KR800000581B1 - Comb filter for video processing - Google Patents

Abstract

In a system receptive to the first composite video signal which has a mominal line frequency and a luminance signal componet, a given band of frequencies & a chrominance signal component are interleaved in a portion of the signal band. this filter comprises conversion means(18,20,26,28,30), a delay apparatus(58), the first signal responding devices(46,48,68),the second signal responding device and synthesizing devices(82,84,118).

Description

Comb filter for video processing

1 is a schematic diagram of a partial block of a video disc player and a code conversion circuit according to an embodiment of the present invention.

Figures 2a-2e show band characteristics in the apparatus of Figure 1;

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to video signal processing, and more particularly, to an apparatus for code conversion of brightness and chromaticity signal components of a composite video signal from one format to another.

In US Patent No. 3,872,498 published by Dalton H. Pritchard on March 18, 1975 under the title “Color Information Conversion Device,” the color signal encoding format is described, which is characterized by a wider chromatic signal component in the form of a modulated subcarrier. Band brightness is staggered in the middle band of the signal. This type of encoded video signal, called embedded subcarrier signal, is formed by first combing at least the brightness signal component at the frequency of the region into which the chroma signal component is to be inserted. By combing this region of the brightness signal, a valley at a frequency equal to half the horizontal frequency is prepared for insertion of the combined chroma signal. Likewise, chromatic signal components can be comb-filtered in such a way as to form a valley in this signal spectrum at a frequency equal to one-half of the horizontal line frequency. The comb-shaped filtered chromaticity and brightness signal are combined to form a composite signal having the chromatic signal components interleaved in the passband of the brightness signal components.

The above-described code and signal format are particularly useful for accumulating information on video discs for the reasons mentioned above in the Prechard application. One type of video disc control device uses an embedded subcarrier format, which detects the capacity between the stylus playback device and the disc record to reconstruct the video information engraved with an emboss in the spiral groove on the record. do. In such a device, the video information is recorded in the form of geometric variations with spiral grooves on the surface of the record. The disk surface comprises a conductive material covered with a thin film of dielectric material. The metal electrode combined with the stylus regenerator forms a capacitance together with the conductive metal and the dielectric coating. Capacitive fluctuations due to geometric fluctuations of the signal display in the helical groove are detected and encoded to provide a video display output signal. John, with the name "Information Record and its Recording / Reproducing Device". K. In a U.S. Patent No. 3,842,194 issued by Clemens on October 15, 1974, a capacitive video disk device is described in detail.

In one device, it is necessary to insert a video disc player as a standard television receiver or television monitor using a standard television circuit. In another device, it is necessary to provide video signal information in a form that can be easily decoded by a standard television circuit. In order to provide such a signal, the embedded subcarrier signal information applied from the video disc player is rearranged in a signal format determined by the NTSC (International Television Standards Association). By rearranging the video signal to a standard form, signal decoding can be achieved by a standard television circuit. In practice, the embedded subcarrier signal is transformed from the embedded subcarrier signal into an NTSC-type signal by removing the chromaticity information from within the brightness signal passband and converting the signal in the form of a sideband of a relatively low frequency subcarrier at a frequency equal to 3.58 MHz that is reinserted into the brightness signal component. May be formed. The resulting signal is not in standard form according to the International Television Standards Association (NTSC), but has characteristics close to that of an NTSC type signal that can be easily decoded by a standard television receiver. The code conversion device of the embedded subcarrier signal is called a "signal conversion device". It is described in US Patent No. 3,872,497, issued March 18, 1975 by Jia Mary et al.

As described in U.S. Patent No. 3,872,497, the signal encoding transfer device transcodes the embedded subcarrier type signal into an NTSC type signal by initially forming a comb color chromatic signal from the composite embedded subcarrier signal. The comb-shaped filtered chromaticity signal component is then extracted from the composite embedded subcarrier signal to provide a comb-filtered lightness signal component that is actually independent of the chromaticity signal information. At this time, the brightness and chroma signal components are recombined, and the chroma signal component becomes a new subcarrier of about 3.58 MHz and becomes the brightness component fundamental band frequency.

