47 results for Cree, Michael J., Conference item

  • Colour image processing and texture analysis on images of porterhouse steak meat

    Streeter, Lee V.; Burling-Claridge, G. Robert; Cree, Michael J. (2005)

    Conference item
    University of Waikato

    This paper outlines two colour image processing and texture analysis techniques applied to meat images and assessment of error due to the use of JPEG compression at image capture. JPEG error analysis was performed by capturing TIFF and JPEG images, then calculating the RMS difference and applying a calibration between block boundary features and subjective visual JPEG scores. Both scores indicated high JPEG quality. Correction of JPEG blocking error was trialled and found to produce minimal improvement in the RMS difference. The texture analysis methods used were singular value decomposition over pixel blocks and complex cell analysis. The block singular values were classified as meat or non- meat by Fisher linear discriminant analysis with the colour image processing result used as ‘truth.’ Using receiver operator characteristic (ROC) analysis, an area under the ROC curve of 0.996 was obtained, demonstrating good correspondence between the colour image processing and the singular values. The complex cell analysis indicated a ‘texture angle’ expected from human inspection.

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  • Using 2D and 3D landmarks to solve the correspondence problem in cognitive robot mapping

    Jefferies, Margaret E.; Cree, Michael J.; Mayo, Michael; Baker, Jesse T. (2005)

    Conference item
    University of Waikato

    We present an approach which uses 2D and 3D landmarks for solving the correspondence problem in Simultaneous Localisation and Mapping (SLAM) in cognitive robot mapping. The nodes in the topological map are a representation for each local space the robot visits. The 2D approach is feature based – a neural network algorithm is used to learn a landmark signature from a set of features extracted from each local space representation. Newly encountered local spaces are classified by the neural network as to how well they match the signatures of the nodes in the topological network. The 3D landmarks are computed from camera views of the local space. Using multiple 2D views, identified landmarks are projected, with their correct location and orientation into 3D world space by scene reconstruction. As the robot moves around the local space, extracted landmarks are integrated into the ASR s scene representation which comprises the 3D landmarks. The landmarks for an ASR scene are compared against the landmark scenes for previously constructed ASRs to determine when the robot is revisiting a place it has been to before.

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  • Defocus restoration for a full-field heterodyne ranger via multiple return separation

    Godbaz, John Peter; Cree, Michael J.; Dorrington, Adrian A.; Künnemeyer, Rainer (2007)

    Conference item
    University of Waikato

    Full-field heterodyne time-of-flight range-imagers allow a large number of range measurements to be taken simultaneously across an entire scene; these range measurements may be corrupted due to limited depth of field. We propose a new method for deblurring heterodyne range images by identifying multiple signal returns within each pixel via deconvolution, thus reducing the spatially variant deblurring problem to a sequence of spatially invariant deconvolutions. We have applied this method to simulated data, showing significant improvement in the restored images.

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  • A high resolution full-field range imaging system for robotic devices

    Carnegie, Dale A.; Cree, Michael J.; Dorrington, Adrian A.; Payne, Andrew D. (2005)

    Conference item
    University of Waikato

    There has been considerable effort by many researchers to develop a high resolution full-field range imaging system. Traditionally these systems rely on a homodyne technique that modulates the illumination source and shutter speed at some high frequency. These systems tend to suffer from the need to be calibrated to account for changing ambient light conditions and generally cannot provide better than single centimeter range resolution, and even then over a range of only a few meters. We present a system, tested to proof-of-concept stage that is being developed for use on a range of mobile robots. The system has the potential for real-time, sub millimeter range resolution, with minimal power and space requirements.

