JP2960528B2 - Motion adaptive YC separation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the reception image quality of a composite color television signal, and more particularly to an image quality improvement circuit of a receiver provided with a motion adaptive YC separation circuit. is there.

SUMMARY OF THE INVENTION The present invention relates to a motion-adaptive YC for a received composite color television signal, especially for a received NTSC standard color television signal.
This is related to improvement of a separation circuit, and a low-pass filter (cutoff frequency of about 3 MHz) for band limitation is additionally inserted only in a moving image processing unit of a Y signal of a conventional motion adaptive YC separation circuit.

Thus, the dot disturbance that occurs on the horizontal edge (horizontal line edge) of the color of the moving image portion is removed while minimizing the reduction in the resolution of the output signal.

(Prior art) A motion adaptive YC separation circuit that performs YC separation that adapts to motion in an image as a recent improvement on the receiver side in order to improve the reception image quality of the received decoded color television signal, especially the NTSC standard system. Is being used.

The specific configuration of the conventional example is compared with the circuit configuration according to the present invention, and will be described later with reference to FIG. 2 (Example). For further details, refer to the following document, for example. I want to.

References Achiba et al .: "Motion Adaptive Signal Processing for IDTV Receivers", Journal of the Institute of Television Engineers of Japan, vol.41, No.7, pp.655-662.
(1987) (Problem to be Solved by the Invention) The motion adaptive YC separation circuit can use a three-dimensional filter of horizontal, vertical, and time for a stationary part in an image, and is therefore an image quality interference component. The cross luminance component and the cross chrominance component can be completely removed.
However, since the two-dimensional YC separation using the conventional horizontal and vertical two-dimensional filters is applied to the moving image portion, the interference component cannot be completely removed. In particular, if there is a sharp horizontal edge (horizontal line edge) that moves in an image, dot interference occurs as a cross luminance component in that portion, and the image quality may be greatly deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a motion adaptive YC separation circuit which does not degrade image quality even when a received image has a sharp moving horizontal edge.

(Means for Solving the Problems) To achieve this object, a motion adaptive YC according to the present invention is used.
A separation circuit is a motion-adaptive YC separation circuit suitable for YC separation of a received composite color television signal including a moving image, wherein the circuit creates a frame-to-frame sum signal of a received input signal, and the input signal Means for generating an inter-frame difference signal, means for extracting high frequency components related to the vertical spatial frequency and horizontal spatial frequency of the input signal, a subtractor for subtracting the high frequency component from the input signal, and the subtractor And a low-pass filter for band-limiting the output signal of the input signal, according to the level of the signal of the motion of the input signal determined separately, between the inter-frame sum signal and the output signal of the low-pass filter, And a first mixer and a second mixer for adaptively selecting, weighting and adding between the inter-frame difference signal and the output signal of the circuit for extracting the high frequency component, and outputting the same. Each of the first and second mixers is provided with a luminance signal output and a chromaticity signal output of the received color television signal.

(Example) Hereinafter, the present invention will be described in detail by way of examples with reference to the accompanying drawings.

FIG. 1 is a configuration block diagram of a motion adaptive YC separation circuit according to an embodiment of the present invention.

The composite color television signal of the NTSC system, which is the input signal of this circuit, is first delayed by one frame time by the one-frame delay (F) 1. A signal delayed by one frame, which is the output of the one-frame delay unit 1, from the input NTSC signal is subtracted through a subtractor 2, and the output of the subtracter 2 is multiplied by 1/2 by a 係数 coefficient unit 3 to obtain an NTSC signal. To obtain an inter-frame difference signal having a dynamic range equal to. This signal becomes the S-side input of the mixer 15 described later. Next, 1
The sum of the frame-delayed signal and the input NTSC signal is obtained via an adder 4, and the sum output is multiplied by 1/2 by a 1/2 coefficient unit 5 to obtain an inter-frame sum signal. This signal becomes the S-side input of the mixer 14 described later.

