JPH01161987A - Luminance/chrominance separating circuit - Google Patents

Abstract

PURPOSE:To attain complete luminance/chrominance separation with small circuit scale by applying frequency shift to a chrominance signal of a composite television signal to a low frequency. CONSTITUTION:The composite television signal fed to an input terminal 20 is subjected to frequency separation into a high frequency component including a chrominance signal (C) and a low frequency component not including the signal, subsampling, 1 frame delay and selection processing are applied to the high frequency component and the C signal is frequency-shifted into a low frequency to apply luminance (Y)/C chrominance separation. Thus, the signal subsampled is fed to a frame memory 25. Thus, the memory capacity of the frame memory 25 is halved in comparison with a conventional circuit and the C signal is subjected to synchronization detection by the frequency shift of the C signal as a result, then no synchronizing detection circuit is required.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention provides a luminance signal and a chrominance signal for separating a composite television signal in which a luminance signal and a chrominance signal are frequency-multiplexed into the luminance signal and chrominance signal. /Relating to chromaticity separation circuit.

(Prior Art) In the current television broadcasting system, a composite television in which a luminance signal (hereinafter referred to as Y signal) and a chromaticity signal (hereinafter referred to as C signal) are frequency multiplexed is used as a television signal. John signal is used. For this reason, the television receiver requires a luminance and seven chromaticity separation circuit for separating the composite television signal into a Y signal and a C signal. Hereinafter, "luminance 7 chromaticities" will be referred to as rY/CJ.

A conventional Y/C separation circuit uses a low-pass filter (hereinafter referred to as L
PF) and a bandpass filter (hereinafter referred to as BPF).

However, in the case of this configuration, since complete Y/C separation cannot be performed, there is a problem that cross color and dot interference occur.

Therefore, recently, a Y/C separation circuit using a comb filter with good Y/C separation performance is often used. However, even if this comb filter is used, there are problems such as a decrease in resolution in diagonal directions.

In order to improve this kind of problem, in recent years Y
/C isolation circuits have been developed.

That is, this Y/C separation circuit performs Y/C separation on still images by calculation between frames, and performs Y/C separation on moving images by calculation between lines.

If a Y/C separation circuit adapted to such image movement is used, when the image is a still image, calculations are not performed in the horizontal and vertical directions of the image, so the Y/C separation circuit can be used without image deterioration. C separation can be carried out.

FIG. 4 shows the configuration of the conventional motion adaptive Y/C separation circuit described above. Note that FIG. 4 particularly shows a portion corresponding to a still image, that is, a portion where Y/C separation is performed between frames.

In FIG.
4. The composite television signal supplied to this frame memory 14 is delayed by one frame, and then
It is supplied to an adder circuit 13 and subtracted from the composite television signal supplied to the input terminal 11. The inter-frame difference signal obtained by this subtraction process does not include the Y signal, but only the C signal. This is because the frequency tsc of the color subcarrier is set to a value where fH is the horizontal synchronization frequency, and the phase of the C signal is inverted every frame.

The addition output of the addition circuit 13 has unnecessary components removed by the BPF 15, and then synchronously detected by the detection circuit 16.

This synchronously detected output signal is supplied to the output terminal 17. The output of the B P F 15 mentioned above is supplied to the adder circuit 12 and subtracted from the composite television signal supplied to the input terminal 11.

As a result, a Y signal is obtained from the adder circuit 12, and this Y signal is supplied to the output terminal 18.

The Y/C separation circuit for still images described above is a complete Y/C separation circuit.
Although C separation can be performed, it requires a large-capacity frame memory, which poses a problem of increasing the circuit scale. For example, if an NTSC television signal is
If we consider the case of sampling with fsc and quantizing it to 8 bits, the capacity of the frame memory 4 will be extremely large, 525 x 910 x 8-4 Mbits.

(Problems to be Solved by the Invention) As mentioned above, in the conventional Y/C separation circuit, if we focus on the part that performs Y/C separation of still images, this part cannot be completely separated. Although Y/C separation can be achieved, a large-capacity frame memory is required, resulting in an increase in circuit scale.

