JPH0435110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an automatic hue correction device for a color television receiver that can automatically correct the hue.

(B) Prior Art An automatic hue correction device that automatically corrects hue has already been filed as Japanese Patent Application No. 60-50869 by the same applicant as the present application. The device is as shown in FIG. 6, and a composite video signal applied to an input terminal 1 is amplified by a first band amplification circuit 2 and a second band amplification circuit 3.
is separated into a chroma signal and a burst signal. The chroma signal is then applied to a demodulation circuit 12 to be demodulated, and the burst signal is applied to a phase comparator 5 to be used to create a CW (local subcarrier) signal and an ACC (automatic chroma control) circuit. 4 and used for gain control. The phase comparator 5 includes a PLL circuit 7 as well as a VCO 6.
The burst signal and the VCO
Since the output signal of VCO 6 is phase-compared with the output signal of VCO 6 by a phase comparator 5, a CW signal synchronized with the burst signal is generated at the output end of the VCO 6. Note that 8 is a hue volume. The CW signal is applied to first and second phase shift circuits 10 and 11 via a hue adjustment circuit 9. The first and second phase shift circuits 10 and 11 generate a CW RY signal and a _{CW BY} signal whose phases are shifted by φ ₁ and φ ₂ from the CW signal, respectively. The CW _RY signal and the CW _BY signal are applied to the demodulation circuit 12 to demodulate the RY color difference signal and the BY color difference signal, respectively. Furthermore, a G-Y color difference signal is obtained by matrixing the demodulated R-Y color difference signal and the B-Y color difference signal. The R-Y color difference signal, the G-Y color difference signal, and the B-Y color difference signal are the first and second signals, respectively.
The signals are transmitted from the third output terminals 13, 14 and 15 to the subsequent stage and used for color reproduction.

The R-Y color difference signal obtained at the first output terminal 13 and the B-Y color difference signal obtained at the third output terminal 15 are combined by the first combining circuit 16, and a Q signal is generated at the output terminal. The Q signal is then amplified by an amplifier circuit 18 and supplied to an average adjustment circuit 20 as an adjustment signal. The average adjustment circuit 20 includes:
The adjustment signal is smoothed and supplied to the hue adjustment circuit 9 as an average adjustment signal. Also, R-Y
The color difference signal and the B-Y color difference signal are generated by the second synthesis circuit 1.
7, the R-Y color difference signal and the inverted B-
The Y color difference signals are combined, and an I signal is generated at the output terminal of the second combining circuit 17. The I signal is then applied to the control circuit 19, where it is compared with a reference signal (Vref). If the level of the I signal is now higher than the level of the reference signal, a control signal is generated from the control circuit 19, the amplifier circuit 18 is activated, and the Q
The signal is amplified to generate the adjustment signal. The adjustment signal is then averaged by an average adjustment circuit 20 and supplied to the hue adjustment circuit 9. On the other hand, if the level of the I signal is lower than the level of the reference signal, the control signal is not generated and the amplifier circuit 18 does not operate, so that automatic hue correction is not performed.

Next, the automatic hue correction operation will be explained. If there is a chroma signal that is deviated by α degree from the I axis indicated by A in FIG. 7, the level of the Q signal will be B, and the level of the I signal will be C. When the level C of the I signal is made higher than the level of the reference signal (Vref), the Q signal is amplified by the amplifier circuit 18, smoothed by the average adjustment circuit 20, and applied to the hue adjustment circuit 9 as an average adjustment signal. be done. When the average adjustment signal is applied to the hue adjustment circuit 9, the phase of the CW signal is rotated according to the level of the average adjustment signal, and the output signals of the first and second phase circuits 10 and 11 are rotated accordingly. The phases of certain CW _RY and CW _BY signals are also rotated. This means that the demodulation axis rotates in the demodulation circuit 12, as shown in FIG.
The R-Y axis rotates α degrees and becomes the (R-Y)' axis,
The B-Y axis is also rotated by α degrees to become the (B-Y)' axis.
In this case, since the Q signal is created from the R-Y color difference signal and the B-Y color difference signal, the I-axis and Q-axis also rotate according to the rotation of the demodulation axis, and when the correction is completed, the chroma Signal A overlaps the I′ axis, and Q
The signal level becomes zero. In other words, this automatic correction rotates the demodulation axis so that the level of the Q signal becomes small.

