GB2362493A - Display device with apparent depth of field - Google Patents

Abstract

An advertising hoarding, billboard or poster comprises a regular array of images 1 at or near the focal plane of an array of lenses 2 with the same or slightly different period. From direction 5 a single magnified image 3 is seen. The image may appear behind the billboard if the lens period is greater than the image period and in front if the period is less. Rotational misalignment 4 between the arrays may make the image appear to move with the observer. The device may be of plastic or glass and may have text (7, figure 2) printed on the front. The image array may be located directly on the rear surface of the lens array. The arrays may be individually mechanically rotated or have different thermal expansion coefficients to alter size and position of the image. The lenses may be Fresnel lenses or zone plates. The image may be a periodic pattern such as a cloth or gauze. The image array may be formed by collimating lens or computer and recorded as photographs, prints, Lippman images or zero order diffraction devices. The period of the arrays may be 0.1mm to 20mm. The arrays may be square, rectangular or hexagonal.

Description

1 il 2362493 Advertising hoarding, billboard or poster with high visual

impact This invention relates to a form of advertising billboard, hoarding or poster.

One of the primary objectives of advertising is to attract the attention of the public and potential customer.

Advertising hoardings, posters, shop windows, point of sale displays and exhibitions have become increasingly sophisticated as advertisers vie for the attention of a public that is becoming increasingly blas6 and immune to their efforts. There is fierce competition to produce a display that will stand out among all the others. Much attention is therefore focussed these days on three dimensional displays. In particular there is a great deal of research directed at the production of the maximum degree of reality in the displays.

Difficulties arise in the production of realistic three dimensional displays because the brain receives from the eyes a variety of different clues about the depth of an object or scene.

Objects that are nearer appear larger than those that are ftirther away.

The eye has to "accommodate" in order to focus on objects at different distances. (Which it does by exerting muscular pressure on the lens of the eye in order to change its shape.) Having focussed on an object those at different distances appear ftizzy and out of focus. The two eyes receive different views of the object and the brain fuses these to provide a stereoscopic sensation of a three dimensional object.

As one moves around an object the view changes due to parallax whereas with a simple photograph it does not. (One can see round a three dimensional object) In order to appear completely realistic a three dimensional display has to provide a set of depth cues which are self consistent, that is to say the same as they would have been from the object itself However, if the depth cues conflict, the brain takes longer to process the image and the observer's attention is attracted for longer. Furthermore, if the eye detects a display of an object that is somehow "not quite righf' the brain is intrigued and the attention of the observer is drawn to the display.

The use of conflicting depth cues in advertising displays in order to attract the attention of an I- observer, and certam practical means by winch this may be achieved, are the subject of the present invention.

The Mo56 Magnifier Whenever two similar grids are superposed but slightly misaligned, regular patterns are generated which are usually in the form of relatively coarse stripes. The term originated from moir6 silks which generate wavy stripy patterns when two woven fabrics are placed together. In the case of the moir6 magnifier a regular array of images (which might for example be a company logo and which we shall refer to as an object array) are combined with a regular array of miniature lenses. Instead of giving rise to a stripy pattern, however, a regular array of magnified images is produced and these have a particularly high visual impact because they appear to float outside the plane of the display and have an unreal perspective. This effect was described by Hutley Stevens and Hunt in Pure and Applied Optics in 1996 and, with a second lens array in place of the object array was the subject of US patent 3,357,772 by Rowland in 1967.

If the period of the object array is exactly the same as that of the lens array but there is a slight angular misalignment between the two, the moire images will appear to move as the angle from which they are viewed changes, but they will move in a direction that is perpendicular to the change in the angle of view. For example as one moves from right to left the images rrAght move vertically upwards and as one moves from left to fight they will move vertically downwards. Tl-s is contrary to anything that is normally observed in everyday life and will therefore draw attention to itself It also has the effect that moire images that are viewed simultaneously with two eyes possess a skew parallax that is not encountered in everyday life and also intrigues the brain. The basis for these effects is described in the paper by Hutley, Stevens and Hunt.

According to the present invention an advertising hoarding billboard or poster is constructed from a regular array of similar objects positioned at or near the focal planes of an array of lenses. The period of the lens array is equal or similar to that of the array of objects and there is some aspect of misalignment between the two arrays so that a moire pattern is generated which consists of an array of magnified images of the similar objects.

Various embodiments of the invention will now be described by way of example with reference to the accompanying drawing in which Figure 1 shows in perspective the juxtaposition of a lens array with an array of objects to form a moire magnified image.

