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Faculty of Informatics - Papers (Archive)

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Articles 1561 - 1590 of 2013

Full-Text Articles in Physical Sciences and Mathematics

Unified Power Quality Index (Upqi) For Continuous Disturbances, V. J. Gosbell, B. Perera, H. M. Herath Oct 2002

Unified Power Quality Index (Upqi) For Continuous Disturbances, V. J. Gosbell, B. Perera, H. M. Herath

Faculty of Informatics - Papers (Archive)

Power quality indices are being developed that attempt to quantify certain aspects of service quality. There has been considerable amount of work on the characterization of individual types of power quality disturbances and corresponding indices. However, there does not exist in the literature a standard approach that allows one to quantify the overall power quality. This paper proposes a unified power quality index (UPQI) as a useful tool for ranking sites as to their overall power quality.

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Calibrating A 4-Wheel Mobile Robot, Phillip J. Mckerrow, D. Ratner Sep 2002

Calibrating A 4-Wheel Mobile Robot, Phillip J. Mckerrow, D. Ratner

Faculty of Informatics - Papers (Archive)

When a mobile robot is constructed the odometry must be calibrated. Calibrating a 4-wheel robot requires the accurate measurement of steering angle as well as translation and rotation. Some measurements are made with a tape measure and some with ultrasonic sensors. The measurements are used to determine the parameters of the odometry calibration matrix and the steering kinematic model. A procedure for calibrating a 4-wheel robot is discussed.

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Analysis And Representation Of Statistical Performance Of Jpeg2000 Encoded Image Over Wireless Channels, J. He, Z. Yang, D. Yang, Z. Tang, J. Hu, Chuntung Chou Sep 2002

Analysis And Representation Of Statistical Performance Of Jpeg2000 Encoded Image Over Wireless Channels, J. He, Z. Yang, D. Yang, Z. Tang, J. Hu, Chuntung Chou

Faculty of Informatics - Papers (Archive)

JPEG2000 is a new coming image standard. In this paper we analyze the performance of error resilience tools in JPEG2000, and present an analytical model to estimate the quality of JPEG2000 encoded image transmitted over wireless channels. The effectiveness of the analytical model is validated by simulation results. Furthermore, analytical model is utilized by the base station to design efficient unequal error protection schemes for JPEG2000 transmission. In the design, a utility function is defined to make a tradeoff between the image quality and the cost for transmitting the image over a wireless channel.

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Highly Scalable Image Compression Based On Spiht For Network Applications, H. Danyali, Alfred Mertins Sep 2002

Highly Scalable Image Compression Based On Spiht For Network Applications, H. Danyali, Alfred Mertins

Faculty of Informatics - Papers (Archive)

We propose a highly scalable image compression scheme based on the set partitioning in hierarchical trees (SPIHT) algorithm. Our algorithm, called highly scalable SPIHT (HS-SPIHT), supports spatial and SNR scalability and provides a bitstream that can be easily adapted (reordered) to given bandwidth and resolution requirements by a simple transcoder (parser). The HS-SPIHT algorithm adds the spatial scalability feature without sacrificing the SNR embeddedness property as found in the original SPIHT bitstream. HS-SPIHT finds applications in progressive Web browsing, flexible image storage and retrieval, and image transmission over heterogeneous networks.

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Decoding Of Images Using Soft-Bits And Markov Random Field Modeling, Alfred Mertins, O. Jamart Sep 2002

Decoding Of Images Using Soft-Bits And Markov Random Field Modeling, Alfred Mertins, O. Jamart

Faculty of Informatics - Papers (Archive)

We combine soft-bit decoding with Markov random field modeling of source signals and apply the proposed technique to image communication over noisy channels. No redundancy is added by the encoder in the form of channel codes. For error correction and concealment, the decoder relies only on the bit-reliability information extracted at the channel output and the random field modeling of natural images. The results obtained show that the proposed method yields excellent performance even under extremely noisy conditions.

