Abstract:
A screen for use in a projection-type image display apparatus having an image displaying element which includes a plurality of pixels for modulating light from a light source so as to form an enlarged picture on the screen. The screen includes a Fresnel lens sheet having Fresnel lenses on a light emission side, a first sheet disposed on the light emission side of the Fresnel lens sheet, and a second sheet disposed on a light emission side of the first sheet and adhered thereto. The first sheet includes a plurality of lenticular lenses formed on a light incident side which extend in a longitudinal direction and are arranged in a horizontal direction, with light passing window portions being formed at positions opposing the lenticular lenses and with light absorbing portions provided therebetween. The second sheet includes a light scattering element therein.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This is a continuation of U.S. application Ser. No. 10/827,338, filed Apr. 20, 2004, which is a continuation of U.S. application Ser. No. 09/412,578, filed Oct. 5, 1999, now U.S. Pat. No. 6,728,031, the subject matter of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     In general, the present invention relates to a projection-type picture display apparatus such as a projection television set and a screen used thereby. More particularly, the present invention relates to a projection-type picture display apparatus which has a small amount of inadvertent inclusion of external light, is capable of suppressing a reduction in contrast and capable of lowering the degree of deterioration of a picture quality by using an optical device having a structure comprising pixels laid out to form a matrix such as a liquid-crystal panel or a DMD (Digital Micromirror Device) as a picture generating source, and relates to a screen used by the projection-type picture display apparatus.  
         [0004]     2. Description of the Related Art  
         [0005]     With the picture source going diverse, the projection-type picture display apparatus is enjoying broad general popularity in the market by virtue of its marketability factors of a projection-type optical apparatus with a large screen such as a small weight, a low cost and a small size. On the other hand, in recent years, a projection-type picture display apparatus using a liquid-crystal panel as a picture generating source starts its participation in the market due to substantial improvement of the precision/fineness and the numerical aperture of the liquid-crystal panel. This projection-type picture display apparatus is designed into a configuration wherein a source picture displayed on the liquid-crystal panel is displayed as an enlarged picture on a screen in full colors by a projection lens unit.  
         [0006]     In an optical system employed in this projection-type picture display apparatus, it is possible to adopt a three-panel technique employing three liquid-crystal panels as shown in FIG. 19 of Japanese Unexamined Patent Publication No. Hei 9-96759, or a single-panel technique employing only one liquid-crystal panel as shown in FIG. 1 of Japanese Unexamined Patent Publication No. Hei 4-60538. First of all, an optical system adopting a single-panel technique employing one liquid-crystal panel is explained by referring to  FIG. 1 .  
         [0007]      FIG. 1  is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting a single-panel technique employing one liquid-crystal panel.  
         [0008]     As shown in the figure, a reflective mirror  29  directs a beam emitted by a white-color light source  28  implemented by a metal halide lamp, a canon lamp, a halogen lamp or a high-pressure mercury lamp to a converging lens  27  with a high degree of efficiency whereas a collimator lens  26  converts the beam into all but parallel white-color lights. Three dichroic mirrors  23 ,  24  and  25  with types different from each other are placed in front of the collimator lens  26 . The dichroic mirrors  23 ,  24  and  25  exhibit characteristics to selectively reflect lights with the green, red and blue wavelengths respectively but to pass on other components. Symbols R, G and B in the figure denote respectively the red, green and blue lights split by the dichroic mirrors  24 ,  23  and  25 . In this conventional configuration, the red-color light is taken as a reference while the blue-color and green-color lights are radiated to a liquid-crystal panel  22  from slanting directions relative to the red-color light.  
         [0009]     The liquid-crystal panel  22  comprises pixels for the 3 primary colors, namely, red, green and blue. The pixels each exhibit an optical transmittivity representing the level of a luminance component of a picture signal. Thus, the red, green and blue lights are modulated in accordance with the level of the picture signal to create a desired image on the liquid-crystal panel  22 . The image displayed on the liquid-crystal panel  22  is then projected by a projection-lens unit  21  on a screen  20  as an enlarged picture.  
         [0010]     In order to radiate an image light emitted by the liquid-crystal panel  22  to the projection-lens unit  21  with a high degree of efficiency, an optical system including a convex lens for converging a light is typically provided between the liquid-crystal panel  22  and the projection-lens unit  21 . It should be noted that such an optical system is not shown in  FIG. 1 .  
         [0011]     The white-color light source  28  itself dissipates heat which can be a cause of a damage. On the other hand, the liquid-crystal panel  22  including a polarizing plate absorbs an incident light, dissipating heat which can also be a cause of a damage. In order to reduce an increase in temperature, a cooling fan not shown in the figure is used to forcibly cool the white-color light source  28  and the liquid-crystal panel  22  so that they can be used at a temperature in a desired range.  
         [0012]     Next, the optical system adopting the conventional three-panel technique, that is, employing three liquid-crystal panels, is explained by referring to  FIG. 2 .  
         [0013]      FIG. 2  is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting the conventional three-panel technique employing three liquid-crystal panels. Configuration components shown in the figure identical with those of the optical system shown in  FIG. 1  are denoted by the same reference numerals as those of the latter. The optical system shown in  FIG. 2  has a configuration wherein a reflective mirror  29  collimates a beam emitted by a white-color light source  28  implemented by a metal halide lamp, a canon lamp, a halogen lamp or a high-pressure mercury lamp into all but parallel white-color lights. Two dichroic mirrors  31  and  32  with types different from each other are placed in front of the reflective lens  29 . The dichroic mirrors  31  and  32  split the beam into color components which are then radiated to their respective liquid-crystal panels  33 ,  34  and  35 . Pictures displayed on the liquid-crystal panels  33 ,  34  and  35  are synthesized by a color synthesizing prism  36  before being projected by a projection-lens unit  21  on a screen  20  as an enlarged picture. Since the operation of the projection-type optical system adopting the conventional three-panel technique employing the three liquid-crystal panels is the same as the conventional system shown in  FIG. 1 , it is not necessary to repeat its explanation.  
