Projection display screen that is light-reflective responsive to intensity of incident projected light

A projection display screen that can electrically alter the reflectivity of a region of the projection display screen in response to the intensity of incident projected light that is applied at the region.

FIELD OF THE INVENTION

The invention generally pertains to displays, and more specifically to projection display screens.

BACKGROUND

Projection display screens are categorized as front projection display screens and rear projection display screens (depending on the direction that the incident projected light is projected upon the projection display screen). Conventional projection display screens find it difficult to provide realistic black levels in that regions of the screen that should appear black to a user do not. Poor black levels also result in insufficient contrast between regions of the screen that should appear black and other regions of the screen.

One cause of the poor black level is that conventional front projection display screens typically are colored white to be able to reflect the incident projected light of many colors other than black. Incident projected light of any color other than black relies on the white background to make the color that is reflected off the screen and is directed to the user correspond to the color of the incident projected light. Regions of the projection display screen at which no incident projected light is directed (or a low intensity of projected light is directed) appear black. If sufficient ambient light is applied to a region of the projection display screen that should appear as black, the white screen reflects the color of the ambient light to the user, thereby producing unrealistic, poor, and/or washed out black levels. When these washed out black levels appear alongside regions that are receiving higher intensity light, a poor contrast between these adjacent regions occur with the washed out black portions appearing especially washed out.

It is therefore desirable to improve the reflective appearances of projection display screens.

The same numbers are used throughout the document to reference like components and/or features.

DETAILED DESCRIPTION

One schematic diagram of an exemplary embodiment of a projection display apparatus100is shown inFIG. 1. The projection display apparatus100includes a projection display screen102and a light projection portion104. The light projection portion104applies an incident projected light108at a region110on the projected display screen102. Considering many projection display system environments, an ambient light source106may be positioned nearby to provide ambient light (e.g., room light) to the user. As such, the projection display screen102is configured to display a realistic image even when it is receiving ambient light in combination with the incident display light on the projection display screen102.

A variety of colors and intensities of light are projected at regions forming the different embodiments of the projection display screen to electronically alter the regions of the screen to a different reflectivity, and make the screen display the desired image within the selected color for that display.

This disclosure provides a mechanism that improves the black levels that result when no light (or light of a sufficiently low level) is projected on the projected display screen for those regions110that are intended to appear black to a user. Within this disclosure, a “low intensity light” relates to light having little or low intensity (or combination of multiple low intensity lights) as perceived by a user of the projection display screen. By comparison, when a particular color is projected at a particular region of the projection display screen, that region assumes the color of the projected color. Any region of the projection display screen that of a given bandwidth (or a combination of bandwidths) that does not appear to the user as low intensity (black) is considered as receiving a high intensity light.

This disclosure provides a mechanism by which a region110of the projection display screen102is in a high reflectivity or a low reflectivity state based on whether high intensity light or low intensity light is applied to that region of the projection display screen102. The transition of the region between its high reflectivity state and its low reflectivity state occurs at a particular intensity threshold value. Low reflectivity regions110reflect little or no ambient or incident projected light, and result when little or no light (or little intensity of a combination of colors of light) is applied to the projection display screen. High reflectivity areas reflect a larger percentage of the ambient of incident projected light.

High intensity projected light is made of one, or a combination of, the primary colors. A region receiving high intensity incident projected light appears to the user as the color of the incident projected light. As described within this disclosure, the application of high intensity light to a particular region of the projection display screen102will cause the region of the screen to turn to its reflective state, and reflect the color of the high intensity light to the user. In certain embodiments, the high intensity light can also include invisible (e.g., ultra-violet or infrared) light that is applied to a region110of the projection display screen that acts to make that region highly reflective.

In certain embodiments, the “intensity threshold” value is provided for one or more bandwidths, colors, or polarizations of light for each region110. The intensity threshold can be either a set value, or can be adjusted by a user or installer considering the ambient light level to which the projection display screen is exposed. The intensity threshold value represents that level of incident projected light (for a selected bandwidth, color, polarization, etc.) of light at which each region110of the projection display screen transitions between its high reflectivity state to its low reflectivity state. In one embodiment, the intensity threshold value for transitioning from its high reflectivity state to its low reflectivity state may differ from the intensity threshold value for the opposite transition (in another embodiment it is the same). It different embodiments, the regions of the projection display screen can apply the intensity threshold value to a number of colors of bandwidths, or only one bandwidth.

