Abstract:
Provided is a method of automatically setting image quality, which maintains a brightness and a contrast of an image regardless of a status of an input signal. The method includes: (a) setting a variable range of brightness and a variable range of contrast; (b) converting a brightness signal included in an input video signal into a digital signal and recording the digital brightness signal in a plurality of registers according to brightness level; (c) changing a brightness value or a contrast value of an output video signal by comparing values of a first register, second register, third register, and fourth register among the registers to predetermined values; and (d) if the changed brightness value is in the variable range of the brightness and the contrast value is in the variable range of the contrast, determining that the compensation of image quality is complete, and returning to step (b).

Description:
BACKGROUND OF THE INVENTION 
   This application claims the priority of Korean Patent Application No. 2003-43572, filed on Jun. 30, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   1. Field of the Invention 
   The present invention relates to a display method, and more particularly, to a method of automatically setting image quality such that brightness (that is, a cut off point) and contrast (that is, a saturation point) of an actual image are maintained at a constant level regardless of a status of an input signal. 
   2. Description of the Related Art 
   In a conventional auto gain control (AGC) method, which processes an input video signal after converting a level of the input video signal that exceeds a reference value, the video signal is compensated for based on a sync level, which is combined with the video signal before being input. Therefore, it is difficult to exactly compensate for the brightness of an actual image. Also, a malfunction of a device performing the AGC process may occur, during which the AGC process cannot exactly compensate for the signal level. 
   Image quality of a broadcast signal and images received from video tapes may be different from each other. Also, image quality of a video signal and of a digital versatile disc (DVD) signal, which are connected to a same DVD player, may be different from each other. Most users usually watch the images as they are. However, some users adjust the brightness and contrast of the image by accessing a user menu. However, the adjustments should be made automatically when the channel is changed or input source is changed. 
     FIGS. 1A and 1B  are flow charts illustrating a conventional method for setting image quality. 
   Referring to  FIG. 1A , a brightness signal included with an input video signal is converted into an 8-bit digital signal (step  100 ). The digital brightness signal is stored in one of a register  50   h  through a register  6 Fh according to a brightness level (step  101 ). The digital brightness signal is input to a scaler (not shown). The upper 4 bits of the 8-bit digital brightness signal are divided into 16 levels according to the brightness level, and resultant values of the division are stored in register  51   h  through register  6 Fh in 2-byte units. That is, the darkest digital brightness signal is stored in register  50   h  and register  51   h , and the brightest digital brightness signal is stored in register  6 Dh and register  6 Fh. 
   Values of registers  51   h / 53   h / 6 Dh/ 6 Fh, which are the registers that compensate image quality, are read to determine whether the values of the registers  51   h / 53   h / 6 Dh/ 6 Fh are 0x00/0xHH/0xHH/0x00 (steps  102  and  103 ). Here, 0xHH does not refer to a specific value, but satisfies 0xHH≠0x00. 
   When the values of registers  51   h / 53   h / 6 Dh/ 6 Fh are 0x00/0xHH/0xHH/0x00, it is determined that the image quality is set to be optimal, and corresponding brightness and contrast values are stored in memory (step  104 ). 
   When the values of registers  51   h / 53   h  are 0x00/0x00, the brightness value of an output video signal is decreased by one level (steps  105  and  106 ). 
   However, when the values of registers  51   h / 53   h  are 0xHH/0xHH, the brightness value of the output video signal is increased by one level (steps  107  and  108 ). 
   In addition, when the values of registers  6 Dh/ 6 Fh are 0x00/0x00, the contrast value of the output video signal is increased by one level (steps  109  and  110 ). 
   However, when the values of registers  6 Dh/ 6 Fh are 0xHH/0xHH, the contrast value of the output video signal is decreased by one level (steps  111  and  112 ). 
   As described above, the brightness/contrast may be changed excessively depending on the status of the image when a cut off level and a saturation level are compensated for by changing the brightness/contrast according to conventional methods, thus a method of preventing this is required. 
   For example, when it is assumed that a night scene is displayed, the dark scene may be displayed too brightly such that a viewer cannot determine whether the scene is a night scene or a day scene, by increasing the contrast to a high level. In this case, there is a need to prevent the contrast from increasing beyond a certain maximum point, to represent the night scene appropriately. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method of automatically setting image quality such that brightness and contrast of an actual image are maintained at a constant level regardless of the state of an input signal. 
