Abstract:
A method of controlling a projection-type display device and a projection-type display device using the same optimizes the contrast ratio of a screen regardless of ambient brightness conditions. A projection-type display device having an aperture for transmitting slight toward a screen includes a sensor for detecting ambient brightness with respect to the projection-type display device; a generator for generating an aperture control signal according to the detected ambient brightness; and a controller for adjusting an open/close range of the aperture according to the generated aperture control signal.

Description:
[0001]     This application claims the benefit of Korean Patent Application No. 10-2005-0079562, filed on Aug. 29, 2005, which is hereby incorporated by reference as if fully set forth herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to display devices, and more particularly, to a method of controlling a projection-type display device and to a projection-type display device using the same.  
         [0004]     2. Discussion of the Related Art  
         [0005]     A projection-type display device realizes a large screen by projecting an image using a system of mirrors and lenses and may be classified according to its picture-displaying system, which includes an optical unit. For example, the optical unit of a projection-type display system may employ a projection CRT, a liquid crystal display, or a is digital light processor, each of which may employ a video generator supplying an input to a pulse width modulation (PWM) controller for adjustably controlling the data range of a PWM signal. Alternatively, the projection-type display system may employ a liquid-crystal-on-silicon (LCoS) optical unit, in which case an LCoS driver and LCoS field-programmable gate array may substitute for the video generator and PWM controller, respectively.  
         [0006]     Meanwhile, an important characteristic of a projection-type display device is its contrast ratio, which greatly affects image quality. The contrast ratio of a screen is the ratio of the respective luminosities of the brightest and darkest colors that the system is capable of producing. Therefore, a high contrast ratio enables the display of clearer and more vivid images on the screen.  
         [0007]      FIG. 1  illustrates a general projection-type display device, which includes a DBA driver  101  for controlling (adjusting) an operational range of a “dynamic black” aperture or DBA, which is a feature of projection video devices and is used to enhance a contrast ratio. The dynamic black aperture is controlled (its degree of opening being set) based on a data range of a PWM signal output from a PWM controller  102  receiving an input signal via a video generator  103 , i.e., an input signal source. The PWM controller  102  adjusts the data range of the PWM signal, and the DBA driver  101  adjusts (sets) an open/closed state of an aperture according to the adjusted data range of the PWM signal, i.e., from 0% to 100%, which corresponds to a quantity of light allowed to pass through the aperture. For example, the DBA driver  101  controls the dynamic black aperture to be in a fully open state when the PWM signal data is 100% and controls the dynamic black aperture to be in a fully closed state when the PWM signal data is 0%.  
         [0008]     In a projection-type display device as described above, the DBA driver  101  adjusts the aperture, i.e., light quantity, based solely on a detected average luminance of a video signal. Therefore, contrast ratio may be effectively reduced by ambient brightness conditions, thereby degrading image quality since the display of clear, vivid images is difficult with low contrast ratios. For instance, the screen may become darker in a brightly lit room or may become brighter in a darkly lit room, which impedes the operation of a low gray scale and reduces a contrast ratio accordingly. Moreover, in controlling aperture operation as above, there is no provision for auxiliary adjustment methods, such as through a user selection made via an on-screen display (user interface) menu for varying a brightness control value.  
       SUMMARY OF THE INVENTION  
       [0009]     Accordingly, the present invention is directed to a projection-type display device control method and projection-type display device using the same that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0010]     An object of the present invention is to provide a method of controlling a projection-type display device and a projection-type display device using the same, which optimizes the contrast ratio of a screen regardless of ambient brightness conditions.  
         [0011]     Another object of the present invention is to provide a method of controlling a projection-type display device and a projection-type display device using the same, which improves image quality.  
         [0012]     Another object of the present invention is to provide a method of controlling a projection-type display device and a projection-type display device using the same, by which a screen can display an image of enhanced quality by compensating a brightness control value and optimizing a contrast ratio.  
         [0013]     Another object of the present invention is to provide a method of controlling a projection-type display device and a projection-type display device using the same, which enables a user selection of a brightness control value regardless of ambient brightness conditions.  
