Patent Publication Number: US-2007103601-A1

Title: Image data processing apparatus and method of processing image data

Description:
Exemplary embodiments of this invention were first described in Japanese Patent Application No. 2005-321674, which is hereby incorporated by reference in its entirety.  
     BACKGROUND  
      Exemplary embodiments of this invention relates to image data processing apparatus that generates a display data to be output to display devices from image data input to the apparatus. This invention also relates to methods of processing image data.  
      In image data display apparatus, a technique is known to improve the contrast of displayed image by performing g-compensations in accordance with the APL (Average Picture Level) of the image signal. That is, of gray-scale levels of bright or dark portions are corrected in accordance of the APL value.  
      For example, Japanese Laid-open Patent No. Hei 6-6820 (Patent Document 1) proposes a technique to prepare a plurality of g-compensation memories for storing respective g-compensation values and to select one of the memories, so that the contrast of the display device is improved by performing the g-compensation in accordance with the APL value. The technique proposed in Patent Document 1 does not ensure that, however, the γ-compensation most suitable for the displayed image is performed, because the same g-compensation memory is selected for different scenes if the APL values are the same. When the APL value is low, for example it is not distinguishable between an image that the entire areas are moderately dark and an image that has a bright area within very dark background. As a result, the same g-compensation memory is selected for both of the scenes.  
      On the other hand, Japanese Laid-open Patent 2001-343957 (Patent Document 2) proposes, in order to solve the above-mentioned problem, to detect the maximum/minimum values of brightness within the frame. That is, the minimum brightness and the maximum brightness are detected for each frame, and setting the brightness characteristic of the display image in accordance with the detected values enhances the contrast. Thereby enables a further precise display of the image. For example, it becomes possible to distinguish between the images that the entire areas are moderately dark and the image that has a bright area within very dark background, even if the APL values of respective images are low and the same. Accordingly, it is possible to select g-compensation memories suitable for the respective images.  
      The method of detecting the maximum brightness value and the minimum brightness value in the frame disclosed in Patent Document 2 is as follows: serially inputting into a comparator input image data and the brightness held in a latch, which in the maximum or the minimum brightness data among the previously input data, and re-holding the larger or the smaller one of the data into the latch depending on the result of the comparison.  
      However, the method of obtaining the maximum or the minimum brightness value of each frame by comparing all of the image data in the frame has problems when some types of noises are incorporated in the image data of the frame. When, for example, an extremely bright pixel exists as a noise in overall dark image, the brightness value of the extremely bright pixel, which is the noise, is stored as the maximum brightness in the latch. While, when an extremely dark pixel exists as a noise in overall bright image, the brightness value of the extremely dark pixel, which is the noise, is stored as the minimum brightness in the latch. If the g-compensation is performed in accordance with thus obtained maximum or minimum brightness value because of the noise, the compensation is performed differently from what should be.  
     SUMMARY  
      Various exemplary embodiments of this invention provide an image data processing apparatus, and a method of image processing that is capable of performing image data processing, even when a noise is incorporated in the image, with high accuracy by suppressing the influence of the noise. Various exemplary embodiments of this invention also provides a method of detecting a brightness characteristic of image data, even when a noise is incorporated in the image, with high accuracy.  
      In order to address or solve the above, various exemplary embodiments of this invention provide an image data processing apparatus for generating display data to be output to a display device from input image data. The apparatus includes a brightness characteristic detection circuit that detects a brightness characteristic of the input image data; and a correction circuit that generates the display data by correcting the input image data with a correction parameter set in accordance with the detected brightness characteristic. The image data includes brightness values of pixels in a frame, and the brightness characteristic detection circuit detects the brightness characteristic of the image data by dividing a specified area of the frame into a plurality of divided areas including respective pluralities of the pixels, calculating respective average brightness characteristics of the divided areas, and comparing the average brightness characteristics of the divided areas with each other to obtain at least one of a maximum and a minimum brightness value of the frame.  
      According to various exemplary embodiments, the detection circuit may calculate accumulated brightness values of the divided areas as the respective average brightness characteristics by accumulating the brightness values of the pixels within each of the divided areas.  
      According to various exemplary embodiments, the detection circuit may capable of setting respective indexes for the divided areas such that the indexes are considered when comparing the average brightness characteristics of the divided areas.  
