JPH01213092A - Chrominance signal removing circuit - Google Patents

Abstract

PURPOSE:To remove only a chrominance signal component without removing a luminance signal component by comparing the signal of 3.58MHz component from a band pass filter and the signal that said signal is 1H-delayed by a delay circuit. CONSTITUTION:An input terminal 5 is connected to a trap circuit 6 to remove 3.58MHz component, and on the other band, it is connected to the band pass filter 7 having a frequency characteristic reverse to that of the circuit 6. The output of the filter 7 is connected to a 1H delay line 8, and on the other hand, it is inputted to maximum value detection circuits 10, 12. The output of the delay line 8 is connected to the circuit 11, 12. The signal of a voltage whose AC component is 0 because of a capacitor 9 and whose DC component is equal to the outputs of the filter 7 and the delay line 8 is inputted to the circuits 10, 11. The outputs of the circuits 10, 11, 12 are inputted to a minimum value detection circuit 13. A logical operation circuit 14 constituted of the circuits 10-13 comes to be the circuit to detect the intermediate level of three signals of the output of the filter 7, the output of the delay line 8 and a DC bias whose AC component was removed by the capacitor 9.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention is capable of effectively removing color signal components from a composite video signal and extracting low wA signals in, for example, a color television receiver. This invention relates to a color signal removal circuit.

(Prior art) In the NTSC system of color television, R (red), G
(1) A primary color signal of B (blue) is transmitted by a luminance signal representing the brightness of the screen and a color signal having information on hue and saturation. In order to prevent mutual interference between the color subcarrier on which the color signal is carried, the video carrier wave, and the audio subcarrier wave, a luminance signal (Y signal) of 0 to 4.2 MHz and a high luminance signal are added to the video signal portion. A color signal (C signal) with 3.579545Ml-1z as a subcarrier is inserted in the negative portion.

Note that the audio subcarrier is 4.5M1-lz.

Therefore, in order to reproduce broadcast signals on a color television receiver, it is necessary to separate the luminance signal and the color signal. The following method is used to separate the luminance signal and color signal.

The first method is to use a color signal trap.

That is, this method involves passing the composite video signal through a 3.58MH7 trap, absorbing the color signal, and extracting only the luminance signal.

However, this trap-based method has the drawback that the high frequency portion of the luminance signal is also removed at the same time as the color signal.

The second method is a comb filter method. This method utilizes the fact that in the NTSC system, the phase of the color subcarrier is inverted (inverse phase) every horizontal period (IH). To briefly explain the principle using FIG. 4, by adding the reference composite video signal and the IHN-extended composite video signal, the reference color subcarrier shown in FIG. The color subcarrier after one day delay shown in FIG. 4(b) is canceled out as shown in FIG. 4(c), and only the luminance signal is extracted.

FIG. 5 shows the structure of the comb filter.

The composite video signal inputted from the input terminal 1 is delayed by IH in the delay circuit 2 and added to the addition circuit 3.

The adder circuit 3 adds the pre-delayed signal and the delayed signal and outputs the result to the output terminal 4. The waveforms of each part of the circuit are as shown in FIG. In Figure 6, (a)
is the reference composite video signal input to input terminal 1, and (b
) is a composite video signal outputted from the delay circuit 2 and delayed by 1 to 1. Also, (C) is (a) and (b)
3 shows a luminance signal obtained by adding the signals shown in FIG.

However, in this comb filter method, the seventh
Problems as shown in the figure may occur. Figure ff17 shows the waveform when a composite video signal with no correlation before and after IH is passed through a comb filter, (a) i, l
A reference composite video signal, (b) is a composite video signal after 1)'' delay, and (C) shows a luminance signal obtained by adding (a) and (b).

As shown in FIG. 7, color signal components remain in the luminance signal for uncorrelated portions around 11'', resulting in problems such as a 1-1 drop at the edges of the reproduced image.

(Problems to be Solved by the Invention) As mentioned above, conventionally, when a trap is used to separate the luminance signal and the chrominance signal, the problem is that the high frequency part of the luminance signal is also removed at the same time as the chrominance signal is removed. was there. Further, when a comb filter is used, there is a problem in that color signal components remain in the luminance signal in areas where there is no correlation around one day, resulting in deterioration of image edge areas.

SUMMARY OF THE INVENTION The present invention is intended to eliminate the above-mentioned problems, and it is an object of the present invention to provide a color signal removal circuit that can effectively remove color signal components from a composite video signal.

