ACCURATE AND FAST PUPIL LOCALIZATION USING CONTRAST STRETCHING, SEED FILLING AND CIRCULAR GEOMETRICAL CONSTRAINTS

Abstract

Iris segmentation is the most contested issue in th e iris recognition system, since noise and poor ima ge quality can significantly affect accuracy of iris l ocalization stage. Therefore, very careful attentio n has to be paid for the segmentation process if only an accura te result is expected. This study presents a new me thod for precise pupil detection capable of handling the unconstrained bad acquisition conditions especiall y those related to low contrast or to the non-uniform brigh tness caused by the position of light sources, spec ular reflection, eyelashes and eyelids. Contrast stretch ing (normalization) technique is used for handling the variations in contrast and illumination in an iris image by stretching’ the range of intensity values. Next, the local integration is applied on the enhanced image, this process will enhance the contrast level betwe en the existing white and black areas of the image; this w ill useful to compute the optimal threshold value r equired to perform a successful image binarization for the purpose of isolation of the pupil region, the seed fill algorithm is used as region growing method to segment the binary image and allocate the pupil as a cir cular black segment with biggest area, the approximate pu pil center is detected then for removing the specul ar reflection, the pupil is filled with black color us ing a simple filling method. Finally a circle fitti ng algorithm is used for precisely allocating the circular pupil region by the fact that richer iris textures are n ot closer to the pupil boundary. A set of tests was conducted on 2,655 iris images which were downloaded from CASIA V3.0-interval standard dataset; the test results in dicated that the proposed method had subjectively 1 00% accuracy rate with pupil localization, process sati sfy the real time constraints even when dealing wit h images have very different brightness or contrast c onditions or they contain eyelashes artifacts.