Abstract
Ambulances using retro-reflective materials are being put into practical use for the purpose of improving visibility at night. This study confirms the night visibility of such ambulances by an experiment using an actual vehicle. In the experiment, RGB data of images taken with a commercially available single-lens reflex camera were converted into the HSB color space and evaluated numerically. The HSB color space is similar to human sensibilities, and it is possible to numerically express subtle color differences.
Three types of vehicles are used in the experiment. 1: A vehicle with a red retroreflective material attached to the rear door only in a strip shape. 2: A vehicle with red retroreflective material attached in a strip shape on the side and rear doors of the vehicle body. 3: In addition to the belt-shaped reflectors on the side and rear doors of the vehicle, white and red Battenberg markings are applied to the side of the vehicle, and red and yellow chevron markings are applied to the rear door. This Battenberg marking and chevron marking vehicle was introduced at the Northern Alps Wide Area Fire Department in Nagano Prefecture and is actually in operation, so it is the subject of this study. A low beam of a general passenger car is emitted from a position 40 m away, and the images are taken with a digital camera near the driverʼs seat. The vehicle to be inspected makes an angle of 0°, 45°, 90° with respect to the projection optical axis. From the obtained images, the white and red of the Battenberg marking and the red and yellow of the chevron marking are analyzed in the HSB color space, and the average hue, saturation, and brightness of each part are quantified.
The experimental results revealed the following. （1） Battenberg marking and chevron marking using a retroreflective material make it easy to recognize a vehicle facing 45 degrees even with a low beam from a distance of 40 meters. （2） By expressing the RGB observation image in the HSB color space, the reflection characteristics of the marking can be quantified. By this method, the effect of marking can be evaluated numerically, and it is considered that it can contribute to the spread of new marking.