There are a variety of techniques to set the intensity threshold. The intensity threshold value can be set above the highest typical amount of ambient light that each region of the projection display screen will often experience. In certain embodiments, a user or installer can set the intensity threshold value based on a level that appears good during normal viewing. In one embodiment, it is desired to use one or more bandwidth or polarization as the intensity threshold value which represents ambient light that the projection display screen infrequently encounters. As such, the selected bandwidth or polarization is considered as a signature bandwidth or frequency of light that only the light projection portion104(and not any ambient light) is likely to apply to the projection display screen. For example, the intensity threshold value can be applied in the invisible (e.g., infrared or ultraviolet) light spectrum by applying a color wheel to the light emitted from the light projection portion104that includes an invisible color filter as well as a visible light filter. Alternately, the intensity threshold value can respond to light of a particular polarization (having a particular polarization angle and/or frequency) that matches the polarization that is applied by the light projection portion104.

As such, the present disclosure also provides a mechanism to improve contrast in the projection display screen102when a variety of light intensities are applied to the projection display screen102. The regions110of the projection display screen to which a low intensity (or lack) of incident projected light is directed (and therefore appears as black) and the regions110at which a high intensity of incident projected light is directed should appear distinct, and the application of the ambient light to the low intensity regions of the projection display screen will absorb any ambient light directed at the low intensity regions, and will therefore not “wash out” the black. This reducing the wash out of the low intensity regions acts to improve the poor black levels and improve the contrast of the projection display screen102. The concepts of the projection display screen100as described in this disclosure can be applied to a variety of display projection applications such as movie theaters, home video entertainment devices, high definition television, and the like.

In conventional front projection systems, the screen is typically colored white (e.g., has a high reflectivity) to display the color of the incident projected light. The white surface of the conventional projection display screen102allows both the color of the incident projected light and the ambient light to be illuminated on the screen. Poor black level and low contrast in conventional systems result when the dark regions110of the projection display screen102appear black by not receiving higher intensity incident light, but is illuminated by some ambient light to yield what is referred to herein as poor black levels (which represent a common deficiency for projection display screens102). When the areas of the screen that appear black but instead appear as one or more colors due to ambient light, then the display will have low contrast between the low intensity regions110of the screen and the high intensity regions110of the screen.

This disclosure addresses the poor black level and poor contrast situations by using a projection display screen102that electronically alters its reflectivity to the incident projected light at each region110in response to the intensity of the incident projected light applied to that region110. Within this disclosure, the regions110can be arranged in a pixellated format; each region can assume an independent arrangement, or another region format can be selected. It is possible for a number of the regions110to be arranged in a regular or an irregular pattern across the projection display screen.

Within different embodiments of the projection display screen102, the regions110use a variety of techniques to electronically change their surface reflectivity in response to variations in intensity of the incident projected light upon the surface of the projection display screen102.

During normal viewing operations, the high reflectivity regions110appear to a user as the color of the incident light. The low reflectivity state appears black in regions110, and exists in those regions110where low intensity incident projected light is applied to the screen even if ambient light is applied to the region. This low reflectivity in the regions110that receives low intensity light improves the contrast between the regions110of the screen (especially since the low reflectivity regions suppress the reflection of ambient room light).

The regions110within the projection display screen transition between a high reflectivity state and a low reflectivity surface state at video frame rates, and are combined with a simple photoconductor circuit that are sensitive to as large or narrow band of projected incident light as desired considering the applications of the projection display screen as described within this disclosure. In effect, each region110on the projection display screen102remains highly absorbent of light until a sufficiently high intensity of light (of the right color or band of light) impinges on the projection display screen, and then the region110becomes highly reflective to reflect the color of the incident applied light to a viewer.

This disclosure now describes the structure and operation of a variety of projection display screens that reduce the reflectance of regions110of the projection display screen102to low intensity incident projected light. This results in the low intensity regions110becoming less reflective as compared with the reflectance of regions of the screen that receive high intensity light. In this disclosure, incident projected light108is considered that light that is applied from the light projection portion104onto the projection display screen102.

