WO2004042684A2

WO2004042684A2 - Multiple image display devices

Info

Publication number: WO2004042684A2
Application number: PCT/IL2003/000896
Authority: WO
Inventors: Itzchak Bar-Yona; Kfir Luzzatto
Original assignee: Lubartech Ltd.
Priority date: 2002-11-07
Filing date: 2003-10-30
Publication date: 2004-05-21
Also published as: IL152713A0; AU2003276654A1; EP1561201A2; WO2004042684A3

Abstract

The present invention is a multi-image display system (20) that is essentially comprised of an indicia carrier on which are printed interlaced images (3), and a stationary electronic grating (7) which, by means of a control circuit alternately reveals the separate images that have been combined to form the interlaced images.

Description

MULTIPLE IMAGE DISPLAY DEVICES

Field of the Invention

The present invention is related to the field of display devices for

advertising or information. Specifically, the present invention relates to devices that alternatively display multiple images especially for point-of-

sale signs, billboards, and the like.

BACKGROUND of the Invention

Many different systems are available today for providing multi-image

displays. These include electronic systems, systems based on lenticular

technology, simple mechanical systems, and hybrid systems involving

elements of two or more of the above technologies.

Using presently available electronic displays, it is possible to easily and

quickly change the image created on the screen and the expense of these

displays is generally justified where it is desired to show large numbers of

images such as in movies or videos, either prerecorded or showing "real

time" events.

The principle on which the electronic displays are based is the ability of the

human eye to add three or more separate small spots (sub-pixels) each composed of one of three primary colors - red, blue, and green - to form a

single spot (pixel) of color. The pixel can be made to have a virtually

unlimited number of colors by varying the intensity of the color of each

subpixel. By building a two-dimensional array containing hundreds,

thousands, or (in the largest available systems) hundreds of thousands of

pixels, and controlling the color of each pixel, a color picture is created. To

change the display, a control circuit which takes its input manually from,

for example, a computer keyboard, or automatically from, for example, a

pre-created computer program, a pre-recorded video tape, or hve from a

video camera is provided to control the intensity of each sub-pixel in the

display.

The most common electronic display is based on the use of a cathode ray

tube (CRT) such as is found in the ordinary television. A color TV employs

three scanning electron beams, one for each of the primary colors. These

beams respectively impinge on dots or stripes of red, green, or blue

phosphors to form the color of a particular pixel. The intensity of the color of

each sub-pixel is controlled by varying the energy of the electrons in the

beam striking the sub-pixel as a function of time. Color TVs based on CRTs

are relatively cheap but very bulky and limited in size. In addition, the light emitted by the phosphors is not extremely bright, with the result that it is

difficult to see the image on the screen in daylight and especially under conditions of full sunlight. One method devised for reducing the bulk and increasing the size of the

display relative to that of a CRT based system is to use a plasma display

system. In this type of display an array of cells is built behind the screen.

The walls of each cell are coated with either a red, green, or blue phosphor.

Three of these sub-pixels, with different color phosphors, form a pixel. The cells contain a gas that is excited by an electric current to form a plasma.

Ultraviolet photons in the plasma strike the walls of the cell and are

converted into visible photons. Each cell is individually addressed such that

a current of variable intensity can be made to flow through it varying the

color of the sub-pixel. The main advantage of such a system is that a very

wide and very thin display can be constructed, also a relatively bright

display results. At the present stage of development plasma displays are

very expensive.

Another type of electronic display uses liquid crystals. Liquid crystal

displays (LCDs) are limited in size by manufacturing difficulties. The pixels

in an active-matrix LCD are dependent on thin film transistors, which

frequently do not function properly. Each bad transistor results in a bad pixel, therefore the rejection rate (and consequently the cost) of LCDs

increases rapidly as the size of the display is increased. In addition, LCDs

do not have high enough intensity to be suitable for use in full sunlight and are relatively slow compared to the other types of electronic displays. The type of electronic display most suitable for very large displays and

especially for use in full sunlight is the so-called jumbo TV screen. In this

type of display, the sub-pixels are red, green, and blue light emitting diodes

(LEDs). The LEDs are arranged in pixel modules containing from three to

tens of individual LEDs and typically ranging in surface area from

4mmx4mm to 40mmx40mm. The modules are arranged in a rectangular array resulting in screens ranging in size from approximately 3m x 2m to

26m x 20m. Each sub-pixel is individually addressed and, by varying the

power to each LED, its intensity and therefore the overall color of the pixel

cal be controlled. In addition to a large initial purchase cost, to a large

extent the result of the cost of the diodes, LED displays require a large

amount of electrical power. In order to produce enough intensity in full

sunlight, the largest units consume up to 300kw of electricity. Another

difficulty with LED display units is that running them at high power greatly

reduces their reliability, forcing frequent replacement of the pixel modules.

