JPH0638664B2 - PAL cyclic noise reduction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PAL system cyclic noise reduction device for performing cyclic noise reduction processing on a PAL system color composite video signal.

[Prior Art] A magnetic recording / reproducing apparatus such as a video tape recorder used for home use has a frequency change / increase which increases as the frequency increases.
In order to remove the triangular noise peculiar to the demodulation method, in general, the high-frequency component is emphasized by the pre-emphasis circuit before frequency-modulating the luminance signal, and the high-frequency emphasis is canceled by the de-emphasis circuit during signal reproduction. I am collecting.

However, since the luminance signal that has passed through the de-emphasis circuit also contains noise, for example, the cyclic noise reduction device 1 shown in FIG. 4 may be connected to the reproduction output terminal 10 of the magnetic recording / reproducing circuit. The cyclic noise reduction device 1 shown in FIG.
A color composite video signal of the SC system suppresses a noise component by utilizing the difference in properties between a video signal having a high frame correlation and a noise component having little frame correlation.
The input video signal Xi is cyclically generated from the output video signal Xo (t).
Since it is added to (t), it is called a cyclic type. Input video signal Xi converted into a digital signal by the AD conversion circuit 2
(T) is first supplied to the subtractor 3, and this subtracter 3
Then, the delayed output video signal Xo (t−τ), which has been delayed by one frame period τ by passing through the frame delay circuit 4 and the chroma inverter circuit 5, is subtracted. The difference signal δX (t) obtained by this subtraction passes through the attenuator circuit 6 whose coefficient K is less than 1, and is then subtracted from the input video signal Xi (t) by the subtractor 7 to obtain the output video signal. Xo (t). Therefore, the output video signal X
o (t) is Xo (t) = (1−K) Xi (t) + KX
signal obtained by multiplying the input video signal Xi (t) and the delayed output video signal Xo (t-τ) by complementary coefficients 1-K and K having a total value of 1 Becomes the output video signal Xo (t). The output video signal Xo (t) is DA
The conversion circuit 8 converts the analog signal and outputs the analog signal. In the color composite video signal of the NTSC system, the chroma inverter circuit 5 delays the input video signal Xi (t) with the input video signal Xi (t) because the color frame frequency considering the phase of the color signal is 15 Hz, which is 1/2 of the frame frequency. Video signal Xo
In view of the fact that the polarity of the color signal is opposite to (t−τ), the polarities of the color signals included in the output of the frame delay circuit 4 are inverted to match the polarities.

In the case of this example, the closer the coefficient K of the attenuator circuit 6 is to 1, the more the degree of SN improvement is improved, but the number of frames to be correlated increases, so that the afterimage of a moving image is fast. Therefore, a motion detecting circuit 9 that operates by detecting the difference signal δX (t) obtained from the subtractor 3 is provided, and the output of the motion detecting circuit 9 causes a moving image in which an afterimage is conspicuous. Only for, the value of the coefficient K is switched to a small value.

[Problems to be Solved by the Invention] The conventional NTSC cyclic noise reduction device 1 is a device for performing cyclic noise reduction processing on an NTSC color composite video signal, and therefore has a different signal format. When handling a PAL-type color composite video signal, it is needless to say that some circuit devise is required. As is well known, a PAL system color composite video signal is quadrature-phase modulated to a phase subcarrier having a 90-degree phase difference between two color difference signals of a red color difference signal RY and a blue color difference signal BY. Is the same as that of the NTSC system, but for the red color difference signal R-Y, the phase of the color subcarrier is inverted by 180 degrees for each line upon modulation, so a phase inversion means such as the chroma inverter circuit 5 is simply used. It cannot be applied.
Generally, a PAL system color television signal is expressed by the following equation.

Y ± Vcos2πsc + Usin2πsc However, V = (R−Y) /1.14 U = (B−Y) /2.03 sc = (n−1 / 4) _H + 25Hz _H is the horizontal synchronizing frequency, and n is 284. Therefore, the actual color sub-carrier frequency sc is 4.4336.
1875, nominally set to 4.43 MHz. In the above equation, 25 Hz is a frame frequency in the PAL system, and is added to reduce dot interference of the carrier color signal because the color sub-carrier frequency sc is selected as the 1/4 line offset frequency. It is a thing.