Automatic hue correction is performed only when there is an I signal of a predetermined level or higher. Therefore, automatic hue correction is performed only when the chroma signal exists near the I-axis, that is, near the skin color. Further, automatic hue correction is performed according to the level of the Q signal, and when the Q signal is large, a large correction is made, and when it is small, a small correction is made.
The automatic correction will be related only to the level of the Q signal.

(c) Problems to be solved by the invention However, the automatic hue correction device shown in FIG.
There has been a problem in that chroma signals that do not need to be corrected are corrected outside a predetermined range near skin color.
That is, the operation of the amplifier 18 is controlled by the first control circuit 19.
Even when the average adjustment circuit 20 is stopped and the average adjustment circuit 20 does not operate, the residual charge in the capacitor placed in the average adjustment circuit 20 causes the hue adjustment circuit 9 to operate, and the hue adjustment circuit 9 operates except for a predetermined range near the skin tone that does not require correction. There was a problem that the chroma signal of the camera was corrected.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a detection means for detecting that a chroma signal exists within a predetermined range near the I-axis, and an average adjustment circuit. and a switch inserted between the hue adjustment circuit and the switch that opens and closes in response to a control signal from the detection means.

(E) Effect Since the switch is controlled in accordance with the control signal from the detection means and the output of the average adjustment circuit is cut off, the hue adjustment is affected by the residual charge of the capacitor disposed in the average adjustment circuit. There is no effect on the circuit.

(F) Embodiment Figure 1 is a circuit diagram showing an embodiment of the present invention.
7 is a second synthesis circuit that synthesizes the color difference signals obtained from the first output terminal 13 and the third output terminal 15 of the demodulation circuit 12, and generates an I signal, a Q+θ ₁ signal, and a Q−θ ₁ signal, respectively; 19 is a second synthesis circuit; 2 a control circuit that compares the level of the output signal of the synthesis circuit 17 with a reference signal (Vref) and generates a control signal; 23 is an average adjustment circuit 20;
and the hue adjustment circuit 9, and the control circuit 1
This is a switch that opens and closes in response to a control signal from 9. Note that circuits in FIG. 1 that are the same as those in FIG. 6 are given the same figure numbers and their explanations will be omitted.

