Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B21/00—Projectors or projection-type viewers; Accessories therefor
  • G03B21/54—Accessories
  • G03B21/56—Projection screens
  • G03B21/567—Projection screens for colour projection
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/32—Holograms used as optical elements
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B21/00—Projectors or projection-type viewers; Accessories therefor
  • G03B21/54—Accessories
  • G03B21/56—Projection screens
  • G03B21/60—Projection screens characterised by the nature of the surface
  • G03B21/62—Translucent screens
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]

Definitions

• This invention relates projection television receivers, and in particular to a projection television screen providing significantly reduced color shift, significantly reduced cabinet depth and a high proportionate exclusion of incident light at an angle of incidence differing from normal to the screen by an angle greater than a predetermined m aximum angle of incidence.
• Background Information Color shift is defined as the change in the red/ blue or green/ blue ratio of a white image formed at the center of a projection screen by projected images from red, green and blue projection tubes, when viewed at different angles in the horizontal plane, by observations made at the peak brightness vertical viewing angle .
• the color shift problem is caused by the need for at least three image projectors for respective images of different colors, for example, red, blue and green.
• a projection screen receives images from the at least three projectors on a first side and displays the images on a second side with controlled light dispersion of all the displayed images.
• One of the projectors usually green and usually in the center of an array of projectors, has a first optical path in a substantially orthogonal orientation with the screen .
• At least two of the projectors, usually red and blue and usually positioned on 2 opposite sides of the central green projector in the array have respective optical paths converging toward the first optical path in a non orthogonal orientation defining angles of incidence.
• Golor shift results from the non orthogonal relationship of the red and blue projectors, relative to the screen and to the green projector .
• color tones may differ at every position on the screen .
• the condition in which the color tone difference is large is often referred to as poor white uniformity .
• Color shift is denoted by a scale of numbers, in which lower numbers indicate less color shift and better white uniformity .
• values for the red, green and blue luminance are measured at the screen center from a variety of horizontal viewing angles, typically from at least about -40° to +40°, to as much as about -60° to +60°, in 5 ° or 10° increments.
• the positive and negative angles represent horizontal viewing angles to the right and left of screen center, respectively . These measurements are taken at the peak vertical viewing angle.
• the red, green and blue data is normalized to unity at 0°.
• equations (I) and (II) are evaluated at each angle:
• Screens for projection television receivers are generally manufactured by an extrusion process utilizing one or more patterned rollers to shape the surface of a thermoplastic sheet material.
• the configuration is generally an array of lenticular elements, also referred to as lenticules and lenslets.
• the lenticular elements may be formed on one or both sides of the same sheet material or on one side only of different sheets which can then be permanently combined as a laminated unit or otherwise mounted adjacent to one another so as to function as a laminated unit.
• one of the surfaces of the screen is configured as a Fresnel lens to provide light diffusion .
• Prior art efforts to reduce color shift and improve white uniformity have focused exclusively on two aspects of the screen.
• One aspect is the shape and disposition of the lenticular elements.
• the other aspect is the extent to which the screen material, or portions thereof, are doped with light 4 diffusing particles to control light diffusion .
• a projection screen includes a light-transmitting lenticular sheet having an input surface and an exit surface.
• the input surface is characterized by horizontally diffusing lenticular profiles having a ratio of a lenticulated depth Xv to a close-axis-curvature radius Rl (Xv/ Rl ) which is within the range of 0.5 to 1 .8.
• the profiles are elongated along the optical axis and form a spherical input lenticular lenses.
• the use of a screen with a double sided lenticular lens is common .
• Such a screen has cylindrical entrance lenticular elements on an entrance surface of the screen, cylindrical lenticular elements formed on an exit surface of the screen and a light absorbing layer formed at the light non convergent part of the exit surface.
• the entrance and the exit lenticular elements each have the shape of a circle, ellipse or hyperbola represented by the following equation (HI):
• the lenslets have a curve to which a term with a higher order than 2nd order has been added .
• a plurality of entrance lenses comprise a cylindrical lens.
• the exit lens is formed of a plurality of exit lens layers, each having a lens surface at the light convergent point of each lens of the entrance lens layer, or in the vicinity thereof.
• a light absorbing layer is also formed at the light non convergent part of the exit lens layer.
• angle ⁇ The angle of incidence defined by the geometric arrangement of the image projectors, referred to as angle ⁇ herein, has generally been limited to the range of greater than 0° and less than or equal to about 10° or 1 1 °.
• the size of the image projectors makes angles of ⁇ close to 0° essentially impossible.
• the best color shift performance which has been achieved is about 5 , as determined in accordance with equations (I) and (II).
• the best color shift performance 7 which has been achieved is not commercially acceptable.
