GB2117995A

GB2117995A - Color video signal processing device for a system for producing recorded color video information

Info

Publication number: GB2117995A
Application number: GB08304625A
Authority: GB
Inventors: Takashi Okano
Original assignee: Pioneer Video Corp
Current assignee: Pioneer Video Corp
Priority date: 1982-02-20
Filing date: 1983-02-18
Publication date: 1983-10-19
Also published as: FR2522236A1; GB8304625D0; DE3305961A1; DE3305961C2; FR2522236B1; GB2117995B

Abstract

A device for processing a color video signal from a PAL system color video information play back unit comprising a PAL phase invertor means (7) for inverting in PAL phase a frequency component of a color carrier signal and a color burst signal and a switching means (55) for selecting either an input color carrier signal or an output signal of the PAL phase invertor means (7). The switching means (55) is operated to select an output signal of the PAL phase invertor means (7) at a transitional time from an ordinary playback mode of the play back unit to a special playback mode of the playback unit. A generating means (8) for generating an additional jump operation signal is provided so that an additional jump operation takes place if the number of the occurrence of recording track jump operations during the special playback mode is odd. <IMAGE>

Description

SPECIFICATION Color video signal processing device for a system for producing recorded color video information Background of the invention Field of the invention The present invention relates to a color video signal processing device to be used in reproducing recorded color video information, and more particularly to a device for a system for reproducing color video information according to the Phase Alternation Line (PAL) system.

Description of the prior art PAL system color composite video signal is characterized in that one of color difference signals alternates in phase per each horizontal scanning line.

Therefore, in PAL system TV receivers, it is necessary to alternate in phase a subcarrier signal corresponding to one of color difference signals per each horizontal scanning line. In order to correctly determine the phase inversion of the subcarrier signal. The PAL system TV receiver is generally provided with a burst phase discriminator which is used for discriminating the phase inversion of color burst signal which represents the phase of the color difference signal. Furthermore, the burst phase discriminator is generally provided with a time constant characteristics to eliminate a quick response to noise signals.

On the other hand, various video playback systems such as video tape recorders or video disc player systems are also used as a source of video information to a display system. In those systems, there are several special playback modes such as a still mode, slow speed mode, double speed mode, triple speed mode and so on. Furthermore, in the case of the video disc player (VDP) there is a scanning mode in which the pickup means is moved in the radial direction of a video disc for the purpose of the searching of the information recorded on the video disc.

During the playback of video signal in those special playback modes and scanning mode, a jump operation, that is, the movement of pickup point from one recording track to another is necessary to enable the tracing of desired recording tracks. In prior art systems for reproducing recorded color information, however, the drawback was that the operation of the phase inversion of the subcarrier signal may be disturbed due to the jump operation during a special playback mode as well as a transitional period between the ordinary playback mode and the special playback mode, and also during the scanning mode of the VDP system.

Summary of the invention An object of the present invention is therefore to provide a color video signal processing device for use with a color video information reproducing system, which can eliminate the disturbance of color reproduction which might occur during a special playback mode, scanning mode, and a transitional period between the ordinary playback mode and a special playback mode.

According to the present invention, a color video signal processing device for use with a PAL system color video information reproducing system is characterized in that a color carrier signal and a playback color burst signal are inverted in phase in accordance with the detection of the phase inversion of the playback color burst signal between before and after a predetermined point of time.

According to another aspect of the present invention, a color video signal processing device comprises a phase inverting means for inverting a color burst signal in phase per every horizontal scanning period, and a multiplying means for generating a low frequency component by multiplication between an output signal of the phase inverting means and a signal having the phase and the frequency equal to those of one of subcarrier signals of the color carrier signal, thereby controlling the phase inversion of the color carrier signal by means of the low frequency component produced by the multiplying means.

According to still another aspect of the invention, a color video signal processing device for use with a PAL system color video information reproducing system comprises: a color carrier signal phase compensation means which includes a phase invertor for inverting a component of color carrier signal and a color burst signal in phase, a first selector for selecting one of input and output signals of the phase invertor, and a summing means for summing a luminance signal and an output signal of the first selector; a second selector for selecting an input signal of the color subcarrier phase compensation means during an ordinary playback mode and selecting an output signal of the phase invertor during transitional period from the ordinary playback mode to the special playback mode, and for controlling the first selected to switch its selection at each receipt of a recording track jump control signal.

