Patent Application
20060126174
The present invention relates to a rear projection screen for professional and consumer applications (television, high resolution graphics workstation, video image walls, etc).
International application WO-A-0067071 discloses such a screen. Reference can be made to that application for a discussion on the ideal properties of screens and for definitions of contrast, transmission and other parameters defining screens.
Another important property for rear projection screens is the angle of view at the output from the screen. This angle is frequently measured both horizontally and vertically or with respect to the normal to the screen. This can be measured using either the extinction angle or the half-luminance angle. The extinction angle corresponds to the value of an angle to the normal for which the screen stops emitting light. The half-luminance angle is the value of the angle to the normal for which luminance has a value equal to half the luminance in the direction normal to the screen surface. The values of these angles of vision depend on the use to which the screen is put: thus, the angle of view in the vertical direction is not an important criterion for a domestic television set; on the contrary, for a graphics monitor, the angle of view in the vertical direction needs to be greater to allow a user to see the full height of images, at a short distance.
U.S. Pat. No. 5,066,099 (Hitachi) discloses a screen formed by a Fresnel lens and flat elements having vertical cylindrical lenticular elements on its entry face and cylindrical lenticular elements on its exit face, separated by ribs. The purpose of the lenticular elements is to ensure an open angle of view at the output from the screen in a direction orthogonal to the direction of the lenticular elements. A diffusion layer is provided on the output face and the ribs are covered by an opaque layer. In order to open up the angle of diffusion in the vertical direction, it is proposed to insert, between the Fresnel lens and the flat element, lenticular elements having horizontal cylindrical lens elements. Devices of the same type are disclosed in U.S. Pat. Nos. 5,590,943, 5,485,308 or 5,515,037.
U.S. Pat. No. 6,307,675 (Toppan) discloses a screen having, in the following order, a first element with horizontal cylindrical lens elements on the entry surface, a three-dimensional diffuser and a Fresnel lens on the output surface, and then a second element with vertical cylindrical lens elements and an alternating sequence of bands which are opaque or allow light to pass. A similar teaching of a three-dimensional diffuser can be found in U.S. Pat. Nos. 5,477,380, 6,271,965 or 6,400,504 (Dai Nippon Printing), or yet again in U.S. Pat. No. 6,256,145 (Sony) and United States Patent Application 2002/0,109,915 (Hitachi).
In all these documents, the angle of view in the horizontal direction is essentially provided by the presence, at the output from the screen, of vertical cylindrical lens elements. In general, for example in U.S. Pat. No. 5,066,099, these lens elements are non-spherical to increase the output angle of view. The contrast in these screens depends notably on the proportion of the screen surface made up by the openings in the black layer. In the Hitachi and Dai Nippon Printing Patents, the opaque layer makes up around 35% of the screen surface; U.S. Pat. No. 6,256,145 (Sony) indicates that the opaque layer makes up 65-75% of the screen surface.
U.S. Pat. No. 4,566,756 discloses a display panel formed from a single plate. This screen has an entry surface with lenticular elements, filaments extending substantially perpendicular to the direction of the lenticular elements and, on the output surface of the single plate, absorbent strips around the focal lines of the lenticular elements. Integrating the optical functions into a single plate, in particular contrast and horizontal and vertical emission angles leads to a detrimental tradeoff regarding characteristics such as contrast, optical transmission and screen resolution. Further, the diffusing filaments are supposed to also reinforce the plate of thickness around 1.5 mm: this is hypothetical and limits screen dimensions. The proposed pitch or period values in that patent correspond to bottom-of-the-range television applications. This type of screen is not easy to produce industrially, and has furthermore never appeared on the market at the time this application was filed.
J. M. Tedesco et al, Holographic Diffusers for LCD Backlights and Projection Screens, SID 93 Digest, pages 29-32 discloses three-dimensional or surface holographic diffusers. In rear projection applications, it is proposed to use such diffusers in combination with a Fresnel lens, instead of a conventional diffuser and a matrix of lens elements.
