JPH0378392A - Chrominance signal processing system - Google Patents

Abstract

PURPOSE:To prevent the loss of hue information by substituting the DC signal of a prescribed level for the input chrominance signal of a carrier wave band in a specified period. CONSTITUTION:The specified period is determined, and by substituting the DC level signal for the input signal in this period by a superposition component removal circuit 30, an achromatic color level is prescribed for the B-Y signal and the R-Y signal of a base band demodulated by demodulators 5, 6. Then, the amplitude relation of each part of the B-Y signal and the R-Y signal to this achromatic color level is never changed according to the size of the superposition component or signal processing, and in addition, these achromatic color levels are clamped by clamp circuits 17, 18 so as to be a prescribed reference level. Accordingly, the B-Y signal and the R-Y signal outputted from the clamp circuits 17, 18 are not impaired at the relation of the level of each part to the achromatic color level. Thus, in a carrier chromatic signal obtained at an output terminal 28, the hue information is maintained correctly, and the color reducibility of a monitor picture is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a color signal processing system that demodulates a carrier color signal into a baseband color signal for processing.

[Prior Art] In order to ensure the color reproducibility of color images, a clamp circuit is used to set the level of the color signal to a certain value and to reproduce the DC component (for example, in Japanese Patent Application Laid-Open No. 1983-1999). 5
1372).

By the way, when a carrier color signal in a carrier wave band obtained by quadrature two-phase modulation of two color difference signals is processed to improve image quality after passing through a transmission system such as a recording/reproducing system, this carrier color signal is It demodulates into two color difference signals in the baseband band, performs desired signal processing on these color difference signals using a comb filter, noise reducer, etc., then clamps each to fix the level, and performs quadrature two-phase modulation. A method is known for generating a carrier color signal.

Hereinafter, such a color signal processing system when used in a VTR will be explained with reference to FIGS. 11 to 13. However, in Fig. 11, 1 and 2 are input terminals, 3 and 4 are amplifiers,
5 to 8 are demodulators, 9.10 is a switch, 11.12 is L
PF (low pass filter), 13.14 is a comb filter, 15.16 is a color signal processing circuit, 17 to 20 are clamp circuits, 21 to 24 are modulators, 25.26 is an adder,
27 is an LPF, and 28 and 29 are output terminals.

Moreover, FIG. 12 is a waveform diagram showing signals of each part in FIG. 11, and signals corresponding to those in FIG. 11 are given the same symbols.

In FIG. 11, during recording, a carrier color signal in a carrier wave band is input from input terminal 2, and after being amplified by amplifier 4,
The signal is supplied to demodulators 7 and 8. The demodulator 7 has the same frequency f as the color subcarrier of the input carrier color signal. A color subcarrier of Oo whose phase coincides with the BY axis with respect to the input carrier color signal is supplied to the demodulator 8, and the frequency is also f. and the phase is R
- A 90" color subcarrier aligned with the Y axis is supplied. As a result, the demodulator 7 demodulates the baseband B-Y signal from the carrier color signal, and the demodulator 8 also demodulates the R-Y signal. demodulated.

Switches 9 and 10 are closed to the R contact side during recording, switch 9 selects the BY signal output from demodulator 7, and switch 10 selects the RY signal output from demodulator 8. do. The B-Y signal selected by switch 9 is
Out-of-band components such as high frequency components and components with no line correlation are removed by the LPFII or comb filter 13, and after being processed by a noise reducer or the like in the one-color signal processing circuit 15, the signal is supplied to a clamp circuit 17.19. switch 1
The RY signal selected as 0 is also subjected to similar processing by the LPF 12, the L-type filter 14, and the color signal processing circuit 16, and then supplied to the clamp circuit 18.20.

In the clamp circuits 19 and 20, the BY signal and the RY signal are each clamped at the DC potential of the blanking period. The BY signal output from the clamp circuit 19 is supplied to a modulator 23, and the RY signal output from the clamp circuit 20 is supplied to a modulator 24. The modulator 23 is supplied with a color subcarrier at a frequency f LIIC that is sufficiently lower than the color subcarrier supplied to the demodulator 7.
supplied to As a result, the modulated B-Y signal is output from the modulator 23, and the modulated R-Y signal is output from the modulator 20, and these are added by the adder 26 to obtain the color subcarrier frequency fC, A carrier color signal quadrature two-phase modulated at aC is obtained. This conveyed color signal is sent to an output terminal 29 for recording after unnecessary high-frequency components are removed by the LPF 27.
is output from.

The carrier color signal outputted from the output terminal 29 is such that the input carrier color signal at the input terminal 2 has a color subcarrier frequency f3c to f's.

This is equivalent to a low-pass converted color signal, and hereinafter this will be referred to as a low-pass converted color signal.

Also, the color subcarrier frequency is f. The carrier color signal will be simply referred to as a carrier color signal.

In the clamp circuits 17 and 18, the BY signal and the RY signal are each clamped at the DC potential during the blanking period. The BY signal output from the clamp circuit 17 is supplied to the modulator 21, and the RY signal output from the clamp circuit 18 is supplied to the modulator 22. The modulator 21 has the same frequency f as the color subcarrier supplied to the demodulator 7.8.
,. A color subcarrier with the same frequency and a phase difference of 90° is supplied to the modulator 22.