      According to various exemplary embodiments, the detection circuit may divide the specified area of the frame such that the divided areas are arranged in a plurality of rows including respective pluralities of the divided areas, and the detection circuit may include: an accumulator that accumulates the brightness values of the pixels within each of the divided areas to produce the accumulated brightness values of the divided areas; a processing memory capable of storing the accumulated brightness values of the divided areas in any one of the rows produced by the accumulator; and a comparator that selects at least one of a largest and a smallest one of the accumulated brightness values of the divided areas stored in the processing memory.  
      In order to solve above-described problems, various exemplary embodiments of this invention provide method of processing image data that includes receiving image data including brightness values of a plurality of pixels in a frame; detecting a brightness characteristic of the image data; and generating a display data by correcting the image data with a correction parameter set in accordance with the detected brightness characteristic. The detecting includes: dividing a specified area of the frame into a plurality of divided areas including respective pluralities of the pixels; calculating average brightness characteristics of the divided areas; and comparing the average brightness characteristics with each other to obtain at least one of a maximum and a minimum brightness value of the frame.  
      According to various exemplary embodiments, the calculating may include accumulating the brightness values of the pixels in each of the divided areas to produce accumulated brightness values of the divided areas as the average brightness characteristics of the divided areas; and the comparing is performed such that at least one of a largest and a smallest one of the accumulated brightness values of the divided areas is selected as the at least one of a maximum and a minimum brightness value of the frame.  
      According to various exemplary embodiments, the dividing may be performed such that the divided areas are arranged in a plurality of rows including respective pluralities of the divided areas; and the calculating and the comparing may include the steps of: (a1) producing the accumulated brightness values of the divided areas in a first one of the rows and storing the produced accumulated brightness values in respective addresses of a processing memory; (a2) selecting at least one of a largest and a smallest one of the values stored in the processing memory and holding the selected one of values in a register; (a3) producing the accumulated brightness values of the divided areas in a next one of the rows and storing the produced accumulated brightness values in the respective addresses of the processing memory; (a4) selecting the at least one of a largest and a smallest one among the values stored in the processing memory and the value previously held in the register, and holding the selected one of the values in the register; and (a5) repeating the steps (a3) and (a4) until the at least one of a largest and a smallest one of the values among the accumulated brightness values of the divided areas in a last one of the rows stored in the respective addresses of the processing memory and the value previously held in the resister is selected and held in the register as the at least one of a maximum and a minimum brightness value of the frame.  
      According to various exemplary embodiments, the plurality of pixels of each of the divided areas may be arranged in a plurality of lines; and the accumulated brightness values of the divided areas may be calculated, for each of the rows, by the steps of: (b1) accumulating the brightness values of the pixels in a first one of the lines in each of the divided areas to produce intermediate accumulated brightness values of the divided areas and storing the produced values of the divided areas in the respective addresses of the processing memory; (b2) accumulating the brightness values of the pixels in a next one of the lines in each of the divided areas to the values previously stored in the respective addresses of the processing memory to produce update intermediate accumulated brightness values of the divided areas and storing the produced values of the divided areas in the respective addresses of the processing memory; and (b3) repeating the step (b2) until the brightness values of the pixels in a last one of the lines in each of the divided areas are accumulated and the produced updated intermediate accumulated brightness values of the divided areas are stored in the respective addresses of the processing memory as the accumulated brightness values of the divided areas.  
