Читать книгу Eye Tracking the User Experience - Aga Bojko - Страница 44
Pupil Illumination Methods
ОглавлениеIn Chapter 1, “Eye Tracking: What’s All the Hoopla?” we discussed how eye tracking works. If you remember, the typical eye tracker knows where someone is looking based on the position of the person’s pupil center in relation to the corneal reflection. Infrared light-emitting diodes illuminate the participant’s face, and cameras in the eye tracker detect and record those two eye features.
What Chapter 1 didn’t mention was that depending on where the diodes are positioned with regard to the cameras, two different methods can be used to illuminate the eyes: bright-pupil method and dark-pupil method (see Table 3.4). Both methods have the same goal: to create as much contrast as possible between the pupil and the iris (the colored part of the eye) in order to make the pupil easily distinguishable. However, the effectiveness of each method depends on the conditions under which it is used and the physical characteristics of the participant’s eyes. Most eye trackers offer either bright-pupil tracking or dark-pupil tracking, but some have both and automatically select the one that provides higher accuracy in a given situation.
TABLE 3.4 COMPARISON OF BRIGHT- AND DARK-PUPIL METHODS
| Bright-Pupil Method | Dark-Pupil Method | |
| How It Works | When the infrared light source is in line with the optical axis of the camera, the pupil appears brighter than the iris because the reflection from the retina is directed toward the camera. (This is the same phenomenon that causes the red-eye effect in photos.) |
