| Popis: |
It is well known that one of the basic functions of security holograms is the maximal complication of their nonauthorized reproduction, in other words - counterfeiting. To solve the problem, concealed images that can be observed only under special conditions are placed into a structure of the hologram. A popular way to place concealed image in Diffractive Optical Variable Device (DOVID) is integration into DOVID's structure of a Concealed Laser-Readable Image (CLRI). Traditionally CLRI is a 2-D Computer-Generated Hologram (2-D CGH), which is a digitized Interference Fringe Data (IFD) structure, computed under the scheme of Fourier-hologram synthesis. Such hologram provides inspection of second level with portable laser reading devices. While it is being read, two (+/- 1 order of diffraction) identical images are formed. In this work a special kind of CGH, which restores image only in one diffractive order or two different images in +1 and -1 orders of diffraction proposed. |