      In order to solve above-described problems, various exemplary embodiments of this invention provide method of detecting a brightness characteristic of image data that includes brightness values of a plurality of pixels in a frame. The method includes: dividing a specified area of the frame into a plurality of divided areas including respective pluralities of the pixels; calculating average brightness characteristics of the divided areas; and comparing the average brightness characteristics with each other to obtain at least one of a maximum and a minimum brightness value of the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Various exemplary details of apparatus and methods are described. with reference to the following figures, wherein:  
       FIG. 1  is a block diagram showing a construction of a first exemplary image data processing apparatus according to this invention;  
       FIG. 2  is a block diagram showing a construction of an exemplary brightness characteristic detection circuit;  
       FIG. 3  is an exemplary arrangement of pixel blocks in a frame according to an exemplary embodiment;  
       FIG. 4  is a schematic diagram showing an exemplary order of processing the pixels;  
       FIG. 5  is a schematic diagram showing an exemplary relationship between the pixel blocks and addresses of the processing memory;  
       FIG. 6  is a flow chart showing an exemplary procedure for calculating maximum brightness value;  
       FIG. 7  is an exemplary block diagram showing another exemplary embodiment of brightness characteristic detection circuit;  
       FIG. 8A  is an exemplary arrangement of valid and invalid pixel blocks;  
       FIG. 8B  is exemplary data in the valid bits memory corresponding to the arrangement shown in  FIG. 8A ;  
       FIG. 9A  is Another exemplary arrangement of valid and invalid pixel blocks; and  
       FIG. 9B  is exemplary data in the valid bits memory corresponding to the arrangement shown in  FIG. 9A . 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
     First Embodiment  
       FIG. 1  is a block diagram showing a construction of a first exemplary image data processing apparatus according to this invention. The exemplary apparatus  10  shown in  FIG. 1  includes a brightness characteristic detection circuit  1 , a correction parameter setting circuit  2 , and a display data generation circuit  3 . The brightness characteristic detection circuit  1  detects a brightness characteristic of input image data. The correction parameter setting circuit  2  sets parameter or parameters of correction in accordance with the brightness characteristic detected by the detection circuit  1 . The display data generation circuit  3  corrects the input image data using the correction parameters set by the correction parameter setting circuit  2  and generates display data to be output to a display device. The correction parameter setting circuit  2  and the display data generation circuit  3  constitutes a correction circuit  4 .  
       FIG. 2  is a detailed block diagram showing a construction of an exemplary brightness characteristic detection circuit  1 . The exemplary brightness characteristic detection circuit  1  includes an adder  11 , accumulated value register  12 , processing memory  13 , comparators  14 A and  14 B, a maximum value register  15 A, a minimum value register  15 B, and dividers  16 A and  16 B. The combination of the adder  11  and the accumulated value register  12  functions as an accumulator.  
      In this exemplary embodiment, a frame of image is divided into a plurality of divided areas (which will be called as “pixel blocks” hereinafter) including the same numbers of pixels. Accumulated brightness values of respective pixel blocks are calculated by accumulating the brightness values of the pixels included in respective pixel blocks. Moreover, maximum or minimum brightness value of the image data is calculated by comparing the accumulated brightness values of the pixel blocks. Thus, even if a large noise is incorporated in a particular pixel, the influence of the noise may be suppressed.  
       FIG. 3  shows an exemplary arrangement of divided areas (pixel blocks) in a frame according to this exemplary embodiment. The frame  21  is divided into a plurality of pixel blocks  22 . As shown in  FIG. 3 , according to this embodiment, the pixel blocks  22  are arranged in the frame  21  in respective pluralities of rows and columns. Specifically, each pixel block  22  has a size of 32·32 pixels, while the frame  21  has a size of 1024·768 pixels (an XGA frame). Accordingly, number of the pixel blocks  22  arranged in the horizontal direction is 32, and number of the pixel blocks  22  arranged in the vertical direction is 24. In other words, the pixel blocks  22  is arranged in 24 rows each including 32 pixel blocks. Needless to say, however, the size of the pixel block may be set arbitrary.  
      An exemplary procedure for calculating a maximum and a minimum brightness values according to this embodiment will be explained in reference to FIGS.  2  to  5 .  FIG. 4  is a schematic diagram showing an exemplary order of processing the pixels.  FIG. 5  is a schematic diagram showing an exemplary relationship between the pixel blocks and addresses of the processing memory.  
      In this exemplary embodiment, the maximum brightness value may be calculated as follows. The image data, which includes brightness values of respective pixels  22 A, is serially input to the brightness characteristic detection circuit  1  in an order beginning from the upper left of the frame  21  as shown by the arrows in  FIG. 4 . Accordingly, brightness values of the pixels in the pixel blocks  22  in the upper-most row, or #0 to #31 blocks of the pixel blocks  22 , are firstly processed.  
      That is, using the adder  11  and the accumulated value register  12 , which are combined to function as an accumulator, and the processing memory  13 , accumulate brightness values of the pixel blocks  22  in the first row (#0 to #331 blocks) are calculated and stored in respective addressed of the processing memory  13 . The processing memory  13  has a number of addresses capable of storing the respective accumulated brightness values of the pixel blocks  22  arranged in each of the rows (i.e., 32 in the case shown in  FIG. 3 ).  
      Then, using the combination of the first comparator  14 A and the maximum value register  15 A and the combination of the second comparator  14 B and the minimum value register  15 B, the accumulated brightness values stored in respective addressed of the processing memory  13  are compared with each other, and a largest and the smallest ones of them are selected and held in the maximum value register  15 A and the minimum value register  15 B, respectively.  