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Secure Authorization, Access Control And Data Integrity In Bluetooth, L. Nguyen, R. Safavi-Naini, Willy Susilo, Tadeusz A. Wysocki Aug 2002

Secure Authorization, Access Control And Data Integrity In Bluetooth, L. Nguyen, R. Safavi-Naini, Willy Susilo, Tadeusz A. Wysocki

Faculty of Informatics - Papers (Archive)

The Bluetooth standard has a provision for mutual authentication of connecting devices but not their actual users and allows access control during connection setup only. We propose a user authorization and pairing (UAP) application, that has the ability to perform authentication and authorization of users using role based model. The pairing procedure, which exchanges link key between devices, is also performed as a part of the user authorization process. The integrity of the message is guaranteed by using message authentication codes. We also extend an attack on a short PIN during the pairing procedure for devices compliant with the Bluetooth …

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Securing Handheld Devices, Willy Susilo Aug 2002

Securing Handheld Devices, Willy Susilo

Faculty of Informatics - Papers (Archive)

Handheld devices are becoming an indispensable part of everyday life. In this paper, we review the security of handheld devices, which are based on the Pocket PC operating system. We then identify the risks and threats of having these handheld devices connected to the Internet, and propose several methods to protect against the threats. We point out some advantages and security threats of porting server applications to handheld devices. We also consider the newest technology in mobile applications using the Microsoft's NET framework and provide the security risk analysis for it. We conclude the paper with an open problem.

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On The (V,5,Λ)-Family Of Bhaskar Rao Designs, G. R. Chaudhry, M. Greig, Jennifer Seberry Aug 2002

On The (V,5,Λ)-Family Of Bhaskar Rao Designs, G. R. Chaudhry, M. Greig, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We establish that the necessary conditions for the existence of Bhaskar Rao designs of block size five are : i). λ(v - 1) ≡ 0 (mod 4) ii). λv(v - 1) ≡ 0 (mod 40) iii). 2|λ. We show these conditions are sufficient: for λ = 4 if v > 215, with 10 smaller possible exceptions and one definite exception at v = 5; for λ = 10 if v > 445, with 11 smaller possible exceptions, and one definite exception at v = 5; and for λ = 20, with the possible exception of v = 32; we also give a …

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Necessary And Sufficient Conditions For Three And Four Variable Orthogonal Designs In Order 36, S. Georgiou, C. Koukouvinos, M. Mitrouli, Jennifer Seberry Aug 2002

Necessary And Sufficient Conditions For Three And Four Variable Orthogonal Designs In Order 36, S. Georgiou, C. Koukouvinos, M. Mitrouli, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We use a new algorithm to find new sets of sequences with entries from {0, ±a, ±b, ±c, ±d}, on the commuting variables a, b, c, d, with zero autocorrelation function. Then we use these sequences to construct a series of new three and four variable orthogonal designs in order 36. We show that the necessary conditions plus (.s1, s2, s3, s4) not equal to 12816 18 816 221313 26721 36 816 4889 12825 191313 23 424 289 9 381015 8899 14425 22 916 are sufficient for the existence of an OD(36; s1, s2 s3, s4) constructed using four circulant …

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Compression Performance Of Jpeg Encryption Scheme, C. Kailasanathan, R. Safavi-Naini, P. Ogunbona Jul 2002

Compression Performance Of Jpeg Encryption Scheme, C. Kailasanathan, R. Safavi-Naini, P. Ogunbona

Faculty of Informatics - Papers (Archive)

Recent development in the Internet and Web based technologies require faster communication of multimedia data in a secure form. A number of encryption schemes for MPEG have been proposed. In this paper, we evaluate the compression performance of JPEG which has been encrypted with the zig-zag permutation algorithm, suggest a security enhancement to the scheme, and propose an alternative to entropy coding recommended by JPEG to compensate for the compression drop occurring due to permutation.