Robert C. Bush, Reflexite Display Optics, Rear Projection Screens for Different Applications discloses rear projection screens made up by a Fresnel lens and a diffusion screen. Reflexite Display Optics is also selling surface relief diffusing micro-structures or SRDMs, allowing light to be diffused with a predetermined gain distribution.
There is still a requirement for a rear projection screen having contrast and angle of view characteristics as high as possible which is also simple to produce and the characteristics of which can readily be adapted.
The invention consequently provides, in one embodiment, a display screen comprising, along the direction of propagation of projected light:
The screen can advantageously have one or more of the following characteristics:
In a preferred embodiment, the display screen also has a Fresnel lens with its active surface directed towards the elongated radiation diagram diffuser. A vertical lenticular element can be provided at the entry to the Fresnel lens.
In this case, the screen can advantageously have one or more of the following characteristics:
The Fresnel lens, the diffuser, the support and the substrate can be assembled by peripheral bonding. On at least one non-scattering surface, an anti-glare layer, preferably of the moth-eye type can be provided. An anti-glare layer can be provided on all non-scattering layers. The support, at the side of the opaque layer, can be bonded onto the substrate.
The screen can have an outer frame in which there are mounted the substrate, a first frame supporting the diffuser and a second frame supporting the Fresnel lens.
The invention also provides a rear projector unit comprising a projector and such a display screen, the Fresnel lens being adapted to collimate the light leaving the projector.
The rear projector unit has a contrast better than 500 under ambient illumination of 100 lux, for a luminous flux from the projector of 500 lumens.
Further characteristics and advantages of the invention will become more clear from the description which follows of various embodiments thereof provided by way of example and with reference to the drawings.
a to 10d show constructional details of a screen; and
Below we shall use the term “diffuser” to mean an optical object which, upon receiving a light beam, outputs a plurality of light beams in different directions. As explained below, a surface diffuser means a diffuser in which a continuous surface separates two different refractive index media; one can distinguish “conventional” surface diffusers and holographic surface diffusers. In a conventional surface diffuser, there is one refracted ray corresponding to a ray incident on the surface. Nevertheless, two rays that are very close are refracted in very different directions; we can thus, by approximation, consider that an incident light beam is transformed into a plurality of beams. This leads to the desired diffuser effect.
Further, for a holographic surface, an incident ray is transformed into several diffracted rays. One can further consider that an incident beam is transformed into several diffracted beams.
We can make a distinction between diffusers as a function of their operating mode and fabrication of surface and three-dimensional diffusers. A three-dimensional diffuser is for example obtained by an “emulsion” of particles in a transparent matrix of refractive index n1; if the particles are very fine (less than 1 micron), there is diffraction of light; if they are larger and of refractive index n2 (with n2>n1) as is the case in TV screen lenticular elements, there is light refraction.
A surface diffuser does not use particles in a volume, but rather a complex and continuous surface separating two media of different refractive indices. The complex and continuous surface has a thickness which is typically less than 10 micron (peak-to-peak distance). Such a diffuser can for example comprise a surface holographic diffuser produced by interference of light with a surface, or by replication of a master surface. Such a diffuser can also comprise a surface diffuser of which one surface has small dimension irregularities, typically less than 10 microns thick. These irregularities can be obtained by sand blasting, by replication or some other process. Media of different refractive indices can be air and a material such as plastic; one can also use a medium of refractive index n1 having a complex surface and a second medium of refractive index n2 that is different, applied to the first medium to fill and flatten off (or surface) the roughness of the first medium.
A screen is characterised in particular by angle of view, most frequently in horizontal and vertical directions. In the horizontal direction, we shall consider the direction of maximum luminance—generally, the normal to the screen; next we measure the angle between this direction of maximum luminance and the direction for which the luminance is equal to half the maximum luminance. This angle corresponds to the half-luminance vision half angle. The half-luminance angle of view in the horizontal direction, supposing the screen has a symmetrical radiation diagram, is equal to twice this half angle. One can also measure the angle of view at light extinction by considering the angle between the direction of maximum luminance and the direction of extinction. We proceed in the same way in the vertical direction. Below, although this is incorrect but is the practice of those skilled in the art, we shall use the term “angle of view” to designate both the half angle and the angle itself; in particular, the notation ±α designates the angle of view, where α is the half angle. Below, the notation α(L/2) will also be used for designating the half angle.