         [0014]     In addition, a forced cooling system of the white-color light source  28  and the liquid-crystal panels each including a polarizing plate is the same as the optical system shown in  FIG. 1 . Furthermore, a radiation system to increase the efficiency of light utilization has become popular in recent years. The radiation system has a polarized-light synthesizing function for synthesizing P and S polarized lights generated by a polarization beam splitter as a result of splitting of a light emitted by the light source.  
         [0015]     A rear-projection-type picture display apparatus employing the optical systems explained above is described by referring to  FIGS. 3 and 4 .  
         [0016]      FIGS. 3 and 4  are each a side-view diagram showing a partial cross section of main components of the rear-projection-type picture display apparatus employing the projection-type optical system. In the figures, reference numerals  11  and  12  denote a radiation system including a light source and a projection lens respectively. Reference numeral  13  denotes an optical-path reflection mirror and reference numeral  14  denotes a screen. Reference numeral  15  denotes a case. The length of an optical path from the projection lens  12  to the screen  14  in the rear-projection-type picture display apparatus shown in  FIG. 3  is equal to that of the apparatus shown in  FIG. 4 . Since the rear-projection-type picture display apparatus shown in  FIG. 3  has a comparatively big depth, its height can be made relatively small. Since the rear-projection-type picture display apparatus shown in  FIG. 4  has a comparatively big height, on the other hand, its depth can be made relatively small. In either of the rear-projection-type picture display apparatuses, by shortening the projection distance of the projection lens  12 , that is, the length of the optical path from the projection lens  12  to the screen  14 , a compact set can be implemented by employing only one optical-path reflection mirror  13 . As the screen  14 , a screen  40  having a two-sheet structure is normally employed. The screen  40  comprising a lenticular lens sheet and a Fresnel lens sheet is used in a projection-type picture display apparatus employing a Braun tube  43  shown in  FIG. 10 .  
         [0017]      FIG. 10  is a side-view diagram showing a partial cross section of main components of the rear-projection-type picture display apparatus employing the projection-type Braun tube  43 . It should be noted that, in the figure, reference numerals  40  and  41  denote a screen and a projection lens respectively whereas reference numerals  42  and  43  denote a bracket and a projection-type Braun tube respectively. Reference numeral  44  denotes an optical path of a light projected from the projection-type Braun tube  43  to the screen  40  provided at the end of a radiation path.  
         [0018]     A detailed configuration of the screen  40  shown in  FIG. 10  is shown in  FIGS. 12 and 13 .  
         [0019]      FIGS. 12 and 13  are each a diagram showing a squint view of main components of the conventional screen  40 . Components of  FIG. 12  identical with those shown in  FIG. 13  are denoted by the same reference numerals as the latter. The screen  40  shown in  FIG. 12  comprises a Fresnel lens sheet  51   a  and a lenticular lens sheet  52 . On the other hand, the screen  40  shown in  FIG. 13  comprises a Fresnel lens sheet  51   b  and a lenticular lens sheet  52 . The lenticular lens sheet  52  comprises a lenticular lens  54  on the incidence surface, a lenticular sheet  56  on the emission surface and a light absorbing layer  57  provided on a protrusion  55 . The Fresnel sheet  51   a  has a flat incidence surface and a Fresnel lens  53  on the emission surface thereof. On the other hand, the Fresnel sheet  51   b  comprises a lenticular lens  58  provided on the incidence surface thereof and a Fresnel lens  53  provided on the emission surface thereof. As described above, the screen  40  shown in  FIG. 12  is different from that shown in  FIG. 13  in that, in the case of the former, no lenticular lens  58  is provided on the image-light incidence surface of the Fresnel sheet  51  while, in the case of the latter, the lenticular lens  58  is provided. It should be noted that the lenticular lens  58  has its longitudinal direction coinciding with the horizontal direction of the screen  40 .  
         [0020]     In a screen having a two-layer structure comprising a lenticular lens sheet  52  and a Fresnel lens sheet  51  used in a rear-projection-type picture display apparatus employing the conventional projection-type Braun tube, the horizontal-direction width of the screen of the light absorbing layer  57  provided on the picture-viewing side of the lenticular lens sheet  52  can be made larger than the width of the lenticular lens  56  on the emission surface. That is, if the width of the lenticular lens  56  on the emission surface is made small, the efficiency of the light utilization decreases. Thus, the width of the light absorbing layer  57  in the screen horizontal direction can not be made large. For this reason, there exists a phenomenon in which an external light is reflected to the lenticular lens  56  provided on the emission surface. This phenomenon raises a first problem that remains to be solved. The problem is that the inadvertent inclusion of an external light can not be reduced to a value below a predetermined amount and the degree of contrast deterioration can not be suppressed below a predetermined level.  
         [0021]     The following description explains in detail reasons why the first problem arises.  
         [0022]      FIG. 11  is a diagram showing a top view of a layout of the rear-projection-type picture display apparatus employing the conventional projection-type Braun tube on a horizontal plane in a simple and plain manner. As described above, the rear-projection-type picture display apparatus employs the conventional projection-type Braun tube in the horizontal-plane layout.  
         [0023]     In  FIG. 11 , reference numerals  7 R,  7 G and  7 B denote red, green and blue projection-type Braun tubes respectively whereas reference numerals  8 R,  8 G and  8 B denote projection lens associated with the red, green and blue projection-type Braun tubes  7 R,  7 G and  7 B respectively. Reference numerals  10 R,  10 G and  10 B denote red, green and blue projected beams respectively. In the optical system of the rear-projection-type picture display apparatus, in actuality, there are reflective mirrors for reflecting the red, green and blue projected beams  10 R,  10 G and  10 B. These reflective mirrors are omitted from  FIG. 11 . Reference numerals  13 R,  13 G and  13 B denote optical axes of the projection lenses  8 R,  8 G and  8 B respectively. The optical axes  13 R,  13 G and  13 B cross each other, forming optical-axis convergence angles θ at a point S 0  in close proximity to the screen  40 .  
