48 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.

    View record details
  • Estimating heading direction from monocular video sequences using biologically-based sensor

    Cree, Michael J.; Perrone, John A.; Anthonys, Gehan; Garnett, Aden C.; Gouk, Henry (2016)

    Conference item
    University of Waikato

    The determination of one’s movement through the environment (visual odometry or self-motion estimation) from monocular sources such as video is an important research problem because of its relevance to robotics and autonomous vehicles. The traditional computer vision approach to this problem tracks visual features across frames in order to obtain 2-D image motion estimates from which the camera motion can be derived. We present an alternative scheme which uses the properties of motion sensitive cells in the primate brain to derive the image motion and the camera heading vector. We tested heading estimation using a camera mounted on a linear translation table with the line of sight of the camera set at a range of angles relative to straight ahead (0◦ to 50◦ in 10◦ steps). The camera velocity was also varied (0.2, 0.4, 0.8, 1.2, 1.6 and 2.0 m/s). Our biologically-based method produced accurate heading estimates over a wide range of test angles and camera speeds. Our approach has the advantage of being a one-shot estimator and not requiring iterative search techniques for finding the heading.

    View record details
  • Vectorised SIMD Implementations of Morphology Algorithms

    Cree, Michael J. (2015)

    Conference item
    University of Waikato

    We explore vectorised implementations, exploiting single instruction multiple data (SIMD) CPU instructions on commonly used architectures, of three efficient algorithms for morphological dilation and erosion. We discuss issues specific to SIMD implementation and describe how they guide algorithm choice. We compare our implementations to a commonly used opensource SIMD accelerated machine vision library and find orders of magnitude speed-ups can be achieved for erosions using two-dimensional structuring elements.

    View record details
  • Scene structure analysis for sprint sports

    Hedayati, M.; Cree, Michael J.; Scott, Jonathan B. (2016)

    Conference item
    University of Waikato

    This work proposes a robust model to analyse the structure of horse races based on 2D velocity vector information. This model is capable of detecting scene breaks, classifying the view of the contenders and extracting the trajectory of the contenders throughout the race. The performance of the system is tested over six video clips from two different broadcast sources. The performance analysis shows the model achieves a high accuracy of view classification with the lowest value of 83%, all in real time.

    View record details
  • Design of a Pseudo-Holographic Distributed Time-of-Flight Sonar Range-Imaging System

    Streeter, Lee; Scott, Jonathan B.; Lickfold, Carl A.; Cree, Michael J. (2016)

    Conference item
    University of Waikato

    The design of an audible sonar distributed sensor time-of-flight range imaging system is investigated, sonar being chosen as a substitute for optical range imaging due to cost and simplicity of implementation. The distributed range imaging system proposed is based on the holographic principle where the sensors detect the self interference of the reflected sound from the scene, and the Fourier analysis computes the reflected object profile. An approximate linearised model used in related holographic imaging techniques is found to be inappropriate for the design, and qualitative assessment of simulations show that removing the linearisation dramatically improves image reconstruction. Quantitatively the nonlinear reconstruction improves the RMSE by a factor of 1.3-2.1 times. The full nonlinear reconstruction is slow, and mathematical development lead to 15 fold reduction in computation time.

    View record details
  • Video-rate or high-precision: A flexible range imaging camera

    Dorrington, Adrian A.; Cree, Michael J.; Carnegie, Dale A.; Payne, Andrew D.; Conroy, Richard M.; Godbaz, John Peter; Jongenelen, Adrian P.P. (2008)

    Conference item
    University of Waikato

    A range imaging camera produces an output similar to a digital photograph, but every pixel in the image contains distance information as well as intensity. This is useful for measuring the shape, size and location of objects in a scene, hence is well suited to certain machine vision applications. Previously we demonstrated a heterodyne range imaging system operating in a relatively high resolution (512-by-512) pixels and high precision (0.4 mm best case) configuration, but with a slow measurement rate (one every 10 s). Although this high precision range imaging is useful for some applications, the low acquisition speed is limiting in many situations. The system’s frame rate and length of acquisition is fully configurable in software, which means the measurement rate can be increased by compromising precision and image resolution. In this paper we demonstrate the flexibility of our range imaging system by showing examples of high precision ranging at slow acquisition speeds and video-rate ranging with reduced ranging precision and image resolution. We also show that the heterodyne approach and the use of more than four samples per beat cycle provides better linearity than the traditional homodyne quadrature detection approach. Finally, we comment on practical issues of frame rate and beat signal frequency selection.

