Motion adaptive luminance signal and color signal separation filter

Claims

We claim:

1. A motion adaptive luminance and color signal separating filter for separating luminance and color signals from a composite color television signal in which the frequency of the color signal is multiplexed over the high-frequency region of the luminance signal, said filter including an interfield correlation device for separating the luminance and color signals in response to interframe correlation, the interfield correlation device comprising:

(A) luminance and color signal separating means for adding and subtracting a signal indicative of an objective sample point in a first field (n-field) and a plurality of signals indicative of sample points located proximate to the objective sample point in a picture and within fields (n-1 and n+1 fields) previously and subsequently adjacent to said first field, to provide a correlation between three fields which is utilized in turn, to perform separation of the color and luminance signals;

(B) correlation detecting means for calculating a difference signal in a set of the sample points whose chrominance subcarriers are in phase between the frames and spaced away from one another by one frame, the calculated difference signal being used to detect a direction of higher correlation for a set of sample points located about said objective sample point; and

(C) selection means for selecting sample points having a direction of higher correlation in said luminance and color signal separating means, based on the direction of correlation detected by said correlation detecting means, to thereby select one set of sample points in which to perform separation of the color and luminance signals using the interfield correlation device.

2. The motion adaptive luminance and color signal separating filter of claim 1, further comprising:

(A) means for detecting motion in the picture based on the interframe correlation;

(B) interframe correlation luminance and color signal separation means for separating the luminance and color signals, based on the interframe correlation; and

(C) mixing means for receiving an output of said interfield correlation device if the motion detected by said motion detecting means is relatively large and for receiving an output of said interframe correlation luminance and color signal separating means if the motion detected by said motion detecting means is relatively small, whereby the luminance and color signals from said interfield correlation device and said interframe correlation luminance and color signal separating means can be mixed.

3. The motion adaptive luminance and color signal separating filter of claim 2 wherein the set of sample points used to detect the difference in said correlation detecting means are present within the n-1 and n+1 fields previously and subsequently adjacent to the n-field including the objective sample point and located with the objective sample point being in the picture therebetween.

4. The motion adaptive luminance and color signal separating filter of claim 3 wherein said luminance and color signal separating means is adapted to extract a color signal by subtracting signals for three sample points having chrominance n-1 field subcarriers which are out of phase relative to the objective sample point by 180.degree., signals for three sample points having chrominance n+1 field subcarriers which are out of phase relative to the objective sample point by 180.degree. and a signal for the objective sample points.

5. The motion adaptive luminance and color signal separating filter of claim 2 wherein said correlation detecting means includes a plurality of absolute value circuits for determining the respective absolute values of a plurality of difference signals; and a minimum value selection circuit for determining the minimum absolute value of the absolute value signals output from said absolute value circuits.

6. The motion adaptive luminance and color signal separating filter of claim 2, further comprising infield luminance and color signal separating means for separating luminance and color signals using infield band limitations.

7. The motion adaptive luminance and color signal separating filter of claim 2, further comprising a plurality of subtracters for calculating difference signals; a plurality of absolute value circuits for determining respective absolute values from difference signals output from said subtracters; a minimum value selection circuit for determining the minimum value of the absolute value signals output from said absolute value circuits; a maximum value selection circuit for determining the maximum value of the absolute value signals output from said absolute value circuits; and a discriminating circuit for comparing outputs of said minimum and maximum value selection circuits with predetermined thresholds, whereby said selection means can be controlled to select said infield luminance and color signal separating means if the output of said maximum value selection circuit is smaller than a first predetermined threshold .alpha. or if the output of said minimum value selection circuit is larger than a second predetermined threshold .beta. and whereby said selection means can be controlled to select said interfield correlation device if the output of said maximum value selection circuit is larger than said first predetermined threshold .alpha. or if the output of said minimum value selection circuit is smaller than said second predetermined threshold .beta..