As a result, the modulated B-Y signal is output from the modulator 21, and the modulated R-Y signal is output from the modulator 22, and these are added by the adder 25 to obtain the color subcarrier frequency f, . A carrier color signal subjected to quadrature two-phase modulation is obtained. This conveyance color signal is output from the output terminal 28 for monitoring during recording.

During reproduction, switches 9 and 10 are switched to the P side. Hereinafter, referring to FIG. 12, the reproduced low-pass conversion carrier color signal a is inputted from input terminal 1, amplified by amplifier 3, and then supplied to demodulators 5 and 6. The demodulator 5 receives the same frequency fLg as the color subcarrier of the input low-pass converted carrier color signal a.

A 0° color subcarrier whose phase coincides with the B-Y axis with respect to the input low-pass conversion carrier color signal a is supplied to the demodulator 6, and the demodulator 6 also has a frequency of f, ac and a phase with the R-Y axis. This provides a 90'' color subcarrier corresponding to .

The demodulator 5 demodulates the baseband B-Y signal from the low-pass converted carrier color signal a, and the demodulator 6 demodulates the same <RY signal.

The B-Y signal output from the demodulator 5 passes through the switch 9 and is processed as described above by the LPFI 1, the comb filter 13, and the color signal processing circuit 15, and then the B-Y signal is
The clamp pulse C supplied at the front porch timing of the blanking period of the signal is clamped by the clamp circuit 17 and supplied to the modulator 21 . Similarly, the R-Y signal output from the demodulator 6 passes through the switch 10 and is sent to the LPFI 2. <t, after being processed by the shape filter 14 and the color signal processing circuit 16, the clamp circuit 18
The signal is clamped at and supplied to the modulator 22.

The modulated B-Y signal and R-Y signal are added by an adder 25, and a carrier color signal d for reproduction monitoring is obtained from an output terminal 28.

Note that although a low-frequency conversion carrier color signal is obtained at the output terminal 29, it is not recorded because it is in the reproduction mode.

As described above, when color signals are processed in the baseband band, even if there are variations in delay time in the delay lines used in comb filters and noise reducers in color signal processing circuits, the characteristics of the comb filter can be maintained. It is possible to obtain the image with high precision, and the characteristics of the noise reducer can also be obtained with high precision, resulting in an improvement in image quality.

FIG. 13 is a circuit diagram showing an example of demodulators 5 to 8 in FIG. 11.

In the figure, the input terminal 54 is connected to the amplifier 3 (see FIG. 11).
A reproduced low-pass conversion carrier color signal a is inputted from the input terminal 1 and supplied to the base of a transistor 60 via a resistor 55. Also,
The DC level of the low frequency conversion carrier color signal a is detected by the resistor 56 and the capacitor 58 and is supplied to the base of the transistor 61. The transistors 60 and 61 form a differential pair because their emitters are connected to a common constant current source, and the resistors 55 and 56 have the same resistance value.

The collector of the transistor 6o is connected to the emitters of the transistors 62 and 63 forming a differential pair, and the collector of the transistor 61
The collector of is connected to the emitters of transistors 64 and 65 forming a differential pair.

Further, a power supply voltage is applied to the collectors of both transistors 62 and 64 via a resistor 66, and the transistor 63
．． A power supply voltage is also applied to the collector of 65 via a resistor 67 which also serves as a load resistance. The collectors of transistors 63 and 65 are connected to output terminal 68. Note that the resistance values of resistors 66 and 67 are equal. moreover,
From the input terminal 53 to the base of the transistor 63.64,
A color subcarrier S0 having a frequency of fL4C phase-locked to one color subcarrier of the modulated color difference signal in the low-pass conversion carrier color signal a is supplied, and this color subcarrier S0 is supplied from the input terminal 52 to the base of the transistor 62.65. A color subcarrier Sc having the same frequency and opposite phase as the carrier wave S0 is supplied.

Therefore, the DC level of the low frequency conversion carrier color signal a is applied to the base of the transistor 61.

With this DC level as a reference level, during a period in which the low frequency conversion carrier color signal a has positive polarity with respect to this reference level, a current of a magnitude corresponding to the level of this period flows through the transistor 60, and with respect to this reference level. During the period of negative polarity, a current of a magnitude corresponding to the level of this period flows through the transistor 61.

On the other hand, if the color subcarriers Sc and Sc are the color subcarriers for demodulation of the R-Y signal, then the modulated R
The transistors 63 and 64 are turned on by the color subcarrier Sc during which the polarity is positive with respect to the reference level of the -Y signal, and a current of a magnitude corresponding to the level of the positive polarity portion of the modulated R-Y signal is generated. Load resistor 67, transistor 63.
60 and outputs this modulated R-
The positive polarity portion of the Y signal will be obtained. Also.