The concepts as described in this disclosure are applied to any projection display screen102that include (but are not limited to) electronic ink (shown as a region110of the screen inFIGS. 2 and 3) such as developed by E Ink Corporation of Cambridge, Mass.; rotatable bi-color minute balls sold under the tradename of SmartPaper™ (shown as a region110of the screen inFIGS. 4 and 5) by Gyricon of Ann Arbor, Mich.; a polarizing layer combined with a liquid crystal layer as described with respect toFIGS. 6 and 7; and a de-wetting mechanism as described with respect toFIGS. 8,9,10, and11.

Each of these embodiments of the projection display screen102act to project light of any desired projected color, bandwidth, and intensity by electronically altering the reflectivity of particular regions110of the projection display screen102in response to the applied incident projected light intensity within a prescribed bandwidth (or combination of bandwidths). Any other embodiment of the projection display screen that performs a similar operation (not limited to intensity threshold of light, spectrum band of light, or polarization of light) is within the intended scope of the present disclosure.

In different embodiments, altering the reflectivity of particular regions110based of a filter (not shown) acts to alter the characteristics of the incident projected light. Such filtering is based on such characteristics of the incident projected light as the intensity of the threshold of the incident projected light, the spectrum band of the incident projected light, or the polarization of the incident projected light. The filter can either filter light that is applied to the photoconductor layer212(e.g., either by placing a filter element in or above the second transparent conductive layer214as shown inFIG. 2); or by alternatively positioning a filter to any layer above the variable surface reflectivity layer204. Positioning a filter above the photoconductor layer212effects the incident projected light to the photoconductor layer that determines the electrical bias produced by the photoconductor layer212that in turn determines whether the variable surface reflectivity layer is in its high reflective state or its low reflective state. Positioning a filter above the variable surface reflectivity layer204determines the characteristics of the light that the variable surface reflectivity layer reflects.

The concepts described herein are applicable to those embodiments of the projection display screen that displays two colors as well as multichromatic projection display screens. Certain embodiments of the projection display screen102include an electrostatic material that automatically change displayed color responsive to applied charge potential or polarity. The structure and operation of different embodiment of the projection display screen102as shown inFIG. 1is now described with respect toFIGS. 2 and 3;FIGS. 4 and 5;FIGS. 6 and 7;FIGS. 8 and 9;FIGS. 10 and 11; andFIG. 12.

In one embodiment as described with respect toFIGS. 2 and 3the projection display screen102includes the following thin film layers that can be fabricated using known processing techniques (such as suitable etching and deposition): a) a back electrode202; b) a variable surface reflectivity layer204that can change its surface reflectivity at specific regions in response to an applied potential (that may be in response to the applying the incident projected light) or by some other mechanism; c) a network of highly conductive metal206(e.g., a high transparency “mesh”) that can be used to conduct electricity from the sides of the projection display screen102to apply an electric potential at the interior of the cells of the projection display screen; d) a thin resistive layer208; e) a first transparent conductive layer210such as Indium Tin Oxide (ITO) that forms a lower layer of a photoconductor layer; f) the photoconductor layer212; and g) a second transparent conductive layer214such as ITO that forms the upper layer of the photoconductor layer212.

The network of highly conductive metal206is formed in a mesh to allow the color of the variable surface reflectivity layer218to be transmitted upwardly to the front of the front projection display screen and thereby be visible to the user. All layers above the variable surface reflective layer204as shown inFIG. 2are light transmissive, and therefore the light reflectivity of the variable surface reflectivity layer204in each region110of the projection display screen102determines whether that region will reflect or absorb light. The network of highly conductive metal206has to be able to apply a varying potential to the variable surface reflectivity layer to change the reflectivity of the variable surface reflector layer as displayed to the front of the projection display screen.

TheFIGS. 2 and 3embodiments of the variable surface reflectivity layer204include electronic ink such as developed by E Ink. The electronic ink is contained within a display region110, and includes black particles215(that may be shaped as spheres, balls, or other shapes) that are colored black (which provides a low reflectivity and high absorption to light) and are suspended in a white reflective fluid216. The mass of the particles can be made roughly equivalent to that of the suspending reflective fluid216such that any electric field applied to the particles will act to displace the particles within the fluid.

All the layers above and including the variable surface reflectivity layer204including the front plane217are optically clear to allow incident projected light to be applied to and/or reflect from the particles. A black (low reflectivity) particle215can be attracted to the front of the variable surface reflectivity layer204(towards the front plane217) or forced towards the back of the variable surface reflectivity layer204(towards the back plane218) based on a polarity applied across the variable surface reflectivity layer204within the region110. If a particular flux is applied to the region110which would result from the application of the low intensity projected light, the black particles215are displaced to adjacent the front plane217as shown inFIG. 2, and the projection display screen102at that region appears black because of the low reflectivity (high absorbance) of the particles.

