JPH0225596B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a noise reduction device for color video signals, and in particular to a noise reduction device for color video signals, and in particular for reducing noise components in color video signals using an N field (where N is a natural number) delay circuit. The present invention relates to a noise reduction device capable of extracting a color video signal with an improved signal-to-noise ratio (S/N ratio).

Prior Art FIG. 1 shows a block system diagram of an example of a conventional color video signal noise reduction device. In the figure, an NTSC color video signal inputted to an input terminal 1 is supplied to a one-frame delay line 4 through a coefficient multiplier 2 that provides a coefficient (1-K) and an adder 3, where the 1 at sampling frequency
After being delayed by a frame period, the signal is supplied to the chroma inverter 5. The chroma inverter 5 is a circuit for matching the phase of the carrier color signal in the NTSC color video signal whose phase differs by 180 degrees from frame to frame, and the phase of the luminance signal delayed by one frame matches that of the input signal. A color video signal consisting of a one-frame delayed carrier color signal is output to a coefficient unit 6 and a subtracter 7, which will be described later. The coefficient unit 6 gives a coefficient K to the input delayed signal and outputs it to the adder 3, where it is added to the color video signal from the coefficient unit 2.

As a result, by averaging the input color video signal temporally for each frame period, the adder 3 outputs a color video signal in which the energy of the signal component hardly changes and only the energy of the noise component is reduced. , one frame delay line 4 and output terminal 9, respectively.

Here, the color video signal has a moving image portion that changes between frames, and this moving image portion appears as an afterimage. That is, when the coefficient K is increased, the degree of S/N improvement becomes better, but the afterimage effect also becomes larger. Therefore, in this conventional device, the input color video signal and the output signal of the chroma inverter 5 are subtracted by the subtracter 7 to extract a difference signal, and the difference signal is supplied to the motion detector 8, where the difference signal is When the amplitude is small, it is regarded as a noise component and converted into a signal with a large value of coefficient K, and on the other hand,
When the amplitude of the signal is large, it is assumed that it is a signal component of a moving image portion, and the signal is converted into a signal that reduces the value of the coefficient K and is supplied to the coefficient multipliers 2 and 6, respectively.

Problems to be Solved by the Invention However, in the conventional device described above, the color video signal is directly supplied to the one-frame delay line 4 without separating it into a luminance signal and a carrier color signal. As the sampling frequency of the memory constituting the device has increased, the memory capacity has become extremely large, requiring the use of high-speed operating elements, and making the device more expensive.

There was also a conventional device that separates a color video signal into a luminance signal and a carrier chrominance signal, but this conventional device required a dedicated delay circuit for each luminance signal and carrier chrominance signal, making the entire device large. The problem was that it was expensive and unsuitable for use as consumer equipment.

Therefore, the present invention separates a color video signal into a luminance signal and a carrier color signal, then combines both signals alternately in time series, and passes this sequential signal through a single N field delay circuit. It is an object of the present invention to provide a noise reduction device that solves the above problems.

Means for Solving the Problems The present invention provides separation means for separating a color video signal into a luminance signal and a carrier color signal, a frequency converter for converting the frequency of the separated carrier color signal to a lower frequency band, and a separation means for separating a color video signal into a luminance signal and a carrier color signal. first and second subtracters to which the converted luminance signal and the output low-pass converted carrier color signal of the frequency converter are respectively supplied, and both output signals of the first and second subtracters or the first , a first switch circuit that outputs a luminance signal and a low-frequency conversion carrier color signal from both output signals obtained through the second comb filter as sequential signals that are synthesized alternately in time series at regular intervals; , the above sequential signals are applied to N fields (however, N
is a natural number); a second switch circuit that switches the output signal of the delay circuit every certain period to alternately select and output the delayed luminance signal and the delayed low-frequency conversion carrier color signal; The delayed luminance signal intermittently taken out from the switch circuit is converted into a continuous delayed luminance signal using the first delay device having a delay time of the predetermined period, and then subtracted from the separated luminance signal. a first signal processing means for obtaining a first difference signal using a second switch circuit; and a second delay device having a delay time of the predetermined period for processing the delayed low-pass conversion carrier color signal intermittently taken out from a second switch circuit. a second signal processing means which obtains a second difference signal by subtracting the signal from the low-frequency converted carrier color signal from the frequency converter after converting the signal into a continuous signal; The signal obtained by amplitude limiting the difference signal of the first and
It consists of first and second limiters that output to a second subtracter, and is configured to extract a luminance signal with reduced noise components and a low-frequency conversion carrier color signal from the first and second subtracters, respectively. An embodiment thereof will be described below with reference to FIGS. 2 to 5.

