Abstract:
An oblique correlation detection section detects correlation in an oblique direction (oblique correlation) of a composite video signal. A line correlation chrominance separation section extracts a first chrominance signal from the composite video signal based on vertical correlation of the composite video signal. A first chrominance signal acquisition section acquires a second chrominance signal based on horizontal self-correlation of the first chrominance signal. The first chrominance signal acquisition section detects the self-correlation within a range corresponding to the degree of the oblique correlation detected by the oblique detection section.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a device and method for separating a luminance signal (Y) and/or a chrominance signal (C) from a composite video signal. 
   In recent years, as TV receivers have been increasingly upsized and enhanced in image quality, higher importance has been placed on enhancement in the performance of a Y/C separation device for separating a luminance signal (Y) and a chrominance signal (C) from a composite video signal. 
   A conventional Y/C separation device will be described with reference to  FIG. 11 .  FIG. 11  is a block diagram of a Y/C separation device disclosed in Japanese Laid-Open Patent Publication No. 5-111051. Referring to  FIG. 11 , an input terminal  31  receives a band-limited chrominance signal output from a multi-line comb filter. Delay circuits  32  to  35 , connected to the input terminal  31  in series, respectively delay the input signal by a half period of the chrominance signal and output the delayed signal. Inverter circuits  36  and  37  are connected to the delay circuits  32  and  34 , respectively. Minimum circuits  38  to  45  are placed to receive the delayed signals. The minimum circuits  38  to  42 , respectively having three input terminals, select the minimum signal among signals input at the three input terminals and output the selected signal. The minimum circuits  43  to  45 , respectively having two input terminals, select the minimum signal among signals input at the two input terminals and output the selected signal. Specifically, the three input terminals of the minimum circuit  38  receive the signals from the inverter circuit  37 , the delay circuit  35  and the input terminal  31 . The three input terminals of the minimum circuit  39  receive the signals from the delay circuit  35 , the input terminal  31  and the inverter circuit  36 . The three input terminals of the minimum circuit  40  receive the signals from the input terminal  31 , the inverter circuit  36  and the delay circuit  33 . The three input terminals of the minimum circuit  41  receive the signals from the inverter circuits  36  and  37  and the delay circuit  33 . The three input terminals of the minimum circuit  42  receive the signals from the delay circuits  33  and  35  and the inverter circuit  37 . The two input terminals of the minimum circuit  43  receive the signals from the inverter circuit  37  and the delay circuit  33 . The two input terminals of the minimum circuit  44  receive the signals from the inverter circuit  36  and the delay circuit  33 . The two input terminals of the minimum circuit  45  receive the signals from the inverter circuits  36  and  37 . The output signals of the minimum circuits  38  to  42  are supplied to a maximum circuit  46 , which selects the signal having the maximum amplitude among the five input signals and outputs the selected signal as a chrominance signal via an output terminal  47 . The output signals of the minimum circuits  43  to  45  are supplied to a maximum circuit  49 , which selects the signal having the maximum amplitude among the three input signals and outputs the selected signal to a subtractor  50 . The subtractor  50  subtracts the output signal of the maximum circuit  49  from a composite video signal input at an input terminal  51  and outputs the result as a luminance signal via an output terminal  52 . 
   The operation of the Y/C separation device configured as described above will be described. 
     FIG. 8  shows output waveforms on the side of the maximum circuit  49  obtained when a 1-period chrominance signal is input at the input terminal  31 .  FIG. 10  shows output waveforms on the side of the maximum circuit  46  obtained when a 1.5-period chrominance signal is input at the input terminal  31 . Description on the progress of the operation of this device is omitted here. See Japanese Laid-Open Patent Publication No. 5-111051 for details. The same reference codes as those used in this publication are used herein for easy reference. On the side of the maximum circuit  49  in  FIG. 11 , any input signal of one period or more is recognized as a chrominance signal. Therefore, an input 1-period signal is output as it is from the maximum circuit  49 . On the side of the maximum circuit  46  in  FIG. 11 , any input signal of 1.5 periods or more is recognized as a chrominance signal. Therefore, an input 1.5-period signal is output as it is from the maximum circuit  46 . 
