DD291664A5 - COMPATIBLE FREQUENCY MULTIPLEX TV SYSTEM - Google Patents

Abstract

In order to provide an improved PAL-compatible television system with reduced cross-talk between luminance and color spectrums which pasces into the existing terrestrial channels, it is proposed to split the luminance signal spectrum into a low-frequency component Y1 and a high-frequency component Y2 on the transmitter side and split the high-frequency component aufzumodulieren a carrier. This modulation takes place in such a way that the spectrum of the resulting modulation signal Y * 2 in the three-dimensional PAL spectrum comes to rest within the prescribed channel width in a spectral space practically unoccupied by useful signal spectra. The modulation signal Y * 2 is transmitted together with the low-frequency component Y1 of the luminance signal spectrum as luminance information Y in the PAL-C signal. On the reception side, in an improved television receiver, the modulation signal Y * 2 is filtered out of the received PAL-C signal and demodulated. The resulting signal corresponding to the high-frequency component Y2 of the luminance signal spectrum is added to the low-frequency component Y1 of the luminance signal spectrum separated from the received PAL-C signal. A conventional PAL receiver utilizes only the low-frequency component Y1 of the luminance signal without being disturbed by the co-transmitted modulation signal Y * 2. The invention is applicable to television receivers with 4: 3 aspect ratio and expanded 16: 9 aspect ratio. enlarged picture aspect ratio; Spectrum splitting; three-dimensional spectrum; Farbtraeger additional modulation; spectrally unoccupied space}

Description

For this 6 pages drawings

Field of application of the invention

The invention relates to a PAL-compatible frequency division multiplex television system.

Characteristic of the known state of the art

Such a television system is known from SMPTE Journal, October 1984, pp. 823-929, as well as from US Pat. Nos. 4,745,460 and 4,662,072. For compatible enhancement of a frequency division multiplex television system, e.g. B. a PAL system, in the sense of a Reduzic; It is well known (BBC Research Report BBC RD1981 / 11, "An Extended PAL System for High Quality Television") that the luminance signal spectrum into a low-frequency component Y ₁ and a high-frequency component are cov- ered by luminance spectra in color spectra Y ₃ and transmit the high-frequency component Y ₂ above the transmission spectrum (5 or 5.5 MHz) of a terrestrial channel Because of the given terrestrial channel spacing of eg 7 or 8 MHz, such a transmission is only in satellite channels with a bandwidth This satellite signal can also be played back compatible on a conventional PAL receiver, but this evaluates only the low-frequency portion Yi of the luminance spectrum, however, since in conventional terrestrial PAL reception due to the usual non-application of Comb filtering anyway only the luminance spectrum is evaluated to about 3.5MHz, is the agony Loss of data at the compatible reception negligible. It is also known from the abovementioned documents to achieve a higher resolution in the luminance signal with unchanged channel bandwidth of the conventional television system (4.2 MHz in the case of the NTSC system) luminance signal components above the video band boundary (eg 4.2 MHz to 6 MHz). in the so-called 'Fukinuki' hole. This is understood in frequency division multiplex systems such as the NTSC and the PAL television system vacant or not effectively used spectral spaces that can be exploited for the transmission of additional information.

For this purpose, the high-frequency luminance signal component (4.2 MHz to 6 MHz), e.g. 1.8 MHz) and the resulting modulation signal is transmitted together with the low-frequency luminance signal component from 0 to 4.2 MHz as luminance information. Since frequency modulation of the high-frequency luminance signal component lying outside the video tape boundary takes place within the limits of the conventional video tape as a result of the modulation, the channel bandwidth is not exceeded. The incorporation of the modulation signal in the occupied by spectrums of the low-frequency luminance signal component and the color signal conventional video tape is virtually trouble-free possible because of the Fukinuki hole.

On the reception side, the modulation signal is filtered out, demodulated and added in the original position of 4.2 to 6 MHz to the low-frequency luminance signal. However, this increase in resolution does not avoid crosstalk of the luminous signal into the color signal (crosscolour), neither in a conventional color television receiver nor in a color television receiver designed to receive the high frequency luminance signal component of 4.2 MHz to 6 MHz.