8. A device for producing a luminance signal from a composite color signal comprising:

separating means for separating a chrominance signal from the composite color signal by using a composite color signal from a first field, a composite color signal from a second field, and a composite color signal from a third field, the first field containing an objective point, said separating means including first means for producing a first and second signal, each first and second signal including a chrominance signal produced by using said objective point, a sample point in said second field, and a sample point in said third field; and

combining means for producing said luminance signal from one of said first and second signals and said composite color signal.

9. The device as claimed in claim 8 wherein said separating means further comprises:

third means for producing a third signal including a chrominance signal produced using the composite color signal of the objective point and the composite color signal of a sample point in said second field; and

selecting means for selecting of said first, second, or third signals based on which signal has a highest correlation;

said combining means subtracting the signal selected by said selecting means from said composite color signal to produce the luminance signal.

10. The device as claimed in claim 9 wherein said third means includes a band pass filter.

11. The device as claimed in claim 8 wherein said separating means mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

12. A device for separating a luminance signal from a composite color signal comprising:

a three-field separating circuit which receives a composite color signal and separates a luminance signal from the composite color signal by processing a composite color signal from a first field, a composite color signal from a second field, and a composite color signal from a third field, said first field containing an objective point, said three-field separating circuit including,

first means for producing a first and second signal, each first and second signal being a higher frequency component of the luminance signal produced by using said objective point, a sample point in said second field, and a sample point in said third field,

second means for producing a third signal having a lower frequency component of luminance signal produced by Using the composite color signal at said objective point and the color composite signal at a sample point in said second field, and

adding means for adding one of said first and second signals with said third signal to produce the luminance signal.

13. The device as claimed in claim 12 wherein said three-field separating circuit further comprises:

third means for producing a fourth signal being a higher frequency component of a luminance signal produced using the composite color signal of the objective point and the composite color signal of a sample point in said second field; and

selecting means for selecting either said first, second, or fourth signals based on which signal has a highest correlation;

said adding means adding the signal selected by said selecting means with said third signal to produce the luminance signal.

14. The device as claimed in claim 13 wherein said three field separating circuit further comprises:

fourth means for producing a fifth signal, said fifth signal being a higher frequency component of the luminance signal produced by using an infield separation process upon the composite color signal of said first field; and

selecting means for selecting either said first, second, fourth, or fifth signals;

said adding means adding the signal selected by said selecting means with said third signal to produce the luminance signal.

15. The device as claimed in claim 14 wherein said three field separating circuit further comprises:

correlation means for calculating a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame and for determining a direction in which sample points, located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

16. The device as claimed in claim 15 wherein said three field separating circuit further comprises:

threshold means for determining when the lowest correlation value is below a first threshold value and the highest correlation value is above a second threshold value;

said selecting means outputting said higher frequency component of said luminance signal produced by 9 the infield separation process when said threshold means determines that the lowest correlation value is below the first threshold value and that the highest correlation value is above the second threshold value;

said selecting means outputting the one of the higher frequency component luminance signals corresponding to the highest correlation value when said threshold means does not determine that the lowest correlation value is below the first threshold value and that the highest correlation value is above the second threshold value.

17. The device as claimed in claim 13 wherein said third means includes a low pass filter.

18. The device as claimed in claim 12 further comprising:

subtracting means for subtracting the luminance signal from the composite color signal to produce a chrominance signal.

19. The device as claimed in claim 12 wherein said separating means mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

20. A device for producing a chrominance signal from a composite color signal comprising:

separating means for generating three distinct separated chrominance signals from the composite signal, each separated chrominance signal being derived from a composite signal of a first field and a composite signal of a second field and for outputting said three distinct separated chrominance signals; and

selecting means, operatively connected to said separating means, for evaluating a correlation relationship between points in different fields and for selecting either one of said three distinct separated chrominance signals in accordance with the correlation evaluation, thereby providing the chrominance signal.

