JP2565182B2 - Noise removal circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removing circuit utilizing correlation.

[0002]

2. Description of the Related Art Conventionally, in video signal processing, for Y / C separation for separating a luminance signal Y and a carrier color signal (chroma signal) C, a horizontal correlation, a vertical correlation and a time ( It is known to utilize frame) correlation.

First, a conventional Y / C separation circuit utilizing each of the above-mentioned correlations will be described with reference to FIGS. In the horizontal correlation type Y / C separation circuit shown in FIG. 7A, the video signal is commonly supplied from the input terminal 1 to the low pass filter 2Y and the band pass filter 2C, and the low pass filter 2Y is supplied.
Of the bandpass filter 2C, that is, the chroma signal CH.
Is led to the output terminal 3C.

In the vertical correlation type Y / C separation circuit shown in FIG. 1B, the video signal is supplied from the input terminal 1 to the 1H delay line 4, the adder 5Y and the subtractor 5C in common and 1H. The output of the delay line 4 is the adder 5Y and the subtractor 5C.
Commonly supplied to. The luminance signal YV is derived from the adder 5Y to the output terminal 6Y, and the chroma signal CV is derived from the subtractor 5C to the output terminal 6C.

Further, the frame correlation type Y / shown in FIG.
In the C separation circuit, the video signal from the input terminal 1 constitutes one frame delay line, the frame memory 7 and the adder 8Y.
And the subtractor 8C are commonly supplied, and the output of the frame memory 7 is commonly supplied to the adder 8Y and the subtractor 8C. The luminance signal YF is derived from the adder 8Y to the output terminal 9Y, and the chroma signal CF is derived from the subtractor 8C to the output terminal 9C.

Although the frame memory 7 originally processes a digitized signal, it is assumed that it can process an analog signal here for simplicity, and the input side analog-digital converter and the output side are processed. The illustration of the digital-analog converter is omitted.

The frequency-amplitude characteristics of the Y / C separation circuits shown in FIGS. 7A to 7C are shown in FIGS. 8A to 8C, respectively.

First, in FIG. 8A, a thick solid line shows the pass characteristic of the low-pass filter 2Y, and a broken line shows the band-pass filter 2C.
Shows the passage characteristics of. In FIG. 7A, a subcarrier trap can be used instead of the low-pass filter 2Y, and the pass characteristic in this case is represented as a thick / thin solid line.

The vertical correlation type Y / C separation circuit shown in FIG. 7B constitutes a well-known comb filter. Its luminance signal Y
As shown by the solid line in FIG. 8B, the pass characteristic with respect to V is the sub-carrier frequency fSC and the horizontal frequency fH above and below it.
The maximum attenuation is obtained at each point separated by an integer multiple of, and an odd multiple (2n + 1) fH / 1/2 of the horizontal frequency fH is obtained in the middle of these points, that is, above and below the subcarrier frequency fSC.
The minimum attenuation is obtained at each point separated by two. Contrary to this, the pass characteristic for the chroma signal CV has a sub-carrier frequency fSC and a horizontal frequency f
The minimum attenuation is obtained at each point that is an integral multiple of H, and is an odd multiple (2n) of the horizontal frequency fH from the subcarrier frequency fSC.
The maximum attenuation is obtained at each point +1) fH / 2 apart.

This is because the spectrum of the chroma signal C is located in the middle of the spectrum of the luminance signal Y shown by the solid line in FIG. 9A by the well-known frequency interleaving, as shown by the broken line in FIG. 9A.

The frame correlation type Y / C separation circuit of FIG. 7C constitutes a well-known comb filter. As shown by the solid line in FIG. 8C, the pass characteristic for the luminance signal YF has the maximum attenuation at the subcarrier frequency fSC and at points above and below which are integer multiples of the frame frequency fF (= fV / 2). At the middle of these points, that is, from the subcarrier frequency fSC up and down, 1 / of the frame frequency fF
The minimum attenuation is obtained at each point that is an odd multiple of 2 (2n + 1) fF / 2. On the contrary, the pass characteristic for the chroma signal CF has a sub-carrier frequency f as shown by a broken line in FIG.
SC and the minimum attenuation at each point separated from this by an integral multiple of the frame frequency fF, and the subcarrier frequency fSC
To an odd multiple of 1/2 of the frame frequency fF (2n + 1)
The maximum attenuation is obtained at points separated by fF / 2.

