Automatic segmentation of fiducial marks using attribute-based mathematical morphology

This paper described a fast and automatic method for segmenting fiducial marks in an image taken with a metric camera. These marks could be at the four corners, four middle sides, or inside an image (réseau marks). The segmentation was realized by using attribute-based mathematical morphology techniques. The attributes that we used in the morphology processing step were the area, aspect ratio and orientation of the best fitted ellipse of an object. The algorithm took about 0.25 second in the automatic segmentation stage. The positions of these automaticly segmented fiducial marks were then refined to sub-pixel accuracy. Dozens of real images with different shapes of fiducial marks were tested and reliable results were obtained. Accuracy comparisons were made using our method and previously published methods.