21. The device as claimed in claim 20 wherein said separating means mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

22. The device as claimed in claim 20 wherein said selecting means comprises:

correlation means for calculating a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame and for determining a direction in which sample points, located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

23. A device for producing a chrominance signal from a composite color signal comprising:

an interfield separating circuit generating three distinct separated chrominance signals from the composite signal, each separated chrominance signal being derived from a composite signal of a first field and a composite signal of a second field and for outputting said three distinct separated chrominance signals; and

a selecting circuit, operatively connected to said interfield separating circuit, to select one of said three distinct separated chrominance signals in accordance with a correlation evaluation.

24. The device as claimed in claim 23 wherein said interfield separating circuit mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

25. The device as claimed in claim 23, further comprising:

a correlator to calculate a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame and to determine a direction in which sample points, located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

26. A method for producing a luminance signal from a composite color signal comprising the steps of:

(a) separating a luminance signal from the composite color signal by using a composite color signal from a first field, a composite color signal from a second field, and a composite color signal from a third field by,

(a1) producing a first and second signal, each first and second signal being a higher frequency component of the luminance signal produced by using the objective point, a sample point in the second field and a sample point in the third field;

(a2) producing a third signal having a lower frequency component of the luminance signal produced by using the composite color signal at the objective point and the color composite signal at a sample point in the second field; and

(a3) adding one of the first and second signals with the third signal to produce the luminance signal.

27. The method as claimed in claim 26 wherein the first field represents a field containing an objective point, the second field representing a field preceding the first field in time, and the third field representing a field following the first field in time.

28. The method as claimed in claim 26 wherein said step (a) further comprises the sub-steps of:

(a4) producing a fourth signal being a higher frequency component of a luminance signal produced using the composite color signal of the objective point and the composite color signal of a sample point in the second field; and

(a5) selecting either the first, second, or fourth signals based on which signal has a highest correlation;

said step (a3) adding the signal selected by said step (a5) with the third signal to produce the luminance signal.

29. The method as claimed in claim 26 wherein said step (a) mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

30. The method as claimed in claim 26 wherein said step (a) further comprises the sub-steps of:

(a6) calculating a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame; and

(a7) determining a direction in which sample points, located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

31. The method as claimed in claim 30 wherein said step (a) further comprises the sub-steps of:

(a8) determining when the lowest correlation value is below a first threshold value and the highest correlation value is above a second threshold value;

(a9) outputting a higher frequency component of said luminance signal obtained by an infield YC separation process when the lowest correlation value is determined to be below the first threshold value and the highest correlation value is determined to be above the second threshold value; and

(a10) outputting the higher frequency component of said luminance signal corresponding to the highest correlation value when the lowest correlation value is not determined to be below the first threshold value and the highest correlation value is not determined to be above the second threshold value.

32. The method of claim 26 further comprising:

(b) subtracting the separated luminance signal from the composite color signal, thereby producing a chrominance signal.

33. A method for producing a luminance signal from a composite color signal comprising the steps of:

(a) developing a first luminance signal from the composite color signal;

(b) generating three distinct separated higher frequency luminance signal portions from the composite signal, each said higher frequency luminance signal portion being derived from a composite signal of a first field and a composite signal of a second field;

(c) evaluating a correlation relationship between points in different fields;

(d) selecting one of the three higher frequency luminance signal portions in accordance with the correlation evaluation; and

(e) combining said first luminance signal and said selected one of said higher frequency luminance signal portions to produce a more accurate luminance signal.

34. The method as claimed in claim 40 wherein said step (b) mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

35. The method as claimed in claim 33 wherein the first field contains an objective sample point and the second field contains a sample point and wherein said step (c) comprises the sub-steps of:

(c1) calculating a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame; and

(c2) determining a direction, in which sample points located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

36. The method as claimed in claim 35 wherein said step (c) further comprises the sub-steps of:

(c3) determining when the lowest correlation value is below a first threshold value and the highest correlation value is above a second threshold value;

said step (d) selecting a higher frequency luminance signal portion obtained by an infield separation process when the lowest correlation value is determined to be below the first threshold value and the highest correlation value is determined to be above the second threshold value;

said step (d) selecting the higher frequency luminance signal portion corresponding to the highest correlation value when the lowest correlation value is not determined to be below the first threshold value and the highest correlation value is not determined to be above the second threshold value.

