Actual Pixel Research Articles

Measurement of the internal diameter of plastic tubes from projection MR images using a model‐based least‐squares fit approach

Hyperpolarized (HP) 3He MRI is an emerging tool in the diagnosis and evaluation of pulmonary diseases involving bronchoconstriction, such as asthma. Previously, airway diameters from dynamic HP 3He MR images of the lung were assessed manually and subjectively, and were thus prone to uncertainties associated with human error and partial volume effects. A model-based algorithm capable of fully utilizing pixel intensity profile information and attaining subpixel resolution has been developed to measure surrogate airway diameters from HP 3He MR static projection images of plastic tubes. This goal was achieved by fitting ideal pixel intensity profiles for various diameter (6.4 to 19.1 mm) circular tubes to actual pixel intensity data. A phantom was constructed from plastic tubes of various diameters connected in series and filled with water mixed with contrast agent. Projection MR images were then taken of the phantom. The favorable performance of the model-based algorithm compared to manual assessment demonstrates the viability of our approach. The manual and algorithm approaches yielded diameter measurements that generally stayed within 1 x the pixel dimension. However, inconsistency of the manual approach can be observed from the larger standard deviations of its measured values. The method was then extended to HP 3He MRI, producing encouraging results at tube diameters characteristic of airways beyond the second generation, thereby justifying their application to lung airway imaging and measurement. Potential obstacles when measuring airway diameters using this method are discussed.

Moving object detection in wavelet compressed video

In many surveillance systems the video is stored in wavelet compressed form. In this paper, an algorithm for moving object and region detection in video which is compressed using a wavelet transform (WT) is developed. The algorithm estimates the WT of the background scene from the WTs of the past image frames of the video. The WT of the current image is compared with the WT of the background and the moving objects are determined from the difference. The algorithm does not perform inverse WT to obtain the actual pixels of the current image nor the estimated background. This leads to a computationally efficient method and a system compared to the existing motion estimation methods.

Vision Based Fire Detection Using Mixture Gaussian Model

Vision based fire detection has many advantages over traditional methods. In vision based fire detection approaches, it is required that systems must have enough robustness and be insensitive to environment. We mainly take advantage of mixture Gaussian model and frame difference techniques to adaptively extract a background image from image sequences captured by ordinary color cameras. These techniques are able to mostly eliminate influences of artificial lights, wind and moving objects disturbance. By subtracting the background image from the incoming frame, foreground objects which are possible fire pixels are thus obtained. After analyzing behavior and spectroscopy of fire, color, shape fluctuation and growth rate are used to determine if a possible pixel is an actual fire pixel. Experiments show that our algorithm is robust for a stationary camera.

Prediction of CMOS APS Design Enabling Maximum Photoresponse for Scalable CMOS Technologies

This brief represents the CMOS active pixel sensor (APS) photoresponse model use for maximum pixel photosignal prediction in scalable CMOS technologies. We have proposed a simple approximation determining the technology-scaling effect on the overall device photoresponse. Based on the above approximation and the data obtained from the CMOS 0.5 /spl mu/m process thorough investigation we have theoretically predicted, designed, measured and compared the optimal (in the output photosignal sense) pixel in a more advanced, CMOS 0.35 /spl mu/m technology. Comparison of both, our theoretically predicted and modeled results and the results obtained from the measurements of an actual pixel array gives excellent agreement. It verifies the presented scaling-effect approximation and validates the usefulness of our model for design optimization in scalable CMOS technologies.

A virtual pixel technique for doubling the PDP resolution of moving images

Abstract—A virtual pixel technique increases the resolution of spatially discrete pixilated display devices when the eye moves relative to the screen. By using this technique, an effective PDP resolution can be doubled for moving images. For instance, 1280‐horizontal‐pixel data can be displayed on a VGA PDP having only 640 horizontal pixels. The positions and sizes of the virtual pixels are controlled by choosing light‐emission timings and durations of the actual pixels as their images move across the retina.

Response to Hirsch (2001)

Response to Hirsch (2001)

CMOS APS MTF modeling

In this paper, a unified model, based on a thorough analysis of experimental data, is developed for the overall modulation transfer function (MTF) estimation for CMOS image sensors. The model covers the physical diffusion effect together with the influence of the pixel active area geometrical shape. Comparison of both our predicted results and the MTF calculated from the point spread function (PSF) measurements of an actual pixel array gives excellent agreement. This confirms the hypothesis that the active area shape together with the photocarrier diffusion effect are the determining factors of the overall CMOS active pixel sensor (APS) MTF behavior, and allows us to extract the minority-carrier diffusion length. The results indicate that for any potential active area shape, a reliable estimate of image performance is possible, so the tradeoff between the conflicting requirements, such as signal-to-noise ratio (SNR) and MTF could be compared per pixel design.