As can be seen from the above equation, since the color sub-carrier frequency sc is selected as the 1/4 line offset frequency in the PAL system color composite video signal, it is 4
The phase of the color difference signal in the video signal matches with the frame period. Moreover, since the horizontal scanning lines 625 lines constituting one frame invert the phase of the red color difference signal for each line, the phase of the color difference signal changes intricately between the odd frame and the even frame. Therefore, N
The chroma inverter circuit 5 as a mere phase inverting means as in the case of the color composite video signal of the TSC system.
Since the phase of the color difference signal included in the delayed output video signal Xo (t-τ) supplied to the subtractor 3 does not match the phase of the color difference signal included in Xi (t) in the input video signal,
Since addition is sometimes performed instead of subtraction, there is a problem in that noise reduction may cause not only the result of doubling noise.

[Means for Solving the Problems] The present invention solves the above problems and relates to a PAL system color composite video signal in which a red color difference signal is phase-inverted for each line, and relates to an input video signal and a frame delay circuit. In the PAL system for performing cyclic noise reduction, the sum of a signal obtained by multiplying a delayed output video signal obtained by signal delay of one frame period in In the cyclic noise reduction device, the frame delay circuit separates a color signal from an output video signal by utilizing line correlation between even lines or odd lines, and a color separation circuit for separating the color signal from the output video signal. Included in the delayed output video signal, which decomposes the color signal into a red color difference signal and a blue color difference signal and has a correlation with the color difference component included in the input video signal. To extract the color difference component by delaying the color difference component in dot units, and to remove the color difference component that is unsuitable when the frame correlation between the input video signal and the delayed output video signal existing in the delayed output video signal is taken. Color difference decomposition processing circuit for extracting the color difference components of the above, an adder for adding the output of this color difference decomposition processing circuit to the output video signal passed through the color separation circuit, and the total delay of the luminance signal including the color separation circuit and the adder. It is characterized in that it is configured by a delay circuit in which a delay time is set so that the time becomes one frame period.

[Operation] In the present invention, the PAL system color composite video signal in which the red color difference signal is phase-inverted line by line is subjected to the cyclic noise reduction process, and the line type correlation between even lines or odd lines is used. The color signal is separated from the output video signal by a filter, the luminance signal and the color signal are separately delayed by one frame period, and the color signal is also decomposed into a red color difference signal and a blue color difference signal, and then the input video signal is obtained. By removing the phase inconsistency related to the color difference signal so that the signal and the delayed output video signal can be frame-correlated, the PAL system color composite system in which the phase relationship between the luminance signal and the color signal is more complicated than the NTSC system color composite video signal The video signal is subjected to a reliable noise reduction process using frame correlation.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a circuit configuration diagram showing an embodiment of a PAL type cyclic noise reduction device of the present invention, and FIG.
The figure is a signal waveform diagram showing the frame structure of the color signal included in the output of the AD conversion circuit shown in FIG.

In FIG. 1, the PAL system cyclic noise reduction device 11 is significantly different from the frame delay circuit 4 in the case where the frame delay circuit 12 is an NTSC system cyclic noise reduction device. The frame delay circuit 12 uses a line correlation between even-numbered lines or odd-numbered lines to separate the color signals in the output video signal Xo (t) according to the comb filter principle, and a color separation circuit 13 for separating the color signals. The color signal separated by the circuit 13 is decomposed into a red color difference signal V and a blue color difference signal U, a color difference component having a correlation with a color difference component included in the input video signal Xi (t) is extracted, and a delayed output video image is obtained. A color difference decomposition processing circuit 14 for extracting a color difference signal for removing an unnecessary color difference component in the signal Xo (t-τ), an output of the color difference decomposition processing circuit 14 and a luminance passed through the color separation circuit 13. An adder 15 for adding signals and a band wave circuit 2 to be described later, which is provided between the color separation circuit 13 and the adder.
A delay element 16 having a delay time d + b obtained by adding one sampling cycle (hereinafter referred to as a dot cycle d) to the signal delay time b in 2 and a total delay time for an output video signal passing through the color separation circuit 13 and the delay element 16. And a delay circuit 17 in which a value obtained by subtracting from the one frame period τ is set as a delay time. The delay circuit 17 is provided in the first stage of the frame delay circuit 12, and its delay time is represented by τ-hdb when the line cycle is h.

The color separation circuit 13 includes two line delay circuits 18 and 19 that delay the output of the delay circuit 17 by two lines, and a subtracter 20 that subtracts the signal delayed by two lines from the other signals.
And the output of the subtractor 20 through a coefficient circuit 21 having a coefficient of 1/2, and a band wave circuit 22 formed of a digital filter for removing unnecessary components.
Is supplied to the color difference separation processing circuit 14. The delayed output video signal is taken out from the middle of the line delay circuits 18 and 19 and is supplied to the delay element 16. After the frame delay is completed by the signal delay of d + b time, it is supplied to the adder 15 to be subjected to the color difference decomposition. The color difference signals from the processing circuit 14 are added to remove unnecessary color difference components.