Object of the invention

The aim of the invention is to avoid disadvantages in the prior art.

Explanation of the essence of the invention

The invention has the object of developing a compatible frequency multiplex television system of the type mentioned in such a way that the crosstalk of luminance signal components is avoided in the color signal without changing the conventional Farbfernsehnorm.

According to the invention, the object is achieved in that the low-frequency component of the luminance signal spectrum up to the evaluation limit (3.5 MHz in the PAL system) of conventional color television receivers, and that the high-frequency component of the luminance signal spectrum from the Auswertegreze to the band limit of the television system (eg, 5MHz on the PAL system) is enough.

According to another embodiment, the television system is characterized in that before the transmission-side modulation of the high-frequency component of the luminance signal spectrum is converted into a low-frequency position, and that the receiving side after the demodulation of the modulation signal, a conversion of the resulting signal is carried out in the original frequency position.

Another feature is that the receiving side, the modulation signal is filtered by vertical-temporal filtering of the received color television signal. The color television signal is high pass or bandpass filtered prior to vertical temporal filtering.

According to another feature, the phase position of the modulation signal always corresponds to the phase position of the color difference signal BY. The level of the modulation signal Y * ₂ is lowered in the transmitter and raised accordingly in the receiver.

It is advantageous dn2 the high frequency component is reacted with an additional carrier with a frequency (η * + 1 2) / 2 times the value of the line rate in the modulated or demodulated. The number η has the value 256.

embodiments

The invention will be explained in more detail with reference to exemplary embodiments. It shows

Fig. 1: a three-dimensional representation of the PAL spectrum;

2 shows a block diagram of the transmitting side of an embodiment of the television system according to the invention; Fig. 3: frequency spectra of luminance and color signals at different points in the block diagram of Fig. 2; 4 shows a block diagram of the receiving side of an embodiment of the television system according to the invention;

5 shows the characteristic of a vertical-temporal filtering of the color signal in the dome block diagram of FIG. 4 with additional signal spectral spaces for a first exemplary embodiment;

FIG. 6 shows a characteristic for the vertical-temporal filtering of the modulation signal Y * 2 in the block diagram of FIG. 4; FIG.

7 shows the characteristic of a vertical temporal filtering of the color signal in the block diagram of FIG. 4 with additional signal spectral spaces for a second exemplary embodiment.

In the case of the three-dimensional representation of the PAL spectrum according to FIG. 1, the following meaning is assigned to the axes f _x , f _y and f marked there:

f _x : Resolution in horizontal direction with band limit 5MHz

f _v : Resolution in the vertical direction with 288 periods per image height

f,: resolution in time direction with 25Hz, due to 25 frames / s and the interlaced.

The boundaries shown in FIG. 1 with a solid line define that spa-temporal space in which (with static image content) no alias components (superimposed spectra) occur. It is essential here that the color difference signals U and V lie exclusively in the first and third quadrants of a coordinate system which is formed by the axes \ " ⁿ df _t for values of the color subcarrier frequency of f _x = ± 4.43 MHz Coordinate systems are essentially devoid of U and V components apart from marginal crosstalk effects This free space has been described in detail by Fukinuki in the SEMPTE Journal, October 1984, pages 923-929.

According to the invention, this so-called Fukinuki hole is used to transmit the high-frequency portion of the luminance signal spectrum there. As can be seen from Fig. 1, is avoided by the transmission of the high-frequency luminance spectra in the second and fourth quadrant of the coordinate system mentioned that these higher-frequency luminance spectra above 3.5 MHz in the color difference spectra of the U and V Komponen.iten Crosstalk in the first and third quadrant. '.

In Fig. 2 is shown in principle, as the above-described principle of the invention circuitry can be implemented on the transmission side. The color value signals red (R), green (G) and blue (B) are converted in a Matrizierstufe 20 in the color difference signals RY and BY and in the luminance signal Y (Fig. 3 a). The color difference signals RY, BY are low-pass filtered in low-pass filters 21 and 22 with a cut-off frequency of 1.3MHz and then modulated in a quadrature modulator 23 to a color carrier F, _c of 4.43 MHz. The resulting, carried color signal C is shown in Fig. 3b, wherein the color carrier f _u is shown in phantom.