   The conventional Y/C separation device described above recognizes input of a signal of 1.5 periods or more as input of a chrominance signal. Therefore, while the device can remove a signal representing input of a fine oblique line of one period or less, for example, it fails to remove a signal representing continuous input of an oblique line, for example, and thus is poor in cross-color suppression effect. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is providing a video signal processing device and method capable of reducing occurrence of cross-color due to leakage of a luminance signal component into a chrominance signal, in an event of input of a luminance signal having continuous correlation in an oblique direction, not only in an event of input of a luminance signal representing a fine oblique line. 
   The video signal processing device of the present invention includes: an oblique correlation detection section, a line correlation chrominance separation section and a first chrominance signal acquisition section. The oblique correlation detection section detects correlation in an oblique direction (oblique correlation) of a composite video signal. The line correlation chrominance separation section extracts a first chrominance signal from the composite video signal based on vertical correlation of the composite video signal. The first chrominance signal acquisition section acquires a second chrominance signal based on horizontal self-correlation of the first chrominance signal. The first chrominance signal acquisition section detects the self-correlation within a range corresponding to the degree of the oblique correlation detected by the oblique detection section. 
   The video signal processing method of the present invention includes steps (a) to (c). In the step (a), correlation in an oblique direction (oblique correlation) of a composite video signal is detected. In the step (b), a first chrominance signal is extracted from the composite video signal based on vertical correlation of the composite video signal. In the step (c), a second chrominance signal is acquired based on horizontal self-correlation of the first chrominance signal. In the step (c), the self-correlation is detected within a range corresponding to the degree of the oblique correlation detected in the step (a). 
   According to the present invention, the correlation of luminance signal components in an oblique direction is detected from 3-line video signals of an input composite video signal. According to the result of this detection, the horizontal correlation detection range is switched. Therefore, in an event that an oblique-direction luminance signal component representing an oblique line, for example, enters the line correlation chrominance separation circuit and fails to be correctly separated by the line correlation chrominance separation circuit, resulting in leakage into the output line correlation chrominance signal, the horizontal correlation range can be widened. By this widening, occurrence of cross-color can be reduced in the output chrominance signal, and in addition, the resolution in the oblique direction can be improved in the output luminance signal. When no oblique line is input, the horizontal correlation range may be narrowed, so that the normal chrominance signal can be correctly output, and thus decolorization and reduction in color saturation, which may occur when the horizontal correlation range is excessively wide, can be suppressed. 
   The video signal processing device of the present invention is suitably used for equipment outputting a video signal, such as a TV receiver including a liquid crystal TV, a plasma display TV and an organic EL TV, a video capture board, a personal computer, a videocassette recorder and the like, to reduce cross-color that may occur when a video signal containing an oblique line is input, or suppress decolorization and reduction in color saturation that may occur when a video signal containing no oblique line is input. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram showing the entire construction of a TV receiver in an embodiment of the present invention. 
       FIG. 2  is a block diagram of a Y/C separation device shown in  FIG. 1 . 
       FIG. 3  is a block diagram of a horizontal 3-point correlation circuit shown in  FIG. 2 . 
       FIG. 4  is a block diagram of a horizontal 5-point correlation circuit shown in  FIG. 2 . 
       FIG. 5  is a block diagram of a horizontal 7-point correlation circuit shown in  FIG. 2 . 
       FIG. 6  is a block diagram of an oblique correlation detection circuit shown in  FIG. 2 . 
       FIG. 7  is a view showing output waveforms of respective sections obtained when a 1-period oblique signal is input into the Y/C separation device of  FIG. 2 . 
       FIG. 8  is a view showing output waveforms of respective sections obtained when a 1-period oblique signal is input into a conventional Y/C separation device. 