Embodiment FIG. 2 shows a block system diagram of an embodiment of the apparatus of the present invention. In the figure, for example, an NTSC color video signal inputted to an input terminal 11 is branched into two, one being supplied to a low-pass filter 12 to separate the luminance signal, and the other being supplied to a bandpass filter 13 to separate the carrier color signal. The signal is separated. The luminance signal is supplied to a first subtractor 14, which will be described later, and the carrier color signal is supplied to a second subtractor 16 after the color subcarrier frequency of 3.58 MHz is frequency-converted to a low frequency of about 710 kHz by a frequency converter 15. supplied to The luminance signal taken out from the subtracter 14 is applied to a terminal 18a of a switch circuit 18 through a comb filter 17, which will be described later. On the other hand, the low frequency conversion carrier color signal extracted by the subtracter 16 is applied to the terminal 18b of the switch circuit 18 through a comb filter 19, which will be described later.

The switch circuit 18 is configured to alternately select and output the input signals of the terminals 18a and 18b every horizontal scanning period (1H).
From the common terminal of 8, a line-sequential signal is obtained by combining the luminance signal and the low-frequency conversion carrier chrominance signal alternately and in time series every 1H period.
This line sequential signal is supplied to the A/D converter 20,
Here, the signal is analog-to-digital converted into a digital signal, and then further supplied to the one-field delay circuit 21. 1 field delay circuit 21
For example, random access memory (RAM)
It consists of 1 field of input digital signal (strictly speaking, 1/2H processing is required, so
1 field + 1/2H period) is output with a delay.
The memory capacity of this 1-field delay circuit 21 is:
Compared to that of the one-frame delay line 4 shown in FIG. 1, the input signal is a line-sequential digital signal, and the carrier color signal is converted to a low frequency band;
Since it is only necessary to delay one field, which is half the period of one frame, the delay is only about 1/4, and therefore low-speed operating elements can be used, thereby simplifying the circuit configuration and making it inexpensive. Can be done.

Moreover, the 1-field delay circuit 21 uses a luminance signal and a carrier color signal (here converted to a low frequency signal).
Since it can be used commonly for both signals, compared to the case where one field delay circuit dedicated to both signals is used,
The device can be downsized and configured at low cost.

The digital signal taken out from the one-field delay circuit 21 is supplied to the A/D converter 22, where it is converted into an analog line sequential signal and then applied to the common terminal of the switch circuit 23. This switch circuit 23 is configured to alternately switch every 1H, similar to the switch circuit 18 described above.
In addition, during the 1H period when the input line sequential signal is a luminance signal, it is connected to the terminal 23a side, and during the 1H period when the input line sequential signal is a low frequency conversion carrier color signal, it is switched and connected to the terminal 23b side.

As a result, the luminance signal delayed by one field from the terminal 23a of the switch circuit 23 is intermittently taken out every 1H and supplied to the 1H delay circuit 24 and the terminal 25a of the switch circuit 25, respectively.
The switch circuit 25 is connected to the terminal 23a side during the 1H period when the 1-field delayed luminance signal is output from the switch circuit 23, and is connected to the terminal 23b side during the next 1H period.
Since the configuration is such that the output signal of the 1H delay circuit 24 is selectively connected to the side and is switched every 1H, the output brightness of the 1H delay circuit 24 is output from the common terminal of the switch circuit 25 every 1H. The one field delayed luminance signal substituted by the signal is continuously taken out and supplied to a subtracter 26.

Similarly, the 1-field delayed low frequency conversion carrier color signal, which is intermittently taken out every 1H from the terminal 23b of the switch circuit 23, is applied to the terminal 28b of the switch circuit 28 through the 1H delay circuit 27; By being directly supplied, the one-field delayed low frequency carrier color signal is continuously taken out from the common terminal of the switch circuit 28 without any signal dropout H period, and is supplied to the subtracter 29 at the next stage.