The R-Y color difference signal obtained at the first output terminal 13 and the B-Y color difference signal obtained at the third output terminal 15 are combined in the first synthesis circuit 16, and a Q signal is generated at the output terminal. The Q signal is supplied to an amplifier 18 as a hue adjustment circuit. Further, the R-Y color difference signal obtained at the first output terminal 13 and the B-Y color difference signal obtained at the third output terminal 15 are combined in the second synthesis circuit 17, and the I signal, Q+
Generates θ ₁ signal and Q-θ ₁ signal. Here, the Q+θ ₁ signal means a signal demodulated with a demodulation axis shifted by +θ ₁ degree with respect to the Q axis, and the Q−θ ₁ signal is a signal demodulated with a demodulation axis shifted -θ ₁ degree with respect to the Q axis. Denotes a demodulated signal. To help understand the phase relationship of each axis, θ ₁ is
Figure 2 shows the case where the angle is 30°. The I signal, Q+θ ₁ signal, and Q−θ ₁ signal obtained from the second synthesis circuit 17 are compared in level with a reference signal (Vref) in a first control section 19A arranged in the control circuit 19. The first control unit 19A, for example,
It has a configuration as shown in the figure. In FIG. 3, the output transistor 28 is turned on and the output terminal 2
When a control signal is supplied from 9 to the amplifier circuit 18 in FIG. 1, the amplifier circuit 18 becomes inactive, and when the output transistor 28 is turned off, the amplifier circuit 18 becomes active. Therefore, the first differential circuit 32 consisting of the first and second transistors 30 and 31 compares the I signal and the reference signal (Vref).
When the signal is large, the first transistor 30 is turned on and the second transistor 31 is turned off. Further, the second differential circuit 35 consisting of the third and fourth transistors 33 and 34 outputs the Q-θ ₁ signal and the reference signal (Vref).
This is used to compare the reference signal (Vref) with Q-
If the θ ₁ signal is set to zero level, the third transistor 33 is turned on and the fourth transistor 34 is turned off when the Q-θ ₁ signal is negative. Further, a third differential circuit 38 consisting of fifth and sixth transistors 36 and 37 is
It compares the Q+θ ₁ signal with the reference signal (Vref), and when the Q+θ ₁ signal is positive, the fifth transistor 3
6 is turned off, and the sixth transistor 37 is turned on.
And the second, fourth and fifth transistors 31,
The collectors of 34 and 36 are the output transistor 2
Since the output transistor 28 is connected to the base of the transistor 8, the output transistor 28 is eventually turned off. Therefore, only when the level of the I signal is high, the Q+θ ₁ signal is positive, and the Q−θ ₁ signal is negative, the first controller 19A controls the amplifier 18.
make it work. The shaded area in FIG. 2 indicates this range, and it is understood that the amplifier circuit 18 operates only when a chroma signal within this range is applied to the demodulation circuit 12. The second control unit 19B arranged in the control circuit 19 has the same circuit configuration as the first control unit 19A, and converts the Q+θ ₁ signal and Q−θ ₁ signal from the second synthesis circuit 17 into a reference signal (Vref). The levels are compared and a control signal for opening and closing the switch 23 is generated. Now, when a chroma signal within the shaded range in FIG. 2 is applied to the demodulation circuit 12,
The Q signal applied to the amplifier 18 as described above is supplied to the average adjustment circuit 20 as an adjustment signal. The adjustment signal is smoothed by a capacitor in the average adjustment circuit 20 and converted into an average adjustment signal corresponding to the average value of the adjustment signal, that is, the average value of the deviation amount of the chroma signal near the I axis from the I axis, It is output from the average adjustment circuit 20. Further, the second control section 19B in the control circuit 19 generates a control signal according to the Q+θ ₁ signal and the Q−θ ₁ signal, and the control signal turns on the switch 23, so that the average adjustment signal is used for hue adjustment. It is supplied to circuit 9. Therefore, hue adjustment is performed based on the average value of the amount of deviation from the I-axis of the chroma signal near the I-axis, that is, near the skin color. In other words,
When a chroma signal within the shaded range in FIG. 2 is applied to the demodulation circuit, hue adjustment is performed.

Next, when a chroma signal outside the shaded range in FIG. 2 is applied to the demodulation circuit 12, the first
The control unit 19A does not operate the amplifier 18, and the output from the amplifier 18 becomes zero. However, the above-described control according to the residual charge of the capacitor in the average adjustment circuit 20 continues, and an attempt is made to supply the average adjustment signal to the hue adjustment circuit 9. In other words, although an attempt is made to correct a chroma signal that does not need to be corrected, the control circuit 19
Since a control signal to turn off the switch 23 is generated from the second control unit 19B in the average adjustment circuit 20
The average adjustment signal from is blocked. Therefore, if a chroma signal outside the shaded range in FIG. 2 is applied to the demodulation circuit, no hue adjustment is performed. The range indicated by the dashed line in FIG. 2 is the range in which the switch 23 is turned on, although it is outside the shaded range, and in this range, control is performed using the residual charge in the capacitor in the average adjustment circuit 20.

