JPH02292993A - Video signal format conversion circuit - Google Patents

Abstract

PURPOSE:To prevent the spread of colors by inhibiting the pass of a band component near the frequency of the color signal component contained in a luminance signal when a color video signal of an NTSC system is converted into another one of a PAL system in terms of the format. CONSTITUTION:An NTSC color video signal (a) is supplied directly to a subtractor 2 and an adder 3 via an input terminal IN as well as to a 1H delay circuit 1. At the same time, the signal (a) is supplied to a switch control signal generating circuit 9 of a digital phase shifter 40. An adder 42 produces an NTSC/PAL system conversion signal (c), and this signal (c) is supplied to a multiplier 4. The multiplier 4 produces a color signal component (d) whose frequency is converted into a component frequency corresponding to a color video signal of a PAL system. A luminance signal component produced by the adder 3 is supplied to a BEF 52 through a delay circuit 51 to inhibit the pass of a band component near the frequency of a chroma signal contained in a luminance signal. Then the luminance signal component is synthesized with a color signal component (d) via an adder 10.

Description

TECHNICAL FIELD The present invention relates to a signal format conversion circuit for video signals.

Background Art A color video signal based on the NTSC system (hereinafter referred to as NTSC)
(referred to as a color video signal), the number of scanning lines is 5.
The field frequency is 60 Hz, and the color subcarrier frequency is 3.58 MHz. In addition, in a color video signal based on the PAL system (hereinafter referred to as a PAL color video signal), the number of scanning lines is 62.
5, the field frequency is 50 Hz, and the color subcarrier frequency is 4.43 MHz.

In order to be able to obtain color images even when playing a disc on which NTSC color video signals are recorded in a PAL video reproducing device such as a television receiver that reproduces images using PAL color video signals,
A format conversion circuit is used to pseudo-convert an NTSC color video signal into a PAL color video signal.

A conventional example of this format conversion circuit is shown in FIG.

In FIG. 4, an NTSC color video signal a read from a disk is directly supplied to a subtracter 2 and an adder 3 via an input terminal IN, and is also supplied to an IH delay circuit 1 for a period of IH (H is a horizontal scanning period). After being delayed, it is supplied to a subtracter 2 and an adder 3. In the subtracter 2, the luminance signal component is canceled and only the color signal component is output.
In the adder 3, the color signal component is canceled and only the luminance signal component is output. The color signal component output from the subtracter 2 is supplied to a multiplier 4 and multiplied by the output of an oscillator 5.

The oscillation frequency of the oscillator 5 is equal to the difference between the frequency of the color subcarrier in the PAL color video signal (4.43MHz) and the frequency of the color subcarrier in the NTSC color video signal (3.58MHz), that is, 8
The frequency is 54kHz. Therefore, in the multiplier 4, a signal obtained by converting the frequency of the color signal component from the subtracter 2 from 3.58 MHz to 4.43 MHz is formed.

The 4.43 MHz color signal component output from the multiplier 4 is supplied to the phase shifter 7.8 and the fixed contact B1 of the changeover switch SW via the band pass filter 6 whose passband center frequency is 4.43 MHz. be done.

The phase shifter 7 is configured to shift the phase of the supplied signal by +45°. Additionally, the phase shifter 8 converts the supplied signal to -
The phase shifter 7 is configured to shift the phase by 45".
．． The output of 8 is the fixed contact A1 and C of the changeover switch SW.
1.

Further, the fixed contact D1 of the changeover switch SW is grounded.

The output of the switching control signal generating circuit 9 is supplied to the control input terminal of the switching switch SW. For example, the switching control signal generation circuit 9 uses a horizontal synchronizing signal in the NTSC color video signal a to detect a period T1 in which a color burst exists in each horizontal scanning period and a period other than this period T1 in which a video information signal exists. During period T1, movable contact E1 alternately contacts fixed contacts AI and C1 every IH, and during period T2, movable contact E. The structure is such that a switching control signal is generated to control the fixed contacts B1 and D1 to alternately contact each other.

The signal derived to the movable contact E1 of the changeover switch SW is
The signal is supplied to the adder 10 and combined with the luminance signal component output from the adder 3 to form a color video signal. The output of this adder 10 is sent to PA via the output terminal OUT.
The data is sent to an L-scheme video playback device (not shown).

In the above configuration, the NTSC as shown in FIG. 5(A)
When the color video signal a is supplied to the input terminal IN, the movable contact E1 of the changeover switch SW receives the color signal component whose frequency has been converted to 4.43MHz by +4 during the period T1.
The signal obtained by shifting the phase by 5'' and the color signal component are -45
A signal obtained by shifting the phase by .degree. is output alternately every IH, and during period T2, the color signal component and a signal with zero amplitude are alternately output every IH. Therefore, the color signal component d output from the movable contact E1 of the changeover switch SW
becomes a signal as shown in FIG. 5(B).

This color signal component d is supplied to the adder 10 and combined with the luminance signal component, so that the color video signal b output from the adder 10 becomes as shown in FIG. 5(C). In this way, a pseudo PAL color video signal can be obtained.

