Showing papers on "Subpixel rendering published in 1998"

A pyramid approach to subpixel registration based on intensity

Abstract: We present an automatic subpixel registration algorithm that minimizes the mean square intensity difference between a reference and a test data set, which can be either images (two-dimensional) or volumes (three-dimensional). It uses an explicit spline representation of the images in conjunction with spline processing, and is based on a coarse-to-fine iterative strategy (pyramid approach). The minimization is performed according to a new variation (ML*) of the Marquardt-Levenberg algorithm for nonlinear least-square optimization. The geometric deformation model is a global three-dimensional (3-D) affine transformation that can be optionally restricted to rigid-body motion (rotation and translation), combined with isometric scaling. It also includes an optional adjustment of image contrast differences. We obtain excellent results for the registration of intramodality positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) data. We conclude that the multiresolution refinement strategy is more robust than a comparable single-stage method, being less likely to be trapped into a false local optimum. In addition, our improved version of the Marquardt-Levenberg algorithm is faster.

An unbiased detector of curvilinear structures

Abstract: The extraction of curvilinear structures is an important low-level operation in computer vision that has many applications. Most existing operators use a simple model for the line that is to be extracted, i.e., they do not take into account the surroundings of a line. This leads to the undesired consequence that the line will be extracted in the wrong position whenever a line with different lateral contrast is extracted. In contrast, the algorithm proposed in this paper uses an explicit model for lines and their surroundings. By analyzing the scale-space behavior of a model line profile, it is shown how the bias that is induced by asymmetrical lines can be removed. Furthermore, the algorithm not only returns the precise subpixel line position, but also the width of the line for each line point, also with subpixel accuracy.

Least squares subspace projection approach to mixed pixel classification for hyperspectral images

Abstract: An orthogonal subspace projection (OSP) method using linear mixture modeling was recently explored in hyperspectral image classification and has shown promise in signature detection, discrimination, and classification. In this paper, the OSP is revisited and extended by three unconstrained least squares subspace projection approaches, called signature space OSP, target signature space OSP, and oblique subspace projection, where the abundances of spectral signatures are not known a priori but need to be estimated, a situation to which the OSP cannot be directly applied. The proposed three subspace projection methods can be used not only to estimate signature abundance, but also to classify a target signature at subpixel scale so as to achieve subpixel detection. As a result, they can be viewed as a posteriori OSP as opposed to OSP, which can be thought of as a priori OSP. In order to evaluate these three approaches, their associated least squares estimation errors are cast as a signal detection problem ill the framework of the Neyman-Pearson detection theory so that the effectiveness of their generated classifiers can be measured by receiver operating characteristics (ROC) analysis. All results are demonstrated by computer simulations and Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data.

Statistics of subpixel registration algorithms based on spatiotemporal gradients or block matching

Abstract: Image registration algorithms based on piecewise linear inter- polators (spatiotemporal gradients or block matching) are analyzed to determine subpixel registration accuracy. Results reveal not only random errors due to image noise but also systematic bias present even if the images are noise free. If the displacement between the images is small, bias is small. However, if the displacement between the images is larger than about 1/25 pixel, the bias component of the registration error ex- ceeds the random component for most imaging conditions. Bias also depends on image content: it is generally larger for images with higher spatial frequency content than for images with lower spatial frequency content. We have developed a reduced-bias registration algorithm that takes advantage of the nearly linear relation between image displace- ment and bias that results for small displacements. The new algorithm is direct (noniterative), increases computational costs by approximately a factor of 4, and reduces the bias by approximately a factor of 4. This improvement is large compared to improvement obtained with averag- ing. For our applications, in which imaging noise is typically 50 dB smaller than the signal, registration errors using the new algorithm are smaller than 1/50 pixel. © 1998 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(98)03804-5)

A full color active matrix organic electroluminescent display panel having an integrated shadow mask

Abstract: A full-color active matrix organic light-emitting color display panel is disclosed which has an integrated shadow mask structure for patterning arrays of color subpixels. The in-situ shadow mask structure is prepatterned on the display substrate by conventional photolithography, and provides a simple, self-alignment feature for successive deposition of color organic electroluminescent (EL) media on designated color subpixel areas. The pillar structure of the shadow mask are particularly effective in the fabrication of high-resolution full-color organic light-emitting diode displays having either color conversion layers or individual red, green, and blue emissive layers.

