Showing papers on "Pixel published in 1998"

Multisensor image fusion in remote sensing: Concepts, methods and applications

Abstract: With the availability of multisensor, multitemporal, multiresolution and multifrequency image data from operational Earth observation satellites the fusion of digital image data has become a valuable tool in remote sensing image evaluation. Digital image fusion is a relatively new research field at the leading edge of available technology. It forms a rapidly developing area of research in remote sensing. This review paper describes and explains mainly pixel based image fusion of Earth observation satellite data as a contribution to multisensor integration oriented data processing.

Layered depth images

Abstract: In this paper we present a set of efficient image based rendering methods capable of rendering multiple frames per second on a PC. The first method warps Sprites with Depth representing smooth surfaces without the gaps found in other techniques. A second method for more general scenes performs warping from an intermediate representation called a Layered Depth Image (LDI). An LDI is a view of the scene from a single input camera view, but with multiple pixels along each line of sight. The size of the representation grows only linearly with the observed depth complexity in the scene. Moreover, because the LDI data are represented in a single image coordinate system, McMillan’s warp ordering algorithm can be successfully adapted. As a result, pixels are drawn in the output image in back-to-front order. No z-buffer is required, so alphacompositing can be done efficiently without depth sorting. This makes splatting an efficient solution to the resampling problem.

The derivation of the green vegetation fraction from NOAA/AVHRR data for use in numerical weather prediction models

Abstract: Fraction of green vegetation, fg, and green leaf area index, Lg, are needed as a regular space-time gridded input to evapotranspiration schemes in the two National Weather Service (NWS) numerical prediction models regional Eta and global medium range forecast. This study explores the potential of deriving these two variables from the NOAA Advanced Very High Resolution Radiometer (AVHRR) normalized difference vegetation index (NDVI) data. Obviously, one NDVI measurement does not allow simultaneous derivation of both vegetation variables. Simple models of a satellite pixel are used to illustrate the ambiguity resulting from a combination of the unknown horizontal (fg) and vertical (Lg) densities. We argue that for NOAA AVHRR data sets based on observations with a spatial resolution of a few kilometres the most appropriate way to resolve this ambiguity is to assume that the vegetated part of a pixel is covered by dense vegetation (i.e., its leaf area index is high), and to calculate fg=(NDVI-NDVI0)/(NDVI8-ND...

A nanotube-based field-emission flat panel display

Abstract: A matrix addressable diode flat panel display has been fabricated using a carbon nanotube–epoxy composite as the electron emission source. Field-emission uniformity has been confirmed by measuring the I–V curves of pixels across the panel. This prototype display demonstrates well-lit pixels under ±150 V biasing signals. The “on” and “off” of the pixels are well controlled by the half voltage “off-pixel” method. Further improvement of this technology may lead to easy-to-make and inexpensive flat panel displays.

A pixel dissimilarity measure that is insensitive to image sampling

Abstract: Because of image sampling, traditional measures of pixel dissimilarity can assign a large value to two corresponding pixels in a stereo pair, even in the absence of noise and other degrading effects. We propose a measure of dissimilarity that is provably insensitive to sampling because it uses the linearly interpolated intensity functions surrounding the pixels. Experiments on real images show that our measure alleviates the problem of sampling with little additional computational overhead.

Color- and texture-based image segmentation using EM and its application to content-based image retrieval

Abstract: Retrieving images from large and varied collections using image content as a key is a challenging and important problem. In this paper we present a new image representation which provides a transformation from the raw pixel data to a small set of image regions which are coherent in color and texture space. This so-called "blobworld" representation is based on segmentation using the expectation-maximization algorithm on combined color and texture features. The texture features we use for the segmentation arise from a new approach to texture description and scale selection. We describe a system that uses the blobworld representation to retrieve images. An important and unique aspect of the system is that, in the context of similarity-based querying, the user is allowed to view the internal representation of the submitted image and the query results. Similar systems do not offer the user this view into the workings of the system; consequently, the outcome of many queries on these systems can be quite inexplicable, despite the availability of knobs for adjusting the similarity metric.

