JPH04104598A - Tv system conversion device - Google Patents

Abstract

PURPOSE:To reduce the deterioration of picture quality at the time of system conversion by performing an average processing while delaying and adding a pair of color difference signals which is the output of a chroma modulation circuit respectively by one horizontal scanning line. CONSTITUTION:A chroma demodulation circuit 2 is; connected to an input terminal, and its output of a R-Y color difference signal and a B-Y color difference signal are respectively supplied to 1H delay circuits (1HDL) 3 and 4. The 1 horizontal scanning line delay circuits 3 and 4 delay input signals respectively by time corresponding to the 1 horizontal scanning line of the PAL system, and its output is respectively supplied to adders 5 and 6. In the other input end of the adders 5 and 6, the R-Y and B-Y signals are respectively supplied, and two lines are averaged by adding these. Thus, the deterioration of the picture quality at the time of system conversion can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to a T
The present invention relates to a V format conversion device, and particularly to a TV format conversion device that is characterized by the configuration of its color signal processing system.

[Conventional technology]

Currently, TV standard systems in the world include the NTSC system used in Japan, the United States, etc., the PAL system adopted in Western European countries, and the SECAM system adopted in France, the Soviet Union, Eastern European countries, etc. These TV systems differ in field frequency, number of scanning lines in the I field, and color signal modulation method. For example, in the NTSC system, the field frequency is 59.9
4Hz, the number of scanning lines in one frame is 525, and the subcarrier frequency of the color signal is quadrature two-phase modulation of 3.579545MHz, whereas in the PAL system, the field frequency is 50Hz and the number of scanning lines is 625. The subcarrier frequency of the color signal is 4.43361875M
Hz, and the color signal is modulated by inverting the polarity of one side of the color difference signal for each line.

Since each TV system is different in this way, TV receivers and VTR
It is also compatible with each TV system. If you want to play back a videotape recorded in a different TV system and watch it on your home country's TV receiver, or if you want to convert it to your home country's TV system and save it as a record, you will need a TV system conversion device.

Conventional TV format converters have often been used primarily for converting signals between broadcasting stations, such as for international relay between regions with different TV formats. Therefore, conventional TV conversion methods perform conversion in accordance with strict standards, and the equipment is large-scale and expensive. However, in recent years, with the increase in overseas travel and study abroad, and the internationalization of schools, companies, government offices, etc., interaction with countries with different TV systems has become active.
Even in ordinary households, people are watching different types of videotapes, and there are exchanges such as exchanging videotapes with foreign countries. Accordingly, video tape recorders have also been developed in which a TV conversion device is built into the video tape recorder so that video tapes of different formats can be played back and recorded. The TV conversion method is (1
) It is necessary to convert the number of horizontal scanning lines, (2) field frequency, and (3) chroma signal modulation method between TV systems.

FIG. 3 is a block diagram showing an example of a chroma signal processing system of a conventional TV format conversion device. In this diagram, input terminal 1
A chroma signal is input to the chroma demodulation circuit 2, which demodulates it into R-Y and B-Y color difference signals, which are respectively applied to low-pass filters 7.8. The low-pass filter 7.8 limits the band so that aliasing noise does not occur when the signal is digitized, and its output is given to the multiplexer (MPX) 9, where it is sampled alternately and time-division multiplexed. Ru. The color difference signals multiplexed on the time axis are converted into digital signals by the A/D converter 10 and provided to the scanning line number converter 11. Scanning line number converter 1
1 is composed of a line memory and a calculation unit, and converts the number of scanning lines by interpolating the signal line to be converted from the previous signal of one line and the current signal, and its output is used for field frequency conversion. Section 12. The field frequency converter 12 converts the field frequency by using a memory having a storage capacity of at least one field or more and controlling the timing of writing and reading from the memory.

Such a processing system for Roma signals is shown, for example, in "Digital Technology in Broadcasting" edited by Japan Broadcasting Corporation, pages 189-200.