   According to an aspect of the present invention, there is provided a method for setting an image quality automatically including: (a) setting a variable range of a brightness and a variable range of a contrast; (b) converting a brightness signal included in an input video signal into a digital signal and recording the digital brightness signal in a plurality of registers according to brightness level; (c) changing a brightness value or a contrast value of an output video signal by comparing values of a first register, a second register, a third register, and a fourth register among the registers to predetermined values; and (d) if the changed brightness value is in the variable range of the brightness and the contrast value is in the variable range of the contrast, determining that the compensation of image quality is complete, and returning to step (b). 
   If the values of a fifth register and a sixth register among the registers contain predetermined values, the image may be determined to be a full-white or a full-black image and the image quality compensating operation may be skipped. 
   In step (c), if the values stored in the first, second, third, and fourth registers are not equal to the predetermined values, the method may include: (c-1) increasing the brightness value of the output video signal by one level, when the values of the first and second registers are a first predetermined value; (c-2) decreasing the brightness value of the output video signal by one level, when the values of the first and second registers are a second predetermined value; (c-3) decreasing the contrast value of the output video signal by one level, when the values of the third and fourth registers are a third predetermined value; and (c-4) increasing the contrast value of the output video signal by one level, when the values of the third and fourth registers are a fourth predetermined value. 
   If the changed brightness is determined not to be in the variable range of the brightness, the brightness may be restored to an initial brightness value, and, if the changed contrast is determined not to be in the variable range of the contrast, the contrast may be returned to an initial contrast value. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIGS. 1A and 1B  are flow charts illustrating a conventional method for setting image quality; 
       FIG. 2  is a block diagram of an apparatus that automatically sets image quality; and 
       FIGS. 3A and 3B  are flow charts illustrating a method of automatically setting the image quality according to a first embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, the present invention will be described in detail with reference to accompanying drawings. 
     FIG. 2  is a block diagram of an apparatus that automatically sets image quality. The apparatus includes a scaler  200 , which scales an input video signal such that the video signal is adjusted for a display specification, a display unit  201 , which displays the scaled signal, and a controller  202 , which controls the scaler  200  and the display unit  201 . The scaler  200  includes an analog-to-digital converter (ADC)  200 - 1 , which converts the input video signal into a digital signal, and registers  51   h  ( 200 - 2 ) through  6 Fh ( 200 - 7 ), which store a digital brightness signal included in a video signal. The scaler  200  further includes an up/down counter (not shown), which increases/decreases the brightness value or contrast value of the input video signal by one level in response to the controller  202 . 
     FIGS. 3A and 3B  are a flow chart illustrating a method of automatically setting image quality according to a first embodiment of the present invention. The method of setting the image quality automatically includes setting variable ranges of the brightness and the contrast (step  300 ), converting the brightness signal included in the input video signal into the digital signal (step  301 ), storing the digital brightness signal in one of the registers  51   h  through  6 Fh according to the brightness level of the digital brightness signal (step  302 ), determining whether the values of registers  5 Ah/ 64   h  are 0x00/0x00 (step  303 ), determining whether the values of registers  51   h / 53   h / 6 Dh/ 6 Fh are 0x00/0xHH/0xHH/0x00 (step  304 ), determining whether the values of registers  51   h / 53   h  are 0x00/0x00 (step  305 ), decreasing a brightness value of an output video signal by one level (step  306 ), determining whether the values of registers  51   h / 53   h  are 0xHH/0xHH (step  307 ), increasing a brightness value of the output video signal by one level (step  308 ), determining whether the values of registers  6 Dh/ 6 Fh are 0x00/0x00 (step  309 ), increasing contrast value of the output video signal by one level (step  310 ), determining whether the values of registers  6 Dh/ 6 Fh are 0xHH/0xHH (step  311 ), decreasing the contrast value of the output video signal by one level (step  312 ), determining whether the changed contrast value is between a first minimum value and a first maximum value (step  313 ), restoring the contrast value to the initial value of the contrast value (step  314 ), determining whether the changed brightness value is between a second minimum value and a second maximum value (step  315 ), restoring the brightness value to the initial value of the brightness value (step  316 ), and determining that the image quality is optimally set (step  317 ). 
   The method for setting the image quality automatically will now be described in more detail with reference to  FIGS. 2 ,  3 A and  3 B. 
   The controller  202  sets variable ranges of the brightness and the contrast, which will be used when compensating for the image quality (step  300 ), by setting first and second minimum values (Min.) and first and second maximum values (Max.) of the brightness and the contrast. Table 1 shows the variable ranges of the brightness and the contrast set by the controller  202 . 
   
