstract: In telepresence applications each user is immersed in a rendered 3D-world composed from representations transmitted from remote sites. The challenge is to compute dense range data at high frame rates, since participants cannot easily communicate if the processing cycle or network latencies are long. Moreover errors in new stereoscopic views of the remote 3D-world should be hardly perceptible. To achieve the required speed and accuracy, we use trinocular stereo, a matching algorithm based on the sum of modified normalized cross-correlations, and subpixel disparity interpolation. To increase speed we use Intel IPL functions in the pre-processing steps of background subtraction and image rectification as well as a four-processor parallelization. To evaluate our system we have developed a testbed which provides a set of registered dense "ground-truth" laser data and image data from multiple views.

Identification of a new source of peak locking, analysis and its removal in conventional and super-resolution PIV techniques

Abstract: One of the key factors that limit accuracy of particle image velocimetry (PIV) is the peak-locking effect In this paper, a previously uncharacterised source of peak locking is presented This source is neither related to the sensor geometry nor the subpixel resolution peak-fitting algorithms It is present even when the particles are well described in terms of sensor spatial resolution (ie for particle diameters larger than 2 pixels) If no specific actions to avoid it are taken, its effect is especially important in those super-resolution systems that are based on iteratively reducing the size of the interrogation window In this work, the mentioned source and its effects are studied and modelled Based on this study, the actions required to avoid this type of peak locking are described This includes the most usual correlation-based PIV systems, as well as super-resolution ones Once this source of inaccuracy is avoided, it is possible to discriminate the performance of different types of correlation algorithms As a consequence, specific proposals for the algorithms in the last steps of multigrid super-resolution PIV systems are given The performances of the proposed solutions are verified using both synthetic and real PIV images

Characterization of surface heterogeneity detected at the MISR/TERRA subpixel scale

Abstract: Vegetation structure can have a significant impact on the degree of anisotropy in the reflected radiation field. With the appropriate characterization of these effects, the analysis of multiangular data, such as provided by the Multi-angle Imaging SpectroRadiometer (MISR) instrument on board TERRA, can yield statistical information about the type of surface heterogeneity that exists at the subpixel scale.

Georegistration of airborne hyperspectral image data

Abstract: A suite of geometric sensor and platform modeling tools has been developed which have achieved consistent subpixel accuracy in orthorectification experiments. Aircraft platforms in turbulent atmospheric conditions present unique challenges and have required creative modeling approaches. The geometric relationship between an image point and a ground object has been modeled by rigorous photogrammetric methods. First and second order Gauss-Markov processes have been used to estimate the platform trajectory. These methods have been successfully applied to HYDICE and HyMap data sets. The most important contributors to the subpixel rectification accuracy have been the first order Gauss-Markov model with control linear features.

Subpixel microscopic deformation analysis using correlation and artificial neural networks.

Abstract: Microscopic deformation analysis has been performed using digital image correlation and artificial neural networks (ANNs). Cross-correlations of small image regions before and after deformation contain a peak, the position of which indicates the displacement to pixel accuracy. Subpixel resolution has been achieved here by nonintegral pixel shifting and by training ANNs to estimate the fractional part of the displacement. Results from displaced and thermally stressed microelectronic devices indicate these techniques can achieve comparable accuracies to other subpixel techniques and that the use of ANNs can facilitate very fast analysis without knowledge of the analytical form of the image correlation function.

Empirical filter estimation for subpixel interpolation and matching

Abstract: We study the low-level problem of predicting pixel intensities after subpixel image translations. This is a basic subroutine for image warping and super-resolution, and it has a critical influence on the accuracy of subpixel matching by image correlation. Rather than using traditional frequency-space filtering theory or ad hoc interpolators such as splines, we take an empirical approach, finding optimal subpixel interpolation filters by direct numerical optimization over a large set of training examples. The training set is generated by subsampling larger images at different translations, using subsamplers that mimic the spatial response functions of real pixels. We argue that this gives realistic results, and design filters of various different parametric forms under traditional and robust prediction error metrics. We systematically study the performance of the resulting filters, paying particular attention to the influence of the underlying image sampling regime and the effects of aliasing ("jaggies"). We summarize the results and give practical advice for obtaining subpixel accuracy.