In one embodiment, the invention provides a screen comprising
It is advantageous for the active surface of the diffuser to be the light exit surface, adjacent to the focusing element support; this limits loss of resolution by scattering within the diffuser. The active surface is then arranged as close as possible to the focusing elements of support 10. In both cases, the advantage of a surface diffuser compared to a three-dimensional diffuser is higher transmission associated with moderate backscattering.
One can also use a surface diffuser of another type other than a holographic or SRDM diffuser. For example, a surface diffuser with microgrooves oriented vertically provides significant scattering in the horizontal direction and low or zero scattering in the vertical direction. Such a diffuser can be obtained by directional sand blasting or by etching or, yet again, by replication using a photoresist from a master diffuser produced by sand blasting or etching.
Focusing element support 10 receives the light coming from the diffuser. It has a light entry surface 16 with cylindrical focusing elements 18; by cylindrical we mean a surface defined by a family of parallel straight lines residing on a curve, this definition being wider than that of a simple cylinder of revolution. The focusing elements can consequently have the shape of an arc of a circle in a plane perpendicular to the straight lines of the family; one can also use non-spherical focusing elements with a shape other than that of an arc of a circle: ellipsoid, parabolic or with other suitable profiles as per U.S. Pat. No. 4,490,010 (DNP). Such a shape contributes to spreading of light rays and can also allow the angle of view to be controlled in the direction perpendicular to the straight lines of the family. Examples are given in reference to
The focusing elements are substantially parallel to the major axis of the diffuser, which is equivalent to saying that the straight lines of the family defining them are substantially horizontal. Ideally, the focusing elements are exactly parallel to this major axis. In practice, in view of assembly constraints, the focusing elements can make an angle with the major axis of the diffuser, as explained later with reference to
The support also has an opaque layer 20, with openings 22 adapted to allow the light focused by the focusing elements to pass. This opaque layer extends, for example, in the focusing plane of the focusing elements and has elongated openings parallel to the focusing elements. This layer can be formed by the methods described in international application WO-A-0067071 or in French patent applications serial numbers 02/02086, 02/10885, 02/10829 or 02/12987. One can, for example, expose the photosensitive layer thereof through the focusing elements or locally destroy the opaque layer thereof using a laser or otherwise, through the focusing elements.
Support 10, which is flexible, provided with the etched opaque layer 20 is bonded onto rigid substrate 24, provided with anti-reflective layer 26. This anti-reflective layer can be of an economical plastic type having a moth-eye structure, replicated in the substrate surface, or have a dielectric multi-layered structure obtained by evaporation or a sol-gel method.
A moth eye-type anti-reflective layer has a reflection coefficient R1 of 0.1% from 0° to 40° light beam incidence angle; this reflection coefficient is limited to 1% for an angle of incidence of 60°, compared to a value of 10% for an acrylic-air interface. In this example, it is-proposed to apply a moth-eye anti-reflective layer, or other, on all non-scattering surfaces of the assembly comprising Fresnel lens, diffuser, support and substrate; in particular, one can apply such a layer to the light entry surface of the Fresnel lens, where the angle of incidence in the corners can be high in the case of a compact design of projector (see U.S. Pat. No. 5,590,943, Hitachi, with angles that can reach 70°). One can further apply such a layer to the surface 16 of the lenticular elements 18 at which the angle of incidence of the light beam can reach 40° or more at the edge of the lenticular elements 18. As explained elsewhere, one can also, or alternatively, provide an anti-reflective layer on the diffuser or on the substrate. The presence of this or these anti-reflective layer(s) is beneficial to the optical transmission of the screen and center-to-edge uniformity of this transmission.
The screen of
Light ray scattering in the vertical direction is principally provided by the lenticular elements, as is illustrated in the examples below.