The subtracter 26 subtracts the one-field delayed luminance signal from the switch circuit 25 from the luminance signal from the low-pass filter 12, thereby removing noise components with no autocorrelation between fields and signal components of the luminance signal that have changed between fields. A first difference signal consisting of the difference is output, and this is output to the limiter 30. Similarly, the subtracter 29 is connected to the frequency converter 15.
Output low frequency conversion carrier color signal from switch circuit 28
By subtracting the 1-field delayed low-pass transformed carrier color signal, a second difference consisting of the noise component with no autocorrelation between fields and the difference in the signal component of the low-pass transformed carrier color signal that has changed between fields is obtained. A signal is output, and this is output to the limiter 31.

Here, the above-mentioned first and second difference signals generally have a large amplitude when a signal component is included, whereas a noise component has a small amplitude. Therefore, the limiters 30 and 31 limit the amplitudes of the input first and second difference signals, extract signals mainly consisting of noise components with small amplitudes, and output the signals to the subtracters 14 and 16. As an example, the limiting levels of the limiters 30 and 31 are selected to be approximately one-tenth of the maximum value of the input difference signal. Also Limituta 3
Since the values of 0 and 31 block the luminance signal component and the low-frequency conversion carrier color signal component, which have a large level, they also have the effect of reducing afterimages.

As a result, the subtracter 14 outputs the low-pass filter 1.
The output luminance signal of No. 2 is extracted with the noise component contained therein substantially canceled and is supplied to the comb filter 17 and the mixing circuit 33, respectively. On the other hand,
The subtracter 16 takes out the output low-pass converted carrier color signal of the frequency converter 15 after substantially canceling out noise components in the signal, and supplies the signal to a comb filter 19 and a frequency converter 32, respectively.

As shown in FIG. 4, the comb filters 17 and 19 each mix the input signal from the input terminal 36 with the signal obtained through the 1H delay circuit 37 and the input signal in the mixing circuit 38, and output the mixed signal. terminal 3
In the case of a 1H comb filter configuration that outputs to 9, the S/N ratio can be improved by about 3 dB. In other words, the input signal to the input terminal 36 is the total of the first half of horizontal scanning line numbers (1) to (262) and (263) for odd fields in the screen as shown by solid lines in FIG.
It is displayed with 262.5 scanning lines, and the next even field is the latter half of the horizontal scanning line number (263) and (264) to (525), which is a total of 262.5, as shown by the broken line in the same figure.
This is a video signal (specifically, a luminance signal or a low-frequency conversion carrier color signal) displayed between each scanning line of an odd field by the scanning lines of a book, and is sent to the output terminal 39 of the comb filter shown in FIG. are two adjacent horizontal scanning numbers (1) + (2), (2) + (3), (3) + (4), (4) + (5),...
Since a video signal consisting of
+(2), (3)+(4), (3)+(4), (5)+(6), (5)+(6),...
In this order, signals consisting of video information of two horizontal scanning line numbers are sequentially extracted.

In addition, in order to extract a signal consisting of video information of two horizontal scanning line numbers from the switch circuits 25 and 28, the delay time of the 1-field delay circuit 21 is as follows.
A delay time of 263H is selected.

By the way, when subtracters 26 and 29 take the difference between the separately obtained luminance signal, low-frequency transformed carrier color signal, and the luminance signal delayed by one field, the low-frequency transformed carrier color signal, the spatial From a perspective, if there are no comb filters 17 and 19, for example, the signal of horizontal scanning line number (2) will be differenced from the signal of horizontal scanning number (264); When comb filters 17 and 19 having the configuration shown in Figure 4 are provided, the difference between the averaged signal of horizontal scanning line number (1) + (2) and the signal of horizontal scanning line number (264) is taken. In this case, since they are spatially closer to each other, the signal components cancel each other out more, leaving only the noise component. Therefore, when 1H comb filters having the configuration shown in FIG. 4 are used as the comb filters 17 and 19, the comb filter 1
Compared to the case where 7 and 19 are not provided, the S/N ratio can be improved by about 3 dB as a noise reduction device.

Furthermore, if comb filters 17 and 19 are used,
Since the video information of all horizontal scanning line numbers can be used, the utilization rate of the video information is higher than in the case where the comb filters 17 and 19 are not provided, and the reproducibility of the signals at the outputs of the switch circuits 25 and 28 is good.