       FIG. 9  is a view showing output waveforms of respective sections obtained when a 1.5-period oblique signal is input into the Y/C separation device of  FIG. 2 . 
       FIG. 10  is a view showing output waveforms of respective sections obtained when a 1.5-period oblique signal is input into the conventional Y/C separation device. 
       FIG. 11  is a block diagram of the conventional Y/C separation device. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   &lt;Entire Construction of TV Receiver&gt; 
     FIG. 1  is a block diagram showing the entire construction of a TV receiver  10  in an embodiment according to the present invention. The TV receiver  10  includes a terrestrial tuner  1 , an AV switch  2 , a Y/C separation device  3 , a chrominance demodulation circuit  4 , a RGB conversion circuit  5 , a monitor  6 , an audio processing circuit  7 , a voice output circuit  8  and a speaker  9 . 
   The terrestrial tuner  1  receives broadcasts allocated for respective channels. The AV switch  2  switches between a terrestrial broadcast signal S 10  received via the tuner  1  and video signal/audio signal input from external equipment such as a videocassette recorder. The Y/C separation device  3  separates a composite video signal S 100  output from the AV switch  2  into a luminance signal S 120  and a chrominance signal S 119 . The chrominance demodulation circuit  4  demodulates the chrominance signal S 119  output from the Y/C separation device  3  to a U signal S 40 U and a V signal S 40 V as color-difference signals. The RGB conversion circuit  5  converts the luminance signal S 120  output from the Y/C separation device  3  and the U signal S 40 U and the V signal S 40 V output from the chrominance demodulation circuit  4  into a R signal S 50 S, a G signal S 50 G and a B signal S 50 B. The monitor  6  displays an image from the R signal S 50 R, the G signal S 50 G and the B signal S 50 B output from the RGB conversion circuit  5 . The audio processing circuit  7  processes an audio signal S 100 A output from the AV switch  2 . The voice output circuit  8  amplifies an audio signal S 70  output from the audio processing circuit  7  and outputs an amplified audio signal S 80  to the speaker  9 . The speaker  9  outputs the audio signal S 80  externally. 
   &lt;Internal Configuration of Y/C Separation Device  3 &gt; 
     FIG. 2  is a block diagram of the Y/C separation device  3  shown in  FIG. 1 . The Y/C separation device  3  includes line memories  101  and  102 , a line correlation chrominance separation circuit  103 , an oblique correlation detection circuit  104 , delay circuits  105  to  110 , inverter circuits  111  to  114 , a horizontal 3-point correlation circuit  115 , a horizontal 5-point correlation circuit  116 , a horizontal 7-point correlation circuit  117 , switch circuits  118  and  119  and a subtractor  120 . 
   The line memory  101  delays the composite video signal S 100  output from the AV switch  2  (see  FIG. 1 ) by one horizontal scanning period (1 line). The line memory  102  delays a video signal S 101  output from the line memory  101  by one horizontal scanning period (1 line). 
   The line correlation chrominance separation circuit  103  extracts a chrominance signal S 103  from the composite video signal based on the correlation among the composite video signal S 100 , the video signal S 101  from the line memory  101  and a video signal S 102  from the line memory  102  (3-line correlation). 
   The oblique correlation detection circuit  104  detects the correlation of luminance signal components of the composite video signal in an oblique direction (oblique correlation). 
   The delay circuits  105  to  110  respectively delay the input chrominance signal by a half period of the chrominance signal. The delay circuit  105  delays the chrominance signal S 103  output from the line correlation chrominance separation circuit  103 . The delay circuits  106  to  110  respectively delay signals S 105  to S 109  output from the preceding delay circuits  105  to  109 . 
   The inverter circuit  111  inverts the chrominance signal S 103  output from the line correlation chrominance separation circuit  103 . The inverter circuits  112 ,  113  and  114  respectively invert the signals S 106 , S 108  and S 110  output from the delay circuits  106 ,  108  and  110 . 