The advantages of the screen in
Further, and by supplying a diffuser having a very flattened radiation diagram—with a small angle in the vertical direction—it can be ensured that rays incident on the focusing element support are substantially horizontal. It is consequently possible to provide, in the opaque layer, openings of small size without simultaneously harming screen transmissivity. Thanks to this, the screen can have high contrast.
The screen can also have high resolution. Horizontal screen resolution is practically equal to that of the diffuser as the lenticular element array has no influence on the horizontal; values greater than 10 pl/mm (pairs of lines per millimetre) are common for a surface diffuser. In the vertical direction, resolution corresponds to twice the distance between two openings in the opaque layer, thus twice the period of the lenticular element array: indeed, two lenticular elements are necessary in order to clearly separate, with modulation better than 30%, a line that is lit (on) from a line which is unlit (off). As illustrated by the examples below, the period of the lenticular element array of the invention is A=150 μm typical; this leads to a vertical resolution of 1/2 A=3.3 pl/mm.
For television applications in which information spreads considerably in the horizontal direction, the invention leads, consequently, to a horizontal resolution that is well above that of the state-of-the-art; the latter involving use of a vertical lenticular element array which limits horizontal screen resolution.
The screen also minimises moire phenomena. Such phenomena are brought about by superimposition of regular structures—for example pixels of LCD or DMD displays, microrelief patterns of the Fresnel lens, the lenticular elements at the light output, in the case of a state-of-the-art device. The presence of a diffuser in the screen limits or eliminates moire phenomena. This is particularly the case when a random surface structure holographic diffuser is used arranged between the Fresnel (periodic) lens and the focusing element (periodic) support. Using a periodic SRDM type diffuser can lead to limited moire phenomena arising through the periodicity of the active surface elements.
In
As
Towards the middle of
γ is the angle of incidence of ray 32 on the opaque layer which, because the refractive indices are the same in the example, is also the angle with which ray 32 is incident on surface 26 of substrate 24.
Ray 32 leaves the screen making an angle β with the normal to the screen.
The following relations hold for the example of
If the limiting angle of the diffuser radiation diagram in the vertical direction is less than or equal to this angle α, all the rays leaving diffuser 8 which are incident on the lenticular elements 18 pass through the opaque layer through the openings. One can thus assure 100% transmission for the screen, neglecting attenuation. From this point of view, it is judicious to adapt the size of the openings in the opaque layer to the value of the diffuser radiation diagram angle in the vertical direction. The greater this angle, the wider the openings in the opaque layer need to be to allow total or practically total transmission. Aperture size has an incidence on screen contrast: the smaller the openings, and the greater light incident on the screen from outside—the right hand side in the figure—is absorbed. This appears clearly from the calculation of contrast discussed below.
Because of the alignment of the lenticular elements and the openings with the major axis of the radiation diagram, light can be spread in the horizontal direction without this harming screen transmission.
To limit astigmatism, it is preferable to operate under Abbe conditions, in other words as close as possible to the optical axis of the lenticular elements; it is consequently useful for A to be strictly less than r. If this is not the case, it remains possible to employ non-spherical lenticular elements in order to correct the inherent astigmatism where r<A<2·r. This correction is less pronounced than that required for spreading light in the horizontal plane of prior art screens which also require correction for astigmatism. The use of non spherical elements is suggested in U.S. Pat. No. 6,256,145, column 3, lines 19-27.
The table below gives examples for lenticular elements supplied by Reflexite Displays-Optics; the values for A and r are given by the manufacturer, the angles i, j et β0 as well as the ratio e/r are calculated as explained with reference to
One can use this value of angle δ as an upper limit on variations introduced in luminous ray angles as a result of an alignment error of diffuser and support. One can then diminish, by this value of δ, the vertical angle of the diffuser's radiation diagram so as to ensure transmission of all the light. The angle of the diffuser is then chosen to be equal to α-δ, to ensure all the light emitted by the diffuser passes through the apertures in the opaque layer and reaches the user.
