Powerful computer chips, highly efficient infrared LEDs and modern camera sensors now make it possible for previously complex eye-tracking systems to be adapted for consumer applications. These systems enable devices to detect the user’s eye movements and recognise what the user would like to do next. In conjunction with established input methods, eye tracking opens up a wealth of new intuitive interactions between man and machine.
Author: Dr. Christoph Goeltner, Osram Opto Semiconductors
Eye tracking systems detect a person’s eye movements and the direction in which they are looking. Originally, they were developed for market research, behavior analysis and usability studies. And they have also been in use for some time to help people who no longer have the use of their hands to operate computers. Many of these systems use infrared light to illuminate the user’s eyes, take a picture with a camera and calculate eye movement from the image data. Such systems needed special high-quality cameras, light sources and software. Sometimes, hardware accelerators were added to process the huge amount of graphic data. Today, extremely powerful chips, compact camera sensors and modern high-power LEDs enable eye-tracking functionality to be integrated in consumer devices such as smartphones. What’s more, in many devices, the camera sensor and the infrared light source are already being used for other functions such as facial recognition or iris identification. All that is then needed is the appropriate software to integrate eye tracking as an additional feature.
These modern eye-tracking systems are based on infrared LEDs (IREDs) for illuminating the eyes and a high-resolution camera sensor that registers the light reflected by the eyes. Image processing algorithms take this raw data and calculate the positions of the pupils. Using information about the position of a reference object, such as the screen, special software is able to determine where exactly the user is looking. Infrared illumination guarantees the necessary contrast between the iris and the pupil, whatever the eye color, particularly in the dark or if the screen background is very bright.
Such systems currently have a range of up to one meter. For smartphones and tablets, the typical working distance is around 30cm and for desktop computers around 60cm. The resolution on the screen corresponds to the raster size of the eyes and is about 1cm for tablets and about 2cm for computers. The number of IREDs used and the specific arrangement of emitters and camera depends on the type of application, in other words, on the working distance and the size of the area to be covered. The setup can also vary with the eye-tracking software used because the geometry of the design depends on the ability of the algorithms to reliably detect the orientation of the pupils. Generally speaking, the emitter and camera sensor have to be arranged at a certain angle and at a certain distance with respect to one another to avoid glare from spectacles or direct reflections from the eyes to the sensor. The greater this distance, the better the signal quality and the more flexible the choice of the optimum distance between the user and the device.
For such applications, Osram has developed the Oslon Black series and has achieved a record efficiency of 48% with SFH 4715A. The 850nm emitter typically delivers an optical output of 770mW at 1A and at present it is the most efficient IRED at this operating current. Even higher outputs are achieved by stack versions in which two emission centres are provided per chip with the aid of nanostack technology. SFH 4715AS typically produces 1,340mW of light at a current of 1A. Two versions with emission angles of 90° and 150° cover a wide range of different designs. The Oslon Black version with an optical output of 990mW at 1A is ideal as a 940nm light source. A particular feature of the Oslon Black is the low component height of only 2.3mm. This IRED therefore fits not only in present-day smartphones but also in the next-gen of devices despite the trend toward thinner devices.