Block-matching subpixel motion estimation from noisy undersampled frames: an empirical performance evaluation

Abstract: The performance of block-matching sub-pixel motion estimation algorithms under the adverse conditions of image undersampling and additive noise is studied empirically This study is motivated by the requirement for reliable sub-pixel accuracy motion estimates for motion compensated observation models used in multi-frame super-resolution image reconstruction Idealized test functions which include translational scene motion are defined These functions are sub-sampled and corrupted with additive noise and used as source data for various block-matching sub-pixel motion estimation techniques Motion estimates computed from this data are compared with the a-priori known motion which enables an assessment of the performance of the motion estimators considered

A high accuracy volume renderer for unstructured data

Abstract: This paper describes a volume rendering system for unstructured data, especially finite element data, that creates images with very high accuracy. The system will currently handle meshes whose cells are either linear or quadratic tetrahedra. Compromises or approximations are not introduced for the sake of efficiency. Whenever possible, exact mathematical solutions for the radiance integrals involved and for interpolation are used. The system will also handle meshes with mixed cell types: tetrahedra, bricks, prisms, wedges, and pyramids, but not with high accuracy. Accurate semi-transparent shaded isosurfaces may be embedded in the volume rendering. For very small cells, subpixel accumulation by splatting is used to avoid sampling error. A revision to an existing accurate visibility ordering algorithm is described, which includes a correction and a method for dramatically increasing its efficiency. Finally, hardware assisted projection and compositing are extended from tetrahedra to arbitrary convex polyhedra.

System and method for adjusting pixel parameters by subpixel positioning

Abstract: A method and system for simulating motion of a polygon on a display screen. The polygon may be included in a set of polygons used to model a three-dimensional object. The position of the polygon is defined by vertices tracked in a subpixel coordinate system existing in a computer-readable medium. The subpixel coordinates of the vertices are used to identify the pixels on the display screen having coordinates that correspond to subpixel coordinates lying within or, optionally, at the boundary of the polygon. The identified pixels are those that are to be lighted on the display screen to generate the image of the polygon. The display properties of the lighted pixels are selected by interpolation based on defined pixel display parameters assigned to the vertices of the triangle. As motion of the polygon is tracked in the subpixel coordinate system, the corresponding display on the display screen is repeatedly adjusted. The method of identifying and interpolating the display parameters of the pixels using the subpixel coordinate system provides the appearance of smooth polygon motion.

Detection of subpixel anomalies in multispectral infrared imagery using an adaptive Bayesian classifier

Abstract: The detection of subpixel targets with unknown spectral signatures and cluttered backgrounds in multispectral imagery is a topic of great interest for remote surveillance applications. Because no knowledge of the target is assumed, the only way to accomplish such a detection is through a search for anomalous pixels. Two approaches to this problem are examined in this paper. The first is to separate the image into a number of statistical clusters by using an extension of the well-known k-means algorithm. Each bin of resultant residual vectors is then decorrelated, and the results are thresholded to provide detection. The second approach requires the formation of a probabilistic background model by using an adaptive Bayesian classification algorithm. This allows the calculation of a probability for each pixel, with respect to the model. These probabilities are then thresholded to provide detection. Both algorithms are shown to provide significant improvement over current filtering techniques for anomaly detection in experiments using multispectral IR imagery with both simulated and actual subpixel targets.

Subpixel sensitivity map for a charge-coupled device sensor

Abstract: The sensitivity across a solid state detector array varies as a result of differences in transmission, diffusion and scattering properties over the sensor. This variation will occur over a range of scale lengths and its knowledge is of importance for improved device design and in a variety of applications, for example, event centroiding in photon counting systems. A measurement of the sensitivity variation on a subpixel scale for a two-phase front-illuminated CCD is reported. The measurement is made using a scanning reflection microscope. A variation in sensitivity between the phases within a pixel is clearly observed, as well as varia- tions on a much smaller spatial scale. © 1998 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(98)03103-1) Subject terms: charge-coupled device; pixel sensitivity; response function; crosstalk.