By the way, the band and energy distribution of the NTSC color video signal are shown in Figures 6 (A) and 7, and the band of the luminance signal is 4 in general broadcasting.
．． 2 MHz, but some recording media such as video discs have even higher resolution, that is, wider bandwidth. Therefore, in the conventional signal format conversion circuit, the color subcarrier is converted from 3.58 MHz to 4.4 MHz.
When converting to 3 MHz, the interleave relationship between the luminance signal and the color subcarrier is broken, and there is a problem that color blur occurs in a color image obtained by a PAL video reproducing device.

Summary of the Invention The present invention has been made in view of the above points, and includes:
It is an object of the present invention to provide a signal format conversion circuit for a video signal that can obtain a good color image without color bleeding even when converting the signal format.

In the signal format conversion circuit according to the present invention, N
The signal format is converted by separating the TSC color video signal into a color signal component and a luminance signal component, converting the frequency of the color signal component to the corresponding component frequency in the PAL color video signal, and then combining it with the luminance signal component. In this case, the configuration is provided with means for blocking passage of band components in the vicinity of the component frequencies in the luminance signal.

Example Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 1, an IH delay circuit 1, a subtracter 2. Adder 3
, multiplier 4 and bandpass filter 6 are connected in the same way as in the circuit of FIG. However, in this example, the multiplier 4 is supplied with the output of the bandpass filter 41. The band pass filter 41 is configured so that the center frequency is equal to 854 kHz. This bandpass filter 41 is supplied with the output of a multiplier 42 . The multiplier 42 is supplied with the output of the digital phase shifter 4o and the output of the oscillator 43. The oscillator 43 is
It is configured to generate a reference signal r2 having the same frequency as the frequency of the color subcarrier of the video signal according to the NTSC system.

The digital phase shifter 40 is supplied with the output of an oscillator 44 . The oscillator 44 is configured to generate a reference signal r1 having a frequency four times that of the color subcarrier of a PAL video signal. In the digital phase shifter 40, the reference signal r1 is frequency-divided by a frequency divider 45 to 1/4, and is directly supplied to the clock input terminal of a D-type flip-flop 47, and is passed through an inverter 48 to the D-type flip-flop 47.
The clock input terminal of the flip-flop 46 is supplied. The output of the frequency divider 45 is supplied to the D input terminal of a D-type flip-flop 46 and also to the fixed contact C1 of the changeover switch SW.

Further, the O output of the D-type flip-flop 46 is supplied to the D input terminal of the D-type flip-flop 47 and also to the fixed contact B1 of the changeover switch SW. Also,
The ○ output of the D-type flip-flop 47 is switched to the selector switch s.
It is supplied to the fixed contact A1 of w. Further, the fixed contact D1 of the changeover switch sw is grounded. The output of the switching control signal generating circuit 9 is supplied to the switching control input terminal of the switching switch sw as in the case of the circuit shown in FIG.

Further, the color signal component output from the bandpass filter 6 is supplied to one input terminal of the adder 10 via the gain control circuit 5o. The gain control circuit 10 includes a means for detecting a period T1 in which a color burst signal exists, for example, by the output of the switching control signal generation circuit 9, and generating a gain reduction command signal, and a means for reducing the gain in accordance with this gain reduction command signal. It consists of a variable gain amplifier. The other input terminal of the adder 10 is supplied with the luminance signal component which is the output of the adder 3 through a band elimination filter 52 after being delayed by a time TD by a delay circuit 51 . The band elimination filter 52 acts to block the passage of a band component near the color subcarrier frequency of 4.43 MHz in the PAL system with respect to the luminance signal component.

As a result, the luminance signal component from which the band component around 4.43 MHz has been removed and the frequency-converted color signal component are added and combined in the adder 10, and this combined output is converted into a color video signal whose signal format has been converted. Derived as a signal. Note that the delay time TD in the delay circuit 51 is NT
It is set to a value equal to the sum of the time corresponding to 1/2 of the difference between the IH in the SC system and the IH in the PAL system and the delay time ΔD in the bandpass filter 6 (=250 ns+ΔD).

In the above configuration, the oscillator 44 outputs a reference signal r1 having a frequency four times that of the color subcarrier of the PAL video signal as shown in FIG. 2(A). Then, the frequency divider 4 divides this reference signal r1 into 1/4.
The output of 5 is as shown in FIG. 2(D). The output of this frequency divider 45 is supplied to the D input terminal of the D-type flip-flop 46 as a phase-shifted signal fsc3 having the same frequency as the color subcarrier in the PAL system, and is also supplied to the fixed contact C1 of the changeover switch SW. Ru.

Since the reference signal r1 is supplied to the clock input terminal of the D-type flip-flop 46 via the inverter 48, the phase shift signal f sag is stored and held in the D-type flip-flop 46 by the falling edge of the reference signal r1. , the O output of the D-type flip-flop 46 is as shown in FIG. 2(C).
The signal obtained by advancing the phase of the phase shift signal fsc3 by 45° is obtained as shown in FIG. This D type flip-flop 4
The Q output of No. 6 is supplied as a phase-shifted signal fsc2 to the D input terminal of the D-type flip-flop 47, and also to the fixed contact B1 of the changeover switch SW.