If an opposed flux is applied to the region110which would result from the application of high intensity projected light, the black particles215are displaced to adjacent the back plane218and the projection display screen102at that region is highly reflective (e.g., appears white) because the high reflectivity of the suspending fluid covers the low reflectivity of the particles. Reducing the reflectivity of the areas of the projection display screen202that are receiving low intensity light assists the display to reduce the black level illumination (with ambient light) in the projection display system. There are several possible designs for a projection display screen102using the rapid response electronic ink (that can be used to improve cost, image quality, etc.).

Conventional projection display screens usually have a continuously white surface to provide a constantly high reflectivity to the incident projected light. When the intensity of the incident projected light is reduced or no incident light is applied (such as occurs in black, or darker, portions of the conventional screens), there is a perceived black level to the projection display screen102for the user. As the ambient light in the room is increased such as occurs when a room becomes brighter, those regions receiving low intensity incident light (e.g., black regions) of conventional systems in the projection display screen102have a greater intensity, and therefore the projected image fades on the projection display screen. The color of these regions of commercially available versions of the projection display screen that receives low intensity light is therefore largely determined by the ambient light that is being applied within the room.

In the embodiment of the projection display screen102as shown inFIGS. 2 and 3, the back electrode202is maintained continuously at +5V potential; while the first transparent conductive (ITO) layer210is initially maintained at +10V; and the second transparent conductive (ITO) layer214is initially held at −10V. It is envisioned that the backplane could be switched off thereby lock the image on the screen and become non-responsive to the projected incident projected light. The particular voltages in the specification are for illustration only, and are not intended to be limiting. When low intensity projected light impinges on the projection display screen102, the photoconductor layer212remains in a high resistance state and the electric field set up across the electronic ink layer between the back electrode (at +5V) and the first transparent conductive layer210(at +10V) results in a low reflectivity (e.g., black) surface being projected to the user through the second transparent conductive layer214since the dark particles are being pulled toward the front plane217.

When incident projected light of a sufficient intensity (at a particular bandwidth, color, polarity, etc., as described above) is applied to the projection display screen102, the electrical resistance of the photoconductor layer212decreases and forms a conductive path between the first transparent conductive layer210and the second transparent conductive layer214. This conductive path between the two conductive layers210and214causes the voltage to drop across the thin resistive layer208, pulling the voltage of the first transparent conductive layer210down from +10V to 0V in the region of the incident projected light. This pulling down of the voltage results in a reversal of the electric field across the variable surface reflectivity (e.g., electronic ink) layer204, and produces a change in the reflectivity of the projection display screen102from low reflectivity (black) to high reflectivity (white).

The operation of the projection display screen102is reversed for example in different embodiments by changing the reflectivity of the suspended particles and the suspending fluid, and by reversing the polarity of the charged particles. The resistivity of the first transparent conductive layer210is configured to be high compared to the highly conductive metal206and the second transparent conductive layer214to provide the necessary voltage pull down to change the reflectivity of the particular region of the projection display screen102.

FIGS. 2 and 3provide the photoconductor layer which is a device responsive to changes in light intensity. When only a low intensity incident projected light is applied to the front of a region of the projection display screen as shown inFIG. 2, the resistance of the photoconductor layer is at its high resistance level, and the voltage of the first transparent conductance layer210is able to be maintained at its high voltage level with respect to the second transparent conductive layer214. By maintaining such a voltage differential between the first transparent conductor layer214to the back electrode (+5 volts) as shown inFIG. 2, the low reflectivity particles215are pulled to the front plane217, and the region of the projection display screen will be in its low reflectivity state.

As a greater intensity of incident projected light is applied to the region of the projection display screen, the electrical resistance of the photoconductor layer212decreases. By decreasing the electrical resistance of the photoconductor layer, the voltage of the first transparent conductive layer is pulled to closer to the voltage of the second transparent conductive layer214(which pulls the first transparent conductive layer212which is 10volts towards 0 volts) inFIG. 3. If the voltage of the first transparent conductive layer210is lower than the back electrode202, then the particles215will be pulled toward the back plane219. In this manner, providing the photoconductive layer with less electrical resistance has the effect of decreasing the reflectivity of those regions of the projection display screen102at which dark light is being applied using electronic ink. Recent developments of electronic ink allow for switching between its high resistanve state to its low resistance state at video frame rates (15 ms) to improve the operation of the projection display apparatus100.