      In practice, the comparison of the accumulated brightness values may be performed using the combination of the comparator  14 A or  14 B and the register  15 A or  15 B shown in  FIG. 2  as follows. Firstly, the first one of the accumulated brightness values is held in the register  15 A and  15 B as a current maximum and a current minimum value, respectively. Then the next one of the accumulated brightness values is compared with the current maximum and the current minimum value held in the registers  15 A and  15 B using the comparators  14 A and  14 B, respectively. The larger and the smaller one of them are held in the register  15 A and  15 B as updated current maximum and minimum values in the registers  15 A and  15 B. The same procedure may be repeated until the last one of the accumulated brightness values stored in the processing memory  13  is compared with the current maximum and minimum values and the larger and the smaller ones of them are held in the registers  15 A and  15 B.  
      Then, the processing of the brightness values of the pixels within the pixel blocks  22  in the next row (#32 to #63 blocks) are performed.  
      That is, using the accumulator (the combination of the adder  11  and the accumulated value register  12 ) and the processing memory  13 , accumulate brightness values of the pixel blocks  22  in the second row are calculated and stored in respective addressed of the processing memory  13 . Further, using the combination of the comparators  14 A and  14 B and the registers  15 A and  15 B, the accumulated brightness values stored in respective addressed of the processing memory  13  are compared with each other. The accumulated brightness values stored in the processing memory  13  are also compared with the values previously held in the registers  15 A and  15 B, which are the maximum and the minimum values among the accumulated brightness values of the pixel blocks in the previous row,. The largest and the smallest ones of them are selected and held in the registers  15 A and  15 B, respectively.  
      The comparison may also be performed using the combination of the comparators  14 A and  14 B and the registers  15 A and  15 B. At this time, the largest and the smallest ones of the accumulated brightness values of the pixel blocks  22  in the previous row are previously held in the maximum value register  15 A and the minimum value register  15 B, respectively. Accordingly, the first and the following ones of the accumulated brightness values stored in the processing memory  13  may be repeatedly compared with the current maximum or minimum value hest in the register  15 A or  15 B, and the larger and the smaller ones of them may be held in the registers  15 A and  15 B, respectively.  
      The same procedure is repeated until the brightness values of the pixels in the pixel blocks  22  in the last one of the rows are processed. As a result, the accumulated brightness values of all pixel blocks are compared with each other and the largest and the smallest ones of them are selected and held in the maximum value register  15 A and the minimum value register  15 B, respectively.  
      Thus, the exemplary brightness characteristic detection circuit  1  shown in  FIG. 2  includes a processing memory  13  capable of storing the accumulated brightness values of the pixel blocks  22  in one of the rows. The processing memory  13  is repeatedly used during for obtaining the maximum or the minimum brightness value. Accordingly, it is not necessary to use a memory that is capable of storing the accumulated brightness values of all the pixel blocks  22 . Thus, the image data processing apparatus requires a small area of the semiconductor substrate and may be realized with a low cost.  
      Furthermore, the processing memory is also used repeatedly for calculating the accumulated brightness values of the pixel blocks  22  in a row.  
      As shown in  FIG. 5 , plurality of pixels  22 A in each pixel block  22  is arranged along a plurality of lines in the horizontal direction. As shown by the arrows in  FIG. 4 , the image data is serially input to the brightness characteristic detection circuit  1  in an order beginning from the pixels in the upper-most line in the pixel blocks  22  in the upper-most row.  
      First of all, brightness values of the 1st to the 32nd pixels in the 1st line of #0 block of the pixel blocks  22  are accumulated, using the adder  11  and the accumulated value register  12 , and a first intermediate accumulated brightness value is produced. The produced value is stored in address 0 h of the processing memory  13 . Further, brightness values of the pixels in the 1st line within #1 to #31 blocks of the pixel blocks  22 , which are arranged in the horizontal direction in the upper-most row, are accumulated. Needless to say, the accumulated value register  12  is cleared before accumulating the brightness values of the pixels  22 A in different pixel blocks  22 . Produced first intermediate accumulated brightness values of the #1 to #31 blocks are stored in addresses 1 h to 1 Fh, respectively, of the processing memory  13 . Here, “h” indicates that the addresses are shown in hexadecimal values.  
