JPH0584992B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a color demodulation circuit for a video reproduction device.
In particular, the present invention relates to a color demodulation circuit for a video playback device that plays back video using a color video signal based on the PAL (Phase Alternation Line) system.

Background technology PAL corresponding to the nth (n is a natural number) scanning line
The color video signal E _Mo of the system is given by the following equation.

E _Mo = Y + E _U sin〓 _ct + (-1) ⁿ E _V cos〓 _ct ……(1) ω _c = 2π _H (m-1/4) ……(2) Here, Y is the luminance signal, E _u and _EV indicate color difference signals B-Y and RY, respectively. Note that B and R indicate blue and red signals, respectively. Further, _H is a horizontal scanning frequency, and m is a natural number.

The coefficient (-1) ⁿ in equation (1) means phase inversion for each horizontal scanning line, and the E _V component of the carrier color signal has a phase difference of 180° from each other for each horizontal scanning line. It is transmitted by balanced modulation of the subcarrier signal (-1) ⁿ cos = _ct . Therefore, the color burst signal is required to have information for inverting the phase of the _EV component subcarrier line by line on the image receiving side. For this reason, the color burst signal is switched line by line to a phase of ±135° around the E _u axis, and the phase-inverted signal is sent out.

FIG. 3 shows a conventional color demodulation circuit in a device that reproduces video using such a PAL color video signal. In FIG. 3, a carrier color signal included in a PAL color video signal is supplied with a color burst signal to a 1H (one horizontal scanning period) delay circuit 1, addition circuit 2, subtraction circuit 3, and burst gate 4. be done. The output of the 1H delay circuit 1 is added and combined with the carrier color signal in the adder circuit 2, and at the same time, a signal corresponding to the difference between the carrier color signal and the output of the 1H delay circuit 1 is generated in the subtracter circuit 3. The outputs of these adder circuit 2 and subtracter circuit 3 are supplied to BY demodulator 5 and RY demodulator 6, respectively.

The burst gate 4 includes a pulse generator (not shown) configured to delay the horizontal synchronization signal and output a gate pulse while the color burst signal is present, for example.
output is also provided. Burst gate 4 is
For example, it consists of an analog switch circuit that turns on and off depending on the output of this pulse generator. After the color burst signal is separated and extracted from the carrier color signal by this burst gate 4, the APC (Auto
The signal is supplied to a subcarrier generator 7 based on the Phase Control method. The subcarrier generator 7 is configured to generate a color subcarrier signal whose phase matches the average phase of the color burst signal. The color subcarrier signal output from this subcarrier generator 7 is passed through a 90° phase shifter 8.
B-Y as subcarrier for detection with 90° phase shift
The signal is supplied to a demodulator 5. This color subcarrier signal is also transferred to a 180° phase shifter 9 that shifts the input phase by 180°.
It is also supplied to the PAL switch 10.
The PAL switch 10 is configured to alternately output the color subcarrier signal and the output of the 180° phase shifter 9 every 1H. This PAL switch 1
The output of 0 is supplied to the RY demodulator 6 as a subcarrier for detection.

In the above configuration, vectors A and B respectively corresponding to the carrier color signal and the color burst signal when there is no color change during consecutive 4H are shown in FIGS. 4A to 4D. As shown in Figures 4A to 4D, a 1/4 line offset is used in which the phase of the subcarrier is shifted by 90° between two consecutive scanning lines in the same field to prevent vertical stripe interference. Therefore, the B-Y axis is
It rotates by 90 degrees every 1H, and the RY axis rotates by 90 degrees every 1H and is reversed at the same time. Also,
The color burst signal is ± centered on the B-Y axis.
Since the phase is switched to 135° every 1H and the phase is inverted, it is sent out.
It will be reversed every 2H. Furthermore, since the R-Y component of the carrier color signal is sent by balanced modulation of the subcarrier signal having a phase difference of 180 degrees every 1H, the carrier color signal is transmitted every 2H like the color burst signal. It will be reversed.

Here, it is assumed that the signal delay time of the 1H delay circuit 1 is set to be longer or shorter than 1H by (π/2)×(1/ω _c ). At this time, vectors A' and B' respectively corresponding to the carrier color signal and color burst signal outputted from the 1H delay circuit 1 during consecutive 4H are shown in FIGS. 5A to 5D. As can be seen from Figures 5A to 5D,
There is no 90° phase difference due to 1/4 line offset between the input and output of the 1H delay circuit. Therefore,
As shown in FIG. 6, vectors A N+1 and B N _{+ 1} respectively correspond to the carrier color signal and color burst signal of the color video signal corresponding to the n+1 scanning line.
If the polar coordinates of are (γ, φ) and (ι, 3π/4), then the color video signal corresponding to the n-th scanning line output from the 1H delay circuit 1 and supplied to the addition circuit 2 and subtraction circuit 3. The polar coordinates of the vectors A _N and B _N corresponding to the carrier color signal and color burst signal, respectively, are (γ, φ) and (ι, 3π/4). As a result, the vector C corresponding to the signal obtained by adding and combining the carrier color signal and the output of the 1H delay circuit 1, and the vector D corresponding to the signal obtained by subtracting the output of the 1H delay circuit 1 from the carrier color signal are As shown in FIG. 6, in the adding circuit 2, one of the carrier color signals is
The _EV component is canceled and only the _EV component is output, and in the subtraction circuit 3, the _EV component of the carrier color signal is canceled and only the _EV component is output. The outputs of the addition circuit 2 and the subtraction circuit 3 are supplied to the BY demodulator 5 and the RY demodulator 6 to demodulate the color difference signals BY and RY.