Extraction of high-resolution video stills from MPEG image sequences

Abstract: The Bayesian high-resolution video stills (HRVS) algorithm has been embedded within the MPEG video compression standard, such that an MPEG-1 intra-coded frame (I-picture) can be enhanced by temporally integrating the neighboring motion-compensated P- and B-pictures. Super-resolution enhancement is achievable if objects within the image sequence move with subpixel increments; thus, the Bayesian HRVS algorithm requires subpixel-resolution motion fields estimated with respect to the I-picture. Half-pel resolution motion fields are provided by the MPEG encoder in the compressed bit stream. These motion vectors are used as initial conditions to a reduced-search block matching algorithm which calculates higher-resolution motion fields with acceptable accuracy. The computation time required to estimate the subpixel motion fields in the Bayesian HRVS algorithm is reduced by a factor of approximately 30 when lower-resolution motion vectors are already available from the MPEG decoder, with little degradation in video still quality.

Interpolation-free subpixel motion estimation techniques in DCT domain

Abstract: Currently existing subpixel motion estimation algorithms require interpolation of interpixel values which undesirably increases the overall complexity and data flow and deteriorates the estimation accuracy. We develop discrete cosine transform (DCT)-based techniques to estimate subpel motion at different desired subpel levels of accuracy in the DCT domain without interpolation. We show that subpixel motion information is preserved in the DCT of a shifted signal under some condition in the form of pseudophases, and we establish subpel sinusoidal orthogonal principles to extract this information. The proposed subpixel techniques are flexible and scalable in terms of estimation accuracy with very low computational complexity O(N/sup 2/) compared to O(N/sup 4/) for the full-search block-matching approach and its subpixel versions. Above all, motion estimation in the DCT domain instead of the spatial domain simplifies the conventional hybrid DCT-based video coder, especially the heavily loaded feedback loop in the conventional design, resulting in a fully DCT-based high-throughput video codec. In addition, the computation of pseudophases is local, and thus a highly parallel architecture is feasible for the DCT-based algorithms. Finally, simulation on video sequences of different characteristics shows comparable performance of the proposed algorithms to block-matching approaches.

A noise subspace projection approach to target signature detection and extraction in an unknown background for hyperspectral images

Abstract: A noise subspace projection (NSP) approach to extraction and subpixel detection of target signatures in an unknown background is presented. The proposed NSP approach is derived from a recently developed subspace orthogonal projection (OSP) method and can be shown to be approximated by an adaptive filter with the optimal weight given by the Wiener-Hopf equation. As a result, the operator resulting from the NSP approach can be used as an OSP operator for scene classification and subpixel detection, on one hand, and also implemented as an adaptive filter, on the other. These advantages make the NSP approach very attractive in practical applications. In particular, the NSP operator takes advantage of the noise subspace projection to prevent from inverting correlation matrices, as required by an adaptive filter.

Practical approach to the registration of multiple frames of video images

Abstract: Image registration deals with finding the geometric mapping, which, when applied to a region of interest (ROI) in one image, adjusts it such that it matches as closely as possible a corresponding ROI in a reference image. In this paper we address the application of image registration in the processing of multiple frames of video sequences. We discuss three levels of difficulty in the image registration problem: mathematical, statistical, and structural. Based on this analysis and the understanding of the requirements in our application, we select region-based methods for registering the video images, and describe these methods in detail. We extend the study to subpixel image registration and propose a new and more accurate subpixel registration method based on cross-spectrum interpolation. To demonstrate the performance of these methods, we apply them to the registration of real data.

Method and apparatus for antialiasing using a non-uniform pixel sampling pattern

Abstract: The invention provides a method and apparatus for an anti-aliasing process that allows for super-sampling at a high subpixel resolution, but does not require the process and memory resources typically required for conventional super-sampling at this subpixel resolution. Each pixel is partitioned into an array that provides for a large number of subpixels, and a smaller set of super-samples from this set of subpixels are sampled and used to determine the resultant pixel values. Because the set of super-samples is substantially smaller in number (less than half) than the number of subpixels, the processing and memory requirements are substantially reduced. The set of super-samples are preferably determined so as to provide for a uniform sampling frequency in each of the major axes, and along each diagonal, even though the super-samples may not provide an uniform sampling of each pixel area.