The foregoing and other objects and advantages for the present invention will become more clearly understood upon review of the following description taken in conjunction with the accompanying drawings.

Brief description of the drawings Fig. 1 is a vector diagram of a color carrier signal of PAL system; Fig. 2 is a schematic diagram of a portion of recording tracks showing the relation between the path of the pickup means and the recording tracks during special playback mode; Fig. 3 is a block diagram of an example of color signal processing circuit of a video disc player; Fig. 4A through 4E are timing charts showing an operation of the circuit of Fig. 3 which might occur without using present invention during a transitional period from the ordinary playback mode to a special playback mode; Fig. 5A through 5E are timing charts similar to Figs. 4A through 4E showing an operation of the circuit of Fig. 3 which might occur without using present invention during a transitional period from a special playback mode to the ordinary playback mode;; Fig. 6 is a block diagram of an embodiment of the color signal processing device according to the present invention, which is to be connected to the control terminals of switches 55 and 6; Fig. 7 is a waveform diagram showing the operation of the circuit of Fig. 6; Fig. 8 is a block diagram of a color signal processing circuit of a PAL system color receiver; Fig. 9 is a waveform diagram showing the phase characteristics of color burst signals during scanning mode of operation; Fig. 10 is a block diagram of a second embodiment of the color signal processing device according to the present invention; Fig. 1 A through 11 E are waveform diagram showing the operation of the circuit of Fig. 10; and Fig. 1 2A through 1 2E are waveform diagram similar to Figs. 1 A through 1 E showing the operation of the circuit of Fig. 10, however, showing the operation when the phase of the color burst signal is inverse relative to that of Figs. 1 A through 11 E.

Detailed description of the preferred embodiments Before entering into the explanation of the preferred embodiments, the color video signal of the PAL system is explained in detail.

Generally the color video signal Ep of the PAL system is expressed by the following equation (1): Ep=Y+(B-Y)sinssst~(R-Y)cosesst (1) in which Y represents luminance signal, B and R represents blue and red signals respectively, and w, is the angular frequency (4.43 MHz) of the subcarrier signal.

The sign + of the equation (1) means the alternation in phase per each horizontal scanning.

Therefore, a component R-Y of the color carrier signal is produced by the amplitude modulation of the subcarrier signal (COSw,t which alternates in phase by 1 80 degrees per each horizontal scanning. The color burst signal, accordingly, has to also represent an information which will be utilized, in a receiver system, to alternate the subcarrier signal for demodulating the R-Y component in phase per each horizontal scanning. Therefore, as shown in the vector diagram of Fig. 1, the color burst signal takes the form of a signal sin(o,t+1350) which alternates by +135 degrees from the B-Y axis per each horizontal scanning. (The dashed line of Fig. 1 will be explained after).

In order to correctly reproduce the color from the video signal of the PAL system in receiving side, it is necessary to invert the subcarrier signal of the R-Y component at every other horizontal scanning in accordance with the result of the phase detection of the color burst signal. For this purpose, a burst phase discriminator is provided to discriminate the phase of the color burst signal. When the phase alternation of the subcarrier signal is inverse to the correct phase alternation and resulted in the reproduction of a negative phase signal -(R-Y), a circuit for inverting the subcarrier signal is reset so as to effect the correct demodulation afterwards.

If, however, the response of the burst phase discriminator is too fast, it is inconvenient in that the reset pulse signal is produced in response to a noise component contained in the color video signal. In order to avoid this kind of malfunction, a time constant is generally set so that the reset pulse signal is generated only when the demodulation of the negative phase signal has continued more than a predetermined period. This method of providing a time constant characteristics is quite effective in the case of receiving the TV broadcasting signal. However if a receiver having this time constant characteristics is utilized to reproduce a picture using a color video signal from a video disc player (VDP), there is a drawback which will be explained hereafter.

In addition to ordinary playback mode, the VDP has various special playback modes such as a still mode, a slow speed mode, a double speed mode, a triple speed mode, and so on. During these special playback mode operation, it is necessary to use a so-called jump operation in which a tracking point of the pickup means is switched from a recording track to the other.