In alternate designs the photoconductor layer212could be replaced with a variety of active thinfilm devices to produce the desired turn off/on characteristics of the projection display screen102when the intensity threshold value of incident projected light is achieved. Another design variation could improve the reflectivity of the projection display screen102by using a single transparent conductive (ITO) layer on the viewing side and making photo-active connections through the variable surface reflectivity layer204to a potential on the backside of the projection display screen102. The particular layers in which the potential is described as being switched are illustrative, and represents a design choice among different embodiments.

FIGS. 4 and 5show another embodiment of projection display screen102that can change its optical reflectivity at each region in response to the intensity of light applied at that region. In theFIGS. 4 and 5embodiment of the projection display screen102, the variable surface reflectivity layer204is filled with a number of bi-color particles402(each color has a different reflectivity such as black and white). One example of the bi-color particles402are minute objects such as balls that are colored half white and half black, with one polarity being associated with each color as developed and made commercially available by Gyricon. The white half of each bi-color particle has greater reflectivity than the white half of the bi-color particle A clear and relatively thin layer of the suspension liquid404is contained within the variable surface reflectivity layer204that suspends the bi-color particles402while permitting free rotation of the particles in their desired direction. As such, when the electric field that is applied across the bi-color particles within the variable surface reflective layer are reversed, the orientation of the white region or the black region of the bi-color particles will be reversed.

When an appropriate potential at an appropriate location is applied, all of the particles402within the variable surface reflective layer will be oriented so their low reflectivity portion is visible (the black half of all of the particles will be visible from the front). When another appropriate potential is applied at an appropriate location, all of the particles402within the variable surface reflective layer will display their high reflective sides (e.g., the white half of all of the particles will be visible from the front).

While the effect of applying a low intensity light to a region of the projection display screen102inFIG. 2will be to force the black particles215within the variable surface reflectivity layer towards the front plane217(and therefore make the projection display screen102appear black), the effect of applying low intensity light inFIG. 4will be to make the bi-color particles402rotate to display their black side out of the front side. The effect of either of these embodiments will be to cause the projection display screen102to display their low reflectivity states when the incident projected light is low intensity. Providing certain gray scale can be permitted by turning certain regions on and others off within the projection display screen in a prescribed percentage. Alternatively, in a pixel-based system, gray scale can be provided by dithering.

While the effect of applying high intensity light to a region of the projection display screen102inFIG. 2will be to force the black particles215within the variable surface reflectivity layer towards the back plane218(and therefore make the projection display screen102highly reflective), the effect of applying high intensity light inFIG. 4will be to make the bi-color particles402rotate to display their highly-reflective side out towards the front plane217. The effect of either of these embodiments inFIG. 2or4will be to cause the region of the projection display screen102to display a highly reflective surface when the incident projected light has a high intensity.

Another embodiment of the projection display screen102with another embodiment of the variable surface reflectivity later204is now described with respect toFIGS. 6 and 7. This embodiment includes a polarizing layer602and a liquid crystal layer604. The back electrode is configured to be reflective to reflect any light traveling downwardly through the polarizing layer604back up into the polarizing layer.FIGS. 6 and 7respectively show a low reflection state and a high reflection state in which the liquid crystal layer604respectively does not rotate the light traveling there through and rotates the light traveling there through.

The polarizing layer602polarizes light that is traveling in a downward direction (relative toFIGS. 6 and 7) in one specific direction that is perpendicular to the downward direction of travel. The liquid crystal layer604can be changed between two liquid crystal states: a first polarizing state in which the liquid crystal layer604does not rotate the polarity of light passing there through, and a second polarizing state in which the liquid crystal layer604rotates the polarity of light passing there through. The layers of the projection display screen, except for the variable surface reflection layer, are similar to that described with respect to the embodiment shown inFIGS. 2 and 3.

When in the first polarizing state, the polarized direction of the light is not rotated, and as such the direction of polarization of the polarized light that has been reflected off the reflective back electrode202that continuing up through the polarizing layer602matches the direction of polarization of the polarizing layer, and therefore this polarized light can pass through the polarization layer to the front of the projection display screen102to the user. The first polarizing state where the liquid crystal layer does not rotate the direction of the polarization of the light therefore is equated to the high reflectivity state for the variable surface reflecting layer.