         [0014]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.  
         [0015]     To achieve these objects and other advantages in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a projection-type display device having an aperture for transmitting light toward a screen. The projection-type display device comprises a sensor for detecting ambient brightness with respect to the projection-type display device; a generator for generating an aperture control signal according to the detected ambient brightness; and a controller for adjusting an open/close range of the aperture according to the generated aperture control signal. In an alternative embodiment, the projection-type display device comprises a memory for storing a brightness control value set according to a user selection; a generator for generating an aperture control signal according to the stored brightness control value; and a controller for adjusting an open/close range of the aperture according to the generated aperture control signal. Yet another embodiment combines the concepts of above two embodiments.  
         [0016]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:  
         [0018]      FIG. 1  is a block diagram of a projection-type display device according to a related art;  
         [0019]      FIG. 2  is a block diagram of a projection-type display device according to a first embodiment of the present invention;  
         [0020]      FIG. 3A  is a cross-sectional diagram of a DBA driver according to the present invention;  
         [0021]      FIG. 3B  is a graph of the data range of a PWM signal according to  FIG. 3A ;  
         [0022]      FIG. 4A  is another cross-sectional diagram of a DBA driver according to the present invention;  
         [0023]      FIG. 4B  is a graph of the data range of a PWM signal according to  FIG. 4A ;  
         [0024]      FIG. 5  is a block diagram of a projection-type display device according to a second embodiment of the present invention;  
         [0025]      FIG. 6  is a graph of the data range of another PWM signal according to the present invention;  
         [0026]      FIG. 7  is a block diagram of a projection-type display device according to a third embodiment of the present invention;  
         [0027]      FIG. 8  is a flowchart of a method of controlling a projection-type display device according to the first embodiment of the present invention;  
         [0028]      FIG. 9  is a flowchart of a method of controlling a projection-type display device according to the second embodiment of the present invention; and  
         [0029]      FIG. 10  is a flowchart of a method of controlling a projection-type display device according to the third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]     Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, like reference designations will be used throughout the drawings to refer to the same or similar parts.  
         [0031]     The present invention automatically improves a contrast ratio, which may become degraded due to the proximity of a light source positioned near a projection-type display device or due to brightness variations made via a user interface menu, thereby enabling higher (optimized) contrast ratios so as to promote the display of an optimized screen image. The present invention may be applied to a projection-type display device employing a projection CRT, liquid crystal display, or digital light processor. As in the case of a general projection-type display device, the projection-type display device of a first, second, or third embodiment of the present invention may employ a liquid-crystal-on-silicon (LCoS) optical unit, as in an LCoS projection television, in which case an LCoS driver and LCoS field-programmable gate array may substitute for the video generator and PWM controller, respectively.  
       First Embodiment  
       [0032]      FIG. 2  illustrates a projection-type display device  200  according to a first embodiment of the present invention. Here, a DBA driver  201  controls an operational range of an aperture, which may be a dynamic black aperture (DBA). The aperture is set based on the data range of a PWM signal output from a PWM controller  202  receiving an input signal via a video generator  203 , i.e., an input signal source. The PWM controller  202  determines the data range of the PWM signal, and the DBA driver  201  controls the aperture&#39;s open/closed state. The PWM controller  202  generates an aperture control signal, e.g., a PWM signal, according to an ambient brightness as detected by a brightness detector  205 .  
         [0033]     The brightness detector  205  detects a level of light, i.e., brightness, present near a screen of the projection-type display device  200 , as an ambient brightness, which is output as a signal (e.g., a voltage value). The ambient brightness value is applied to a controller  204 , which determines whether bright or dark ambient conditions are present by comparing the detected ambient brightness value to a specific reference value that may be preset by the brightness detector  205 . For example, the room or area in which the projection-type display device  200  is installed may become relatively bright or dark at any time. Ambient brightness conditions could be determined as “dark” if the currently detected brightness were to drop below, say, 50 cd/m 2 , and could be determined as “bright” if the currently detected brightness were to exceed, say, 200 cd/m 2 , such that a normal ambient brightness value might occur between the above specific reference values.  