This is due to the well-known frequency interleaving, as shown in FIG. 9B, which is a partially enlarged view of FIG. 9A, and the vertical frequency fV accompanying the odd harmonics of the horizontal frequency fH.
The sidebands (shown by white circles) and the sidebands with vertical frequency fV (shown by black circles) accompanying the even harmonics are mutually spaced at the frame frequency fF = fV / 2.
This is because the subcarrier frequency fSC and the accompanying sideband of the vertical frequency fV are located in the middle of the frequency interval of F.

[0013]

However, in the conventional Y / C separation circuit in which the above-described various correlations are independently used, the image quality is deteriorated in the portions having no correlation.

That is, when the horizontal correlation is used, FIG.
When the levels of the luminance signal Y and the chroma signal C rapidly change in the horizontal direction like the side edges of the vertical stripes on the screen as shown in A, image quality deterioration such as frequency characteristic deterioration and crosstalk occurs. .

When vertical correlation is used, FIG.
When the levels of the luminance signal Y and the chroma signal C change rapidly in the vertical direction, such as the side edges of the horizontal stripes on the screen as shown in FIG. 5, crosstalk occurs, image quality deterioration such as subcarrier dot visible, etc. Occurs.

Further, when the frame correlation is used, as shown in C1 to C3 in the figure, when the graphic on the screen moves in the direction of each arrow, a part of the peripheral edge of the graphic is associated with the moving direction. Or, crosstalk occurs at all, and multi-line interference or other significant image quality deterioration in which the periphery is doubled or tripled occurs.

In order to solve such a problem, it is conceivable to switch the separation output at an appropriate time according to the amount of movement of the pixel. In this case, however, the movement detecting section is required and the circuit configuration is large. The problem of scale and complexity arises.

In view of the above point, an object of the present invention is to provide a noise removing circuit which can improve the quality of a reproduced image without requiring motion detection.

[0019]

According to the present invention, there is provided a first luminance signal separating means for separating a first luminance signal from an input video signal by using a horizontal correlation of the video signal, and a first luminance signal separating means for separating the first luminance signal in the vertical direction. Second luminance signal separating means for separating a second luminance signal from the input video signal by using correlation, and third luminance signal from the input video signal by using correlation in the time axis direction of the video signal. A third luminance signal separating means, and the first
Level of the first luminance signal from the luminance signal separating means, the second luminance signal from the second luminance signal separating means, and the level of the third luminance signal from the third luminance signal separating means. The first chroma signal is separated from the input video signal by using the first intermediate value selecting means for comparing and selecting and outputting the luminance signal of the intermediate value based on the comparison result and the horizontal correlation of the video signal. A second chroma signal from the input video signal by using the first chroma signal separating means and the vertical correlation of the video signal.
Second chroma signal separating means for separating the chroma signal of
Third chroma signal separating means for separating a third chroma signal from the input video signal by using the correlation of the video signal in the time axis direction, and the first chroma signal separating means from the first chroma signal separating means.
Of the chroma signal, the second chroma signal from the second chroma signal separating means, and the level of the third chroma signal from the third chroma signal separating means are compared, and based on the comparison result, the intermediate Second intermediate value selecting means for selecting and outputting the chroma signal of the value.

[0020]

According to the present invention described above, the first luminance signal and the second luminance separated by the first intermediate value selecting means using the correlation in the horizontal direction from the first luminance signal separating means. Level of the second luminance signal separated by using the correlation in the vertical direction from the signal separating means, and level of the third luminance signal separated by using the correlation in the time axis direction from the third luminance signal separating means Are compared, the luminance signal of the intermediate value is selected and output based on the comparison result, and is separated by the second intermediate value selecting means using the correlation in the horizontal direction from the first chroma signal separating means. The vertical correlation from the first chroma signal and the second chroma signal separating means is used to obtain the second chroma signal.
, And the levels of the separated third chroma signals using the correlation in the time axis direction from the third chroma signal separating means are compared, and the intermediate chroma signal is selected based on the comparison result. Is output.

