| 摘要 |
An optical security device (10; 700) is provided which includes a transparent or translucent substrate (15; 705), at least one first array of repeating elements (20; 720) in or on a first side (16; 706) of the substrate (15; 705), at least one second array of repeating elements (30; 730) on a second side of the substrate. The second array of repeating elements (20; 720) is substantially in register with the first array of elements (30; 730), whereby a first image (130; 725) is visible when viewing the device from the first side, and a second image (200; 735) is visible when viewing the device from the second side. The brightness or colour levels of repeating image elements (30; 720, 730) on at least one side of the substrate may be modulated region-wise to produce a greyscale or coloured image. In one embodiment, the first array of repeating elements in or on a first side of the substrate is an array of focussing elements (20), and the second array of repeating elements in or on the second side of the substrate is an array of image elements (30) having substantially identical shape to each other, such that, when viewing the device from the first side, a magnified image including at least one magnified version of the image element shape is visible, and when viewing the device from the second side, the greyscale or coloured image is visible. In another embodiment, the repeating elements of both the first and second arrays are partially or fully opaque image elements (720, 730) which respectively form the first and second images (725;735). |
