JP3679208B2 - Motion detection circuit for composite video signal - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motion detection circuit for a composite video signal, and more particularly to a composite video signal for detecting motion between frames of a composite video signal input to a three-dimensional Y / C separation circuit, a cyclic noise removal circuit, and other space-time processing circuits. The present invention relates to a motion detection circuit.
[0002]
[Prior art]
FIG. 6 is a block diagram showing an example of a conventional composite video signal motion detection circuit (conventional example 1). In the figure, 61 is a low-pass filter that passes a frequency band of 2 MHz or less, 62 is a one-frame delay circuit that delays one frame of a luminance signal (hereinafter referred to as Y signal), and 63 is a subtractor.
[0003]
In operation, the composite video signal is input to the low-pass filter 61 to remove the subcarrier (hereinafter referred to as C signal) to obtain the Y signal. The Y signal is delayed by one frame by a one-frame delay circuit. Next, the output of the 1-frame delay circuit 62 is subtracted from the Y signal output from the low-pass filter 61 by the subtractor 63 to obtain a motion signal.
[0004]
FIG. 7 is a block diagram showing another example (conventional example 2) of a conventional composite video signal motion detection circuit. In the same figure, 71 and 72 are 1 frame delay circuits, respectively, 73 is a subtractor. In the operation in this case, the motion signal is obtained by subtracting the composite video signal delayed by two frames from the composite video signal.
[0005]
FIG. 8 is a block diagram showing still another example (conventional example 3) of the conventional composite video signal motion detection circuit. This example is a combination of Conventional Example 1 and Conventional Example 2. That is, out of the output of the motion detection circuit composed of the low-pass filter 61, the one frame delay circuit 62, and the subtractor 63, and the output of the motion detection circuit composed of the one frame delay circuits 71 and 72, and the subtractor 73. A maximum value detection circuit 81 that outputs a large value is provided, and the output is used as a motion signal.
[0006]
[Problems to be solved by the invention]
FIG. 9 is a waveform diagram for explaining problems in the motion detection circuit of the conventional example 1 shown in FIG. In the figure, the spectrum of the NTSC composite video signal is shown, where Y is a luminance signal and C is a subcarrier signal. The luminance signal Y has a band of 0 to 5 MHz or more, and the subcarrier signal C has a band of ± 1.5 MHz centering on 3.58 MHz. Although most of the subcarrier signal C is removed by the low-pass filter 61 that passes only the component of about 2 MHz or less, the Y signal of about 2 MHz or more is also removed at the same time. Therefore, the conventional circuit of FIG. 6 has a problem in that it cannot detect the motion between frames of a composite video signal including a Y signal having a horizontal frequency band of 2 MHz or more.
[0007]
Further, the low pass filter 61 that passes a component of about 2 MHz or less passes a component having a frequency slightly lower than 2 MHz at a high gain, as shown schematically in the figure, depending on its characteristics, but from 2 MHz at a low gain. A slightly lower frequency component is also passed. For this reason, the portion of the subcarrier signal C in the high horizontal frequency band (the portion away from the center frequency of 3.58 MHz) cannot be removed by the 2 MHz low-pass filter 61 and is mixed into the luminance signal Y that has passed through the low-pass filter 61. End up. Since the phase of the subcarrier signal C is inverted every frame, even in the case of a still image, when the signal delayed by one frame is subtracted from the output of the low-pass filter 61, the mixed subcarrier C appears as a frame difference. For example, in the case of a still image, if the value of the C signal that has passed through the low-pass filter 61 at a certain point is c, the value of the C signal after one frame is −c. Therefore, the difference signal between frames is c − (− c) = 2c. As described above, the difference signal between frames in the conventional example 1 includes an incorrect value due to the mixing of the subcarrier signal C in the portion of the subcarrier signal C where the horizontal frequency is high (the portion away from the center frequency). There is a problem that movement between frames of a video signal cannot be detected accurately.
[0008]
FIG. 10 is a diagram for explaining a problem in the motion detection circuit of the second conventional example shown in FIG. In the circuit of FIG. 7, since the subtraction is carried out with the composite video signal without performing the filtering process, there is no band where the motion cannot be detected. Also, since the subcarrier signal has the same phase as the signal delayed by 2 frames, the value becomes 0 when subtracting the signal delayed by 2 frames from the subcarrier signal in the composite video signal in the case of a still image. There is no problem of erroneous detection as in Conventional Example 1.
[0009]
However, by subtracting the signal delayed by two frames from the input composite video signal, the range of motion frequencies that can be detected is approximately the range of motion frequencies that can be detected when the signal delayed by one frame is subtracted. It is halved (since 1 frame period is 1/30 second, 2 frame period is 1/15 second). That is, there is a problem that a fast motion of 15 Hz or more cannot be detected.
[0010]
The conventional example 3 shown in FIG. 8 solves the problems of the conventional example 1 and the conventional example 2, but has a problem that the circuit scale is large and the cost is high.
An object of the present invention is to provide a motion detection circuit for a composite video signal that is capable of accurately detecting motion at low cost in view of the problems in the above-described conventional example.
