Glint-Pupil Vector

To compute the glint-pupil vector it is necessary to extract the centers of the pupil and the glint. Since the field of view is very narrow, the pupil is the biggest round blob obtained after the labeling algorithm. To estimate the center the pupil a window slightly larger than the enclosing box of the pupil is created. Then gray scale pixels in the difference image are summed horizontally and vertically (Radon transform). The x, y center is computed as the center of mass of the horizontal and vertical projections (sums). A search procedure for very bright pixels around the pupil is used to detect the glint and compute its center of mass. Ideally all coordinates are computed with sub-pixel repeatability. Figure 6 shows the bright, dark, and the dark pupil image with two crosses superimposed, that correspond to the computed centers of the pupil and glint.
 
 

Figure 6: (a) Bright and (b) dark pupil images. (c) Dark pupil image superimposed by two crosses, marking the center of the pupil and the glint (for monitoring and debugging purposes).

 

1999-07-13