On the other hand, the NTSC signal is input to the one-line delay (H) 6 and is delayed by a time corresponding to one scanning line. The subtracter 7 subtracts the signal delayed by one line, which is the output of the one-line delay unit 6, from the input NTSC signal, and multiplies the output of the subtracter 7 by に お い て in the 係数 coefficient unit 8. The elements 6, 7, and 8 form a 2-tap VHPF (high-pass filter for vertical spatial frequency) 9 as a whole. In this embodiment, two tap VH
Although PF is shown, the present invention is not limited to this, and VH of 3 taps or more
PF may be used. From the output signal of VHPF9, 2.1MHz H
A PF (high-pass filter having a cutoff frequency of 2.1 MHz) 10 extracts high-frequency components of 2.1 MHz or more. Filter 10
Will be described later. This is the M-side input of the mixer 15. The output of the filter 10 is also guided to the subtractor 11 at the same time.
, The output signal of the filter 10 is subtracted from the input NTSC signal, and the output signal of the subtractor 11 is band-limited by a 3 MHz LPF (low-pass filter with a cutoff frequency of 3 MHz) 12. The output of the filter 12 becomes the M-side input of the mixer 14.

The mixers 14 and 15 select or mix the S-side input and the M-side input for each pixel in accordance with the level of the motion signal output from the motion detector 13, and output the selected or mixed input. That is, for example, assuming that the level “0” represents the stillness of the image and the level “1” represents the motion in the motion signal, the mixers 14 and 15 output S when the level is “0”.
Select and output the side input. When the level is "1", select and output the M side input. When the level is between "0" and "1", weight the S and M inputs according to the level. Add and output. The output of the mixer 14 is the Y signal (luminance signal) output of the YC separation circuit of the present invention, and the output of the mixer 15 is the C signal (carrier color signal) output.

The motion detector 13 performs motion detection using the NTSC signal as input, and outputs, for example, “0” as a motion signal for a still pixel and “1” for a motion pixel as described above. . “0” and “1” depending on the amount of movement if the amount of movement is small
Output the intermediate level of. The motion detector 13 can be realized by a conventional technique.

FIG. 2 shows an example of the configuration of a conventional motion adaptive YC separation circuit in the sense of comparison with the embodiment of the present invention. 2nd illustrated element
The functions of 1,2,3,6,7,8,9,10,13,15 are completely the same as the corresponding elements shown in FIG.
Making the output of the mixer 15 a C signal output is the same as that shown in FIG. 1, and the C signal output in FIG. 2 is equal to the C signal output in FIG. On the other hand, as for the Y signal output, in the conventional example shown in FIG. 2, the C signal which is the output of the mixer 15 is subtracted from the input NTSC signal by the subtractor 21,
Are output as Y signal outputs.

When the motion signal is "0" in the mixer 15 shown in FIG.
That is, when the S-side input is selected, the subtractor 21
The frame difference signal is subtracted from the NTSC signal to form a frame sum signal, and this signal becomes the Y signal output. Therefore, when the motion signal is "0", the configuration shown in FIGS. 1 and 2 is equivalent for the Y signal output. This can be expressed by the following equation.

F ₀ : Input NTSC signal F ₁ : If signal F ₀ is delayed by one frame, On the other hand, when the motion signal is "1", different signals are output in the configurations shown in FIGS. That is, the first
In the configuration shown, the output of the 2.1 MHz high-pass filter 10 is subtracted from the input NTSC signal, and the signal is subtracted from the 3 MHz low-pass filter.
After limiting the band at 12, and outputting it as a Y signal,
In the configuration shown in FIG. 2, the output of the subtracter 21 obtained by subtracting the output of the filter 10 from the input NTSC signal is used as the Y signal.

Next, FIG. 3 is a diagram for explaining the situation of YC separation for a moving image portion (moving pixels) in the configuration shown in FIG.
The horizontal axis in the figure is the horizontal spatial frequency μ (MHz), and the vertical axis is the vertical spatial frequency ν (cph = cycle per height). N
Since the transmission path bandwidth of the TSC signal is 4.2 MHz, the frequency μ is displayed up to 4.2 MHz. In addition, NTSC signal is
Since there are five lines, the frequency ν is displayed up to 525/2 cph. A broken line a in the figure indicates a boundary between the separation of the Y signal and the C signal in the second configuration circuit. That is, input NTSC
Of the signals, the frequency components in the inner region of the broken line a are output as C signals, and the components in the outer region (region A in the figure) are output as Y signals. In a general image, the C signal component in the NTSC signal waits for a frequency component such as a region b in the figure centering on f _sc (color subcarrier), so that the YC separation is performed well. However, in the case of an image including a sharp horizontal edge (horizontal line edge), the signal component has a frequency component like the region b in FIG. For this reason, among the components indicated by d in the region, the hatched components leaking to the region A side are output as Y signals. This component causes dot disturbance as a cross-luminance component and causes deterioration in the image quality of the received image.

