Figure 4.

A tracking algorithm emulating the analog DPI. (A) Characteristics of Purkinje images. Data are obtained from the model in Figure 3, using a collimated 10 mm beam provided by a 2 mW source at 20° on both axes. Exposure time was set to 1 ms. The top panel shows the profile of P₁ before clipping intensity at the saturation level. The bottom panel shows both P₁ (with saturated intensity; blue curve) and P₄ (orange curve). The red horizontal bars represent the diameters of the reflections exceeding 10 dB. (B) Flowchart of the tracking algorithm. A low-resolution image of the eye (solid line) is first used to detect P₁ and P₄ and determine their approximate locations. Failure in detecting one of the two reflections is labeled as blink. High-resolution localization of the Purkinje images (dashed lines) is then obtained from selected regions of interest (ROI₁ and ROI₄).