[0021]

【Example】

[Embodiment] The noise removing circuit of the present invention will be described in detail below with reference to FIGS.

The configuration of one embodiment of the present invention is shown in FIG. In FIG. 1, the noise removal circuit 50 is a correlation detection circuit 51, 52 and 53 in each direction of horizontal, vertical and time (frame), and an intermediate value selection to which each output of these correlation detection circuits 51 to 53 is supplied. And a circuit 54. Each of the correlation detection circuits 51 to 53 has, for example, a luminance signal Y described later.
The same type of signals such as H, YV, and VF are output.

In FIG. 1, the luminance signal processing system and the chroma signal processing system are shown as one circuit. Of course, the processing system for the luminance signal and the processing system for the chroma signal may be separated.

FIG. 2 shows a more specific circuit configuration example of FIG. The intermediate value selection circuit 54 shown in FIG.
Corresponding to the intermediate value selecting circuit 12Y and the intermediate value selecting circuit 12C shown in FIG.
C is configured as shown in FIG. 3 or FIG. 4, respectively.

When the processing system for the luminance signal and the processing system for the chroma signal are formed by one circuit and used as a noise elimination circuit for the luminance signal, the luminance signal is input and, at that time, the intermediate value selecting circuit 12C. Do not use the output of. On the other hand, when it is used as a noise elimination circuit for a chroma signal, the chroma signal is input, and at that time, the intermediate value selection circuit 12
Do not use the output of Y. If you do this,
There is an advantage that the number of manufacturing processes can be one.

On the other hand, when the processing system for the luminance signal and the processing system for the chroma signal are separated, the circuit shown in FIG. 2 may be simply divided into the processing system for the luminance signal and the processing system for the chroma signal. That is, the processing system of the luminance signal is the low-pass filter 2
Y, adder 5Y, 1H delay line 4, adder 8Y, frame memory 7 and intermediate value selection circuit 12Y. On the other hand, the chroma signal processing system includes a bandpass filter 2C, a subtraction circuit 5C, a 1H delay line 4, a subtraction circuit 8C, a frame memory 7, and an intermediate value selection circuit 12C. In the case where the noise removal circuit is configured by separating the luminance signal processing system and the chroma signal processing system in this way, the manufacturing process has two systems, but only the system to be used can be mounted on the device. There are merits such as.

Here, YH is a luminance signal obtained by horizontal correlation detection, YV is a luminance signal obtained by vertical correlation detection, and YF is a luminance signal obtained by time correlation detection.

CH is a chroma signal obtained by horizontal correlation detection, CV is a chroma signal obtained by vertical correlation detection, and CF is a chroma signal obtained by time correlation detection.

In the noise elimination circuit shown in FIG. 1, for any one of the input luminance signal Y and chroma signal C, the signals other than the extracted signal are noise. Also, in general, the video signals are correlated,
Since the noise has no correlation, it is easily understood that the present embodiment separates the video signal from the noise, in other words, removes the noise from the video signal. That is, in this example, the luminance signal Y and the chroma signal C that have already been separated are
It is intended to solve the above-mentioned problems by performing noise removal processing on the. Here, noise means, when the luminance signal Y and the chroma signal C are separated, noise components other than the chroma component and the video signal mixed in the luminance signal Y and the video signal mixed in the chroma signal C. The noise component of is shown.

In FIG. 2, HCcorr, VCorr, and FCCorr are horizontal-correlation-type, vertical-correlation-type, and frame-correlation-type Y / Cs as shown in FIGS. 7A, B and C, respectively.
The separation circuit of the luminance signal in the separation circuit is shown, and the input terminal 1
The video signal from 1 is commonly supplied. The intermediate value selection circuit 12Y is supplied with the low-pass filter 2Y and the outputs YH, YV, and YF of both adders 5Y and 8Y, and the intermediate value selection circuit 12C is supplied with the bandpass filter 2C and both subtractors 5Y.
The respective outputs CH, CV and CF of C and 8C are supplied.