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On A Use Of Golay Sequences For Asynchronous Ds Cdma Applications, Jennifer Seberry, Beata J. Wysocki, Tadeusz A. Wysocki Jul 2002

On A Use Of Golay Sequences For Asynchronous Ds Cdma Applications, Jennifer Seberry, Beata J. Wysocki, Tadeusz A. Wysocki

Faculty of Informatics - Papers (Archive)

Golay complementary sequences, often referred to as Golay pairs, are characterised by the property that the sum of their aperiodic autocorrelation functions equals to zero, except for the zero shift. Because of this property, Golay complementary sequences can be utilised to construct Hadamard matrices defining sets of orthogonal spreading sequences for DS CDMA systems of the lengths not necessary being a power of 2. In the paper, we present an evaluation, from the viewpoint of asynchronous DS CDMA applications, of some sets of spreading sequences derived from Golay complementary sequences. We then modify those sets of sequences to enhance their …

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Face Recognition Using A Similarity-Based Measure In Image Database For Crime Investigation, V. Srisarkun, J. Cooper Jun 2002

Face Recognition Using A Similarity-Based Measure In Image Database For Crime Investigation, V. Srisarkun, J. Cooper

Faculty of Informatics - Papers (Archive)

A method to handle searching a face image database (FID) is proposed to support police officers when searching criminal records from a central registration database system (CRDS). The proposed method assumes that each FID consists of a fixable object and object correlation. The proposed method employs a database search, so that all images with a similarity-based measure are retrieved. Consequently, the proposed method is much faster than sequential searching, especially when an additional set of attributes, like scar, is defined. Moreover it requires less storage space.

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Modulated, Perfect Reconstruction Filterbanks With Integer Coefficients, Alfred Mertins, T. Karp Jun 2002

Modulated, Perfect Reconstruction Filterbanks With Integer Coefficients, Alfred Mertins, T. Karp

Faculty of Informatics - Papers (Archive)

We present design methods for perfect reconstruction (PR) integer-modulated filterbanks, including biorthogonal (low-delay) filterbanks. Both the prototype filter and the modulation sequences are composed of integers, thus allowing efficient hardware implementations and fast computation. To derive such filterbanks, we first start with the PR conditions known for cosine modulation and extend them to more general, integer modulation schemes. For the design of biorthogonal PR integer prototypes, a lifting strategy is introduced. To find suitable integer modulation schemes, new algebraic methods are presented. We show solutions where the PR conditions on the prototype filters and the modulation matrices are entirely decoupled …

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Frame Bounds For Biorthogonal Cosine-Modulated Filter Banks, Alfred Mertins May 2002

Frame Bounds For Biorthogonal Cosine-Modulated Filter Banks, Alfred Mertins

Faculty of Informatics - Papers (Archive)

We derive explicit expressions for the eigenvalues of the frame operator for cosine-modulated filter banks. The filter banks may be critically sampled or oversampled by an integer factor. The analysis of low-delay, biorthogonal filter banks shows that prototypes solely designed to minimize the stopband energy may lead to wide open frames and thus to an undesirable numerical behavior. Because the computational cost of determining the frame bounds with the proposed method is very low, we can directly use the bounds during prototype optimization and obtain prototypes with minimum stopband energy under the condition of fixed frame bounds.

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A Search For Hadamard Matrices Constructed From Williamson Matrices, J. Horton, C. Koukouvinos, Jennifer Seberry May 2002

A Search For Hadamard Matrices Constructed From Williamson Matrices, J. Horton, C. Koukouvinos, Jennifer Seberry

Faculty of Informatics - Papers (Archive)

We describe the implementation of a distributed computer search that uses Williamson's construction for Hadamard matrices. The search program is used to perform a complete search for matrices of orders 100 through 148. No new results are found, confirming existing results. We are convinced that no further matrices of any order less than 156 may be constructed. For reference purposes, we present tables of Hadamard matrices of orders 100 through 180 constructed using four circulant symmetric (1, -1) matrices in the Williamson array.