Therefore, the present invention aims to produce a still image Y/R with a small circuit scale.
It is an object of the present invention to provide a Y/C separation circuit that can completely perform C separation.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention divides a composite television signal into a first component containing a C signal and a second component not containing a C signal. After frequency separation and subsampling of the first component in synchronization with the color subcarrier, the signal is delayed by one frame,
The delayed output and the sub-sample output are alternately selected in synchronization with the color subcarrier, and after the selected output is frequency-separated into a Y signal and a C signal, the Y signal is combined with the second component. It is something.

(Function) Since the phase of the C signal is inverted every frame, the first component is subsampled in synchronization with the color subcarrier,
By alternately selecting this subsampling output and its one-frame-delayed output in synchronization with the color subcarrier, the C signal can be shifted out of the band of the first component.

Therefore, by frequency-separating the selection output, the first component C signal and Y signal can be separated. Then, by combining this Y signal and the second component, a separated output of the entire Y signal can be obtained.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention.

In FIG. 1, a composite television signal is input to an input terminal 20. This composite television signal is transmitted to the PLL circuit 21. Bypass filter (hereinafter referred to as HPF) 22
and is supplied to the LPF 23. The PLL circuit 21 outputs pulses that are phase-locked to the color subcarrier of the composite television signal.

The HPF 22 extracts high frequency components including the C signal from the input signal. On the other hand, the LPF 23 extracts a low frequency signal that does not include the C signal from the input signal.

The high-frequency components extracted by the HPF 22 are sent to the PLL circuit 2 described above.
Sub-sampling is performed by a switch circuit 24 that turns on and off according to a switching pulse 5WPI supplied from 1. This subsampling output is supplied to the frame memory 25 and also to one input terminal of the switch circuit 26. The subsample output supplied to the frame memory 25 is delayed by one frame, and then
The signal is supplied to the other input terminal of the switch circuit 26.

This switch circuit 26 connects both human power signals to the PLL circuit 21.
The color subcarriers are alternately selected according to the switching pulses 5WP2 synchronized with the color subcarrier outputted from the color subcarriers.

This selection output is supplied to LPF27 and BPF28. The LPF 27 extracts the C signal from the input signal. This C
The signal is supplied to output terminal 29.

On the other hand, the BPF 28 extracts the Y signal from the input signal.

This Y signal is supplied to the adder circuit 30, and the LPF 27
It is added to the low frequency component extracted by . This addition output is supplied to the output terminal 31 as a separated output of the Y signal.

The operation of the above configuration will be explained with reference to FIGS. 2 and 3.

FIG. 2 is a timing chart showing the operation of FIG. 1.

FIG. 2(a) shows a switching pulse 5WPI that controls the operation of the switch circuit 24. FIG. The switch circuit 24 is turned on while this signal is at a high level. FIG. 2B shows the high frequency component of the composite television signal output from the HPF 22. This high-frequency component has a form in which the I signal and the Q signal are alternately frequency-multiplexed onto the Y signal. This means that the composite television signal supplied to the input terminal 21 is
This is because it has a frequency of fs c (fs c is the carrier color signal frequency) and is sampled by a clock locked to the IQ axis. By subsampling this high frequency component by the switch circuit 24 according to the switching pulse 5WPI as described above,
A signal as shown in FIG. 2(c) is obtained from the switch circuit 24.

FIG. 4(d) shows a switching pulse 5WP2 that controls the operation of the switch circuit 26. This switching pulse 5WP2 is similar to the previous switching pulse 5W.
It has the opposite phase to PI.

The switch circuit 26 receives this switching pulse 5WP2.
When is at a low level, the subsampling output from the switch circuit 24 is selected, and when it is at a high level,
Select the delayed output of the frame memory 25. This selection output is shown in FIG. 2(g).

By the way, the switching pulse sw shown in FIG. 2(a)
The phase of pt is opposite between the current frame and the previous frame. This is the color subcarrier frequency f
Since SC has the following relationship, fH-525fp However, fF: frame frequency Also, since the color subcarrier frequency fsc has the above relationship, the phases of the I signal and Q signal one frame before are also as shown in Fig. 2 (e) As shown in FIG. 3, it is reversed from the current one shown in FIG. Therefore, the subsampling output of the switch circuit 24 one frame before is as shown in FIG. 2(f). This signal is selected during the period when the switching pulse 5WP2 is at high level, and the signal shown in FIG. 2(c) is selected during the period when this pulse is at low level. g).

Now, consider the Y signal and C signal included in the selection output of the switch circuit 26.

If the Y signal is a still image, the waveforms of the current frame and the previous frame are exactly the same, so the Y signals Yl, Y2,
3... exists as it is in the high range.