Furthermore, the comb filters 17 and 19 are not limited to the above-mentioned 1H comb filters, but may also be configured as 2H comb filters. As shown in FIG.
A signal obtained by delaying the input signal by 1H and a signal delayed by a total of 2H by passing this input signal through 1H delay circuits 41 and 42 respectively are mixed by a mixing circuit 43, and this is output to an output terminal 44. ing. When using a 2H comb filter with such a configuration, the output terminal 44 has three adjacent horizontal scanning line numbers (1)+(2)+
(3), (2) + (3) + (4), (3) + (4) + (5), (4) + (5) + (6),
Since a video signal consisting of ... is output every 1H, each output terminal of the switch circuits 25 and 28 has (1) + (2) + (3),
(1)+(2)+(3),(3)+(4)+(5),(3)+(4)+(5),(5)+
(6)+
Signals consisting of video information of three horizontal scanning line numbers are sequentially extracted in the order of (7), (5)+(6)+(7), . . . .

By the way, when the subtracters 26 and 29 calculate the difference between the luminance signal and the low-frequency conversion carrier color signal, which have a time difference of one field from each other, when viewed spatially in FIG. 3, the comb having the configuration shown in FIG. For example, if a type filter is used, the horizontal scanning line number (1) + (2) + (3)
The difference between the averaged signal and the signal of the horizontal scanning line number (265) is taken, and this is the case when no comb filter is provided and the 1H signal shown in Figure 4.
In any case where a comb filter is provided, the two signals whose difference is taken are spatially close to each other, so the signal components cancel each other out, leaving only the noise component. Therefore, when 2H comb filters having the configuration shown in FIG. 5 are used as the comb filters 17 and 19, the comb filter 1
As a noise reduction device, the S/N ratio can be improved by approximately 4.8 dB compared to the case where 7,19 is not used, and the S/N ratio is improved even more than when a 1H comb filter is used. Recognize.

As a result, a luminance signal with significantly suppressed noise components is extracted from the subtracter 14, and a low-frequency converted carrier color signal with significantly suppressed noise components is extracted from the subtracter 16. This low-band converted carrier color signal is supplied to a frequency converter 32, where it is returned to the carrier color signal of the original band and then supplied to a mixing circuit 33. As a result, the mixing circuit 33 generates an NTSC color video signal by mixing the luminance signal with significantly reduced noise components and the low frequency conversion carrier color signal, and sends this color video signal to the output terminal 34.
Output to.

Although the vertical resolution of the output is degraded by the comb filters 17 and 19, there is no problem in practice because the limiters 30 and 31 limit the amplitude of the signal components to a certain level.

Application Examples The present invention is not limited to the above-mentioned embodiments, and various other application examples are possible. For example, even without providing the comb filters 17 and 19, the desired S/N ratio improvement effect can be obtained. In addition, when reducing noise in PAL or SECAM color video signals, the 1H delay circuits 24 and 27 must be changed to 2H delay circuits, since the carrier color signals of these color video signals have a correlation every 2H. , and the present invention can be applied by changing the configuration so that the switch circuits 18, 23, 25, and 28 are switched and connected every 2H period. Furthermore, instead of the one-field delay circuit 21, a delay circuit that delays two or more arbitrary field periods may be used.

Effects As described above, according to the present invention, the sequential signals in which the luminance signal and the low-frequency conversion carrier chrominance signal are alternately synthesized in time series are passed through a single N-field delay circuit. , this N-field delay circuit can be constructed using a memory with a smaller capacity and elements that operate at a slower speed than conventional ones, making it inexpensive and easy to construct the circuit, and reducing afterimages compared to conventional motion detectors. This can be done with a limiter that has a simpler circuit configuration and is cheaper than the conventional one. Furthermore, when a comb filter is used, the S/N ratio of the color video signal can be further improved than when a comb filter is not used. In addition, since video information from all lines can be used, the utilization rate of video information can be increased, and compared to a device that performs noise reduction by passing the luminance signal and carrier color signal through dedicated N-field delay circuits, respectively. This device has a number of advantages, such as being able to reduce the number of N-field delay circuits by half, making the entire device more compact, and being able to be constructed at a lower cost.