37. A method for motion adaptive separating luminance and color signals from a composite color television signal in which the frequency of the color signal is multiplexed over the high-frequency region of the luminance signal, said filter including an interfield correlation device for separating the luminance and color signals in response to interframe correlation, the interfield correlation device comprising the steps of:

(a) adding and subtracting a signal indicative of an objective sample point in a first field and a plurality of signals indicative of sample points located proximate to the objective sample point in a picture and within fields previously and subsequently adjacent to the first field, to provide a correlation between three fields which is utilized, to perform separation of the color and luminance signals;

(b) calculating a difference signal for a set of the sample points whose chrominance subcarriers are in phase between the frames and spaced away from one another by one frame, the calculated difference signal being used to detect a direction of higher correlation for a set of sample points located about the objective sample point; and

(c) selecting a sample point having a direction of higher correlation based on the direction of correlation detected by said step (b), thereby selecting one of the three fields in which to perform separation of the color and luminance signals using the interfield correlation device.

38. The method as claimed in claim 37, further comprising the steps of:

(d) detecting motion in the picture based on the interframe correlation;

(e) separating the luminance and color signals, based on the interframe correlation; and

(f) mixing the luminance and chrominance signals produced by said steps (c) and (e) by using a greater quantity of the interfield correlated signals if the motion detected by said step (d) means is relatively large and using a greater quantity of the interframe correlated luminance and color signal if the motion detected by said step (d) is relatively small, thereby mixing the luminance and color signals according to the motion of the image.

39. A device for producing a luminance signal from a composite color signal comprising:

first luminance signal development means for developing a first luminance signal from the composite color signal;

separating means for generating three distinct separated higher frequency luminance signal portions from the composite signal, each said higher frequency luminance signal portion being derived from a composite signal of a first field and a composite signal of a second field and for outputting said three distinct separated higher frequency luminance signal portions; and

selecting means, operatively connected to said separating means, for evaluating a correlation relationship between points in different fields and for selecting one of said three higher frequency luminance signal portions in accordance with the correlation evaluation;

means, operatively connected to said first luminance signal development means and said selecting means, for combining said first luminance signal and the selected one of said higher frequency luminance signal portions, thereby producing a more accurate luminance signal.

40. The device as claimed in claim 39 wherein said separating means mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

41. The device as claimed in claim 39 wherein the first field contains an objective point and the second and the third fields contain sample points and wherein said selecting means comprises:

correlation means for calculating a difference signal among the sample points in which chrominance subcarriers are in phase between frames and spaced apart from one another by one frame and for determining a direction in which sample points, located proximate to the objective sample point, has a highest correlation value and a direction which has a lowest correlation value.

42. The device as claimed in claim 39 wherein said selecting means comprises:

threshold means for determining when the lowest correlation value is below a first threshold value and the highest correlation value is above a second threshold value;

said separating means further using infield YC separation to generate a fourth higher frequency luminance signal portion;

said selecting means outputting the fourth higher frequency luminance signal portion obtained by infield YC separation when said threshold means determines that the lowest correlation value is below the first threshold value and that the highest correlation value is above the second threshold value;

said selecting means outputting the one of said three distinct separated higher frequency luminance signal portions corresponding to the highest correlation value when said threshold means does not determine that the lowest correlation value is below the first threshold value and that the highest correlation value is above the second threshold value.