We shall further consider the example of a 70 inch diagonal screen i.e. with picture dimensions of 1550 mm by 872 mm in a 16/9 format. The support 10 has 250 lenticular elements per inch. The black matrix has an aperture ratio of 20% equivalent to an aperture size of 20 μm. Horizontal resolution is 1500 pixels per line corresponding to a 1 mm pixel. If we consider an alignment tolerance of ±1 μm at the edges of an individual pixel, an angle δ of 1/00 radians is obtained. Alignment tolerance at the edges of a 1500 mm long screen is ±750/500 equivalent to ±1.5 mm. If an alignment tolerance of 0.75 mm is imposed at the screen edge—which is perfectly feasible industrially—an alignment tolerance less than 0.5 μm at an individual pixel is obtained. This ensures excellent optical transmission and the possibility of still further improving contrast, for example by decreasing the aperture ratio to 10% for the black matrix.
The tables below give examples of angles α and β for various aperture angles X% in the opaque layer. We have considered examples of refractive index n of 1.5. The calculations were done using the formulae given above with reference to
A is chosen to be compatible with the required resolution; for the vertical, a pair of lines—a black line and a white line—can be projected over a distance 2·A; a value of A of 150 μm is taken by way of example. The emission angle for a surface diffuser at half-luminance is approximately equal to two-thirds of the angle at extinction.
Application to Television
In the horizontal direction, a diffuser and consequently the screen emit at a half-luminance at ±40°; a value of ±48° is possible. The table gives angles in degrees, for the vertical, with
X% is the aperture ratio of the opaque layer, as explained above.
In the vertical direction, the habitual television specification requires a half luminance angle P(L/2) at the screen output better than ±10°. r=0.150 mm is suitable with a lenticular elements thickness e=0.420 mm. Diffusers with a half-luminance emissivity of ±0.5° at ±3° for the vertical are suitable.
Holographic surface diffusers from the POC company can be used. These diffusers have half-luminance angles in the following ranges:
Application to a graphics monitor and elements of a large dimension video wall In a horizontal direction, the usual specification requires a half-luminance angle P(L/2) at the output from the screen greater than ±40°; a value of ±48° is possible. In the vertical direction, the usual specification requires a half-luminance angle P(L/2) at the output from the screen greater than ±30°.
An example, illustrated in
We mentioned above the example of a surface holographic diffuser. We note the very small backscattering from a holographic diffuser. This diffuser has the advantage of having a readily adaptable scattering diagram; one could even provide for several lobes in the same horizontal direction. This diffuser also has the advantage discussed in
In the case of a conical diffuser of angle 2° (half angle at half luminance, equivalent to ±3.5° at extinction) on surface 12, resolution is slightly deteriorated since the incident beam size increases through diffuser 8; at the entry to diffuser surface 14 a dot size of 2×2 mm×tan(3.5°), equivalent to 250 microns for a 2 mm thick diffuser is obtained. This degradation is acceptable.
Like in the previous case, a further symmetrical diffuser can also be provided at the entry to the Fresnel lens. In every case, it is advantageous for this supplementary diffuser to have a half-luminance diffusion angle of ±2.5°. Such a diffuser is available from Reflexite Display Optics under reference BP311 or from POC under reference 5° LSD.
One could further arrange such a diffuser at the surface of substrate 24 bonded to the opaque layer, and/or yet again arrange this diffuser on the surface of the lenticular element support before depositing the opaque layer. The solutions may require the use of an adhesive of a different refractive index so as to preserve a complex surface separating two media of differing refractive indices. The solutions make it possible to preserve a smooth surface on the outside of the screen, facing the user, so as to prevent any soiling and increase robustness of the screen.
Thus, it is possible to add to the diffuser having an elongated radiation diagram, one or several supplementary diffusers with, preferably, a low diffusion angle—smaller than the vertical angle of the diffuser with an elongated radiation diagram. This or these supplementary diffuser(s) fulfil one or several of the following functions:
This or these supplementary diffuser(s) can be surface diffuses and be arranged:
One could also use, by way of a supplementary diffuser, a three-dimensional diffuser in the Fresnel lens, in the diffuser, in the lenticular elements or in the substrate.