         [0024]     As shown in  FIG. 11 , the projected beams  10 R,  10 G and  10 B are each spreading before hitting the screen  40 . Pay attention to a specific projected beam, that is, the red projected beam  10 R for example. Lights of the red projected beam  10 R emanating from the projection lens  8 R toward pixels on the screen  40  are not parallel. Instead, those lights are becoming more distant from the main light hitting the center pixel on the screen  40  or the optical axis  13 R.  
         [0025]     A light hitting a pixel on the screen  40  in the same direction as the main light hitting the center pixel has the highest intensity among the lights reaching the pixels on the screen  40 . That is, the direction of the main light is a direction of the highest intensity. Thus, to a viewer at a fixed position, only a portion of the picture is bright while surrounding portions are dark. This phenomenon is referred to as a color shift. In order to reduce the effect of the color shift, in the screen  40  shown in  FIG. 12  or  13 , a spread picture beam arriving at the incidence surface of the Fresnel lens sheet  51  is converted into an almost parallel beam passing through the Fresnel lens  53  and leaving for the lenticular lens sheet  52  for each of the red, green and blue colors.  
         [0026]      FIGS. 14 and 15  are each a diagram showing a partial enlarged cross section of the lenticular lens cut in a direction A-A 1  shown in  FIG. 13 .  
         [0027]     In these figures, reference numeral  54  denotes the lenticular lens provided on the surface of incidence of the picture light and reference numeral  56  denotes the lenticular lens provided on the surface of emission of the picture light.  
         [0028]     According to a conventional technology disclosed in Japanese Unexamined Patent Publication No. Sho 58-59436, the lenticular lens  54  provided on the incidence surface has a surface resembling a portion of the surface of an elliptical cylinder. The direction of the major axis of the ellipse coincides with the direction of a thickness between the incidence surface  54  and the emission surface  56  which is indicated by notation  1 - 1 ′ in  FIGS. 14 and 15 . One of the two foci of the ellipse is placed at an inner portion in close proximity to the lenticular lens  54  provided on the incidence surface. The other focus is placed at a position in close proximity to the lenticular lens  56  provided on the emission surface. The eccentricity e of the ellipse is set at a value approximately equal to the reciprocal of the refractive index n of the material of the lenticular lens sheet  52 .  
         [0029]     In such a configuration, all incident lights arriving at the lenticular lens  54  provided on the incidence surface in a direction parallel to the major axis of the ellipse are converged on the focus in close proximity to the lenticular lens  56  provided on the emission surface and spread in screen surface horizontal directions from this focus.  
         [0030]     As for the lenticular lens  56  provided on the emission surface, the shape of the emission surface resembles the surface of an elliptical cylinder all but similar to the surface of an elliptical cylinder on the incidence-surface side. For an incident beam  60  at an edge shown in  FIG. 14 , the lenticular lens  56  provided on the emission surface functions to make the directional characteristic of the emitted light all but symmetrical with respect to the optical axis indicated by notation  1 - 1 ′ in the figure. Furthermore, for an incident beam  62  coming from a slanting direction of the red or blue color as shown in  FIG. 15 , the lenticular lens  56  provided on the emission surface has a correcting function to make the directional characteristic of the emitted light all but symmetrical with respect to the optical axis indicated by notation  1 - 1 ′ in the figure. In addition, the beam is not converged at a point due to frame aberration occurring at a location in close proximity to the emission surface at that time. Instead, the beam is spread in screen horizontal directions.  
         [0031]     Inside the actual lenticular lens sheet  52 , a scattering material  58  such as glass bead exists as shown in  FIGS. 12 and 13 , causing the beam to be actually further spread. Basically, however, the width of the light absorbing layer  57  in the screen horizontal direction can not be increased to a value greater than the width of the lenticular lens  56  provided on the emission surface. As a result, the quantity of light reflected due to inadvertent inclusion of an external light can not be reduced and a decrease in contrast can not be made lower than a predetermined value.  
         [0032]     In addition, an incident beam  62  coming from the red or blue slanting direction is not converged at a point due to frame aberration occurring at a location in close proximity to the emission surface. Instead, the beam is spread in screen horizontal directions as described above. As a result, the width of the surface of the lenticular-lens surface can not be reduced. Thus, in the case of the lenticular lens sheet  52  adopting the conventional technique employing the lenticular lenses  54  and  56  on both the incidence and emission surfaces, there is raised a second problem that the lenticular-lens pitch in the screen horizontal direction can not be reduced to a value smaller than 0.5 mm.  
         [0033]     For the reason described above, the total focus performance (horizontal resolution) of the rear-projection-type picture display apparatus is determined mainly by the lens pitch of the lenticular lens  52  which has a performance inferior to that exhibited by the projection-type Braun tube and the projection lens.  
         [0034]     In addition, since the pitch of the lenticular lens  56  provided on the emission lens can not be reduced, a third problem is raised. To put it in detail, when an optical device having a structure comprising pixels laid out to form a matrix such as a liquid-crystal panel or a DMD (Digital Micromirror Device) is used as a picture generating source, the quality of a picture deteriorates due to moires generated on the entire screen  40 . The generation of such moires is attributed to three causes, namely, projected and enlarged pixels on the screen  40 , the lenticular lenses  54  and  56  provided on the lenticular lens sheet  52  and the Fresnel lens  53 .  
       SUMMARY OF THE INVENTION  
       [0035]     It is an object of the present invention addressing the problems encountered in the conventional technology described above to provide a screen and a projection-type display apparatus capable of reducing inadvertent inclusion of an external light and reducing a decrease in contrast when producing a projected and enlarged picture on the screen by using a projection lens from an image created by a picture generating source implemented by an optical device such as a liquid-crystal panel and a DMD (Digital Micromirror Device) with a structure comprising pixels laid out to form a matrix.  
         [0036]     It is another object of the present invention addressing the problems encountered in the conventional technology described above to provide a screen and a projection-type display apparatus capable of reducing a decrease in picture quality caused by moires when producing a projected and enlarged picture on the screen by using a projection lens from an image created by a picture generating source implemented by an optical device such as a liquid-crystal panel and a DMD (Digital Micromirror Device) with a structure comprising pixels laid out to form a matrix.  