   The horizontal 3-point correlation circuit  115  detects the correlation of the chrominance signal S 103  based on the three signals S 112 , S 107  and S 113  each delayed by a half period of the chrominance signal, and outputs a signal S 115  indicating the median level of the signals S 112 , S 107  and S 113 . 
   The horizontal 5-point correlation circuit  116  detects the correlation of the chrominance signal S 103  based on the five signals S 105 , S 112 , S 107 , S 113  and S 109  each delayed by a half period of the chrominance signal, and outputs a signal S 116  indicating the median level of the signals S 105 , S 112 , S 107 , S 113  and S 109 . 
   The horizontal 7-point correlation circuit  117  detects the correlation of the chrominance signal S 103  based on the seven signals S 111 , S 105 , S 112 , S 107 , S 113 , S 109  and S 114  each delayed by a half period of the chrominance signal, and outputs a signal S 117  indicating the median level of the signals S 111 , S 105 , S 112 , S 107 , S 113 , S 109  and S 114 . 
   The switch circuit  118  switches between the horizontal 3-point correlation output signal S 115  and the horizontal 5-point correlation output signal S 116  according to a detection result S 104  of the oblique correlation detection circuit  104 . 
   The switch circuit  119  switches between the horizontal 5-point correlation output signal S 116  and the horizontal 7-point correlation output signal S 117  according to the detection result S 104  of the oblique correlation detection circuit  104 . 
   The subtractor  120  subtracts an output signal S 118  of the switch circuit  118  from the 1-line delayed composite video signal S 101 . 
   &lt;Internal Configuration of Horizontal 3-Point Correlation Circuit  115 &gt; 
     FIG. 3  is a block diagram of the horizontal 3-point correlation circuit  115  shown in  FIG. 2 . The horizontal 3-point correlation circuit  115  includes minimum circuits  201  to  203  and a maximum circuit  204 . The minimum circuits  201  to  203  respectively receive two signals (S 107  and S 113 ), (S 113  and S 112 ) and (S 112  and S 107 ) among the adjacent three signals (S 112 , S 107  and S 113 ) of the chrominance signal delayed by a half period each, and select the minimum from the input signals. The maximum circuit  204  selects the maximum from output signals S 201  to S 203  of the minimum circuits  201  to  203  and outputs the result. 
   &lt;Internal Configuration of Horizontal 5-Point Correlation Circuit  116 &gt; 
     FIG. 4  is a block diagram of the horizontal 5-point correlation circuit  116  shown in  FIG. 2 . The horizontal 5-point correlation circuit  116  includes minimum circuits  301  to  305  and a maximum circuit  306 . The minimum circuits  301  to  305  respectively receive three signals (S 107 , S 113  and S 109 ), (S 112 , S 107  and S 113 ), (S 105 , S 112  and S 107 ), (S 109 , S 105  and S 112 ) and (S 113 , S 109  and S 105 ) among the adjacent five signals (S 105 , S 112 , S 107 , S 113  and S 109 ) of the chrominance signal delayed by a half period each, and select the minimum from the input signals. The maximum circuit  306  selects the maximum from output signals S 301  to S 305  of the minimum circuits  301  to  305  and outputs the result. 
   &lt;Internal Configuration of Horizontal 7-Point Correlation Circuit  117 &gt; 
     FIG. 5  is a block diagram of the horizontal 7-point correlation circuit  117  shown in  FIG. 2 . The horizontal 7-point correlation circuit  117  includes minimum circuits  401  to  407  and a maximum circuit  408 . The minimum circuits  401  to  407  respectively receive four signals (S 107 , S 113 , S 109  and S 114 ), (S 112 , S 107 , S 113  and S 109 ), (S 105 , S 112 , S 107  and S 113 ), (S 111 , S 105 , S 112  and S 107 ), (S 114 , S 111 , S 105  and S 112 ), (S 109 , S 114 , S 111  and S 105 ), (S 113 , S 109 , S 114  and S 111 ) among the adjacent seven signals (S 111 , S 105 , S 112 , S 107 , S 113 , S 109  and S 114 ) of the chrominance signal delayed by a half period each, and select the minimum from the input signals. The maximum circuit  408  selects the maximum from output signals S 401  to S 407  of the minimum circuits  401  to  407  and outputs the result. 
