Abstract:
A video signal processing apparatus comprises an A/D converter for digitizing an analog video signal, an integration circuit for integrating the digitized video signal within a predetermined integration range, a picture display device for displaying a picture based on an integration output, and a control unit which, when an offset adjustment signal is inputted to the A/D converter, corrects the offset value so as to eliminate a difference between the integration value of the integration circuit and a preliminarily set specified value, and determines whether or not offset adjustment is completed based on the number of times when the corrected offset value is within a range defined by adding a predetermined error to the specified value.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-178482, filed Jun. 16, 2004, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a video signal processing apparatus and a video signal processing method for displaying video signals on particularly a flat panel type display.  
         [0004]     2. Description of the Related Art  
         [0005]     As well known, in recent years, a flat panel type display using for example, a liquid crystal display panel, a plasma display panel or the like has been widely prevalent. As this kind of the flat panel type display, a picture projection type display or a projector also has tended to be prevail.  
         [0006]     In such a flat panel type display, after an analog video signal to be inputted in the form of an RGB signal or a YCbCr signal is digitized, the digitized signal is subjected to integral processing and supplied to the display panel, thereby displaying a picture.  
         [0007]     In this flat panel type display, it is necessary to implement offset adjustment and gain adjustment on an analog/digital (A/D) converter for digitizing an analog video signal in order to obtain optimal A/D conversion accuracy.  
         [0008]     Jpn. Pat. Appln. KOKAI Publication No. 5-243998 has disclosed a configuration for adjusting an A/D converter to obtain an optimal output when an offset adjustment reference voltage is inputted and for adjusting the A/C converter to obtain an optimal output when a gain adjustment reference voltage is inputted.  
         [0009]     However, the A/D conversion technology for digitizing the analog video signal is still on a development stage, so that development of a method more suitable for actual realization has been strongly demanded in several viewpoints as regards the offset and gain adjustments.  
       BRIEF SUMMARY OF THE INVENTION  
       [0010]     According to one aspect of the present invention, there is provided a video signal processing apparatus comprising: an A/D converting unit configured to digitize an inputted analog video signal; an integration unit configured to integrate the video signal digitized by the A/D converting unit within a predetermined integration range; a picture display unit configured to display a picture based on an output signal of the integration unit; a detecting unit configured to, when an analog video signal to be inputted to the A/D converting unit is an adjustment signal of the A/D converting unit, detect a difference between an integration value obtained by the integration unit and a preliminarily set specified value; a correcting unit configured to, when the difference is detected by the detecting unit, correct an adjusted value of the A/D converting unit such that the integration value is equal to the specified value; and a determining unit configured to determine whether or not the adjustment is completed based on the number of times when the adjusted value corrected by the correcting unit is within a range defined by adding a predetermined error to the specified value.  
         [0011]     According to another aspect of the present invention, there is provided a video signal processing method comprising: a first step of digitizing an inputted analog video signal by an A/D converting unit; a second step of integrating the digitized video signal by an integration unit within a predetermined integration range; a third step of displaying a picture by a picture display unit based on an output signal of the integration unit; a fourth step of, when an analog video signal to be inputted to the A/D converting unit is an adjustment signal of the A/D converting unit, detecting a difference between an integration value obtained by the integration unit and a preliminarily set specified value; a fifth step of, when the difference is detected, correcting an adjusted value of the A/D converting unit such that the integration value is equal to the specified value; and a sixth step of determining whether or nor the adjustment is completed based on the number of times when the adjusted value corrected by the correcting unit is within a range defined by adding a predetermined error to the specified value. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0012]      FIG. 1  is a front view for explaining an appearance of a picture display apparatus according to an embodiment of the present invention;  
         [0013]      FIG. 2  is a block diagram for explaining a signal processing system of the picture display apparatus according to the embodiment;  
         [0014]      FIG. 3  is a diagram for explaining adjustment of offset and gain of an A/D converter according to the embodiment;  
         [0015]      FIG. 4  is a flow chart for explaining the offset adjustment operation of the A/D converter according to the embodiment;  
         [0016]      FIG. 5  is a flow chart for explaining the gain adjustment operation of the A/D converter according to the embodiment;  
         [0017]      FIG. 6  is a flow chart for explaining the adjustment of offset and gain of the A/D converter with an RGB signal according to the embodiment;  
         [0018]      FIG. 7  is a diagram for explaining the RGB signal for use in the adjustment of offset and gain of the A/D converter according to the embodiment;  
         [0019]      FIG. 8  is a flow chart for explaining the offset adjustment operation of the A/D converter with a YCbCr signal according to the embodiment;  
         [0020]      FIG. 9  is a diagram for explaining the YCbCr signal for use in the offset adjustment operation of the A/D converter according to the embodiment;  
         [0021]      FIG. 10  is a flow chart for explaining that the adjustment of offset and gain of the A/D converter with the RGB signal and the adjustment of the offset with the YCbCr signal are carried out continuously;  
         [0022]      FIG. 11  is a block diagram for explaining a modification of the embodiment; and  
         [0023]      FIG. 12  is a block diagram for explaining another modification of the embodiment. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.  FIG. 1  is a front view of a flat panel type picture display apparatus  11  of this embodiment.  