The color difference data converted into the number of scanning lines and field frequency of the desired TV system is sent back to R-Y, B by the D/A converter 13, 14 at the time division timing of the multiplexer 9.
- Converted to an analog signal corresponding to the Y signal. These signals are then given to the chroma modulation circuit 15 to obtain the desired T.
The signal is converted to the V-scheme modulation system and outputted from the output terminal 16 as a converted chroma signal.

When converting from the PAL system to the NTSC system, the chroma demodulation circuit 2 is composed of a PAL system demodulation circuit, and the scanning line number converter 11 converts the 625 scanning lines of the PAL system into NTSC.
Convert to 525 SC format.

Also, the field frequency is to convert 59.94Hz to 50)tz, and the chroma modulation circuit 15 converts the color difference signal into N
It is configured as a modulation circuit that converts to the TSC system.

FIG. 4 is a block diagram showing an example of the chroma demodulation circuit 2 of the PAL system. In the figure, an ACC circuit 21 is connected to the input end of the chroma demodulation circuit 2 to keep the chroma signal level at a constant level. This signal is transmitted to the burst extraction circuit 22.
The extracted burst signal is applied to an automatic phase control circuit (APC) 23. The APC 23 is composed of a PLL loop consisting of a VXO 26 that changes the oscillation frequency depending on the voltage of the input signal of a phase comparator 24 and a loop filter 25, and a frequency divider 27 that divides the signal, and has a subcarrier frequency that is phase-locked to the burst signal. Outputs the signal. Also, the output of ACC26 is l horizontal scanning line (
1H) is applied to the delay circuit 28. The output of the 1H delay circuit 28 is applied to a subtracter 29 and an adder 30. Subtractor 29
．． The adder 30 outputs a RY signal and a BY signal by subtracting and adding the input signals, respectively. As mentioned above, the PAL signal has an RY signal of 18 degrees per scanning line.

Since it is inverted and modulated, the output of the subtracter 29 has R.
- Only the Y component is extracted. FIG. 5(a) is a vector diagram showing this operation. If the chroma signal vector of the first line is OF, then the chroma signal vector of the next line is OP, '.

Then, by subtracting both, the vector component O in the B-Y direction
P is canceled and the vector component OR0 in the R-Y direction
only will be taken out.

By adding the vector vector σ and the vector σ under τ′, we get R−
The vector component in the Y direction is canceled and only the vector component OB in the BY direction is extracted. The chroma signal components in the R-Y and B-Y directions extracted in this way,
The APC 23 is multiplied by the phase-locked subcarrier obtained by multiplication circuits 31 and 32 to perform synchronous detection. Then, after removing high frequency components obtained by multiplication using low-pass filters (LPF) 33 and 34, R-
The signal is output from the output terminal of the chroma demodulation circuit 2 as Y and B-Y color difference signals. Here, the B-Y component multiplier 32 has 0
(rad) subcarriers are used, and the RY acid component multiplier 31 includes a +π/2 (rad) phase shifter 35 and a +π/2 (rad) subcarrier.
The output of the 2 (rad) phase shifter 36 is alternately switched for each line by a switch 37, and multiplication is performed using subcarriers matched to the phase inversion of the RY component for each line.

In this way, the PAL chroma signal is demodulated into a color difference signal, the number of scanning lines and field frequency are converted, and the chroma modulation circuit modulates the signal into an NTSC signal.The vector of the modulated chroma signal is shown in Figure 5. However, the chroma signal of the PAL system is converted to the chroma signal of the NTSC system.

[Problem to be solved by the invention]