During the period in which the modulated R-Y signal has negative polarity with respect to the reference level, the color subcarrier turns on the transistors 62 and 65, and a current corresponding to the level of this period flows through the load resistor 67 and It flows through transistors 65 and 61, and this negative polarity portion is obtained at the output terminal 68 with the same polarity as the positive polarity portion.

In this way, the RY signal modulated from the low-pass converted carrier color signal a is obtained at the output terminal 68 in a full-wave rectified form using its DC level as a reference level.

This R-Y signal is applied to the LPF 1 shown in FIG. 11, for example.
2 to remove the color subcarrier component, a baseband RY signal is obtained.

Similarly, by supplying the input terminals 53 and 52 with a color subcarrier synchronized with the color and subcarrier of the modulated B-Y signal in the low-frequency converted carrier signal a, the B-
A Y signal is obtained, and the demodulators 7 and 8 in FIG. 11 only need to supply the carrier color signal to the input terminal 54 and the color subcarrier of frequency f, 6 to the input terminals 53 and 52. . The circuit shown in FIG. 13 also supplies a baseband color difference signal to the input terminal 54, and input terminals 53 and 52
ni f,. Alternatively, by supplying a color subcarrier with a frequency of fL3°, it can be used as the modulators 21 to 24 in FIG. 11.

[Problems to be Solved by the Invention] By the way, the reproduced low-frequency conversion carrier color signal contains unnecessary components such as crosstalk and carrier leakage from adjacent tracks on the magnetic tape, and as shown in FIG. , as shown in FIG. 12, the amplifier 3 outputs a low-band carrier color signal a containing the unnecessary component N, and the demodulator 5 demodulates it to generate a baseband color difference signal. , the level of the blanking period must be an achromatic color level that originally determines the reference level of the color signal period, but due to the unnecessary component N, it becomes different from this achromatic color level.

After processing this color difference signal using a comb filter 13 or the like as shown in FIG.
．． When the blanking period is clamped by the clamp pulse C at 18, the blanking period at a level different from the achromatic color level is clamped to a predetermined reference level.
The original achromatic color level will be different from this reference level, that is, a level different from the reference level in the color signal period of the color difference signal will be set in the blanking period.

For this purpose, when the carrier color signal d is created by two-phase modulating the color difference signal after clamping, the level of the carrier color signal d during the blanking period is the reference level in the color signal period, as shown in FIG. (broken line), the amplitude level of the original carrier color signal cannot be reproduced, and color information, especially hue information, is lost.

Furthermore, when demodulating a carrier color signal, a subcarrier for demodulation that is phase-synchronized with the color burst signal included in the carrier color signal is formed.

In the case of the carrier color signal of the NTSC system, there is no problem because the phase of the color burst signal is fixed, but in the case of the carrier color signal of the PAL system, the phase of the color burst signal changes for each IH, For this purpose, the phase of the subcarrier for demodulation is fixed every 2H using the waveform obtained by detecting the color burst signal. Therefore, a signal component of 1/2 fK is generated in this subcarrier, and the signal demodulated from the carrier color signal is influenced by this signal component.

To prevent this, in a 5-VH3 VTR that records and plays back PAL color video signals, a pilot burst signal with a constant phase component is always added in addition to the color burst signal during recording. A technique has been proposed in which a color subcarrier for demodulation is obtained from this pilot burst signal during reproduction.

However, since this pilot burst signal is added separately from the color burst signal within the blanking period of the carrier color signal, the reproduced low-pass converted carrier color signal a to which this pilot signal is added will be explained in FIG. As described above, when demodulating and processing the baseband color difference signal, clamping it in the clamp circuits 17 and 18, and encoding it into the carrier color signal d, the portion excluding the color burst signal and pilot burst signal during the blanking period is becomes very narrow.

The clamp period by the clamp circuits 17 and 18 becomes very narrow. For this reason, the color difference signals are not clamped sufficiently, resulting in loss of hue information.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color signal processing system that eliminates such problems and prevents loss of color information, particularly hue information, when processing carrier color signals in the baseband band. It is in.

A further object of the present invention is to provide a color signal processing system that can secure a sufficient ramp period for clamping after processing in the baseband band.

[Means for Solving the Problems] In order to achieve the above object, the present invention sets a specific period for an input carrier band color signal before demodulating it into a baseband color signal. and replace it with a DC signal of a predetermined level.

The present invention further provides for the specific period to be made up of a part on the leading end side of the blanking period in the input color signal of the carrier band and a part on the end side of the color signal period immediately before the blanking period. .

[Operation] By determining a specific period and replacing the DC signal with a DC signal at a predetermined level during this period, the level during this specific period can be kept at a constant achromatic color level even if there is crosstalk or carrier leak. For this reason, this specific period in the baseband color signal obtained by demodulating the carrier band input color signal also has a constant achromatic color level, and the baseband color signal after processing clamps the specific period. When clamped as a period, the specific period is fixed at a certain correct reference level for the color signal period. Therefore, the color signal of the carrier band obtained by modulating the clamped color signal of the baseband band has a waveform in which hue information is not impaired.