Making faces

Abstract: We have created a system for capturing both the three-dimensional geometry and color and shading information for human facial expressions. We use this data to reconstruct photorealistic, 3D animations of the captured expressions. The system uses a large set of sampling points on the face to accurately track the three dimensional deformations of the face. Simultaneously with the tracking of the geometric data, we capture multiple high resolution, registered video images of the face. These images are used to create a texture map sequence for a three dimensional polygonal face model which can then be rendered on standard 3D graphics hardware. The resulting facial animation is surprisingly life-like and looks very much like the original live performance. Separating the capture of the geometry from the texture images eliminates much of the variance in the image data due to motion, which increases compression ratios. Although the primary emphasis of our work is not compression we have investigated the use of a novel method to compress the geometric data based on principal components analysis. The texture sequence is compressed using an MPEG4 video codec. Animations reconstructed from 512x512 pixel textures look good at data rates as low as 240 Kbits per second.

Combining agricultural crop models and satellite observations: from field to regional scales

Abstract: This review article gives an overview of how satellite observations are used to feed or tune crop models and improve their capability to predict crop yields in a region. Relations between crop characteristics which correspond to models state variables and satellite observations are briefly analysed, together with the various types of crop models commonly used. Various strategies for introducing short wavelength radiometric information into specific crop models are described, from direct update of model state variables to optimization of model parameter values, and some of them are exemplified. Methods to unmix crop-specific information from mixed pixels in coarse resolution-high frequency imagery are analysed. The conditions of use of the various methods and types of information are discussed.

Organic smart pixels

Abstract: The fabrication and characteristics of organic smart pixels are described. The smart pixel reported in this letter consists of a single organic thin-film field effect transistor (FET) monolithically integrated with an organic light-emitting diode. The FET active material is a regioregular polythiophene. The maximum optical power emitted by the smart pixel is about 300 nW/cm2 corresponding to a luminance of ∼2300 cd/m2.

A 256/spl times/256 CMOS imaging array with wide dynamic range pixels and column-parallel digital output

Abstract: A 256x256 CMOS active pixel sensor (APS) is described for an automotive stereo-vision system. Illumination may vary over several orders of magnitude, requiring a high dynamic range imager. Dynamic range is increased 20/spl times/ using a special clocking scheme for the lateral overflow gate. This dynamic range enhancement offers improvements over previously-described techniques. It simultaneously provides flexibility, user-adjustability, and digital control, with no reduction of fill factor. On-chip column-parallel cyclic analog-to-digital converters (ADCs) produce digital output at frame rates from 30 to 390 frames/s.

Improving image quality in poor visibility conditions using a physical model for contrast degradation

Abstract: In daylight viewing conditions, image contrast is often significantly degraded by atmospheric aerosols such as haze and fog. This paper introduces a method for reducing this degradation in situations in which the scene geometry is known. Contrast is lost because light is scattered toward the sensor by the aerosol particles and because the light reflected by the terrain is attenuated by the aerosol. This degradation is approximately characterized by a simple, physically based model with three parameters. The method involves two steps: first, an inverse problem is solved in order to recover the three model parameters; then, for each pixel, the relative contributions of scattered and reflected flux are estimated. The estimated scatter contribution is simply subtracted from the pixel value and the remainder is scaled to compensate for aerosol attenuation. This paper describes the image processing algorithm and presents an analysis of the signal-to-noise ratio (SNR) in the resulting enhanced image. This analysis shows that the SNR decreases exponentially with range. A temporal filter structure is proposed to solve this problem. Results are presented for two image sequences taken from an airborne camera in hazy conditions and one sequence in clear conditions. A satisfactory agreement between the model and the experimental data is shown for the haze conditions. A significant improvement in image quality is demonstrated when using the contrast enhancement algorithm in conjuction with a temporal filter.

Comprehensive Colour Image Normalization

Abstract: The same scene viewed under two different illuminants induces two different colour images. If the two illuminants are the same colour but are placed at different positions then corresponding rgb pixels are related by simple scale factors. In contrast if the lighting geometry is held fixed but the colour of the light changes then it is the individual colour channels (e.g. all the red pixel values or all the green pixels) that are a scaling apart. It is well known that the image dependencies due to lighting geometry and illuminant colour can be respectively removed by normalizing the magnitude of the rgb pixel triplets (e.g. by calculating chromaticities) and by normalizing the lengths of each colour channel (by running the ‘grey-world’ colour constancy algorithm). However, neither normalization suffices to account for changes in both the lighting geometry and illuminant colour.