Fig. 2 exemplanary shows a path of the tracking point of the pickup means during still mode operation. As shown by the dashed line 1, the tracking point switches from the recording track 3 to the recording track 2. Each section of the recording tracks 2 and 3 corresponds to each horizontal scanning section. In the case of a constant angular velocity (CAV) disc, as shown, the portions of the recording track for each horizontal synchronization signal, i.e., the boundaries of each section, are aligned in the direction of the radius of the disc, in adjacent recording tracks. Furthermore, a PAL phase, that is, the phase of the signal (R-Y)cosw,t is, as shown, determined to be in the inverse relating in adjacent two recording tracks. Accordingly, the phase alternation state of the PAL signal is reversed at every jump operation between adjacent two recording tracks. Such a reversal of phase alternation slate will result in an incorrect color reproduction or cause an operation of a color killer circuit since the response of the color burst phase discriminator (PAL phase discriminator) is delayed by the time constant characteristics.

In order to avoid this kind of disturbance during jump operation, the VDP is equipped with such a circuit as shown in Fig. 3.

In Fig. 3, a playback color video signal is supplied to a delay circuit 4 and to a PAL phase compensator (color carrier signal phase compensator) generally designated by 5. An output signal A2 of the delay circuit 4 and an output signal B2 of the PAL phase compensator 5 are supplied to a second switch 6 whose output signal is connected to a display system. The PAL phase compensator 5 has a band pass filter (BPF) 51 and a low pass filter (LPF) 52 for separating the color carrier signal and the luminance signal. The BPF 51 picks up only frequency components of the color carrier signal. An output signal of BPF 51 is applied to a first switch 55 as an input signal B1 after passing through a PAL phase invertor 7 which is made by a multiplier circuit 53 and a LPF 54.The output signal of the BPF 51 is also directly applied to the first switch 55 as an input signal Al. An output signal of the first switch 55 is added to the luminance signal from the LPF 52 at a summing circuit 56 which provides the output signal B2 of the PAL phase compensator 5. A subcarrier signal generator 8 is provided for picking up only a color burst component from the output signal of the BPF 51, following the average phase of the color burst signal and producing a subcarrier signal cosw,t having the same frequency as the color burst signal. The output signal of the subcarrier signal generator 8 is then applied to a frequency multiplier 9 to produce a signal cos2w,t. The signal is then applied to the multiplier 53 as a multiplying signal of the output signal of the BPF 51.In this way, the phase inversion of the PAL signal takes place by means of a so-called heterodyne conversion.

More specifically, the color carrier signal including the color burst signal is expressed as sin(c,)St+0), then the output signal of the multiplier circuit 53 will be expressed as follows: cos2st . sin(o,t+)=l /2Isin(3w,t+)+sin(w,t-)j (2) By means of the BPF 54, a fundamental wave component is selected to provide a signal sin(w,t--9). With respect to the B-Y component of the color carrier signal, the phase is unchanged since the value of 9 is equal to zero (see Fig. 1). Conversely, the R-Y component is inverted in phase since the value of b is equal of n/2. In other words, the R-Y component of the output signal of the BPF 54 is sin(w,t--7t/2) in contrast to the component of the input signal sin(w,t-t-n/2) of the PAL phase invertor 7.

As for the color burst signal (=+1350), the output signal of the BPF 54 sin(St+ 135 ) is alternated in phase with respect to the color burst component sin(w,t-l 1350) of the input signal of the PAL phase invertor 7. In this way, the PAL phase inversion is performed. A known type circuit such as the glass delay line system may be used instead of the heterodyne conversion system.

In this arrangement, during ordinary playback mode operation, the second switch 6 is controlled to select the signal A2 so as to bypass the PAL phase compensator 5 and to eliminate the signal deterioration. In addition, the delay circuit 4 for providing a delay time corresponding to the delay characteristics of the PAL phase compensator 5 can be omitted.

During the special playback mode such as the still mode, the second switch 6 is controlled to receive the signal B2 from the PAL phase compensator 5. In this state, the first switch 55 is operated at each occurrence of jump operation so that one of the signals A2, B1 is in turn selected. In this way, the phase alternation, state of the PAL signal is maintained correctly even during the jump operation.

However, since the second switch 6 can be operated without respect to the position of the first switch 55, the phase alternation state of the PAL signal can be discontinuous when the second switch 6 is operated. Since the PAL phase discriminator of the display system (to be connected to this circuit) has the time constant characteristics as mentioned before, such a discontinuity of the phase alternation state would cause a disturbance of the color reproduction or the action of the color killer circuit.