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  • Comparison of various methods to delineate blood vessels in retinal images

    Cree, Michael J.; Leandro, J.J.G.; Soares, J.V.B.; Cesar, R.M., Jr.; Tang, G.; Jelinek, H.F.; Cornforth, D.J. (2005)

    Conference item
    University of Waikato

    The blood vessels in the human retina are easily visualisable via digital fundus photography and provide an excellent window to the health of a patient affected by diseases of blood circulation such as diabetes. Diabetic retinopathy is identifiable through lesions of the vessels such as narrowing of the arteriole walls, beading of venules into sausage like structures and new vessel growth as an attempt to reperfuse ischaemic regions. Automated quantification of these lesions would be beneficial to diabetes research and to clinical practice, particularly for eye-screening programmes for the detection of eye-disease amongst diabetic persons.

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  • Classification of pathology in diabetic eye disease

    Jelinek, H.F.; Leandro, J.J.G.; Cesar, R.M., Jr.; Cree, Michael J. (2005)

    Conference item
    University of Waikato

    Proliferative diabetic retinopathy is a complication of diabetes that can eventually lead to blindness. Early identification of this complication reduces the risk of blindness by initiating timely treatment. We report the utility of pattern analysis tools linked with a simple linear discriminant analysis that not only identifies new vessel growth in the retinal fundus but also localises the area of pathology. Ten fluorescein images were analysed using seven feature descriptors including area, perimeter, circularity, curvature, entropy, wavelet second moment and the correlation dimension. Our results indicate that traditional features such as area or perimeter measures of neovascularisation associated with proliferative retinopathy were not sensitive enough to detect early proliferative retinopathy (SNR = 0.76, 0.75 respectively). The wavelet second moment provided the best discrimination with a SNR of 1.17. Combining second moment, curvature and global correlation dimension provided a 100% discrimination (SNR = 1).

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  • Volume measurement using 3D Range Imaging

    Shrivastava, Vipul; Cree, Michael J.; Dorrington, Adrian A. (2010)

    Conference item
    University of Waikato

    The use of 3D Range Imaging has widespread applications. One of its applications provides us the information about the volumes of different objects. In this paper, 3D range imaging has been utilised to find out the volumes of different objects using two algorithms that are based on a straightforward means to calculate volume. The algorithms implemented succesfully calculate volume on objects provided that the objects have uniform colour. Objects that have multi-coloured and glossy surfaces provided particular difficulties in determining volume.

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  • Advantages of 3D time-of-flight range imaging cameras in machine vision applications

    Dorrington, Adrian A.; Kelly, Cameron B.D.; McClure, Shane H.; Payne, Andrew D.; Cree, Michael J. (2009)

    Conference item
    University of Waikato

    Machine vision using image processing of traditional intensity images is in wide spread use. In many situations environmental conditions or object colours or shades cannot be controlled, leading to difficulties in correctly processing the images and requiring complicated processing algorithms. Many of these complications can be avoided by using range image data, instead of intensity data. This is because range image data represents the physical properties of object location and shape, practically independently of object colour or shading. The advantages of range image processing are presented, along with three example applications that show how robust machine vision results can be obtained with relatively simple range image processing in real-time applications.

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  • Image intensifier characterization

    Payne, Andrew D.; Dorrington, Adrian A.; Cree, Michael J.; Carnegie, Dale A. (2006)

    Conference item
    University of Waikato

    An image intensifier forms an integral part of a full-field image range finder under development at the University of Waikato. Operating as a high speed shutter with repetition rates up to 100 MHz, a method is described to characterise the response, both temporally and spatially, of the intensifier in order to correct for variations in the field of view and to optimise the operating conditions. A short pulse of visible light is emitted by a laser diode, uniformly illuminating the image intensifier, while a CCD camera captures the output from the intensifier. The phase of the laser pulse is continuously varied using a heterodyne configuration, automatically producing a set of samples covering the modulation cycle. The results show some anomalies in the response of our system and some simple solutions are proposed to correct for these.