The problem when comb-induced brightness components are formed by taking comb-induced chroma signal components from a synthetic embedded subcarrier signal is that the unnecessary phase shift or delay in the combined circuit through which the comb-induced chroma signal passes is not necessary. It may also cause an inaccurate phase relationship between the part and the chroma signal. If the phase relationship between these two signals is incorrect, improper removal of the chroma signal from the composite signal unnecessarily isolates the brightness signal component with chroma information therein. Phase shifts and minimum delays in circuits combined with comb-filtered chromatic signal components may be caused by device drift. If the device's delay occurs in the path of the chromatic signal drift comb filtered by about 23ns, a phase error of about 30 ° may occur. The phase error between the comb-filtered chroma signal and the composite embedded subcarrier signal can greatly reduce the attenuation of the chroma signal component from the synthesized signal component. If the brightness component fails to actually weaken the chromatic components, the shape of the dot appears in the display image that brings up the low quality screen. In order to eliminate this problem of device drift, it is necessary to use a device which takes out one of these components from the synthesized signal and flows out the comb filtered brightness and chromatic components without forming the other.

There is also a need to provide a combed light signal component with a relatively flat frequency response over the entire bandwidth. In conventional devices, light signal components having a relatively flat frequency response are difficult to form because of the manner in which signals are added and subtracted to make up these components. Brightness signal components with non-uniform frequency responses over their bandwidth may provide an unwanted video response on a television monitor. This may be indicated in the resulting television image in the form of white light as the unwanted response transitions from black to white. It is therefore necessary to provide a combed zero signal component with a relatively flat frequency response over the bandwidth of the brightness signal. It is required that these and other desirable properties must be made in a simple and economical manner suitable for mass production.

Therefore, according to the present invention, an interleaved in the bandwidth portion of an associated brightness signal component can provide a simple device that responds to a first video signal having a chroma signal component of a specific bandwidth in the form of a modulated subcarrier of a first frequency. . The apparatus can code convert the first video signal into a second video signal having a brightness signal component and a chroma signal component in the form of a subcarrier modulated at a second frequency. The device includes a device for receiving a first video signal. Since there is a device for converting the component frequency portion of the first video signal to a frequency corresponding to the sum and difference of the component frequency portion and the third frequency, a part of the converted signal has chromatic subcarriers at the frequency according to the second frequency. . The filter device is coupled to the converter and coupled to the converter for attenuating the frequency converted signal around the frequency corresponding to the sum of the first and third frequencies described above. The delay unit is also coupled to the converter, which causes a delay in the signal passing through it. Chromaticity signal components irrelevant to the brightness signal are formed from the first video signal by a second device responsive to the signal applied by the frequency converter and the delay device.

The detection device is coupled to the output of the first device to demodulate the signal applied thereto. The signals applied by the detection device and the second device are combined by the device for forming the video output signal. The video output signal is a synthesized video signal composed of brightness components and chroma subcarriers at the second frequency.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

