Showing papers on "Subpixel rendering published in 2002"

Detection algorithms for hyperspectral imaging applications

Abstract: We introduce key concepts and issues including the effects of atmospheric propagation upon the data, spectral variability, mixed pixels, and the distinction between classification and detection algorithms. Detection algorithms for full pixel targets are developed using the likelihood ratio approach. Subpixel target detection, which is more challenging due to background interference, is pursued using both statistical and subspace models for the description of spectral variability. Finally, we provide some results which illustrate the performance of some detection algorithms using real hyperspectral imaging (HSI) data. Furthermore, we illustrate the potential deviation of HSI data from normality and point to some distributions that may serve in the development of algorithms with better or more robust performance. We therefore focus on detection algorithms that assume multivariate normal distribution models for HSI data.

Extension of phase correlation to subpixel registration

Abstract: In this paper, we have derived analytic expressions for the phase correlation of downsampled images. We have shown that for downsampled images the signal power in the phase correlation is not concentrated in a single peak, but rather in several coherent peaks mostly adjacent to each other. These coherent peaks correspond to the polyphase transform of a filtered unit impulse centered at the point of registration. The analytic results provide a closed-form solution to subpixel translation estimation, and are used for detailed error analysis. Excellent results have been obtained for subpixel translation estimation of images of different nature and across different spectral bands.

Spatial/spectral endmember extraction by multidimensional morphological operations

Abstract: Spectral mixture analysis provides an efficient mechanism for the interpretation and classification of remotely sensed multidimensional imagery. It aims to identify a set of reference signatures (also known as endmembers) that can be used to model the reflectance spectrum at each pixel of the original image. Thus, the modeling is carried out as a linear combination of a finite number of ground components. Although spectral mixture models have proved to be appropriate for the purpose of large hyperspectral dataset subpixel analysis, few methods are available in the literature for the extraction of appropriate endmembers in spectral unmixing. Most approaches have been designed from a spectroscopic viewpoint and, thus, tend to neglect the existing spatial correlation between pixels. This paper presents a new automated method that performs unsupervised pixel purity determination and endmember extraction from multidimensional datasets; this is achieved by using both spatial and spectral information in a combined manner. The method is based on mathematical morphology, a classic image processing technique that can be applied to the spectral domain while being able to keep its spatial characteristics. The proposed methodology is evaluated through a specifically designed framework that uses both simulated and real hyperspectral data.

Methods, systems, and programming for computer display of images, text, and/or digital content

Abstract: A bitmap of a shape, such as a font, can be subpixel optimized by producing for each of a display's subpixels a coverage value representing the percent of its area covered by the shape being represented and by distributing, to prevent color imbalance, an amount of a given subpixel's coverage value to nearby subpixels of different colors as a function of the percent of the given subpixel's coverage value that causes color imbalance. Web pages can be displayed with scaled-down and subpixel optimized images. A given layout of a Web page can be displayed at each of at least two different selected scale factors, with the font bitmaps used to represent characters in the display at each scale factor having their shape and pixel alignment selected to improve readability for the particular pixel size at which they are displayed at each such scale factor.

Subpixel eye gaze tracking

Abstract: This paper addresses the accuracy problem of an eye gaze tracking system. We first analyze the technical barrier for a gaze tracking system to achieve a desired accuracy, and then propose a subpixel tracking method to break this barrier. We present new algorithms for detecting the inner eye corner and the center of an iris at subpixel accuracy, and we apply these new methods in developing a real-time gaze tracking system. Experimental results indicate that the new methods achieve an average accuracy within 1.4/spl deg/ using normal eye image resolutions.

An Algebraic Algorithm for Nonuniformity Correction in Focal-Plane Arrays

Abstract: A scene-based algorithm is developed to compensate for bias nonuniformity in focal-plane arrays. Nonuniformity can be extremely problematic, especially for mid- to far-infrared imaging systems. The technique is based on use of estimates of interframe subpixel shifts in an image sequence, in conjunction with a linear-interpolation model for the motion, to extract information on the bias nonuniformity algebraically. The performance of the proposed algorithm is analyzed by using real infrared and simulated data. One advantage of this technique is its simplicity; it requires relatively few frames to generate an effective correction matrix, thereby permitting the execution of frequent on-the-fly nonuniformity correction as drift occurs. Additionally, the performance is shown to exhibit considerable robustness with respect to lack of the common types of temporal and spatial irradiance diversity that are typically required by statistical scene-based nonuniformity correction techniques.

Color flat panel display sub-pixel arrangements and layouts for sub-pixel rendering with split blue sub-pixels

Abstract: Various embodiments of a sub-pixel octal grouping are disclosed. The octal grouping may comprise three-color (red, green and blue) sub-pixels with blue colored subpixel comprising twice the number of positions within the octal sub-pixel grouping as the red and green colored sub-pixels. Various embodiments for performing sub-pixel rendering on the sub-pixel groupings are disclosed.