From the luminance signal Y in accordance with FIG. 3a, the low-frequency component Yι is filtered out with the aid of a low-pass filter 241 having a cutoff frequency of 3.5 MHz and fed both to a first adder stage 26 and to a subtractor stage 243. The second input of the subtracting stage 243 is acted upon by the Le ychtdichtesignal Y delayed by a delay t in a LaufzeitschaUung 242, so that at the output of the subtractor 243 of the high-frequency component Y _{2 of} the luminance signal Y is available. The proportions Y ₁ and Y ₂ are shown spectrally in FIG. 3 c.

The high-frequency component Y ₂ is converted into a deep free-pass with the aid of a mixer 244, which is supplied with a mixer frequency of 6/5 f, _c . ! Position implemented, as shown in Figure 3d, share Y ' ₂ can be seen. The high-frequency component Y ' ₂ produced as a mirror image of the mixer frequency during the mixing is suppressed via the downstream low-pass filter 245 with a limiting frequency of 2 MHz.

The specified mixer frequency of 6/5 f _tc is exemplary and represents the lowest possible value. For example, another possible mixer frequency would be 7/8 f, _c .

The high-frequency, right flank of the high-frequency Antuüs Y ₂ is in the mixture due to the occurring reflection of the proportion Y ₂ to the low-frequency edge of the proportion Y ' _2nd This edge should preferably be brought as close as possible to the frequency OHz by a suitable choice of the mixer frequency. In the subsequent modulation of the proportion Y ' ₂ in the amplitude modulation stage 247 with a field by Teilbüd 180 ° in phase switched color carrier f _K is due to the re-mirroring the low-frequency edge of the share Y' ₂ again to the high-frequency edge of the interesting lower sideband the resulting modulation signal Y * ₂ . The upper sideband of the resulting modulation signal Y * ₂ shown by dashed lines in FIG. 3e is only partially suppressed with the aid of a low-pass filter 25 with a cutoff frequency of 5 MHz.

In order to generate the chrominance carrier f, _c switched from field to field by 180 ° in phase, the carrier frequency f, _c and the vertical synchronization pulse V are supplied to a phase switch 246. Since without further measures a conventional PAL receiver would detect the modulation signal Y * ₂ because of its modulation with the color carrier f _K as a color signal with falsified color, the modulation stage 247 supplied color carrier except the already mentioned teilbildsoquentiellen phase switching by 180 ° to obtain a certain phase , Namely, the phase position 90 ° corresponding to the axis of the color difference signal RY or 07-180 ° corresponding to the axis of the color difference signal BY is alternatively selected in each line. In the case of the latter alternative, the color carrier f, _{c is switched} from line to line by 180 ° in the phase, to which the phase switch 246, the horizontal sync pulse H is supplied.

Due to the Teilbildsequenzielle switching the phase de. ¹ ! Color carrier f _K by 180 °, the spectrum of the modulation signal Y * 2 is transposed into the above-mentioned Fukinuki hole.

The filtered modulation signal Υ * ₂ is combined in a first adder 26 with the low-frequency component Yi and the resulting Leuchtdichto signal is in a second adder 27 with the color signal C to the resulting PAL-C (compatible) CVBS signal according to r j. 3o combined. This signal can then be fed to a conventional terrestrial television transmitter for terrestrial transmission. This terrestrial radiated signal can be processed by a conventional PAL receiver, wherein only the low-frequency component Y _{1 of} the luminance signal spectrum is evaluated. However, as already explained, this is not a disadvantage, since notch filters are used in the standard PAL transmission in the transmitter-side coder and the receiver-side decoder, which limit the luminance signal to about 3.5 MHz. An advantage of the compatible PAL reception, however, is that a crosstalk of luminance spectra in color spectra and vice versa is largely avoided because the higher-frequency components of the luminance signal are not transmitted in accordance with the PAL standard.

