Pixel Configuration Research Articles

OPTIMAL LINEAR IMAGE COMBINATION

A simple, yet general, formalism for the optimized linear combination of astrophysical images is constructed and demonstrated. The formalism allows the user to combine multiple undersampled images to provide oversampled output at high precision. The proposed method is general and may be used for any configuration of input pixels and point spread function; it also provides the noise covariance in the output image along with a powerful metric for describing undesired distortion to the image convolution kernel. The method explicitly provides knowledge and control of the inevitable compromise between noise and fidelity in the output image. We present a first prototype implementation of the method, outlining steps taken to generate an efficient algorithm. This implementation is then put to practical use in reconstructing fully-sampled output images using simulated, undersampled input exposures that are designed to mimic the proposed \emph{Wide Field InfraRed Survey Telescope} (\emph{WFIRST}). We examine results using randomly rotated and dithered input images, while also assessing better-known "ideal" dither patterns: comparing results we illustrate the use of the method as a survey design tool. Finally, we use the method to test the robustness of linear image combination when subject to practical realities such as missing input pixels and focal plane plate scale variations.

Evaluation of the full operational cycle of a CMOS transfer-gated photodiode active pixel

In this paper we evaluate the full operational cycle of the active-pixel circuit for CMOS image sensors in which four field-effect transistors are suitably combined with an ordinary photodiode; meaning a vertical p–n junction, as opposed to photogates, and with no custom pinned layer. Although this circuit topology itself is not novel, this evaluation intends to shine new light on the use of regular photodiodes. They became largely in disuse in four-transistor image chips under earlier process and design circumstances because the fourth transfer-gate FET did not hold a constant signal long enough and not for a fixed time. Our aim is to investigate the full underlying operational regimen of the transfer gate to propose that a regular photodiode might again be a choice to consider in the four-transistor pixel configuration, not only in conventional imaging but also in dedicated optical applications. The use of an ordinary p–n junction photodiode is advantageous as it offers full compatibility with even elementary mainstream CMOS processes. This investigation resorts to experiments and models both with fabricated integrated pixels and with a macro-pixel circuit implementation.

Single Pixel Transflective Liquid Crystal Display with Cholesteric Half Mirror

We propose a transflective liquid crystal display (LCD) operated in a whole pixel configuration consisting of the single-polarized LC cell and the broadband cholesteric LC (ChLC) half mirror. The broadband spectrum ChLC film is used for a polarization-sensitive mirror which reflects a given circular polarization but transmits its orthogonal polarization. Our transflective LCD can be demonstrated by just replacing the polarizer, placed toward a backlight unit in the conventional cross-polarized LC modes, with the ChLC half mirror.

MESH FREE ESTIMATION OF THE STRUCTURE MODEL INDEX

The structure model index (SMI) is a means of subsuming the topology of a homogeneous random closed set under just one number, similar to the isoperimetric shape factors used for compact sets. Originally, the SMI is defined as a function of volume fraction, specific surface area and first derivative of the specific surface area, where the derivative is defined and computed using a surface meshing. The generalised Steiner formula yields however a derivative of the specific surface area that is – up to a constant – the density of the integral of mean curvature. Consequently, an SMI can be defined without referring to a discretisation and it can be estimated from 3D image data without need to mesh the surface but using the number of occurrences of 2×2×2 pixel configurations, only. Obviously, it is impossible to completely describe a random closed set by one number. In this paper, Boolean models of balls and infinite straight cylinders serve as cautionary examples pointing out the limitations of the SMI. Nevertheless, shape factors like the SMI can be valuable tools for comparing similar structures. This is illustrated on real microstructures of ice, foams, and paper.

Time-of-Flight 3-D Imaging Pixel Structures in Standard CMOS Processes

In this investigation we examine different pixel structures and readout principles to be used in imagers fabricated in standard CMOS processes, for example, the 0.5 and 0.35 processes available at the Fraunhofer IMS. The targeted applications are high-speed near-infra-red (NIR) 3-D imaging based on time-of-flight (TOF) measurements. We discuss various issues ranging from charge-coupling possibilities to noise, spectral responsivity and fill-factor, and present an extensive study of pixel configurations based on inverse biased p-n junction and MOS-C based photodetectors. We also discuss the possibilities of using a novel CMOS imaging pixel for TOF imaging applications: the charge-injection photogate (CI-PG) which presents parametric time-compression amplification. Finally, we compare and discuss all the pixel configurations examined.

