Abstract:
An apparatus, system, and method for a fold-mirror assembly with a dynamically adjustable mirror element for use in a projection device are disclosed herein.

Description:
FIELD  
       [0001]     Embodiments of the invention relate generally to the field of projection systems, and more particularly to providing a dynamically adjustable fold-mirror assembly for use in such systems.  
       BACKGROUND  
       [0002]     Multimedia projection systems have become popular for purposes such as conducting sales demonstrations, business meetings, classroom training, and for use in home theaters. In typical operation, multimedia projection systems receive analog video signals from an input device and convert the video signals to digital information to control one or more digitally driven light modulators. Depending on the cost, brightness, and image quality goals of the particular projection systems, the light modulators may be of various sizes and resolutions, be transmissive or reflective, and be employed in single or multiple display configurations.  
         [0003]     Current projection systems are capable of creating millions of colors by using light modulator pixels to selectively transmit or reflect primary colored light through a projection lens for viewing. However, current projection systems have difficulty reproducing frames with wide ranges of luminances from deep black to bright white, while still providing adequate resolutions. This is particularly noticeable in frames primarily composed of image pixels on the darker end of the luminance spectrum. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]     Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like references indicate similar elements and in which:  
         [0005]      FIG. 1  illustrates a projection system having a projection device and an image source, in accordance with an embodiment of the present invention;  
         [0006]      FIG. 2  illustrates the projection device in greater detail, in accordance with an embodiment of the present invention;  
         [0007]      FIG. 3  illustrates a mask for use in the projection device, in accordance with an embodiment of the present invention; and  
         [0008]      FIG. 4  illustrates a manner for reducing light through a projection device, in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0009]     Illustrative embodiments of the present invention include a dynamically adjustable fold mirror to adjust the amount of light throughput through a projection device, and methods practiced thereon.  
         [0010]     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific materials and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. In particular, a wide variety of optical components not specifically shown such as, but not limited to, prisms, mirrors, lenses, and integration elements may be used as appropriate to fold, bend, or modify the illumination for the intended application.  
         [0011]     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.  
         [0012]     The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise.  
         [0013]      FIG. 1  illustrates a projection system  100  having a projection device  104  coupled to an image source  108 , in accordance with an embodiment of the present invention. The projection device  104  may be configured to receive an image signal, from the image source  108 , and to project an image based at least in part on the image signal.  
         [0014]     For the purpose of this description, a still image may be considered as a degenerate or special video where there is only one frame. Accordingly, both still image and video terminologies may be used in the description to follow, and they are not to be construed to limit the embodiments of the present invention to the rendering of one or the other.  
         [0015]     The projection device  104  may include a light source  112  optically coupled to a fold-mirror assembly  116 , which may be in turn optically coupled to a light modulator  120 . As used herein, “optically coupled” means the capability of light to be directly or indirectly provided from one component to another. In the present embodiment, the light source  112  may provide light to the fold-mirror assembly  116 , which may have a mirror element angularly disposed relative to the light source  112 . The fold-mirror assembly  116  may then reflect the light towards a light modulator  120 , thereby optically coupling the light source  112  to the light modulator  120 . As used herein, the fold-mirror assembly  116  may be any assembly capable of facilitating this optical coupling of the light source  112  to the downstream light modulator  120 .  
         [0016]     A controller  128 , which may be coupled to receive the image signal from the image source  108 , may transmit light modulator control signals to the light modulator  120  based at least in part on the image signal. The light modulator control signals may cause matrix-addressable elements of the light modulator  120  to modulate the light, through selective reflection or transmission, thereby outputting an image corresponding to the image signal. The image may then be projected, by a projection lens  124 , onto a screen or some other mechanism for viewing. In this embodiment, the projection lens  124  is shown with two lens elements; however, it may have more or less lens elements in other embodiments.  
         [0017]     The controller  128  may also be coupled to the fold-mirror assembly  116 . Given certain predefined conditions, e.g., an image that is below a predetermined brightness value, which may be determined by reference to the image signal, the controller  128  may adjust the angular disposition of the mirror element of the fold-mirror assembly  116  thereby adjusting the amount of light provided to the light modulator  120  and ultimately projected. The adjustment of the angular disposition of the mirror element may be between, e.g., a full-luminance position and a reduced-luminance position. In various embodiments, there may be any number of reduced-luminance positions, including gradual increments to a substantially no-luminance position.  
         [0018]     The resulting reduction of luminance may allow for more grayscale resolution to be displayed in the darker image frames by adapting the light modulator control signals to the reduced luminance. For example, assuming that during a dark frame, the majority of the modulating elements are activated between 0-20 percent. If the overall luminance is reduced by half in those dark frames, the modulating elements may be activated twice the amount, e.g., 0-40 percent, thereby gaining twice the grayscale resolution.  
         [0019]     Furthermore, dynamic luminance reduction taught by embodiments of the present invention may facilitate the improvement of black-level performance of the projection device  104 .  
         [0020]     The image source  108  may include a computing device, DVD, set-top box (STB), video camera, video recorder, an integrated television tuner, or any other suitable device to transmit signals, e.g., image signals, to the projection device  104 . In various embodiments, the system  100  may be, for example, a projector or a projection television.  
         [0021]     In one embodiment the light source  112  may include a polychromatic light source such as a gaseous discharge lamp (e.g., high-pressure mercury, tungsten, halogen, or metal halide). In other embodiments, monochromatic light sources may be used to produce light of the desired color. Examples of monochromatic light sources that may be used include, but are not limited to, light-emitting diodes and laser diodes.  
