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Fig. 1


Illustration of the histogram of oriented gradients (HOG) method. A pair of images (panels aand b) are characterized by the norm and the orientation of their gradients (panels c and d). The relative orientation angles between their gradients (panel e) are summarized in the histogram of oriented gradients (panel f). The number of histogram counts around 0° corresponds to the coincidence of gradient orientations in both images, which is quantified by using the mean resultant vector, Eq. (2), and the projected Rayleigh statistic, Eq. (3). Two completely uncorrelated images would produce a flat histogram while two identical images would produce a histogram having the form of a Dirac delta function centered at 0°.

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