Furthermore, by including a part of the end of the color signal period immediately before the blanking period in the specific period, the width of this specific period can be expanded, and a sufficiently long clamping period can be ensured, resulting in very good results. A ramp is performed. Furthermore, since the end portion of the color signal period does not appear on the screen, even if the specific period is extended, this will not affect the reproduced screen.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the color signal processing system according to the present invention, in which 30 is a superimposed component removal circuit;
1 is a DC level detection circuit; 32 is a switch;
Portions corresponding to those in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

Since this embodiment is the same as the conventional example shown in FIG. 11 at the time of recording, its explanation will be omitted.

Further, FIG. 2 is a waveform diagram showing signals at each part of FIG. 1 during reproduction, and signals corresponding to those in FIG. 1 are given the same reference numerals.

In FIGS. 1 and 2, during playback, switch 9
, 10 are closed to the P contact side, and a low frequency conversion carrier color signal a reproduced from a recording medium (not shown) is inputted from the input terminal 1 and amplified by the amplifier 3.
0.

In the superimposed component removal circuit 30 , the low-pass converted carrier color signal a output from the amplifier 3 is supplied to the A contact of the switch 32 and the DC level detection circuit 31 .

This DC level detection circuit 31 detects the DC level of the low frequency conversion carrier color signal a, and a signal (hereinafter referred to as
A DC level signal) is output. This DC level signal is supplied to the B contact of the switch 32. switch 3
2 is controlled by a switch pulse b having the same pulse period length and the same timing as the clamp pulse e supplied to the clamp circuits 17 to 20, and is normally closed to the a contact side to select the low frequency conversion carrier color signal a. During the pulse period of switch pulse b, the DC level detection circuit 3 closes to the B contact side.
Select the DC level signal from 1.

Therefore, as shown in FIG. 2, the low-frequency conversion carrier signal a contains undesired components N such as crosstalk and carrier leakage from adjacent tracks that occur during reproduction from a recording medium.
(these are the superimposed components) are superimposed, but the low-pass conversion carrier color signal C
, one superimposed acid component is removed during the generation period of the switch pulse b within the blanking period (in this case, located within the front porch) and set to the DC level of the low frequency conversion carrier color signal a.

The output low frequency conversion color signal C of the superimposed component removal circuit 30 is supplied to the demodulator 5, where the baseband B-Y signal d is demodulated, and after being subjected to the same processing as in FIG. 11, it is sent to the clamp circuit 17. Supplied. The RY signal demodulated by the demodulator 6 is also supplied to the clamp circuit 18 in the same manner.

In the clamp circuits 17 and 18, clamping is performed during the period in which the DC level signal is replaced by the switch 32 for the BY signal and the RY signal by the clamp pulse e, respectively. B- output from these clamp circuits 17°18
The Y signal and the RY signal are processed in the same manner as in FIG. 11, and a carrier color signal f is obtained at the output terminal 28.

As described above, in this embodiment, the superimposed component removal circuit 30 replaces the DC level signal with the baseband B-Y signal demodulated by the demodulators 5 and 6 and the R-
An achromatic color level is defined for the Y signal, and the amplitude relationship of each part of the B-Y signal and R-Y signal with respect to this achromatic color level is as follows.
They do not change depending on the size of the superimposed component or signal processing, and the achromatic color levels are clamped by the clamp circuit 17.18 to a predetermined reference level, so that the achromatic color levels are output from the clamp circuit 17.18. In the BY signal and the RY signal, the relationship of the level of each part with respect to the achromatic color level is not impaired. Therefore, the hue information is correctly held in the carrier color signal obtained at the output terminal 28, and the color reproduction of the monitor image is greatly improved.

Note that, hereinafter, the period for defining the achromatic color level on the front porch during the blanking period of the low-frequency conversion carrier color signal will be referred to as a level specifying period.

FIG. 3 is a circuit diagram showing a specific example of the superimposed component removal circuit 30 in FIG. 1.

In the same figure, the low frequency conversion carrier color signal a output from the amplifier 3 is input from the input terminal 33, and is supplied to the base of the transistor 36 in the switch 32.
The signal is supplied to a DC level detection circuit 31 consisting of a resistor 34 and a capacitor 35.

The DC level detection circuit 31 averages the level of the low frequency conversion carrier color signal a using a resistor 34 and a capacitor 35, and generates a DC level signal representing the DC level. This DC level signal is applied to the transistor 39 in the switch 32.
supplied to the base of

In the switch 32, a switch pulse b is supplied from an input terminal 43, and a switch pulse b obtained by inverting the level of this switch pulse b is supplied from an input terminal 42.

When the switch pulse b is not supplied from the input terminal 43, the transistor 41 is turned off, and the transistor 40 is turned on by the switch pulse b from the input terminal 42. As a result, the transistors 36 and 37 operate, and the low frequency conversion carrier color signal a is outputted to the output terminal 44 via the transistor 37. When the switch pulse b is supplied from the input terminal 43, the transistor 41 is turned on and the transistor 40 is turned off.

As a result, the transistors 38 and 39 operate, and the DC level signal from the DC level detection circuit 31 is outputted to the output terminal 44 via the transistor 38.