         [0025]     The picture display apparatus  11  is mainly comprised of a cabinet  12  and a supporting base  13  for supporting the cabinet  12 . In the cabinet  12 , a display panel  14   a  of a picture display device  14 , which will be described later, is disposed in the center of a front face thereof.  
         [0026]     Further, in the cabinet  12 , an operation unit  15  including a power switch  15   a , a reception unit  15   b  for receiving operation information sent from a wireless remote controller (not shown) and the like is disposed on both sides of the display panel  14   a.    
         [0027]     On the other hand, the supporting base  13  is coupled with the center of the bottom face of the cabinet  12  freely rotatably, and is configured to support the cabinet  12  in its standing position in a state in which it rests on a predetermined base  16  horizontally.  
         [0028]      FIG. 2  shows a signal processing system of the picture display apparatus  11 . That is, in  FIG. 2 , reference numeral  17  denotes a video signal input terminal. In the video signal input terminal  17  is inputted an analog video signal in the form of an RGB signal or in the form of a YCbCr signal.  
         [0029]     The analog video signal inputted to the video signal input terminal  17  is supplied to an A/D converter  18 , which converts the signal to a digital signal. The digital signal is integrated for a specified period by means of an integration circuit  19 , and then supplied to the picture display device  14  and displayed on the display panel  14   a.    
         [0030]     Here, in the picture display apparatus  11 , its entire operation including the above-described display operation is totally controlled by a control unit  20 . The control unit  20  incorporates a central processing unit (CPU) and the like, which receives operation information from the operation unit  15  and controls respective units so as to reflect contents of the operation.  
         [0031]     In this case, the control unit utilizes a memory unit  21 . That is, the memory unit  21  mainly comprises a read only memory which stores a control program to be executed by the CPU of the control unit  20 , a random access memory which provides the CPU with a work area, and a nonvolatile memory which stores various kinds of specified values, setting information, control information and the like.  
         [0032]     The control unit  20  outputs an integral range control signal indicating an integral range to the integration circuit  19 , reads an integral value outputted from the integration circuit  19  in this integral range and executes offset adjustment and gain adjustment of the A/D converter  18  in accordance with the integral value.  
         [0033]     When the inputted analog video signal is the RGB signal, the A/D converter  18 , the integration circuit  19  and the control unit  20  perform A/D conversion processing, integration processing and adjustment processing upon the R signal, G signal and B signal. When the inputted analog video signal is the YCbCr signal, the A/D converter  18 , the integration circuit  19  and the control unit  20  perform A/D conversion processing, integration processing and adjustment processing upon the Y signal, Cb signal and Cr signal.  
         [0034]      FIG. 3  describes adjustments of offset and gain which are to be adjusted by the A/D converter  18 . That is, comparison is made between a case where a signal conversion range when the A/D converter  18  converts an inputted analog video signal  22  to a digital signal has a gain A substantially corresponding to the amplitude of the analog video signal  22  and a case where it has gain B wider than the gain A.  
         [0035]     Assuming that the gain A is ⅔ times the gain B in this case, the case where it is set by the gain A provides a value 1.5 times the case where it is set by the gain B as for a digital signal produced by conversion to the same analog video signal  22 .  