System and method for improving the sharpness of a video image

Abstract: There is disclosed an apparatus for sharpening an edge in a video image. The apparatus comprises: 1) a first circuit for determining a first luminance value of a first pixel associated with the first edge and a second luminance value of a second pixel associated with the first edge, wherein the first and second pixels are adjacent pixels; 2) a second circuit for determining a position of a first subpixel disposed between the first and second pixels, wherein the first subpixel position is disposed approximately at a center of the first edge; 3) a third circuit for increasing a luminance value of a second subpixel disposed on a first side of the first edge center; and 4) a fourth circuit for decreasing a luminance value of a third subpixel disposed on a second side of the first edge center opposite the first side.

An ROC analysis for subpixel detection

Abstract: ROC (Receiver Operating Characteristic) analysis has been widely used to evaluate detection performance. It is based on the Neyman-Pearson detection theory, which solves binary hypothesis testing problems. In mixed pixel classification many algorithms that are developed to estimate abundance fractions (of image endmembers) generally produce gray scale images. As a result, they are not directly applied to hypothesis testing problems. Instead of using the standard ROC curve generated by the detection power versus the false alarm probability, a 3-dimensional (3D) ROC curve is developed in this paper for subpixel detection. It is a 3D plot derived from the mean-detection probability versus the mean-false alarm rate with the third dimension specified by abundance fractions produced by subpixel detection algorithms. In order to illustrate the utility of the proposed 3D ROC analysis in subpixel detection, several linear unmixing-based algorithms are used for performance evaluation.

Liquid crystal display element with a defect repairing function

Abstract: A liquid crystal display (LCD) element with a defect repairing function and a defect repairing method of the same. In an embodiment of the invention, a pixel is associated with a plurality of scan lines and a plurality of data lines. Along with separate spare lines, melting connection can be obtained to form a circuit path and to compensate for broken wires. A single pixel can also have a plurality of subpixels with spare conduction ports and meltable joints so that defective electrodes can be separated. The spare conduction ports can be melted and connected so that other subpixels support and compensate for the defective subpixel to minimize pixel signal loss.

Practical aspects of grayscale calibration of display systems

Abstract: Five aspects of grayscale calibration of display systems are discussed: (1) As has been shown before, it is very desirable that the discrete luminance levels on the calibrated display function are placed with high accuracy. The accuracy of a calibration with a commercial system is demonstrated. The effect of 8-bit versus 10-bit precision in computing the required luminance levels on contrast and noise in images is illustrated. (2) Display controllers of liquid crystal displays predominantly offer 8-bit precision. A subpixel modulation technique to increase the grayscale accuracy is presented. (3) LCDs may exhibit characteristic curves with non-monotonically changing first derivatives. To achieve a high degree of calibration accuracy, these curves must be represented by a sufficient number of strategically placed measurement points. (4) Photometers of commercial calibration systems for CRT monitors have wide acceptance angles. For display systems with non-uniform angular emission distribution, these photometers may indicate luminance values that do not represent the luminance perceived through the small acceptance angle of the eyes of observers. Techniques for adapting these photometers to luminance measurements for liquid crystal displays are proposed. (5) The suitability of built-in photo-sensors (attached to the tapered glass envelope of the CRT) for calibrating a monitor according to the DICOM Display Function Standard is investigated.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laser beam deflectometry based on a subpixel resolution algorithm

Abstract: A deflectometric method for the characterization of optical systems is presented. It is based on the use of a CCD camera and a subpixel resolution algorithm for the measurement of the deflection of a laser beam that propagates through the system. To obtain accurate results, three different algorithms for measuring the position of the deflected beam are tested and compared. Based on this comparison, an algorithm based on the calculation of the phase of the fast Fourier transform (FFT) is selected, and an accuracy of 0.024 pixels is obtained on the determination of the beam position in our setup. Using an XY scanning stage, the proposed method is completely automated and applied for the characterization of ophthalmic lenses. In this application, the gradients of the wavefront refracted by the lens are measured directly, and from them, the thickness and the local power of the lens are computed.

Curvature in digital 2d images

Abstract: The paper presents an analysis of sources of errors when estimating derivatives of numerical or noisy functions. A method of minimizing the errors is suggested. When being applied to the estimation of the curvature of digital curves, the analysis shows that under the conditions typical for digital image processing the curvature can rarely be estimated with a precision higher than 50%. Ways of overcoming the difficulties are discussed and a new method for estimating the curvature is suggested and investigated as to its precision. The method is based on specifying boundaries of regions in gray value images with subpixel precision. The method has an essentially higher precision than the known methods.