FIG. 4 is a block diagram showing another embodiment of the color signal processing system according to the present invention, in which reference numeral 45 denotes a clamp circuit, and 46
11 is a capacitor, 47 is a switch, and parts corresponding to those in FIG. 11 are given the same reference numerals, and redundant explanation will be omitted.

This embodiment uses a clamp circuit 45, as shown in FIG. 4, in place of the superimposed component removal circuit 30 in FIG.

That is, in FIG.
The signal is supplied to a clamp circuit 45 consisting of. In the clamp circuit 45, when the switch pulse b is supplied during the level specific period (in this case, the front porch) of the blanking period in the low frequency conversion carrier color signal a, the switch 47 is closed, and this level specific period is changed to a specific level specific period. Clamping is performed so that the DC level is E8.

As a result, the low frequency converted carrier color signal C output from the clamp circuit 45 becomes similar to the low frequency converted carrier color signal C having the waveform shown in FIG. A similar effect can be obtained.

FIG. 5 is a block diagram showing still another embodiment of the color signal processing system according to the present invention, in which 48 is a DC level conversion circuit, 49 is a switch, 50 is a resistor, 51 is a DC power supply, and FIG. Corresponding parts are given the same reference numerals and redundant explanations will be omitted.

In this embodiment, instead of the superimposed component removal circuit 30 in FIG. 1, a DC level conversion circuit 48 is provided at the front stage of the amplifier 3, as shown in FIG.

In FIG. 5, a low frequency conversion carrier color signal input from input terminal 1 is supplied to a DC level conversion circuit 48. In FIG. In this DC level conversion circuit 48, normally the switch 49 is closed, and the low frequency conversion carrier color signal is outputted by superimposing the DC potential of the output DC voltage of the DC power supply 51 to a specific level by the resistor 50. , when a switch pulse b having the same pulse period length and the same timing as the clamp pulse supplied to the clamp circuits 17 to 20 is supplied, the switch 4
9 is opened, and only the DC level signal at the specific level determined by the output voltage of the DC power supply 51 and the resistor 50 is output.

In this way, in the low frequency conversion carrier color signal output from the DC level conversion circuit 48, the clamp circuits 17 to 20
The DC level by the DC level signal is set in the level specific period of the blanking period clamped by the clamp circuit 17, and in periods other than this period, this DC level is superimposed on the low frequency conversion carrier color signal. The DC level set during the period when 20 is clamped is set as the achromatic color level, and the relationship between the level of each part and the achromatic color level in other periods is maintained during the signal processing period,
Therefore, like the embodiment shown in FIG. 1, the carrier color signal obtained from the output terminal 28 retains the original hue information.

FIG. 6 is a circuit diagram showing the main parts of still another embodiment of the color signal processing system according to the present invention, in which 52 to 54 are input terminals, 55 and 56 are resistors, 57 is an on/off switch, 58 is a capacitor, 59 is an input terminal, 60 to 65 are transistors, 66 and 67 are resistors, and 68 is an output terminal.

In this embodiment, a demodulator for a low-frequency converted carrier color signal is provided with an achromatic color level defining function.

For example, it has the functions of the superimposed component removal circuit 30 and the demodulator 5 shown in FIG.

In FIG. 6, the reproduced low frequency conversion carrier color signal a is inputted to the input terminal 54 and is supplied to the base of the transistor 60 via the resistor 55. Further, the open/close switch 57 is normally closed, and the DC level of the low frequency conversion carrier color signal a is detected by the resistor 56 and the capacitor 58 and is supplied to the base of the transistor 61. transistor 60
61 form a differential pair because their emitters are connected to a common constant current source, and the resistors 55 and 56 have the same resistance value.

A switch pulse b similar to that of the previous embodiment is inputted to the input terminal 59 during a level specific period in the front porch of the blanking period of the low-frequency conversion carrier color signal a, and thereby the open/close switch 57 is opened.

Therefore, at this time, signals of the same level (front porch level) are applied to the bases of transistors 60 and 61.

The collector of the transistor 60 is connected to the emitters of transistors 62 and 63 forming a differential pair, and the collector of the transistor 61
The collector of is connected to the emitters of transistors 64 and 65 forming a differential pair.

In addition, a resistor 66 is connected to the collector of the transistor 62 and 64.
A power supply voltage is applied through the transistors 63 and 65.
A power supply voltage is also applied to the collector of the transistor 2 through a resistor 67 serving as a load resistance. And transistor 63.65
The collector of is connected to the output terminal 68. Note that the resistance values of resistors 66 and 67 are equal. Furthermore, the input terminal 53
to the bases of transistors 63 and 64, a chrominance subcarrier S of a frequency f t, sc is phase-locked to one chrominance subcarrier of the modulated chrominance signal in the low-pass conversion carrier chrominance signal a.
c is supplied from the input terminal 52 to the transistor 62゜6.
A color subcarrier Sc having the same frequency and an opposite phase as this color subcarrier Sc is supplied to the base of the color subcarrier Sc.

Therefore, during the period when the open/close switch 57 is closed, the DC level of the low-frequency converted carrier color signal a is applied to the base of the transistor 61. During the period when the polarity is positive with respect to the reference level, a current of a magnitude corresponding to the level of this period flows through the transistor 60, and during the period when the polarity is negative with respect to this reference level, the current flows through the transistor 61 according to the level of this period. A current of magnitude flows.