         [0037]     An optical system of the projection-type picture display apparatus provided by the present invention employs an optical device such as a liquid-crystal panel and a DMD (Digital Micromirror Device) with a structure comprising pixels laid out to form a matrix as a picture generating source besides one projection lens shown in  FIGS. 1 and 2 . For this reason, since red and blue image lights are not radiated in slanting directions with respect to the green image light, no frame aberration is generated on the screen.  
         [0038]     As a result, since the width of a lenticular lens provided on the image-light emission surface of a lenticular sheet can be reduced while the width of a light absorbing layer can be increased to a relatively large value, it is possible to reduce inadvertent inclusion of an external light and reduce a decrease in contrast.  
         [0039]     A lens of provided on the incidence surface of the lenticular lens sheet is designed into a shape resembling the surface of an elliptical cylinder or a portion of a high-order non-spherical cylinder. When designed into the surface of an elliptical cylinder, the direction of the major axis of the ellipse coincides with the direction of the thickness between the incidence and emission surfaces. In addition, one of the two foci of the ellipse is placed at a position in close proximity to a lenticular lens provided on the incidence surface whereas the other focus is placed at a position in close proximity to a lenticular lens provided on the emission surface. In this case, the eccentricity e of the ellipse is set at a value approximately equal to the reciprocal of the refractive index n of the material of the lenticular lens.  
         [0040]     In such a configuration, incident lights hitting the lenticular lens on the incidence surface in a direction parallel to the major axis of the ellipse are all converged on the focus in close proximity to the emission surface and then spread from this focus in screen surface horizontal directions. For this reason, the width in the screen horizontal direction of the lenticular lens provided on the emission surface can be reduced. In this case, the lens provided on the incidence surface of the lenticular lens sheet can be designed into a shape of a high-order non-spherical surface in order to further increase the efficiency of the light convergence.  
         [0041]     Because of the reasons described above, since the-screen-horizontal-direction width of the lenticular lens provided on the emission surface can be reduced, the lens pitch of the lenticular lens can also be reduced as well. As a result, the total focus performance (horizontal resolution) of the rear-projection-type picture display apparatus using this screen can be improved.  
         [0042]     In addition, in the screen provided by the present invention, the lens pitch of the lenticular lens can also be reduced as described above. Thus, even if the screen provided by the present invention is used in the projection-type picture display apparatus employing an optical device having a structure comprising pixels laid out to form a matrix such as a liquid-crystal panel or a DMD (Digital Micromirror Device) as a picture generating source, moires generated on the entire screen due to three causes are no longer striking. As described above, the three causes are projected and enlarged pixels on the screen, the lenticular lenses provided on the lenticular lens sheet and the Fresnel lens.  
         [0043]     The objects of the present invention can be achieved as follows. According to a first aspect of the present invention, there is provided a screen characterized in that, in order to allow a light generated by a light source and modulated by a picture display device comprising pixels laid out to form a matrix to produce an image thereon to be projected by using a projection optical means on the screen as an enlarged picture, the screen is provided with: a Fresnel lens sheet placed on an emission side of the picture display device; a first configuration element having: lenticular lenses provided on an incidence side of a light passing through the Fresnel lens sheet; and light absorbing layers each provided at a place in close proximity to the focal point of one of the lenticular lenses and are separated from each other by a predetermined distance for forming the light passing unit; and a second configuration element having a light passing plate fixed on the emission side of the first configuration element and a pitch of the light passing units is made smaller than a pitch of pixels projected and enlarged on the screen from the image produced by the picture display device.  
         [0044]     In the screen according to first aspect of the present invention, an emission surface of the light passing plate is subjected to a reflection preventing process for preventing reflection of a visible light. As an alternative, on the emission side of the light passing plate, there can also be provided a reflection preventing film for preventing reflection of a visible light.  
         [0045]     In the screen according to the first aspect of the present invention, a light scattering material is mixed inside the light passing plate. As an alternative, a light scattering layer can also be provided between the light passing plate and the first configuration element.  
         [0046]     In a screen according to the first aspect of the present invention, Fresnel lenses of the Fresnel lens sheet are laid out at a pitch Fp; the light passing units are laid out in a horizontal direction of the screen at a pitch Lp; and  
         [0047]     a ratio Lp/Fp of the pitch Lp to the pitch Fp is set at a value in the range 1.588 to 1.649.  
         [0048]     According to a second aspect of the present invention, there is provided a screen for projecting an enlarged picture on the screen from a displayed picture output by a picture display apparatus comprising: a light source; a picture display device implemented as a matrix of pixels each having a means for modulating the intensity of a light generated by the light source; and a projection optical means for projecting the displayed picture appearing on the picture display device. The screen is provided with: a first configuration element having a plurality of lenticular lenses provided on a light-emission side of the projection optical means and light absorbing layers provided on a light-emission side of the first configuration element, and a light passing second configuration element provided on the light-emission side of the first configuration element. The lenticular lenses have a longitudinal direction coinciding with a screen surface vertical direction and are laid out contiguously in a screen surface horizontal direction; the light absorbing layers are sandwiched by boundaries of any two adjacent openings each provided at a location in close proximity to a focal point of one of the lenticular lenses associated with the opening; the first and second configuration elements are bound or stuck to each other; a pitch of the openings is made smaller than a pitch of pixels projected and enlarged on the screen from the displayed picture output by the picture display device; and a pitch of interference lines caused by both interference sources is set at a value about equal to or smaller than the pitch of pixels projected and enlarged on the screen from the displayed picture output by the picture display device.  
         [0049]     In the screen according to second aspect of the present invention, an emission surface of the light passing plate is subjected to a reflection preventing process for preventing reflection of a visible light. As an alternative, on the emission side of the light passing plate, there can also be provided a reflection preventing film for preventing reflection of a visible light.  
         [0050]     In the screen according to the second aspect of the present invention, a light scattering material is mixed inside the light passing plate. As an alternative, a light scattering layer can also be provided between the light passing plate and the first configuration element.  