Lenticular display systems comprise two main elements: a sheet or panel,

on which is created an array of lenticular lenses, and an indicia carrier, on

which is printed an interlaced image. These two elements must be

supported rigidly such that the distance between each lens in the array and the corresponding line of print is constant. The individual images are

revealed in one of two ways: by changing of the observers viewing angle in static displays and by causing relative motion between the two elements in

dynamic displays. As opposed to electronic displays, existing dynamic

lenticular displays are capable of showing only a limited number of images,

typically two to four, and can not show movies or real time events. To

change the set of images, it is necessary to replace the indicia carrier. On

the other hand, lenticular displays are relatively inexpensive when

compared to electronic displays. In addition they can have very large display

areas and can operate under ambient fight conditions ranging from full

sunlight to total darkness with the aid of either external or internal

fighting. The operating and maintenance costs are minimal compared to

those of electronic displays of similar size.

Multiple image display systems of various types that are based on lenticular

technology have been known for many years; however, many inherent

problems of the technology exist and the solution to them, especially for

dynamic systems is often relatively complex and expensive. These problems

and methods of overcoming them are discussed in, for example United States Patents US 6,219,948 and US 6,226,906 and in published

International Patent Application WO 02/23510 all by the same inventor

hereof, the descriptions of which are incorporated herein by reference.

Methods of creating the composite print consisting of the interlaced images of the two or more images to be displayed are well known in the art. According to these methods, the original images are cut into strips and then

compressed before forming the interlaced image, thus preserving all of the

information that was present in the original images. In other methods of

forming the interlaced image, part of the original information is deleted.

Typical of this type of interlacing methods are those disclosed in U.S. 5,924,870 and U.S. 5,098,302.

A third type of display system, based on parallax barrier methods, is

disclosed in the above mentioned U.S. 5,098,302. This system uses an

interlaced image, but instead of lenticular lenses, the separate images are

alternately revealed by lining up the axis of a grid with the lines of print

and moving it back and forth over the interlaced image. The grid consists of

alternating opaque bars and clear windows. The width of each pair

consisting of a bar and a window is equal to the width of a line of print. The

relative widths of the bars and windows are in a ratio that depends on the

number of images, i.e. 1:1 for two images, 2:1 for three images, 3:1 for three

images, etc. The multiple images are viewed either by causing relative

motion between the interlaced print and the grid or by use of parallax, i.e. the observer moves his head resulting in differing viewing angles of the

stationary interlaced print through the windows of the stationary grid.

Another type of multi- image display is a purely mechanical one constructed

of a set of prisms that are arrayed in a planar rectangular frame with their long axes parallel to each other. The axes of each of the prisms are

connected together by a suitable arrangement, such as one comprising gears

or cables or a combination of these, such that all of the prisms can be

rotated together. An image to be displayed is attached in strips to one face of

each of the prisms, a second image to a second face, etc. such that when the

set of prisms rotates a different image is displayed in the frame. Compared

to the other types of display it is quite a complicated operation to replace the

images to be viewed with different ones. Additionally, such a display, while

comparatively simple, is rather expensive to maintain suffering from all of

the problems associated with mechanical systems.

It is a purpose of this invention to provide a new type of multi-image display

system that overcomes the difficulties associated with the operation of existing systems.

It is another purpose of this invention to provide a new type of multi-image

display system that comprises no optical elements.

It is a further purpose of this invention to provide a new type of multi-image

display system that comprises no moving parts.

Further purposes and advantages of this invention will appear as the description proceeds. Summary of the Invention

The present invention is a multi-image display system that is essentially

comprised of an indicia carrier on which are printed interlaced images, and

a stationary electronic grating which, by means of a control circuit

alternately reveals the separate images that have been combined to form

the interlaced images.