18.1: Electronic Compensation for Fringe‐Field Effects in VAN LCOS Microdisplays

AbstractAlthough fringe field effects in LCOS projection panels can be suppressed sufficiently not to interfere with the optical performance needed for consumer applications, precise grey‐level reproduction in professional applications still requires a detailed knowledge of the occurrence of disclinations at all driving voltages and neighboring pixel configurations. Such a study is presented in this paper, allowing the implementation of an electronic compensation for the fringe field effects.

Global Shutter CMOS Image Sensor With Wide Dynamic Range

A novel concept for global shutter CMOS image sensors with wide dynamic range (WDR) implementation is presented. The proposed imager is based on the multisampling WDR approach and it allows an efficient global shutter pixel implementation achieving small pixel size and high fill factor. The proposed imager provides wide DR by applying adaptive exposure time to each pixel, according to the local illumination intensity level. Two pixel configurations, employing different kinds of a 1-bit in-pixel memory were implemented. An imager, including two different pixels was designed and simulated in 0.18-mum CMOS technology. System architecture and operation are discussed and simulation results are presented.

New CdTe Pixel Gamma-Ray Detector with Pixelated Al Schottky Anodes

We developed a new Al Schottky CdTe pixel detector and measured its spectral performance. It has pixelated anodes made of aluminum and a common cathode made of platinum. Because of the low leakage current and the high bias voltage owing to the Schottky diode characteristic and the anode pixel configuration, a good spectral performance including a high energy resolution was achieved. When the pixel detector with a thickness of 0.75 mm was subjected to a bias voltage of 400 V and was operated at -20 °C, the full-width-half-maximum (FWHM) energy resolution of 1.1 and 1.8 keV at 59.5 and 122 keV, respectively, were successfully obtained. The spectral performance obtained with the Al Schottky CdTe pixel detector exceeded that obtained with the conventional In Schottky CdTe pixel detector, which has an In common anode and Pt pixelated cathodes, under the same operating conditions.

An Overview of the "Triangle Method" for Estimating Surface Evapotranspiration and Soil Moisture from Satellite Imagery

An overview of the ‘triangle’ method for estimating soil surface wetness and evapotranspiration fraction from satellite imagery is presented here. The method is insensitive to initial atmospheric and surface conditions, net radiation and atmospheric correction, yet can yield accuracies comparable to other methods. We describe the method first from the standpoint of the how the triangle is observed as obtained from aircraft and satellite image data and then show how the triangle can be created from a land surface model. By superimposing the model triangle over the observed one, pixel values from the image are determined for all points within the triangle. We further show how the stretched (or ‘universal’) triangle can be used to interpret pixel configurations within the triangle, showing how the temporal trajectories of points uniquely describe patterns of land use change. Finally, we conclude the paper with a brief assessment of the method’s limitations.

Measurement of features from tomographic images of materials structures

In materials’ science, as well as in other research fields, the Euler number (or its density) is used as a characteristic describing the connectivity of the components (constituents) of a composite material or the pore space of a porous medium, see [1]. From a theoretical point of view the Euler number of a 3-dimensional set X in the Euclidean space is a basic quantity of integral geometry. By means of Crofton’s intersection formulae, the intrinsic volumes (e.g. the surface area, the total length of curved fibres, the mean breadth of a particle, the integral of Germain’s curvature) can be expressed in terms of the Euler numbers of intersections of X with lines and planes, respectively. This is the basis of the measurement of the quantities in 3d-image analysis. The observation of a set X on a homogeneous point lattice implies a discretization of the Crofton’s formulas. This leads to an efficient expression of the intrinsic volumes as a scalar product of two vectors. The fist vector depends on the image. Its components (the frequencies of pixel configurations) can easily be measured by a marching cube method. The second vector is independent of the image. Its components depends on the lattice spacings (lateral resolution), the adjacency system assumed for the pixels and the quadrature rule applied in the numerical computation of the integrals occuring in Crofton’s formulas [2,3]. The approach basing on Crofton’s intersection formulas has clear advantages over other methods where the weights are determinedmore or less empirically. It leads to higher accuracy of measurement, it can be applied to a wide range of features and it supplies multigrid convergence under weak conditions for the discretization of the set X. The applicability of the method is demonstrated for a wide range of materials, e.g. open foams, fleeces and autoclaved aerated concrete.