• Polaroid Corporation sells a photo polymer designated DMP- 128®, which Polaroid C rporation can manufacture as a three dimensional hologram, using proprietary processes.
• the holographic manufacturing process is described, in part, in US 5,576,853.
• a three dimensional holographic screen for a projection television was proposed by Polaroid Corporation, as one of many suggestions made during efforts to establish a market for the DMP-128® photo polymer holographic product.
• the proposal was based on advantages which Polaroid Corporation expected in terms of higher brightness and resolution, lower manufacturing cost, lower weight, and resistance to the abrasion to which two-piece screens are subjected during shipping.
• Polaroid Corporation never proposed any particular holographic configuration for the volume holographic elements which might make up such a holographic projection television screen, and never even considered the problem of color 8 shift in projection television screens of any type, holographic or otherwise .
• a projection television receiver in accordance with the inventive arrangements taught herein provides such a significant improvement in color shift performance, measured in orders of magnitude, that a color shift of 2 or less can be achieved with projection television receivers having angles of incidence ⁇ in the range of less than 10° or 1 1 °. Moreover, the color shift performance is so significant that commercially acceptable projection television receivers having angles of incidence up to about 30° can be provided, in much smaller cabinets.
• the color shift performance of 9 such large ⁇ angle receivers is at least as good as conventional small ⁇ angle receivers, for example having a color shift of 5 , and can be expected to approach or even reach values as low as about 2, as in the small ⁇ angle receivers.
• ⁇ projection television receiver in accordance with an inventive arrangement has a screen formed by a three dimensional hologram formed on a substrate, for example, a polyethylene film , such as Mylar®.
• a three dimensional holographic screen was originally developed for its expected advantages in term s of higher brightness and resolution, and lower manufacturing cost, lower weight and resistance to abrasion to which two-piece screens are subjected, for example during shipping.
• the discovery of the color shift performance of the three dimensional holographic screen came about when testing to determine if the optical properties of the three dimensional screen would be at least as good as a conventional screen .
• the color shift performance of the three dimensional holographic screen, as measured by equations (I) and (II) was so unexpectedly low as to be shocking.
• the barriers which limited prior art improvements to incremental steps had been eliminated altogether.
• smaller cabinets with projection geometry characterized by larger ⁇ angles of incidence can now be developed .
• a projection television having the unexpected properties associated with three dimensional holographic screens, and in accordance with the inventive arrangements taught herein, 1 0 comprises : at least three im age projectors for respective images of different colors; a projection screen formed by a three dimensional hologram disposed on a substrate, the screen receiving im ages from the projectors on a first side and displaying the images on a second side with controlled light dispersion of all the displayed images; one of the projectors having a first optical path in a substantially orthogonal orientation with the screen and at least two of the projectors having respective optical paths converging toward the first optical path in a non orthogonal orientation defining angles of incidence ; and, the three dimensional hologram representing a three dimensional diffraction array having a configuration effective for reducing color shift in the displayed im ages, the screen having a color shift less than or equal to approximately 5 for all the angles of incidence in a range greater than 0° and less than or equal to approximately 30°, as determined by the maximum value obtained from at least
• Q ⁇ is the color shift at angle ⁇
• red( ⁇ ) is the red luminance level at angle ⁇
• blue( ⁇ ) is the blue luminance level at angle ⁇
• green( ⁇ ) is the green luminance level at angle ⁇ .
• the color shift of the screen can be expected to be less than 5 , for example, less than or equal to 1 1 approximately 4 , 3 or even 2.
• the color shift of the screen is less than or equal to approximately 2 for all the angles of incidence in a first subrange of angles of incidence greater than 0° and less than or equal to approximately 10°; and, the color shift of the screen is less than or equal to approximately 5 for all the angles of incidence in a second subrange of angles of incidence greater than approximately 10° and less than or equal to approximately 30°.
• the screen further comprises a light transmissive reinforcing member, for example, of an acrylic material in a layer having a thickness in the range of approximately 2 - 4 mm .
• the substrate comprises a highly durable, transparent, water-repellent film , such as a polyethylene terephthalate resin film .
• the substrate can be a film having a thickness in the range of about 1 - 10 mils. A thickness of about 7 mils has been found to provide adequate support for the three dimensional hologram. The thickness of the film is not related to performance.
• the three dimensional hologram has a thickness in the range of not more than approximately 20 microns.
• the projection television also comprises one or more mirrors between the image projectors and the screen so as to reflect the desired light from the lens onto the screen, but does not require the inclusion of light baffles to exclude the direct "line of sight" light transmission from the lens to the screen .
• a projection television is provided 1 2 comprising at least three image projectors for projecting respective im ages of different colors wherein the image projectors output a quantity of scattered light that is incident upon at least a portion of a projection screen .