The interlaced images are produced by any of the methods known in the art

and in a preferred embodiment are printed on the indicia carrier in the form

of parallel lines having equal width. In another embodiment the interlaced

images are printed in the form of a two-dimensional matrix of pixels.

The electronic grating for use with the indicia carrier on which the printing

comprises parallel lines is comprised of a substrate of suitable transparent

material on which are printed or applied by any suitable technique, parallel

arrays of rectangularly shaped strips. The strips comprise a number of superimposed layers and are the equivalent of the bars on a physical

grating. Each of the strips of the grating has a width substantially equal to

the width of the printed lines of the interlaced image divided by the number

of separate images to be displayed and a length equal to the height of the

display for vertical lines of printing, or equal to the width of the display for horizontal orientation of the printing. Each of the strips is, in its most

general form, a layered structure comprising a pair of transparent electrodes separated by a layer or layers of active material. Each of the

strips is physically and electrically isolated from its neighbors and

individually addressed by a control circuit that is capable, on command, of

creating a localized electric field, heat, or causing an electric current to flow

between the electrodes of the pair. The active material in each strip has the

property that, when an electrical potential is applied between the electrodes

and thus causing, for example, an electric field to be created or localized

heating in the volume occupied by the active material between the

electrodes, its optical transparency in the visible region will be reversibly

changed between an opaque state and a transparent state, or vice versa. Preferred embodiments of the invention utilize active material suitable for

use with any of the technologies included in, but not limited to those of the

following group: electrochromism, thermochromism, electroluminescence,

liquid crystals, and suspended particles.

The multi-image display of the invention operates in the following manner:

if, for example in a display having four images, every fourth pair of

electrodes is connected in parallel to form a set of strips that will be

activated simultaneously and the control system alternately applies an electric potential to each set such then at first the first, fifth, ninth, ... bars

become transparent while the rest are opaque, the second, sixth, tenth, ...

are made transparent followed by the third and forth sets. In this way, and in any order selected by the control system, one image at a time is revealed. The display can be illuminated by means of reflected ambient or artificial

light or, in some embodiments by transmission, using artificial backlighting

built into the display case and in one embodiment by the electroluminescent active material in the strips of the grating.

When electroluminescence is employed, it is the light generated by it that highlights the selected picture from the interlaced image from its back, said

interlaced image being provided on a transparent substrate, thereby to

display said selected image.

In the embodiment in which the interlaced image is a two dimensional

matrix, the electrodes are dispersed on the surfaces of the substrate in a

manner consistent with the arrangement of the interlaced image.

All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative

description of preferred embodiments thereof, with reference to the appended drawings.

Brief Description of the Drawings

Figs. 1 to 4 schematically illustrate a method of creating an interlaced image; Fig. 5 shows the interlaced image created according to the method

shown in Figs. 1 to 4;

Fig. 6 shows a grating for use in creating a multi-image display;

Figs. 7 and 8 show the two images comprising the interlaced image of

Fig. 5 displayed separately with the aid of the grating of Fig. 6;

Figs. 9 and 10 illustrate schematically a preferred embodiment of the

electronic grating of the invention;

Fig. 11A shows schematically a display unit according to the invention;

Fig. 11B is a cross-sectional view showing the internal parts of the

display unit of Fig. 11A;

Fig. 11C is an enlarged view of an area of Fig. 11B showing details of

the structure of a preferred embodiment of the electronic grating of the invention;

Fig. 12A schematically illustrates a pixel according to another method

of creating an interlaced image; and

Fig. 12B schematically illustrates a preferred embodiment of the

grating of the invention and the electrical connections for use with an interlaced image created according to the method of Fig. 12A.

Detailed Description of Preferred Embodiments

For the sake of simplicity, the basic idea of the invention is demonstrated in Figs. 1 to 8 for a display system having two separate images. In the context of this invention the term "multi-image" means two or more images. In Fig.

1 is shown one of the images, in this case house 1, and in Fig. 2 the second

image, automobile 2.

In the next step, shown in Figs. 3 and 4, the sizes of both images are

adjusted to be equal having height H and width W. Each of the images is then cut into n equal strips having height H and width w, where w = W/n. In

the present example, n = 20 and the strips of images 1 and 2 are labeled

respectively A1-A20 and B1-B20.