A bistable viologen‐TiO2 color switch

Abstract— The electro‐optical characteristics of a pixel configuration used in electrochromic viologen‐TiO2 passive‐matrix devices are studied. The configuration has two stable color states in an intermediate voltage regime. Color switching is performed by applying voltages outside this regime. The bistability is due to electrolyte‐additive controlled electron trapping in the color‐changing viologen molecules.

A 64 × 64 CMOS Active Pixel Sensor Operative at a Very Low Illumination Level

A CMOS image sensor that focuses on very low illumination applications is described. The sensor uses a 0.35 μm 2-poly 4-metal standard CMOS process and is realized as a 64 × 64 array of 7.8 × 7.4 μm2 active pixels with a fill factor of 33%. The unit pixel contains 3 NMOSFETs and a gate-body tied PMOSFET photodetector. The image sensor features highly sensitive characteristics because of the photodetector which has a maximum photo-responsivity of 2.5 × 102 A/W, and a pixel configuration with a voltage gain of about 1.3 and a pixel sensitivity of 1.2 × 10 V/lx·s. Furthermore, this sensor has a well-defined output voltage at a very low illumination level of sub-10 lx, such as with a photo-sensitivity of 35mV/lx without adjusting gain and integration time.

P-127: Multidomain Twisted Vertically Aligned Display by Microrubbing and its Simulations

A microrubbing (μ-rubbing) technique is used to create multidomain vertically aligned liquid crystal pixels for wide viewing angle liquid crystal display (LCD) applications. A metallic sphere of 1 mm diameter is used to rub a homeotropic polyimide surface to manipulate the local pretilt angle to create a four-domain pixel configuration. We use μ-rubbing to accurately control the surface pretilt angle of the liquid crystal from the normal, which directs the liquid crystal molecules to respective direction on applying a voltage. We report on the twisted vertically aligned (TVA) configurations showing symmetric isointensity curves, high contrast and attractive electro-optic performance parameters. The viewing angle and electro-optical characteristics are simulated and compared with the experimental results.

1/4-inch 2-mpixel MOS image sensor with 1.75 transistors/pixel

This paper presents new MOS image sensor technologies that realize ultra-small pixel size, i.e., 2.25/spl times/2.25 /spl mu/m/sup 2/, with high sensitivity and low supply voltage. A 1/4-inch 2-Mpixel MOS image sensor has been developed by a new pixel configuration and by a new pixel design with a 0.25-/spl mu/m CMOS process. In the new pixel configuration, a unit pixel consists of one photodiode (PD), one transfer transistor, and an amplifier circuit with three transistors which are shared by four pixels. As a result, the unit pixel has 1.75 transistors. High sensitivity has been achieved by a high aperture ratio of 25%. In the new pixel design, the low supply voltage of 2.5 V has been realized by optimizing both the potential profile in the PD and the gate length of the transfer transistor.

A CMOS/LCOS Image Transceiver Chip for Smart Goggle Applications

The design of a novel, CMOS-liquid-crystal-based image transceiver device (ITD) is described. The device combines both functions of imaging and display by means of a dual-function array formed in a single-processed chip. The image transceiver system design allows the integration of the see-through, aiming, imaging, and display of a superposed image into a single, compact, head-mounted goggle. The timing, sequencing, and control of the ITD array are designed in a pipeline array-processing scheme. The CMOS-based pixel elements are designed to provide efficient imaging in the visible range as well as driver capabilities for the overlying liquid crystal modulator. The image sensor part of the pixel consists of an n-well photodiode and a three-transistor readout circuit and is based on a back-illuminated sensor configuration. In order to provide a high imager fill-factor, two pixel configurations were conceived and analyzed: 1) a p++/p/sup -//p-well silicon structure using twin-well CMOS process and 2) an n-well processed silicon structure with a micro-lens array. The display portion of the ITD, based on LCOS micro-display technology, consists of a silicon-based reflective, active matrix driver, using a nematic liquid crystal. Details of the device design and its control system are presented.

Development of monolithic active pixel sensors for charged particle tracking

Monolithic active pixel sensors introduce a detection technique, where the active detecting element is a thin, moderately doped, and undepleted silicon layer and the readout electronics is implanted on top of it. The built-in potential, resulting from differences in doping, screens both parts, as well as it confines the charge diffusing to the readout electrodes. The R&D was triggered by the increasing need of high performance flavour identification capabilities that should be provided by future vertex detectors. The viability of the technology and its high tracking performances were demonstrated with small-scale prototypes, made of small arrays of a few thousands of pixels and more recently with a first prototype of a serviceable size of one million pixels. This paper summarizes results from tests performed with relativistic charged particles on prototypes essentially fabricated with a classical 3-transistor pixel configuration. Within the last year, two novel ideas optimising the pixel design for a vertex detector have been developed. They are presented with test results assessing their suitability.