      Then, the brightness values of the pixels in the second line within #0 to #31 pixel blocks  22  are accumulated, using the same combination of the adder  11  and the accumulated value register  12 , to the first intermediate accumulated brightness values, which are read from the respective addresses of the processing memory  13 . Produced updated intermediate accumulated brightness values are stored again in the respective addresses of the processing memory  13 .  
      The same procedure is repeated until the brightness values of the pixels  22  in the last (the lower-most) line are accumulated, and the accumulated brightness values of all pixels  22 A in the pixel blocks  22  are produced and stored in the respective addresses of the processing memory  13 .  
      The procedure for obtaining the maximum brightness value of the frame  21  will be further explained with reference to  FIG. 6 .  FIG. 6  is a flow chart showing an exemplary procedure for calculating a maximum brightness value. Note that, although  FIG. 6  only shows an exemplary procedure for calculating the maximum brightness value, the exemplary procedure may similarly be used for calculating a minimum brightness value.  
      After clearing the processing memory  13  (Step S 1 ), accumulation of the brightness value of a pixel in a line (Step S 3 ) is repeated until the brightness values of all pixels in a line within a block are accumulated (Step S 4 ). The accumulated brightness value (intermediate accumulated brightness value) thus produced is stored in a corresponding address of the processing memory  13  (Step S 5 ). The same procedure is further repeated until the brightness values of pixels in the line within all blocks in a row is accumulated and stored in the corresponding addresses of the processing memory  13  (Step S 6 ).  
      Next, the brightness values of the pixels in the second lines in #0 to #31 blocks of the pixel blocks  22  are processed. Prior to the accumulation of the brightness values of the pixels in the second line of the #0 block of the pixel blocks  22 , the intermediate accumulated brightness value of the first line of #0 block of the images blocks  22  is read from the processing memory  13  (Step S 2  in  FIG. 6 ). The brightness values of 32 pixels in the second line within the #0 block of the pixel blocks  22  are accumulated to the read value (Steps S 3  and S 4  in  FIG. 6 ) and re-written into the address 0 h of the processing memory  13  (Step S 5  in  FIG. 6 ).  
      The same procedure is repeated until all intermediate accumulated brightness values of the first line of #0 to #31 blocks of the images blocks  22  are read from the processing memory  13 , and the brightness values of respective 32 pixels in the second line within all pixel blocks in a row are accumulated to the read values, and re-written into respective addresses 0 h to 1 Fh of the processing memory  13  (Steps S 2  through S 6  in  FIG. 6 ). At this point, 32 intermediate accumulated brightness values of the pixels in the 1st and the 2nd lines of #0 to #31 blocks of the images blocks  22  are stored in addresses 0 h to 1 Fh of the processing memory  13 .  
      The same procedure is further repeated until the brightness values of the pixels in the 32nd line are accumulated (Steps S 2  through S 7  in  FIG. 6 ). At this point, brightness values of all 1,024 pixels within all blocks in the upper-most row, or #0 to #31 blocks of the pixel blocks  22 , are accumulated and the accumulated brightness values are stored in respective addresses 0 h to 1 Fh of the processing memory  13 .  
      Next, the largest one of the accumulated brightness values stored in the processing memory  13  is selected.  
      Firstly, for example, the accumulated brightness value read from address 0 h of the processing memory  13  is stored in the maximum values register  15 A as a current maximum value MAX (current). Then, the accumulated brightness values stored in the processing memory  13  are read from the next address 1 h and compared with the current maximum value MAX (current) using the comparator  15 A (Step  8  in  FIG. 6 ), and the large one of them is stored in the maximum value register  15 A as an updated current maximum value MAX (current) (Step  9  in  FIG. 6 ). This procedure is repeated until all pixel blocks  22  in the upper-most row is processed (Steps S 8  through S 10  in  FIG. 6 ), i.e., until the accumulated brightness values store in all addresses of the processing memory  13  are read and compared. At this point, the largest one of the accumulated brightness values of 32 (#0 to #31) pixel blocks  22  in the upper-most row (MAX (0-31)) is selected and stored in the maximum value register  15 A.  
      The same procedure (Steps S 1  through S 10  in  FIG. 6 ) is repeated for the #32 to #63 pixel blocks  22  and the largest one of the accumulated brightness values of the pixels within the #32 to #63 blocks MAX (32-63) is selected. The largest value MAX (32-63) is compared with MAX (0-31) and the larger one of them is stored in the maximum value register  15 A as the updated current maximum brightness value MAX (current).  