Using saddle points for subpixel feature detection in camera calibration targets

Abstract: The determination of reliable features with subpixel accuracy is an important requirement of any camera calibration algorithm. This paper offers a simple and computationally attractive method for extracting X-junctions with subpixel precision from images of calibration checkerboards by showing how the saddle points associated with them can be determined without any surface fitting required by standard feature detection algorithms.

Invariant subpixel material detection in hyperspectral imagery

Abstract: We present an algorithm for subpixel material detection in hyperspectral data that is invariant to the illumination and atmospheric conditions. The algorithm does not require atmospheric correction. The target material spectral reflectance is the only required prior information. A target material subspace model is constructed from the reflectance using a physical model and a background subspace model is estimated directly from the image. These two subspace models are used to compute maximum-likelihood estimates (MLEs) for the target material component and the background component at each image pixel. These estimates form the basis of a generalized likelihood ratio test for subpixel material detection. We present experimental results, using Hyperspectral Digital Imagery Collection Experiment (HYDICE) imagery, that demonstrate the utility of the algorithm for subpixel material detection under varying illumination and atmospheric conditions.

13.3 Co‐Optimization of Color AMLCD Subpixel Architecture and Rendering Algorithms

Abstract: Color subpixel rendering is enhanced by co-optimizing the color subpixel architecture and algorithms with respect to human vision, resulting in the PenTile Matrix™ subpixel architecture to double the addressability and the MTF limit in both horizontal and vertical axes while reducing driver count. Results of prototype AMLCD panels demonstrate improved text and full color image quality.

Subpixel variability of remotely sensed soil moisture: an inter-comparison study of SAR and ESTAR

Abstract: The representation of subpixel variability in soil moisture estimates from passive microwave data was investigated through sensitivity analysis and by comparison against the spatial structure of soil moisture fields derived from radar data. This work shows that the subpixel variability not represented in brightness temperature fields is directly associated with the spatial organization of soil hydraulic properties and the spatial distribution of vegetation. The significant implication of this result is that the physical connection between soil moisture estimates at the pixel scale and local values within the pixel weakens strongly as the sensor resolution decreases. Subsequently, the application of scaling and fractal interpolation principles to downscale passive microwave data to the spatial resolution of radar data was investigated as a means to recover spatial structure. In particular, ESTAR soil moisture data was successfully downscaled from 200 to 40 m using only one radar frequency (e.g., L-band). This application suggests that the combined use of active and passive single-band microwave remote-sensing of soil moisture is a viable approach to improve the spatial resolution of soil moisture remote-sensing.

Spectral imaging system analytical model for subpixel object detection

Abstract: Data from multispectral and hyperspectral imaging systems have been used in many applications including land cover classification, surface characterization, material identification, and spatially unresolved object detection. While these optical spectral imaging systems have provided useful data, their design and utility could be further enhanced by better understanding the sensitivities and relative roles of various system attributes; in particular, when application data product accuracy is used as a metric. To study system parameters in the context of land cover classification, an end-to-end remote sensing system modeling approach was previously developed. In this paper, we extend this model to subpixel object detection applications by including a linear mixing model for an unresolved object in a background and using object detection algorithms and probability of detection (P/sub D/) versus false alarm (P/sub FA/) curves to characterize performance. Validations with results obtained from airborne hyperspectral data show good agreement between model predictions and the measured data. Examples are presented which show the utility of the modeling approach in understanding the relative importance of various system parameters and the sensitivity of P/sub D/ versus P/sub FA/ curves to changes in the system for a subpixel road detection scenario.

Improved display resolution of subsampled colour images using subpixel addressing

Abstract: Subsampling based on subpixel addressing has been successfully applied to the problem of font rendering on an LCD. The increased horizontal resolution of the process makes otherwise fuzzy or aliased text look noticeably clearer, but the increased luminance resolution comes at the cost of chrominance aliasing. Also, the technique has only been applied to achromatic imagery. A new algorithm is presented which, based on a human perceptual model, successfully removes visible chrominance aliasing while retaining the invisible aliased components that contribute to enhanced resolution. The algorithm is applicable to both achromatic and natural colour imagery.