Device, method and storage medium for recognizing a document image

Abstract: A color image input from a document image inputting unit is converted into a gray-scale image by a brightness image extracting unit. The gray-scale image is then converted into an image having a higher resolution according to the resolution of the original gray-scale image. When this conversion is performed, subpixels are generated between the original pixels, and the values of the subpixels are obtained with an interpolation method. Furthermore, a threshold value for a binarization process is generated by using an original pixel value and a subpixel value. The characters included in the binarized image are recognized by a binary image recognizing unit, and a recognition result is output from a recognition result outputting unit.

Design of shapes for precise image registration

Abstract: This correspondence deals with the problem of designing planar shapes for subpixel image registration. Basic theoretical considerations are shown to lead to a lower bound on location accuracy. Optimal registration marks achieving this bound are discussed. These optimal designs, however, require very high printing or etching resolution and are inherently very sensitive to variations in the image sampling model (like scaling of grid size and rotation). More robust, optimal and suboptimal "topology-preserving" registration marks are then introduced and analyzed.

Measurement of the subpixel structure of AXAF CCD's

Abstract: The authors present a method to measure the subpixel structure of a charge-coupled device (CCD), information necessary to accurately determine (<1% uncertainty) the absolute detection efficiency of the device. Their approach uses a thin metal film with periodically spaced holes (small, compared to the pixel size) to localize incident X-rays to a particular region of the pixel. The mesh is rotated to create a small angular misalignment between the grid holes and the CCD pixels, producing a moire effect in the data. The resultant moire pattern is compared to a CCD model, and a best fit minimization technique is used to constrain the parameters that describe the subpixel structure. This technique was developed to measure and calibrate the X-ray CCD's that will comprise one of the two focal plane instruments on-board AXAF, but it is applicable for measuring the structure of any pixelated solid state device.

Non-contact laser inspection for the inner wall surface of a pipe

Abstract: A non-contact laser sensor based on the ring optical cutting image method to measure the size and profile of the inner wall of a pipe is developed. The sensor consists of a laser diode light source, an optical ring pattern generator and a CCD camera. The optical ring pattern from the optical ring pattern generator is projected onto the inner wall of the pipe, which is then viewed by the CCD camera. Reasonable parameters according to the theory of light scattering and reflection are chosen to simulate and optimize the measurement system. The adaptive weighted average value filter and the subpixel technique on several-step computing and half Gaussian fitting are deployed to obtain the edge and the centre of the ring image in order to filter the noise of the image and raise the resolution of the measurement system. The experimental results show that the principle is correct and the techniques are realizable.

HSRS-An Infrared Sensor for Hot-Spot-Detection

Abstract: The observation of high temperature events (HTE) is an important field of the remote sensing because of their influence on the global change of the environmental processes. Currently a small satellite BIRD (Bispectral Infrared Detection) dedicated to this task is under development in the German Aerospace Center. Considering the restrictions of an 80 kg satellite a bispectral infrared push broom scanner working in the Midwave and in the Thermal Infrared based on the latest technology of linear detector arrays was developed. The identical design for both infrared channels was realized to save resources and to guarantee the reliability. Because of the limited number of elements per line a subpixel detecting concept was chosen to estimate the parameters of the HTE with a reasonable ground resolution and swath wide. A special dual band optics and a compact sensor head design will ensure the required geometric stability. The subpixel measurement method for the hot spot detection requires a high detectivity and a large dynamic range. A special signal processing concept has been implemented at the sensor head controller. Recently the first airborne experiments were carried out together with a push broom scanner in the visible. During this experiments the sensor control, onboard signal processing and data transmission routines were tested.

Moment and curvature preserving technique for accurate ellipse boundary detection

Abstract: Circles and their elliptic projections are very commonly used image features in computer vision applications. Thus, it is very important to be able to determine their location in an accurate manner. A technique for determining an ellipse boundary with subpixel precision is proposed. The technique, called the moment and curvature preserving detection (MCP), utilizes the first three intensity moments and the intensity gradient of the image. The idea of using moments for subpixel edge detection is not new, but in the case of ellipses the moments do not provide sufficient information for precise detection. However, if the local curvature is augmented to the observations, the ellipse boundary can be determined reliably.