FIG. 3 shows a configuration example of each intermediate value selection circuit.
In FIG. 3, input terminals 21H, 21V and 21F
Corresponds to the separation circuits HCCorr, VCorr, and FCCorr in FIG. 2, respectively. The input signal from terminal 21H is
The input signals from the terminal 21V are supplied to the third and first maximum value selection circuits 24 and 22, and the input signals from the terminal 21F are supplied to the first and second maximum value selection circuits 22 and 23. Second and third maximum value selection circuits 23 and 2
4 is supplied. First to fourth maximum value selection circuits 22-2
Each output of 4 is supplied to the minimum value selection circuit 25, and the output of the minimum value selection circuit 25 is led to the terminal 13.

Next, the operation of the intermediate value selection circuit of FIG. 3 will be described. Now, the amplitudes of the luminance signals YH, YV and YF supplied from the respective separation circuits of FIG. 2 to the respective input terminals 21H, 21V and 21F of the intermediate value selection circuit 12Y of FIG. 3 are, for example, YH>YV> YF. Suppose

At this time, since YH and YV are supplied to the first maximum value selection circuit 22, the larger one of them, that is, YH appears in the output (A). Further, YV and YF are supplied to the second maximum value selection circuit 23, and the larger YV appears at the output (B). Further, YF and YH are supplied to the third maximum value selection circuit 24, and the larger YH appears at the output (C).

From the maximum value selection circuits 22 to 24, the outputs (A), (B) and (C), that is, YH, YV, and
YH is supplied. The output of the minimum value selection circuit 25 is YH
Is smaller than the YV. As mentioned above, YH>YV>
Since it is YF, the intermediate value YV is selected by the configuration of FIG.

When the magnitude relation of the three luminance signals YH, YV, YF is different from the above, the intermediate value selection circuit of FIG. 3 operates as shown in Table 1, and in any case, the intermediate value of the three luminance signals is intermediate. The value is selected.

[0036]

[Table 1]

When the two inputs of the maximum value selection circuits 22 to 24 have the same magnitude, either of them may be output. In this case, the intermediate value selection circuit 12Y of FIG. 3 selects the third input. The relationship shown in Table 1 holds.

The intermediate value selection circuit shown in FIG. 3 operates in the same manner as described above for each of the chroma signals CH, CV and CF.

[Operation] As described above, the image shown in FIG. 8A has a correlation in the vertical direction, and the image shown in FIG. 8B has a correlation in the horizontal direction. Further, C1 to C3 in FIG.
When the image is still, as shown in, there is a correlation in the frame (time) direction.

As described above, when the image has a correlation in the horizontal, vertical, or temporal direction, each separation circuit HC in FIG.
Among the outputs of orr, VCorr, and FCCorr, the probability that the output corresponding to the direction having the correlation becomes the intermediate value has the highest probability, and the output corresponding to the direction having no correlation is larger or smaller than the output in the direction having the correlation. Will be either. Therefore, in FIG. 2, one of the intermediate value selection circuits 12Y is
Thus, the luminance signal Y corresponding to the direction in which the images have correlation is selected, the most suitable noise removal is performed for various images that change at any time, and the quality of the reproduced image is improved.

As shown in FIG. 4, the intermediate value selecting circuit replaces the maximum value selecting circuits 22, 23, 24 of FIG. 3 with the minimum value selecting circuits 26, 27, 28, respectively, and also has the minimum value of FIG. The value selection circuit 25 can be replaced by a maximum value selection circuit 29.

The intermediate value selection circuit of FIG. 4 operates as shown in Table 2 for six magnitude relationships of the three luminance signals YH, YV, YF, and for each chroma signal CH, CV, CF. Works exactly the same.

[0043]

[Table 2]

When the two inputs of the minimum value selection circuits 26 to 28 have the same magnitude, the intermediate value selection circuit 12 of FIG.
Also in C, the third input is not selected, and Table 2
The relationship is established.

[Other Embodiments]

Next, another embodiment of the present invention will be described with reference to FIGS. 5 and 6, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. Also in this other embodiment, the circuit configuration of the luminance signal processing system and the chroma signal processing system is one in the figure, but as in the above-described embodiment, the luminance signal processing system and the chroma signal processing system are The processing system may be configured separately.