In the apparatus of FIG. 1, the video disc player 10 having the signal pick-up arm 12 senses the signal information on the combined video disc 14. The signal processing circuit 16 receives a signal from the player 10 and applies a composite video signal to the modulator 18. The synthesized video signal applied by the processing circuit 16 has a baseband brightness component and a chromatic component interleaved in the form of a subcarrier modulated at a frequency of about 1.53 MHz. A voltage controlled generator (VCO) 20 with a 5.11 MHz nominal frequency is also coupled to modulator 18 and applies a mixed video mixed signal thereto. Modulator 18 is a single balance to balance the video input. By using a balanced modulator, the baseband video modulation component is actually removed from the modulator output signal. VCO20 is also arranged such that modulator 18 is driven with chopping mode. The chopping mode modulator needs to reduce the intermodulation product between the chromatic carrier and the VCO signal to an acceptable level. The signal provided by modulator 18 is combined via low pass filter 22. Filter 22 drives to pass the first modulated red signal provided by modulator 18 and attenuates all other signals of higher frequency. Amplifier 24 receives the signals from lowpass filter 22 and amplifies these signals. The signal applied by amplifier 24 is coupled to bandpass filter 26. Filter 26 has a passband at about 3.58 MHz center that corresponds to the location of the chroma subcarrier of the applied signal. In response to the horizontal synchronization signal provided by the video processing circuit 16, the burst gate 28 gates the burst reference signal component provided by the signal passing through the bandpass filter 26. The signals applied at gate 28 are applied to phase detector 30 where they are phase compared to the signals applied at 3.58 MHz crystal oscillator 32. The phase detection error signal applied at the output side of the phase detector 30 is coupled to the low pass filter 34 to pass only the difference signal between the signals applied at the burst gate 28 and the oscillator 32. The signals applied at filter 34 are coupled to VCO20 and also operate to control the output frequency of this voltage controlled generator.

The signals provided at amplifier 24 are also coupled to band notch filter 36. Filter 36 attenuates these signals centered around a frequency of 6.64MHz and consists of a parallel combination of inductor 38 and capacitor 40. A delay circuit consisting of a combination of inductor 42, capacitor 44 and resistor 45 is coupled to the output of filter 36. In the latter delay circuit the signal provided by delayed filter 36 is coupled to the input of summing amplifier 48 via summing resistor 46. Delay line 58 receives the signal from amplifier 24 via resistor 50 and delays approximately 63.5 μs. Inductor 60 is coupled across the input of delay line 58 to ensure proper impedance matching. Similarly, the parallel coupling of the indicator 62 and the resistor 63 is connected across the output end of the delay line 58 to match the output impedance of the delay line. Buffer amplifier 65 receives the signal applied at delay line 58 via resistor 67. The signal provided by amplifier 65 is coupled to the input of differential amplifier 70 via a resistor 69. The second input of differential amplifier 70 receives a signal applied from amplifier 26 via a resistor 72. The signal provided by the buffer amplifier 65 is also coupled to the input of the differential amplifier 70 via a resistor 69. The second input of differential amplifier 70 receives a signal applied from amplifier 26 via a resistor 72. The signal provided by the buffer amplifier 65 is also coupled to the summing amplifier 48 via a second band notch filter 74 in parallel coupling of the capacitor 78 and the inductor 76 with the resistor applied at the resistor 68. Filter 74 attenuates approximately 5.11 MHz and forms the frequency response required for the delay signal applied by summing amplifier 48.

Envelope detector 89 is coupled to the output of amplifier 48 via capacitor 88. The detector 89 consists of a transformer 90 arranged in the form of a pair of common wave diodes 92 and 94 coupled to the output terminal of the transformer 90 as a fule wave detector. The detection signals applied to the common connection diodes 92 and 94 are coupled to a low pass filter composed of inductors 98 connected in series in the? Form of the capacitors 100 and 102. The output of detector 98 is coupled to delay line 104. Resistor 108 is coupled across the output terminal of delay line 104 to impedance match the delay line. The signal applied to the output of the delay line 104 is applied to the deemphasis circuit 110. The de-emphasis circuit 110 is composed of a series resistor 112 shunt-coupled with a capacitor 116. The add resistor 118 couples the signal to the input terminal of the output amplifier 82 in the de-emphasis circuit 110. Amplifier 82 also receives the signal applied at cutoff amplifier 70 and synthesizes these signals with those applied via resistor 118.

The bandpass filter 80 intersects between the differential amplifier 70 and the output amplifier 82. A transformer 86 composed of a variable secondary winding resonating with a capacitor 50 coupled to a resistor 52 of the filter 80 and a variable primary winding resonating with a shunt capacitor 87. A series RC coupling circuit consisting of resistor 84 and capacitor 54 is coupled between filter 80 and amplifier 82.