However, with such conventional TV format conversion devices,
Chroma signal demodulation and modulation circuits are generally constructed using analog circuits that can be realized at relatively low cost, except for high-precision TV format converters used in broadcasting stations and the like. Therefore, the stability of the circuit against component variations and temperature changes is poor, and there are problems unique to analog circuits. One of these problems is the problem caused by the demodulation accuracy of the PAL chroma demodulation circuit. That is, in PAL demodulation, R-
Phase shifter circuits 35 and 36 shift the +π/2 and −π/2 phases for demodulation of the Y signal component.
Demodulation is performed by switching subcarriers with different 0° phases for each line. However, it is difficult to make the phase difference of the phase shifters 35 and 36 completely 180 degrees, and generally a variation or drift of about ±26 occurs. Therefore, during demodulation, the demodulation angle shifts, resulting in error components entering the color difference signal. For example, the demodulation angle in the RY direction is φ as shown by the dashed line in FIG. 5(a). φ1〉φ for =90°. (φ1-φ.=Δφ.), the mapping of vector OPo' in the R-Y direction during demodulation is O
R,', and the absolute value of the vector becomes smaller than in the normal case. Therefore, the demodulated amplitude of the RY multiplied signal is l for each line.
0ROI and (OR1'1) will appear alternately,
There was a drawback that the demodulated waveform had a line flicker component as shown in Figure 6 (aJ).Also, when converting a color difference signal with such a line flicker component to an NTSC system chroma signal, it was O shown in FIG. 5(b)
The vector that should be focused on one point of P is OPo for each line.
This results in the image being divided into two vectors, OP1 and OP1, resulting in uneven hue and horizontal noise on the TV screen, which significantly impairs the image quality after conversion.

Also, when a delay error occurs in the 1H delay circuit 28, the subtracter 29. The output of the adder 30 completely R-Y, B-Y
The components are not separated, and the B-Y component is mixed into the subtracter 29 and the R-Y component is mixed into the adder 30 and demodulated. As a result, the demodulated output has a demodulated waveform having a line flicker component as shown in FIG. 6(a).

The present invention has been made to solve these conventional problems, and is intended to eliminate line flicker components when the demodulation axis shifts line by line or when delay errors occur in the 1H delay circuit during demodulation of PAL signals. It is an object of the present invention to provide a system conversion device that does not cause hue unevenness or side-scanning noise even when the signal has the following characteristics.

[Means to solve the problem]

The invention of claim 1 of the present application is a TV system converting device for converting a chroma signal of a first TV system into a chroma signal of a second TV system, the chroma signal of the first TV system being converted into a pair of color difference signals. A chroma demodulation circuit that demodulates, two averaging circuits that average signals between two lines of color difference signals output from the chroma demodulation circuit, and a pair of color difference signals obtained from each averaging circuit in the time axis direction. an A/D converter that converts the output signal of the multiplexer into a digital signal, and a scanning device that converts the number of scanning lines of the output signal of the A/D converter to the number of scanning lines of the second TV system. a field frequency converter that converts the output signal of the scanning line number converter into a field frequency of the second TV system; and a D/A converter that converts the output signal of the field frequency converter from D/A to
The color difference output obtained from the A converter and the D/A converter is
a chroma modulation circuit that modulates the chroma signal of the TV system;
It is characterized by comprising the following.

The invention according to claim 3 of the present application is a TV system converting device for converting a chroma signal of a first TV system into a chroma signal of a second TV system, which converts the chroma signal of the first TV system into a pair of color difference signals. a chroma demodulation circuit that demodulates the chroma demodulation circuit, a multiplexer that multiplexes the color difference signals of the chroma demodulation circuit in the time axis direction, and an A/D converter that converts the output signal of the multiplexer into a digital signal.
A D converter, an averaging circuit that averages the signals between two lines in the output signal of the A/D converter, and the number of scanning lines of the output signal of the averaging circuit is set to the number of scanning lines of the second TV system. a field frequency converter that converts the output signal of the scan line number converter into the field frequency of the second TV system; and a D/A converter that converts the output signal of the field frequency converter from D/A to the field frequency of the second TV system. , a chroma modulation circuit that modulates the color difference output obtained from the D/A converter into a chroma signal of the second TV system.

[Effect]

According to the invention of claim 1 of the present application having such features, each of the pair of color difference signals, which is the output of the chroma demodulation circuit, is
Averaging processing is performed by delaying and adding only the horizontal scanning line. In this way, the amplitude changes for each line are averaged, so that image quality deterioration at the time of format conversion can be reduced. Further, in the invention of claim 3 of the present application, the chroma signal converted to a digital signal via the multiplexer is delayed by one horizontal scanning line using a line memory, and is added to the original signal to perform averaging processing. ing. In this way, amplitude changes between lines are similarly averaged, and image quality deterioration during format conversion can be reduced.