      In practice, when using the exemplary brightness characteristic detection circuit  1  shown in  FIG. 2 , the selection of the largest one of the accumulated brightness values of the pixels within the #32 to #63 pixel blocks and the comparison with MAX (0-31) may be performed by repeatedly reading the accumulated brightness values of the #32 to #63 pixel blocks from the processing memory  13 , comparing with the current maximum value MAX (current) stored in the maximum value register  15 A, and storing the larger one of them as the updated current maximum brightness value MAX (current) in the maximum value register  15 A (Steps S 8  though S 10  in  FIG. 6 ).  
      The same procedure (Steps S 1  through SS 10  in  FIG. 6 ) is further repeated until all pixel blocks are processed (Step S 11  in  FIG. 6 ), i.e., until accumulated brightness values of the blocks  22  in the lower-most row (#736 to #767 blocks in the case shown in  FIG. 3 ) are compared with the current maximum value MAX (current). At this point, the largest one of the accumulated brightness values of all 768 pixel blocks  22  is selected and stored in the maximum value register  15 A as the current maximum value MAX (current).  
      Because each pixel block  22  includes 32·32=1,024 pixels, the maximum brightness value may be calculated by dividing the MAX (current) by 1,024 using the divider  16 A. Note that a simple procedure of discarding a predetermined number of the lowest bits may perform the division operation in the divider  16 A. The division may also be performed during the calculation of the accumulated brightness values. In other words, the accumulated brightness values stored in the processing memory  13  may be the values divided with the number of pixels in a pixel block  22 .  
      It is also possible to supply the value MAX (current) to the corrosion property setting circuit  2  as the maximum brightness value, without performing the division. In practice, however, it is preferable to perform the division so that the maximum brightness value is obtained as a data having a number of bits that is easy to be handled in the correction parameter setting circuit  2 .  
      According to this exemplary embodiment, the average brightness characteristic is detected by accumulating the brightness values of the pixels in each of the pixel blocks. The maximum brightness value of the frame  21  is obtained by selecting the largest one of the accumulated brightness values. Accordingly, even when a noise is incorporated into a pixel block, the influence of the noise may be suppressed.  
      This exemplary embodiment is based on an idea of, instead of detecting brightness characteristics of individual pixels, obtaining the maximum brightness value from average brightness characteristics detected for respective pixel blocks. Accordingly, even if pixel data with a high gray-scale level exists in the frame  1  as a noise, the influence of the noise may be suppressed to a level that may be ignored.  
      In determining average brightness characteristic of each pixel blocks, it is not always necessary to use the brightness values of all pixels in the pixel block. It is also possible to use brightness values of selected ones of the pixels as long as a number of pixels sufficient to suppress the influence of the noise are selected. In such a case, when calculating the maximum brightness value using the flow shown in  FIG. 6 , it is preferable to select the same number of pixels for detecting the average brightness characteristic in each of the pixel blocks.  
      The minimum brightness value within a frame may also be obtained using the similar procedure. In the description of the exemplary embodiment for obtaining the maximum brightness value described above, “larger” and “largest” may be substituted with “smaller” and “smallest”, and “maximum” and “MAX” may be substituted with “minimum” and “MIN”, respectively.  
      Same as the case of obtaining the maximum brightness value, even if pixel data with a low gray-scale level exists in a frame  1  as a noise, the influence of the noise to the minimum brightness value may be suppressed to a level that may be ignored.  
      It is not always necessary to use brightness values of pixels in the entire area of the frame to detect the brightness characteristic. The influences of brightness values of pixels in some areas, such as peripheral areas, to the brightness characteristic of the frame  21  are small. Accordingly, it is possible to exclude, from the beginning, such a low influence areas from the processing. That is, the pixel blocks  22  for detecting the average brightness characteristics may be arranged in a specified area of the frame, which may be the entire area of the frame  21  or a partial area within the frame  21 .  
      In the exemplary embodiment, accumulated brightness values of the pixel blocks  22  are calculated during processing for obtaining the maximum brightness value. Thus, an average brightness value for the entire frame  21  may be obtained by adding the accumulated brightness values of all pixel blocks  22  in the frame  21 . In other words, the exemplary brightness characteristic detecting circuit  1  shown in  FIG. 3  may also calculate the average brightness value for the entire frame by only adding small number of additional components. A more appropriate setting of the correction parameters may be realized by using the average brightness value in addition to the maximum and/or the minimum brightness values.  