The output signal from amplifier 82 is coupled to modulator 120 where the RF carrier according to at least one television channel frequency is modulated. The modulated RF signal from the modulator 120 is applied to the television receiver 122 to reproduce the information derived from the player 10.

In the circuit operation, the signal embossed on the video disk 14 is decoded by the action of the video processing circuit 16 and the pick-up arm 12. The signal applied by the processing circuit 16 is embedded subcarrier waveform. The embedded subcarrier waveform consists of a bandwidth of about 3 MHz and a narrow-band chromaticity component of about 0.4 MHz and includes wideband brightness components in the form of sidebands of subcarriers modulated and suppressed at 1.53 MHz. 2a denotes a passband characteristic at the output of the circuit 16, and an area occupied by both brightness and chromaticity components refers to a cross-hatch region. The chroma signal component is similar to its NTSC counterpart, within which the chroma signal component contains the sum of the subcarrier phase amplitudes associated with each quadrature phase modulated by the red and blue difference signals (R-Y, B-Y). The embedded subcarrier signal also includes a reference burst oscillation during the horizontal blanking interval at the embedded subcarrier frequency (1.53 MHz). This reference burst coincides with the standard color sync signal components except for the frequency and the number of cycles.

It should be noted that at the time of the prechar application, unnecessary variation occurs in the speed of the relative motion between the pickup needle and the record groove in the video disc reproducing operation, which may cause pseudo fluctuations of the recorded signal frequency. As such, the reproduced embedded subcarrier signal is liable to cause screen instability around other than the required position in the frequency spectrum.

The jitter of the video signal applied from the processing circuit is stabilized so that the interleaved luminance and chroma signal components are accurately separated. Mechanical darkeners can also be used to reduce signal jitter. One type of mechanical cancer expander is to mechanically reposition the needle of the signal pick-up arm along the information groove of the record in synchronization with the instability in the reproduced signal. Dark organs are known as "speed regulators" on January 16, 1973. Seed. It is described in US Patent No. 3,711,641 issued by Palmer. Signal stability is not sufficient to reduce signal jitter. To improve the signal stability problem, the video signal applied in circuit 16 is heterodyned in modulator 18 by 5.11 MHz. A specific signal component for which the entire video signal is stabilized is a color reference burst signal. Thus, at least the resulting converted chromatic signal component (around the jittering 5.11 MHz carrier) is at least jitter free. The signal applied at modulator 18 is passed through low pass filter 22 and amplifier 24. Filter 22 has a passband of about 8 MHz, which allows the frequency to pass through the converted video signal. An indication of the frequency response characteristic at the output of filter 22 is shown in FIG. 2B.

The transitioned video signal has upper and lower sideband components and each includes a brightness signal component combined with an antired chromatic signal component. In the lower sideband portion of the converted video signal, the chroma subcarrier burst signal generated in the baseband signal at 1.53 MHz is converted to 3.58 MHz by the 5.11 MHz carrier signal in frequency (cross hatch area in FIG. 2B). By phase-detecting the converted subcarrier signal and comparing it with the signal applied from the reference oscillator, signal jitter indicating an error signal is generated to control the 5.11 MHz VCO. In forming an appropriate error signal, a bandpass filter 26 having a center frequency of 3.58 MHz is used to pass the converted subcarrier burst signal through the burst gate 28. The burst gate 28 gates the subcarrier signal converted in response to the horizontal synchronization signal applied by the processing circuit 16, and passes the gated signal to the phase detector 30. Phase detector 30 compares the reference burst signal to a 3.58MHz crystal oscillator 32 and generates a signal based on the sum and difference of the two compared signals. The low pass filter 34 passes only the difference signal (error signal) applied to the VCO 20 in the detector 30, and the VCO 20 is thus transitioned within the output frequency to eliminate these error signals. The 5.11MHz output signal with jitter of the VCO 20 is combined with the composite video signal in modulator 18 to form a converted video signal around the nominal 5.11MHz carrier.