43. A device for producing a luminance signal from a composite color signal comprising:

first luminance signal development means for developing a first luminance signal from the composite color signal;

an interfield separating circuit generating three distinct separated higher frequency luminance signal portions from the composite signal, each said higher frequency luminance signal portion being derived from a composite signal of a first field and a composite signal of a second field and for outputting said three distinct separated higher frequency luminance signal portions; and

a selecting circuit, operatively connected to said interfield separating circuit, to select one of said three higher frequency luminance signal portions in accordance with a correlation evaluation; and

a combining circuit, operatively connected to said first luminance signal development means and said selecting circuit, combining said first luminance signal and the selected one of said three higher frequency luminance signal portions to produce a more accurate luminance signal.

44. A method for producing a chrominance signal and a luminance signal from a composite color signal comprising the steps of:

(a) generating three distinct separated chrominance signals from the composite signal, each separated chrominance signal being derived from a composite signal of a first field and a composite signal of a second field;

(b) selecting one of the three distinct separated chrominance signals; and

(c) combining said composite color signal and said selected chrominance signal to form a luminance signal.

45. The method as claimed in claim 44 wherein the first field contains an objective point, the second field precedes the first field in time, and a third field follows the first field in time.

46. The method as claimed in claims 44 wherein said step (a) mathematically sums a signal indicative of an objective sample point in a first field and one of a plurality of signals indicative of sample points located proximate to the objective sample point in a second field to provide interfield processing of the composite color signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motion adaptive luminance signal and color signal separating filter for separating a luminance signal (hereinafter referred to as "Y signal" or simply "Y") and a color signal (hereinafter referred to as "C signal" or simply "C") from a composite color television signal (hereinafter referred to as "V signal") in which the frequency of the C signal is multiplexed on the high frequency region of the Y signal.

The motion adaptive YC separating filter is a filter which locally judges whether a picture is a still picture or a motion picture and executes YC separation suitable to the pixel signal in that picture, at each of the locations thereof.

2. Description of the Related Art

The current NTSC signal system provides a composite signal comprising a C signal and a Y signal having its high-frequency region on which the frequency of the C signal is multiplexed. Therefore, television sets require YC separation. Imperfect YC separation causes the picture quality to deteriorate in cross color, dot crawl and so on.

With development of large-capacity digital memories, there have been proposed various types of signal processing circuits for improving the quality of picture. For example, one system which includes the use of a motion adaptive YC separation which utilizes a delay circuit having a delay time equal to or greater than the vertical scanning frequency of a television signal.

FIG. 10 is a block diagram showing one example of the conventional motion adaptive YC separating filters. In FIG. 10, the filter receives, at its input terminal 1, a V signal 101 according to the NTSC system. This signal is input to both the respective input terminals of infield YC separation circuit 4, interframe YC separating circuit 5, Y-signal motion detecting circuit 6 and C-signal motion detecting circuit 7.

In the infield YC separating circuit 4, the input signal is infield separated into a Y signal 102 and a C signal 103 through an infield filter (not shown), the Y and C signals then being applied respectively to the first inputs of Y-signal mixing circuit 9 and C-signal mixing circuit 10.

In the interframe YC separating circuit 5, the input signal is interframe separated into a Y signal 104 and a C signal 105. These Y and C signals are then supplied respectively to the second inputs of the Y-signal and C-signal mixing circuits 9 and 10.

On the other hand, a signal 106 indicative of the movement of Y signal detected by the Y-signal motion detecting circuit 6 is applied to one of the inputs of a synthesizer 8 while a signal 107 representative of the movement of C signal detected by the C-signal motion detecting circuit 7 is supplied to the other input of the synthesizer 8.

The synthesizer 8 forms a motion detection signal 108 which is input to the respective third inputs of the Y-signal and C-signal mixing circuits 9 and 10. Thus, the Y-signal motion detecting circuit 6, C-signal motion detecting circuit 7 and synthesizing circuit 8 define a motion detecting circuit 80.

The output 2 of the Y-signal mixing circuit 9 provides a motion adaptive separated Y signal 109 while the output 3 of the C-signal mixing circuit 10 provides a motion adaptive separated C signal 110.