This problem will be more clearly explained with reference to Figs. 4A through 4E and Figs. 5A through 5E. In still mode, the jump operation as shown in for example Fig. 2, that is, the switching of the tracking point from a line n+4 of the track 3 to a line n+5 of the track 2, takes place every one rotation of the video disc. Fig. 4A shows the level of a playback mode signal for controlling the second switch 6. As shown, the second switch 6 is switched from the ordinary playback mode position at a time t1. Fig. 4B shows the jump signals which is used as a trigger signal of flip-flop circuit for generating a control signal of the first switch 55. Fig. 4C illustrates the switching A2 and B2. Figs. 4D and 4E illustrate the switching state of the first switch 55 which selects one of the signals Al and B1 alternately.As shown, two types of the switching sequences of the first switch 55 respectively shown by Fig. 4D and Fig. 4E are conceivable depending on the initial position of the first switch 55. In the case of Fig. 4D, the continuity of the PAL phase alternation is maintained since the first switch 55 selects the inverted signal B1 of the PAL phase invertor 7 at the first jump operation. However, in the case of switching operation shown in Fig. 4E, the first switch 55 selects the non-inverted signal Al of the PAL phase invertor 7 at the first jump operation. Furthermore, this reversed state of the PAL phase alternation goes on by the succeeding operation of the first switch 55.Thus, in the case of the state shown in Fig. 4E, the color reproduction of the display system would be disturbed at least several frames after the jump operation.

Similarly, the operation in the transitional period from the special playback mode to the ordinary playback mode will be explained with reference to Figs. 5A through 5E. Figs. 5A through 5E respectively correspond to Figs. 4A through 4E. As in the previous case, two types of the switching sequence of the first switch 55 are conceivable. In the case of the switching sequence shown in the Fig. 5D, the continuity of phase alternation of the PAL signal is maintained since the non-inverted signal A1 is selected by the first switch 55 just before the operation of the second switch 6 at the time t3. However, in the case of the switching sequence shown in Fig. 5E, the phase alternation state of the PAL signal is reversed at the time t3. This reversed phase alternation state causes the same problem as explained before.

The first embodiment of the color signal processing device according to the present invention will be explained hereafter with reference to Fig. 6. The circuit shown in Fig. 6 produces the signals for controlling the first switch 55 of the circuit shown in Fig. 3. The playback mode signal used for controlling the second switch 6 of the circuit of Fig. 3 is also applied to a terminal (a) of the circuit of Fig. 6. The playback mode signal is then applied to an input terminal of an OR gate 11 (negative logic) via an invertor 10. A jump timing signal is applied to the other input terminal of the OR gate 11 and the output signal of the OR gate 11 is applied to a flip-flop circuit 12 and to an AND gate 13. An inverted signal of the playback mode signal is applied to the flip-flop circuit as a clear signal.An output signal of the flip-flop circuit 1 2 is used as a trigger signal of the monostable multivibrator (MMV) 14 and as a control signal of the first switch 55 of the circuit shown in Fig. 3. A Q output signal of MMV is applied to an OR gate 1 5 which also receives a playback mode signal. An output signal of the OR gate 1 5 is applied to the AND gate whose output signal of the OR gate 1 5 is applied to the AND gate whose output signal is used as the jump signal.

The operation of this circuit will be explained with reference to the timing charts 7A through 7G.

Figs. 7A through 7G respectively illustrate the signal waveform at various points (a) through (g) of the circuit shown in Fig. 6. In this explanation, it is assumed that the first and the second switches 55 and 6 respectively select the signals B1 and B2 when a high level control signal is applied thereto and select the signals Al and A2 when a low level control signal is applied thereto. Therefore, for example, the second switch 6 switches from the position of the signal A2 to the position of the signal B2 at the time of transition from the ordinary playback mode to the special playback mode.

During the special playback mode, the still mode from time t2 to the time t3 for example, the flipflop 12 is triggered by the jump timing signal which is applied through the gate circuit 11 as shown in Fig. 7C.

The flip-flop 12 which has been cleared by the application of the playback mode signal at a clear terminal thereof is triggered by the first jump signal Ca (see Fig. 7C) and the Q output signal thereof turns from a lower level to a high level (see Fig. 7D). Since this 0 output signal of the flip-flop is used as the control signal of the first switch 55, the initial operation of the first switch 55 is determined in a manner that the signal Al is selected before the occurrence of the first jump signal Ca and the signal B1 is selected upon occurrence of the first jump signal Ca.