Even with such diffusers, one obtains a screen having, in combination with the Fresnel lens, transmission better than 0.60 or even 0.70 or more.
The speckle phenomenon can appear when a scattering surface struck by a narrow beam reacts like a multitude of small independent sources the emissions of which interfere to create a picture with fine and highly luminous white, and blacks—whence the impression of speckle. Speckle is not a particular problem at large distances like in television and video image wall applications. For a short distance monitor applications, the observer may find this bothersome. In the case of DMD projectors, the micromirror pixel reflects a very thin luminous beam towards the optical system which, although widened by the optical system, reaches the screen pixel at an angle well below 1°; the dot from scattering in the optical system is around 100 microns on the screen and can exhibit speckle as a result of a periodicity of the scattering surface well below 100 microns (see Proceedings of the SPIE, February 1997); this holds also for the surface of a 800 μm×600 μm pixel for a 800 mm×600 mm screen illuminated by a DMD micromirror.
In the vertical direction, there is an integration effect of the phenomenon since a 600 μm height pixel sees as it were its information compressed and then redistributed by 4 horizontal lenticular elements of period A=150 μm.
As explained above, it is possible to minimize this phenomenon by providing one or several conical diffusers, periodic or otherwise, in the screen: the aim here is to widen out the angle the light beam strikes diffuser 8 at by placing a second diffuser in front of it to avoid speckle from the diffuser 8; or minimize speckle by means of a second diffuser after diffuser 8.
We shall now give examples for calculating contrast. As known per se, contrast is representative on the ratio L0/ln between luminance L0 of the screen in those regions where light is transmitted (ON regions) and the luminance ln in those regions where light is not transmitted (OFF regions). Using the following notation:
Using these notations, contrast C is given by:
For measuring R, the projector is switched off; under ambient lighting, the luminance ln0 of a reflective Lambert diffuser (for example of MgO) placed against the screen surface is measured. Next, screen luminance ln is measured. Coefficient R is now ln/ln0.
For measuring contrast of a projector, the ANSI standard proposes dividing screen surface into 9 equal parts 5 of which are ON and 4 of which are OFF with the ON zones at the four comers and the center; the luminance mean L0 is measured with a photometer on the 5 ON zones, the mean ln being the means of luminances measured on the 4 OFF zones, the screen being under ambient lighting with the projector switched off, ambient lighting being a mean for measurements made with a luxmeter on the different zones of the screen.
Under these conditions, for the screen of
Diffuse reflection R of the screen is limited in view of the rear position of diffuser 8 with respect to support 10, which constitutes the originality of the invention with respect to the state of-the-art.
For television applications, luminous flux is low to limit power consumption; typically, we have a power F less than 500 lumens. A transmission of 60%, an illumination value of 100 lux and a 1 square metre surface area give, for an aperture X% of 20°, a contrast of:
In a television application, flat emission is looked for, and the gain is typically greater than 2.5 compared to a Lambert profile. Contrast is better than 500.
In a monitor application, luminous flux of the monitor can reach 1000 lumens. Emission is more homogeneous, leading to a gain better than 1.5. Contrast is:
and is consequently typically better than 600. Screen contrast is consequently better than 500. This is a reasonable calculation taking account of the low gain of 2.5 proposed and the transmission T which can be greater than 0.70; in practice, screen gain is higher, which would further increase contrast.
The diffuse reflection coefficient of the screen, R, is given as follows:
This value for diffuse reflection R2 is explained as follows; the lenticular element with an etched opaque layer plays the role of a neutral filter for ambient light passing through it; this light is subject to back-scattering by the internal diffuser or by the holographic diffuser, and passes again through the filter formed from the opaque layer to go towards the observer. With a surface area of the black matrix apertures of X%, ambient light is degraded to a minimum by a coefficient of X%2. If the surface diffuser 14 back-scatters R0% of stray light, and then the diffuse reflection coefficient of the screen, in the absence of the anti-glare layer, is R2=R0 X%2.
For a surface diffuser, R0 is less than 10% (see Tedesco article above).
