| 摘要 |
A security device including a surface relief structure having a plurality of regions. The plurality of regions includes gray scale regions which together form a macroscopic gray scale image when illuminated by incident light and viewed by an observer. Each gray scale region has at least one dimension smaller that 0.25 mm. Each gray scale region includes a plurality of scattering centres for scattering incident light, each scattering centre including one or more surface relief structure elements. Each gray scale region has a gray scale value determined by the degree of scattering caused by the scattering centres and surface relief structure elements. |