The color difference decomposition processing circuit 14 includes a signal line 23 provided with a dot delay element 23a for extracting a color difference signal regarding a dot which vertically sandwiches a central dot in the frame-delayed output video signal, and a succeeding dot adjacent to the central dot. A signal line 24 for extracting a color difference signal regarding dots sandwiching
And three signal lines of the signal line 25 provided with the two dot delay elements 25a and 25b for extracting the color difference signals regarding the dots vertically sandwiching the preceding dot adjacent to the center dot, the three signal lines of the band wave circuit 22 are It is branched and connected to the output side. One of the signal lines 24 and 25 is selected by a changeover switch 27 that is switched by the output of the color difference determination circuit 26, and is connected to the adder 28 together with the signal line 23.
Therefore, in the embodiment, the signal lines 24 and 25 function so as to extract only the red color difference signal V and the blue color difference signal U which are unnecessary for the cyclic noise reduction. Color difference determination circuit 26
Is connected to a burst extraction circuit 29 that extracts a color burst signal from the output of the AD conversion circuit 2, and determines the type of color difference signal by utilizing the fact that the phase of the color burst signal changes depending on the color difference signal. Here, AD
When the output of the conversion circuit 2 includes the red color difference signal V,
The changeover switch 27 is switched to the signal line 25 side,
When the output of the AD conversion circuit 2 includes the blue color difference signal U, the changeover switch 27 is switched to the signal line 24 side. The clock signal necessary for generating each delay time τ, h, d, b divides the output of the sync separation circuit 30 connected to the reproduction output terminal 10 into a system clock generation circuit 30.
It is supplied from a.

By the way, the color signal included in the output of the AD conversion circuit 2 is
Viewed on a frame-by-frame basis, as shown in FIG. 2, four color difference signals V, U, -V, -U take a signal form in which they are time-division multiplexed. This is because the sampling frequency ck of the AD conversion circuit 2 is four times the color sub-carrier frequency sc,
This is because the color difference signals of V, U, −V, and −U are alternately sampled, and as described above, the color subcarrier frequency sc
Is selected as the 1/4 line offset frequency, and since one frame is composed of the horizontal scanning line 625 (= 4k + 1) lines, the delayed output video signal Xo (t-τ) and the input video signal have a 4-frame cycle. It can also be seen that the phases of Xi (t) match.

Then, for example, focusing on the red color difference signal V surrounded by the dotted line in the nth frame, the blue color difference signal U also surrounded by the dotted line is similarly countered with the frame period in the (n-1) th frame which is one frame before. You can see that However, only the luminance signal has the frame correlation. Therefore, in order to perform the cyclic noise reduction, instead of the blue color difference signal U, which is the central dot surrounded by the dotted line in the n-1th frame, the position close to the blue color difference signal U is used. It is necessary to extract the red color difference signal V for In this case, since the changeover switch 27 is switched to the signal line 25 side by the output of the color difference determination circuit 26, a position where the preceding dot adjacent to the central dot is vertically sandwiched from the signal line 24, that is, one point in FIG. 2 surrounded by chain line
The color difference signal −U for each dot is extracted. The color difference signal −U is added to the adder 15 via the adder 28.
Is supplied to the frame delay output video signal to be used for removing an inappropriate color difference component U. On the other hand, regarding the red color difference signal V necessary for reducing the cyclic noise, the signal line 23
Above, the color difference signal V regarding the dot at the position sandwiching the central dot above and below, that is, the dot surrounded by the two-dot chain line in FIG. 2 is extracted, and this is added via the adder 28 as a signal for frame correlation. Is supplied to the container 15.

When the output of the AD conversion circuit 2 includes the blue color difference signal U, the changeover switch 27 is switched to the signal line 24 side. Therefore, in this case, as the color difference signal regarding the dot that vertically sandwiches the succeeding dot adjacent to the center dot, The red color difference signal -V is extracted and used for removing the unnecessary component V. Of course, the color-difference signal U regarding the dots at the positions sandwiching the central dot in the upper and lower sides is used for the cyclic noise reduction.