First, FIG. 5 will be described. In FIG.
The transversal filter 31 includes four unit delay lines 32a, 32b, 32c and 32d connected in series and a weighting addition circuit 33, and the input side of the first unit delay line 32a and each of the first to fourth units. Each of the connection points of the delay lines 32a to 32d and the output side of the fourth unit delay line 32d are connected to the weighting addition circuit 33. The transversal filter 31 corresponds to the horizontal correlation type Y / C separation circuit HCorr including the low pass filter 2Y and the band pass filter 2C shown in FIG. 2, and operates with a clock of 4 fsc, for example. The delay time of each of the unit delay lines 32a to 32d is D.

The output of the fourth unit delay line 32d of the transversal filter 31 is supplied to the memory 34, the output of this memory 34 is supplied commonly to the adder 35Y and the subtractor 35C, and the second and third units are also supplied. Unit delay line 32b
And the output of the connection midpoint of 32c are commonly supplied to the adder 35Y and the subtractor 35C. The delay time of the memory 34 is 1
The memory 34 and the third and fourth unit delay lines 32 of the transversal filter 31 are set to H-2D.
c and 34d form a 1H line memory with a delay time, and this line memory, adder 35Y and subtractor 3
A vertical correlation type separation circuit VCorr is constructed with 5C.

The output of the memory 34 is supplied to the second memory 35, the output of the memory 35 is commonly supplied to the second adder 38Y and the subtractor 38C, and the second and the third of the transversal filter 31 are supplied. 3 unit delay line 32b
And the output of the connection midpoint of 32c is commonly supplied to the adder 38Y and the subtractor 38C. The delay time of the memory 35 is 1
F-1H, and a frame memory having a delay time of 1F (one frame cycle) by the memory 35, the first memory 34, and the third and fourth unit delay lines 32c and 32d of the transversal filter 31. Is configured,
This frame memory, the second adder 38Y and the subtractor 3
A frame correlation type separation circuit FCorr is configured with 8C.

The transversal filter 31 and the outputs YH, YV, YF of the two adders 35Y and 38Y are supplied to one intermediate value selection circuit 12Y, and the transversal filter 31 and both subtractors are supplied to the other intermediate value selection circuit 12C. Outputs CH, CV, and CF of 35C and 38C are supplied.

Each intermediate value selection circuit 12Y, 12 of the present embodiment.
A configuration example of C is shown in FIG. In FIG. 6, the maximum value selection circuit 41, the minimum value selection circuit 42, and the adder 43 respectively include
Input signals from the input terminals 21H, 21V and 21F are commonly supplied. The outputs (G) and (H) of the maximum value selection circuit 41 and the minimum value selection circuit 42 are supplied to the second adder 44. The output (J) of the second adder 44 is supplied to the subtractor 45 while the output of the adder 43 is supplied to the subtractor 45.
, Which is subtracted from the output of the adder 43.

The intermediate value selection circuit of FIG. 6 operates as shown in Table 3 for the six magnitude relationships of the three luminance signals YH, YV, YF, and for each chroma signal CH, CV, CF. Works exactly the same.

[0053]

[Table 3]

Note that even if two inputs have the same magnitude among the three inputs, the relationship in Table 3 holds.
Further, the intermediate value selection circuits 12Y and 12C shown in FIG.
Horizontal correlation type and frame correlation type separation circuits HCo of FIG.
It is composed of a digital circuit together with rr and FCorr.
The same applies to the intermediate value selection circuits of FIGS. 3 and 4.

In this way, the embodiment of FIG. 5 operates in exactly the same way as the embodiment of FIG. 2 already described, and for an image that changes from time to time, the luminance signal Y in the direction having the image correlation is selected, The most suitable noise removal is performed and the quality of the reproduced image is improved.

[0056]

According to the present invention described above, the first luminance signal and the second luminance signal separated by the first intermediate value selecting means by using the correlation in the horizontal direction from the first luminance signal separating means are used.
Second luminance signal separated by using the correlation in the vertical direction from the luminance signal separating means, and third luminance signal separated by using the correlation in the time axis direction from the third luminance signal separating means. Are compared, the luminance signal of the intermediate value is selected and output based on the comparison result, and the horizontal correlation from the first chroma signal separating means is used by the second intermediate value selecting means. First chroma signal separated, second
Of the second chroma signal by using the correlation in the vertical direction from the chroma signal separating means of the second chroma signal and the level of the third chroma signal separated by using the correlation in the time axis direction from the third chroma signal separating means. Comparison is made, and an intermediate value chroma signal is selected and output based on the comparison result. Therefore, since correlations in a plurality of directions are detected and an intermediate value of these correlation detection values is selected, it is possible to use the correlation in the most suitable direction without performing motion detection for an image that changes at any time. As a result, the chroma component mixed in the luminance signal,
Removes noise components mixed in luminance signal and chroma signal,
There is an effect that the quality of the reproduced image can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a noise removal circuit according to the present invention.