[0011]
[Means for Solving the Problems]
The motion detection circuit for a composite video signal provided by the present invention includes, in addition to the circuit of the conventional example 1, a bandpass filter that passes a subcarrier in the composite video signal, and an I signal and a Q signal from the output of the bandpass filter. A demodulator for demodulating the signal, an edge amount detecting means for extracting a portion having a high horizontal frequency from the I signal and the Q signal, and outputting a large value of the extracted portions as the edge amount of the subcarrier signal, and an edge amount And a second subtracting unit for subtracting a value corresponding to the size of the frame difference signal from the frame difference signal to obtain a motion amount.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the same reference numbers represent the same items.
FIG. 1 is a block diagram of a composite video signal motion detection circuit according to an embodiment of the present invention. In the figure, 11 is a bandpass filter of 3.58 MHz ± 1.5 MHz that passes the subcarrier signal C, 12 is a demodulator that demodulates the I signal and Q signal from the subcarrier signal C, and 13 and 14 are I signals. And an edge extraction circuit for extracting a portion having a high horizontal frequency from the Q signal, 15 is an edge amount detecting means for outputting a large value of the extracted portions as an edge amount of the subcarrier signal, 16 is a multiplier, and 61 is 2 MHz or less. A low-pass filter that passes the frequency band, 62 is a one-frame delay circuit that delays one frame of the luminance signal Y, 63 is a subtractor, and 17 is a value corresponding to the size of the edge amount. The second subtracter obtains the motion amount by subtracting from the obtained frame difference signal.
[0013]
In operation, the composite signal including the luminance signal Y and the subcarrier signal C is first passed through a 2 MHz low-pass filter (LPF) 61 to remove the subcarrier signal C component as in the conventional example 1 shown in FIG. Get Y. Subtraction between the luminance signal Y and the signal obtained by delaying the luminance signal Y by one frame is performed by the subtractor 63 to obtain a frame difference signal (* 1).
[0014]
As described above, when the subcarrier signal C component is removed by the 2 MHz low-pass filter 61, the portion of the subcarrier signal C having a high horizontal frequency cannot be completely removed and is mixed into the luminance signal Y. Since the phase of the subcarrier signal C is inverted every frame, if a signal delayed by one frame is subtracted from the output value c of the low-pass filter 61, a frame difference of 2c appears as described above even in the case of a still image.
[0015]
Thus, the frame difference signal (* 1) includes an incorrect value due to the mixing of the subcarrier signal C.
In this embodiment of the present invention, the incorrect value focuses on the fact that the high-frequency component of the subcarrier signal C is mixed in the output of the low-pass filter 61. Circuits 11 to 17 are provided to remove illegal values from the signal (* 1).
[0016]
That is, the composite video signal is passed through the bandpass filter 11 of 3.58 MHz ± 1.5 MHz to obtain the subcarrier signal C, and the subcarrier signal C is demodulated into the I signal and the Q signal by the demodulator 12. Then, the edge extraction circuits 13 and 14 extract the edges of the I signal and the Q signal, respectively. Then, the larger one of the edges is selected by the edge amount detection means 15 and input to the multiplier 16. The multiplier 16 multiplies the selected edge by a coefficient α and inputs the result to the second subtracter 17. The second subtracter 17 subtracts the output of the multiplier 16 from the frame difference signal (* 1) that is the output of the first subtracter 63. As a result, a motion signal from which most of the illegal signal included in the frame difference signal is removed is obtained.
[0017]
The value of the coefficient α input to the multiplier 16 is set to an appropriate value in consideration of the attenuation amount of the subcarrier signal C and the gain of the IA demodulation embodiment as in the 2 MHz low-pass filter 61.
The circuit b comprising the multiplier 16 and the second subtracter 17 uses a look-up table using a read only memory (ROM) or a random access memory (RAM), or a subcarrier signal as a frame difference signal. A method of attenuating by applying a coefficient corresponding to the size of the edge of C is conceivable.
[0018]
FIG. 2 is a diagram for explaining the effect of the above embodiment of the present invention. In the figure, erroneous detection in motion detection of a color bar video (still image) is shown in comparison with the conventional example 1. That is, in the case of the conventional example 1, a motion detection signal is detected between the colors shown in (1), but in the embodiment of the present invention, as shown in (2), the motion detection signal is almost the same size. Since the edge extraction signal of the subcarrier signal C is obtained at the output of the multiplier 16 and is subtracted from the frame difference signal, the motion detection signal is close to zero as shown in (3), which is erroneous compared to the conventional case. Less detection.
[0019]
FIG. 3 is a circuit diagram when the motion amount detection of the present invention is applied to a three-dimensional Y / C separation circuit. As is well known, the three-dimensional Y / C separation circuit includes a three-line comb filter 31 that passes the subcarrier signal C from the composite signal, a one-frame delay circuit 32 that delays the composite signal by one frame, and one frame from the composite signal. A subtractor 33 that subtracts the delay signal to obtain a subcarrier signal C, a motion adaptive mixing circuit 34 that obtains a subcarrier signal C that adapts motion based on these subcarrier signals C, and a motion adaptive mixing circuit 34 from the composite signal. And a subtractor 35 for subtracting the output of the above. Even in this three-dimensional Y / C separation circuit, dot interference occurs in the portion where motion is detected, but the occurrence of dot interference can be reduced by applying the present invention described above.