In this way, the inversion of the PAL phase takes place without fail at the first jump operation (this corresponds the state shown by Fig. 4D). Therefore, the color disturbance in the display system such as a color monitor device, which might occur without using the device of the present invention, is eliminated.

Subsequently, the output signal of the flip-flop 12 is inverted at each occurrence of the jump signal. Therefore, the proper PAL phase alternation is mentioned by the subsequent operation of the first switch 55. In addition, during this time, period from t1 to t3 of the special playback mode, the MMV is triggered by the trailing edge of the Q output signal of the flip-flop 12 and produces low level single pulses (shown in Fig. 7E). However, since the gate 15 is closed during this period, the low level output pulses of the MMV 14 are not transmitted to the gate 13. Therefore, the gate 13 directly transmits the output signal of the gate 11 as the jump signal to be applied to the control circuit of the pickup means.

Then, the operation of this circuit during the transitional period from the special playback mode to the ordinary playback mode will be explained. There are two possibilities of the 0 output signal level upon occurrence of a last jump signal Cf which would be produced just before the time t3. Firstly, if the O output signal of the flip-flop 12 turns from the high level to the low level as shown by the solid line of the Fig. 7D, the operation of the first switch 55 is that the signal Al is selected after the occurrence of the last jump signal Cf. Therefore, when the second switch 6 selects the signal A2 at the time t3, the proper PAL phase alternation state will be maintained.

On the other hand, if the Q output signal of the flip-flop 1 2 turns from the low level to the high level at the occurrence of the last jump signal Cf, the output signal turns low at the time t3 by means of the change in the signal level of the playback mode signal which is applied to the clear terminal of the flip-flop 12 (see dashed line of Fig. 7D). Subsequently, the MMV 14 is triggered by the trailing edge of the 0 output signal of the flip-flop 12 and produces a low level single pulse as shown by the dashed line in Fig. 7E. This single pulse signal is applied to the gate 13 via the open passage of the gate 1 5.

Then, the gate 13 produces an additional jump signal directly after the time t3 as shown by the dashed line of Fig. 7G. By this additional jump signal, a jump operation takes place just after the time t3 so as to cause the phase inversion or alternation of the PAL signal. In this way, the proper phase alternation state of the PAL signal is maintained during the transitional period from the special playback mode to the ordinary playback mode.

In other words, the operation of this circuit is to produce an additional jump signal in the event that the number of the jump signals during the time period of the special playback mode is odd.

Therefore, the number of the jump signals can be detected by means of a counter circuit instead of the flip-flop circuit used in this embodiment. Furthermore, the same operation is enabled by using a microprocessor operated arrangement.

In addition, the initial position of the first switch at the transitional periodfrom the ordinary playback mode to the special playback mode may be determined so as to select the inversed PAL signal in accordance with a signal responsive to the termination of the previous special playback mode.

Moreover, although the embodiment has been explained by way of example of the still mode as the special playback mode, it is to be noted that the device of the present invention can be applicable to various playback modes of the playback system.

Turning to Fig. 8 through Fig. 12 the second embodiment of the present invention will be explained. Reference is first made to Fig. 8 in which a PAL system color video signal demodulator circuit of a display system is illustrated. In the figure, a PAL system color video signal is applied to a Y C separator 21 in which the color video signal is separated into a Y (luminance) signal and a C (chroma) signal. The C signal is then applied to a burst phase discriminator 22 and to a color carrier signal separator 23. A color burst signal sin(wt+1 350) is picked up in the burst phase discriminator 22 and transmitted to a subcarrier signal generator 24.A subcarrier signal sin(w,t+900)=cosw,t generated in the subcarrier signal generator 24 is shifted by 900 in phase relative to a signal sinw,t which has an average phase of the color burst signal sin(wt+1 350) The subcarrier signal generator 24 takes the form of a phase lock loop (PLL) circuit and an output signal of a voltage controlled oscillator (VCO) of the circuit is used as the subcarrier signal cosw,t. The subcarrier signal cosw,t is then directly applied to a switch 26 and to a phase shifter 25 which produces a 900 phase shifted signal and a 1 800 phase shifted signal. The 900 phase shifted signal, that is, a signal sinw,t is applied to a first synchronous detector 27 as a detection subcarrier signal.The 1 800 phase shifted signal -cosa;9t is applied to the switch 26. An output signal *cosw8t of the switch 26 is applied to a second synchronous detector 28 as a detection subcarrier signal.