FIG. 4 shows another embodiment of the present invention, in which a third synthesis circuit 21 and a second control circuit 22 are provided in place of the second control section 19B of FIG.
The third synthesis circuit 21 synthesizes the color difference signals obtained from the first output terminal 13 and the third output terminal 15 of the demodulation circuit 12, and generates a Q+θ ₂ signal and a Q−θ ₂ signal, respectively. The circuit 22 uses the level of the output signal of the third synthesis circuit 21 as a reference signal (Vref).
It generates a control signal. In order to help understand the phase relationship of each axis, the second synthesis circuit 1
FIG. 5 shows a case where θ ₁ of the third synthesis circuit 17 is set to 30° and θ ₂ of the third synthesis circuit 17 is set to 40°. First control circuit 1
9 operates the amplifier 18 when a chroma signal in the range indicated by diagonal lines a is applied to the demodulation circuit 12. Similar to the embodiment of FIG. 1, the first control circuit 1
9 is the average value of the deviation amount of the chroma signal from the I axis,
This is to determine the range for applying to the hue adjustment circuit 9 as an average adjustment signal. On the other hand, the second
The control circuit 22 turns on the switch 23 when a chroma signal in the shaded range b is applied to the demodulation circuit 12. That is, like the second control section 19B in the embodiment shown in FIG. 1, the second control circuit 22 generates a control signal to turn on the switch 23 when a chroma signal within Q±40° is applied. be. Therefore, when the chroma signal applied to the demodulation circuit 12 is within the shaded range a in FIG. 5, hue adjustment is performed based on the average value of the amount of deviation from the range a. If the applied chroma signal is within the shaded range b in FIG. 5 and outside the shaded range a, the switch 23 is turned on but the amplifier 18 is not operated. However, since there is a residual charge in the capacitor of the average adjustment circuit 20, the same adjustment as previously applied by the chroma signal within the range a is continued. Therefore, hue correction is also performed when applying a chroma signal in this range. Furthermore, if the chroma signal is outside the range indicated by diagonal lines in b, the switch 23 is turned off, the average adjustment signal is not applied to the hue adjustment circuit 9, and no hue adjustment is performed. It is possible to prevent the signal from being affected by the residual charge of the capacitor in the average adjustment circuit 20. In the case of FIG. 4, since the second control circuit 22 is provided with a different operating range from the first control circuit 19, the range for generating the average adjustment signal and the range for hue correction can be made different. can.

(G) Effects of the Invention Therefore, according to the present invention, the influence of the residual charge of the capacitor in the average adjustment circuit is eliminated by the control circuit opening and closing the switch.
It is possible to prevent chroma signals that do not require hue correction from being corrected. Further, according to the first embodiment, by selecting the range in which the average adjustment signal is generated, the range to be hue-corrected can be selected at the same time, which simplifies the adjustment.
The number of circuits can be reduced. Furthermore, as in the second embodiment, if the range θ ₁ for generating the average adjustment signal and the range θ ₂ for hue correction are made different, it is possible to perform hue correction according to the design concept.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figure 2 is a circuit diagram showing an embodiment of the present invention.
The figure is a vector diagram to explain the operation of Figure 1.
3 is a circuit diagram showing a specific circuit example of the control circuit shown in FIG. 1, FIG. 4 is a circuit diagram showing another embodiment of the present invention, and FIG. 5 is a vector diagram for explaining the operation of FIG. 4. 6 are circuit diagrams showing a conventional automatic hue correction device, and FIGS. 7 and 8 are vector diagrams for explaining the operation of FIG. 6. Explanation of main drawing numbers, 9...hue adjustment circuit, 12...
... demodulation circuit, 19 ... first control circuit, 20 ... average adjustment circuit, 22 ... second control circuit, 23 ... switch.

Claims (1)

[Claims] 1. An automatic hue correction device that corrects hue by applying an adjustment signal generated according to a color difference signal from a demodulation circuit to an average adjustment circuit, and applying an output signal of the average adjustment circuit to a hue adjustment circuit. is inserted between a detection means for detecting that the chroma signal exists within a predetermined range near the I-axis, and the average adjustment circuit and the hue adjustment circuit, and is opened and closed in response to a control signal from the detection means. A hue correction device comprising a switch.