When in the second polarizing state as shown inFIG. 6, the direction of polarization is not rotated within the liquid crystal device layer. As such, the rotated polarized light cannot return from the liquid crystal layer604into the polarizing layer602to be projected out of the front of the projection display screen102. As such, as shown inFIG. 5, incident projected light passes from the front of the projection display screen and continues into the polarizing layer602(where the light is polarized), and into the liquid crystal layer604in which the polarizability of the light is rotated. The light then continues to the reflective back electrode202and reflects to return through the polarizing layer). Since the polarizability of the light is rotated within the liquid crystal layer604, the light returning through the liquid crystal layer cannot enter the polarizing layer, and therefore the incident projected light that enters through the polarizing layer602of the variable surface reflecting layer204cannot return through the polarizing layer (and in effect becomes absorbed by the variable surface reflecting layer). The second polarizing state therefore is equated to the low reflectivity state for the variable surface reflecting layer.

As shown inFIGS. 6 and 7, the variable surface reflecting layer can be altered from the low first polarizing state to the second polarizing state by the application of high intensity light to the front of the projection display screen that travels to the photoconductor layer. The transition of the liquid layer604into the second polarizing states is a result of the photoconductive layer becoming less electrically resistant in response to the increased intensity of the incident light. As a result, this region110of the projection display screen102will be more reflective in theFIG. 7high incident projected light instance than in theFIG. 6low incident projected light instance.

FIGS. 8 and 9show a region110of the projection display screen102including another embodiment of the variable surface reflective layer802. The variable surface reflective layer802includes an ink layer804that is contained within an optically transmissive liquid. The ink layer804can be transitioned between a wetted state as shown inFIG. 8in which the ink forms in a substantially even layer, or in a de-wetted state as shown inFIG. 9in which the ink forms in globules.

When in the wetted state as shown inFIG. 8, the ink layer804is spread substantially evenly across the width of the variable surface reflective layer802to cover the entirety of the variable surface reflective layer. The ink layer is in the wetted state when low intensity incident projected light is applied to the upper surface, the photoconductor layer212is in its highly resistive state, and the resulting potential is applied between the first transparent conductor layer210and the back electrode202to the ink. Under the first potential, the ink absorbs the light applied thereto, and little light is reflected off the reflective back electrode202.

When in the de-wetted state as shown inFIG. 9as results from the application of a second potential, the ink layer804forms spherical globules that are distributed across the width of the variable surface reflective layer802. While the dimensions of the globules804of the ink as shown inFIG. 9is relatively large compared to the depth thin layer as shown inFIG. 8, inFIG. 9the globules cover only a small percentage of the horizontal plane of the variable surface reflective layer (e.g., 10% to 20%). In front-lit versions of the embodiments of the projection display screen102shown inFIGS. 8 and 9, the back electrode202is optically reflective to reflect light to pass into the variable surface reflective layer802. As such, light that is applied from above (e.g., the high intensity incident projected light806) will primarily pass between the globules804, reflect off the reflective back electrode202, and be transmitted upwardly again towards the front of the projection display screen102. Light that is absorbed by the substantially even ink layer804as shown inFIG. 8will not be able to be reflected off the back electrode218.

Incident light can be applied from either the front or the back of the projection display screen102as indicated by respective front incident light arrow806and the back incident light arrow808. When light is applied to the front of the wetted ink layer804of the variable surface reflective layer802as shown inFIG. 8, the light reflects off the surface of the ink and colored filtered light is directed out of the front of the projection display screen. When light is applied to the back of the wetted ink layer804of the variable surface reflective layer802, the light is transmitted and filtered through the depth of the ink and colored filtered light and is directed out of the front of the projection display screen as shown by arrow810. The wetted state as shown inFIG. 8corresponds to the low reflectance state for light that is applied to either the front or the back of the projection display screen.

All of the embodiments of the projections display screen102as described with respect toFIGS. 2 to 9are front projection display screen devices since incident projected light is applied to the front of the projection display screen. One back-lit embodiment of the projection display screen102is shown inFIGS. 10 and 11that include a similarly operating variable surface transmissive layer1002to the variable surface reflectance layer802as described with respect to the embodiment described inFIGS. 8 and 9. In theFIGS. 10 and 11embodiment, an optically transparent back electrode1004is provided to allow light to pass into the variable surface transmissive layer1002.