The first and second synchronous detectors 27 and 28 respectively receive signals (B-Y)sinw,t and +(R-Y)cosw,t which are generated by color carrier signal separator 23. A pair of low pass filters (LPF) 29 and 30 are respectively connected to the first and the second synchronous detectors 27 and 28 to provide a pair of demodulated signals (B-Y) and (R-Y).

A horizontal drive pulse signal is produced by synchronous separator 31 which receives the PAL color video signal, and triggers a flip-flop 32 whose output signal control the switching operation of the switch 26.

The phase alternation state of the color burst signal, that is, the regular phase inversion per each horizontal scanning, is detected by the burst phase discriminator and a reset signal is applied to the flip-flop 12 in the event that the phase alternation state is reversed in phase to the proper phase alternation state.

As described before, the PAL system color video signal features that the polarity of the (R-Y) component of the color carrier signal alternates per each horizontal scanning.

Therefore, in order to properly reproduce the color in the receiving side, it is necessary to change the polarity of the subcarrier signal corresponding to the (R-Y) component in accordance the phase alternation of the color burst signal. By this reason, the burst phase discriminator 32 is used to reset the flip-flop 32 when a signal(R-Y) is produced by the synchronous detector 28 (as described in the above).

However, if the speed of the response of the burst phase discriminator is too fast, there will be a problem that the reset pulse signal is produced in response to a noise component contained in the color video signal, as mentioned before. To avoid this problem, the time constraint characteristics is provided to the burst phase discriminator. This time constraint characteristics cause a problem when a video disc player (VDP) is used as a source of the PAL video signal especially during a scanning mode.

More specifically, during the scanning mode, the pickup means is translated along the direction of the radius of a disc to search a desired recording track while a tracking servo loop is controls the position of the tracking point of the pickup means by means of a control signal produced from the playback information signal. In order to keep the tracing of the recording track during scanning mode, means for shifting the tracking point of the pickup means along the direction of the radius of the disc, such as a tracking mirror, is operated in a manner as will be described hereafter. Since the playback of the recorded information takes place also during scanning mode, the tracking mirror turns around its axis so that a read out light beam is focused on a recording track in spite of the radial movement of the pickup means. When the tracking mirror is turned to an extremity of its movable range, the tracking mirror is immediately turn to another extremity of the movable range so as to start the read out of the information from a new start point of the recording track. In other words, a so-called jump operation takes place every time this rapid movement of the tracking mirror occurs. Furthermore, since the portions of recording tracks for recording each horizontal synchronization signal are aligned in a radial direction of the disc, the operation of a servo system of the disc rotation is maintained properly during this scanning mode. Moereover, due to a rapid phase lock characteristics of the VCO provided therein, the PLL circuit of the subcarrier signal generator 24 can be easily locked to the input signal within a field (one horizontal scanning) after each jump operation during this scanning mode.

However the problem of the scanning mode is that the phase alternation state of the color burst signal may be reversed after a jump operation since the number of skipped tracks of one jump operation is not constant (see Fig. 9). If the phase alternation state is reversed after a jump operation as shown in Fig. 9, it causes the disturbance of color reproduction or the actuation of a color killer circuit.

Turning to Fig. 10, the second embodiment of the color signal processing device will be explained. A PAL color video signal which is produced by a detection operation of a playback RF (Radio Frequency) signal from a recording disc is applied to a low pass filter (LPF) 33 and to a Band Pass Filter (BPF) 34. In the LPF 33 and the BPF 35, the PAL color video signal is respectively separated into a luminance signal and to a color carrier signal (including the color burst signal) having the frequency of 4.43 MHz. The color carrier signal from the BPF 34 is then applied to a PAL phase invertor 35 of the heterodyne conversion type. The PAL phase invertor 35 includes a multiplier circuit 351 and a band pass filter (BPF) 352. In the multiplier circuit 351, the color carrier signal is multiplied by a signal cos2w8t from a frequency multiplier 36.The BPF 352 is used for picking up a fundamental frequency component (Ws) of the output signal of the multiplier circuit 351. An output signal of the BPF 352 is applied to a switch 37 as an input signal. The switch 37 also receives a signal directed from the BPF 34.