The frequency-converted signals applied at the output of amplifier 24 are coupled via one passage including the band notch filter 36 and the delay line 58 via the other passage. The signal passing through filter 36 is reduced to a frequency of 6.64 MHz. The 6.64 MHz frequency corresponds to the position of the chromatic subcarrier component combined with the upper sideband of the frequency-converted video signal. The need to attenuate the chroma signal on the upper sideband will be described later in this specification for reference in forming the brightness signal component.

The signal applied to delay line 58 is delayed by about 63.5µs (1H time for one horizontal scan line), and the band is limited by the delay line to 3db bandwidth of 2.8MHz to 5.5MHz. The frequency response characteristic at the output terminal of the delay line 58 is described in FIG. 2d. It can be seen that delay lines with relatively narrow bandwidth, such as delay line 58, are more economical than acquiring wide bandwidth delay lines used in other code conversion devices.

The signal applied to the output of the delay line 58 includes a chromatic component with a 180 ° phase shift from the chroma component of the non-delayed signal applied from the amplifier 24 and a brightness component in phase with the non-delayed signal. These delayed video signals having phase shifted chromatic components are useful for extracting brightness and luminance signals from non-delayed composite video signals.

In the form of the brightness signal component, the delay signal applied to the output side of the delay line 58 passes through the band notch filter 74. Band notch filter 74 is a notch filter centered at about 5.11 MHz frequency. Filter 74 attenuates the frequency in the 5.11 MHz region so that the applied signal matches only the lower band of the synthesized video signal, which is actually frequency-converted, from 2.8 MHz to 5.11 MHz. FIG. 2E shows the passband response at the output of filter 74. FIG. The delay signal applied to the output of filter 74 is added at the sum of resistors 46 and 68 and the non-delay signals that have passed through filter 36. When the delay signal and the non-delay signal are added, the in-phase component (brightness component) is added and the shifted phase component (chromatic component) is deleted. Since the chromaticity portion of the delay line (the signal occupied by the crosshatch region in FIG. 2e) is mainly in the low side band of this region, the deletion of the chromaticity component in the non-delay signal mainly occurs in the corresponding low side band. In the upper side band of the non-delay signal, the chroma signal is attenuated by a notch filter 36 having a center frequency at 6.64 MHz. FIG. 2C shows the passband characteristics shown at the output of filter 36. FIG. Therefore, the resulting signal applied to the output of amplifier 48 is actually independent of the chromatic signal component.

The vertical detail signal in the recorded image is provided by a signal around the first 400 KHz, which is a baseband video signal. This vertical detail signal has a phase characteristic similar to the chromaticity component and thus becomes a phase inversion when passed through the 1H delay line 58. Filter 74 is used to prevent the vertical detail signal from being removed at the sum of resistors 46 and 68. Filter 74 is used to prevent the vertical detail signal from being removed at the sum of resistors 46 and 68. Filter 74 has a center frequency at 5.11 MHz and also has 30 db points at the center frequency, i.e. 400 KHz, of the required vertical detail bandwidth. The vertical detail bandwidth is indicated in figure 2e by the letter “f”. By eliminating the delay signal around the required vertical detail signal area, the removal of the vertical detail signal within the non-delay signal (at the sum of resistors 46 and 68) is avoided. The 3db point of filter 36 is adjusted in the same way as filter 74 to apply the required passband of the vertical detail signal to each end of the 5.11 MHz carrier (see bandwidth “f” in Figure 2c).

Amplifier 48 amplifies the summed signal at its output and applies it to detector 89. The detector 89 is arranged in a propagation type to extract the positive and negative peak values of the applied signal. This type of detection allows the extraction of video information at a frequency twice the carrier frequency, ie 10.22 MHz. The lowpass filter, which consists of capacitors 100, 102 and inductor 98, has an up-transition frequency of about 4MHz and attenuates the sampling frequency of 10.22MHz after signal detection. The resulting signal applied to the output of detector 89 is a baseband brightness signal component independent of the chroma signal component.