In a video playback device that performs color demodulation using the conventional color demodulation circuit as described above, if it is desired to change the hue according to the user's preference, a separate circuit with a complicated configuration for processing color difference signals is required, for example. I didn't like it.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color demodulation circuit for a video reproducing device that can change the hue according to the user's preference and has a simple configuration.

The color demodulation circuit of the video reproducing apparatus according to the present invention includes the output of the first signal synthesizing means for adding and synthesizing the input and output of the signal delaying means for delaying the carrier color signal and the color burst signal by a predetermined time, and the input and output of the signal delaying means. The circuit is configured to demodulate two color difference signals respectively included in the output of a second signal synthesis means for synthesizing signals according to the difference between the outputs, and the circuit demodulates the output of the signal delay means for a time corresponding to a command. The configuration includes variable delay means for delaying the signal.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.

In Fig. 1, 1H delay circuit 1, adder circuit 2,
subtraction circuit 3, burst gate 4, B-Y demodulator 5, R-Y demodulator 6, subcarrier generator 7,
90° phase shifter 8, 180° phase shifter 9, PAL switch 10
are connected in the same way as the circuit in FIG. However, in this example, the output of the 1H delay circuit 1 is supplied to the addition circuit 2 and subtraction circuit 3 via the variable delay circuit 11. The variable delay circuit 11 is configured such that the signal delay time is changed in accordance with a command issued in response to a user's operation of a hue adjustment operation button (not shown) in the operation section of the video reproducing apparatus, for example. The output of the variable delay circuit 11 is also input to the burst gate 4.

In the above configuration, as in FIG. 6, the polar coordinates of vectors A _N+1 and B _{N+1 corresponding to the carrier color signal and color burst signal of the color video signal corresponding to the n+1} scanning line are shown in FIG. 2. As shown in FIG.
The polar coordinates of vectors A _N and B _N corresponding to the carrier color signal and color burst signal of the color video signal corresponding to the main scanning line are (γ, −φ), (ι,
5π/4). Furthermore, if the signal delay time of the variable delay circuit 11 corresponds to the phase θ of the color subcarrier, it corresponds to the carrier color signal outputted from the variable delay circuit 11 and supplied to the addition circuit 2 and the subtraction circuit 3. The vector A' _N is the vector A _N rotated by θ. Therefore, the polar coordinates of vector A′ _N are (γ, −φ+θ). Similarly, the polar coordinates of the vector _B'N corresponding to the color burst signal output from the variable delay circuit 11 and supplied to the addition circuit 2 and the subtraction circuit 3 are (ι, 5π/4+θ).

On the other hand, since the subcarrier generator 7 is configured to generate a subcarrier whose phase matches the average phase of the color burst signal whose phase is inverted every 1H, the B-Y demodulator 5 and the R-Y demodulator 6
The detection subcarriers supplied to the respective detection subcarriers are obtained by rotating the detection subcarriers by θ/2 when the signal delay time of the variable delay circuit 11 is zero. Therefore, the demodulation axes at this time are the B-Y axis and the R
The (B-Y)' and (R-Y)' axes are obtained by rotating the -Y axis by θ/2. These (B-Y)′ axes,
The polar coordinates of the vectors A _N+1 and A′ _N along the (RY)′ axis are (γ, φ−θ/2) and (γ, −(φ−θ/2), respectively.
). Therefore, the same color as when the phase of the carrier color signal is rotated by -θ/2 will be reproduced, and the hue of the obtained color will change according to the command.

In the above embodiment, the variable delay circuit 11 is
Although the variable delay circuit 11 is connected as a circuit after the 1H delay circuit 1, the variable delay circuit 11 may be connected as a circuit before the 1H delay circuit 1. Further, the signal delay time by the 1H delay circuit 1 and the variable delay circuit 11 may be any time before or after 1H as long as the phase relationship shown in FIG. 6 is obtained.

Effects of the Invention As detailed above, the color demodulation circuit of the video reproducing apparatus according to the present invention includes variable delay means for delaying the output of the signal delay means for delaying the carrier color signal and the color burst signal by a time corresponding to a command. With this configuration, the phase of the carrier color signal can be rotated according to a command with a simple configuration, and the hue can be changed according to the user's preference.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a vector diagram showing signals of each part in the circuit of FIG. 1, and FIG. 3 is a block diagram showing a conventional color demodulation circuit. FIG. 4 is a vector diagram showing input PAL carrier color signals and color burst signals;
FIG. 5 is a vector diagram showing the carrier color signal and color burst signal delayed by the 1H delay circuit 1, and FIG. 6 is a vector diagram showing the signals of each part of the circuit of FIG. 1. Explanation of symbols of main parts, 1...1H delay circuit, 2
...addition circuit, 3..subtraction circuit, 11..variable delay circuit.

Claims (1)

[Claims] 1. In a video reproducing device that reproduces video using a PAL color video signal in which one of the orthogonal modulation components of the carrier color signal and the color burst signal is phase-inverted every horizontal scanning period, the carrier color signal and the color burst signal are A signal delaying means for delaying a predetermined time, a first signal synthesizing means for adding and synthesizing the input and output of the signal delaying means, and a second signal synthesizing means for synthesizing a signal according to the difference between the input and output of the signal delaying means. and a color demodulation circuit configured to demodulate two color difference signals included in each of the outputs of the first and second signal synthesis means, the color demodulation circuit comprising: A color demodulation circuit for a video reproducing device, characterized in that it is equipped with variable delay means for delaying by time.