A receiver which also evaluates the carrier-transmitted high-frequency component of the luminance signal spectrum, ie, the modulation signal Υ * ₂ and thereby provides a higher luminance resolution, is explained in the block diagram of FIG.

From the incoming PAL-C-FBAS signal, the low-frequency component Yi is filtered out via a low-pass filter 48 having a cutoff frequency of 3.5 MHz and fed to a first input of a first adder 47, which in a manner to be described in more detail the high-frequency component Y ₂ receives at its second input and the low-frequency component Y) added to form the original luminance signal Y.

To obtain the high-frequency component Y ₂ and the color difference signals RY and BY, the incoming PAL-C-CVBS signal is further supplied to a band-pass filter 41 having a lower limit frequency of 3.5 MHz and an upper limit frequency of 5 MHz. A downstream field comb filter, comprising a 312-line delay 42, a subtractor 421 and a second adder 422, provides the color signal C at the output of the subtractor 421 and the modulation signal Y ^# ₂ at the output of the second adder 422.

The associated filter characteristics are illustrated in Figures 5 and β, which show the filtering in the vertical temporal region (axes f _y and f,) with respect to the color signal C and the modulation signal Y * ₂ . The areas hatched in FIGS. 5 and 6 are the blocking areas, while the remaining, non-hatched areas represent the pass areas. As can be seen from a comparison of FIGS. 5 and 6, in the case of the filter characteristics shown there, the blocking and passage regions are formed exactly complementary.

On the mode of action of vertical-temporal filtering:

With the assumed phase position for the components C and Y * ₂ in the PAL standard, a phase inversion of the color vectors and a phase fidelity of the luminance vectors result after every 312 lines. In the addition (second adder 422) and subtraction (subtractor 421) of the undelayed and delayed by 312 lines components, the color component C and the luminance component Yj on. This mutual cancellation correspond to the illustrations in FIGS. 5 and 6.

From the vertically-temporally filtered color component C, the color difference signals RY and BY are obtained in a conventional manner by demodulation in a first demodulation stage 431, which is supplied to the color carrier f _K. The luminance component at the output of the second adder 422 represents the geträgerto high-frequency luminance signal Y * ₂ , which is demodulated in a second demodulation stage 432. For this purpose, the second demodulation stage 432 in the same manner as the transmission-side modulation stage 247 of a phase switch 433 a Teilbildsequenziell -180 ° in the phase alternating color carrier f, _c supplied, which is not switched according to the selected phase of the color carrier or not from line to line 180 ° is switched. Accordingly, the phase switch 433 is supplied with the color carrier f, _c , the vertical synchronizing pulse V and the horizontal synchronizing pulse H. The demodulated signal at the output of the demodulation stage 432 is filtered for screening unwanted demodulation products in a low-pass filter 44 with a cutoff frequency of 2MHz, whereupon the resulting, in its frequency position offset, high-frequency luminance component Y ' ₂ a mixer 45 is supplied, which converts this proportion into the original , transported back in Fig. 3c frequency position shown. For this purpose, a mixing frequency 6/5 f, _{0 is} supplied to the mixer, as was correspondingly the case at the transmitting end Mischsiufo 244 the case. Alternatively, as in the transmitting side mixing stage 244, the receiving side mixing stage 45 is supplied with a mixing frequency of 7/8 f, _c .

The high-frequency component Y2 transported back into its correct frequency position is screened via a bandpass filter 46 with a lower limit frequency of 3.5 MHz and an upper limit frequency of 5 MHz and then fed to the first adder 47. The exact spectral position of the modulation signal Y * ₂ in FIGS. 5, 6 and 7 depends on the phase position of the color carrier f, _c and the mixing frequency. From a number of different possibilities, two are shown in Figs. 5 and 6, respectively. For example, with a mixing frequency of 7/8 f, _c and modulation with the phase Lafo + V in the first field and -V in the second field, the spectra of Y * j are 72 periods / image height and -20.3Hz and -216 periods / Picture height and 4.7Hz. At a mixing frequency of 6 / 5f _K and modulation with the phase angle + V in the first field and -V in the second field, the spectra are 288 periods / image height and -20.3Hz and at 0 periods / image height and 4.7 Hz.