         [0051]     In the screen according to the second aspect of the present invention, a third configuration element having Fresnel lenses is provided on a light-incidence side of the first configuration element; the Fresnel lenses of the third configuration element are laid out at a lens pitch Fp; the openings of the first configuration element are laid out in a horizontal direction of the screen at a pitch Lp; a ratio Lp/Fp of the lens pitch Lp to the pitch Fp is set at a value in the range 1.588 to 1.649; a pitch Mp 1  of moire lines caused by both interference sources is set at a value smaller than a pitch Iph of pixels projected and enlarged on the screen in a screen horizontal direction from the displayed picture output by the picture display device; and a pitch of interference lines caused by the both interference sources is set at a value about equal to or smaller than a pitch of pixels projected and enlarged on the screen from the displayed picture output by the picture display device.  
         [0052]     According to a third aspect of the present invention, there is provided a projection-type picture display apparatus comprising:  
         [0053]     a light source; a picture display device implemented as a matrix of pixels for modulating the intensity of a light generated by the light source; and a projection optical means for projecting a picture appearing on the picture display device. A Fresnel lens sheet placed on an emission side of the picture display device; a first configuration element having: lenticular lenses provided on an incidence side of a light passing through the Fresnel lens sheet; and light absorbing layers; and a second configuration element having a light passing plate fixed on the emission side of the first configuration element. The light absorbing layers are each provided at a place in close proximity to the focal point of one of the lenticular lenses and are separated from each other by a predetermined distance for forming the light passing unit; and a pitch of the light passing units is made smaller than a pitch of pixels projected and enlarged on a screen from the picture generated by the picture display device.  
         [0054]     In a projection-type picture display apparatus according to the third aspect of the present invention, on an emission side of the light passing plate, there is provided a reflection preventing film for preventing reflection of a visible light.  
         [0055]     In a projection-type picture display apparatus according to third aspect of the present invention, a light scattering material is mixed inside the light passing plate. As an alternative, a light scattering layer can also be provided between the light passing plate and the first configuration element.  
         [0056]     In a projection-type picture display apparatus according to the third aspect of the present invention, Fresnel lenses of the Fresnel lens sheet are laid out at a pitch Fp; the light passing units are laid out in a horizontal direction of the screen at a pitch Lp; and a ratio Lp/Fp of the pitch Lp to the pitch Fp is set at a value in the range 1.588 to 1.649.  
         [0057]     According to a fourth aspect of the present invention, there is provided a projection-type picture display apparatus comprising: a light source; a picture display device implemented as a matrix of pixels each having a means for modulating the intensity of a light generated by the light source; a projection optical means for projecting a displayed image appearing on the picture display device; and a screen used by the projection optical means to project the displayed image as an enlarge picture and provided with: a first configuration element having a plurality of lenticular lenses provided on a light-emission side of the projection optical means and light absorbing layers provided on a light-emission side of the first configuration element, and a light passing second configuration element provided on the light-emission side of the first configuration element. The lenticular lenses have a longitudinal direction coinciding with a screen surface vertical direction and are laid out contiguously in a screen surface horizontal direction; the light absorbing layers are sandwiched by boundaries of any two adjacent openings each provided at a location in close proximity to a focal point of one of the lenticular lenses associated with the opening; the first and second configuration elements are fixed to each other; a pitch of the openings is made smaller than a pitch of pixels projected and enlarged on the screen from the displayed image output by the picture display device; and a pitch of interference lines caused by both interference sources is set at a value about equal to or smaller than the pitch of pixels projected and enlarged on the screen from the displayed image output by the picture display device.  
         [0058]     In the projection-type picture display apparatus according to the fourth aspect of the present invention, an emission surface of the second configuration element is subjected to a reflection preventing process for preventing reflection of a visible light.  
         [0059]     In the projection-type picture display apparatus according to the fourth aspect of the present invention, a light scattering material is mixed inside the second configuration element. As an alternative, a light scattering layer is provided between the second configuration element and the first configuration element.  
         [0060]     In the projection-type picture display apparatus according to the fourth aspect of the present invention, a third configuration element having Fresnel lenses is provided on a light-incidence side of the first configuration element; the Fresnel lenses of the third configuration element are laid out at a lens pitch Fp; the openings of the first configuration element are laid out in a horizontal direction of the screen at a pitch Lp; a ratio Lp/Fp of the lens pitch Lp to the pitch Fp is set at a value in the range 1.588 to 1.649; a pitch Mp 1  of moire lines caused by both interference sources is set at a value smaller than a pitch Iph of pixels projected and enlarged on the screen in a screen horizontal direction from the displayed image output by the picture display device; and a pitch of interference lines caused by the both interference sources_is set at a value about equal to or smaller than a pitch of pixels projected and enlarged on the screen by the picture display device.  
         [0061]     These and other objects, features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0062]      FIG. 1  is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting the conventional single-panel technique employing one liquid-crystal panel;  
         [0063]      FIG. 2  is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting the conventional three-panel technique employing three liquid-crystal panels;  
         [0064]      FIG. 3  is a side-view diagram showing a partial cross section of main components of a rear-projection-type picture display apparatus employing a projection-type optical system;  
         [0065]      FIG. 4  is a side-view diagram showing a partial cross section of main components of another rear-projection-type picture display apparatus employing a projection-type optical system;  
         [0066]      FIG. 5  is a diagram showing a squint view of main components employed in a screen implemented by a first embodiment of the present invention;  
         [0067]      FIG. 6  is a diagram showing a squint view of a screen implemented by a second embodiment of the present invention which corresponds to a cross section B-B 1  shown in  FIG. 5 ;  
         [0068]      FIG. 7  is a diagram showing a squint view of a screen implemented by a third embodiment of the present invention which corresponds to the cross section B-B 1  shown in  FIG. 5 ;  
         [0069]      FIG. 8  is a diagram showing a top view of a lenticular-lens screen to explain a relation between enlarged pixels obtained as a result or projection and enlargement of a picture on a screen used in conjunction with a three-panel technique employing three liquid-crystal panels and the screen itself;  
         [0070]      FIG. 9  is a diagram showing a top view of a lenticular-lens screen to explain a relation between enlarged pixels obtained as a result or projection and enlargement of a picture on the screen used in conjunction with a single panel technique employing one liquid-crystal panel and the screen itself;  
         [0071]      FIG. 10  is a side-view diagram showing a partial cross section of main components of a rear-projection-type picture display apparatus employing a projection-type Braun tube;  
         [0072]      FIG. 11  is a diagram showing a top view of a layout of the rear-projection-type picture display apparatus employing a projection-type Braun tube on a horizontal plane in a simple and plain manner;  
         [0073]      FIG. 12  is a diagram showing a squint view of main components of a conventional screen;  
         [0074]      FIG. 13  is a diagram showing a squint view of main components of another conventional screen;  
         [0075]      FIG. 14  is a diagram showing a partial enlarged cross section of a lenticular lens cut in a direction A-A 1  shown in  FIG. 13 ; and  
         [0076]      FIG. 15  is a diagram showing a partial enlarged cross section of a lenticular lens cut in a direction A-A 1  shown in  FIG. 13 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0077]     Some preferred embodiments of the present invention are described by referring to diagrams as follows.  