Color flat panel display device

Abstract: A flat panel display device includes a cathode (58) in parallel opposed position to and vertically separated from an anode (56). Red (46), green (44), and blue (42) subpixels are sequentially arrayed on the anode (56). Electron emitter subpixels (50, 52, 54) are arrayed on the cathode (58) in paired relationship to the red, green, and blue subpixels (46, 44, 42) located on the anode (56). To provide enhanced color performance, the surface area of the blue subpixel (42) is greater than the surface area of either the green subpixel (44) or the red subpixel (46). Additionally, the red subpixel (46) is horizontally shifted toward the green subpixel (44) and away from the blue subpixel (42).

High frequency shingled multiple drop per pixel ink overprinting method

Abstract: A method of printing an image on a recording medium with a liquid ink printhead moving in a scanning direction having drop ejectors depositing ink drops on a recording medium at a given default frequency and in a plurality of pixel locations spaced by a predetermined resolution, the method comprising the steps of (a) determining a pixel size drop volume of liquid ink necessary at the predetermined resolution to fill one of the pixel locations; (b) determining a reduced subpixel size drop volume of liquid ink for subpixel drops to be printed by dividing the pixel size drop volume by a factor of at least three; (c) determining a frequency for firing and printing the subpixel drops in a fast scan direction such that a succeeding subpixel drop lands on the recording medium before a preceding subpixel drop has completely spread, and so as to preserve throughput; and (d) firing and depositing multiple subpixel drops each having the determined reduced volume of liquid ink, at the determined frequency, and in a shingled overlapping manner in which adjacent subpixel drops overlap by at least one third the diameter of the overlapped subpixel drop, thereby resulting in synergistic slow scan direction combined spreading, and thereby enabling a relatively high number of gray scale levels, and high quality printed images.

Stereo Matching with Implicit Detection of Occlusions

Abstract: In this paper we introduce a new stereo matching algorithm, in which the matching of occluded areas is suppressed by a self-organizing process. In the first step the images are filtered by a set of oriented Gabor filters. A complex-valued correlation-based similarity measurement, which is applied to the responses of the Gabor filters, is used in the second step to initialize a self-organizing process. In this self-organizing network, which is described by coupled, non-linear evolution equations, the continuity and the uniqueness constraints are established. Occlusions are detected implicitly without a computationally intensive bidirectional matching strategy. Due to the special similarity measurement, dense disparity maps can be calculated with subpixel accuracy. Unlike phase-difference methods the disparity range is not limited to the modulation wavelength of the quadrature-filter. Therefore, there is no need for a hierachical coarse-to-fine control strategy in our approach.

System and apparatus for single subpixel elimination with local error compensation in an high addressable error diffusion process

Abstract: A system and method for processing image data converts a pixel of image data having a first resolution to a plurality of subpixels, the plurality of subpixels representing a second resolution, the second resolution being higher than the first resolution. The plurality of subpixels are thresholded to generate a group of subpixel values for each pixel and a threshold error value. It is then determined if the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel. If the group of subpixel values from the thresholding process produce a pattern containing an isolated subpixel, the group of subpixel vales is modified to produce a pattern without an isolated subpixel. The modification process produces a subpixel error value which is compensated for localized error before being diffused to adjacent pixels.

Subpixel object detection using hyperspectral imaging for search and rescue operations

Abstract: Time critical search & rescue (s&r) operations often requires the detection of small objects in a vast area While an airborne search can cover the area, no operational instrumental tools currently exist to actually replace the human operator By producing the spectral signature of each pixel in a spatial image, multi- and hyper-spectral imaging (HSI) sensors provides a powerful capability for automated detection of subpixel size objects that are otherwise unresolved objects in conventional imagery This property of HSI naturally lends itself to s&r operations A lost hiker, skier, life raft adrift in the ocean, downed pilot or small aircraft wreckage targets, can be detected from relatively high altitude based on their unique spectral signatures Moreover, the spectral information obtained allows the search craft to operate at substantially reduced spatial resolution thereby increasing scene coverage without a significant loss in detection sensitivity The paper demonstrates the detection of objects as small as 1/10 of an image pixel from a sensor flying at over 6 km altitude A subpixel object detection algorithm using HSI, based on local image statistics without reliance on spectral libraries is presented The technique is amenable to fast signal processing and the requisite hardware can be built using inexpensive off the shelf technology This makes HSI a highly attractive tool for real-time, autonomous instrument-based implementation It can complement current visual-based s&r operations or emerging synthetic aperture radar sensors that are much more expensive