Detection of microcalcifications in digital mammograms using wavelets

Abstract: This paper presents an approach for detecting micro-calcifications in digital mammograms employing wavelet-based subband image decomposition. The microcalcifications appear in small clusters of few pixels with relatively high intensity compared with their neighboring pixels. These image features can be preserved by a detection system that employs a suitable image transform which can localize the signal characteristics in the original and the transform domain. Given that the microcalcifications correspond to high-frequency components of the image spectrum, detection of microcalcifications is achieved by decomposing the mammograms into different frequency subbands, suppressing the low-frequency subband, and, finally, reconstructing the mammogram from the subbands containing only high frequencies. Preliminary experiments indicate that further studies are needed to investigate the potential of wavelet-based subband image decomposition as a tool for detecting microcalcifications in digital mammograms.

Pixel circuit display apparatus and electronic apparatus equipped with current driving type light-emitting device

Abstract: A display apparatus is provided with a current driving type light-emitting device and a driving device for controlling a driving current flowing through the light-emitting device for each pixel of the display apparatus. The display apparatus consists of power source units for supplying power for causing a driving current to flow via the driving device to the light-emitting device via a power source wire, and signal wire driving units for supplying a data signal to the driving device via signal wires. In addition, voltage adjusting units adjust a voltage for the power source units or a data signal from the signal wire driving units so that a quantity of a driving current flowing through the light-emitting device when a data signal of a predetermined voltage is supplied to the driving device via signal wires or a quantity of emitted light emitted from the light-emitting device comes close to a predetermined reference value.

Image coding system

Abstract: An image coding system includes an optical system 1 , an image pick-up unit 2 , a color space/pixel number converting unit 4 , an orthogonal converting unit 5 , a quantizing unit 6 , a variable run length coding unit 7 and a storing/transmitting unit 10 . The system further includes a code volume control unit 8 for providing, in a first coding process, image data obtained from the color space/pixel number converting unit 4 as a result of omission of at least the color space conversion, among the color space and pixel number conversions, to the orthogonal conversion unit 5 , and computing quantizing coefficient data adequate for obtaining a target code volume from the code volume of coded data provided from the orthogonal converting unit 5 and the target code volume. In a second coding process, the color space/pixel number converting unit 4 executes both of the color space and pixel number conversions and provides resultant image data to the orthogonal converting unit 5 or storage and/or transmission of coded data provided as a result from the orthogonal converting unit 5.

Super-resolution display

Abstract: A super-resolution display derives a map by selectively driving the display while sensing the display output. A stored pixel correction function based on the mapping is applied to pixel data corresponding to the images to be displayed, and the display is driven from the corrected or modified pixel data. This can be used to correct for many types of distortion and to blend images from plural projectors. Pixel data is stored in a frame buffer, and the pixel correction function is applied to the pixel data between the frame buffer and the display, or alternatively, the pixel correction function is applied first, and corrected pixel data is stored in the frame buffer. The display is then driven from the corrected pixel data. In a preferred embodiment, the display comprises a plurality of projectors. The pixel correction function corrects for misalignment of projected overlapping pixel arrays, and blends the overlapping projection regions. In another embodiment, the projected images from plural projectors completely overlap, and the projectors have a small fill factor, resulting in a super-high resolution display. A single projector embodiment corrects for imperfections across the display. The correction functions are derived by composing a screen to sensor mapping with projector to sensor mappings. These mappings are established by optically sensing physical or projected test charts. Preferably, the optical sensor comprises at least one camera, such as a CCD camera. Alternatively, the optical sensor may comprise a pair of orthogonal linear sensor arrays.

An optimal multiedge detector for SAR image segmentation

Abstract: Edge detection is a fundamental issue in image analysis. Due to the presence of speckle, which can be modeled as a strong, multiplicative noise, edge detection in synthetic aperture radar (SAR) images is extremely difficult, and edge detectors developed for optical images are inefficient. Several robust operators have been developed for the detection of isolated step edges in speckled images. The authors propose a new step-edge detector for SAR images, which is optimal in the minimum mean square error (MSSE) sense under a stochastic multiedge model. It computes a normalized ratio of exponentially weighted averages (ROEWA) on opposite sides of the central pixel. This is done in the horizontal and vertical direction, and the magnitude of the two components yields an edge strength map. Thresholding of the edge strength map by a modified version of the watershed algorithm and region merging to eliminate false edges complete an efficient segmentation scheme. Experimental results obtained from simulated SAR images as well as ERS-1 data are presented.