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Design Of Redundant Fir Precoders For Arbitrary Channel Lengths Based On An Mmse Criterion, Alfred Mertins Apr 2002

Design Of Redundant Fir Precoders For Arbitrary Channel Lengths Based On An Mmse Criterion, Alfred Mertins

Faculty of Informatics - Papers (Archive)

The joint design of transmitter and receiver for multichannel data transmission over dispersive channels is considered. In particular, the practically important case where the transmitter consists of FIR filters and the channel impulse response has arbitrary length is addressed. The design criterion is the minimization of the mean squared error at the receiver output under the constraint of a fixed transmit power. The proposed algorithm allows a straightforward transmitter design and yields (in general) a near-optimal solution for the transmit filters. Under certain conditions, the exact solution for the optimal transmitter is obtained.

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A New Approach To Teaching Software Risk Management With Case Studies, A. Fuller, P. Croll, L. Dei Feb 2002

A New Approach To Teaching Software Risk Management With Case Studies, A. Fuller, P. Croll, L. Dei

Faculty of Informatics - Papers (Archive)

Software development is inherently risky, however the need to adapt processes intended for larger organisations introduces a new element of risk. In addition, the nature of many new software products can be described as "critical" and therefore should undergo a formal risk assessment procedure. Despite the majority of software projects involving these additional elements of risk, risk management planning is virtually non-existent, as managers have not been trained in risk management. Few current software engineering curricula provide comprehensive coverage of risk, nor any practical experience in risk assessment. In this paper we propose that risk be repositioned in the software …

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Golay Sequences For Ds Cdma Applications, Jennifer Seberry, Beata J. Wysocki, Tadeusz A. Wysocki Jan 2002

Golay Sequences For Ds Cdma Applications, Jennifer Seberry, Beata J. Wysocki, Tadeusz A. Wysocki

Faculty of Informatics - Papers (Archive)

Golay complementary sequences, often referred to as Golay pairs, are characterised by the property that the sum of their aperiodic autocorrelation functions equals to zero, except for the zero shift. Because of this property, Golay complementary sequences can be utilised to construct Hadamard matrices defining sets of orthogonal spreading sequences for DS CDMA systems of the lengths not necessary being a power of 2. In the paper, we present an evaluation, from the viewpoint of DS CDMA applications of some sets of spreading sequences based on Golay complementary sequences. We then modify those sets of sequences to enhance their correlation …

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Asymptotic Inference For Spatial Cdfs Over Time, Jun Zhu, S N. Lahiri, Noel A. Cressie Jan 2002

Asymptotic Inference For Spatial Cdfs Over Time, Jun Zhu, S N. Lahiri, Noel A. Cressie

Faculty of Informatics - Papers (Archive)

A spatial cumulative distribution function (SCDF) is a random function that provides a statistical summary of a random process over a spatial domain of interest. In this paper, we consider a spatio-temporal process and establish statistical methodology to analyze changes in the SCDF over time. We develop hypothesis testing to detect a difference in the spatial random processes at two time points, and we construct a prediction interval to quantify such discrepancy in the corresponding SCDFs. Using a spatial subsampling method, we show that our inferences are valid asymptotically. As an illustration, we apply these inference procedures to test and …

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Spatial Mixture Models Based On Exponential Family Conditional Distributions, M Kaiser, Noel A. Cressie, J Lee Jan 2002

Spatial Mixture Models Based On Exponential Family Conditional Distributions, M Kaiser, Noel A. Cressie, J Lee

Faculty of Informatics - Papers (Archive)

Spatial statistical models are applied in many problems for which dependence in observed random variables is not easily explained by a direct scientific mechanism. In such situations there may be a latent spatial process that acts to produce the observed spatial pattern. Scientific interest often centers on the latent process and the degree of spatial dependence that characterizes it. Such latent processes may be thought of as spatial mixing distributions. We present methods for the specification of flexible joint distributions to model spatial processes through multi-parameter exponential family conditional distributions. One approach to the analysis of these models is Monte …