This conventional YC separating circuit will now be described in operation.

On YC separation of V signal 101, the motion detecting circuit 80 judges whether the V signal 101 is one indicative of a still or motion picture, based on the output signal from the synthesizer 8 in which the outputs of the Y-signal and C-signal motion detecting circuits 6 and 7 are synthesized.

As shown in FIG. 11, the Y-signal motion detecting circuit 6 may comprise a one-frame delay circuit 53, a subtracter 54, a low pass filter 55 (hereinafter referred to as "LPF"), an absolute value circuit 56 and a nonlinear converting circuit 57. V signal 101, inputted to the Y-signal motion detecting circuit 6 at its input 51, is delayed by one frame at the one-frame delay circuit 53. The V signal 101 is also applied directly to the subtracter 54 and then subtracted from the one-frame delayed signal to determine one-frame difference therebetween. The one-frame difference signal is passed through the low pass filter 55 (hereinafter referred to as "LPF") and then applied to the absolute value circuit 56 whereat the absolute value thereof is determined. The determined absolute value is then converted by the nonlinear converting circuit 57 into a signal 106 indicative of the amount of movement of the low frequency component in the Y signal. This signal 106 is outputted from the output 52 of the Y-signal detecting circuit 6. The nonlinear converting circuit 57 serves to convert an absolute value into data having a magnitude which can be more easily handled by the system.

As shown in FIG. 12, the C-signal motion detecting circuit 7 may comprise a two-frame delay circuit 81, a subtracter 82, a band pass filter 83 (hereinafter referred to as "BPF"), an absolute value circuit 84 and a nonlinear converting circuit 85. V signal 101 inputted to the C-signal motion detecting circuit 7 at its input 11 is delayed by one frame at the two-frame delay circuit 81. The V signal 101 is also applied directly to the subtracter 82 and then subtracted from the two-frame delayed signal to determine two-frame difference therebetween. The two-frame difference signal is passed through the band pass filter 83 and then applied to the absolute value circuit 84 whereat the absolute value thereof is determined. The determined absolute value is then converted by the nonlinear converting circuit 85 into a signal 107 indicative of the amount of movement in the C signal. This signal 107 is outputted from the output 89 of the C-signal detecting circuit 7.

The synthesizing circuit 8 is adapted to select and output one of the Y-signal and C-signal movement signals 106 and 107, which is larger than the other movement.

Such a judgement is represented by a control signal 108 in the form of motion coefficient (0.ltoreq.k.ltoreq.1). If a picture is judged to be a complete still picture, the motion coefficient k is equal to zero. If the picture is judged to be a complete motion picture, the motion coefficient k is equal to one.

Generally, if a picture is a still picture, the interframe correlation is utilized to perform the interframe YC separation such that Y and C signals are separated from each other.

As shown in FIG. 13, the interframe YC separating circuit 5 may comprise a one-frame delay circuit 64, an adder 65 and a subtracter 66. V signal 101, inputted to the interframe YC separating circuit 5 at its input 61, is delayed by one frame at the one-frame delay circuit 64 to form a one-frame delay signal which in turn is added to the V signal directly inputted to the adder 65. The resultant one-frame sum provides a YF signal 104 which is outputted from one output 62 in the interframe YC separating circuit 5. At the same time, the subtracter 66 subtracts the YF signal 104 from the V signal 101 directly applied from the input 61 to the subtracter 66 to extract a CF signal 105 which in turn is outputted from the output 63 of the interframe YC separating circuit 5.

In general, if a picture is a motion picture, the infield correlation is utilized to perform the infield YC separation such that the Y and C signals are separated from each other.