• the projection screen is formed by a three dimensional hologram disposed on a substrate and representing a three dimensional diffraction pattern or interference array. The screen receives images from the projectors on a first side and displays the im ages on a second side with controlled light dispersion of all the displayed images.
• the screen selectively excludes the quantity of scattered light.
• FIGURE 1 is a diagrammatic representation of a projection television in accordance with the inventive arrangements taught herein.
• FIGURE 2 is a simplified diagram of projection television geometry useful for explaining the inventive arrangements.
• FIGURE 3 is a side elevation of a reinforced projection screen according to the inventive arrangements.
• FIGURE 4 is a graphical representation of the vertical light exclusion properties of the present invention.
• FIGURE 5 is a graphical representation of the horizontal light exclusion properties of the present invention .
• FIGURE 6 is a schematic representation of the testing fixture used to obtain the data displayed in FIGURES 4 and 5. 1 3 DESCRIPTION OF THE PREFERRED EMBODIMENTS
• a projection television receiver 10 is illustrated in FIGURE 1 .
• An array 12 of projection cathode ray tubes 14, 16 and 18 provide red, green and blue im ages respectively.
• the cathode ray tubes are provided with respective lenses 15 , 17 and 19 that are adapted to project their respective signals onto projection screen 22.
• the projected images are reflected by a mirror 20 onto a projection screen 22. Additional mirrors can also be utilized, depending on the particular geometry of the optical paths.
• the green cathode ray tube 16 projects the green image along an optical path 32 , which is orthogonal to screen 22 (i.e., at right angles to the screen).
• the red and blue cathode ray tubes have respective optical paths 34 and 36, which converge toward the first optical path 32 in a non orthogonal orientation defining angles of incidence ⁇ .
• the screen 22 comprises a three dimensional hologram 26 disposed on a substrate 24.
• the screen receives images from the projectors on a first, entrance surface side 28 and displays the images on a second, exit surface side 30, with controlled light dispersion of all the displayed images.
• screen 22 comprises different optical symmetry properties than the conventional screens disclosed 1 4 hereinabove. More particularly, the optical symmetry is nearly perfect, i.e., optical properties of screen 22 are identical, regardless of the screen's physical orientation (e.g., horizontal or vertical).
• Holographic screens of the type contemplated for use with the present invention typically exhibit highly elliptical optical properties, i.e., higher transmissive properties along one axis (e.g., major) and lower transmissive properties along another axis (e.g., minor).
• a conventional screen i.e., those prior art screens comprising lenticular lenses and the like
• the relevant optical properties are multi- stepped, and therefore, not symmetric.
• holographic screen 22 is very elliptical, outputting light in a narrow vertical envelope. In other words, it will only accept light that is incident on its surface at a very narrow range of vertical angles. As a result, stray scattered or reflected light, that is incident on screen 22 outside of a few degrees of the vertical nominal, is not transmitted by screen 22, thus improving the overall image contrast.
• FIGURES 4 and 5 The vertical and horizontal exclusion properties of the invention are graphically shown in FIGURES 4 and 5.
• the data used to create the graphs of FIGURES 4 and 5 were collected using the test setup 25 shown in FIGURE 6.
• the screen assembly 30 is adapted to be rotated about one of its vertical sides 1 5 (FIGURE 6). Thus, the screen receives green light from different angles ⁇ as the screen assembly is rotated .
• Light sensor 29 is kept normal to screen 22 so that, at screen center, the percent transmission of the light incident at the measured incidence angle may be recorded.
• measurements were made with the holographic diffusion screen in the vertical (90 degree rotated) position so as to simulate the diminution of light directly from PTV lens 15 , 17 , 19.
• Theta Green Theta Green.
• FIGURES 4 and 5 show the level of exclusion of input light in the vertical and horizontal directions.
• the vertical holographic effect excludes input light at any but the intended input angles, e.g., 50% at about 2.5 degrees, 90% at about 7 degrees, and essentially zero beyond 20 degrees.
• the horizontal holographic effect excludes the 1 6 input 50%at about 18 degrees and 90%at about 45 degrees.
• a direct image of the lens is visible from the exit surface side 30 of the screen in a conventional PTV.
• the direct image of the lens is also visible through the holographic screen .
• screen 22 is placed in its normal orientation, the direct image of lens 15 , 17 , 19 is missing from exit surface side
• the hologram is blocking the unwanted stray or scattered light that is incident on the screen from steep vertical angles.
• light baffles have been necessary to remove such direct lens im ages from the image.
• the substrate of screen 22 comprises a highly durable, transparent, water-repellent film, such as a polyethylene terephthalate resin film .
• a highly durable, transparent, water-repellent film such as a polyethylene terephthalate resin film .