[Structure of the Invention] (Means for Solving Problem 1) The color signal removal circuit of the present invention inputs an NTSC composite video signal containing a color signal component of 3.58M1-(z, and removes a 3.58MHz a 1 to Clapp path for removing component signals; and a bandpass filter having frequency characteristics opposite to the 1 to Clapp path, inputting the composite video signal and passing the 3°58 M l-1y component signal. and a delay circuit that delays the output of this band-pass filter by 11'', and a platform that receives two signals, the output of the band-pass filter and the output of the delay circuit, and that the relationship between these two signals is in phase. outputs a signal that is in phase with the two signals, and if the relationship between the two signals is in reverse phase or if one of the two signals has a 3.58 MHz color signal component,
The device includes a logic circuit that outputs a signal from which the color signal component of 3.58M1-IZ has been removed, and an adder circuit that adds the output of this logic circuit and the output of the trap circuit.

(Function) In the present invention, 3.58M from the bandpass filter
1-]z component signal and this signal in a delay circuit for 1Hu
If the two signals are in phase,
The 3.58'MHz component signal is regarded as a measurement signal, and the logic circuit outputs an in-phase signal, which is added to the signal obtained by removing the 3°58M l-1z component from the composite video signal in the trap circuit. As a result, the 3.58 MHz luminance signal component is transmitted without being removed. Further, when the above two signals have opposite phases, the 3.58 MHz component signal is a color signal, and the logic circuit outputs an output with an AC component of O, that is, a signal from which the color signal component has been removed.

Also, only one of the above two signals has 3.5
If there is an 8 MHz component, the signals are uncorrelated before and after 1H, and the logic circuit outputs an output with an AC component of O, that is, a signal from which the color signal component has been removed. Therefore, in the case of opposite phases or when there is a 3.58 MHz component in only one side, a signal with the 3.58 MHz component removed by the trap circuit will be output. As a result of the above, it becomes possible to effectively remove only the color signal component without removing the luminance signal component.

(Example) The present invention will be described below based on the example shown in the drawings.

FIG. 1 is a block diagram showing an embodiment of the color signal removal circuit of the present invention.

In this figure, input terminal 5 is a terminal into which an NTSC video signal is input, and this input terminal 5 has a 3.58 MHz
While connected to a trap circuit 6 for removing the component, it has a frequency characteristic opposite to that of this trap circuit 6 (i.e., 3.5
It is connected to a band pass filter (BPF) 7 which has a characteristic of passing only the 8 MHz component. Bandpass filter 7
The output terminal of is connected to the 1 to 1 delay line 8 and is input to the maximum value detection circuit 10 and the maximum value detection circuit 12. The output end of the 1H delay line 8 is connected to a maximum value detection circuit 11 and a maximum value detection circuit 12. For the maximum value detection circuits 10 and 11, a capacitor 9 is used to generate a signal whose AC component is O■ and whose DC component (DC bias) is a voltage equal to the output of the bandpass filter 7 and the output of the delay line 8. Please enter it as follows. The respective outputs of the maximum value detection circuits 10, 11 and 12 are input to a minimum value detection circuit 13 which compares the three signals and selects and outputs the signal with the lowest level. In addition, the circuit 14 composed of the maximum value detection circuit 10, 11, 12 and the minimum value circuit 13 is connected to the output of the bandpass filter 7, 1H
It is a logic circuit that detects the intermediate level of three signals: the output of the delay line 8 and the DC bias from which AC components have been removed by the capacitor 9. The output of the minimum value detection circuit 13 is added to the output of the trap circuit 6 in an adder circuit 15. The output of the adder circuit 15 is output to an output terminal 16.

Next, the operation of the above circuit will be explained.

FIG. 2 is an explanatory diagram of the operation when a composite video signal containing a color signal component is input from the input terminal 5.

2(a) to 2(j) correspond to the signals of each circuit section aj of FIG. 1. In FIG. 2, (a) shows a composite video signal that includes a color signal component input to the input terminal 5 and has no correlation before or after one day.
．． The 58 MHz component is removed, resulting in a signal as shown in Figure (b). On the other hand, the video signal shown in -0- (a) passes through the band pass filter 7 and becomes a signal of only 3.58 MH2 components as shown in (C). The signal shown in (C) is the 1H delay line 8
The signal is delayed by one horizontal period (one day), resulting in a signal as shown in (d). (e) is a DC bias obtained by removing the AC component from the signal shown in (C) or (d) by the capacitor 9.

