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Computer vision for the blind

August 15, 2002

The white cane used by the blind as a travel aid may be universal, but it is not always adequate when it comes to pedestrian crossings. Although some crossings make a sound when it is safe to cross, many do not, and it is at these crossings that the blind need to know when the green man is showing. Adaptations of the white cane have been made, which use laser or ultrasonic waves to detect more distant obstacles, but they do not give information about the width of the road or colour of the traffic lights. Professor Shioyama and his colleagues at Kyoto Institute of Technology, Japan have developed a new method to assist the blind in such a situation. Published today in the Institute of Physics journal, Measurement Science and Technology, the device can measure the length of a crossing to within one step length and detect the colour of the traffic light.

Using images from a single camera, the device has a simple structure and does not need camera calibration, unlike sophisticated stereo camera systems, as the information is obtained using what is known as a “camera coordinate system”. This means that separate images do not need to be taken to calibrate the device. The length of a pedestrian crossing is measured by projective geometry, where the camera makes an image of the white lines painted on the road. Using the properties of geometric shapes as seen in the image, the actual distances are determined. Experiments carried out by the researchers showed that the crossing length could be measured to within an error of only 5 percent of the full length – which is less than one step.

The new device can also “see” the colour of the traffic light, even if the person is moving and the image changes. Together, the information gathered by this device will be enough to allow a blind person to know whether or not it is safe to cross a pedestrian crossing.

Prof Shioyama said:
“Travel aids that use laser and ultrasonic waves cannot obtain enough information about the user’s environment. This device is the first step in developing a system which allows the blind to cross the road safely and independently. We hope that the work in this article stimulates the development of such devices to assist the blind.”

Institute of Physics