Motion estimation and compensation of video object planes for interlaced digital video

Abstract: A motion estimation and compensation technique is provided for interlaced digital video such as video object planes (VOPs). Predictor motion vectors for use in differentially encoding a current field coded macroblock are obtained using the median of motion vectors of surrounding blocks or macroblocks. When a surrounding macroblock is itself interlaced coded, an average motion vector for that macroblock is used, with fractional pixel values being mapped to the half-pixel. When the current block is not interlaced coded but a surrounding block is, the field motion vectors may be used individually or averaged. In a repetitive padding technique for an interlaced coded VOP, the even and odd lines of the VOP and surrounding block are grouped. Within each field, exterior pixels are padded by setting them to the value of the nearest boundary pixel, or to an average of two boundary pixels. The lines are then reordered to provide a single padded reference VOP image.

Active matrix light emitting diode pixel structure and method

Abstract: A LED pixel structure (200, 300, 400, 600, 700) that reduces current nonuformities and threshold voltage variations in a 'drive transistor' of the pixel structure is disclosed. The LED pixel structure incorporates a current source for loading data into the pixel via a data line. Alternatively, an auto zero voltage is determined for the drive transistor prior to the loading of data.

Method and apparatus for determining the position of eyes and for correcting eye-defects in a captured frame

Abstract: The present apparatus and method captures at least a pair of images in relatively quick succession with an illumination source being fired during the capture of one of the images. The illumination source is located adjacent to the optical lens or close to the optical axis of the camera. Next the illumination level of the images is compensated to make them equal in illumination. Following that an analysis of the images is performed to determine the difference between the illumination compensated images. After the illumination compensation the difference has to be caused by eye-defects or specular reflections from glasses. The pixel coordinates of the transitory eye-defect regions are recorded and analyzed to determine the spacing of the potential eye locations and/or the spatial structure of the eyes for plausibility. Once confirmed the coordinates are output and recorded.

Optoelectronic camera and method for image formatting in the same

Abstract: An optoelectronic camera comprises an objective system formed by a number of optical active structures (L), particularly refractive structures in the form of microlenses or lenslets provided in an array. A detector device (D) is assigned to the lens array and comprises detectors (Dn) formed by sensor elements (E) which define pixels in the optical image. Each detector (Dn) defines a sample of the optical image and optimally all samples are used to generate a digital image. The optoelectronic camera may be realized as a colour image camera, particularly for recording images in an RGB system. In a method for digital electronic formatting of an image recorded with the optoelectronic camera, zoom and pan functions are implemented in the camera.

Wide dynamic range optical sensor

Abstract: A system and method is described for increasing effective integration time of an optical sensor including holding a first signal within each pixel cell, proportional to light integrated by the pixel cell over the previous frame period, generating a second signal within each pixel cell proportional to light integrated by the pixel cell over the current frame period, and summing the first signal and the second signal from each pixel, thereby producing an output signal representing the light integrated by each pixel over two frame periods. If saturation of pixel cells is possible, a further method of extending dynamic range is described including generating and storing a first signal in each pixel cell indicative of light integrated by the pixel cell over a long period, generating a second signal in each pixel cell indicative of light integrated by the pixel cell over a short period, and determining an output for each pixel as the first signal whenever the first signal is less than a threshold value, otherwise determining the output as the second signal. Also included are double correlated sampling for noise reduction, interlacing for increased integration time, and individual pixel reset for additional gains in dynamic range.

Computerized characterization of masses on mammograms: The rubber band straightening transform and texture analysis

Abstract: A new rubber band straightening transform (RBST) is introduced for characterization of mammographic masses as malignant or benign. The RBST transforms a band of pixels surrounding a segmented mass onto the Cartesian plane (the RBST image). The border of a mammographic mass appears approximately as a horizontal line, and possible spiculations resemble vertical lines in the RBST image. In this study, the effectiveness of a set of directional texture features extracted from the RBST images was compared to the effectiveness of the same features extracted from the images before the RBST. A database of 168 mammograms containing biopsy-proven malignant and benign breast masses was digitized at a pixel size of 100 μm×100 μm . Regions of interest (ROIs) containing the biopsied mass were extracted from each mammogram by an experienced radiologist. A clustering algorithm was employed for automated segmentation of each ROI into a mass object and background tissue. Texture features extracted from spatial gray-level dependence matrices and run-length statistics matrices were evaluated for three different regions and representations: (i) the entire ROI; (ii) a band of pixels surrounding the segmented mass object in the ROI; and (iii) the RBST image. Linear discriminant analysis was used for classification, and receiver operating characteristic (ROC) analysis was used to evaluate the classification accuracy. Using the ROC curves as the performance measure, features extracted from the RBST images were found to be significantly more effective than those extracted from the original images. Features extracted from the RBST images yielded an area (A z ) of 0.94 under the ROC curve for classification of mammographic masses as malignant and benign.