The chroma signal component irrelevant to the brightness signal component has a form similar to the brightness signal component. The signal applied at the delay line 58 is extracted from the non-delay video signal applied to the input of the amplifier 70. Subtracting the delay signal applied at the delay line 58 from the non-delay combined signal applied at the amplifier 24 removes the brightness signal component from the low band portion of the non-delayed time signal, while adding the chroma signal component at the low side band. In providing an output signal consisting only of chroma signal components, it is necessary to attenuate the brightness components in the resulting signal that are not eliminated in the subtraction process. A bandpass filter 80 with a passband in the range of 3 to 4 MHz is used to attenuate unremoved components. The signal applied to the output of the bandpass filter 80 is only a chroma signal component with the required subcarrier frequency of 3.58 MHz. The NTSC type video signal component may be formed by combining the detected brightness signal component (output signal of detector 89) and the chroma signal component derived from filter 80. Delay line 104 is used to combine the brightness and chroma components in the corresponding phase relationship. Delay line 104 is coupled to the output of detector 89 and operates to give the necessary delay to the brightness signal component. De-emphasis circuit 110 is also arranged in the light signal component path to compensate for preemphasis entering the signal during the recording process. The signal applied to the output of the emphasis circuit 110 is added to the chroma signal component by the summing amplifier 82. The brightness and chroma signal components combined in amplifier 82 form a composite video signal with a relatively uniform frequency response. The relatively uniform frequency response of the synthesized signal depends on the delay and non-delay signal characteristics. The baseband brightness signal component is formed by adding delay and non-delay signals. The delay and non-delay signals are passed through the detector 89 after being combined through the filters 36 and 74, respectively. The passband characteristics of delayed and non-delayed signals are described in FIGS. 2e and 2c, respectively. For the following example, the converted video signal applied at amplifier 24 has a uniform signal energy over a frequency range of 2 to 8 MHz. Thus, the signal applied to the output of the filter 36 has a frequency spectrum shown in Figure 2c. If only this signal passes through detector 89, the resulting detection signal is uniform except for a 6 db drop in the 1.53 MHz region. This degradation occurs because there is no signal energy in the upper sideband of the 6.64 MHz region. By adding the signal applied by the filter 74 to the signal applied by the filter 36 in the form as shown in FIG. 2E, the 6db reduction is effectively eliminated. The resulting brightness signal component is formed with a relatively uniform frequency response.

The synthesized video signals applied to the output of the amplifier 82 apply an output signal of equal frequency to at least one standard television channel. Therefore, the signal applied to the embedded subcarrier format in the video disk is code-converted into the same format as the NTSC video signal and applied to the standard television receiver at the RF carrier frequency.

Claims (1)

As detailed above and shown in the figures, it is sensitive to a first video signal 2a having an chromatic signal component interleaved within a portion of the passband of the associated brightness signal component and in the form of the sideband of the subcarrier at the first frequency. And a comb filter device in a system for transcoding the first video signal into a second video signal having a chromatic signal component in the form of sidebands of a subcarrier at a second frequency. A device 18, 20, 26, 28, 30 for frequency converting the corresponding frequency portion of the first video signal so that a portion of the converted signal has chromatic subcarriers at a frequency corresponding to the second frequency (3.58 MHz) And to the converter 18, 20, 26, 28, 30 to attenuate the frequency converted signal for a frequency corresponding to the sum of the first and third frequencies. A filter device 36 and a delay device coupled to the converters 18, 20, 26, 28, 30 to provide a predetermined delay in the passing signal with a passband of at least bandwidth of the chromatic signal component ( 58) and first devices 46, 48, 68 responsive to the signals provided by the filter device 36 and the delay device 58 to form a brightness signal component that is actually independent of the chroma signal. A second device responsive to a signal provided by the signal conversion device (18, 20, 26, 28, 30) and the delay device (58) to form a chromatic signal component independent of the signal, and the second video output signal. And a device (82, 84, 118) for synthesizing signals defined by respective first and second response devices for providing.

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