Robust circular marker localization under non-uniform illuminations based on homomorphic filtering

Abstract

Circular markers are widely used in image-based measurement fields, e.g. vision system calibration, displacement measurement, and vibration monitoring. Generally, the marker positioning error inevitably leads to inaccurate results. As one of the key factors, the non-uniform illumination seriously affects the localization precision of circular markers. In order to reduce the influences of uneven lighting, a homomorphic filtering-gray weighted centroid method (HF-GWCM) is presented in this work. Firstly, the basic principles of both HF and its combination with GWCM are introduced. Subsequently, some simulation examples are conducted to analyze the localization accuracy of concentric circle markers under non-uniform illumination situations, which comprise the influences of HF parameters and different localization methods. Finally, a single camera imaging system with multiple light sources is employed to perform some tests for the effectiveness validation of HF-GWCM. Both positioning accuracy and stability of HF-GWCM are analyzed under different uneven illumination situations, including lighting movement, multiple light sources, and shaded region. Results demonstrate that HF-GWCM owns the ability to resist the interference of non-uniform illuminations, and it is also an effective way to improve the localization accuracy of circular markers.