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  • The Waikato range imager

    Cree, Michael J.; Dorrington, Adrian A.; Conroy, Richard M.; Payne, Andrew D.; Carnegie, Dale A. (2006)

    Conference item
    University of Waikato

    We are developing a high precision simultaneous full-field acquisition range imager. This device measures range with sub millimetre precision in range simultaneously over a full-field view of the scene. Laser diodes are used to illuminate the scene with amplitude modulation with a frequency of 10MHz up to 100 MHz. The received light is interrupted by a high speed shutter operating in a heterodyne configuration thus producing a low-frequency signal which is sampled with a digital camera. By detecting the phase of the signal at each pixel the range to the scene is determined. We show 3D reconstructions of some viewed objects to demonstrate the capabilities of the ranger.

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  • Heterodyne range imaging as an alternative to photogrammetry

    Dorrington, Adrian A.; Cree, Michael J.; Carnegie, Dale A.; Payne, Andrew D.; Conroy, Richard M. (2007)

    Conference item
    University of Waikato

    Solid-state full-field range imaging technology, capable of determining the distance to objects in a scene simultaneously for every pixel in an image, has recently achieved sub-millimeter distance measurement precision. With this level of precision, it is becoming practical to use this technology for high precision three-dimensional metrology applications. Compared to photogrammetry, range imaging has the advantages of requiring only one viewing angle, a relatively short measurement time, and simplistic fast data processing. In this paper we fist review the range imaging technology, then describe an experiment comparing both photogrammetric and range imaging measurements of a calibration block with attached retro-reflective targets. The results show that the range imaging approach exhibits errors of approximately 0.5 mm in-plane and almost 5 mm out-of-plane; however, these errors appear to be mostly systematic. We then proceed to examine the physical nature and characteristics of the image ranging technology and discuss the possible causes of these systematic errors. Also discussed is the potential for further system characterization and calibration to compensate for the range determination and other errors, which could possibly lead to three-dimensional measurement precision approaching that of photogrammetry.

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  • A synchronised Direct Digital Synthesiser

    Payne, Andrew D.; Carnegie, Dale A.; Dorrington, Adrian A.; Cree, Michael J. (2005)

    Conference item
    University of Waikato

    We describe a Direct Digital Synthesiser (DDS) which provides three frequency-locked synchronised outputs to generate frequencies from DC to 160 MHz. Primarily designed for use in a heterodyning range imaging system, the flexibility of the design allows its use in a number of other applications which require any number of stable, synchronised high frequency outputs. Frequency tuning of 32 bit length provides 0.1 Hz resolution when operating at the maximum clock rate of 400 MSPS, while 14 bit phase tuning provides 0.4 mrad resolution. The DDS technique provides very high relative accuracy between outputs, while the onboard oscillator’s stability of ±1 ppm adds absolute accuracy to the design.

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  • Multiple frequency range imaging to remove measurement ambiguity

    Payne, Andrew D.; Jongenelen, Adrian P.P.; Dorrington, Adrian A.; Cree, Michael J.; Carnegie, Dale A. (2009)

    Conference item
    University of Waikato

    Range imaging systems use a specialised sensor to capture an image where object distance (range) is measured for every pixel using time-of-flight. The scene is illuminated with an amplitude modulated light source, and the phase of the modulation envelope of the reflected light is measured to determine flight time, hence object distance for each pixel. As the modulation waveform is cyclic, an ambiguity problem exists if the phase shift exceeds 2π radians. To overcome this problem we demonstrate a method that superposes two different modulation frequencies within a single capture. This technique reduces the associated overhead compared with performing two sequential measurements, allowing the system to retain high range measurement precision at rapid acquisition rates. A method is also provided to avoid interference from aliased harmonics during sampling, which otherwise contaminate the resulting range measurement. Experimental results show the potential of the multiple frequency approach; producing high measurement precision while avoiding ambiguity. The results also demonstrate the limitation of this technique, where large errors can be introduced through a combination of a low signal to noise ratio and suboptimal selection of system parameters.