On the other hand, if the color subcarrier Sc is the color subcarrier for demodulation of the 5cti-RY signal, then the period color subcarrier has positive polarity with respect to the above reference level of the modulated RY signal of the low-pass conversion carrier color signal a. Transistors 63 and 64 are turned on by S0, and a current corresponding to the level of the positive polarity portion of the modulated R-Y signal flows through the load resistor 67 and the transistor 6.
3.60, and the positive polarity portion of this modulated R-Y signal is available at output terminal 68. Also,
During the period when the modulated R-Y signal has a negative polarity with respect to the reference level, the color subcarrier S0 turns on the transistor 62.65, and a current corresponding to the level during this period flows through the load resistance 67°. transistor 65.61
This negative polarity portion is obtained at the output terminal 68 with the same polarity as the positive polarity portion.

In this way, the RY signal modulated from the low-pass converted carrier color signal a is obtained at the output terminal 68 in a full-wave rectified form using its DC level as a reference level.

By passing this RY signal through an LPF 12 to remove the color subcarrier component, as in the embodiment shown in FIG. 1, for example, a baseband RY signal is obtained.

When the switch 57 is opened by the switch pulse b from the input terminal 59 during the level specific period of the blanking period of the low-pass conversion carrier color signal a, the same potential is applied to the bases of the transistors 60 and 61.
The collector currents of 61 are equal. These collector currents are
Even if the level of the level specifying period of the blanking period of the low-pass converted carrier color signal a varies from blanking period to blanking period, it is always constant, being half the magnitude of the current flowing through the constant current source. Therefore, the signal level obtained at the output terminal 68 during this level specific period is also constant. As a result, in the R-Y signal obtained at the output terminal 68, the achromatic color level is defined in the level specifying period.

Note that this achromatic color level may be different from the level at the output terminal 68 with respect to the DC level of the low-pass conversion carrier color signal a. As in the embodiment shown in FIG. 1, each process is performed and the clamp circuit clamps the achromatic color level, and the level at the output terminal 68 with respect to the DC level of the low-frequency conversion carrier signal a is also constant. Since it is constant, the achromatic color level after clamping and the level relative to the DC level are also always constant, and hue information is not impaired.

Note that the same applies to the BY signal.

FIG. 7 is a circuit diagram showing the main parts of still another embodiment of the color signal processing system according to the present invention, in which reference numerals 69 and 70 are input terminals, 71 and 72 are open/close switches, 73 is a capacitor; Portions corresponding to the figures are given the same reference numerals and redundant explanations will be omitted.

In this embodiment as well, the achromatic color level is defined by demodulating the low frequency conversion carrier color signal.

In FIG. 7, the changeover switch 71 is turned on and off by the switch pulse b from the input terminal 69, and the changeover switch 72 is turned on and turned off by the switch pulse b from the input terminal 70, which has a level inversion relationship with the switch pulse b. Controlled off.

Normally, the open/close switch 71 is open and the open/close switch 72 is closed, and the capacitors 58 and 73 of the same capacity are charged to the DC level by the low-frequency conversion carrier color signal a input from the input terminal 54. A level is applied to the base of transistor 61. Then, it operates like the embodiment shown in FIG.

During the level specific period of the blanking period of the low-pass conversion carrier color signal a, the open/close switch 71 is closed, the open/close switch 72 is opened, and the capacitor 73 is set to the DC level by the low-pass conversion carrier color signal a via the resistor 55. It will be charged.

Therefore, the capacitor 73 is connected to the base of the transistor 60.
The DC level of the low frequency conversion carrier color signal a detected by charging is applied. At this time as well, this DC level due to the charging of the capacitor 58 is applied to the base of the transistor 61. Therefore, the base potentials of transistors 60 and 61 are equal, and as in the embodiment shown in FIG.
An achromatic color level is defined in the color difference signal obtained at the output terminal 68.

FIG. 8 is a circuit diagram showing the main parts of still another embodiment of the color signal processing system according to the present invention, in which 74 is an input terminal;
75 is an opening/closing switch, and parts corresponding to those in FIG. 6 are given the same reference numerals and redundant explanations will be omitted.

This embodiment also defines the achromatic color level by demodulating the low-frequency conversion carrier color signal, and has a simpler circuit configuration than the embodiment shown in FIG.

In FIG. 8, the normal on/off switch 75 is open;
The base of the transistor 60 is supplied with the low frequency conversion carrier color signal a inputted from the input terminal 54.

A resistor 56 and a capacitor 58 are connected to the base of the transistor 61.
The DC level of the low-pass converted carrier color signal a detected by is supplied. During the level specifying period of the blanking period of the low-pass converted carrier color signal a, the switch pulse b is supplied from the input terminal 74 to close the open/close switch 75, and the DC level of the low-pass converted carrier color signal a changes to the level of the transistor 61. It will also be supplied to the base of transistor 60 along with the base.