Liquid crystal display device, el display device and drive method therefor and display pattern evaluation method of subpixel

Abstract: (57) [Problem] To provide a gray scale display based on a digital image signal without providing a digital / analog conversion circuit by using an area gray scale method by pixel division and a capacitive coupling drive method, and to reduce power consumption. Provided is a liquid crystal display device capable of reducing the number of pixels. A liquid crystal display device according to the present invention is an active matrix liquid crystal display device having a structure in which a plurality of unit pixels are arranged in a matrix, and each unit pixel is divided into a plurality of sub-pixels. ing. Each sub-pixel individually has a sub-pixel electrode, a pixel transistor connected to the sub-pixel electrode, and a voltage control capacitor connected to the sub-pixel electrode. Further, a voltage control capacitor line for supplying a compensation voltage signal is connected to the voltage control capacitor. After the writing to the sub-pixel is completed, the potential of the compensation voltage signal is changed, and the sub-pixel electrode is changed via the voltage control capacitor. Is modulated to a predetermined potential.

A fast edge location measurement with subpixel accuracy using a CCD image

Abstract: This paper describes an analogue-based approach to fast subpixel-level edge detection. Although the most common subpixel edge detection methods employ digital-based approaches, they at present show certain drawbacks such as difficulty of fast, in-line subpixel edge detection, the necessity of implementing expensive high-resolution A/D converters, and difficulty in performing continuous, dynamic subpixel edge detection. We propose a new analogue-based first derivative subpixel edge detection approach to surmount these drawbacks. Our method involves the approximation of the distribution curve of the first derivative of the output of a CCD by using the second-order polynomial, and thus can accurately detect a peak position of the differential curve by means of the interpolating calculation, the operation of which is realized primarily through the use of analogue circuitry. The measurements of a concrete form using the prototype system demonstrate that its resolution under ideal conditions is about 1/10 pixels. We thus conclude that the approach described is effective for fast subpixel edge detection.

A novel subpixel edge detection system for dimension measurement and object localization using an analogue-based approach

Abstract: This paper describes an analogue-based approach to subpixel-level edge detection for dimension measurement and object localization. Although the most common subpixel edge detection methods employ digital-based approaches, at present they show certain drawbacks such as the difficulty of real-time, in-line subpixel edge detection, the necessity of implementing expensive high-resolution A/D converters, and difficulty in performing continuous, dynamic subpixel edge detection. These drawbacks present a difficult problem in digital-based systems industrial applications. We propose a new analogue-based first derivative subpixel edge detection approach to overcome these drawbacks. Our method involves the approximation of the distribution curve of the first derivative of the output of a CCD by using the second-order polynomial, and thus can accurately detect a peak position of the differential curve by means of the interpolating calculation, the operation of which is realized primarily through the use of analogue circuitry. The measurements of a concrete form using the prototype system demonstrate that its resolution under ideal conditions is about 1×10-1 pixels. While the resolution of this system decreases in an actual situation, the resolution remains at an acceptable subpixel level. We thereby conclude that the approach described in this paper is effective for real-time, low cost edge detection.

Subpixel Spatial Resolution of the X-Ray Charge-Coupled Device Based on the Charge Cloud Shape

Abstract: When an X-ray photon lands into a pixel (event pixel), the primary charge is mainly collected into the event pixel. If the X-ray landing position is sufficiently close to the pixel boundary, the primary charge spills over to the adjacent pixel forming split events. We can easily understand that there are three parameters coupled together; the X-ray landing position inside the pixel, the X-ray event pattern and the primary charge cloud shape. We can determine any one of them from the other two parameters. Since we know the charge cloud shape using the multi-pitch mesh experiment, we can calculate the X-ray landing position with subpixel resolution using the event pattern. We applied our method to Ti–K X-rays for the charge-coupled device with 12 µm square pixel. Once the primary charge splits into the adjacent pixel, we can determine the X-ray landing position with subpixel resolution. Using three- or four-pixel split events, we can determine the X-ray landing position with an accuracy of less than 1 µm. For a two-pixel split event, we obtained a similar position accuracy in the split direction with no improvement in the direction perpendicular to it. We will discuss the type of charge-coupled device (CCD) which can achieve the subpixel resolution for the entire area of the CCD.