Modeling spatial dependence in high spatial resolution hyperspectral data sets

As either the spatial resolution or the spatial scale for a geographic landscape increases, both latent spatial dependence and spatial heterogeneity also will tend to increase. In addition, the amount of georeferenced data that results becomes massively large. These features of high spatial resolution hyperspectral data present several impediments to conducting a spatial statistical analysis of such data. Foremost is the requirement of popular spatial autoregressive models to compute eigenvalues for a row-standardized geographic weights matrix that depicts the geographic configuration of an image's pixels. A second drawback arises from a need to account for increased spatial heterogeneity. And a third concern stems from the usefulness of marrying geostatistical and spatial autoregressive models in order to employ their combined power in a spatial analysis. Research reported in this paper addresses all three of these topics, proposing successful ways to prevent them from hindering a spatial statistical analysis. For illustrative purposes, the proposed techniques are employed in a spatial analysis of a high spatial resolution hyperspectral image collected during research on riparian habitats in the Yellowstone ecosystem.

Modelling and 3D optimisation of CdTe pixels detector array geometry – Extension to small pixels

CdTe and CdZnTe pixel detectors offer great interest for many applications, especially for medical and industrial imaging. Up to now, the material, generally, used and investigated for pixel arrays was CZT (Hamel et al., IEEE Trans. Nucl. Sci. 43 (3) (1996) 1422; Barrett et al., Phys. Rev. Lett. 75 (1) (1995) 156; Bennett et al., Nucl. Instr. and Meth. A 392 (1997) 260; Eskin et al., J. Appl. Phys. 85 (2) (1999) 647; Brunett et al., J. Appl. Phys. 86 (7) (1999) 3926; Luke, Nucl. Instr. and Meth. A 380 (1996) 232), but cadmium telluride can also be an appropriate choice, as shown here. However, we clearly demonstrate here that the optimal pixel configuration is highly dependent on the electrical transport properties of the material. Depending on the field of primary interest, either energy resolution or counting rate efficiency in the photopeak, the geometry for each case has to be optimised. For that purpose, we have developed a calculation of the signal induced onto the pixel. Two distinct parts are used: after showing our approach for the weighting potential calculation, we present our results performed by a “pseudo-Monte Carlo” simulation. Results are supported by a few experimental comparisons. We argue about the optimum sizes with clarifying the problems caused by too small and too large pixel sizes. The study field is chosen to be vast, i.e. pixel size to detector thickness ratios ( W/ L) of 1/8–1, and detector thickness of 1.0–8.0 mm. In addition, several electrical transport properties are used. Since efficiency is often of primary interest, thick detectors could be very attractive, which are shown to be really feasible even on CdTe.

36.1: 6‐Bit Digital VGA OLED

AbstractWe developed 0.7 inch VGA TFT‐OLED with a 64 gray‐scale integrated driver circuit. The TFT‐OLED has good image uniformity due to digital operation. Control in a time‐ratio was useful for achieving large gray‐scale level. Our simplified pixel configuration accomplished high resolution.

An analysis of some common scanning techniques for lossless image coding

Though most image coding techniques use a raster scan to order pixels prior to coding, Hilbert and other scans have been proposed as having better performance due to their superior locality preserving properties. However, a general understanding of the merits of various scans has been lacking. This paper develops an approach for quantitatively analyzing the effect of pixel scan order for context-based, predictive lossless image compression and uses it to compare raster, Hilbert, random and hierarchical scans. Specifically, for a quantized-Gaussian image model and a given scan order, it shows how the encoding rate can be estimated from the frequencies with which various pixel configurations are available as previously scanned contexts, and from the corresponding conditional differential entropies. Formulas are derived for such context frequencies and entropies. Assuming an isotropic image model and contexts consisting of previously scanned adjacent pixels, it is found that the raster scan is better than the Hilbert scan which is often used in compression applications due to its locality preserving properties. The hierarchical scan is better still, though it is based on nonadjacent contexts. The random scan is the worst of the four considered. Extensions and implications of the results to lossy coding are also discussed.