     Second Embodiment  
      In the first exemplary embodiment, the brightness characteristics, or the accumulated brightness values, of all pixel blocks are equally utilized in determining the brightness characteristic of the frame. That is, the accumulated brightness values of all pixel blocks are compared with each other to obtain the maximum or the minimum brightness value without treating any of them differently. However, it is possible to set indexes to be considered in comparing the brightness characteristics of the pixel blocks.  
       FIG. 7  is an exemplary block diagram showing another exemplary embodiment of brightness characteristic detection circuit  1 . In this exemplary embodiment, valid bits are set for the pixel blocks as the indexes and are stored in a valid bits memory  17 . In order to use the valid bits, necessary ones of them are read from the valid bit memory  17  and held in a valid bit register  18 . The valid bits held in the valid bit register  18  controls the maximum value register  15 A and the minimum value register  15 B. Thereby, each of the pixel blocks is set, depending on the value of the corresponding valid bit, to be valid or invalid during obtaining the maximum or the minimum brightness value.  
      It is assumed that the frame  21  is divided as shown in  FIG. 3 . That is, the frame  21  is divided into 32 pixel blocks in the horizontal direction and into 24 pixel blocks in the vertical direction, or into 765 divided blocks in total.  FIG. 8A  shows an exemplary arrangement of valid and invalid pixel blocks. In the example shown in  FIG. 8A , the upper-most three rows  23  and the lower-most three rows  24  are set to be invalid, and are excluded from the processing.  FIG. 9A  shows another exemplary arrangement of valid and invalid pixel blocks. In the example shown in  FIG. 9A , the pixel blocks in the predefined area  25  are set to be valid and are used for the processing. The remaining blocks are set to be invalid and excluded from the processing.  
      In this exemplary embodiment, the valid bit is provided for each of the pixel blocks  22  as a flag. When calculating the maximum or the minimum brightness value, each block is determined to be valid or invalid referring to the value of the valid bit. In the exemplary circuit construction shown in  FIG. 7 , the valid bits memory  17  is constructed as a 32-bits·24-words memory block. One-bit memory element is provided for each pixel block. As shown in  FIG. 8B and 9B , “1” is written in the bits corresponding to valid blocks, and “0” is written in the bits corresponding to invalid blocks.  
      Before starting to process the accumulated brightness values of the first pixel block in a row, the valid bits corresponding to the pixel blocks in the row may be read from the valid bit memory  17 . Each of the valid bits indicates whether the corresponding one of the 32 pixel blocks in the row is valid or invalid. The valid bits may be held in the valid bid register and be referenced, when reading and comparing the accumulated brightness values from the processing memory  13 . That is, the accumulated brightness value is stored as MAX (current) or MIN (current) only when the corresponding pixel block is valid.  
      As explained above, valid bits corresponding to respective pixel blocks may be provided, and the valid bits may be referenced to specify the pixel blocks to be utilized for obtaining the maximum or the minimum brightness value.  
      Further, it is also possible to provide a plurality of valid bits, instead of a single bit, for each of the pixel blocks. Thereby, it is possible to give weights to specific pixel blocks, instead of merely setting each of the blocks to be valid or invalid. When 2-bits valid bits are provided for each of the pixel blocks, for example, four levels of weight coefficients, i.e., “00”, “01”, “10”, and “11” may be set for each of the pixel blocks. The weight coefficient is considered when comparing the accumulated brightness values of the pixel blocks. Thus, the maximum or the minimum brightness value that is to be used in the correction of, for example, contrast of the image, may be calculated by differentiating the areas, or the pixel blocks of high and low importance.  
      As explained above, according to exemplary embodiments of image data processing apparatus, methods of processing image data, and methods of detecting brightness characteristic according to this invention, a frame is divided into a plurality of divided areas and brightness characteristic of the image data is obtained by calculating a maximum or a minimum brightness value by detecting average brightness characteristics of respective divided areas. Accordingly, even if a noise is incorporated into a pixel, the influence of the noise may be suppressed.  
      So far, exemplary image data processing apparatus, methods of processing image data, and methods of detecting brightness characteristic according to this invention are explained in detail in reference to specific embodiments. However, this invention is not limited to the embodiments described above, but various improvements and modifications may be made within the spirit of this invention.