A layered approach to stereo reconstruction

Abstract: We propose a framework for extracting structure from stereo which represents the scene as a collection of approximately planar layers. Each layer consists of an explicit 3D plane equation, a colored image with per-pixel opacity (a sprite), and a per-pixel depth offset relative to the plane. Initial estimates of the layers are recovered using techniques taken from parametric motion estimation. These initial estimates are then refined using a re-synthesis algorithm which takes into account both occlusions and mixed pixels. Reasoning about such effects allows the recovery of depth and color information with high accuracy even in partially occluded regions. Another important benefit of our framework is that the output consists of a collection of approximately planar regions, a representation which is far more appropriate than a dense depth map for many applications such as rendering and video parsing.

Particle image velocimetry with optical flow

Abstract: An optical Flow technique based on the use of Dynamic Programming has been applied to Particle Image Velocimetry thus yielding a significant increase in the accuracy and spatial resolution of the velocity field. Results are presented for calibrated synthetic sequences of images and for sequences of real images taken for a thermally driven flow of water with a freezing front. The accuracy remains better than 0.5 pixel/frame for tested two-image sequences and 0.2 pixel/frame for four-image sequences, even with a 10% added noise level and allowing 10% of particles of appear or disappear. A velocity vector is obtained for every pixel of the image.

Software pixel interpolation for digital still cameras suitable for a 32-bit MCU

Abstract: This paper discusses the interpolation technique applied to the Bayer primary color method, used frequently as the pixel structure of CCD image sensors for digital still cameras. Eight typical types of interpolation methods are discussed from three viewpoints: the characteristics of the interpolated images, the processing time required to realize their methods based on a 32-bit MCU for embedded applications, and the quality of the resultant images. In terms of reducing the occurrences of pseudocolor and achieving good color restoration, the linear interpolation method taking G's correlation determined by using R/B pixels into consideration was found to be excellent. The measured machine cycle of the interpolation methods was approximately 46 cycles per pixel. Therefore, every method was able to interpolate a VGA-size image in approximately 0.2 seconds with the MCU operating at 60 MHz. In terms of the S/N ratio, a good image quality was obtained through the linear interpolation methods, even with shorter processing time. Based on these results it is concluded that the linear interpolation method, which takes correlation into consideration, is the most suitable for consumer product applications such as digital still cameras.

Locating facial region of a head-and-shoulders color image

Abstract: This paper addresses our proposed method to automatically locate the person's face from a given image that consists of a head-and-shoulders view of the person and a complex background scene. The method involves a fast, simple and yet robust algorithm that exploits the spatial distribution characteristics of human skin color. It first uses the chrominance component of the input image to detect pixels with skin color appearance. Then, bused on the spatial distribution of the detected skin-color pixels and their corresponding luminance values, the algorithm employs some regularization processes to reinforce regions of skin-color pixels that are more likely to belong to the facial regions and eliminate those that are not. The performance of the face localization algorithm is illustrated by some simulation results carried out on various head-and-shoulders test images.

Optical display system and method with optical shifting of pixel position including conversion of pixel layout to form delta to stripe pattern by time base multiplexing

Abstract: An optical display system and method selectively displaces delta triad pixels vertically. The first raster line of picture information is removed from the video signal, and each subsequent raster line of picture information (data) is displaced upward. Next, the entire picture is optically displaced down by a distance equal to one vertical pixel pitch placing the picture back in its original vertical position, but horizontal position of the pixels has changed. Thus picture information is displaced horizontally a distance equal to one and one half times horizontal pixel pitch. Odd pixel rows are displaced in one direction, and even pixel rows are displaced in the opposite direction. The technique can be used to double pixel density and, thus, resolution, in the horizontal direction by the selective shifting technique and coordination with the input video signals. Two views of a picture alternate at the frame rate fast enough to fuse them into a single image, and two successive frames are combined over time to act as a single super frame. This is time based multiplexing of a spatial pattern. Thus, a composite picture is formed using a strip pixel pattern with twice the horizontal pixel density of the original delta pattern. The triads in the first half of this super frame may partially overlap the triads in the second half of the super frame. This technique can be applied to either progressive or interlace scan formats.