High‐resolution digital elevation models derived from Viking Orbiter images: Method and comparison with Mars Orbiter Laser Altimeter Data

Abstract: The purpose of this paper is to present a method to derive local and high-resolution digital elevation models (DEM) of Mars from Viking Orbiter images. We focus on two aspects that appear to be new in photogrammetry applied to Mars: the correlation method and the relative orientation method based on the analysis of the coplaneity. We demonstrate that a DEM from two Viking Orbiter images selected according to the criteria of parallax height ratio, resolution, and illumination conditions can be obtained with a better spatial lateral resolution than the interpolated Mars Orbiter Laser Altimeter (MOLA) data. Two images on the Deuteronilus Mensae area satisfy these criteria. The algorithm of reconstruction of the topography is divided into two steps. First, a correlation method at subpixel level based on Fourier transform has been adapted to extract image location of homologous points. As initial camera positions and angles are known with poor accuracy, an adjustment is then carried out by the method of relative orientation which requires no absolute control points and takes advantage of the subpixel accuracy of our matching algorithm. Finally, the DEM is projected into a Martian reference frame and registered to MOLA data for validation. The spatial resolution depends on the roughness of the area and is locally close to the distance between individual MOLA foot prints along one profile (300 m), as demonstrated from the comparison with MOLA profiles. These first results of high-resolution DEM from Viking Orbiter images should be used with MOLA data for many geological studies that require high-resolution topographic data.

Advanced thermal image processing for medical and biological applications

Abstract: In this paper, new image processing tools are presented for conversion thermal and visual images, mainly for application in medicine and biology. A novel method for area and distance evaluation based on statistical differencing is discussed. In order to increase the measurements accuracy, the interpolation and subpixel bitmap processing are chosen.

A system to evaluate the accuracy of a visual mosaicking methodology

Abstract: When underwater vehicles navigate close to the ocean floor, computer vision techniques can be applied to obtain motion estimates. A complete system to create visual mosaics of the seabed is described in this paper. Unfortunately, the accuracy of the constructed mosaic is difficult to evaluate. The use of a laboratory setup to obtain an accurate error measurement is proposed. The system consists on a robot arm carrying a downward looking camera. A pattern formed by a white background and a matrix of black dots uniformly distributed along the surveyed scene is used to find the exact image registration parameters. When the robot executes a trajectory (simulating the motion of a submersible), an image sequence is acquired by the camera. The estimated motion computed from the encoders of the robot is refined by detecting, to subpixel accuracy, the black dots of the image sequence, and computing the 2D projective transform which relates two consecutive images. The pattern is then substituted by a poster of the sea floor and the trajectory is executed again, acquiring the image sequence used to test the accuracy of the mosaicking system.

Adaptive parallel rendering on multiprocessors and workstation clusters

Abstract: This paper presents the design and performance of a new parallel graphics renderer for 3D images. This renderer is based on an adaptive supersampling approach that works for time/space-efficient execution on two classes of parallel computers. Our rendering scheme takes subpixel supersamples only along polygon edges. This leads to a significant reduction in rendering time and in buffer memory requirements. Furthermore, we offer a balanced rasterization of all transformed polygons. Experimental results prove these advantages on both a shared-memory SGI multiprocessor server and a Unix cluster of Sun workstations. We reveal performance effects of the new rendering scheme on subpixel resolution, polygon number, scene complexity, and memory requirements. The balanced parallel renderer demonstrates scalable performance with respect to increase in graphic complexity and in machine size. Our parallel renderer outperforms Crow's scheme in benchmark experiments performed. The improvements are made in three fronts: (1) reduction in rendering time, (2) higher efficiency with balanced workload,: and (3) adaptive to available buffer memory size. The balanced renderer can be more cost-effectively embedded within many 3D graphics algorithms, such as those for edge smoothing and 3D visualization. Our parallel renderer is MPI-coded, offering high portability and cross-platform performance. These advantages can greatly improve the QoS in 3D imaging and in real-time interactive graphics.

The contracting curve density algorithm and its application to model-based image segmentation

Abstract: The article addresses the problem of model-based image segmentation by fitting deformable models to the image data. From uncertain a priori knowledge of the model parameters, an initial probability distribution of the model edge in the image is obtained. From the vicinity of the surmised edge, local statistics are learned for both sides of the edge. These local statistics provide locally adapted criteria to distinguish the two sides of the edge, even in the presence of spatially changing properties such as texture, shading, or color. Based on the local statistics, the model parameters are iteratively refined using a MAP estimation. Experiments with RGB images show that the method is capable of achieving high subpixel accuracy and robustness even in the presence of texture, shading, clutter, and partial occlusion.