In this way, the same operation as the embodiment shown in FIG. 7 can be performed and the same effect can be obtained, but in addition, compared to FIG. 7, the number of on-off switches and capacitors can be reduced by one. It is possible to reduce the number of parts and simplify the configuration.

FIG. 9 is a block diagram showing still another embodiment of the color signal processing system according to the present invention, in which 30' is a superimposed component removal circuit, 31' is a DC level detection circuit, 32' is a switch, and 76.77 is a pilot. The burst pulse (P, B) removal circuit and 78 and 79 are pilot burst pulse addition circuits, and parts corresponding to those in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

In this embodiment, a 5-
This is applied to VTRs that record and reproduce by adding a pilot burst signal with a constant phase component, such as VHS type VTRs, and the waveforms of the signals in each part of Fig. 9 during the blanking period are shown below. The operation of this embodiment will be explained below using FIG. 10 shown in FIG. However, in Figure 10,
Signals corresponding to those in FIG. 9 are given the same reference numerals.

9 and 10, during recording, the switches 9 and 10 are closed to the R contact side, and the PAL carrier color signal a amplified by the amplifier 4 is transmitted to the superimposed component removal circuit 30'.
The 6-superimposed component removal circuit 30' supplied to
By using the switch pulse b having the same timing and the same pulse width as the clamp pulse f supplied to the clamp pulses f supplied to the terminals 7 to 20, the superimposed component removal circuit 30 adjusts the DC level of the carrier color signal a of the PAL system during the specific level period. However, 5-VH8 which records and plays PAL video signals
In this type of VTR, a pilot burst signal having a constant phase component is added before the color burst signal during the blanking period of the low-pass conversion carrier color signal. Therefore, in this embodiment, a level specifying period for defining the DC level is provided immediately before the pilot burst signal, but in order to ensure sufficient clamping during this period, as shown in FIG. , the switch pulse b is made to last a short period ΔT (for example, about 1 μsec) at the end portion of the signal period immediately before the blanking period that does not affect the screen, and the blanking period is extended to obtain a level specifying period of a desired length. I'm trying to get it.

The carrier color signal C output from the superimposed component removal circuit 30' is supplied to demodulators 7 and 8, and demodulated into a baseband BY signal d and an RY signal.

In these, the DC level is defined in the above-mentioned level specification period.

The demodulated B-Y signal and R-Y signal are processed in the same manner as in the embodiment shown in FIG. 1 through switches 9 and 10, respectively, and then sent to a pilot burst pulse addition circuit 78.
79, and a pulse (pilot burst pulse) for generating a pilot burst signal is added between the color burst pulse of the blanking period and the level specifying period. Pilot burst pulse addition circuit 78
The B-Y signal e outputted from the circuit is clamped by a clamp pulse f in a clamp circuit 19 so that the level specific period becomes a constant level, and the frequency is changed by a modulator 23 as in the embodiment shown in FIG. is modulated on the color subcarrier of the f LSC. As a result, the BY axis components of the pilot burst signal and the color burst signal are generated from the pilot burst pulse and the color burst pulse within the blanking period of the modulated BY signal.

Similarly, the R-Y signal output from the pilot burst pulse adding circuit 79 is also clamped by the clamp circuit 20 and modulated by the modulator 24, and is modulated with a pilot burst signal and a color burst signal within the blanking period. A RY signal is obtained.

These modulated B-Y signals and R-Y signals are sent to an adder 2.
6, and a low-pass converted carrier color signal g of the color subcarrier frequency f r, BG is obtained. This low-frequency conversion carrier color signal g
In the blanking period, the level specifying period is fixed at a constant level, and a pilot burst signal with a frequency f, , sc and a constant phase is added before the color burst signal.

The processed B-Y signal and R-Y signal are also supplied to pilot burst pulse removal circuits 76 and 77, respectively, but since they do not have a pilot burst pulse, they pass through as is, and are shown in FIG. Similar to the embodiment described above, a carrier color signal for monitoring is generated.

During reproduction, a low-frequency conversion carrier signal to which a pilot burst signal is added is inputted from the hexagonal terminal 1 as shown in FIG. After the DC level is specified for a specific period (Fig. 10), the demodulators 5 and 6
-Y signal and RY signal. In these BY signal and RY signal, a pilot burst pulse due to a pilot burst signal exists during the blanking period. Therefore, these B-Y signal and R-Y signal are respectively processed in the same manner as in the embodiment shown in FIG. The pulse is removed. B-Y with these pilot burst pulses removed
A PAL carrier color signal for monitoring is generated from the RY signal.

As described above, in this embodiment, even if a pilot burst signal exists, the level specifying period for clamping can be set sufficiently long, and clamping can be performed with high precision to prevent loss of hue information. It can be prevented.

