JPH0585118B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a PAL cyclic noise reduction device that performs cyclic noise reduction processing on a PAL color composite video signal.

[Prior Art] Magnetic recording and reproducing devices such as video tape recorders used for home use generally do not perform frequency modulation on luminance signals before frequency modulating them in order to remove triangular noise, which increases as the frequency increases and is specific to the frequency/demodulation method. A pre-emphasis circuit is used to emphasize high-frequency components, and a de-emphasis circuit is used to cancel the high-frequency emphasis during signal reproduction.

However, since the luminance signal that has passed through the de-emphasis circuit also contains noise, the cyclic noise reduction device 1 shown in FIG. 4, for example, may be connected to the reproduction output terminal 10 of the magnetic recording and reproduction circuit. The illustrated cyclic noise reduction device 1 suppresses noise components in an NTSC color composite video signal by utilizing the difference in properties between a video signal with a high frame correlation and a noise component with almost no frame correlation. It is called a cyclic type because the output video signal X ₀ (t) is cyclically added to the input video signal Xi(t). Input video signal converted to digital signal by AD conversion circuit 2
Xi(t) is first supplied to the subtracter 3, where the delayed output video signal is delayed by one frame period by passing through the frame delay circuit 4 and chroma inverter circuit 5. Xo(t-
〓) is subtracted. The difference signal 〓 Signal Xo(t)
It is said that Therefore, the output video signal Xo(t) is
(t)=(1-K)Xi(t)+KXo(t-〓),
Input video signal Xi(t) and delayed output video signal Xo(t-
〓) and complementary coefficients 1-K whose sum is 1
The sum of the signals multiplied by K and K becomes the output video signal Xo(t). The output video signal Xo(t) is converted into an analog signal by the DA conversion circuit 8 and output. In the NTSC color composite video signal, the color frame frequency that takes into account the phase of the color signal is 15Hz, which is half the frame frequency, so the chroma inverter circuit 5 has a delay output between the input video signal Xi(t) and the delayed output. Considering that the polarity of the color signal is opposite to that of the video signal Xo(t-〓), the polarity is matched by inverting the polarity of the color signal included in the output of the frame delay circuit 4.

In the case of this example, the closer the coefficient K of the attenuator circuit 6 is to 1, the better the SN improvement will be, but at the same time the number of frames subject to correlation will also increase, so for fast-moving videos, afterimages may occur. If the afterimage becomes conspicuous, a negative effect will occur. Therefore, a motion detection circuit 9 is provided which operates by detecting the difference signal 〓X(t) obtained from the subtractor 3, and the output of this motion detection circuit 9 makes the afterimage noticeable. The value of the coefficient K is switched to a small value only for such videos.

[Problems to be solved by the invention] The above conventional NTSC type cyclic noise reduction device 1
is a device that performs cyclic noise reduction processing on NTSC color composite video signals. Therefore, when handling PAL color composite video signals, which have different signal formats, it is natural that some kind of processing is required. Some circuitry is required. As is well known, the color composite video signal of the PAL system uses two color difference signals, the red color difference signal R-Y and the blue color difference signal B-Y, to perform quadrature phase modulation on phase subcarriers that have a phase difference of 90 degrees from each other. is the same as the NTSC system, but for the red color difference signal R-Y, the phases of the color subcarriers are changed line by line for modulation.
Since the phase is inverted by 180 degrees, it is not possible to simply apply phase inverting means such as the chroma inverter circuit 5. Generally, a PAL color television signal is expressed by the following equation.

Y±Vcos2〓fsc+Usin2〓fsc However, V=(RY)/1.14 U=(B-Y)/2.03 fsc=(n-1/4)=6 _H +25Hz f _H is the horizontal synchronization frequency, Since n is set to 284, the actual color subcarrier frequency fsc is
4.43361875, nominally set to 4.43MHz. In addition,
In the above equation, 25Hz is the frame frequency in the PAL system, and since the color subcarrier frequency fsc was selected as the 1/4 line offset frequency, it was added to reduce dot interference in the carrier color signal. It is something.