Since the variable surface transmissive layer1002operates as described with respect to theFIGS. 8 and 9embodiment, when the ink layer804is in the form of an even layer, low intensity incident projected light1006from below will not pass upwardly because the ink will absorb the incident projected light, and let little light pass.

When high intensity incident projected light1106as shown inFIG. 11is applied to the back of the de-wetted ink layer804of the variable surface reflective layer1002, the majority of the light is allowed to pass (e.g., is transmitted) through to pass out the front of the projection display screen as shown by arrow1112since only a small percentage is filtered by contacting the globules of the ink layer. The de-wetted state as shown inFIG. 10corresponds to the highly transmissive state for light that is applied to the back of the projection display screen.

FIG. 12shows one embodiment of a dedicated reflectivity screen control mechanism1202in which a dedicated reflectivity screen control mechanism1202can suitably adjust the light reflectivity of the corresponding region of the projection display screen102in response to an intensity of the incident projected light as determined from the light projection portion to the projection display screen (as compared to an intensity of light that is received at the projection display screen). The dedicated reflectivity screen control mechanism1202reduces the reflectivity of the low intensity region considering the incident projected light transmitted out of each region of the light projection portion. Different embodiments of the dedicated reflectivity screen control mechanism1202can be either digital (processor) or analog (electronic) based. The dedicated reflectivity screen control mechanism1202thereby coordinates the reflectivity of the projection display screen102with the intensity of the light that is projected from the light projection portion104for that region of the projection display screen.

According to the embodiment of the projection display apparatus100as described with respect toFIG. 12, a dedicated screen reflectivity control mechanism1202adjusts the reflectivity of the regions110of the projection display screen102based on the corresponding intensity of light projected by the light projecting portion104at the projection display screen102based on the sensed intensity or band of light (e.g., by sensing the color or intensity of the light projected by the light projection portion) for a corresponding location of the light projection portion to the region110of the screen. The location of the light projection display screen102are related to the location of light projected from the light protection portion by the relative position relative to the image (e.g., the region110is located a certain percentage of the distance across the image and another percentage from the top of the image).

Alternatively, the intensity of light generated at a particular pixel location within the light projection portion104can be quantified and compared to the intensity threshold. If the projected light intensity at that projected pixel location is above the intensity threshold value, then the dedicated reflectivity screen control mechanism can be actuated at that pixel, and convert the corresponding region110to a high reflectivity level to reflect the incident display light. If the projected light intensity at that projected pixel location is below the intensity threshold value, then the dedicated reflectivity screen control mechanism is not actuated at that pixel, and the corresponding region110is not converted to a high reflectivity level (and the incident display light is not reflected). Any of these techniques operate such that the light intensity at each region110of the light projection display screen is determined, and the reflectivity/absorbance of the screen is suitably adjusted, based on the wavelength of the light (or lack of light) of the incident projected light108at each region110.

The dedicated screen reflectivity control mechanism1202can also operate using an invisible frequency of light (e.g., infrared) that is also associated with the incident light applied from the light projection portion104. For instance, a color wheel can be incorporated in front of the light projection portion104that contains not only the common visible spectrums of red, green, and blue, but also the invisible spectrum of infrared. Those invisible light regions will be used to convert that region to its high reflectivity state as described above. The intensity threshold of the regions of the projection display screen can be set to respond to only the invisible light, and as such the invisible light will control which regions of the projection display screen are in a highly reflective state and which regions are in a low reflectance state.

FIG. 13shows a block diagram summarizing a number of different embodiments of a region of the projection display screen102as described with respect toFIGS. 1 to 12. Each embodiment of the projection display screen102includes the variable surface reflectance layer204. The variable surface reflectance layer204transitions the projection display screen between its high reflectance and its low reflectance state based on the intensity of the incident projected light. The photoconductor layer202exists in certain embodiments, and receives the incident projected light, and in general alters the biasing of the variable surface projection layer204that acts to transition the projection display screen between its high reflectance and its low reflectance state.

This disclosure thereby can relatively inexpensively provide good contrast to large images to projection display systems. Having herein set forth preferred embodiments of the present invention, it is anticipated that suitable modifications can be made thereto which will nonetheless remain within the scope of the present invention.