Since the reference signal "1" is directly supplied to the clock input terminal of the D-type flip-flop 47, the phase shift signal f_sex is stored and held in the D-type flip-flop 47 by the rising edge of the reference signal r1, and the D-type flip-flop 47 The Q output of step 47 is a phase-shifted signal f as shown in FIG. 2(B).
The signal is obtained by advancing the phase of sc2 by 45 degrees. The 0 output of this D-type flip-flop 47 is the phase shift signal f
It is supplied as sc+ to the fixed contact A1 of the changeover switch SW.

Here, the NTSC color video signal a as shown in FIG. 3(A) is input to the input terminal! When supplied to E!N, the movable contact E! of the changeover switch SW is controlled by the changeover control signal generation circuit 9. are fixed contacts AI, CI, Bl * DI
as shown in FIGS. 3(B) to 3(E). That is, the period T1 in which the color burst exists
, the movable contact E1 alternately contacts the fixed contacts A1 and C1 every IH, and the period T2 in which the video information signal exists
In this case, the movable contact E1 alternately contacts the fixed contacts B1 and DI every IH. Then, in period T1, the phase-shifted signals fsc+ and fsc3 are alternately led out to the movable contact E1 every IH, and in the period T2, the phase-shifted signal fsc2 and the ground level signal are alternately led out to the movable contact E1 every IH. derived. The signal derived from the movable contact E1 is supplied to the multiplier 42 and multiplied by the 3.58 MHz reference signal ``2. 2 i.e. 854kHz
A conversion signal as shown in FIG. 3(F) in which the phase alternately changes by +45° and -45° every IH during period T1, and the amplitude becomes zero every IH during period T2. C is formed.

The conversion signal C of 854kHz is passed through the bandpass filter 4.
1 to the multiplier 4. Then, in the multiplier 4, a 4.43 MHz signal whose frequency differs by 854 kHz from the color signal component according to the NTSC system, the phase of the color burst signal changes alternately by +451 and -456 every IH, and the video information section The amplitude of IH
The color signal component d, as shown in FIG. 3 (G), becomes zero every other time.
is formed. This color signal component d is fed to the gain control circuit 50 via the bandpass filter 6, and the level of the color burst is lowered by a predetermined value.

? The color signal e as shown in FIG. The band component is added and combined with the removed luminance signal component to form a color video signal b as shown in FIG. 3(1).

In this way, the NTSC car video signal can be converted into PAL.
In order to convert to a car video signal, it is necessary to convert the color subcarrier frequency from 3.58 MHz to 4.43 MHz and at the same time manipulate the phase of the color burst line by line. By using the phase shift method, the fourth
Analog phase shifter 6 used in the conventional example shown in the figure
．． 7 is not necessary, so a good color image can be obtained without being affected by variations in the values of the constituent elements of the analog phase shifter or temperature characteristics.

In addition, after removing the band component near 4.43 MHz of the luminance signal component in the band eliminator filter 52, it is combined with the frequency-converted color signal component to create a pseudo PA.
By obtaining an L color video signal, even if the interleaving relationship between the luminance signal and the color subcarrier is disrupted due to frequency conversion, there is no luminance signal component around 4.43MHz, so even if the signal format is converted, the color will not change. This means that a good color image without bleeding can be obtained.

Effects of the Invention As explained above, the signal format conversion circuit according to the present invention separates an NTSC color video signal into a color signal component and a luminance signal component, and converts the frequency of the color signal component into the corresponding component in the PAL color video signal. When the signal format is converted by converting it into a frequency and then combining it with the luminance signal component, the structure is configured to block the passage of band components in the vicinity of the component frequency in the luminance signal, so that the signal format conversion is performed. Even if the interleaving relationship between the luminance signal and the color subcarrier is disrupted, a good color image without color bleeding can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams showing the operation of each part of the circuit in FIG. 1, and FIG. 4 is a block diagram showing a conventional format conversion circuit. ,
Figure 5 is a waveform diagram showing the action of each part of the circuit in Figure 4;
This figure shows the band of the video signal, and FIG. 7 shows the energy distribution of the NTSC color video signal. Explanation of symbols of main parts 40... Digital phase shifter 42... Multiplier 43, 44... Oscillator 50... Gain control circuit 51... ...Delay circuit 52...Band elimination filter applicant
Pioneer Corporation

Claims (2)

[Claims] (1) Separation means for separating a color video signal according to the NTSC system into a color signal component and a luminance signal component, and color signal component processing for converting the frequency of the color signal component into a corresponding component frequency in a color video signal according to the PAL system. and a synthesizing means for synthesizing the output of the color signal component processing means and the luminance signal component, the circuit comprising: 1. A signal format conversion circuit for a video signal, comprising a blocking means for blocking. (2) A signal format conversion circuit for a video signal according to claim 1, wherein said blocking means is a band elimination filter.