         [0036]     That is, assume that respective central levels of the gain A, gain B and analog video signal  22  coincide at a position indicated by a dot and dash line in  FIG. 3 . In the case of the gain A, a maximum level portion  22   a  of the analog video signal  22  reaches substantially near the maximum level Max of the signal conversion range, and a minimum level portion  22   b  of the analog video signal  22  reaches substantially near the minimum level Min of the signal conversion range.  
         [0037]     Contrary to this, in the case of the gain B, the maximum level portion  22   a  of the analog video signal  22  reaches a position lower by α than the maximum level Max of the signal conversion range, and the minimum level portion  22   b  of the analog video signal  22  reaches a position higher by α than the minimum level Min of the signal conversion range.  
         [0038]     As a result, gain adjustment of the A/D converter  18  is needed according to the amplitude of the inputted analog video signal  22 .  
         [0039]     Even if the same gain width as the gain B indicated with a solid line is provided, the central level, namely, a central point of conversion to digital signals may be deflected by an amount corresponding to β depending on a situation as a gain B′ indicated with a dotted line in the figure. In this case, as compared with the case of the gain B, offset by the amount corresponding to β is generated with respect to a central level portion  22   c  of the analog video signal  22 .  
         [0040]     Thus, the offset adjustment of the A/D converter  18  is necessary according to the central level of the inputted analog video signal  22 . For the YCbCr signal to be inputted, a pedestal level after digitalization is preferred to be 80 h. Accordingly, the offset adjustment is needed such that the pedestal level after the digitalization becomes 80 h.  
         [0041]      FIG. 4  shows a flow chart of the offset adjustment operation. First, after the processing is started (step S 1 ), an analog video signal for offset adjustment is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 2 .  
         [0042]     Here, when the analog video signal for offset adjustment is the RGB signal, a minimum level Min (black) level is inputted. In addition, when the analog video signal for offset adjustment is the YcbCr signal, its central level is inputted. If the amplitude range after digitalization is 00 h to FFh, the pedestal level after digitalization is 80 h.  
         [0043]     Then, in step S 3 , the control unit  20  sets an integration range to the integration circuit  19 , that is, a signal pickup range for reading an integration value from the integration circuit  19 , and in step S 4 , the control unit  20  reads an integration value in the previously set integration range from the integration circuit  19 .  
         [0044]     Thereafter, in step S 5 , the control unit  20  compares the integration value read out from the integration circuit  19  with the specified value preliminarily set in the memory unit  21 , and determines which state is established from among the following three states, “integration value=specified value”, “integration value&lt;specified value” and “integration value&gt;specified value”.  
         [0045]     If it is determined that “integration value=specified value” is established, the control unit  20  determines that the offset adjustment is completed in step S 10 , and terminates the processing (step S 12 ).  
         [0046]     If it is determined that “integration value&lt;specified value” is established in the step S 5 , the control unit  20  controls the A/D converter  18  to increment a current offset value with 1 in step S 6 .  
         [0047]     On the other hand, if it is determined that “integration value&gt;specified value” is established in the step S 5 , the control unit  20  controls the A/D converter  18  to decrement a current offset value with 1 in step S 7 .  
         [0048]     That is, the control unit  20  corrects the offset value of the A/D converter  18  step by step such that the integration value becomes equal to the specified value.  
         [0049]     After the step S 6  or S 7 , the control unit  20  determines whether or not the number of times when the integration value is within a range of ±1 to the specified value exceeds a preliminarily set number of times (for example, 30 to 40). When it is determined that it does not exceed (NO), the procedure is returned to the processing of step S 5 .  
         [0050]     If it is determined that the number of times when the integration value is within the range of ±1 to the specified value exceeds the preliminarily set number of times (YES) in the step S 8 , the control unit  20  executes final determination to determine whether or not the integration value is within the range of ±1 to the specified value in the step S 9 .  
         [0051]     If it is determined that it is within the range (YES), the control unit  20  determines that the offset adjustment is completed in step S 10 , and terminates the processing (step S 12 ). If it is determined that it is not within the range (NO), the control unit  20  determines that the offset adjustment is disabled in step S 11 , and terminates the processing (step S 12 ).  