Geometrical modulation transfer function for different pixel active area shapes

In this work we consider the effect of the pixel active area geometrical shape on the modulation transfer function (MTF) of an image sensor. When designing a CMOS Active Pixel Sensor (APS), or a CCD or CID sensor for this matter, the active area of the pixel would have a certain geometrical shape which might not cover the whole pixel area. To improve the device performance, it is important to understand the effect this has on the pixel sensitivity and on the resulting MTF. We perform a theoretical analysis of the MTF for the active area shape and derive explicit formulas for the transfer function for pixel arrays with a square, a rectangular and an L shaped active area (most commonly used), and generalize for any connected active area shape. Preliminary experimental results of subpixel scanning sensitivity maps and the corresponding MTFs have also been obtained, which confirm the theoretical derivations. Both the simulation results and the MTF calculated from the Point Spread Function (PSF) measurements of the actual pixel arrays show that the active area shape contributes significantly to the behavior of the overall MTF. The results also indicate that for any potential pixel active area shape, the effect of its diversion from the square pixel could be calculated, so that tradeoff between the conflicting requirements, such as SNR and MTF, could be compared per each pixel design for better overall sensor performance.

Lossless Image Compression Using Predictive Codebooks

This paper describes a method for lossless image compression where relative pixel values of prediction regions in a set of training images are stored as a codebook. In order to achieve decorrelation of the pixels comprising an image, each pixel's prediction neighborhood is assigned to a neighborhood in the codebook, and the difference between the actual pixel value and the predicted value from the codebook is coded using an entropy coder. Using the same codebook, one can achieve perfect reconstruction of the image. The method is tested on several standard images and compared with previously published methods. These experiments demonstrate that the new method is a suitable alternative to existing lossless image compression techniques.

Performance measurement in point source target detection

Certain point target detection algorithms applied to digital images can be evaluated through a formalism involving the generation of a threshold picture, i.e., replacing each actual pixel value with a threshold calculated from the background. Methods to evaluate the strengths and weaknesses of each algorithm are presented using the threshold picture. Moreover, the calculation of an electro-optical system sensitivity parameter (minimum detectable signal) is presented, based on the threshold image.

Microcomputer-based classification of environmental data in municipal areas

Multivariate data-processing methods used in mineral resource identification can be used to classify urban regions. Using elements of expert systems, geographical information systems, as well as known classification and prognosis systems, it is possible to outline a single model that consists of resistant and of temporary parts of a knowledge base including graphical input and output treatment and of resistant and temporary elements of a bank of methods and algorithms. Whereas decision rules created by experts will be stored in expert systems directly, powerful classification rules in form of resistant but latent (implicit) decision algorithms may be implemented in the suggested model. The latent functions will be transformed into temporary explicit decision rules by learning processes depending on the actual task(s), parameter set(s), pixels selection(s), and expert control(s). This takes place both at supervised and nonsupervised classification of multivariately described pixel sets representing municipal subareas. The model is outlined briefly and illustrated by results obtained in a target area covering a part of the city of Berlin (Germany).

Grade 6 Children's Ability to Use a Landsat Digital Data Computer Program

Abstract This research project1 examines the ability of grade 6 children to use a Landsat digital data computer program and derive information from it. The project successfully replicated the Kirman and Unsworth procedure for teaching grade 6 children about Landsat digital data (Journal of Geography, Januarypebruary 1991). In this project the children first hand-colored actual pixel scenes and then used a computer program to locate and color specific pixels to choose an appropriate building site for a house. This research shows that the children in this project were able to use and understand the computer program to solve a geographic problem involving digital data.

Sonar Feature-Based Bandwidth Compression

A sonar bandwidth compression (BWC) technique which, unlike conventional methods, adaptively varies the coding resolution in the compression process based on a priori information is described. This novel approach yields a robust compression system whose performance exceeds the conventional methods by factors of 2-to-1 and 1.5-to-1 for display-formatted and time series sonar data, respectively. The data is first analyzed by a feature extraction routine to determine those pixels of the image that collectively comprise intelligence-bearing signal features. The data is then split into a foreground image which contains the extracted source characteristic and a larger background image which is the remainder. Since the background image is highly textured, it suffices to code only the local statistics rather than the actual pixels themselves. This results in a substantial reduction of the bit rate required to code the background image. The feature-based compression algorithm developed for sonar imagery data is also extended to the sonar time series data via a novel approach involving an initial one-dimensional DCT transformation of the time series data before the actual compression process. The unique advantage of this approach is that the coding is done in an alternative two-dimensional image domain where, unlike the original time domain, it is possible to observe, differentiate, and prioritize essential features of data in the compression process. The feature-based BWC developed for sonar data is potentially very useful for applications involving highly textured imagery. Two such applications are synthetic aperture radar and ultrasound medical imaging.

