| 摘要 |
<p>A security device comprises first and second holographic or diffraction effect generating structures recorded in respective sets of substantially non-overlapping regions of a record medium. The regions of one set are interleaved with regions of the other set, whereby both interleaved line structures are substantially non-visible to the unaided eye, whereby the security device generates two or more holographic images or diffractive images which to the naked eye overlap but which are viewed from separate viewing directions around the device and normally seen by tilting the device. Each holographic image or diffraction effect in a viewing direction is generated in whole or part by the holographic or diffraction effect generating structure associated with a respective set of interleaved lines. At least one of the holographic or diffraction effect generating structures includes one or more holographically or lithographically recorded continuous boundary lines, wherein each boundary line has a line width below the normal resolution of the eye, and extends at least partly along a boundary of the holographic image or diffraction effect generating structure.</p> |
