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Ridge detection.

Figures 9-11 show corresponding ridge curves detected from the other hand image. Observe how a coarse-scale ridge descriptor is obtained for the arm as a whole, whereas the individual fingers give rise to ridge curves at finer scales.

  
Figure 9: The 10 strongest bright ridge curves obtained by with automatic scale selection.

  
Figure 10: Three-dimensional view of the five strongest ridge curves in scale-space.

  
Figure 11: Backprojections of the five strongest ridge curves to the image domain in terms of unions of bright circles centered at the ridge curves and with the radius proportional to the selected scale.