Figure 2 shows the change in apparent position of the moire images with a change of viewing position Figure 3 shows the juxtaposition of the moire magnifier with conventional text or artwork.

Figure 4 shows various means of mounting the object array to be in the focal plane of the lens array Figure 5 shows a convenient way of generating an array of photographic images.

3.

Refening to tile drawing, the billboard or poster shown in figure I consists of an array of similar objects 1, which shaft be referred to as the 'object array' which is positioned at or near the focal plane of an array of lenses 2. In figure I the object array is shown by way of example as a square array of images of the musical symbol the treble clef The size and pattern of the lens array is sirnilar to that of the object array so that in general each lens can be said to be associated with a single object of the object array. However, there may be a slight difference in the period (repeat distance) of the two arrays or there may be slight angular misalignment 4 between the axes of the two arrays so that a moire pattem is generated between the two. When the billboard or poster is viewed from a particular direction 5 each lens presents to the observer a view of a different section of object that is repeated in the object array with the result that a magnified image 3 of the repeat object is seen.

The efFects may be enhanced by providing some local reference in or near the plane of the lens array which emphasises the fact that the appearance of moire magnified images is different to that of a material object. Such a reference may be provided as shown in figure 2 for example by a frame 6 round the lens array or by text or artwork 7 printed either directly on the surface of the lens array or on transparent material located at or near the plane of the lens array.

If the period of the object array is slightly greater than that of the lens array, the moire images will appear to be located in front of the lens array, that is to say in a plane between the lens array and the observer. If it is slightly less than that of the lens array the images will appear to be located behind the lens array, that is in a plane which is further away from the observer than is the lens array. If the relative spacing of the lens array and the object array is changed, for example by differential thermal expansion, the moire images may be made to move backwards and forwards through the display.

Figure 3 illustrates the appearance of the array of moire images as the viewing direction is changed for different configurations of the invention.

Figure 3 a shows a cross section of the device with a fiducial mark 6 and two directions of view 8 and 9. In this example 8 is perpendicular to the plane of the lens array and 9 is at an arbitrary angle to the right.

Figure 3b shows a typical section of the array of moire images when viewed from direction 8 with a reference mark 6 in the form of a cross.

Figure 3e shows the appearance of the moire images when viewed from direction 9 when the lens array has a period which is slightly less than that of the object array so the moire images appear to be formed in front of the lens array.

Figure 3d shows the appearance of the moire images when viewed from direction 9 when the lens array has a period which is slightly greater than that of the object array so the moire images appear to be formed behind the lens array.

Figure 3e shows the appearance of the moire images when viewed from direction 9 when the lens array has a period which is equal to that of the object array but in which there is a slight angular inisalignment between the two.

L - If the degree of angular misalignment between the object array and the lens array changes, the magnification and period of the moire images also changes. This also produces an attractive effect. Variable moire fringes produced from grids have long been used in advertising displays to attract attention. We are not, however, aware of moire images previously having been used for this purpose.

For an effective display for advertising and other purposes it is preferable that the moii-6 magnified image should have a reasonable number of resolved elements (pixels) which by way of typical example might be of the order of 200 x 200, and that it should be in colour. If the size of the moii-6 magnified image is, for example, 100 nim it follows that the individual lenses must have a diameter no greater than 0. 5 nim or 500 micrometres. It therefore follows that in this example the size of the individual images in the object array must be no greater than 500 rriicrometres and since they must contain 200 pixels across this diameter, the pixels must be 2.5 micrometres across or less. To achieve this requires a printing process with very high resolution and lens arrays of good quality.

The lens arrays may be cast, stamped, injection moulded or embossed in plastic from a mould or they may be produced by similar techniques in glass. They may be arranged so that the focal plane 10 of the lenses is situated on the other side of the substrate I I as shown in figure 4a. In this way the object array may conveniently be located in focus by placing it in mechanical contact with the substrate. Alternatively, as depicted in figure 4b it may be that in order to save cost and weight the lens array is made on a thin substrate and separated from the object array by spacers 12 which maintain the correct focal distance. A further altemative is shown in figure 4c in which the lens array 2 is embossed onto a thin sheet 13 of, most probably but not exclusively, plastic material and attached to a rigid sheet 14 of glass or plastic. Additionally, in order to reduce cost and weight ant to overcome the difficulties associated with replicating deep structures the lenses may be Fresnel lenses or Fresnel-zone plates (otherwise known as diffractive optical elements). Fresnel-zone plates possess particularly high levels of chromatic dispersion which can also be used to enhance the novelty of the display.