As can be seen from the above equation, in the color composite video signal of the PAL system, the color subcarrier frequency fsc is selected to be the 1/4 line offset frequency, so when viewed in terms of frame period, the video signal is The phases of the color difference signals match. Moreover, since the phase of the red color difference signal is inverted for each line of the 625 horizontal scanning lines constituting one frame, the phase of the color difference signal changes in a complicated manner between odd and even frames. therefore,
If the chroma inverter circuit 5 is used as a simple phase inversion means, as is the case with the color composite video signal of the NTSC system, the color difference contained in the delayed output video signal Xo(t-〓) supplied to the subtracter 3 will be The phase of the signal does not match the phase of the color difference signal included in Xi(t) in the input video signal, and sometimes addition is performed instead of subtraction, which results in doubling the noise rather than reducing noise. There were some problems, such as it could lead to problems.

[Means for solving the problem] This invention solves the above problem, and the red color difference signal has a phase inversion for each line.
Regarding a PAL color composite video signal, the sum of the input video signal and the delayed output video signal obtained by the signal delay of one frame period in the frame delay circuit is multiplied by a complementary coefficient whose sum is 1. The PAL type cyclic noise reduction device performs cyclic noise reduction by outputting a video signal as an output video signal, and the frame delay circuit includes a luminance/color separation means for separating the output video signal into a luminance signal and a color signal. and decomposes the color signal separated by this luminance/color separation means into a red color difference signal and a blue color difference signal,
In order to avoid mismatches in color matching for each color difference signal when comparing the input video signal and delayed output video signal at the same time, the delay amount of the delayed output video signal is determined based on the burst signal and synchronization signal of the input video signal. A color difference separation processing circuit that performs color matching processing by identifying and extracting color difference signals of the same type existing at the point closest to one frame cycle; an adder that adds the luminance signals separated by the luminance signals;
The present invention is characterized by comprising a color separation means and a delay circuit including an adder, in which a delay time of a signal is set such that the delay time of the signal is one frame period.

[Function] When subjecting a PAL color composite video signal in which the phase of the red color difference signal is inverted line by line to cyclic noise reduction processing, the frame delay circuit that delays the output video signal by one frame period is configured to In addition to separately delaying the signal and color signal,
The color signal is also separated into a red color difference signal and a blue color difference signal, and then the input video signal and the delayed output video signal are removed from each color difference signal. This technology uses frame correlation to perform reliable noise reduction processing on PAL color composite video signals, which have complex phase relationships between luminance and chrominance signals.

[Example] Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a circuit configuration diagram showing an embodiment of the PAL type cyclic noise reduction device of the present invention, and FIG. 2 is an AD
FIG. 3 is a signal waveform diagram showing a color signal included in the output of the conversion circuit in terms of a frame period.

In Figure 1, PAL type cyclic noise reduction device 11
is significantly different from the frame delay circuit 4 in which the frame delay circuit 12 is an NTSC type cyclic noise reduction device. This frame delay circuit 12 includes a low frequency circuit 1 as a volatility/color separation means for separating the delayed output video signal Xo(t-〓) into a volatility signal and a color signal.
3 and the band wave circuit 14, and this band wave circuit 1
The color signal separated by 4 is converted into a red color difference signal V
and blue color difference signal U, input video signal Xi
(t) and the delayed output video signal an adder 16 that adds the output of the decomposition processing circuit 15 and the luminance signal separated by the low frequency circuit 13; and a low frequency circuit 1.
3 and a delay circuit 17 in which the delay time of the signal including the adder 16 is set so that the delay time is one frame period. The delay circuit 17 is provided at the first stage of the frame delay circuit 12, and in this embodiment has a delay time equal to the frame period 〓 minus one sampling period T (〓-T). Therefore, the signal delay time in the reduced wave circuit 13 and the adder 16 is set to approximately one sampling period T.