Fig. 5 illustrates the interlacing procedure. Strips A1-A20 and B1-B20 are

compressed in the horizontal direction until their widths are essentially half

of their original width. The forty strips of width w/2 are then arranged in

the order Al, Bl, A2, B2, .... A20, B20 to form the composite interlaced

image 3. Image 3 has the same size as each of the original images, i.e.

height H and width W.

Fig. 6 shows a grating 4 having a size that is the same or larger than that of

the composite image 3. Grating 4 is composed of alternating opaque bars 5 and transparent windows 6. All of the bars and windows have equal widths, substantially equal to w/2. Placing grating 4 on top of the interlaced image 3 and aligning them such

that the bars 5 are on top of strips A1-A20 and the windows 6 on top of

strips B1-B20 results in the situation shown in Fig. 7, i.e. only the

automobile 2 is visible. Horizontally sliding the grating relative to the

interlaced image a distance equal to w/2 (or mw/2, where m is an integer)

will expose the image of the house 1 and hide the second image. This

situation is shown in Fig. 8.

According to the methods of the prior art the two separate images could be

alternately viewed by physically moving either the grating or the interlaced

print or both relative to each other. Alternatively, the separate images could

be viewed by the parallax effect by changing the observation angle, if the grating and interlaced image were rigidly supported in separate parallel

planes an appropriate distance apart. If a sufficient number of strips is

provided, the human eye will make up for the missing strips, thus

perceiving a whole image. Of course, as will be apparent to the skilled

person, the number of strips required depends on the distance from which the image is to be viewed.

According to the present invention, it is possible to view the separate images

without either using parallax effects or moving the grating and interlaced image relative to each other. Viewing of the individual images is accomplished by supplying an electronic grating comprised of a substrate on which are created an array of identical parallel strips. Each of these strips is

physically and electrically isolated from its neighbors and individually

addressed by a control circuit that is capable, on command, of creating a

localized electric field, heat, or causing an electric current to flow between the electrodes of the pair, thus reversibly changing the optical transparency

of an active material located in one or more layers that are situated in the

space between the pair of electrodes in each strip. The active material has

the property that the individual strip will change from transparent to

opaque (or vice versa) to visible light in response to an electrical or thermal

stimulus and will return to its original state when the stimulus is removed.

A front view of an electronic grating 7 according to the invention is

schematically shown in Fig. 9. Grating 7 is comprised of a multitude of

strips, each of width w/2 where w is the width of each line of the interlaced

print (Fig. 9 shows a grating designed to be used with an interlaced image

comprised of two separate images, in general the strip width is w/n where n

is the number of images that have been interlaced to form the combined

image). The strips are printed or deposited on the surface of a transparent

substrate and are physically and electrically isolated from each other. The exact technique for creating the strips of which the electronic grating is

composed will depend on the nature of the active material being used as

well as economic and manufacturing considerations. In any case the knowledge, equipment, and techniques necessary for the creation of the grating is readily available and known to those active in the many areas of

technology that make use of, for example, printing and/or vacuum deposition techniques.

A representative strip 8 can be made up of, for example, three layers: a

transparent electrode, a layer or layers associated with the active material,

and a second transparent electrode. The detailed structure of the strips will

be discussed hereinbelow with reference to Fig. llC.

One of the electrodes on all of the strips is electrically connected to a

common contact 11. The other electrode is connected to one of two contacts 9

or 10. With strips 1, 3, 5, etc. connected to 10 and strips 2, 4, 6, etc

connected to contact 9. Thus by connecting contact 11 alternately to either

contact 9 or 10 through an external control circuit an electric potential is applied providing the necessary stimulus to bring about the desired change

in the optical properties of the active material in the affected strips.

In Fig. 10 is schematically shown the case in which contacts 10 and 11 are

connected, i.e. a grating analogous to that of Fig. 6 has been created.

Alternately connecting contacts 9 or 10 to common contact 11 using, for example, a timer will periodically change the state of alternate strips. If this electronic grating is placed over an interlaced image comprised of two

images printed on an indicia carrier using lines of print of width w, then each image will be separately displayed, the images changing with the same

periodicity as the change in the electric connections.

Fig. HA shows a display device 20 according to the present invention. The

display comprises a hollow box 21 on whose front face is disposed the indicia

carrier on which is printed the interlaced image 3 and electronic grating 7,

both protected from the external environment by a transparent layer 22.