Dynamic characteristics of leakage current in amorphous silicon thin‐film transistors

AbstractThe transient off‐currents of thin‐film transistors (TFTs) have been characterized. The authors connected the TFT to a capacitor equivalent to an actual pixel capacitance and made accurate measurements of the voltage at the capacitor under a drive condition actually used for the TFT‐LCDs. The currents were calculated from the measured voltages. Inverted staggered‐type TFTs were used with the gate on‐voltage Vgs = 20 V and the drain voltage Vsig = Vsigc ± 5 V (Vsigc = 4 ± 10 V). It has been found that the off‐current shows an increase or decrease with a time delay of a few milliseconds. The change in the off‐current has been characterized as a relation between the gate bias voltage Vgs and the off‐current Ids. Comparing the results with the dc characteristics, it has been found that the Ids vs. Vgs curves approach the dc curves from the positive side of Vgs' i.e., the transient current curves shift from their dc curves in the positive direction of Vgs. The authors have verified that this behavior of the off‐current with time delay can be explained by introducing a trap level inside the TFT.

A distributed approach to integrated inquiry and display for radiology

Picture archive and communications (PACS) systems should be flexible and modular in design so that new advances in storage, computation, and display technology can be introduced into the system without a significant redesign of existing software. The acquisition, storage, and management of radiologic images must be carefully integrated with a radiology information system. Our architecture is based on a four-level data model: (1) patient information, (2) examination information and reports, (3) image information, and (4) instances of images. The PACS being developed at the Mallinckrodt Institute of Radiology within the Electronic Radiology Laboratory consists of three primary components: application clients, database servers and image servers. One type of application client is an image-capable workstation that supports a radiology image viewing application. The application client queries the database server for information regarding patient and examination data in response to user-level requests. The database server responds to the request by retrieving the appropriate patient demographics and examination information, along with a pointer to the image/instance data from a central database. The client then uses the image data pointer to query the image server for the actual pixel data. The image server responds by transmitting the pixel data to the requesting application client or a designated auxiliary display device. Other clients act as image data acquisition nodes. Queries to the database servers are made via a library of callable subroutines. Software integrity is maintained throughout the system by dynamically loading software from a code-control database. Inquiry and display transactions, supported on a local-area network (Ethernet), have been measured and analyzed. Results and observations are presented.

Pattern recognition by the use of multivariate statistical evaluation of macro- and micro-PIXE results

The importance of statistical evaluation of multielemental data is illustrated using the data collected in a macro- and micro-PIXE analysis of human brain tumours. By employing a multivariate statistical classification methodology (SIMCA) it was shown that the total information collected from each specimen separates three types of tissue: High malignant, less malignant and normal brain tissue. This makes a classification of a given specimen possible based on the elemental concentrations. Partial least squares regression (PLS), a multivariate regression method, made it possible to study the relative importance of the examined nine trace elements, the dry/wet weight ratio and the age of the patient in predicting the survival time after operation for patients with the high malignant form, astrocytomas grade III–IV. The elemental maps from a microprobe analysis were also subjected to multivariate analysis. This showed that the six elements sorted into maps could be presented in three maps containing all the relevant information. The intensity in these maps is proportional to the value (score) of the actual pixel along the calculated principal components.

NTERPRETING THE PIXEL STANDARD DEVIATION STATISTIC FROM AN X-RAY TOMOGRAPHIC SCANNER

ABSTRACThe mean absorption and pixel standard deviation represent two quantitative outputs from x-ray computed tomography (X-ray CT). The standard deviation is a measure of dispersion of individual pixel absorption values. An approach for using the standard deviation statistic in interpreting image texture was developed and was investigated using specially constructed fixtures. The theory assumes a scanned region could be divided into two or three subregions having known absorption values and having a known background standard deviation. Using the model, predicted vs. observed standard deviation agreed within 10%. Prediction of pixel numbers representing pore media compared with actual pixels occupied by pore space agreed within 20%. The standard deviation statistic appears to be a significant aid in quantifying relative proportions of two constituent zones within images representing two zones.

On properties of discretized convex curves

The connection between a continuous convex curve and its discrete image is investigated using an appropriate definition of discrete convexity. It is shown that the discrete image of continuous convex curve may not be convex; however, its deviation from convexity (in the discrete definition) is bounded by a small constant. The actual pixel patterns that are obtained by discretizing convex curves are studied. Certain constraints on the context of discrete images of continuous convex curves were discovered. >