In the second embodiment, the crosstalk from the luminance to the color is further reduced. For this purpose, the phase position corresponding to the axis of the color difference signal BY is selected in each line. The phase of the color carrier f, _c supplied to the phase switch 246 is set so as to correspond to the standard phase of the BY vector in each line. The horizontal sync pulse H no longer needs to be supplied.

As a result of the partial image sequential switching of the phase of the color carrier f _K by 180 °, the spectrum of the modulation signal Y * _{2 is} transported into the mentioned Fukinuki hole as in the first exemplary embodiment, but becomes more advantageous by a larger distance from the spectra of the U and V components The associated f _y -f, spectral space is shown in Fig. 7. The hatched area is the stop area for the chroma signal C. The modulation signal Y » ₂ and the U and V components are separated by a digital filter with three or more coefficients.

In the receiver for the second embodiment, the phase switch 433 is supplied with a color carrier corresponding to that of the transmitter, and the horizontal synchronizing pulse H is no longer required in the phase switch 433.

Due to the in-phase nature of the color carrier f _K with the color difference signal BY for the modulation / demodulation of the signal Y * 2, the positions of Y * _{2 shown} in FIG. 7 result at ± 144 periods / image height and at the temporal frequencies of + 17.2 Hz and at -7.8Hz.

For compatibility with before! In the case of receivers, it is advantageous to lower the level of the modulation signal Y ^# j in the transmitter and to raise it accordingly in the receiver. The inventive method offers the following advantages;

Both the compatible PAL reception and the improved PAL reception are largely free of cross color interference;

- Even the high-frequency component Y _{2 of} the luminance signal is free of crosstalk from the original luminance signal, since the latter was limited at 3.5 MHz;

the improved PAL receiver shows a full resolution of the luminance signal;

- The device implementation on both the transmitting and on the receiver side is relatively simple.

Claims (8)

Compatible frequency multiplex television system in which, on the transmitting side, the luminance signal spectrum is split into a low-frequency component and a high-frequency antilock and modulated on a carrier in such a way that the spectrum of the resulting modulation signal in the three-dimensional color television signal spectrum is virtually unoccupied by useful signal spectra within spectral space the predetermined channel bandwidth comes to lie, wherein the modulation signal is transgressed together with the tiaffrequenten portion of the luminance signal spectrum as luminance information in the color television signal and at the receiving end, the modulation signal from the received color television signal is filtered out and demodulated and the resulting, the high-frequency component of the Luminance signal spectrum corresponding signal from the received color television signal from the received color television signal separated low-frequency component of the luminance signal spectrum s, characterized in that the low-frequency component (Yi) of the luminance signal spectrum reaches up to the evaluation limit (3.5 ¹ MHz in the PAL system) of conventional color television receivers, and that the high-frequency component (Y2) of the luminance signal spectrum from the evaluation limit to the band limit of the television system (eg MHz in the PAL system) is sufficient. 2. Television system according to claim 1, characterized in that before the transmission-side modulation of the high-frequency component (Y ₂ ) of the luminance signal spectrum is converted into a low-frequency position, and that the receiving side after the demodulation of the modulation signal (Y * 2) an implementation of resulting signal is in the original frequency position. 3. Television system according to claims 1 or 2, characterized in that the receiving side, the modulation signal (Y * ₂ ) is filtered out by vertical-temporal Filtorung from the received color television signal. 4. Television system according to claim 3, characterized in that the color television signal before the vertical-temporal filtering hochpaß- or bandpass filter is'. 5. Television system according to claims 1 to 4, characterized in that the phase position of the modulation signal (Y * ^) always corresponds to the phase position of the color difference signal B-Y. 6. Television system according to claims 1 to 5, characterized in that the level of the modulation signal (Y * ₂ ) is lowered in the transmitter and raised accordingly in the receiver. 7. Television system according to one or more of claims 1 to 4 and 6, characterized in that the high-frequency component (Y ₂ ) with an additional carrier having a frequency which has the (2 * η + 1) / 2 times the line frequency, is modulated or demodulated. 8. Television system according to claim 7, characterized in that the number has the value 256.