The color difference separation processing circuit 15 includes a signal line 21 of a signal line 20 for extracting a red color difference signal V and a signal line 21 for extracting a blue color difference signal U.
In addition to providing two delay elements 22 and 23,
A color signal is separated into color difference signals U and V by selecting one of the signal lines 20 and 21 by a changeover switch 25 which is switched by the output of the color difference discrimination circuit 24. The delay time given to the delay elements 22 and 23 is just one sampling period T.
be equivalent to. The color difference discrimination circuit 24 is the AD conversion circuit 2
The color burst signal is connected to a burst extraction circuit 26 that extracts the color burst signal from the output of the color burst signal, and the type of the color difference signal is determined by utilizing the fact that the phase of the color burst signal changes depending on the color difference signal. Here, when the output of the AD conversion circuit 2 includes the color difference signal V, the changeover switch 25 is connected to the signal line 20.
When the color difference signal U is included in the output of the AD conversion circuit 2, the changeover switch 25 is switched to the signal line 21 side. Note that the delay element 2
The clock signal necessary for setting the delay time T for the clocks 2, 23, etc. is supplied from a system clock generation circuit 28 which divides the output of a sync separation circuit 27 connected to the reproduction output terminal 10.

By the way, the color signal included in the output of the AD conversion circuit 2 is in the form of a signal in which four color difference signals V, U, -V, -U are time-division multiplexed, as shown in Fig. 2, when viewed in frame units. Take. This is because the sampling frequency fck of the AD conversion circuit 2 is four times the color subcarrier frequency fsc, so each color difference signal of V, U, -V, and -U is sampled alternately. As mentioned above, the color subcarrier frequency fsc is selected as the 1/4 line offset frequency, and since one frame is composed of 625 (=4k+1) horizontal scanning lines, the delayed output video signal Xo ( It can also be seen that the phase of the input video signal Xi(t) matches that of the input video signal Xi(t).

Therefore, when the red color difference signal V is colored, there is a phase advance of just one sampling period T in the next (n+1)th frame with respect to the nth frame, but the phase has passed through the delay circuit 17 and the band wave circuit 14. The phase of the red color difference signal V delayed by -T matches the phase of the red color difference signal V included in the input video signal Xi(t). Furthermore, regarding the blue color difference signal U, the nth
In the +1 frame, there is a phase delay of just one sampling period T, but the blue color difference signal U is delayed by +T after passing through the delay circuit 17, the band wave circuit 14, and the two delay elements 22 and 23. This matches the phase of the blue color difference signal U included in the input video signal Xi(t). That is, the color difference separation processing circuit 15 solves the problem of color signal phase management, which is essential for PAL color composite video signals, by decomposing the color signal into a red color difference signal V and a blue color difference signal U, and applying a predetermined signal delay to each. By doing so, you can deal with the problem appropriately.

In this manner, the PAL cyclic noise reduction device 11 subjects the PAL color composite video signal in which the red color difference signal V has a phase inversion line by line to cyclic noise reduction processing using frame correlation. A frame delay circuit 12 delays the output video signal Xo(t-〓) by one frame period, separately delays the luminance signal and the color signal, and also separates the color signal into a red color difference signal V and a blue color difference signal U. NTSC
It is possible to perform reliable noise reduction processing using frame correlation on the PAL color composite video signal, which has a more complex phase relationship between the luminance signal and the color signal than the PAL color composite video signal. In addition, for color signals with a narrower occupied band than luminance signals, even if the frame correlation slightly deviates from the strict sense, the SN
Since this does not lead to ratio 6 deterioration, even if the frame period, which is the delay time of the entire frame delay circuit 12, is affected to some extent in the phase matching process of the color difference signals separated in the color difference separation processing circuit 15. ,
The effect is not as bad as the disturbance of delay time management regarding the luminance signal, and therefore the regulation of the delay time set in the delay circuit 17 is relaxed to some extent, and the reduced wave circuit 13 and band wave circuit 14, which are luminance/color separation means, are It is possible to have some leeway in the selection range in relation to the delay time in etc.

