Abstract: A method of determining the optical quality of a glazing which includes at least one area having a reduced light transmission, involves producing a shadowgraph image of the glazing and measuring the illumination of the glazing at a plurality of measurement points arranged in an array extending over the glazing. The deviation in illumination from a desired value at each measurement point is determined and the at least one area of reduced light transmission is omitted from the array of measurement points.

Abstract: A method of forming a shadowgraph image is described, comprising the steps of illuminating a glazing (52), e.g., a vehicle windscreen, with light from a localised light source (50), said light being expanded and collimated by a lens optical system (54) or a mirror optical system, forming a virtual shadowgraph image of the glazing in a virtual image plane (56), which may be positioned behind or in front of the glazing: and imaging the virtual image onto a CCD camera (62). The glazing may be moving relative to the light source or may be stationary.