The calculation result (maximum value detection result) of the maximum value detection circuit 10 for the signal shown in (C) and the DC bias shown in (e) is (
The result is a signal as shown in f). In addition, the maximum value detection circuit 1 for the DC bias shown in (e) and the signal shown in (d)
The operation result of 1 becomes a signal as shown in (q). Also,
The calculation result of the maximum value detection circuit 10 of the signal shown in (C) and the signal shown in (d) is a signal shown in (h).

The signals shown in (f), (Q), and (h) are the minimum value circuit
3, and the calculation result (minimum value detection result) is (1
) as shown in (f) and (q).

It becomes equal to the DC level of (h). Then, the signal shown in (i) and the signal shown in (b) are added in an adder circuit -10=15, resulting in a signal from which the color signal component has been removed, as shown in (j) of the same figure. Become.

FIG. 3 is an explanatory diagram of the operation when a luminance signal containing a 3.58 MHz luminance component is input from the input terminal 5. Third
In the figure, (a) to (j) represent the circuit parts a to j in Figure 1.
corresponds to the signal in

In this figure, (a) represents 3 input from input terminal 5.
, 58 MHz, and this signal (a) becomes a signal from which the 3.58 MHz2 component is removed by the wrap circuits 1 to 6 as shown in (b).

This 3.58 MHz luminance signal component is a signal that is in phase around the first eye.

On the other hand, the input signal (a>) is supplied to the band pass filter 7, and only the signal of the 3.58 MHz component is extracted as shown in (C).The signal (C) is
The signal is delayed by H, resulting in a signal as shown in (d). (e) is the DC bias from which the AC component is removed by the condenser 9 from the signal (C) or (d). The output of the maximum value detection circuit 11 of the DC bias (e) and the signal (d) becomes a signal as shown in (()). Also, the signal (C) and the signal ( The output point of the maximum value detection circuit 12 with d) is not shown in (h), and the signal J: is the same.The above signals (f>, (a), (h) are input to the minimum value detection circuit 13, and the output of the maximum value detection circuit 12 is The minimum value detection output is (i
), it becomes a signal similar to signal (h). Then, this signal (i>) and the signal (j) are added in an adder circuit 15, resulting in a signal (, j) having a luminance component of 3°58 M l - I Z.

This signal (j) is similar to the input signal (a) and is 3.5
8M1-(z signal component is transmitted without loss.

[Effects of the Invention] As described above, according to the present invention, 11
"It is now possible to effectively remove color signal components from video signals even when there is no correlation between the front and back, and it is also possible to remove color signals without removing the 3.58 MHz components included in the luminance signal. Become.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a color signal removal circuit showing an embodiment of the present invention, Figures 2 and 3 are waveform diagrams explaining the circuit operation of Figure 1, and Figure 4 is color signal removal using a comb filter. 5 is a block diagram illustrating the structure of the comb filter, and FIGS. 6 and 7 are waveform diagrams illustrating the circuit operation and problems of FIG. 5. 5... Input terminal, 6... Trap circuit, 7... Band pass filter, 8... 1 delay line, 9... Capacitor, 10.11.12... Maximum value detection circuit , 13... Minimum value detection circuit, 14... Logic circuit, 15... Addition circuit, 16... Output terminal.

Claims (1)

[Scope of Claims] A trap circuit that inputs an NTSC composite video signal containing a color subcarrier and removes a signal in the frequency band of the color subcarrier, the trap circuit having a frequency characteristic opposite to that of the trap circuit, and having a frequency characteristic opposite to that of the trap circuit; a bandpass filter that receives a composite video signal and passes a signal in the frequency band of the color subcarrier; a delay circuit that delays the output of the bandpass filter by one horizontal period; and a delay circuit that delays the output of the bandpass filter and the delay circuit. When the relationship between these two signals is in the same phase, it outputs a signal that is in phase with the two signals, and when the relationship between the two signals is in reverse phase, or the two signals If there is a frequency component of the color subcarrier in one of the two, a logic circuit outputs a signal from which the frequency component of the color subcarrier is removed, and the output of this logic circuit and the output of the trap circuit are added. A color signal removal circuit characterized by comprising an addition circuit.