[Brief explanation of drawings]

FIG. 1 is a block system diagram showing an example of a conventional device, FIG. 2 is a block system diagram showing an embodiment of the device of the present invention, FIG. 3 is a diagram showing scanning lines in the screen, and FIGS. Each figure is a block system diagram showing each embodiment of the comb filter in the block system shown in FIG. 1, 11...Input terminal, 4...1 frame delay line, 5...Chroma inverter, 8...Motion detector, 9...Output terminal, 12...Low-pass filter for luminance signal separation, 13... Carrier color signal separation band filter, 14, 16, 26, 29... Subtractor, 15, 32... Frequency converter, 17, 19...
...Comb filter, 18, 23, 25, 28...
switch circuit, 21...1 field delay circuit,
24, 27, 37, 41, 42...1H delay circuit,
30, 31... Limiter, 33... Mixed circuit, 3
4...Color video signal output terminal, 38, 43...
mixed circuit.

Claims (1)

[Scope of Claims] 1. Separating means that separates a color video signal into a luminance signal and a carrier color signal, a frequency converter that converts the frequency of the separated carrier color signal to a lower frequency band, and the separated luminance signal. first and second subtracters to which the signal and the output low-pass converted carrier chrominance signal of the frequency converter are respectively supplied; a first switch circuit that outputs the low-pass conversion carrier color signal as a sequential signal that is synthesized alternately and in time series at regular intervals;
a delay circuit that delays; a second switch circuit that switches the output signal of the delay circuit every certain period of time to alternately select and output a delayed luminance signal and a delayed low-frequency conversion carrier color signal; The delayed luminance signal intermittently taken out from the circuit is converted into a continuous delayed luminance signal using the first delay device having a delay time of the certain period, and then subtracted from the separated luminance signal. a first signal processing means that obtains a first difference signal by using a second switch circuit; a second signal processing means for obtaining a second difference signal by converting the signal into a continuous signal using a frequency converter and subtracting the signal from the low-frequency converted carrier color signal from the frequency converter; It consists of first and second limiters that output a signal obtained by limiting the amplitude of the difference signal between the two to the first and second subtracters, and the noise component is reduced by the first and second subtracters. A noise reduction device for a color video signal, characterized in that the device is configured to extract a luminance signal and a low frequency converted carrier color signal, respectively. 2. Separating means for separating a color video signal into a luminance signal and a carrier color signal, a frequency converter for converting the frequency of the separated carrier color signal to a lower frequency band, and the separated luminance signal and the frequency converter. first and second subtracters to which the output low-pass conversion carrier color signals are respectively supplied, and first and second combs to which the output signals of the first and second subtractors are supplied. The luminance signal and the low frequency conversion carrier color signal are synthesized alternately in time series at regular intervals from both output signals of the filter and the first and second comb filters, and output as a sequential signal. a first switch circuit; a delay circuit that delays the sequential signal by N fields (where N is a natural number); and a delay luminance signal and a delayed low-frequency conversion carrier color that switch the output signal of the delay circuit every certain period of time. a second switch circuit that alternately selects and outputs the signal; and a first delay device having a delay time of the certain period to continuously output the delayed luminance signal that is intermittently taken out from the second switch circuit. a first signal processing means for obtaining a first difference signal by subtracting the delayed luminance signal from the separated luminance signal; After converting the delayed low-pass conversion carrier color signal into a continuous signal using a second delay device having a delay time of the predetermined period, subtraction is performed with the low-pass conversion carrier color signal from the frequency converter. a second signal processing means for obtaining a second difference signal; first and second signal processing means for outputting a signal obtained by amplitude limiting the first and second difference signals to the first and second subtracters; Noise reduction of a color video signal, characterized in that the first and second subtracters are configured to take out a luminance signal with a reduced noise component and a low-frequency conversion carrier color signal, respectively. Device. 3. The first and second comb filters include a 1H delay circuit having a delay time of one horizontal scanning period, and a 1H delay circuit having a delay time of one horizontal scanning period.
3. The color video signal noise reduction device according to claim 2, comprising a mixing circuit that mixes input and output signals of the 1H delay circuit, respectively. 4 The first and second comb filters receive a first delayed signal obtained by delaying the input signal by one horizontal scanning period, and a second delayed signal obtained by delaying the input signal by two horizontal scanning periods. 3. The noise reduction device for a color video signal according to claim 2, wherein the noise reduction device is configured to mix and output the respective input signals together with the input signal.