     
       
             
             
           
             
             
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Brightness 
               Contrast 
             
           
        
         
             
                 
               Default 
                 
                 
               Default 
                 
             
             
               Min. 
               value 
               Max. 
               Min. 
               value 
               Max. 
             
             
                 
             
             
               fac. save 
               0 × 2B 
               fac. save 
               fac. save 
               0 × 70 
               fac. save 
             
             
               0 × 00~0 × 2A 
                 
               0 × 2C~0 × 3F 
               0 × 50~0 × 6F 
                 
               0 × 71~0 × 9F 
             
             
                 
             
           
        
       
     
   
   The controller  202  controls the scaling operation of the scaler  200  and the display operation of the display unit  201  to compensate the image quality. 
   The input video signal may be a video signal received via an antenna (not shown), or may be a video signal input from an external device such as a digital versatile disc (DVD) player or a set top box (STB). 
   The input video signal is input to the scaler  200 , and the scaler  200  scales the input video signal such that the video signal is adjusted for the specification of the display unit  201 . 
   The ADC  200 - 1  of the scaler  200  converts the input video signal into an 8-bit digital signal (step  301 ). The input video signal includes a color signal and a brightness signal, and the ADC  200 - 1  converts the color signal and the brightness signal into the digital signal. The digital brightness signal is used to compensate the image quality. 
   The scaler  200  stores the digital brightness signal received from the ADC  200 - 1  in one of the register  51   h    200 - 2  through register  6 Fh  200 - 7  according to the brightness level. The upper 4 bits of the 8-bit digital brightness signal are divided into 16 levels according to the brightness level, and the divided signals are stored in the register  51   h    200 - 2  through register  6 Fh  200 - 7  in 2-byte units (step  302 ). The scaler  200  includes register  51   h    200 - 2  through register  6 Fh  200 - 7  to compensate the image quality. The darkest digital brightness signal is stored in the  51   h  register  200 - 2 , and a brighter digital signal than the digital signal stored in the register  51   h    200 - 2  is stored in the register  52   h  (not shown). The digital brightness signals are stored in the registers, such that brightness signals at higher levels are stored in higher register and the brightest signal is stored in the register  6 Fh  200 - 7 . 
   The controller  202  determines whether the values stored in the register  5 Ah  200 - 4  and the register  64   h    200 - 5  are both 0x00(step  303 ). When a channel is changed or an input source is changed, the values of the register  5 Ah  200 - 4  and the register  64   h    200 - 5  are set to be 0x00. When the values of the register  5 Ah  200 - 4  and the register  64   h    200 - 5  represent full-black or full-white (0x00/0x00) due to a change of the channel or the input source, the image quality compensating operation is skipped. 
   However, if the values of the register  5 Ah  200 - 4  and the register  64   h    200 - 5  are not both 0x00, the controller  202  determines that the values of the registers  51   h / 53   h / 6 Dh/ 6 Fh  200 - 2 ,  200 - 3 ,  200 - 6 , and  200 - 7  are predetermined values 0x00, 0xHH, 0xHH, and 0x00, respectively (step  304 ). Here, the value 0xHH does not mean a certain number, but means the values besides 0x00. In a case where the values of registers  51   h / 53   h / 6 Dh/ 6 Fh ( 200 - 2 ,  200 - 3 ,  200 - 6 , and  200 - 7 ) are 0x00, 0xHH, 0xHH, and 0x00, and step  313  is performed. 
   However, when the values of registers  51   h / 53   h / 6 Dh/ 6 Fh ( 200 - 2 ,  200 - 3 ,  200 - 6 , and  200 - 7 ) are not 0x00, 0xHH, 0xHH, and 0x00, respectively, the controller  202  determines whether the values of registers  51   h / 53   h  ( 200 - 2  and  200 - 3 ) are both 0x00, which are first certain values (step  305 ). 