[0020]
That is, the subcarrier signal C obtained at the output of the 3-line comb filter 31 is input to the demodulator 12, and the subtractor 36 subtracts the subcarrier signal C, which is the output of the 3-line comb filter 31, from the composite signal. Get Y. Thereby, the circuit a composed of the bandpass filter 11 and the lowpass filter 61 in FIG. 1 can be replaced with the three-line comb filter 31 and the subtractor 36 in the existing three-dimensional Y / C separation circuit. Then, a motion detection signal is obtained at the output of the subtractor 17 in the same manner as in FIG. 1, and this is input to the motion adaptive mixing circuit 34 in the three-dimensional Y / C separation circuit. Accordingly, the subcarrier signal C and the luminance signal Y with less dot interference can be obtained by adjusting the subcarrier signal C, which is the output of the subcarrier signal.
[0021]
FIG. 4 is a circuit diagram when the motion amount detection of the present invention is applied to a cyclic noise removal circuit. Even when motion detection is applied to a cyclic noise removal circuit, the effect of noise removal is reduced at a portion where motion is erroneously detected. However, by using the motion detection signal obtained by the circuit of FIG. The rate of reduction in removal effect is less than in the conventional method.
[0022]
That is, the cyclic noise removing circuit for removing noise from the luminance signal Y obtained at the output of the low-pass filter 61 subtracts the luminance signal Y output from the low-pass filter 61 from the output of the one-frame delay circuit 42. 1, which receives the output of the subtractor 17 that is the output of the circuit of FIG. 1 and outputs the coefficient 1−β, and the multiplier that multiplies the output of the subtractor 41 by the coefficient 1−β. 44 and an adder 45 for adding the output of the multiplier 45 and the output of the 1-frame delay circuit 42 are added. As a result, the rate of reduction in the noise removal effect is less than in the conventional method.
[0023]
FIG. 5 is a circuit diagram when the motion detection of the present invention is applied to an interlaced scanning → sequential scanning conversion circuit.
Also in this case, an adder 56 adds the outputs of the intra-field sequential scan conversion circuit 51 and the output of the inter-frame sequential scan conversion circuit 52 multiplied by the motion adaptive coefficients β and β−1, respectively. An output converted to progressive scanning is obtained. By obtaining the motion adaptive coefficients β and 1-β based on the output of the subtractor 17 by the motion adaptive coefficient unit 53, a progressive scanning output with higher image quality is obtained. It is done.
[0024]
【The invention's effect】
As is clear from the above description, according to the present invention, the error signal included in the frame difference signal detected from the composite signal including the luminance signal and the subcarrier signal can be reduced, so that the three-dimensional Y / C Errors in motion detection in the separation circuit, cyclic noise removal circuit, and other spatio-temporal processing circuits can be reduced, and accurate motion detection can be performed at low cost.
[Brief description of the drawings]
FIG. 1 is a block diagram of a motion detection circuit for a composite video signal according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the effect of the embodiment of FIG. 1;
FIG. 3 is a block diagram showing an example in which the present invention is applied to a two-dimensional Y / C separation circuit according to another embodiment of the present invention.
FIG. 4 is a block diagram showing an example in which the present invention is applied to a cyclic noise removal circuit according to still another embodiment of the present invention.
FIG. 5 is a block diagram showing an example in which the present invention is applied to an interlaced scanning → sequential scanning conversion circuit according to still another embodiment of the present invention.
FIG. 6 is a block diagram showing an example (conventional example 1) of a conventional composite video signal motion detection circuit;
FIG. 7 is a block diagram showing another example (conventional example 2) of a conventional composite video signal motion detection circuit;
FIG. 8 is a block diagram showing still another example (conventional example 3) of a conventional composite video signal motion detection circuit;
FIG. 9 is a waveform diagram for explaining a problem in the motion detection circuit of the first conventional example.
FIG. 10 is a diagram for explaining a problem in a motion detection circuit of Conventional Example 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Band pass filter 12 ... Demodulator 13 ... Edge embodiment extraction circuit 14 ... Edge embodiment extraction circuit 15 ... Edge amount detection means 16 ... Multiplier 17 ... Second subtractor 61 ... Low pass filter 62 ... 1 frame delay circuit 63: First subtractor

Claims (1)

Among the composite video signal including the luminance signal and the subcarrier signal, a low-pass filter that mainly passes the luminance signal;
First subtracting means for subtracting the output delayed by one frame from the output of the low-pass filter to obtain a frame difference signal;
A bandpass filter that passes the subcarrier of the composite video signal;
A demodulator that demodulates the I and Q signals from the output of the bandpass filter;
Edge amount detection means for extracting a portion having a high horizontal frequency from each of the I signal and the Q signal, and outputting a large value of the extracted portions as an edge amount of the subcarrier signal;
A motion detection circuit for a composite video signal, comprising: a second subtracting unit that subtracts a value corresponding to the magnitude of the edge amount from the frame difference signal to obtain a motion amount.

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