         [0034]     For a detected ambient brightness determined as above to be “dark,” the brightness detector  205  outputs a corresponding signal to the controller  204 , which in turn controls (sets) the PWM controller  202  to set the data range of a PWM signal to be wider than the data range according to normal (preset) conditions, which may be set by a manufacturer. Conversely, for a detected ambient brightness determined as above to be “bright,” the brightness detector  205  outputs a corresponding signal to the controller  204 , which in turn controls the PWM controller  202  to set the data range of a PWM signal to be narrower than the data range according to the preset normal conditions. An upper limit of the PWM data range may be set to be roughly equivalent or comparable to the upper limit of the normal data range.  
         [0035]     As shown in  FIGS. 3A and 4A , the projection-type display device  200  includes a shutter  301  or  401  for opening and closing an aperture  302  or  402  for transmitting light toward a screen. The shutter adjusts a quantity of transmitted light via the aperture.  FIGS. 3A and 4A  each show fully closed states, while  FIGS. 3B and 4B  show exemplary PWM data ranges corresponding to the shutter/aperture state of  FIG. 3A  or  4 A.  
         [0036]     Meanwhile, the PWM data range may correspond to a range of the aperture control signal. That is, the data range of the PWM signal is determined by the controller  204  and PWM controller  202 , so that the DBA driver  201  is able to drive the aperture accordingly. For instance, assuming a PWM data range under normal conditions to be 10˜100%, a PWM data range in dark ambient conditions may be set to 0˜100%, as in  FIG. 3B . At the same time, that is, assuming the same PWM data range under normal conditions to be 10˜100%, a PWM data range in bright ambient conditions may be set to 20˜100%, as in  FIG. 4B .  
         [0037]     For instance, if under normal conditions a fully closed state corresponds to a 10% aperture opening (90% closed), a fully closed state in dark ambient conditions may correspond to a 0% aperture opening (100% closed), and as shown in  FIG. 3A , all but 10% of the area of the aperture  302  is covered by the shutter  301 . Here, a 0% aperture opening would denote a complete covering of the entire area of the aperture  302 . At the same time, again assuming that under normal conditions a fully closed state corresponds to a 10% aperture opening, a fully closed state in bright ambient conditions may correspond to a 20% aperture opening, as shown in  FIG. 4A .  
         [0038]     Accordingly, for a determination of dark ambient conditions, the DBA driver  201  controls a fully closed state of a DBA operation to be more closed than in preset normal conditions, as in  FIG. 3A , so that normal display characteristics of a video signal can be maintained in dark ambient conditions. Conversely, for a determination of bright ambient conditions, the DBA driver  201  controls a fully closed state of a DBA operation to be less closed than in preset normal conditions, as in  FIG. 4A , so that normal display characteristics of a video signal can likewise be maintained in bright ambient conditions.  
         [0039]     A method of controlling a projection-type display device according to the first embodiment of the present invention is shown in  FIG. 8 . Here, the projection-type display device  200  is provided with means for detecting ambient brightness, for example, a sensor positioned with respect to an area forward of the screen or in the immediate proximity of the projection-type display device, so as to sense (detect) a current brightness with respect to the screen.  
         [0040]     Referring to  FIG. 8 , ambient brightness is detected, that is, light levels proximate to the projection-type display device are sensed by the brightness detector  205  (S 801 ). Based on the detection, it is determined whether ambient conditions are consistent with a brightly lit room or a darkly lit room (S 802 , S 803 ). If it is determined that the room is neither unusually dark or bright, DBA operation is controlled normally, that is, in accordance with preset conditions that may be determined by a manufacturer (S 804 ). On the other hand, for dark ambient conditions, the data range of a PWM signal is set to be wider than the PWM data range of the preset normal conditions (S 805 ), and DBA operation is controlled accordingly. Namely, the fully closed state of a DBA operation is controlled so as to be “more closed” than in the case of a fully closed state of the preset normal conditions (S 806 ). In other words, DBA operation is controlled such that the degree of aperture closing, when fully closed, is more than it would be under normal conditions.  