   &lt;Internal Configuration of Oblique Correlation Detection Circuit  104 &gt; 
     FIG. 6  is a block diagram of the oblique correlation detection circuit  104  shown in  FIG. 2 . The oblique correction detection circuit  104  includes band-pass filters  501 ,  502  and  503 , adders  504  and  505 , delay circuits  506  and  507 , subtractors  508  and  509 , absolute value circuits  510  and  511 , comparison circuits  512  and  513  and an OR circuit  514 . The band-pass filters  501 ,  502  and  503  respectively extract band-limited signals S 501 , S 502  and S 503  from the composite video signals S 100 , S 101  and S 102  with a chrominance subcarrier frequency of 3.58 MHz as the center frequency. The adder  504  adds the band-limited signals S 501  and S 502  output from the band-pass filters  501  and  502 . The adder  505  adds the band-limited signals S 502  and S 503  output from the band-pass filters  502  and  503 . The delay circuits  506  and  507  respectively delay signals S 504  and S 505  output from the adders  504  and  505  at a clock frequency four times as large as the chrominance subcarrier frequency. The subtractors  508  and  509  respectively subtract signals S 507  and S 506  output from the delay circuits  507  and  506  from the signals S 504  and S 505  output from the adders  504  and  505 . The absolute value circuits  510  and  511  respectively compute the absolute values of the outputs of the subtractors  508  and  509 . The comparison circuits  512  and  513  respectively compare the values output from the absolute value circuits  510  and  511  with a reference value. The OR circuit  514  outputs a determination of being “correlated” if at least one of the comparison circuits  512  and  513  outputs this determination. 
   &lt;Operation of Y/C Separation Device  3 &gt; 
   The operation of the Y/C separation device  3  having the configuration described above will be described. 
   First, the line memories  101  and  102  receive the composite video signal S 100  from the AV switch  2 , and provide the composite video signal S 102  delayed by one line and the composite video signal S 102  delayed by another line based on the received composite video signal S 100 . 
   The oblique correlation detection circuit  104  receives the 3-line composite video signals S 100 , S 101  and S 102  provided by the line memories  101  and  102 . 
   In the oblique correction detection circuit  104 , the band-pass filters  501 ,  502  and  503  respectively band-limit the input composite video signals S 100 , S 101  and S 102  with a pass frequency band having a center frequency of 3.58 MHz, to obtain the 3.58 MHz band-limited signals S 501 , S 502  and S 503 . 
   The adder  504  adds the band-limited signal S 502  for the center line and the band-limited signal S 501  apart by one line from the signal S 502 . The color phase inverts by 180 degrees between the adjacent lines. Therefore, by adding the band-limited signals S 502  and S 501  apart by one line from each other with the adder  504 , the chrominance signal components cancel each other out, and as a result, the band-limited luminance component signal S 504  is obtained. Likewise, the adder  505  adds the band-limited signal S 502  for the center line and the band-limited signal S 503  apart by one line from the signal S 502 . By this addition, the chrominance signal components cancel each other out, and as a result, the band-limited luminance component signal S 505  is obtained. 
   The delay circuits  506  and  507  respectively delay the luminance component signals S 504  and S 505  output from the adders  504  and  505  every clock, to obtain the delayed luminance component signals S 506  and S 507 . 
   The subtractor  508  computes the difference between the band-limited luminance component signal S 504  and the luminance component signal S 507  delayed by the delay circuit  507 , to thereby obtain an oblique-direction correlation value S 508  of the luminance signal component from the difference between sample points deviated from each other in an oblique direction. 
