Fig. 1. The pupil alignment device

Fig. 2. Flow chart of pupil alignment

Fig. 3. The Sobel operator matrix

Fig. 4. Flow chart of imaging system center localization

Fig. 5. The center of the imaging system, the original image, and the effective region for four randomly selected images

Fig. 6. The histograms of the effective area and the core region for the four images

Fig. 7. Flow chart of pupil center localization

Fig. 8. Images of (a) morphological operations and (b) pupil center

Fig. 9. Images obtained by maximum inter-class variance method. (a) The center of imaging system; (b) core region; (c) binarization results; (d) morphological results; (e) pupil center

Fig. 10. Pupil center determined by histogram valley method. (a) The center of the imaging system; (b) core region; (c) using twice maximum between-cluster results; (d) binarization results; (e) morphological results; (f) pupil center

Fig. 11. Localization results of imaging system center and pupil center

Fig. 12. Euclidean distance of deviation of pupil center located by the proposed algorithm and circle approximation algorithm from manually marked pupil center

Fig. 13. The original image and the pupil-aligned images. (a) The original image and (b) it’s pupil localization results; (c) the aligned original image and (d) it’s pupil localization results