As shown in FIG. 14, the infield YC separating circuit 4 may comprise a one-line delay (one horizontal line . . . 1 H delay) circuit 74, an adder 75 and a subtracter 76. V signal 101 inputted to the infield YC separating circuit 4 at its input 71 is delayed by one line at the one-line delay circuit 74 to form a one-line delay signal which in turn is added to the V signal directly inputted to the adder 75. The resultant one-line sum provides a Yf signal 102 which is outputted from one output 72 in the infield YC separating circuit 5. At the same time, the subtracter 76 subtracts the Yf signal 104 from the V signal 101 directly applied from the input 71 to the subtracter 76, to extract a Cf signal 103 which in turn is outputted from the output 73 of the infield YC separating circuit 4.

Since the infield and interframe YC separating circuits 4 and 5 are arranged parallel to each other, the motion adaptive YC separation filter can cause the Y-signal mixing circuit 9 to calculate the following equation using the motion coefficient k synthesized by the synthesizer 8:

where Yf is an output Y signal 102 from the infield YC separation and YF is an output Y signal 104 from the interframe YC separation. There is thus obtained a motion adaptive YC separation Y signal 109 which in turn is outputted from the motion adaptive YC separation filter at the output 2.

Similarly, the control signal 108 is utilized to cause the C-signal mixing circuit 10 to calculate the following equation:

where Cf is an output signal 103 from the infield YC separation and CF is an output signal 105 from the interframe YC separation. There is thus obtained a motion adaptive YC separation C signal 110 which in turn is outputted from the output 3.

The C-signal motion detecting circuit 7 may be arranged as shown in FIG. 15. In this figure, V signal 101 inputted to the circuit 7 at the input 11 is demodulated by a color demodulating circuit 86 into two color difference signals R-Y and B-Y. These color difference signals R-Y and B-Y are then applied to a time division multiplexer 87 in which they are time-division multiplexed at a certain frequency. The output signal from the time division multiplexer 87 is then subjected to subtraction from an output signal from a two-frame delay circuit 81. There is thus obtained a two-frame difference signal.

The two-frame difference signal is passed through LPF 88 wherein a Y-signal component is removed therefrom. The output signal of the LPF 88 is then applied to an absolute value circuit 84 to extract an absolute value therefrom. The absolute value is then applied to a nonlinear converter 85 wherein it is nonlinearly converted into a C-signal motion detection signal 107 which in turn is outputted from the output 89 of the C-signal motion detecting circuit 7.

It will be apparent from the foregoing that Yf and Cf signals from the infield YC separating circuit 4 and YF and CF signals from the interframe YC separating circuit 5 are respectively mixed with each other, based on the amount of movement which is obtained by synthesizing the motion signals from the respective Y-signal and C-signal motion detecting circuits 6 and 7.

Therefore, the filter characteristics for the still picture will be completely different from that for the motion picture. If a picture is switched from a still to a motion picture or vice versa, the resolution is subjected to severe change such that the quality of picture will be remarkably degraded upon processing of the motion picture.

SUMMARY OF THE INVENTION

In order to overcome the above problem in the prior art, it is therefore an object of the present invention to provide a motion adaptive YC separation filter which can reproduce even such a multi-switched picture as described above with an increased resolution and with a reduced degradation of image quality.

To this end, the present invention provides a motion adaptive YC separation filter comprising YC separation in three fields circuit means which can provide Y and C signals from the YC separation in three fields by locally detecting the correlation between frames when a motion picture is detected by a motion detecting circuit. The detected results are then used to perform the adaptive selection of plural interfield processing operations including calculations in three fields.

If a motion picture is detected by the motion detecting circuit, the motion adaptive YC separating filter of the present invention detects the correlation between the frames. The motion adaptive YC separating filter includes three YC separating in three fields circuits. One of those depending on the magnitude of the detected correlation, is selected to provide Y and C signals from the YC separation in three field.

In accordance with the present invention, the motion adaptive YC separating filter comprises YC separation in three fields circuit means which includes YC separating in three fields filters performing luminance signal band limitations from three different three-interfield calculations. This is achieved by detecting the local interframe correlation when a motion picture is detected by the motion detecting