• a polyethylene terephthalate resin film is available from E I. du Pont de Nemours & Co. under the trademark Mylar®.
• the film substrate has a thickness in the range of about 1 - 10 mils, equivalent to about .001 - .01 inches or about 25.4 - 254 microns.
• a film having a thickness of about 7 mils has been found to provide adequate support for the three dimensional hologram disposed thereon.
• the thickness of the film does not affect screen performance in general or color shift performance in particular, and films of different thickness may be utilized.
• the three dimensional hologram 26 has a thickness of not more than approximately 20 microns.
• Three dimensional holographic screens are available from at 1 7 least two sources.
• Polaroid Corporation utilizes a proprietary , wet chemical process to form three dimensional holograms in its
• a preferred embodiment of the three dimensional holographic screens used in the projection television receivers described and claimed herein were manufactured by the Polaroid Corporation wet chemical process, in accordance with the following performance specifications:
• Horizontal half viewing angle 38° ⁇ 3°
• Vertical half viewing angle 10° ⁇ 1 °
• Color shift ⁇ 3 , where the horizontal and vertical viewing angles are measured conventionally, screen gain is the quotient of light intensity directed from the source toward the rear of the viewing surface, and light intensity from the front of the viewing surface toward the viewer, measured orthogonal to the screen, and color shift is measured as described above.
• FIGURE 2 is a simplified projection television diagram , omitting the mirror and lenses, for explaining color shift performance .
• the optical axes 34 and 36 of the red and blue cathode ray tubes 14 and 1 8 are aligned symmetrically at angles of incidence ⁇ with respect to the optical axis 32 of the green cathode 1 8 ray tube 16.
• the minimum depth D of a cabinet is determined by the distance between the screen 22 and the rear edges of the cathode ray tubes. It will be appreciated that as the angle ⁇ becomes smaller, the cathode tubes move closer together, and must be spaced further from the screen to avoid hitting one another. At a sufficiently small angle ⁇ , such interference cannot be avoided . This undesirably increases the minimum depth D of a cabinet.
• the cathode ray tubes can be moved closer to the screen 22 , reducing the minimum depth D of a cabinet.
• two horizontal half viewing angles are designated - ⁇ and + ⁇ . Together, a total horizontal viewing angle of 2 , ⁇ is defined .
• the half viewing angles may typically range from ⁇ 40° to ⁇ 60°. Within each half angle are a plurality of specific angles ⁇ , at which color shift can be measured and determined, in accordance with equations (I) and (II) explained above.
• the color shift of the three dimensional holographic screen is less than or equal to approximately 2 for all the angles of incidence in a first subrange of angles of incidence greater than 0° and less than or equal to approximately 10°; and, the color shift of the screen is less than or equal to approximately 5 for all the angles of incidence in a second subrange of angles of incidence greater than approximately 10° and less than or equal to approximately 30°. It is expected that a color shift of less than or equal to approximately 2 , 1 9 as in the first subrange, can also be achieved in the second subrange of larger angles of incidence.
• the substrate 24 comprises a transparent film , such as Mylar®, as described above.
• the photo polymer material from which the three dimensional hologram 26 is formed is supported on the film layer 24.
• a suitable photo polymer material is DMP- 128®.
• the screen 22 may further comprise a light transmissive reinforcing member 38 , for example, of an acrylic material, such as polymethylmethacrylate (PMMA). Polycarbonate materials can also be used .
• the reinforcing member 38 is presently a layer having a thickness in the range of approximately 2 - 4 mm .
• the screen 22 and the reinforcing member are adhered to one another throughout the mutual boundary 40 of the holographic layer 26 and the reinforcing member 38. Adhesive, radiation and/ or thermal bonding techniques may be utilized.
• the surface 42 of the reinforcing layer may also be treated, for example by one or more of the following: tinting, an ti- glare coatings and anti-scratch coatings.
• Various surfaces of the screen and/ or its constituent layers may be provided with other optical lenses or lenticular arrays to control aspects of the projection screen bearing on performance characteristics other than color shift performance, as is known to do with conventional projection screens, without impairing the improved color shift performance of the three dimensional holographic projection screen .

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• 1998
  • 1998-01-29 EP EP98903795A patent/EP1051855A1/de not_active Withdrawn
  • 1998-01-29 WO PCT/US1998/001627 patent/WO1999039511A1/en not_active Application Discontinuation
  • 1998-01-29 JP JP2000529843A patent/JP2002502197A/ja not_active Withdrawn
  • 1998-01-29 CN CN98813391A patent/CN1284235A/zh active Pending
  • 1998-01-29 KR KR1020007008335A patent/KR20010040479A/ko not_active Application Discontinuation
  • 1998-01-29 AU AU60471/98A patent/AU6047198A/en not_active Abandoned

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