Methods and apparatus for retroreflective surface inspection and

Abstract

Methods for improving and calibrating a retroreflection defects determination system are disclosed. The retroreflection system includes a light source which directs light to an area of a surface such that the light is reflected therefrom, a retroreflective member positioned such that the reflected light from the surface area impinges thereon and is thus returned to the surface area and re-reflected therefrom and an imaging device whereby the re-reflected light is imaged as a retroreflection image and scanned for intensity variations. In the identifying method, the retroreflective member of the system has a divergence angle, and the imaging step is repeated after the divergence angle has been appropriately changed. According to the calibrating methods, a first retroreflection image of a system is obtained. Then, one of the test conditions of the system is changed or the test surface is changed. The subsequent retroreflection image is then compared to the first in order to calibrate the system. A method for returning or calibrating the system to a previous condition is also disclosed. According to this method, a stored reference is displayed alternately and in quick succession on a visual display with a current image so that differences therebetween appear as a flicker. Then, the flickers are reduced by adjusting variables of the system and hence to return the system to the previous condition.