         [0041]     Meanwhile, for bright ambient conditions, a converse DBA operation is performed. Here, the data range of a PWM signal is set to be narrower than the PWM data range of the preset normal conditions (S 807 ), and DBA operation is controlled accordingly. Namely, the fully closed state of a DBA operation is controlled so as to be “less closed” than in the case of a fully closed state of the preset normal conditions (S 808 ). In other words, DBA operation is controlled such that the degree of aperture closing, when fully closed, is less than it would be under normal conditions.  
       Second Embodiment  
       [0042]      FIG. 5  illustrates a projection-type display device  500  according to a second embodiment of the present invention. Here, a DBA driver  501  controls an operational range of an aperture, e.g., a dynamic black aperture. The aperture is set based on the data range of a PWM signal output from a PWM controller  502  receiving an input signal via a video generator  503 , i.e., an input signal source. The PWM controller  502  determines the data range of the PWM signal, and the DBA driver  501  controls the aperture&#39;s open/closed state. The PWM controller  502  generates an aperture control signal, e.g., a PWM signal, according to a brightness control value stored in a memory  506 . The brightness value may be adjusted and set (stored) through manipulation of a user interface menu, using a user input unit (not shown) of the projection-type display device  500 .  
         [0043]     Once set, the brightness control value is stored in the memory  506 , which may include any device capable of storing a range of brightness control values, and the stored value is supplied to a controller  504 , which controls (sets) the data range of a PWM signal accordingly. For example, if the stored value is less than or equal to (i.e., not greater than) a preset reference value, the controller  504  sets the data range of a PWM signal to be narrower than the data range for preset normal conditions and controls the PWM controller  502  such that the fully open state of a DBA operation is less open than in the preset normal conditions. The preset reference value may be set to about 50%, considering an adjustable range of the brightness control value of 0˜100%. A range corresponding to an image being more darkly displayed than under a normal condition may be set less than or equal to the reference value.  
         [0044]     If a normal-condition PWM data range is 0˜100%, in case of the PWM data range adjusted narrower than the data range of the normal state, a lower limit is set equal to or similar to that of the normal state. An upper limit can be set to 80% of the normal conditions, as shown in  FIG. 6 , since a darker display of a readily visible image is possible with lower brightness levels when there is a significant reduction in a numerical value of the is upper limit. Here, the data range of the PWM signal is determined by the controller  504  and PWM controller  502 , so that the DBA driver  501  is able to drive the aperture accordingly.  
         [0045]     For a stored brightness control value of less than the reference value, the DBA driver  501  is able to control a fully open state of a DBA operation to be less open than in a normal condition, so that normal display characteristics of a video signal can be maintained in dark ambient conditions. For a stored brightness control value greater than the preset reference value, on the other hand, the DBA driver  501  controls the aperture normally, since an image is being more brightly displayed when a brightness control value exceeds a reference value. Hence, it is unnecessary to manipulate the aperture separately.  
         [0046]     A method of controlling a projection-type display device according to the second embodiment of the present invention is shown in  FIG. 9 . Here, the projection-type display device  500  is provided with means for setting a brightness value through, for example, manipulation of a user interface menu.  
         [0047]     Referring to  FIG. 9 , a brightness adjustment value (V adj ) set as above is stored in the memory  506  (S 901 ). The stored brightness adjustment value is then compared to a brightness reference value (V ref ), which may be determined by a manufacturer and pre-stored in memory (S 902 ). If the stored value is greater than the reference value, DBA operation is controlled normally, that is, in accordance with preset conditions that may be determined by the manufacturer (S 903 ). On the other hand, if the stored value is less than or equal to (i.e., not greater than) the reference value, the data range of a PWM signal is set to be narrower than the PWM data range of the preset normal conditions (S 904 ), and DBA operation is controlled accordingly. Namely, the fully open state of a DBA operation is controlled so as to be “less open” than in the case of a fully open state of the preset normal conditions (S 905 ). In other words, DBA operation is controlled such that the degree of aperture opening, when fully open, is less than it would be under normal conditions.  