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Fast, Resolution-Consistent Spatial Prediction Of Global Processes From Satellite Data, Hsin-Cheng Huang, Noel A. Cressie, John Gabrosek Jan 2002

Fast, Resolution-Consistent Spatial Prediction Of Global Processes From Satellite Data, Hsin-Cheng Huang, Noel A. Cressie, John Gabrosek

Faculty of Informatics - Papers (Archive)

Polar orbiting satellites remotely sense the earth and its atmosphere, producing datasets that give daily global coverage. For any given day, the data are many and measured at spatially irregular locations. Our goal in this article is to predict values that are spatially regular at different resolutions; such values are often used as input to general circulation models (GCMs) and the like. Not only do we wish to predict optimally, but because data acquisition is relentless, our algorithm must also process the data very rapidly. This article applies a multiresolution autoregressive tree-structured model, and presents a new statistical prediction methodology …

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The Estimation Of Continuous Pq Disturbance Levels In Distribution Systems, Victor J. Gosbell, D A. Robinson Jan 2002

The Estimation Of Continuous Pq Disturbance Levels In Distribution Systems, Victor J. Gosbell, D A. Robinson

Faculty of Informatics - Papers (Archive)

A simple method is given for estimating the continuous PQ disturbance level at a site. It is based on determining a "Voltage Distortion Increment" (VDI) for each segment of the network and then adding the VDIs from a given site back to an upstream site where levels are taken to be zero. The VDI is conveniently expressible in the form of S(MVA) times length (km), where "length" correspond to the physical length in the case of MV overhead lines and an equivalent length for other components. The method is verified by a comparison with field survey data. The voltage distortion …

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Sources Of Error In Unbalance Measurements, Victor J. Gosbell, H Herath, Sarath Perera, D A. Robinson Jan 2002

Sources Of Error In Unbalance Measurements, Victor J. Gosbell, H Herath, Sarath Perera, D A. Robinson

Faculty of Informatics - Papers (Archive)

The paper aims to assess sources of error in attempting to meet standards for the measurement and reporting of negative sequence voltage unbalance. This is of importance when making use of low performance instrumentation where three difficulties may arise: (i) rms voltages rather than the fundamental is used; (ii) the magnitude but not the phase of line-neutral voltages are available; and (iii) voltage values are averaged over a period longer than standards require. The presence of harmonics at normal levels is shown to give negligible error on unbalance calculations. When lineneutral voltages are used, and zero sequence is present, the …

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Cohomology Of Buildings And Finiteness Properties Of An-Groups, Jacqueline Ramagge, Wayne W. Wheeler Jan 2002

Cohomology Of Buildings And Finiteness Properties Of An-Groups, Jacqueline Ramagge, Wayne W. Wheeler

Faculty of Informatics - Papers (Archive)

Borel and Serre calculated the cohomology of the building associated to a reductive group and used the result to deduce that torsion-free S-arithmetic groups are duality groups. By replacing their group-theoretic arguments with proofs relying only upon the geometry of buildings, we show that Borel and Serre's approach can be modied to calculate the cohomology of any locally nite ane building. As an application we show that any nitely presented e An-group is a virtual duality group. A number of other niteness conditions for e An-groups are also established.