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  • A Monte Carlo study of two Compton camera’s first plane detectors

    Uche, Chibueze Zimuzo; Round, W. Howell; Cree, Michael J. (2011)

    Conference item
    University of Waikato

    Purpose: The suitability of two possible detectors, silicon and germanium as the Compton camera’s first plane detector has been investigated using a robust Monte Carlo approach. Methods: The GEANT4 simulation software was used to simulate the radiation transport and interactions with matter. Investigations were first done by relating the impact of Doppler broadening on the Compton camera angular uncertainty, energy spectra and reconstructed source image. Then, the impact of geometry and interaction type on the Compton camera performance was evaluated as well. Results: Analyses suggest that silicon of about 1 cm thickness would be suitable as the Compton camera first plane detector. The choice of silicon is however not completely flawless, Doppler broadening for this detector material contributes as much as 7.3 mm and 2.4 mm to full-width-half-maximum image resolution at 140.5 keV and 511 keV respectively. Conclusions: It is envisioned that with improved reconstruction technique, silicon would be the best first plane detector for the Compton camera.

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  • Effect of the time characteristics of the Compton camera on its performance

    Uche, Chibueze Zimuzo; Round, W. Howell; Cree, Michael J. (2011)

    Conference item
    University of Waikato

    Purpose: The effect of the time characteristics of the Compton camera data acquisition (DAQ) system on the camera’s performance has been studied. Methods: The GEANT4 simulation software was used to simulate radiation transport and interactions with matter. Further investigations were carried out by utilizing straightforward approximations to estimate the charge collection times and their relationship to finding coincident events, setting thresholds to reject noise, and the resultant impacts on the Compton camera performance. Results: The results show that the time characteristics of the Compton camera DAQ account for about 17% and 13% reduction in detection efficiency at 140.5 keV and 511 keV, respectively, but made no significant difference on the Compton camera resolution. Conclusions: Findings suggest that the detection efficiency of the Compton camera has been overestimated by previous investigators who did not predict count rate losses under clinical conditions.

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  • Shape and deformation measurement using heterodyne range imaging technology

    Conroy, Richard M.; Dorrington, Adrian A.; Cree, Michael J.; Künnemeyer, Rainer; Gabbitas, Brian (2006-11)

    Conference item
    University of Waikato

    Range imaging is emerging as a promising alternative technology for applications that require non-contact visual inspection of object deformation and shape. Previously, we presented a solid-state full-field heterodyne range imaging device capable of capturing three-dimensional images with sub-millimetre range resolution. Using a heterodyne indirect time-of-flight configuration, this system simultaneously measures distance (and intensity), for each pixel in a cameras field of view. In this paper we briefly describe our range imaging system, and its principle of operation. By performing measurements on several metal objects, we demonstrate the potential capabilities of this technology for surface profiling and deformation measurement. In addition to verifying system performance, the reported examples highlight some important system limitations. With these in mind we subsequently discuss the further developments required to enable the use of this device as a robust and practical tool in non-destructive testing and measurement applications.

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  • A fast Maximum Likelihood method for improving AMCW lidar precision using waveform shape

    Godbaz, John Peter; Cree, Michael J.; Dorrington, Adrian A.; Payne, Andrew D. (2009)

    Conference item
    University of Waikato

    Amplitude Modulated Continuous Wave imaging lidar systems use the time-of-flight principle to determine the range to objects in a scene. Typical systems use modulated illumination of a scene and a modulated sensor or image intensifier. By changing the relative phase of the two modulation signals it is possible to measure the phase shift induced in the illumination signal, thus the range to the scene. In practical systems, the resultant correlation waveform contains harmonics that typically result in a non-linear range response. Nevertheless, these harmonics can be used to improve range precision. We model a waveform continuously variable in phase and intensity as a linear interpolation. By approximating the problem as a Maximum Likelihood problem, an analytic solution for the problem is derived that enables an entire range image to be processed in a few seconds. A substantial improvement in overall RMS error and precision over the standard Fourier phase analysis approach results.

