Optical device for providing synthetic integral image and method for identifying objects

Abstract

An optical device for providing a synthetic integral image (25) comprises a polymer foil stack. A first interface of the polymer foil stack comprises optically distinguishable image data bearer structures (16A-C) in a first array. A second interface of the polymer foil stack has focusing elements (1) in a second array. A ratio between distances between neighbouring objects in the first array and of focusing elements in the second array in a first direction is different from a ratio between distances between neighbouring objects in the first array and of focusing elements in second array in a second direction. This leads to that the synthetic integral image corresponding to the image data bearer structures is perceptible with requested proportions when the polymer foil stack is given a certain curvature. Also polymer foil stacks giving rise to synthetic integral image only when viewed from a very short distance are described. The appearance of the synthetic integral image during bending or moving of the polymer foil stack is used for authentication. A change in apparent image depth during rotation is alternatively used for authentication.

Description

technical field [0001] The present invention relates generally to optical devices, and more particularly to optical devices providing composite images. Background technique [0002] Planar optical arrangements that allow the creation of images that change their appearance at different angles, or composite images, have been used in many applications. Apart from purely artistic use, such arrangements have also been used as security markings, eg on bank notes or other valuable documents, identification documents and the like. Synthetic images, often with more or less prominent three-dimensional features, have also been used to provide a better geometrical understanding of complex shapes, eg in two-dimensional information documents. [0003] In published international patent application WO 94 / 27254 a safety device is disclosed. The security device includes an array of microimages that produce a magnified image when viewed through a corresponding array of substantially spherica...

AI Technical Summary

Problems solved by technology

The disadvantage of such an arrangement is that such image generation has to be done when the film is applied at its final substrate

This makes it very difficult to efficiently mass-produce

The method of generating axial markers by illumination via microspheres also imposes severe restrictions on what types of images can be generated

Moreover, this type of safety device cannot be used for irradiating sensitive items, since the generation of axial markings has to be performed by means of intense irradiating at the end product

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