For X%=20%, we have R2=0.4% and R=1.4%
For X%=30%, we have R2=0.9% and R=1.9%
which is consistent with the values for R given above for screen contrast evaluation.
The screen provides better resolution than that of the state-of-the-art. Toppan (Japan) has announced vertical lenticular elements 0.150 mm wide and 0.098 mm wide for the future; the corresponding resolution in pl/mm, for a period of two lenticular elements being 3.3 pl/mm to 5 pl/mm in the future. The screen discussed in the examples has, in the horizontal direction, a resolution which is that of diffuser 8 employed, and which is better than 10 pl/mm. In the vertical direction, resolution is less important for television applications; resolution is given by the number of line pairs visible per mm of screen. It depends, in the examples discussed, on the size of the lenticular elements, one pair of lines corresponding to two lenticular elements.
The screens discussed in the examples can typically allow one or several of the following characteristics to be achieved:
Numerous patents describe how to make non-spherical lenticular elements for correcting astigmatism and focusing and spreading light emitted perpendicular to the lenticular element axis: U.S. Pat. Nos. 4,387,959, 4,490,010, 4,432,010, 6,256,145—the latter two envisage ellipsoid lenticular elements with ellipse eccentricity ε equal to the inverse of refractive index n for minimizing focusing aberrations. The teachings of these various documents can be used and applied to the focusing elements of the support.
The axis XX′ is used to construct the limiting ray 32 delivered by diffuser 8. This ray passes at the edge of aperture 22 in opaque layer 20 and practically through the center O, in view of the small value of the angle α between ray XX′ and the axis F1F2 of the two foci (or the normal to the screen). We have
Increasing the value of β(L/2) up to ±30° or more is possible by applying a second surface diffuser in the apertures of the opaque layer; this contributes to minimizing speckle if appropriate.
Clearly, the invention is not limited to the embodiments described. Regarding manufacture,
In the examples of the figures, the screen is used in a rear projection application, with a Fresnel lens. In the examples proposed, we have considered a distance A of 150 microns between lenticular elements. One could also choose a greater distance, for example 500 microns at the most; a value of 250 microns at the most nevertheless improves resolution.
To conclude, in the various examples discussed above:
In the case of the graphics monitor and video image wall application in the examples of the invention, the vertical emission angle is provided by the non-spherical horizontal lenticular elements.
The characteristics of
The associated diffuser 8 has the following characteristic angles:
on the minor axis, which is in the field of the achievable. On the major axis, the half-luminance angle is ±40° or even ±48° (see holographic diffuser from POC). The asymmetric surface diffuser from Reflexite Display Optics sold under reference SN 1375 with a half-luminance angle α of ±7% on the minor axis for an aperture value X%t=20% can also be used. The angle of scatter on the major axis of this diffuser is ±33° at half luminance; this value is low but can be improved.
Producing support 10 involves the photopolymer method (see above) for forming the lenticular elements 18 on a support base film around 0.075 mm thick.
The associated diffuser 8 has the following characteristic angles
A support 10 thicker than that for
The examples illustrated by
In both cases, a diffuser having the smallest possible angle on the minor axis is applied to constitute apertures in the opaque layer with the X% value minimized; with the stated aim of increasing screen contrast.
a-10d show constructional details of a screen, and
b shows a frame 72 on which there is laminated diffuser 8, with active surface 14. The basic surface of frame 72, identified by reference numeral S2, can be accurately cut-out or machined after lamination of diffuser 8, in correspondence with the major axis of elliptical emission of diffuser 8. This diagram also shows the position of the Fresnel lens. The latter is mounted onto frame 78 or laminated thereon (shown in
c is a sectional view of the assembled screen. An outer frame 82 shown in detail in
To obtain the assembled screen of
The assembly of
The examples above show the use of a structure composed of three separate elements, allowing firstly all screen characteristics to be optimized and secondly, adaptation to all applications (notably television and graphics monitors). The three elements are successively:
The function of the support is that of:
| Number | Date | Country | Kind |
|---|---|---|---|
| 03/04125 | Apr 2003 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR04/00839 | 4/2/2004 | WO | 1/5/2006 |