       Third Embodiment  
       [0048]     A configuration of the present invention according to the third embodiment generally combines configurations of the first and second embodiments. Accordingly, some overlapping explanation will be omitted in the following description.  
         [0049]      FIG. 7  illustrates a projection-type display device  700  according to a third embodiment of the present invention. Here, a DBA driver  701  controls an operational range of an aperture, e.g., a dynamic black aperture. The aperture is set based on a data range of a PWM signal output from a PWM controller  702  receiving an input signal via a video generator  703 , i.e., an input signal source. The PWM controller  702  determines the data range of the PWM signal, and the DBA driver  501  controls the aperture&#39;s open/closed state.  
         [0050]     A brightness detector  705  detects ambient brightness with respect to the projection-type display device  700 . A memory  706  stores a brightness control value set via a user input unit (not shown) of the projection-type display device  700 . The controller  704  adjusts, by controlling the PWM controller  702 , the data range of a PWM signal according to the detected ambient brightness and the stored brightness control value. A DBA driver  701  is able to differently operate an extent of a fully closed state or a fully open state of the aperture according to the PWM signal data range adjusted under control of the controller  704 . If the currently detected ambient brightness is lower than a preset “dark condition” brightness, the DBA driver  701  controls a fully closed state of a DBA operation to be more closed than that of a preset normal condition, so that normal display characteristics of a video signal can be maintained in dark ambient conditions. On the other hand, if the currently detected ambient brightness is higher than a preset “bright condition” brightness, the DBA driver  701  controls a fully closed state of a DBA operation to be less closed than that of a preset normal condition, so that normal display characteristics of a video signal can likewise be maintained in bright ambient conditions.  
         [0051]     Meanwhile, if the controller  704  determines that the brightness control value stored in the memory  706  is less than or equal to a reference value, the controller  704  outputs to the DBA driver  701  a corresponding control signal for controlling a fully open state of the DBA operation to be less open than in preset normal conditions. Hence, normal display characteristics of a video signal can be maintained in dark ambient conditions.  
         [0052]     A method of controlling a projection-type display device according to the third embodiment of the present invention is shown in  FIG. 10 . Here, the projection-type display device  700  is provided with both means for setting a brightness value as in the first embodiment and means for detecting ambient brightness as in the second embodiment.  
         [0053]     Referring to  FIG. 10 , ambient brightness is detected by the brightness detector  705 , and a brightness adjustment value is stored in the memory  706  (S 1001 ). Based on the detection, it is determined whether ambient conditions are consistent with a brightly lit room or a darkly lit room (S 1002 , S 1003 ), and if it is determined that the room is neither unusually dark or bright, the stored value is compared to a reference value (S 1004 ). Accordingly, DBA operation is controlled such that, relative to preset normal conditions, the fully closed state is more closed in dark ambient conditions and is less closed in bright ambient conditions (S 1005 , S 1006 ). Meanwhile, for intermediate levels of ambient brightness, and when the stored value is not greater than the reference value, DBA operation is controlled such that the fully open state is less open than preset normal conditions (S 1007 ); otherwise, namely, if the stored value is greater than the reference value, it is determined again whether the ambient brightness conditions are relatively normal, for example, falling in an intermediate range of brightness levels (S 1008 ). Accordingly, if it is determined that the room is neither unusually dark or bright and that the stored value is greater than the reference value, DBA operation is controlled normally, that is, in accordance with preset conditions that may be determined by a manufacturer (S 1009 ).  
         [0054]     By adopting the present invention, reduction of a contrast ratio of the screen of a projection-type display device, which may occur due to the proximity of a light source or to brightness variations made via a user interface menu, is prevented. Thus, the higher contrast ratio of a projection-type display device according to the present invention promotes the display of clear, vivid images on the screen and enables an optimized contrast ratio in projection-type display devices.  
         [0055]     It will be apparent to those skilled in the art that various modifications can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers such modifications provided they come within the scope of the appended claims and their equivalents.