         [0078]      FIG. 5  is a diagram showing a squint view of main components employed in a screen implemented by a first embodiment of the present invention. In the figure, reference numerals  77  and  76  denote a screen and a Fresnel lens sheet (a third configuration element) respectively whereas reference numeral  75  denotes a lenticular lens sheet. The Fresnel lens sheet  76  and lenticular lens sheet  75  are joined to each other at their edges which are not shown in the figure. The basic materials of the Fresnel lens sheet  76  and lenticular lens sheet  75  are both an all but transparent thermoplastic resin material. Reference numeral  79  denotes the surface of incidence of an image light of the Fresnel lens sheet  76 . The screen implemented by this embodiment has a shape wherein lenticular lenses  80  with the longitudinal direction thereof coinciding with the screen surface horizontal direction are laid out contiguously in the screen vertical direction. A Fresnel convex lens  78  is provided on the surface of emission of the image light. The Fresnel convex lens  78  is created by a compression formation technique. As an alternative, the Fresnel convex lens  78  can also be created at a much lower cost by stacking layers of UV resin on a thermoplastic resin base material. In addition, in the case of the Fresnel convex lens  78  made of UV resin, only one die serving as a master is required. Even if the pitch of the Fresnel convex lens  78  is made finer, there will be no increase in cost. Thus, practically, fine fabrication resulting in a pitch in the range 120 microns to 60 microns is possible. Reference numeral  74  denotes a lenticular lens provided on the incidence surface of a first configuration element  73  in a configuration wherein the lenticular lenses  74  with the longitudinal direction thereof coinciding with the screen surface vertical direction are laid out contiguously in the screen horizontal direction. A light passing window  81  for letting an image beam pass through is provided at a location in close proximity to the focus of each of the lenticular lenses  74 . In addition, a light absorbing layer  72  is provided between any adjacent two of the light passing windows  81  to prevent the contrast performance from deteriorating due to an effect of an external light. In this embodiment, the lenticular lenses  74  are provided on the incidence surface of the first configuration element  73  whereas the light passing windows  81  and the light absorbing layers  72  are provided on the emission surface of the first configuration element  73 . A second configuration element  71  is implemented by a light passing plate  91 .  
         [0079]     By the way, the optical-axis-direction thickness of the first configuration element  73  is about 1.5 times the lens pitch in the case of an elliptical lens shape. Even if a non-spherical surface is used and the focal point is shifted, the thickness is about 5 times the lens pitch. For this reason, if the lens pitch is reduced, the thickness is also decreased, resulting in a small strength. In order to solve this problem, in this embodiment, the first configuration element  73  is bound or stuck to the second configuration element  71  to give a strength that does not cause a problem in the practical use. It should be noted that, from the cost point of view, the second configuration element  71  is normally made of thermoplastic resin. In the case of a screen with a diagonal of 50 inches, a thickness of at least 1 inch gives a strength that does not cause a problem in the practical use. In this case, an air boundary surface between the first configuration element  73  and a second configuration element  71  disappears, allowing the reduction in contrast due to an unnecessary reflected light to be reduced. The screen can be made better by providing a reflection preventing film  70  on the observation-side surface of the second configuration element  71 . In such a configuration, the degree of deterioration of the picture quality due to reflection of an external light can be lowered. For example, if for example a special low-reflection film made by NIPPON OIL AND FATS CO., LTD. (product name:ReaLook) is used as the reflection preventing film  70  bound or stick to the observation-side surface of the second configuration element  71 , in the visible wavelength region, the reflectance is reduced to a value not exceeding 1%. As a result, it is possible to substantially lower the degree of deterioration of the picture quality due to inadvertent inclusion of an external light.  
         [0080]     The embodiment implementing a screen provided by the present invention has been described so far. It should be noted that the surface of incidence of an image light of the Fresnel lens sheet  76  can be fabricated into a plane surface or a mat surface. As an alternative, the incidence surface can be subjected to another fabrication technique.  
         [0081]      FIG. 6  is a diagram showing a squint view of a screen implemented by a second embodiment of the present invention which corresponds to a cross section B-B 1  shown in  FIG. 5  and  FIG. 7  is a diagram showing a squint view of a screen implemented by a third embodiment of the present invention which corresponds to the cross section B-B 1 . Components of the screens of  FIGS. 5, 6  and  7  denoted by the same reference numeral are identical components.  
         [0082]     In the screen shown in  FIG. 6 , an image light  81  entering the surface  79  on the image-source side (or the incidence surface  79 ) of the Fresnel lens sheet  76  is converted into all but parallel lights by the lens effect of the Fresnel convex lens  78 . The parallel lights then hit the lenticular lens  74  provided on the incidence light of the lenticular lens sheet  75 . Then, due to the lens effect of the lenticular lens  74 , the lights pass through the light passing windows  81  instead of entering the light absorbing layers  72 . A scattering layer  89  including a scattering material  82  is provided between the first configuration element  73  and the second configuration element  71 . The scattering layer  89  is bound or stuck firmly to the first configuration element  73  and the second configuration element  71 . The scattering layer  89  contributes to some of scattering of the image beam in the vertical and horizontal directions of the screen. The image beam scattered by the scattering layer  89  travels through the second configuration element  71  toward the observation side and then passes through the reflection preventing film  70  before being emitted to the observation side.  
