Optical: systems and elements – Stereoscopic – Stereo-viewers
Reexamination Certificate
1999-02-16
2001-07-24
Chang, Audrey (Department: 2872)
Optical: systems and elements
Stereoscopic
Stereo-viewers
C359S462000
Reexamination Certificate
active
06266187
ABSTRACT:
FIELD OF INVENTION
The present invention relates to substrates which provide one or more three-dimensional images.
BACKGROUND
There are many applications where three-dimensional optical images are required or are desirable. A number of devices have been proposed in the past, which comprise a two-dimensional substrate arranged to provide a three-dimensional optical image to a viewer.
We have now devised a substrate arranged to present a three-dimensional image to a viewer and providing a number of advantages.
SUMMARY
In accordance with the present invention, there is provided a substrate which is arranged to present one or more three-dimensional optical images to a viewer, the substrate being formed with a plurality of stereo pairs of elements, each stereo pair of elements providing the viewer with an image of a point at a predetermined distance from the plane of the substrate, the plurality of such point images forming said three-dimensional optical images.
The two elements of each stereo pair provide light to the respective eyes of the viewer, when the viewer observes the substrate from a particular position or range of positions. The light may be provided to the viewer either by reflection from the elements of the stereo pair, or by these elements refracting light transmitted through the substrate (where this is of transparent or semi-transparent material). The two elements of each stereo pair may comprise grooves or ridges formed in or on the substrate surface: they may comprise reflective printing provided on a document, particularly a document of value (e.g. a banknote).
Preferably each stereo pair of elements comprises two short linear elements (particularly grooves or ridges), the relative orientations of which determine the distance of the corresponding point image from the plane of the substrate.
For each point image, a plurality of stereo pairs are preferably provided, so that the same point can be viewed from different angles.
The stereo pairs for each point image may all be positioned on a common straight line. The different stereo pairs may be displaced from that line to ensure that the point image remains stationary as the viewer changes his angle of view, or alternatively so that the point image moves: in the latter case, an image of a moving object can be created.
However, it is not necessary for the successive stereo pairs for a given point image to be positioned on a common line. Indeed, the pairs can be displaced to desired positions spaced from the common line, for example they may be positioned along any curved line, if appropriately positioned and oriented relative to each other. In this way, the set of stereo pairs for the different image points can be kept apart and so prevented from intersecting or otherwise interfering with each other.
If the stereo pairs are positioned in the manner described above, it is not possible to relate their positions to the shape of the object, adding complexity to the object encryption and therefore security value. Moreover, the individual lines of the stereo pairs can vary from finite length to become elemental points.
In the case of a three-dimensional object viewed ordinarily, then whilst from a given angle of view certain parts of the object are visible, other parts (e.g. remote side surfaces) are obscured: from the different angles of view, different parts of the object are visible and different parts are obscured. For the substrate in accordance with this invention to provide a realistic image of a three-dimensional object, the image needs to show certain parts of the object when the substrate is viewed from certain angles, but not when viewed from other angles.
Preferably therefore, predetermined stereo pairs are omitted from the set of stereo pairs for predetermined image points, so that the related image point is obscured when the substrate is viewed from the corresponding angle of view. The overall arrangement is such that different parts of the three-dimensional object are visible from different angles of view, to give a realistic image of the object.
A substrate in accordance with the invention will comprise a large number of sets of stereo pairs, each set defining the same image point viewable from different angles of view, so that in total a large number of different point images are created, spaced apart horizontally and vertically, and at different predetermined spacings from the substrate plane. These point images contribute to forming a three-dimensional image. Some of the image points may together define a linear image (e.g. the edge or boundary of an object or part of an object), whilst others may define “shading” to provide the image of a surface.
A three-dimensional object typically includes surfaces (e.g. side surfaces) which are at an oblique angle to the viewer, when the object is viewed from certain angles or range of angles. We have found that a good image definition can be achieved by a reduction in the density of stereo pairs provided for the image of such an oblique surface, relative to the image of a surface being viewed front on. This enables a reduction to be achieved in the total number of stereo pairs which must be formed on the substrate.
As mentioned previously, the stereo pairs on the substrate may be arranged to provide more than one image. In this case, different images may be visible from different angles of view.
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Dunn Paul
Rowe Andrew
Chang Audrey
Fryco Limited
Schindler Edwin D.
Winstedt Jennifer
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