Also provided, but not shown in any of the figures, is a door or opening allowing access to the interior of the box. This arrangement allows for easy

and inexpensive replacement of the indicia carrier as frequently as desired

to change the content of the multi-image display. Inside the box 21 are

dispersed lights, to be used for back-lighting of the images, and their electric lighting circuit, symbolically indicated by plug 23, as well as the electronic

control system for the grating. The control circuit for the electronic grating

is neither shown in the figures nor are embodiments described since they

are conventional and familiar to the experienced person.

Fig. 1 IB is a cross-sectional view showing the interior of the display of Fig.

HA. In the figure are schematically shown box 21, cover 22, and lights 23

which can be, for example, a number of fluorescent tubes arranged in a parallel configuration close to the rear side of the display. Fig. 11C is an enlarged view of area C in Fig. 11B. Numeral 22 represents

the front cover of the display which is made ' of a sheet of transparent

material such as, for example, glass or plexiglass. The cover is optional but

desirable to protect the other elements of the display from damage caused

by the weather or vandals. Inside the cover is the interlaced image 3

described hereinabove printed on a transparent indicia carrier, followed by

electronic grating 7. It should be noted that, although the figures in this

application show displays in which the print on the indicia carrier and the

bars of the grating are aligned vertically, a horizontal or other alignment is,

of course, also possible.

The strips of grating 7 are shown symbolically in Fig. 11C as being

composed of four layers. The first layer is a transparent substrate 31,

composed of a suitable material such as glass or plastic. The two electrodes

32 and 34 are made of a transparent electrically conducting material, such

as an oxide or conducting polymer. Layer 33 is the layer (or in some cases

layers) containing the active material. According to a preferred embodiment

of the invention, the active material can be any material which has the

property that its optical transparency in the visible region can be reversibly changed between an opaque state and a transparent state (or vice versa),

when activated by a stimulus, e.g. electric field or locahzed heating, or that its luminescence can be activated by applying a stimulus, whereby to cause

an image to be selectively seen from a plurality of interlaced images. Technologies associated with materials that have this property include, but

are not limited to the following: electrochromism, thermochromism,

electroluminescence, liquid crystals, and suspended particle devices (light

valves).

Preferred embodiments of the invention utilize active materials selected from those used in the technologies mentioned hereinabove and the exact

nature and structure of layer 33 depends on the requirements of the

technology chosen. For example, in the embodiment of the invention

employing electroluminescence, the material in the space between the

electrodes is a phosphor that "glows" when an electric field is created in the

space between the electrodes. The indicia carrier is placed between the

electronic layer and the observer. When the electricity is applied through

the control circuit, the electroluminescent material in the strips that are

stimulated begin to emit light. Since the stimulated strips are positioned

behind the appropriate sub image for each line of the printing on the indicia carrier, a single image is seen while the other images that comprise the

interlaced image are not illuminated and therefore are not visible.

The embodiment of the electronic grating shown in Fig. 11C can be altered

in many ways, depending on the application and materials employed. For example, one of the electrodes, which is at a constant potential for all of the

strips can be made of a single layer that covers the entire surface area of the display. In this case, if the common electrode is that designated by numeral

32, it is possible to use it as the substrate on which the rest of the grating is

created. In another example, the layer containing the active material is

continuous and only those areas of this layer that are stimulated by the

electrode directly covering them will undergo the desired change of optical

transparency. It is to be noted that, in some embodiments of the display

devices of the invention, the electronic grating can be located in front of the

transparent indicia carrier as well as behind it, as described hereinabove.

The electronic grating of the invention is preferably created by using

printing techniques, however any other method appropriate for the type of

materials used can be employed. Examples of possible methods include, but

are not limited to, spin-casting of polymers and evaporation/deposition and

etching techniques used in the electronics and semiconductor industries.

An additional optional feature of the display described in Figs. HA to 11C is

a reflecting surface 24 positioned behind the lights 23 in order to increase the intensity of the backlighting. The path of typical photons from the light

source through the grating toward the observer is indicated in Fig. 11C by

the broken lines (arrows). If an effort is made to make the layer containing the active material reflecting and not absorbing when it is in the opaque

state, then this will contribute greatly to the intensity of the display. The

reflection from the grating back into the box indicates the reflection from the back surface of layer 33 in those areas where the active material is in its opaque state

As mentioned hereinabove, there are many techniques of creating the

interlaced images and suitable electronic gratings for use with these images

can be created mutatis mutandis. In one method the interlaced image is

printed on the indicia carrier in the form of a two-dimensional matrix of

pixels, where each pixel is comprised of a number of subpixels corresponding

to the number of images that have been interlaced to form the combined

image. In Fig. 12A is shown a typical pixel for an interlaced image comprised of four distinct images.