Although the configuration is slightly different from the PAL type cyclic noise reduction device 11 shown in the above embodiment, the basic principle of noise reduction is the same as that of the PAL type cyclic noise reduction device 11 shown in FIG.
There is a cyclic noise reduction device 31. The PAL type cyclic noise reduction device 31 shown in the figure uses a signal obtained by multiplying the input video signal Xi(t) by a coefficient (1-K) in the attenuator circuit 32, and a delayed output video signal Xo.
(t-〓) multiplied by a coefficient K in the attenuator circuit 33 is added in the adder 34 to obtain the output video signal Xo(t), but the frame delay circuit 12 described above is used. Needless to say, by using this method, it is possible to properly deal with the phase problem related to the color signal of the PAL color composite video signal.

Furthermore, the phase matching of the color difference signals in the color difference separation processing circuit 15 is not limited to the method shown in the embodiment, but a configuration that produces the same effect may be achieved by using, for example, a polarity inversion circuit in addition to the delay element. is also possible.

[Effects of the Invention] As explained above, the present invention has the advantage that when a PAL color composite video signal in which the phase of the red color difference signal is inverted line by line is subjected to cyclic noise reduction processing using frame correlation, the output video signal 1
A frame delay circuit that delays the frame period delays the luminance signal and the color signal separately, and also separates the color signal into a red color difference signal and a blue color difference signal, and then separates the input video signal and delayed output video signal. , because the configuration eliminates color mismatches for each color difference signal, the phase relationship between the luminance signal and color signal is more complex than in the NTSC color composite video signal.
Reliable noise reduction processing using frame correlation can be applied to PAL color composite video signals, and color signals with narrow occupied bands compared to luminance signals can be processed even if they slightly deviate from frame correlation in the strict sense. This does not immediately lead to a deterioration of the SN ratio, so even if the frame period, which is the delay time of the entire frame delay circuit, is slightly affected during the phase matching process of the color difference signals separated in the color difference separation processing circuit. , it is not as bad as the disturbance of delay time management regarding luminance signals, and therefore the regulation of the delay time set in the delay circuit is relaxed to some extent, and the selection range is adjusted in relation to the delay time in luminance/color separation means, etc. This has excellent effects such as being able to provide a certain amount of leeway.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an embodiment of the PAL type cyclic noise reduction device of the present invention, and FIG.
FIG. 1 is a signal waveform diagram of the color signal included in the output of the AD conversion circuit shown in the frame period. FIG. 3 is a circuit configuration diagram showing another embodiment of the PAL type cyclic noise reduction device of the present invention. , Figure 4 shows the conventional
FIG. 2 is a circuit configuration diagram showing an example of an NTSC type cyclic noise reduction device. 11, 31...PAL type cyclic noise reduction device,
12...Frame delay circuit, 13...Low frequency circuit, 14...Band wave circuit, 15...Color difference separation processing circuit, 16...Adder, 17...Delay circuit.

Claims (1)

[Claims] 1 The phase of the red color difference signal is reversed for each line.
Regarding a PAL color composite video signal, the sum of the input video signal and the delayed output video signal obtained by the signal delay of one frame period in the frame delay circuit is multiplied by a complementary coefficient whose sum is 1. The PAL type cyclic noise reduction device performs cyclic noise reduction by converting the output video signal into an output video signal, and the frame delay circuit includes a luminance/color separation means for separating the output video signal into a luminance signal and a chrominance signal. Then, the color signal separated by this luminance/color separation means is separated into a red color difference signal and a blue color difference signal, and when the input video signal and the delayed output video signal are compared at the same time, color matching is performed for each color difference signal. To avoid mismatches, identify and extract the color difference signal of the same type that exists at the point in time when the delay amount of the delayed output video signal is closest to one frame cycle based on the burst signal and synchronization signal of the input video signal. a color difference separation processing circuit that performs color matching processing; an adder that adds the output of the color difference separation processing circuit to the luminance signal separated by the luminance/color separation means; and the luminance/color separation means and the adder. A PAL type cyclic noise reduction device comprising a delay circuit whose delay time is set so that the delay time of a signal including the signal is one frame period.