   The absolute value circuit  510  computes the absolute value of the correlation value S 508  output from the subtractor  508  to thereby obtain an oblique-direction difference value S 510 . 
   The comparison circuit  512  compares the oblique-direction difference value S 510  output from the absolute value circuit  510  with an oblique component reference level S 500 . If the oblique-direction difference is small enough to be less than the oblique component reference level S 500 , the comparison circuit  512  determines that there is oblique-direction correlation and outputs a signal S 512  indicating “correlated” to the OR circuit  514 . If the oblique-direction difference is large enough to be more than the oblique component reference level S 500 , the comparison circuit  512  determines that there is no oblique-direction correlation and outputs the signal S 512  indicating “not correlated” to the OR circuit  514 . 
   Similarly, to detect an oblique component opposite to the direction of the oblique component described above, the subtractor  509 , like the subtractor  508 , computes the difference between the band-limited luminance component signal S 505  and the luminance component signal S 506  delayed by the delay circuit  506 , to thereby obtain an oblique-direction correlation value S 509  of the luminance signal component from the difference between sample points deviated from each other in an oblique direction. 
   Like the absolute value circuit  510 , the absolute value circuit  511  computes the absolute value of the correlation value S 509  output from the subtractor  509  to thereby obtain an oblique-direction difference value S 511 . 
   The comparison circuit  513  compares the oblique-direction difference value S 511  output from the absolute value circuit  511  with the oblique component reference level S 500 . If the oblique-direction difference is small enough to be less than the oblique component reference level S 500 , the comparison circuit  513  determines that there is oblique-direction correlation and outputs a signal S 513  indicating “correlated” to the OR circuit  514 . If the oblique-direction difference is large enough to be more than the oblique component reference level S 500 , the comparison circuit  513  determines that there is no oblique-direction correlation and outputs a signal S 513  indicating “not correlated” to the OR circuit  514 . 
   The OR circuit  514  outputs the signal S 104  indicating “correlated” to the switch circuits  118  and  119  if at least one of the signal S 512  output from the comparison circuit  512  and the signal S 513  output from the comparison circuit  513  indicates “correlated”, or outputs the signal S 104  indicating “not correlated” to the switch circuits  118  and  119  if both the signal S 512  and the signal S 513  indicate “not correlated”. 
   The line correlation chrominance separation circuit  103  puts limitations on the input 3-line composite video signals S 100 , S 101  and S 102  with band-pass filters having a pass frequency band with a center frequency of 3.58 MHz, and adopts a majority decision or use a median value to determine the 3-line correlation of the chrominance signal, to thereby obtain the 3-line correlation chrominance signal S 103 . 
   The delay circuits  105  to  110 , connected in series downstream the line correlation chrominance separation circuit  103 , respectively delay the input chrominance signal by a half period each. 
   The inverter circuits  111 ,  112 ,  113  and  114  respectively invert the line correlation chrominance signal S 103  and the delayed signals S 106 , S 108  and S 110 , to obtain the inverted delayed signals S 111 , S 112 , S 113  and S 114 . 
   The horizontal 3-point correlation circuit  115  receives the delayed signal S 107  delayed by the delay circuit  107  and the inverted delayed signals S 112  and S 113  respectively inverted by the inverter circuits  112  and  113 , and outputs the median value S 115  determined from the magnitudes of the input three signals. 
   The horizontal 5-point correlation circuit  116  receives the delayed signals S 105 , S 107  and S 109  respectively delayed by the delay circuits  105 ,  107  and  109  and the inverted delayed signals S 112  and S 113  respectively inverted by the inverter circuits  112  and  113 , and outputs the median value S 116  determined from the magnitudes of the input five signals. 
   The horizontal 7-point correlation circuit  117  receives the delayed signals S 105 , S 107  and S 109  respectively delayed by the delay circuits  105 ,  107  and  109  and the inverted delayed signals S 111 , S 112 , S 113  and S 114  respectively inverted by the inverter circuits  111 ,  112 ,  113  and  114 , and outputs the median value S 117  determined from the magnitudes of the input seven signals. 