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  • Monte Carlo evaluation of a Compton camera in breast and brain imaging

    Uche, Chibueze Zimuzo; Round, W. Howell; Cree, Michael J. (2013)

    Conference item
    University of Waikato

    Background: The Compton camera is increasingly becoming the subject of investigation for possible implementa- tion in nuclear medical imaging. It is likely to have advantages over Anger camera in medical imaging. However, very little has been done to characterize its performance for specific medical imaging techniques. There is therefore a need to fill in the gaps in knowledge relating to realistic evaluation of the viability of the camera for nuclear medical imaging. Objective: The present study has sought to explore the viability of a prototype Compton camera in breast and brain imaging. Methods: The GEANT4 simulation software was used to model the radiation transport and interactions with matter. Simulations were carried out of a Si/CZT Compton camera being used in breast and brain imaging. In order to study a challenging detection case, the volumes of two simulated breast tumours were chosen to be 0.65 mL, and embedded in the medial region of the breast. For the brain imaging, a multitracing approach was used, and imaging was done parallel to the orbitomeatal line of the brain. Results: The results suggest that the Compton camera would visualize small breast tumours of about 0.65 mL volume, placed at the medial region of an average compressed human breast. Although brain imaging using the Compton camera seems to be promising, analyses suggest however that beyond a distance difference of 2 cm between two brain tumours, there may be a need to rotate the camera around the human head for efficient brain imaging. Conclusions: It is envisioned that with further work, the Compton camera could replace the Anger camera in breast and brain imaging.

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  • Toward-1mm depth precision with a solid state full-field range imaging system

    Dorrington, Adrian A.; Carnegie, Dale A.; Cree, Michael J. (2006)

    Conference item
    University of Waikato

    Previously, we demonstrated a novel heterodyne based solid-state full-field range-finding imaging system. This system is comprised of modulated LED illumination, a modulated image intensifier, and a digital video camera. A 10 MHz drive is provided with 1 Hz difference between the LEDs and image intensifier. A sequence of images of the resulting beating intensifier output are captured and processed to determine phase and hence distance to the object for each pixel. In a previous publication, we detailed results showing a one-sigma precision of 15 mm to 30 mm (depending on signal strength). Furthermore, we identified the limitations of the system and potential improvements that were expected to result in a range precision in the order of 1 mm. These primarily include increasing the operating frequency and improving optical coupling and sensitivity. In this paper, we report on the implementation of these improvements and the new system characteristics. We also comment on the factors that are important for high precision image ranging and present configuration strategies for best performance. Ranging with sub-millimeter precision is demonstrated by imaging a planar surface and calculating the deviations from a planar fit. The results are also illustrated graphically by imaging a garden gnome.

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  • A power-saving modulation technique for time-of-flight range imaging sensors

    Conroy, Richard M.; Dorrington, Adrian A.; Payne, Andrew D.; Künnemeyer, Rainer; Cree, Michael J. (2011)

    Conference item
    University of Waikato

    Time-of-flight range imaging cameras measure distance and intensity simultaneously for every pixel in an image. With the continued advancement of the technology, a wide variety of new depth sensing applications are emerging; however a number of these potential applications have stringent electrical power constraints that are difficult to meet with the current state-of-the-art systems. Sensor gain modulation contributes a significant proportion of the total image sensor power consumption, and as higher spatial resolution range image sensors operating at higher modulation frequencies (to achieve better measurement precision) are developed, this proportion is likely to increase. The authors have developed a new sensor modulation technique using resonant circuit concepts that is more power efficient than the standard mode of operation. With a proof of principle system, a 93–96% reduction in modulation drive power was demonstrated across a range of modulation frequencies from 1–11 MHz. Finally, an evaluation of the range imaging performance revealed an improvement in measurement linearity in the resonant configuration due primarily to the more sinusoidal shape of the resonant electrical waveforms, while the average precision values were comparable between the standard and resonant operating modes.

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