The electronic grating of the invention for use with this interlaced image

would then be constructed as a two-dimensional matrix whose unit cell has the same dimensions as that of the pixel of the indicia carrier. Each of the

unit cells of the grating is comprised of four separate subcells corresponding

to the subpixels on the indicia carrier. Fig. 12B shows a portion of one and

one half rows of unit cells of the grating according to this embodiment of the

invention. Also schematically shown in Fig. 12B are the electrical

connections necessary to operate the grating together with the indicia carrier as a multi-image display system. Although embodiments of the invention have been described by way of

illustration, it will be understood that the invention may be carried out with

many variations, modifications, and adaptations, without departing from its spirit or exceeding the scope of the claims.

Claims

1. A multi-image display system comprising a transparent indicia carrier,

upon which are provided two or more interlaced images, and means for

applying an external stimulus to selectively allow light to highlight parts

of said indicia carrier that belong to a single image of said two or more

interlaced images; whereby, upon application of said external stimulus a

single image is displayed.

2. A multi-image display system comprising a stationary electronic grating

and a stationary indicia carrier upon which are printed interlaced

images, wherein said grating comprises individually addressable areas

corresponding to the lines, pixels, or subpixels of printing on said indicia

carrier, wherein each of said areas comprises a pair of electrodes, and an active material located in the space between said electrodes, said active

material being such that, upon application of a stimulus to said pair of

electrodes, a property of said active material changes from one state to

another and, upon removal of said stimulus, said property returns to its initial state, thereby revealing or obscuring said lines, pixels, or subpixels of printing.

3. A multi-image display system according to claim 2, wherein the property

is the optical transparency of said active material which, upon application of the stimulus is changed from a transparent to an opaque state, or vice versa, and upon removal of said stimulus, returns to its original state.

4. A multi-image display system according to claim 2, wherein the property

is the electroluminescence of said active material which, upon

application of the stimulus is changed from a luminescent to a non-

luminescent state, or vice versa, and upon removal of said stimulus,

returns to its original state.

5. A multi-image display system according to claim 2, wherein the stimulus is the application of an electric potential causing effects including, but

not limited to, creation of a localized electric field and/or locahzed

heating in the space between said electrodes and/or causing an electric

current to flow between said electrodes.

6. A multi-image display system according to claim 2, wherein the active

material exhibits one of the properties included in, but not limited to, the

following group: electrochromism, thermochromism, electroluminescence;

or is chosen from the group including, but not limited to: liquid crystals, and suspended particles of the types used in light valves.

7. A multi-image display system according to claim 2, wherein the printing

on the indicia carrier is in the form of parallel lines and the corresponding individually addressed areas of the grating comprise an

array of parallel strips.

8. A multi-image display system according to claim 2, wherein the printing

on the indicia carrier is in the form of a two-dimensional matrix of pixels,

wherein each pixel comprises a number of subpixels corresponding to the

number of distinct images that comprise the interlaced image, and the

corresponding individually addressable areas of the grating comprise a two-dimensional matrix the unit cell of which has the same dimensions

as that of said pixel, wherein each unit cell is divided into separately

addressable subcells corresponding to said subpixels and wherein said

unit cells and said subcells are arranged with the same geometric

relationship that exists between said pixels and said subpixels.

9. A multi-image display system according to claim 2, further comprising

an array of lights to back-light the image.

10. A multi-image display system according to claim 2, further comprising

a control circuit to apply the stimulus in a predetermined manner.

11. A multi-image display system according to claim 10, wherein the predetermined manner is applying the stimulus simultaneously to the

set of all the areas of the grating corresponding to all the lines or subpixels associated with one of the distinct images, thereby displaying

said distinct image.

12. A multi-image display system according to claim 11, further comprising

a means for alternating, in a predetermined manner, between sets of

areas of the grating, wherein each of said sets corresponds to all the lines

or subpixels associated with each one of the distinct images, thereby

displaying each of said distinct images individually in a predetermined

sequence.