   If the values of the registers  51   h / 53   h  ( 200 - 2  and  200 - 3 ) are both 0x00, the controller  202  decreases the brightness value of an output video signal by one level (step  306 ). The controller  202  commands the scaler  200  to decrease the brightness value of the output video signal by one level. 
   If the values of the registers  51   h  ( 200 - 2 ) and  53   h  ( 200 - 3 ) are not determined to both be 0x00 in step  305 , the controller  202  determines whether the values of the registers  51   h / 53   h  ( 200 - 2  and  200 - 3 ) are both 0xHH, which are second certain values (step  307 ). 
   If the values of the registers  51   h / 53   h  ( 200 - 2  and  200 - 3 ) are both 0xHH, the controller  202  increases the brightness value of the output video signal by one level (step  308 ). The controller  202  commands the scaler  200  to increase the brightness value of the output video signal by one level. 
   However, if the values of the registers  51   h / 53   h  ( 200 - 2  and  200 - 3 ) are not both 0x00, or 0xHH, then step  313  is performed. 
   When the values of the registers  51   h / 53   h / 6 Dh/ 6 Fh ( 200 - 2 ,  200 - 3 ,  200 - 6  and  200 - 7 ) are not 0x00, 0xHH, 0xHH, and 0x00 respectively, the controller  202  determines whether the values of the registers  6 Dh/ 6 Fh ( 200 - 6  and  200 - 7 ) are both 0x00, that is, third certain values (step  309 ). 
   If the values of the registers  6 Dh/ 6 Fh ( 200 - 6  and  200 - 7 ) are both 0x00, the controller  202  increases the contrast value of the output video signal by one level (step  310 ). The controller  202  commands the scaler  200  to increase the contrast value of the output video signal by one level. 
   If the values of the registers  60   h  ( 200 - 6 ) and  6 Fh ( 200 - 7 ) are not both 0x00 in step  310 , the controller  202  determines whether the values of the registers  6 Dh/ 6 Fh ( 200 - 6  and  200 - 7 ) are both 0xHH, which are fourth certain values (step  311 ). 
   If the values of the registers  6 Dh/ 6 Fh ( 200 - 6  and  200 - 7 ) are both 0xHH, then the controller  202  decreases the contrast value of the output video signal by one level (step  312 ). The controller  202  commands the scaler  200  to decrease the contrast of the output video signal by one level. 
   However, if the values of the registers  6 Dh/ 6 Fh ( 200 - 6  and  200 - 7 ) are not both 0x00, or 0xHH, step  313  is performed. 
   Then, the controller  202  determines whether that the changed contrast value is between the first minimum value and the first maximum value set in step  300  (step  313 ). In step  300 , the controller  202  sets the variable range of the contrast value between the minimum value and the maximum value. 
   If the changed contrast value is not between the first minimum and maximum values, the controller  202  restores the output video signal to the initial value of the contrast value, and performs step  301  (step  314 ). 
   If the contrast value is determined to be between the first minimum value and first maximum value in step  313 , the controller  202  determines whether the changed brightness value is between the minimum value and the second maximum value set in step  300  (step  315 ). In step  300 , the controller  202  sets the variable range of the brightness value having the minimum value and the maximum value so that the brightness can be changed within the variable range. 
   If the changed brightness value is not between the second minimum and maximum values, the controller  202  restores the output video signal to the initial value of the brightness value, and performs step  301  (step  316 ). 
   If the contrast values and the brightness values of the registers  51   h / 53   h / 6 Dh/ 6 Fh ( 200 - 2 ,  200 - 3 ,  200 - 6  and  200 - 7 ) are between the first and second minimum and maximum values, respectively, the controller  202  determines that the optimal image quality is set, and stores the corresponding brightness and contrast values (step  317 ). 
   As described above, according to exemplary embodiments of the present invention, variable ranges of the brightness and the contrast are set according to the image status to prevent the brightness and the contrast from changing greatly when changing the channel, changing the input source, or changing the screen mode. Also, the brightness and contrast are not changed when a full-white pattern or a full-black pattern is displayed, thus, preventing the image quality from changing excessively. 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.