The output signal of BPF 34 is also applied to a burst gate 38 in which a color burst signal is picked up. The color burst signal from the burst gate 38 is then applied to a phase invertor circuit 39 and to a subcarrier signal generator 40 which has the same arrangement as the subcarrier signal generator 24 of Fig. 8 employing a phase locked loop (PLL) circuit. In the phase invertor 39, the color burst signal from the burst gate 38 is inverted in phase in accordance with a phase inversion control signal, from a line (a), which has a period of 2H (H being one horizontal scanning period). An output signal of the phase invertor 39 is then applied to a burst demodulator 41 in which the signal from the phase invertor 39 is multiplied with the signal cosw,t from the subcarrier signal generator 40.The thus demodulated signal from the burst demodulator 41 is applied to a zero level comparator 42. The switch 37 is controlled by an output signal of the zero level comparator, and the output signal thereof is added to the luminance signal in the adder circuit 43 so as to provide a playback PAL color signal. The playback PAL color signal is for example, then applied to the circuit shown in Fig. 8 of the display system.

The operation of the circuit of Fig.10 will be further explained hereafter when reference to Figs.

11 and 12. Figs. 11 A through 11 E and Figs. 1 2A through 1 2E respectively are waveform diagrams of various points (a) through (e) of the circuit of Fig. 10. Figs. 11 A through 11 E show the waveforms of the case in which the phase alternation state of the color burst signal is in proper condition. In the phase invertor 39, one component of the color burst having the phase of -1350, which is present in every two horizontal scanning (2H) is inverted to be a signal having the phase +450 (see the dashed line of Fig. 1). Therefore, the output signal of the phase invertor 39 takes the form of signals sin(o,t+1350) and sin(w3t+450) which in turn appear in each 1 H as shown in Fig. 11 D.In the burst demodulator 41, the multiplication takes place between the output signal sin(w,t+1350), sin(o,t+450) and the output signal cos St of the subcarrier signal generator 40. The output signal of the burst demodulator 41 is mathematically expressed as follows: sin(w,t+1350) . cosw,t=1/2[sin(20,t+ 1350)+sin1350] (3) sin(a,,,t+450) . coso,t=1/2[sin(2w,t+450)+sin450] (4) Since the only low frequency components are picked up, the output signal of the burst demodulator 41 takes the form of the d-c voltage signal of the positive polarity as shown in Fig. 1 OD.Upon receipt of this positive d-c signal, the zero level comparator 42 produces a high level control signal which controls the switch 37 to directly select the output signal of the BPF 34. Therefore, in this case, the PAL system color video signal is applied to a display device without passing through the color carrier phase inversion process.

Conversely, if the phase alternation state of the color burst signal is inverse to the above case, see Fig. 1 2B, the operation of the circuit is as follows. The output signal of the phase invertor 39, in this case, takes the form of signals sin(t-1 350) and sin(-450) which in turn appear in each 1 H as shown in Fig. 1 2C. The output signal of the burst demodulator 41 is expressed as follows: sin(St135 ) . cosa;st=1/2[Sin(2st1 350 +(-1 350)] (5) sin(wt+450) . coso,t=1/2[sin(2w,t-450)+sin(-450)1 (6) Therefore, the output signal of the burst demodulator 41 will be a d-c voltage having the negative polarity.By this negative d-c voltage, the zero level comparator 42 produces a low level output signal to operate the switch 37 to select the output signal of the PAL phase invertor 35. The operation of the PAL phase invertor 35 will be explained more specifically. If the color carrier signal including the color burst signal is expressed as sin(w,t+4), the output signal of the multiplier circuit 351 is as follows: cosw,t . sin(o,t+)= 1/2[sin(30,t+) +sin(w,t-) (7) After passing through the BPF 352, the only fundamental frequency component sin(w,t--) is applied to the switch 37.As for the B-Y component of the color carrier signal, the phase of the output signal sinw,t of the BPF 352 has the same as the phase invertor input signal since the b value thereof is equal to zero (=0). Conversely, as for the R-Y component of the subcarrier signal, the phase of the output signal sin(o,t-7t/2) of the BPF 352 is inverse to the phase of the phase invertor input signal sin(St+X/2) since # value there of is 7t/2(=?t/2). Similarly, as for the color burst signal, the phase of the output signal sin(ss5t+135 ) is inverse to the phase of the input signal sin(w,t+1350). In this way, the PAL phase inversion is performed.The output signals of the switch 37 in both cases are thus made identical as shown in Figs. E and 12E.