[Effects of the Invention] As explained above, according to the present invention, it is possible to define an achromatic color level as a relative reference level for the color signal of the baseband band, and furthermore, this achromatic color level is not defined. By making the period sufficiently long, it is possible to accurately clamp this period to a constant level, and the color signal in the carrier band is processed after demodulating into the color signal in the baseband band. It is possible to prevent changes in hue information when modulating to generate a color signal in the original carrier band.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the color signal processing system according to the present invention, FIG. 2 is a waveform diagram showing signals of each part in FIG. 1, and FIG. 3 is an example of the superimposed component removal circuit in FIG. FIGS. 4 and 5 are block diagrams showing other embodiments of the color signal processing system according to the present invention, and FIGS. 6 to 8 are circuit diagrams showing specific examples of the color signal processing system according to the present invention. Circuit diagram showing main parts of still another embodiment, No. 9
The figure is a block diagram showing an embodiment of the color signal processing system according to the present invention, FIG. 10 is a waveform diagram showing signals of each part in FIG. 9, and FIG. 11 is an example of a conventional color signal processing system. 12 is a waveform diagram showing signals of each part in FIG. 11, and FIG. 13 is a circuit diagram showing an example of the modulator and demodulator in FIG. 11. 1... Input terminal for reproduction low-frequency conversion carrier color signal, 2
...Input terminal for conveying color signals for recording, 5-
8... Demodulator, 9, 1o... Switch, 17-20... Clamp circuit, 21-24.
...Modulator, 25゜26...Adder, 28...
...Output terminal for monitor carrier color signal, 29...
・Output terminal for low frequency conversion color signal for recording, 30, 30'・
...Superimposed component removal circuit, 31°31'...
・DC level detection circuit, 32, 32'... switch, 45... clamp circuit, 48...
・DC level conversion circuit, 76.77...Pilot burst pulse removal circuit, 78.79...
Pilot Figure 3 Figure 7 Figure Figure /4 JL Figure 10 Figure 12

Claims (1)

[Claims] 1. In a color signal processing system that demodulates and processes an input color signal in a carrier band into a color signal in a baseband band, a specific period of the input color signal in the carrier band is set to a predetermined level. A color signal processing system characterized in that a DC signal is substituted. 2. The color signal processing system according to claim 1, wherein the specified period of the processed color signal of the baseband band is set as a clamp period to clamp the color signal of the baseband band. 3. The color signal processing system according to claim 2, wherein the clamped baseband band color signal is modulated to generate a carrier band output color signal. 4. The color signal processing system according to claim 1, 2 or 3, wherein the DC signal at the predetermined level is a signal at the DC level of the input color signal detected from the input color signal in the carrier band. 5. In claim 1, 2 or 3, the means for replacing a specific period of the input color signal in the carrier band with a DC signal of a predetermined level is a clamp circuit that uses the specific period as a clamp period. Color signal processing system. 6. In claim 1, 2 or 3, the means for replacing a specific period of the input color signal in the carrier band with a DC signal of a predetermined level comprises a first means for generating a DC signal of the predetermined level; a color signal processing system comprising: a second means for outputting only the DC signal during a period, and outputting a color signal of the carrier band with a DC level equal to the level of the DC signal outside the specific period; . 7. First and second transistors forming a differential pair, the input color signal in the carrier wave band is supplied to the first transistor, the DC signal is supplied to the second transistor, and the input color signal in the carrier wave band is supplied. In a color signal processing system that includes a demodulator that demodulates a signal into a color signal of a baseband band and processes the color signal of the baseband band demodulated by the demodulator, the input color signal of the carrier band is 1st to detect DC level
means for supplying the input color signal of the carrier wave band to the first transistor as well as the second transistor during a specific period of the input color signal of the carrier wave band, and detecting the input color signal of the carrier wave band by the first means outside the specific period. and second means for supplying the DC level signal to the second transistor as the DC signal. 8. First and second transistors forming a differential pair, an input color signal of a carrier wave band is connected to the first transistor, a DC signal is supplied to the second transistor, and the input color signal of the carrier wave band is connected to the first transistor. In a color signal processing system that includes a demodulator that demodulates a color signal into a color signal of a baseband band, and processes the color signal of the baseband band demodulated by the demodulator, the input color signal of the carrier band is The first to detect the DC level of
, second means, third means for supplying the DC level signal detected by the first means to the second transistor as the DC signal, and a specific period of the input color signal of the carrier wave band. and fourth means for supplying the DC level signal detected by the second means to the first transistor instead of the input color signal of the carrier band. . 9. The color signal processing system according to claim 8, wherein the first and second means are the same means. 10. The color signal processing system according to claim 7, 8 or 9, wherein the specified period of the processed color signal of the baseband band is set as a clamp period to clamp the color signal of the baseband band. 11. The color signal processing system according to claim 10, wherein the clamped color signal in the baseband band is modulated to generate an output color signal in the carrier band. 12. In a color signal processing system that demodulates and processes an input color signal in a carrier band into a color signal in a baseband band, a part of the front end side of the blanking period of the input color signal in the carrier band and A color signal processing system characterized in that a period consisting of a part of the terminal side of a color signal period immediately before a blanking period is defined as a specific period, and the specific period is replaced with a DC signal of a predetermined level. 13. The color signal processing system according to claim 12, wherein the specific period of the processed color signal of the baseband band is set as a clamp period to clamp the color signal of the baseband band. 14. The color signal processing system according to claim 13, wherein the clamped baseband band color signal is modulated to generate a carrier band output color signal.