         [0083]     In the embodiment shown in  FIG. 7 , the scattering layer  89  shown in  FIG. 6  is not employed. The embodiment shown in  FIG. 7  has the same configuration as that of  FIG. 6  except that a scattering material  82  is introduced in the second configuration element  71  over the entire surface of the light passing plate  91 .  
         [0084]     By configuring the screen  77  as described above, it is possible to substantially reduce the deterioration in picture quality due to inadvertent inclusion of an external light. In addition, even if the pitch of the lenticular lens  74  employed in the first configuration element  73  is reduced, the strength of the screen can be sustained at a sufficient value. The screen can thus adopt fine pitches. As a result, the possibility of the horizontal resolution&#39;s becoming poorer is lowered.  
         [0085]     Next, a means for solving the moire problem is explained.  
         [0086]     The following description explains a technology for reducing moires which are generated in a case where an optical device having a matrix structure is employed in the optical system of the projection-type picture display apparatus as a picture generating source. It is needless to say that the technology exhibits the same effect for other devices such as the digital micromirror device used as a picture generating source.  
         [0087]      FIG. 8  is a diagram showing a top view of a lenticular-lens screen to explain a relation between enlarged pixels obtained as a result or projection and enlargement of a picture on the screen used in conjunction with a three-panel technique employing three liquid-crystal panels and the screen itself. In order to make the description simple, the explanation of the Fresnel lens is omitted.  
         [0088]     In actuality, there is no case in which pixels on any one of the three liquid-crystal panels all overlap those on the other panels. Also in order to make the description simple, however, pixels on any one of the three liquid-crystal panels are assumed to all overlap those on the other panels.  
         [0089]     Reference numeral  72  denotes a light absorbing layer provided on the first configuration element  73  employed in the lenticular sheet which is shown by a line. Reference numeral  83  denotes the liquid-crystal panel&#39;s light shielding area hatched with slanting lines. Reference numeral  84  denotes the liquid-crystal panel&#39;s pixel (an effective area) not hatched with slanting lines. The drawing as well as the explanation of the Fresnel lens are omitted.  
         [0090]     The historical development of the screen is long. A technique to reduce moires generated by the Fresnel and lenticular lenses is disclosed in Japanese Examined Patent Publication No. Hei 3-72972. According to this conventional technique, the ratio of the pitch Lp of the lenticular lens to the pitch Fp of the Fresnel lens is set at the following value: 
 
 Lp/Fp=N+α 
 
         [0091]     where the symbol N denotes a natural number in the range 1 to 12 and the symbol a denotes a constant having a value in the range 0.35 to 0.43.  
         [0092]     In addition, according to Japanese Examined Patent Publication No. Hei 5-63781, 
 
 Lp/Fp= 5.525 to 5.682 or 6.472 to 6.645 
 
         [0093]     Furthermore, in Japanese Examined Patent Publication No. Hei 7-117818, the following ratio is disclosed: 
 
 Lp/Fp=N+ 0.5 
 
         [0094]     where the symbol N is a natural number.  
         [0095]     However, these technologies are developed for a case in which a Braun tube is used as a picture displaying source. For an optical device having a structure comprising pixels laid out to form a matrix, none are disclosed.  
         [0096]     In the embodiment shown in  FIG. 8 , the vertical and horizontal dimensions of a liquid-crystal pixel are denoted by notations H and W respectively whereas the vertical and horizontal dimensions of an effective area of the liquid-crystal pixel are denoted by notations HA and WA respectively. Let Iph and Ipv denote the pixel pitch in the horizontal direction and the pixel pitch in the vertical direction respectively whereas Fp and Lp respectively denote the pitch of the Fresnel lens  76  shown in  FIGS. 6 and 7  and the pitch of the light absorbing layer  72 , that is the light passing window  81  provided on the first configuration element  73  employed in the lenticular lens sheet  75  as shown in  FIGS. 6 and 7 . A moire pitch caused by the pitch Lp of the light absorbing layer  72  and the pitch Fp of the Fresnel lens  78  is denoted by notation Mp 1  or, to be more specific, Mp 1   h  in the horizontal direction and Mp 1   v  in the vertical direction. On the other hand, a moire pitch caused by the pitch Lp and the pitch Ip (with the pitches Iph and Ipv in horizontal and vertical directions respectively taken into consideration) of an enlarged pixel is denoted by notation Mp 2  or, to be more specific, Mp 2   h  in the horizontal direction and Mp 2   v  in the vertical direction. A moire pitch caused by the pitches Mp 1  and Ip is denoted by notation Mp 3  or, to be more specific, Mp 3   h  in the horizontal direction and Mp 3   v  in the vertical direction. First of all, a range with few generated moires was found by computation. In the case of the actual apparatus, an optimum condition was found with a projection size or the projection magnification of the pixel used as a parameter on the basis of a Fresnel lens sheet with a fine pitch and a lenticular sheet with a fine pitch which can be obtained at the present point of time, and a prototype was then built for verification purposes.  
         [0097]     A moire frequency Fm (k, 1) expressed in terms of cycles/mm was computed by using the following approximation formula. 
 
 Fm ( k,  1)= k/Fp− 1 /Lp  
 
         [0098]     where notation k denotes the Fresnel harmonic order.  
         [0099]     In this case, a positive polarity of Fm indicates generated elliptical moires whereas a negative polarity of Fm indicates generated hyperbolic moires.  
         [0100]     Data of an optical system completing a verification experiment is given as follows.  