         [0022]     In one embodiment, the light modulator  120  may include, e.g., a liquid crystal light modulator. Examples of these types of light modulators include, but are not limited to, transmissive displays, e.g., using thin-film-transistors (TFT) on polysilicon (P-Si), as well as reflective displays such as LCoS (Liquid Crystal on Silicon). In other embodiments, the light modulator may have one or more digital micromirror displays (DMDs).  
         [0023]      FIG. 2  illustrates the projection device  104  in greater detail, according to one embodiment of the present invention. Light reflected off of the fold-mirror assembly  116 , and more particularly, off of a mirror element  200  of the fold-mirror assembly  116 , may be transmitted to an integrating device  202 . The integrating device  202 , which may be a flyseye-lens integrator, an integrating tunnel, etc., may homogenize and/or shape the light received from the fold-mirror assembly  116 . The integrating device  202  may also facilitate transmission of the light through a mask  204 .  
         [0024]     The mask  204 , shown in greater detail in  FIG. 3  in accordance with an embodiment of the present invention, may include one or more apertures  300 . Light directed through the apertures  300  may be transmitted to a polarization beam splitter (PBS)  208 . The PBS  208  may polarize the light in a manner to facilitate the selective modulation from the light modulator  120 , which in this embodiment may be a liquid crystal device.  
         [0025]     The apertures  300  of the mask  204  may be arranged in a way to facilitate the light being incident upon the PBS  208  in a manner that may result in a greater chance that the PBS  208  polarize the light appropriately for the downstream light modulator  120 . The mask  204  being used in this manner may also be referred to as a PBS mask.  
         [0026]     Although the embodiment shown depicts four apertures  300  as substantially uniform rectangles, other embodiments may have other number of apertures and may additionally/alternatively employ apertures of other shapes.  
         [0027]     While the fold-mirror assembly  116  is in a full-luminance state, the mirror element  200  may be angled such that a majority of the light from the light source  112  is directed through the apertures  300 , via the lens  202 . The controller  128  may determine that a reduction in the total luminance provided to the light modulator  120  is desirable and may therefore switch the fold-mirror assembly  116  to a reduced-luminance state by controlling a mechanical actuator  216  to transition the mirror element  200  so that less light is directed through the apertures  300 . The mask  204  may reflect the light back towards a light-absorbing area of a frame or towards a reflector of the light source  112 .  
         [0028]     Preventing at least a portion of the light from hitting downstream components, e.g., the PBS  208  and the light modulator  120 , while the fold-mirror assembly  116  is in the reduced-luminance state may protect the components from unnecessary high levels of light. This may, in turn, increase performance and the longevity of the components.  
         [0029]     In this embodiment, the actuator  216  may rotate the mirror element  200  around a centrally located axis (as shown). In another embodiment, the mirror element  200  may have a rotational axis closer to, or at an edge.  
         [0030]     In various embodiments, the actuator  216  may be a device such as, but not limited to, a voice coil, a linear actuator, and a step motor.  
         [0031]     In one embodiment, the amount of light reduction due to the adjustment of the fold-mirror assembly  116  may be proportional to the brightness of the image. This may be determined by analysis of the image signal received from the image source  108 . In various embodiments, a wide variety of algorithms may be developed to correlate the light reduction to the image brightness.  
         [0032]     As shown in  FIG. 2 , the fold-mirror assembly  116  has a single mirror element, i.e., mirror element  200 . In other embodiments, the fold-mirror assembly  116  may include a number of mirror elements. These mirror elements may be controlled in a manner such that while the fold-mirror assembly  116  is in a full-luminance state, the mirror elements are substantially parallel to one another and direct the light downstream to the light modulator  120 . The controller  128 , in response to a darker image frame, may then adjust the mirror elements in order to reduce the amount of light presented to the light modulator  120 . In one embodiment, the controller  128  may adjust a first set of the mirror elements, which may be any number of elements from one to all of the elements, to reflect light in a manner such that it is not transmitted through the apertures  300  of the mask  204 . The mirror elements not of the first set, if any, may continue to transmit a portion of the light through the apertures  300 . In one embodiment, an integration tunnel may be used to integrate the light reflected from the fold-mirror assembly  116  prior to processing by the light modulator  120 .  
         [0033]     While embodiments of the present invention discuss the fold-mirror assembly  116  causing at least a portion of the light to be blocked by the mask  204  while in the reduced-luminance state, other embodiments may rely on other techniques to cause at least a portion of the light to not be processed through the downstream components. For example, in one embodiment, the fold-mirror assembly  116  may reflect at least a portion of the light outside of the light-processing capabilities of the downstream components, sometimes referred to as the etendue, while in a reduced-luminance state.  
         [0034]      FIG. 4  illustrates a manner for reducing light through a projection device in accordance with one embodiment of the present invention. The elements discussed in reference to the present embodiment may be similar to like-named elements discussed above.  
         [0035]     In the present embodiment, a controller may receive an image signal from an image source  400 . The controller may analyze the image signal and develop an image brightness value  404 . This image brightness value may then be compared to a predetermined threshold value  408 . If the image brightness value is greater than the threshold value, the controller may adjust one or more fold-mirror elements to be in a full-luminance position  412 . If, however, the image brightness value is less than the threshold value, the controller may adjust the one or more fold-mirror elements to be in a reduced-luminance position  416 .  
         [0036]     As discussed above, in various embodiments there may be a number of reduced-luminance states and/or threshold values. This may provide a light modulator with a graduated reduction of light commensurate with a graduated reduction of image brightness levels.  
         [0037]     In other embodiments, other statistical operations may be used to determine whether an image frame would benefit from a reduction of the total illumination provided to the light modulator.  
         [0038]     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.