Spectral imaging system analytical model for subpixel object detection

Abstract: Data from multispectral and hyperspectral imaging systems have been used in many applications including land cover classification, surface characterization, material identification, and spatially unresolved object detection. While these optical spectral imaging systems have provided useful data, their design and utility could be further enhanced by better understanding the sensitivities and relative roles of various system attributes; in particular, when application data product accuracy is used as a metric. To study system parameters in the context of land cover classification, an end-to-end remote sensing system modeling approach was previously developed. In this paper, we extend this model to subpixel object detection applications by including a linear mixing model for an unresolved object in a background and using object detection algorithms and probability of detection (P/sub D/) versus false alarm (P/sub FA/) curves to characterize performance. Validations with results obtained from airborne hyperspectral data show good agreement between model predictions and the measured data. Examples are presented which show the utility of the modeling approach in understanding the relative importance of various system parameters and the sensitivity of P/sub D/ versus P/sub FA/ curves to changes in the system for a subpixel road detection scenario.

Constrained total least‐squares computations for high‐resolution image reconstruction with multisensors

Abstract: Multiple undersampled images of a scene are often obtained by using a charge-coupled device (CCD) detector array of sensors that are shifted relative to each other by subpixel displacements. This geometry of sensors, where each sensor has a subarray of sensing elements of suitable size, has been popular in the task of attaining spatial resolution enhancement from the acquired low-resolution degraded images that comprise the set of observations. With the objective of improving the performance of the signal processing algorithms in the presence of the ubiquitous perturbation errors of displacements around the ideal subpixel locations (because of imperfections in fabrication), in addition to noisy observation, the errors-in-variables or the total least-squares method is used in this paper. A regularized constrained total least-squares (RCTLS) solution to the problem is given, which requires the minimization of a nonconvex and nonlinear cost functional. Simulations indicate that the choice of the regularization parameter influences significantly the quality of the solution. The L-curve method is used to select the theoretically optimum value of the regularization parameter instead of the unsound but expedient trial-and-error approach. The expected superiority of this RCTLS approach over the conventional least-squares theory-based algorithm is substantiated by example. © 2002 John Wiley & Sons, Inc. Int J Imaging Syst Technol 12, 35–42, 2002

FFT based image registration

Abstract: We present a new unified approach to FFT based image registration. Prior works divided the registration process into two stages: the first was based on phase correlation (PC) which provides pixel accurate registration [5], while the second step provides subpixel registration accuracy [1, 3]. By extending the PC method we derive a FFT based image registration algorithm which is able to estimate large translations with subpixel accuracy. The algorithm's properties resemble those of the Gradient Methods [4] while outperforming it by exhibiting superior convergence range.

Antialias mask generation

Abstract: An antialiased mask generation technique where a patch of pixels is tested in parallel for fragment membership, and this test is looped with successive subpixel vector offsets from a programmed set. Antialiasing smoothness can be traded off for throughput by varying the size of the programmed set.

Methods, systems, and programming for producing and displaying subpixel-optimized images and digital content including such images

Abstract: A method of accessing digital content from a device in which said content is stored. Performing a down scaling and subpixel optimization process. Basic processes and data representations that may be used according to present invention. Digital content (100), including one or more bitmap images (102) and text (104) is displayed in a subpixel optimized downscaled format (106).

Efficient, Active 3D Acquisition, Based on a Pattern-Specific Snake

Abstract: The paper discusses a structured light setup for fast, one-shot 3D acquisition. The projection pattern consists of equidistant, vertical stripes. The main problem is the determination of the stripe-boundaries. They are extracted with sub-pixel accuracy by a pattern-specific snake. An initialization procedure yields the rough contours. Subpixel accuracy is reached through an iterative relaxation process. The labeling problem is automatically solved if all boundaries are located. Interpolation guarantees that the correct number of boundaries is initialized.

Fast motion estimation using Bidirectional Gradient Methods

Abstract: Gradient based motion estimation techniques (GM) are considered to be in the heart of state-of-the-art registration algorithms [2], being able to account for both pixel and subpixel registration and to handle various motion models (translation, rotation, affine, projective). These methods estimate the motion between two images based on the local changes in the image intensities while assuming image smoothness. This paper introduces two new bidirectional formulations of the GM, improving the convergence properties for large motions. Experimental results demonstrate the applicability of these algorithms to real images.

Display device for decompressing compressed image data received

Abstract: A display device including a plurality of blocks of pixels each of which includes a red subpixel, a green subpixel, and a blue subpixel, each of the blocks including pixels in a form of a matrix having N rows and M columns includes a first active element shared among three subpixels of each pixel and a second active element connected to a second active element formed in each subpixel connected to the first active element. Ma gradation voltage lines (Ma is an integer; M≧Ma≧2) respectively of red, green, and blue subpixels in a direction of the column are commonly connected. The display device directly displays a compressed image signal without developing the image signal into a bit map in which each subpixel has gradation information.

