A previously developed apparatus that tracks the orientation of the human eye has been modified to make it less susceptible to error induced by ambient infrared light. The apparatus is a commercial product intended primarily for use as a computer-control interface for a person who is physically unable to use a keyboard.
The unmodified apparatus includes a near-infrared source that illuminates the eye, plus an infrared video camera that monitors the eye. The source and camera optics are combined so that the infrared illumination strikes the eye along the optical axis of the video camera. The total video image comprises a bright image of the pupil plus a very bright specular reflection from the cornea. The total video image is processed to obtain a vector between the center of the pupil and the corneal reflection. This vector constitutes the desired information on the orientation of the eye (the gaze direction).
The unmodified apparatus incorporates several features to minimize the effect of ambient infrared light: The infrared source is a narrow-band light-emitting diode (LED) that operates at high power. A band-pass optical filter is placed in front of the video camera to block as much ambient infrared light as possible while passing the infrared light from the LED. Despite these features, infrared light from the Sun, incandescent lamps, and other sources can decrease the signal-to-noise ratio of the pupil and corneal-reflection images so much as to introduce errors or even cause the apparatus to lose track of the eye. Thus, to ensure reliable operation, the unmodified apparatus must be used indoors, with shades drawn to reduce sunlight, and with no incandescent lamps lit (fluorescent lamps are acceptable).
Accordingly, modifications were made to increase the signal-to-noise ratio in the presence of ambient infrared light. The modifications were (1) replacement of the LED by a different LED of narrower spectral width and of greater power within eye-safe limits and (2) replacement of the band-pass optical filter with another one that is better matched to the new infrared LED. The new infrared LED operates at a power of 32 mW in a wavelength band 40 nm wide at a nominal wavelength of 880 nm. The new optical band-pass filter has a wavelength pass band only 10 nm wide. Although the filter wavelength pass band is only 1/4 as wide as the emission wavelength band of the LED, computer simulations nevertheless showed that a greater signal-to-noise ratio could be achieved with this filter than with a filter of 40-nm bandwidth.
The modifications have increased the signal-to-noise ratio by a factor >20. The modified apparatus operates under ordinary indoor lighting, without need to turn off incandescent lamps.
This work was done by John Morookian and James Lambert of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Electronics & Computers category. NPO-20398
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Improved Eye-Tracking Apparatus
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Overview
The document discusses an improved eye-tracking apparatus developed by John Morookian and James Lambert at NASA's Jet Propulsion Laboratory (JPL). This apparatus is designed primarily for individuals who are physically unable to use a keyboard, serving as a computer-control interface. The original eye-tracking system utilized a near-infrared (IR) light source and an infrared video camera to monitor eye orientation by calculating the vector between the center of the pupil and the corneal reflection. However, the system was vulnerable to interference from ambient IR light sources, such as sunlight and incandescent bulbs, which degraded the quality of the video images and affected the accuracy of eye tracking.
To address these issues, the modified apparatus incorporates several enhancements aimed at maximizing the signal-to-noise ratio. Key modifications include the use of a high-power LED operating at 32 mW within a narrow optical bandwidth of 40 nm centered around 880 nm, and an optical bandpass filter with a much narrower pass band of only 10 nm. This combination effectively blocks ambient IR light while allowing the LED's light to pass through, significantly improving the clarity of the pupil and corneal reflection images.
Computer simulations indicated that the new filter design achieves a greater signal-to-noise ratio than previous designs, enhancing performance by a factor of over 20. As a result, the modified eye-tracking system can operate effectively in uncontrolled indoor lighting environments without the need for strict lighting conditions, such as drawing shades or turning off incandescent lamps, which were necessary for the unmodified version.
The document emphasizes the practical implications of these improvements, highlighting that users can now utilize the eye-tracking system in a wider range of lighting conditions, making it more versatile and user-friendly. This advancement not only enhances the reliability of the eye-tracking technology but also broadens its accessibility for individuals with disabilities.
Overall, the improved eye-tracking apparatus represents a significant step forward in assistive technology, providing a more effective means for users to interact with computers and other devices through eye movement, thereby promoting greater independence and accessibility.