[Embodiment] FIG. 1 is a block diagram showing a conversion device for converting a PAL chroma signal into an NTSC chroma signal according to a first embodiment of the present invention, and the same parts as in the conventional example described above are denoted by the same reference numerals. The detailed explanation will be omitted. In this embodiment, a chroma demodulation circuit 2 is connected to the input terminal, and its outputs, an RY color difference signal and a BY color difference signal, are respectively applied to a 1H delay circuit (1HDL) 3.4. The one horizontal scanning line delay circuits 3.4 each delay the input signal by a time corresponding to one horizontal scanning line of the PAL system, and their outputs are given to adders 5 and 6, respectively. Adders 5 and 6
The RY and B-Y signals are applied to the other input terminal of the line, respectively, and by adding these signals, the two lines are averaged.

That is, the 1H delay circuit 3 and adder 5, and the 1H delay circuit 4 and adder 6 are R-Y of the chroma demodulation circuit 2, respectively.

Averaging circuits 40 and 41 are configured to average the BY signal. This signal is applied to a low-pass filter 7.8 as in the conventional example described above, and subjected to time division multiplex conversion via a multiplexer 9. Then, the signal is converted into a digital signal by an A/D converter 10, and the scanning line number is converted by a scanning line number converter 11.

The signal is then given to the field frequency converter 12, which reads out the signal from the field memory at the timing of time division multiplex conversion by the multiplexer 9, and converts the signal to the D/A converter 13.
．． 14, by converting each into an analog signal, N
TSC method RY.

B-Y signals are obtained respectively. This signal is modulated by a chroma modulation circuit 15 and a chroma signal is output from an output terminal 16. Now, in this embodiment, as shown by the dashed line in FIG. 5(a), the demodulation axis shift occurs line by line, and the vectors of the RY components are OR.

Even in this case, the output of the adder 5 becomes (lOR61+lOR,l)/2=0R2 and is averaged as shown in FIG. 5(b). Therefore, even if the amplitudes of OR and ORI change alternately for each line as shown in Figure 6(a),
The output of the adder 5 is averaged to remove line flicker components as shown in FIG. 6(b).

In this way, in this embodiment, the 1H delay circuits 3 and 4 and the adder 5
By inserting an averaging circuit using 2 and 6 into the output side of the chroma demodulation circuit 2, line flicker components that are likely to occur during demodulation of PAL chroma signals are averaged, and NTS
Vector cracking in the chroma signal, which was easily noticeable when converted to the C format, can be removed. Therefore, it is possible to reduce hue unevenness and horizontal scanning noise in the TV system.

FIG. 2 is a block diagram showing the configuration of a second embodiment of the present invention, and the same parts as in the conventional example described above are given the same reference numerals and detailed explanations will be omitted. In this embodiment, a line memory 17 and an adder 18 are provided on the output side of the A/D converter 10. The line memory 17 delays the input signal by one horizontal scanning line, and the signal and the adder 18 constitute an averaging circuit 42 that averages the input signal. In this way, since the input signals are multiplexed in the time axis direction by the multiplexer 9, the same effect as in the first embodiment can be obtained with only one averaging circuit. Furthermore, since the line memory 17 is used, stable operation is possible compared to the delay elements 3 and 4 for one horizontal scanning line made up of analog elements.

Note that the first example shown here. In the second embodiment, averaging processing between lines is performed using a delay circuit or line memory for one horizontal scanning line and an adder 5°6.18. However, if you constantly perform averaging processing between lines, the vertical resolution will deteriorate.
This results in the disadvantage that the color fringing of the converted chroma signal increases. Therefore, a correlation detector is provided to detect the correlation between signals between lines, and when there is little correlation between lines, the averaging process is stopped and the weighting during addition is adaptively controlled, thereby increasing the vertical direction. It also becomes possible to prevent resolution deterioration.