FIG. 2 is a block diagram showing a specific configuration example of the noise removal circuit of FIG.

FIG. 3 is a block diagram showing an internal configuration example of an intermediate value selection circuit of FIG.

FIG. 4 is a block diagram showing an internal configuration example of an intermediate value selection circuit of FIG.

5 is a block diagram (another embodiment) showing a specific configuration example of the noise removal circuit of FIG.

6 is a block diagram showing an example of the internal configuration of the intermediate value selection circuit of FIG.

FIG. 7 is a block diagram showing a configuration of a conventional Y / C separation circuit and a diagram showing characteristics.

FIG. 8 is a block diagram showing a configuration of a conventional Y / C separation circuit and a diagram showing characteristics.

FIG. 9 is a spectrum diagram of a video signal used for explaining a conventional example.

FIG. 10 is a conceptual diagram showing a reproduced image by a conventional Y / C separation circuit.

[Explanation of symbols]

 12C, 12Y, 54 Intermediate value selection circuit 51 Horizontal correlation detection circuit 52 Vertical correlation detection circuit 53 Time (frame) correlation detection circuit HCorr Horizontal correlation type Y / C separation circuit VCorr Vertical correlation type Y / C separation circuit FCorr Frame correlation type Y / C separation circuit

Claims (3)

(57) [Claims] 1. A first luminance signal separating means for separating a first luminance signal from an input video signal by using horizontal correlation of the video signal, and the input video signal by using vertical correlation of the video signal. A second luminance signal separating means for separating the second luminance signal from the input video signal, and a third luminance signal separating means for separating the third luminance signal from the input video signal by using the correlation in the time axis direction of the video signal. The first luminance signal from the first luminance signal separating means, the second luminance signal from the second luminance signal separating means, the third luminance from the third luminance signal separating means First intermediate value selecting means for comparing the signal levels and selecting and outputting a luminance signal of an intermediate value based on the comparison result; First chroma signal separation hand to separate the chroma signal A second chroma signal separating means for separating a second chroma signal from the input video signal by using the correlation in the vertical direction of the video signal; and a second chroma signal separating unit from the input video signal by using the correlation in the time axis direction of the video signal. Third chroma signal separating means for separating a third chroma signal, the first chroma signal from the first chroma signal separating means, and the second chroma signal from the second chroma signal separating means , Second intermediate value selecting means for comparing the levels of the third chroma signals from the third chroma signal separating means and selecting and outputting an intermediate value chroma signal based on the comparison result. Noise removal circuit characterized by. 2. A first separating means for separating a first luminance signal from an input video signal by using a horizontal correlation of the video signal, and a first separating means from the input video signal by using a vertical correlation of the video signal. Second separating means for separating the second luminance signal; third separating means for separating the third luminance signal from the input video signal by using the correlation of the video signal in the time axis direction; and the first separating means. Comparing the levels of the first luminance signal from the means, the second luminance signal from the second separating means, and the third luminance signal from the third separating means, and based on the comparison result. And an intermediate value selecting means for selecting and outputting an intermediate value luminance signal. 3. A first separating means for separating a first chroma signal from an input video signal by using a horizontal correlation of the video signal, and a first separating means from the input video signal by using a vertical correlation of the video signal. Second separating means for separating the second chroma signal, third separating means for separating the third chroma signal from the input video signal by using the correlation of the video signal in the time axis direction, and the first separating means. Said first chroma signal from said means, said second chroma signal from said second separating means, said third
Noise removal circuit, which compares the levels of the third chroma signals from the separating means, and selects an intermediate value chroma signal based on the comparison result, and outputs the selected intermediate value chroma signal.