                                                                                         TABLE 1                       (Item)   (Performance)                                Lenticular lens sheet   Pitch 0.155   mm            Fresnel lens sheet   Parameter            Conjugate point (52.5-inch projection)   690   mm       (40.3-inch projection)   530   mm       Projected-pixel horizontal-direction pitch:   1.334   mm       (52.5-inch projection)       Projected-pixel horizontal-direction pitch:   1.024   mm       (40.3-inch projection)       Projected-pixel vertical-direction pitch:   1.0005   mm       (52.5-inch projection)       Projected-pixel vertical-direction pitch:   0.768   mm       (40.3-inch projection)            Pixel count (dot)   800 (horizontal)   600 (vertical)            Projection lens   F value   1.5           Half picture angle   44 degrees                  
 
         [0101]     Moires generated in the horizontal direction were calculated and evaluated for a 40.3-inch projection. The moire pitch Mp 1   h  caused by the pitch Lp of the light absorbing layer  72  and the pitch Fp of the Fresnel lens  78  was changed over the range 1.55 to 1.65 with the pitch Fp of the Fresnel lens  78  taken as a parameter and evaluation was made at intervals of 0.025. The results of the calculation and the evaluation set the moire pitch Mp 3   h  caused by the pitch Mp 1   h  and the pixel Iph in the horizontal direction at a value of about 1.02 mm for a 40.3-inch projection. The value of 1.02 mm is about equal to the pixel pitch Iph in the horizontal direction on the screen. This combination was verified by using an actual machine to find out that almost no moires were generated to cause a problem in the practical use such as substantial deterioration of the picture quality. At that time, if the moire pitch Mp 1   h  caused by the pitch Lp of the light absorbing layer  72  and the pitch Fp of the Fresnel lens  78  had a value in the range 1.575 to 1.625, the fact that a good performance was obtained was confirmed by using the actual machine. At that time, values of the Fresnel pitch were 0.0984 mm, 0.0969 mm and 0.0954 mm. In addition, since the ratio (Ipv/Fp) of the pixel pitch Ipv in the vertical direction to the pitch Fp of the Fresnel lens is close to 4, almost no moires were recognized by virtue of an optical scattering effect of the scattering layer  89  employed in the lenticular lens sheet  75 .  
         [0102]     By the same token, moires generated in the horizontal direction were calculated and evaluated for a 52.5-inch projection. The moire pitch Mp 1   h  caused by the pitch Lp of the light absorbing layer  72  and the pitch Fp of the Fresnel lens  78  was changed, being set at values of 1.55, 1.558, 1.600 and 1.649 with the pitch Fp of the Fresnel lens  78  taken as a parameter, and evaluation was made. The results of the calculation and the evaluation set the moire pitch Mp 3   h  caused by the pitch Mp 1   h  and the pixel Iph in the horizontal direction at a value of about 1.334 mm for a 52.5-inch projection. The value of 1.334 mm is about equal to the pixel pitch Iph in the horizontal direction on the screen. This combination was verified by using an actual machine to find out that almost no moires were generated to cause a problem in the practical use such as substantial deterioration of the picture quality. At that time, if the moire pitch Mp 1   h  caused by the pitch Lp of the light absorbing layer  72  and the pitch Fp of the Fresnel lens  78  had a value in the range 1.558 to 1.649, the fact that a good performance was obtained was confirmed by using the actual machine. At that time, the Fresnel pitch was 0.0995 mm, 0.0969 mm and 0.0940 mm. In addition, since the ratio (Ipv/Fp) of the pixel pitch Ipv in the vertical direction to the pitch Fp of the Fresnel lens is close to 4, almost no moires were recognized by virtue of an optical scattering effect of the scattering layer  89  (the second configuration element  71  with the scattering material  82  mixed therein) employed in the lenticular lens sheet  75 .  
         [0103]     As described above, it is necessary to reduce moires generated by the horizontal-direction component Iph and the vertical-direction component Ipv of the pitch Ip of enlarged pixels, the pitch of the lenticular lens  74  and the pitch Fp of the Fresnel lens  78 . This is because such moires cause the picture quality to deteriorate substantially over the entire projection area of the screen when a source picture appearing on a device comprising pixels laid out to form a matrix is projected on the screen as an enlarged picture by using a projection lens. In order to reduce such moires it is thus necessary to set the ratio (Lp/Fp) of the pitch Lp of the light absorbing layer  72  provided on the first configuration element  73  employed in the lenticular lens sheet  75  to the pitch Fp of the Fresnel lens  78  at a value of about 1.6, as well as to set the moire pitch Mp 1  caused by the pitches Lp and Fp at a value about equal to the horizontal component Iph of the pitch Ip. In addition, it also necessary to set the ratio (Ipv/Fp) the vertical-direction component Ipv of the of the pixel pitch Ip of enlarged pixels to the pitch Fp of the Fresnel lens at a value of at least two.  
         [0104]     Then, the same evaluation was made with the pitch of the Fresnel lens  78  set at 60 microns to verify by using an actual machine that a more excellent performance not recognizing moires of even higher orders could be obtained.  
         [0105]     The above description explains a case in which a picture is projected and enlarged on a screen by using an optical device adopting the three-panel technique utilizing three liquid-crystal panels. In the case of a single-panel system using only one liquid-crystal panel like the one shown in  FIG. 9 , it has been confirmed by using an actual machine that a pixel-trio pitch can be treated to be the same as the pixel pitch of the three-panel technique described above. The pixel-trio pitch is a pitch with 3 pixels treated as a set.  
         [0106]      FIG. 9  is a diagram showing a top view of a lenticular-lens screen to explain a relation between enlarged pixels obtained as a result or projection and enlargement of a picture on the screen used in conjunction with a single panel technique employing one liquid-crystal panel and the screen itself. In the figure, reference numeral  72  denotes a light absorbing layer whereas reference numerals  85 ,  86  and  87  each denote a pixel. The symbol d denotes the width of a blocked-light area of the liquid-crystal panel and the symbol D denotes the width of an effective area of the liquid-crystal panel.  
         [0107]     By employing a screen with a configuration described above in a projection-type picture display apparatus for projecting an image appearing on an optical device such as a liquid-crystal panel or a DMD (Digital Micromirror Device) with a structure comprising pixels laid out to form a matrix on the screen as an enlarged picture by using a projection lens, inadvertent inclusion of an external light can be reduced so that the contrast deterioration can be decreased and, at the same time, the resolution degradation can be made smaller while the deterioration of the picture quality can also be lessened so that, as a result, it is possible to implement a good performance.  
         [0108]     The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive. That is, the scope of the present invention is indicated by the appended claims rather than by the foregoing description. In addition, all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.