In this embodiment, the chroma demodulation circuit 2 is explained for the PAL system, and the case where the PAL system is converted into an NTSC system TV signal is described, but the present invention also applies to conversion between other TV systems. A similar effect can be obtained. However, in the case of the NTSC system, hue unevenness, side-scanning noise, etc. are easily noticeable, and a visually effective effect can be obtained.

〔Effect of the invention〕

As described in detail above, according to the present invention, line flicker noise, which tends to occur when demodulating a chroma signal, is averaged by an averaging circuit, thereby preventing line flicker noise.

Therefore, even when the present invention is applied to a TV format conversion device for home use, it is possible to perform TV format conversion with less hue unevenness and line drawing noise with a relatively simple configuration.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the main parts of the TV system converter according to the first embodiment of the present invention, FIG. 2 is a block diagram showing the main parts of the TV system converter according to the second embodiment of the invention, and FIG. The figure is a block diagram showing the main parts of a conventional TV format conversion device.
FIG. 4 is a block diagram showing the configuration of a PAL system chroma demodulation circuit, FIG. 5 is a vector diagram during chroma demodulation, and FIG. 6 is a waveform diagram of a chroma demodulation signal. 2----- Chroma demodulation circuit, 3, 4-------
-LH delay circuit, 5, 6, 18---
−1 adder, 9−−−−−−− multiplexer,
10------A/D converter, 11-・Scanning line number conversion section, conversion section, 13.14 ・-Chroma modulation circuit, 40.41.42.. 12-・------ Field frequency change -D/A
converter, 15 17---line memory, averaging circuit. Figure 5 Patent applicant Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] (1) A TV format conversion device that converts a chroma signal of a first TV format to a chroma signal of a second TV format, the chroma demodulation circuit demodulating the chroma signal of the first TV format into a pair of color difference signals. and two averaging circuits that respectively average signals between two lines of color difference signals output from the chroma demodulation circuit, and multiplexing the paired color difference signals obtained from each of the averaging circuits in the time axis direction. an A/D converter that converts the output signal of the multiplexer into a digital signal; and a scanning line that converts the number of scanning lines of the output signal of the A/D converter to the number of scanning lines of a second TV system. a field frequency converter that converts the output signal of the scanning line number converter into a field frequency of the second TV system; and a D/A converter that converts the output signal of the field frequency converter from D/A to analog. a converter; and a color difference output obtained from the D/A converter to the second T.
A TV format conversion device comprising: a chroma modulation circuit that modulates a V format chroma signal. (2) The averaging circuit includes a 1H delay line that delays the color difference signal by one horizontal scanning line, and an adder that adds the input and output of the 1H delay line. TV format conversion device. (3) A TV format conversion device that converts a chroma signal of a first TV format to a chroma signal of a second TV format, the chroma demodulation circuit demodulating the chroma signal of the first TV format into a pair of color difference signals. a multiplexer that multiplexes the color difference signals of the chroma demodulation circuit in the time axis direction; an A/D converter that converts the output signal of the multiplexer into a digital signal; and 2 lines of the output signal of the A/D converter. an averaging circuit that averages the signals between the signals, a scanning line number converting section that converts the number of scanning lines of the output signal of the averaging circuit to the number of scanning lines of a second TV system, and the scanning line number converting section. a field frequency converter that converts the output signal of the field frequency converter into a field frequency of the second TV system; a D/A converter that converts the output signal of the field frequency converter from D/A to the field frequency of the second TV system; The obtained color difference output is
A TV format conversion device comprising: a chroma modulation circuit that modulates a V format chroma signal. (4) The averaging circuit includes a 1H line memory that delays the A/D conversion output by one horizontal scanning line, and an adder that digitally adds input and output of the 1H line memory. Item 3. The TV format conversion device according to item 3. (5) The TV format conversion device according to any one of claims 1 to 4, wherein the first TV format is a PAL format. (6) The TV format conversion device according to any one of claims 1 to 5, wherein the second TV format is an NTSC format.