Color Properties of Specular Reflections

A study has been carried out on the effect of the optical density of inks on the specular reflectance of a printed surface. Samples of cyan, magenta, and yellow ink were printed with a liquid electrophotographic, an offset lithographic, and a thermal transfer printer. Specular reflectance was measured using a goniophotometric instrument to produce the bidirectional reflectance distribution function. The results clearly demonstrated that the amount of specular light reflected from a printed surface depends strongly on the optical density of the ink. A linear correlation was observed between the total amount of specular light reflected from the surface and the square of the transmittance of the ink layer. A highly transparent ink (e.g., yellow ink measured with red light) reflected approximately twice as much specular light than a highly absorbing ink (e.g., yellow with blue or cyan with red). It is suggested that specular reflections from surfaces below the ink layer can contribute significantly to overall specular reflectance of a printed image.