The object arrays may be printed using any of the standard printing techniques. Alternatively they may be generated photographically either by using a step-and-repeat camera or by forming multiple images of a single object at the focal plane of a lens array and by recording the multiple images in an appropriate photographic medium.

The photographic medium may be conventional photographic material in colour or black and white, it may be photoresist from which it is possible using well known techniques of photolithography to generate an object array in the form of a surface relief structure that can replicated by techniques such as stamping, casting, injection moulding and embossing. The recording of the object arrays may also involve less conventional photographic techniques such as the process described by Lippmann in 1891 in the Comptes Rendus of the Academic de Sciences in Paris volume 114 pages 961 and 962, m which the image is recorded in the form of a periodic modulation of the optical properties of throughout the bulk of the recording medium. A further possibility is to record the images "zero order difflaction" structures as desedbed by Gale and Knopp which have the advantage of combining large scale replicability by mechanical means, with the ability to reproduce colour.

A convenient apparatus for the photographic generation of object arrays is shown in figure 5 and consists of an illuminated object 15 which might be a photographic or computer generated L-) transparency illuminated by a fight box 16, a collimating lens 17 with an aperture equal to that of the lens array, and a lens array 18 similar to that which is to be used in the display.Each lens of this array generates a diminished image 19 of the object which is recorded in a suitable photosensitive material 20. A further option is to use a collimating lens which possesses significant aberrations and distortions. This distorts the object array and the objects within it in such a way as to generate an array of moire images that is itself distorted and consitutes a further feature which the attention of the passer by is drawn to the display. Distorted arrays may also be generated on a computer and printed using standard techniques.

Claims (1)

1. Claims

   1 An advertising hoarding, billboard or poster consisting of a regular array of images at or near the focal plane of an array of lenses with the same or similar period as shown diagrammatically in figure 1.

   2 An advertising hoarding, billboard or poster according to claim 1 in which text or other artwork is printed conventionally at or near the plane of the lenses.

   3 A device according to claim 1 in which the period of the lens array is greater than that of the image array so that the moire magnified images appear to be situated behind the billboard.

   4 A device according to claim 1 in which the lens array is less than that of the object array so that the moire magnified images appear to be situated in front of the billboard A device according to claim I in which the period of the lens array is the same as that of the object array but in which there is a slight rotational misalignment so that as an observer travels past the billboard the moire images appear to move in a direction nearly orthogonal to the direction of motion of the observer.

   6 A device according to claim 1 in which the lenses are formed on one surface of a piece of transparent material and the focal plane is on the other surface so that the object array may be located directly on the second surface of the lens array 7 A device according to claim 1 in which the lens array is cast, injection moulded or embossed in plastic.

   8 A device according to claim 1 in which the material of the lens array is glass.

   9 A device according to claims 1, 3, 4 and 5 in which either the lens array or the object array is rotated with respect to the other by a mechanical means in order to cause the apparent size and position of the moire images to change A device according to claims 1,3,4 and 5 in which the object array and the lens array are made of materials of dilferent coefficient of thermal expansion so that the size and position of the moire images changes with the climatic conditions.

   11 A device according to any of the above claims in which the lens array is an array of Fresnel lenses or an array of Fresnel-zone plates.

   12 A device according to any of the above claims in which the object array is an array of printed images 13 A device according to claims 1-11 in which the object array is an array of photographic images.

   14 A device according to claims 1 - 11 in which the object array is a regular periodic structure, 1 such as for example woven fabric, mesh or gauze, which was produced primarily for some other purpose but used in this application by virtue of its periodic nature.

   A device according to any of the above claims in which the object array is created by photographing a single object through the same or a similar lens array.

   16 A device according to claim 11 in which the single object is photographed through a large collimating lens which has significant distortion or aberrations in order to generate a distorted array of moire magnified images 17 A device similar to that of claim 16 in which a distorted object array is generated on a suitable graphical output device from a computer.

   18 A device according to claim 15 in which the object array is recorded on conventional photographic material.

   19 A device according to claim 15 in which the object array is recorded in the form of a series of " Lipprnan7' images.

   A device according to claim 15 in which the object array is recorded and replicated in the form of "zero order diffraction" devices.

   21 A device according to claim 1 in which the period of the lens array and the object array is between 0. 1 nun and 20 mm.

   22 A device according to claim I in which the lens and object arrays are square, rectangular or close-packed hexagonal.