It should be noted that a glass delay line system can be used for the PAL phase invertor 35 instead of the heterodyne system used in this embodiment.

It will be appreciated from the foregoing, that according to the present invention, the proper phase alternation state of the PAL color video signal is maintained during the scanning mode and the transitional period between the normal playback mode and a special playback mode such as a still mode.

Furthermore, by providing the color signal processing device of the present invention to the side of the playback system such as a VDR, the conventional video display system such as a monitor TV can be used without causing the color disturbance which has been inevitable in the case of the prior art systems.

Above, preferred embodiments of the present invention have been described. It should be noted, however, that the foregoing description is for illustrative purpose only, and is not intended to limit the scope of the invention. Rather, there are numerous equivalents to the preferred embodiments, and such are intended to be covered by the appended claims.

Claims

1. A color video signal processing device for use with a PAL system color video information playback unit having an ordinary playback mode and a special playback mode, comprising: a color carrier signal phase compensator connected to said PAL system color video information playback unit, including a separator means for selectively transmitting a frequency component of a color carrier signal out of an output signal of said PAL system color information playback unit, a phase alternator means connected to said separator means for alternating in PAL phase said frequency component of said color carrier signal, a first switch for selecting one of output signals of said separator means and said phase alternator means, and a summing means for combining an output signal of said first switch and the luminance signal component of said output signal of PAL system color video information playback unit; a second switch for selecting said output signal of PAL system color video information playback unit during said ordinary playback mode and selecting an output signal of said color carrier signal phase compensator during said special playback mode; and a control means for controlling said first switch to select said output signal of said phase alternator means at a transitional time from said ordinary playback mode to said special playback mode and to alternate switching positions thereof in response to each occurrence of a recording track jump operation during said special playback mode.

2. A color video signal processing device of Ciaim 1, further comprising a generating means for generating a signal for providing an additional jump operation if the number of occurrence of said recording track jump operations during said special playback mode is odd.

3. A color video signal processing device for use with a PAL system color video information playback unit having an ordinary playback mode and a special playback mode, comprising: a color carrier signal phase compensator connected to said PAL system color video information piayback unit, including a separator means for selectively transmitting a frequency component of a color carrier signal out of an output signal of said PAL system color information playback unit, a phase alternator means connected to said separator means for alternating in PAL phase said frequency component of said color carrier signal, a first switch for alternatively selecting one of output signals of said separator means and said phase alternator means in response to each occurrence of a recording track jump operation during said special playback mode, and a summing means for combining an output signal of said first switch and the luminance signal component of said output signal of PAL system color video information playback unit; a second switch for selecting said output signal of PAL system color information playback unit during said ordinary playback mode and selecting an output signal of said color carrier signal phase compensator during said special piayback mode; and a generating means for generating a signal for providing an additional jump operation if the number of occurrence of said recording track jump operations during said special playback mode is odd.

4. A color video signal processing device for use with a PAL system color video information playback unit comprising: a separator means for selectively transmitting a frequency component of a color carrier signal including a color burst signal out of an output signal of said PAL system color information playback unit; a phase alternation detection means connected to said separator means for detecting a change in a phase alternation state of said color burst signal before and after a specific time point and producing a control signal; a phase alternator means connected to said separator means for inverting in PAL phase said frequency component of said color carrier signal; and a switching means for selecting an output signal of said separator means when said control signal is not present and selecting an output signal of said phase alternator means when said control signal is present.

5. A color video signal processing device of Claim 4, wherein said phase alternation detection means comprises: a color burst signal phase invertor means for inverting in phase said color burst signal at each horizontal scanning; a subcarrier signal generation means for generating a subcarrier signal from said colour burst signal; and a multiplier means for multiplying an output signal of said color burst signal phase invertor means with a signal having a frequancy and a phase equal to those of said subcarrier signal to provide a d-c component indicative of said phase alternation state of said color burst signal; and a control signal generator means for generating said control signal in accordance with said d-c component provided by said multiplier means.

6. A color video signal processing device substantially as hereinbefore described with reference to Figures 1 to 3 and 6 to 1 2 of the accompanying drawings.