FIG. 4 is a diagram for explaining a situation of YC separation for a moving image portion (moving pixel) in the first illustrated circuit according to the embodiment of the present invention. The vertical axis, horizontal axis, and component area d in the figure are exactly the same as those in FIG. The shape and position of the boundary a of the frequency component region are exactly the same as those in FIG. In the circuit having the configuration shown in FIG.
Therefore, the frequency component of the region B on the hatched side of the boundary e in FIG. Therefore, even if the C signal has a component like the area d, it does not leak to the Y signal output, and no dot disturbance occurs. At this time, as apparent from a comparison between the region A shown in FIG. 3 and the region B shown in FIG. 4, the two-dimensional pass band of the Y signal output is reduced at the cost of breaking the dot disturbance, but it is minimized. Therefore, a decrease in the resolution of the output image can be suppressed to the minimum necessary.

Although one embodiment according to the present invention has been described in detail above, the present invention is not limited thereto, and it is obvious that various modifications and changes can be made within the scope described in the claims. In particular, the VHPF 9, the number of taps, and the cutoff frequency of the action filter can be used with values other than the values shown.

(Effect of the Invention) As described in detail above, the motion adaptive YC of the present invention is used.
According to the separation circuit, the horizontal edge portion of the color, which is a problem in the conventional circuit, moves by band-limiting the output signal of the moving image processing unit of the Y signal of the received composite color television signal to about 3 MHz or less. Occasionally occurring dot interference can be eliminated, and the image quality of the composite color television signal receiver can be improved. At this time, a decrease in resolution required for removing dot interference is minimized.

[Brief description of the drawings]

FIGS. 1 and 2 are block diagrams showing the configuration of a YC separation circuit according to an embodiment of the present invention and a conventional example, respectively. FIGS. 3 and 4 are diagrams showing moving image portions of the conventional example and the embodiment of the present invention, respectively. It is a figure showing a two-dimensional frequency spectrum showing a situation of YC separation. 1 ... Frame delay device 2,7,11,21 ... Subtractor 3,5,8 ... 1/2 coefficient device 4 ... Adder, 6 ... 1 line delay device 9 ... High relative to vertical spatial frequency Bandpass filter (VHP
F) 10: High-pass filter (HPF) 12: Low-pass filter (LPF) 13: Motion detector, 14, 15: Mixer

Claims (4)

(57) [Claims] 1. A motion-adaptive YC separation circuit suitable for YC separation of a received composite color television signal containing a moving image, the circuit comprising: means for creating a frame-to-frame sum signal of a received input signal; Means for generating an inter-frame difference signal of the signal, means for extracting high frequency components related to the vertical spatial frequency and horizontal spatial frequency of the input signal, a subtractor for subtracting the high frequency component from the input signal, and subtraction thereof A low-pass filter for band-limiting the output signal of the filter, and according to the level of the motion signal of the input signal separately obtained, between the inter-frame sum signal and the output signal of the low-pass filter, and A first mixer and a second mixer for adaptively selecting, weighting and adding between the inter-frame difference signal and the output signal of the circuit for extracting the high frequency component, and outputting A motion-adaptive type wherein the outputs of the first mixer and the second mixer are respectively a luminance signal output and a chromaticity signal output of the received color television signal. YC separation circuit. 2. The YC separation circuit according to claim 1, wherein said means for extracting a high-frequency component related to the vertical spatial frequency is a two-tap vertical spatial frequency high-pass filter. 3. When the composite color television signal is an NTSC standard color television signal, the means for extracting a high-frequency component related to the horizontal spatial frequency is a high-pass filter having a cut-off frequency of 2.1 MHz. The YC separation circuit according to claim 1 or 2. 4. A cut-off frequency of a low-pass filter for band-limiting an output signal of the subtractor when the composite color television signal is a color television signal of an NTSC standard system is 3 Hz. 3 Any of
YC separation circuit.