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Use Of Cryoelectronics To Reduce Power Losses, Christopher J. Hawley, Steve Gower, Dominic Cuiuri Jan 2002

Use Of Cryoelectronics To Reduce Power Losses, Christopher J. Hawley, Steve Gower, Dominic Cuiuri

Faculty of Informatics - Papers (Archive)

The operational characteristics of power electronics operating at ambient temperatures are well known. Less well known are the characteristics of these devices when operating at cryogenic temperatures. This emerging field is known as cryoelectronics. The primary driver for operation at reduced temperatures is the promise of a resultant reduction in device operation losses. The operating characteristics of Metal Oxide Silicon Field Effect Transistors (MOSFETs) and Insulated Gate Bipolar Transistors (IGBTs) at Liquid Nitrogen (LN) temperature have been experimentally analysed. The results have been used to evaluate the viability of using cryoelectronics in medium - high power applications, considering trade-offs between …

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Modelling Of High Temperature Superconducting Wires And Coils, Christopher David Cook, T Hardono Jan 2002

Modelling Of High Temperature Superconducting Wires And Coils, Christopher David Cook, T Hardono

Faculty of Informatics - Papers (Archive)

This paper discusses modelling techniques for high temperature superconducting (HTSC) wires and coils. Models are developed based on the behaviour of Bi-2223/Ag wires and coils. For many power-engineering applications it is necessary to form HTSC wires into coils. PSpice models for HTSC coils will be presented in this paper. The aim is to develop models for HTSC wires and coils so that they can be treated as circuit elements in PSpice. The critical current of a coil will in general be different from the wire it is manufactured from and this change in current for a HTSC coil will be …

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Sensorless Force Estimation For Robots With Friction, John L. Simpson, Christopher David Cook, Zheng Li Jan 2002

Sensorless Force Estimation For Robots With Friction, John L. Simpson, Christopher David Cook, Zheng Li

Faculty of Informatics - Papers (Archive)

No abstract provided.

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Cmos Sensor Cross-Talk Compensation For Digital Cameras, Wanqing Li, Philip Ogunbona, Yu Shi, Igor Kharitonenko Jan 2002

Cmos Sensor Cross-Talk Compensation For Digital Cameras, Wanqing Li, Philip Ogunbona, Yu Shi, Igor Kharitonenko

Faculty of Informatics - Papers (Archive)

This paper presents two algorithms for removing the cross-talk effect in CMOS sensor based color-imaging systems. The algorithms work on the Bayer raw data and have low computational complexity. Experimental results on Macbeth color chart and real images demonstrated that both algorithms can effectively eliminate the cross-talk effect and produce better quality images with conventional color interpolation and correction algorithms designed for CCD image sensors. Complexity of the algorithms is also analyzed.

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Modelling Of Color Cross-Talk In Cmos Image Sensors, Wanqing Li, Philip Ogunbona, Yan Shi, Igor Kharitonenko Jan 2002

Modelling Of Color Cross-Talk In Cmos Image Sensors, Wanqing Li, Philip Ogunbona, Yan Shi, Igor Kharitonenko

Faculty of Informatics - Papers (Archive)

This paper presents a way to model the cross-talk effect in CMOS image sensors. Two algorithms are derived from the model; both of them work on the Bayer raw data and have low computational complexity. Experiments on Macbeth color chart and real images have shown the effectiveness of the modeling to eliminate the cross-talk effect and produce better quality images with traditional color interpolation and correction algorithms designed for CCD image sensors.

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Method Of Color Interpolation In A Single Sensor Color Camera Using Green Channel Separation, Chaminda Weerasinghe, Igor Kharitonenko, Philip Ogunbona Jan 2002

Method Of Color Interpolation In A Single Sensor Color Camera Using Green Channel Separation, Chaminda Weerasinghe, Igor Kharitonenko, Philip Ogunbona

Faculty of Informatics - Papers (Archive)

This paper presents a color interpolation algorithm for a single sensor color camera. The proposed algorithm is especially designed to solve the problem of pixel crosstalk among the pixels of different color channels. Interchannel cross-talk gives rise to blocking effects on the interpolated green plane, and also spreading of false colors into detailed structures. The proposed algorithm separates the green channel into two planes, one highly correlated with the red channel and the other with the blue channel. These separate planes are used for red and blue channel interpolation. Experiments conducted on McBeth color chart and natural images have shown …

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