Rotate Angle Estimating For Iris Recognition

On the collection of iris image, there is a rotate angle between the collected iris image and the original iris image in the database because of the deflexion of the face or the turn of the eyeball. In this paper, the estimation of this rotate angle is researched, and two novel algorithms are proposed to calculate this angle based on the image moment.According to the physical characteristic of the geometric moments, it is known that the orientation of a region can be represented by the angle between the horizontal axis and the principal axis of this region which is the line with the smallest turning inertia of the region. So the angle of a region rotated from the horizontal axis can be regarded as the orientation of this region. Making the segmented iris image as the target region, the geometric moments based angle estimating method can get the rotate angle of the iris by calculating the smallest turning inertia of the target region.Because Zernike moment has rotation invariance, the primal iris image and the rotated iris image have the same Zernike moment modules except for the different phase angle. The relative rotate angle can be got by calculating the difference between the Zernike moments phase angles of different images. The Zernike moment based angle estimating algorithm regards the located iris gray image as the target region and maps it on the unit disk. Then the corresponding phase angel of the Zernike moment is computed and the relative rotate angle can be obtained according to the Zernike moment phase angles of two iris images.The experimental results shown that both these two proposed algorithms can basically estimate the rotated angle and improve the performance of the iris recognition system.