In this way, the PAL cyclic noise reduction device 11 is used.
Is a PAL in which the red color difference signal is phase-inverted line by line.
Method When a color composite video signal is subjected to cyclic noise reduction processing, a color separation circuit 1 comprising a comb filter that utilizes the line correlation between even lines or odd lines
3, the color signal is separated from the output video signal, the luminance signal and the color signal are separately delayed by one frame period, and the color signal is also decomposed into a red color difference signal and a blue color difference signal. Since the phase difference between the color difference signals is removed so that the frame correlation between the signal and the delayed output video signal can be obtained, the PAL system in which the phase relationship between the luminance signal and the color signal is more complicated than that of the NTSC system color composite video signal The color composite video signal can be subjected to reliable noise reduction processing using frame correlation. Also,
By using a comb filter to separate the luminance signal and the chrominance signal, it is possible to avoid deterioration of the signal due to band limitation found in the signal separation method using the reduction wave circuit or the band wave circuit, and improve the horizontal resolution. Further, in the case of a color signal having a narrow occupied band, a slight deviation from the frame correlation in the strict sense does not immediately lead to deterioration of the SN ratio, but by using the comb filter, the color difference decomposition processing circuit 14 decomposes it. Since the phase adjustment of the color difference signals can be easily and accurately realized, it is possible to perform the strict delay time management of the color signals as well as the luminance signals.

In the above embodiment, the adder 28 may be integrated with the adder 15.

Further, although the configuration is slightly different from the PAL-type cyclic noise reduction apparatus 11 shown in the above embodiment, the PAL-type cyclic noise reduction apparatus 31 shown in FIG. 3 has the same basic principle of noise reduction. The PAL cyclic noise reduction apparatus 31 shown in the figure has a delayed output video signal Xo (t-τ) and a signal obtained by multiplying an input video signal Xi (t) by a coefficient (1-K) in an attenuator circuit 32. The signal multiplied by the coefficient K in the attenuator circuit 33 is added in the adder 34 to obtain the output video signal Xo (t). By using the frame delay circuit 12, the PAL The same problem can be dealt with for the phase problem related to the color signal of the system color composite video signal.

[Effects of the Invention] As described above, according to the present invention, even when the PAL system color composite video signal in which the red color difference signal is phase-inverted line by line is subjected to the cyclic noise reduction processing, even lines or odd lines are processed. The color signal is separated from the output video signal by the comb filter using the line correlation of, and the luminance signal and the color signal are separately delayed by one frame period, and the color signal is also divided into the red color difference signal and the blue color difference signal. Since the input video signal and the delayed output video signal are frame-correlated by eliminating the phase mismatch related to the color difference signal, the luminance signal and the color signal are compared to the NTSC system color composite video signal. It is possible to perform a reliable noise reduction process using frame correlation on a PAL color composite video signal having a complicated phase relationship of By using a comb filter to separate the degree signal and the color signal, it is possible to avoid deterioration of the signal due to the band limitation found in the signal separation method using the reduction wave circuit or the band wave circuit, and improve the horizontal resolution. Furthermore, for a color signal with a narrow occupied band, a slight deviation from the frame correlation in the strict sense does not immediately lead to deterioration of the SN ratio, but by using a comb filter, it is decomposed in the color difference decomposition processing circuit. Further, the phase matching of the color difference signals can be easily and accurately realized, and thus, the color signals can be controlled in the same strict delay time as the luminance signals, which is an excellent effect.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a PAL system cyclic noise reduction apparatus of the present invention, and FIG. 2 is a frame configuration of color signals included in the output of the AD conversion circuit shown in FIG. FIG. 3 is a signal waveform diagram, FIG. 3 is a circuit configuration diagram showing another embodiment of the PAL system cyclic noise reduction device of the present invention, and FIG. 4 is a circuit showing an example of a conventional NTSC system cyclic noise reduction device. It is a block diagram. 11, 31 ... PAL type cyclic noise reduction device, 12 ...
... Frame delay circuit, 13 ... Color separation circuit, 14 ... Color difference resolution processing circuit.

Claims (1)

[Claims] 1. A PAL color composite video signal in which a red color difference signal is phase-inverted for each line, and is added to an input video signal and a delayed output video signal obtained by a signal delay of one frame period in a frame delay circuit. A PAL-type cyclic noise reduction device that performs cyclic noise reduction by using a sum of signals multiplied by complementary coefficients having a value of 1 as an output video signal, wherein the frame delay circuit comprises:
A color separation circuit that separates the color signal from the output video signal by using the line correlation between even lines or odd lines, and a color signal separated by this color separation circuit into a red color difference signal and a blue color difference signal. A color difference component having a correlation with a color difference component included in the input video signal, which is obtained by delaying the color difference component included in the delayed output video signal in dot units, and an input video signal existing in the delayed output video signal And a color difference separation processing circuit for extracting a color difference component for removing a color difference component which is inappropriate when the frame correlation between the delayed output video signal is obtained, and an output of the color difference decomposition processing circuit through the color separation circuit. An adder for adding to the output video signal, and a delay circuit including the color separation circuit and the adder, in which the delay time is set so that the total delay time of the luminance signal is one frame period. PAL scheme recursive noise reduction apparatus comprising a.