Analysis of displacement errors in high-resolution image reconstruction with multisensors

Abstract: An image-acquisition system composed of an array of sensors, where each sensor has a subarray of sensing elements of suitable size, has recently been popular for increasing the spatial resolution with high signal-to-noise ratio beyond the performance bound of technologies that constrain the manufacture of imaging devices. Small perturbations around the ideal subpixel locations of the sensing elements (responsible for capturing the sequence of undersampled degraded frames), because of imperfections in fabrication, limit the performance of the signal-processing algorithms for processing and integrating the acquired images for the desired enhanced resolution and quality. The contributions of this paper include an analysis of the displacement errors on the convergence rate of the iterative approach for solving the transform based preconditioned system of equations. Subsequently, it is established that the use of the MAP, L/sub 2/ norm or H/sub 1/ norm regularization functional leads to a proof of linear convergence of the conjugate gradient method in terms of the displacement errors caused by the imperfect subpixel locations. Results of simulation support the analytical results.

Precise subpixel estimation on area‐based matching

Abstract: Area-based matching is a common procedure in various fields such as image-based measurements, stereo image processing, and fluidics. Subpixel estimation using parabola fitting over three points with their similarity measures is also a common method to increase the resolution of matching. However, few investigations or studies concerning the characteristics of this estimation have been reported. In this paper, we have analyzed the subpixel estimation error by using an approximate image function and three kinds of similarity measures for matching. The results illustrate some inherently problematic phenomena such as so-called “pixel-locking.” In addition, we propose a new algorithm to greatly reduce subpixel estimation error. This method is independent of the similarity measure and quite simple to implement. The advantage of our novel method is confirmed through experiments using three different types of images. © 2002 Wiley Periodicals, Inc. Syst Comp Jpn, 33(7): 1–10, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.10098

Measurement of the presampled two-dimensional modulation transfer function of digital imaging systems.

Abstract: The purpose of this work was to develop methods to measure the presampled two-dimensional modulation transfer function (2D MTF) of digital imaging systems A custom x-ray "point source" phantom was created by machining 256 holes with diameter 0107 mm through a 05-mm-thick copper plate The phantom was imaged several times, resulting in many images of individual x-ray "spots" The center of each spot (with respect to the pixel matrix) was determined to subpixel accuracy by fitting each spot to a 2D Gaussian function The subpixel spot center locations were used to create a 5 x oversampled system point spread function (PSF), which characterizes the optical and electrical properties of the system and is independent of the pixel sampling of the original image The modulus of the Fourier transform of the PSF was calculated Next, the Fourier function was normalized to the zero frequency value Finally, the Fourier transform function was divided by the first-order Bessel function that defined the frequency content of the holes, resulting in the presampled 2D MTF The presampled 2D MTF of a 01 mm pixel pitch computed radiography system and 02 mm pixel pitch flat panel digital imaging system that utilized a cesium iodide scintillator was measured Comparison of the axial components of the 2D MTF to one-dimensional MTF measurements acquired using an edge device method demonstrated that the two methods produced consistent results

Automated detection of subpixel hyperspectral targets with adaptive multichannel discrete wavelet transform

Abstract: This paper introduces the use of adaptive multichannel discrete wavelet transforms (AMDWTs), allowing for a customized design of optimum mother wavelets, for the detection of a constituent absorption band within a hyperspectral curve. Even when the target's amplitude is only 3% of the background signal's amplitude, the AMDWT approach produces target detection rates of 90%.

13.4: Subpixel Image Scaling for Color Matrix Displays

Abstract: The apparent resolution of matrix displays is increased when the relative position of the color subpixels is taken into account. This paper shows that a general method to achieve this for any subpixel arrangement, can be incorporated in an image scaler at low additional cost, allowing simple quality trade-off control.

Subpixel sensitivity maps for a back-illuminated charge-coupled device and the effects of nonuniform response on measurement accuracy

Abstract: A measurement program designed to investigate the varia- tions in sensitivity of focal plane arrays on a subpixel scale has produced such information for a front-illuminated CCD device, results for which have been previously presented. New measurements have been made to provide information on sensitivity variations within a single pixel for a back-illuminated CCD. The measurements were made using a stable broadband light source and two high-precision translation stages. The pixel scans were obtained using four different spectral filters (three broadband and one narrowband). These results are compared to the pixel response functions of the front-illuminated CCD. These experimen- tally measured pixel response functions were used to determine their effect on photometric and astrometric measurements. The uncertainty introduced into such measurements, especially when using under- sampled CCD data, is significant. It was also found that the form of the subpixel response is dependent on the wavelength of illuminating light. Therefore, the position of the optical center of weight of a pixel varies with wavelength. © 2002 Society of Photo-Optical Instrumentation Engineers.

High quality antialiased lines with dual sampling pattern

Abstract: Antialiased lines are classified according to their orientation, e.g. as x-major or y-major depending whether the x or y extent of the line is larger. Different subpixel sampling patterns are used for different lines, in accordance with this classification. This permits antialiased rendering to achieve increased visual quality of the line without adding in more sample points.