   The switch circuit  118  outputs the input signal S 116  as the chrominance signal S 118  for luminance separation when receiving the signal indicating “obliquely correlated” from the oblique correlation detection circuit  104 , or outputs the input signal S 115  as the chrominance signal S 118  for luminance separation when receiving the signal indicating“not obliquely correlated” from the oblique correlation detection circuit  104 . 
   The subtractor  120  subtracts the chrominance signal S 118  for luminance separation from the composite video signal S 101  for the center line, to thereby separate the luminance signal S 120  and output the luminance signal S 120  to the RGB conversion circuit. 
   The switch circuit  119  outputs the input signal S 117  as the chrominance signal S 119  to the chrominance demodulation circuit when receiving the signal indicating “obliquely correlated” from the oblique correlation detection circuit  104 , or outputs the input signal S 116  as the chrominance signal S 119  to the chrominance demodulation circuit when receiving the signal indicating “not obliquely correlated” from the oblique correlation detection circuit  104 . 
     FIG. 7  shows waveforms of the signals S 103 , S 105  to S 120  and S 101  obtained when an oblique line having a frequency component of one period is input. 
   In the conventional Y/C separation device, when a signal of one period of the chrominance signal is included in the line correlation chrominance signal S 103 , the 1-period signal remains in the chrominance signal S 118  for luminance separation as it is (see  FIG. 8 ). In this embodiment, however, the Y/C separation device  3  can remove this 1-period signal. 
     FIG. 9  shows waveforms of the signals S 103 , S 105  to S 120  and S 101  obtained when an oblique line having a frequency component of one and a half periods is input. 
   In the conventional Y/C separation device, when a signal of 1.5 periods of the chrominance signal is included in the line correlation chrominance signal S 103 , the 1.5-period signal remains in the chrominance signal S 119  as it is (see  FIG. 10 ). In this embodiment, however, the Y/C separation device  3  can remove this 1.5-period chrominance signal. 
   &lt;Effect&gt; 
   In this embodiment, the oblique correlation detection circuit  104  detects correlation of a luminance signal component in an oblique direction from the 3-line video signals of the input composite video signal. The switch circuits  118  and  119  respectively switch the horizontal correlation detection range according to the result of the above detection. For example, conventionally, when oblique-direction luminance signal components representing oblique stripes, for example, in the signals S 100 , S 101  and S 102  to be input into the 3-line correlation chrominance separation circuit are input in the line correlation chrominance separation circuit  103 , such components may fail to be correctly separated by the line correlation chrominance separation circuit  103 , resulting in leaking into the line correlation chrominance signal S 103 . However, in the Y/C separation device  3  of this embodiment, the horizontal correlation range is widened in an event of input of such an oblique line. This can reduce occurrence of cross-color in the output chrominance signal S 119  and also improve the oblique-direction resolution in the output luminance signal S 120 . In addition, since the horizontal correlation range can be narrowed when no oblique line is input, a normal chrominance signal can be output correctly, and this can suppress decolorization and reduction in color saturation that may occur due to excessively wide horizontal correlation range. 
   The above embodiment was described using switching between the horizontal 3-point correlation circuit  115  and the horizontal 5-point correlation circuit  116  and switching between the horizontal 5-point correlation circuit  115  and the horizontal 7-point correlation circuit  116  according to the result of the detection by the correlation detection circuit  104 . The number of horizontal correlation points provided for oblique correlation may be increased to nine, eleven or more. Naturally, as the number of horizontal points is greater, the number of periods of a signal enabling suppression of cross-color is greater. 
   In this embodiment, the TV receiver was mentioned as equipment to which the present invention was applied. Alternatively, it may specifically be a liquid crystal TV, a plasma display TV and an organic EL TV, a video capture board, a personal computer, a videocassette recorder and the like. 
   While the present invention has been described in a preferred embodiment, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than that specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.