On the other hand, the phase of the C signal is reversed between the current frame and the previous frame, as is clear from the comparison of FIGS. 2(b) and 2(e).

Therefore, the C signal output from the switch circuit 26 has no phase inversion in the color subcarrier period, as shown in FIG. 2(g). This means that the C signal has been synchronously detected as a result, and it means that the C signal has been returned to the baseband band.

In this way, the Y signal included in the switch circuit 26 is
It has exactly the same band as the Y signal included in the output of F22,
The C signal is frequency shifted to lower frequencies. Therefore, by supplying the output of the switch circuit 26 to the LPF 27, the C signal can be extracted. Also, convert this output to B
By supplying the signal to the PF 28, the high frequency component YH of the Y signal extracted by the HPF 22 can be extracted.

The high frequency component Y of this Y signal is added to the low frequency component Y2 of the Y signal included in the extracted output by the LPF 23. This makes it possible to obtain separated outputs of the entire Y signal band.

FIG. 3 is a frequency spectrum diagram showing the operation of FIG. 1.

FIG. 3(a) shows the frequency spectrum of the composite television signal supplied to the input terminal 21. FIG. This composite television signal is frequency-separated by the HPF 22 and LPF 2B along the dotted line shown in FIG. 3(a). Then, the components higher than the dotted line, that is, the high frequency components of the composite television signal including the high frequency components YH of the Y signal and the C signal, are subjected to subsampling processing and selection operation.

FIG. 3(b) shows the selected output of the switch circuit 26. As shown in the figure, in this selection output, the frequency band of the high frequency component YH of the Y signal does not change, but the frequency band of the C signal is shifted to the baseband.

As described above, this embodiment frequency-separates a composite television signal into high-frequency components that include the C signal and low-frequency components that do not include the C signal, and performs subsampling, one-frame delay, and selection processing on the high-frequency components. The Y/C separation is carried out by frequency-shifting the C signal to a lower frequency range.

According to such a configuration, since the subsampled signal is supplied to the frame memory 25, the memory capacity IQ of the frame memory 25 can be halved compared to the conventional one. This allows the circuit scale to be significantly reduced compared to conventional configurations.

Further, according to this embodiment, the frequency shift of the C signal results in synchronous detection of the C signal, so there is an advantage that a synchronous detection circuit is not required.

Note that the present invention is of course applicable to Y/C separation of composite television signals of systems other than the NTSC system. That is, the present invention can be applied to general Y/C separation of composite television signals in which the C signal is frequency multiplexed into a part of the frequency band of the Y signal and the C signal is inverted at the frame period.

It goes without saying that various other modifications can be made without departing from the spirit of the invention.

[Effects of the Invention] As described above, according to the present invention, complete Y/C separation in a still image can be performed with a small circuit scale.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of an embodiment of the present invention, and FIG.
The figure is a timing chart to explain the operation of Figure 1, Figure 3 is a frequency spectrum diagram to explain the operation of Figure 1, and Figure 4 is a circuit showing the configuration of a conventional Y/C separation circuit. be. 20...Input terminal, 21...PLL circuit, 22...
・HPF, 23.27...LPF, 24.26...
Switch circuit 25...frame memory, 28...B
P.F. 29.31...Output terminal, 30...Addition circuit.

Claims (1)

[Scope of Claims] An input terminal to which a composite television signal in which a luminance signal and a chromaticity signal are frequency-multiplexed is supplied, and a first input terminal including the chromaticity signal to which the composite television signal supplied to the input terminal is supplied.
a first frequency separation means for frequency-separating the frequency into a component of the chromaticity signal and a second component that does not include the chromaticity signal; A subsampling means for subsampling in synchronization with the color subcarrier, and a subsampling output of this subsampling means
a frame delay means for delaying by a frame; a selection means for alternately selecting the delayed output of the frame delay means and the subsampling output of the subsampling means in synchronization with the color subcarrier; a second frequency separation means for separating the frequencies into a chromaticity signal and a luminance signal; a first output terminal for outputting the chromaticity signal separated by the second frequency separation means; and from the first frequency separation means. The present invention further comprises a combining means for combining the obtained second component and the luminance signal obtained from the second frequency separation means, and a second output terminal for outputting the luminance signal obtained by the combining means. Features a luminance/chromaticity separation circuit.