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  • 1.
    Ahlberg, Carl
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Embedded high-resolution stereo-vision of high frame-rate and low latency through FPGA-acceleration2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Autonomous agents rely on information from the surrounding environment to act upon. In the array of sensors available, the image sensor is perhaps the most versatile, allowing for detection of colour, size, shape, and depth. For the latter, in a dynamic environment, assuming no a priori knowledge, stereo vision is a commonly adopted technique. How to interpret images, and extract relevant information, is referred to as computer vision. Computer vision, and specifically stereo-vision algorithms, are complex and computationally expensive, already considering a single stereo pair, with results that are, in terms of accuracy, qualitatively difficult to compare. Adding to the challenge is a continuous stream of images, of a high frame rate, and the race of ever increasing image resolutions. In the context of autonomous agents, considerations regarding real-time requirements, embedded/resource limited processing platforms, power consumption, and physical size, further add up to an unarguably challenging problem.

    This thesis aims to achieve embedded high-resolution stereo-vision of high frame-rate and low latency, by approaching the problem from two different angles, hardware and algorithmic development, in a symbiotic relationship. The first contributions of the thesis are the GIMME and GIMME2 embedded vision platforms, which offer hardware accelerated processing through FGPAs, specifically targeting stereo vision, contrary to available COTS systems at the time. The second contribution, toward stereo vision algorithms, is twofold. Firstly, the problem of scalability and the associated disparity range is addressed by proposing a segment-based stereo algorithm. In segment space, matching is independent of image scale, and similarly, disparity range is measured in terms of segments, indicating relatively few hypotheses to cover the entire range of the scene. Secondly, more in line with the conventional stereo correspondence for FPGAs, the Census Transform (CT) has been identified as a recurring cost metric. This thesis proposes an optimisation of the CT through a Genetic Algorithm (GA) - the Genetic Algorithm Census Transform (GACT). The GACT shows promising results for benchmark datasets, compared to established CT methods, while being resource efficient.

  • 2.
    Ahlberg, Carl
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Leon, Miguel
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekstrand, Fredrik
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    The Genetic Algorithm Census TransformManuscript (preprint) (Other academic)
  • 3.
    Ahlberg, Carl
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Leon, Miguel
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekstrand, Fredrik
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Unbounded Sparse Census Transform using Genetic Algorithm2019In: 2019 IEEE WINTER CONFERENCE ON APPLICATIONS OF COMPUTER VISION (WACV), IEEE , 2019, p. 1616-1625Conference paper (Refereed)
    Abstract [en]

    The Census Transform (CT) is a well proven method for stereo vision that provides robust matching, with respect to object boundaries, outliers and radiometric distortion, at a low computational cost. Recent CT methods propose patterns for pixel comparison and sparsity, to increase matching accuracy and reduce resource requirements. However, these methods are bounded with respect to symmetry and/or edge length. In this paper, a Genetic algorithm (GA) is applied to find a new and powerful CT method. The proposed method, Genetic Algorithm Census Transform (GACT), is compared with the established CT methods, showing better results for benchmarking datasets. Additional experiments have been performed to study the search space and the correlation between training and evaluation data.

  • 4.
    Loni, Mohammad
    et al.
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ahlberg, Carl
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Daneshtalab, Masoud
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Ekström, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Sjödin, Mikael
    Mälardalen University, School of Innovation, Design and Engineering, Embedded Systems.
    Embedded Acceleration of Image Classification Applications for Stereo Vision Systems2018In: Design, Automation & Test in Europe Conference & Exhibition DATE'18, 2018Conference paper (Other academic)
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