    View record details
  • Analysis of the SoftKinetic DepthSense for Range Imaging

    Cree, Michael J.; Streeter, Lee V.; Conroy, Richard M.; Dorrington, Adrian A. (2013)

    Conference item
    University of Waikato

    We analyse the SoftKinetic DepthSense 325 range imaging camera for precision and accuracy in ranging out to 3 m. Flat planar targets (one a grey board, the other made from retroreflective material) are imaged at a variety of distances. Straight-forward image processing is used to identify the target and calculate the range and the root mean square variation in ranging to the target. It is found that inaccuracies in ranging of up to 2 cm occur to the grey board when imaging over 0 m to 1.5 m and the precision in ranging degrades from just below 1 cm at 0 m to almost 10 cm at 1.5 m. Similar inaccuracies occur with the retroreflective target but the precision is always under 1 cm even out to 3 m due to the strong signal return received from the target.

    View record details
  • Calibration and control of a robot arm using a range imaging camera

    Kelly, Cameron B.D.; Dorrington, Adrian A.; Cree, Michael J.; Payne, Andrew D. (2010)

    Conference item
    University of Waikato

    Time of flight range imaging is an emerging technology that has numerous applications in machine vision. In this paper we cover the use of a commercial time of flight range imaging camera for calibrating a robotic arm. We do this by identifying retro-reflective targets attached to the arm, and centroiding on calibrated spatial data, which allows precise measurement of three dimensional target locations. The robotic arm is an inexpensive model that does not have positional feedback, so a series of movements are performed to calibrate the servos signals to the physical position of the arm. The calibration showed a good linear response between the control signal and servo angles. The calibration procedure also provided a transformation between the camera and arm coordinate systems. Inverse kinematic control was then used to position the arm. The range camera could also be used to identify objects in the scene. With the object location now known in the arm's coordinate system (transformed from the camera's coordinate system) the arm was able to move allowing it to grasp the object.

    View record details
  • Range imager performance comparison in homodyne and heterodyne operating modes

    Conroy, Richard M.; Dorrington, Adrian A.; Künnemeyer, Rainer; Cree, Michael J. (2009)

    Conference item
    University of Waikato

    Range imaging cameras measure depth simultaneously for every pixel in a given field of view. In most implementations the basic operating principles are the same. A scene is illuminated with an intensity modulated light source and the reflected signal is sampled using a gain-modulated imager. Previously we presented a unique heterodyne range imaging system that employed a bulky and power hungry image intensifier as the high speed gain-modulation mechanism. In this paper we present a new range imager using an internally modulated image sensor that is designed to operate in heterodyne mode, but can also operate in homodyne mode. We discuss homodyne and heterodyne range imaging, and the merits of the various types of hardware used to implement these systems. Following this we describe in detail the hardware and firmware components of our new ranger. We experimentally compare the two operating modes and demonstrate that heterodyne operation is less sensitive to some of the limitations suffered in homodyne mode, resulting in better linearity and ranging precision characteristics. We conclude by showing various qualitative examples that demonstrate the system’s three-dimensional measurement performance.

    View record details
  • Multiple range imaging camera operation with minimal performance impact

    Whyte, Refael Z.; Payne, Andrew D.; Dorrington, Adrian A.; Cree, Michael J. (2010)

    Conference item
    University of Waikato

    Time-of-flight range imaging cameras operate by illuminating a scene with amplitude modulated light and measuring the phase shift of the modulation envelope between the emitted and reflected light. Object distance can then be calculated from this phase measurement. This approach does not work in multiple camera environments as the measured phase is corrupted by the illumination from other cameras. To minimize inaccuracies in multiple camera environments, replacing the traditional cyclic modulation with pseudo-noise amplitude modulation has been previously demonstrated. However, this technique effectively reduced the modulation frequency, therefore decreasing the distance measurement precision (which has a proportional relationship with the modulation frequency). A new modulation scheme using maximum length pseudo-random sequences binary phase encoded onto the existing cyclic amplitude modulation, is presented. The effective modulation frequency therefore remains unchanged, providing range measurements with high precision. The effectiveness of the new modulation scheme was verified using a custom time-of-flight camera based on the PMD19-K2 range imaging sensor. The new pseudo-noise modulation has no significant performance decrease in a single camera environment. In a two camera environment, the precision is only reduced by the increased photon shot noise from the second illumination source.

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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).

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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.

    View record details
  • 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.

    View record details