         [0052]      FIG. 5  shows a flow chart of the gain adjustment operation. After the processing is started (step S 13 ), an analog video signal for gain adjustment is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 14 . In this case, the analog video signal for gain adjustment is the RGB signal, and its maximum level Max (white level) is inputted.  
         [0053]     Then, the control unit  20  sets an integration range to the integration circuit  19 , that is, a signal pickup range for reading out an integration value from the integration circuit  19  in step S 15 , and reads out an integration value in the previously set integration range from the integration circuit  19  in step S 16 .  
         [0054]     Thereafter, the control unit  20  compares the integration value read from the integration circuit  19  with the specified value set in the memory unit  21 , and determines which state is established from among the following three states, “integration value=specified value”, “integration value&lt;specified value” and “integration value&gt;specified value”.  
         [0055]     If it is determined that “integration value=specified value” is established, the control unit  20  determines that the gain adjustment is completed in step S 22 , and terminates the processing (step S 24 ).  
         [0056]     If it is determined that “integration value&lt;specified value” is established in the step S 17 , the control unit  20  controls the A/D converter  18  to increment a current offset value with 1 in step S 18 .  
         [0057]     On the other hand, if it is determined that “integration value&gt;specified value” is established in the step S 17 , the control unit  20  controls the A/D converter  18  to decrement the current offset value with 1 in step S 19 .  
         [0058]     That is, the control unit  20  corrects the gain value of the A/D converter  18  step by step such that the integration value becomes equal to the specified value.  
         [0059]     After the step S 18  or S 19 , the control unit  20  determines whether or not the number of times when the integration value is within a range of ±1 to the specified value exceeds a preliminarily set number of times (for example, 30 to 40). When it is determined that it does not exceed (NO), the procedure is returned to the processing of step S 17 .  
         [0060]     If it is determined that the number of times when the integration value is within the range of ±1 to the specified value exceeds the preliminarily set number of times (YES) in the step S 20 , the control unit  20  executes final determination to determine whether or not the integration value is within the range of ±1 to the specified value in the step S 21 .  
         [0061]     If it is determined that it is within the range (YES), the control unit  20  determines that the offset adjustment is completed in step S 22 , and terminates the processing (step S 24 ). If it is determined that it is not within the range (NO), the control unit  20  determines that the offset adjustment is disabled in step S 23 , and terminates the processing (step S 24 ).  
         [0062]     According to the above-mentioned embodiment, even if an integration value obtained by inputting offset adjustment and gain adjustment analog video signals to the A/D converter  18  does not coincide with a preliminarily set specified value, if it is within the allowance range obtained by incrementing/decrementing the specified value with 1 at a predetermined number of times or more, it is determined that the adjustment is completed. Consequently, the efficiency of the offset adjustment and gain adjustment to the A/D converter  18  can be intensified.  
         [0063]      FIG. 6  shows a flow chart of an operation for automatically adjusting the offset and gain by inputting offset adjustment and gain adjustment analog RGB signals to the A/D converter  18 .  
         [0064]     First, after the processing is started (step S 25 ), the adjustment analog RGB signal is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 26 . In the adjustment analog RGB signal, a minimum level Min for offset adjustment and a maximum level Max for gain adjustment are mixed within a single horizontal period as shown in  FIG. 7 .  
         [0065]     In this case, the control unit  20  sets an offset adjustment integration range in a portion of the minimum level Min of the inputted RGB signal and a gain adjustment integration range in a portion of the maximum level Max.  
         [0066]     As a consequence, the control unit  20  executes the offset adjustment described in  FIG. 4  on the offset adjustment integration range in step S 27 , and executes the gain adjustment described in  FIG. 5  on the gain adjustment integration range in step S 28 .  
         [0067]     In step S 29 , the control unit  20  readjusts the offset slightly deflected by the gain adjustment in step S 28 , determines that the automatic adjustment of the offset and gain is completed in step S 30 , and terminates the processing (step S 31 ).  
         [0068]     As for the offset adjustment and gain adjustment, if the offset adjustment is performed first and then they are executed alternately several times, a more reliable adjustment can be achieved.  
         [0069]     A result of the offset adjustment with the G signal in steps S 27 , S 29  can be also applied to the Y signal. Further, a result of the gain adjustment with the RGB signal in step S 28  can be also applied to the YCbCr signal.  
         [0070]      FIG. 8  shows a flow chart of an operation of automatically adjusting the offset by inputting the offset adjustment analog CbCr signal to the A/D converter  18 . First, after the processing is started (step S 32 ), the offset adjustment analog CbCr signal is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 33 .  
         [0071]     The analog CbCr signal needs to be a colorless flat signal, for example, a mono-chrome signal as shown in  FIG. 9  for usage. Then, the control unit  20  sets an offset adjustment integration range at an arbitrary portion of the inputted CbCr signal.  
         [0072]     Then, the control unit  20  executes the offset adjustment described in  FIG. 4  upon the offset adjustment integration range in step S 34 . Because the analog CbCr signal is used in this case, the specified value is a central level between the maximum level Max and the minimum level Min, that is, in case of 8 bits, 80 h which is the central value of 00 h to FFh. Thereafter, the control unit  20  confirms that the automatic adjustment of the offset is completed in step S 35 , and terminates the processing (step S 36 ).  
         [0073]      FIG. 10  shows a flow chart of an operation of inputting the offset adjustment and gain adjustment analog RGB signals into the A/D converter  18  so as to automatically adjust the offset and gain, and subsequently, inputting the offset adjustment analog CbCr signal into the A/D converter  18  so as to automatically adjust the offset.  
         [0074]     That is, after the processing is started (step S 37 ), the adjustment analog RGB signal is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 38 . Then, the control unit  20  executes the offset adjustment described in  FIG. 4  on the offset adjustment integration range in step S 39 , and executes the gain adjustment described in  FIG. 5  on the gain adjustment integration range in step S 40 .  
         [0075]     Then, in step S 41 , the control unit  20  readjusts the offset slightly deflected in the gain adjustment in step S 40 , and in step S 42 , the control unit  20  confirms that the automatic adjustment of the offset and gain is completed.  
         [0076]     Thereafter, the offset adjustment analog CbCr signal is inputted to the A/D converter  18  through the video signal input terminal  17  in step S 43 . Then, the control unit  20  executes the offset adjustment described in  FIG. 4  upon the offset adjustment integration range in step S 44 . After that, the control unit  20  confirms that the automatic adjustment of the offset is completed in step S 45 , and terminates the processing (step S 46 ).  
         [0077]      FIG. 11  shows a modification of the above-described embodiment. Explaining by attaching like reference numerals to the same components as in  FIG. 2 , a cursor insertion unit  23  for displaying a cursor on the picture display device  14  under the control of the control unit  20  is disposed between the integration circuit  19  and the picture display device  14 .  
         [0078]     If a signal obtained by processing a video signal within the integration range of the integration circuit  19  to a specified level is used as a cursor, an integrated range is displayed on the display panel  14   a  of the picture display device  14  during adjustment of the offset or gain. Thus, the user can determine whether or not the adjustment operation is being carried out properly because the integrated portion is displayed, thereby intensifying the reliability of adjustment.  
         [0079]      FIG. 12  shows further another modification of the above-described embodiment. Explaining by attaching like reference numerals to the same components as in  FIG. 11 , in  FIG. 12 , this embodiment includes a peak value detecting unit  24  for detecting maximum and minimum peak values of a video signal from the output of the integration circuit  19 .  
         [0080]     When, as a result of detection result of the peak value detecting unit  24 , a detected video signal has a level higher than currently set gain, the specified value set in the memory unit  21  is changed such that the amplitude of the video signal is within the gain. Consequently, crush of a fine black detail or crush of a white portion of the video signal can be prevented.  
         [0081]     In the meantime, the present invention is not restricted to the above-described embodiment but may be embodied by modifying its components in various ways within a scope not departing from the gist of the invention. In addition, by combining plural components disclosed in the above-described embodiment appropriately, various aspects of the invention can be achieved. For example, it is permissible to delete some components from the entire components indicated in the embodiment. Moreover, it is permissible to combine components of different embodiments appropriately.