Television – Synchronization – Phase locking regenerated subcarrier to color burst
Patent
1996-12-19
1998-07-21
Grant, Chris
Television
Synchronization
Phase locking regenerated subcarrier to color burst
348584, H04N 945
Patent
active
057841187
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to video signal phase synchronizing method, circuit and synthesizing apparatus for use in synthesizing video signals, for example, and particularly to video signal synchronizing method, circuit and synthesizing apparatus for use in synthesizing an image expressed by a digital video signal and an image expressed by an analog video signal.
BACKGROUND ART
As image compression and expansion technique is improved, communication network is digitized, computers are widespread and digital satellite broadcasting and digital CATV become commercially available, recently, there is an increasing possibility that a digitized video signal (television signal) can be used.
On the other hand, social base of conventional analog video signal is arranged as video devices such as existing television broadcasting network, home television receivers, VTRs are widespread, and hence it is not considered at present that such analog video signal becomes useless. Accordingly, at present, a video signal is generally used in the condition that the analog video signal and the digitized video signal are existing in the mixed state and used simultaneously.
Therefore, when a plurality of video signals are used simultaneously, there is examined a method of displaying a video signal in the synthesized state, such as displaying a plurality of video signals on a single display screen. As a method of synthesizing an analog video signal, for example, there are known techniques disclosed in Japanese laid-open patent publication No. 64-11477 and Japanese laid-open patent publication No. 1-190176.
Specifically, in Japanese laid-open patent publication No. 64-11477, a first video signal is converted into digital data and stored in three memory means sequentially. Then, these memory means are read out in synchronism with a second video signal, whereby the first video signal stored in these memory means is synchronized with the second video signal and the first and second video signals can be synthesized.
However, according to the above arrangement, although the first and second video signals are synchronized with each other in the level of synchronizing signal, a phase synchronization of a color subcarrier signal with a higher frequency is not considered at all. Therefore, according to this arrangement, color signals cannot be synthesized. Hence, color signals can be synthesized only when the first video signal, for example, is a luminance signal (black and white signal).
On the other hand, in Japanese laid-open patent publication No. 1-190176, RGB signals are respectively decoded from first and second composite video signals and stored in the first and second frame memories in accordance with synchronizing signals. Then, these frame memories are read out in synchronism with any one of video signals and the first and second video signals thus read out are synthesized in the state of RGB signals and a composite video signal is again encoded from the synthesized RGB signal.
According to this arrangement, since the first and second video signals are synthesized in the form of RGB signals, a problem of synchronization of carrier chrominance signal does not occur. However, in this arrangement, three systems of RGB should be required in the circuits from the A/D converters 61c, 62c to the D/A converter 72, resulting in a circuit arrangement become extremely large in scale. On the other hand, when a plurality of video signals are synthesized in the form of a composite video signal, not only the synchronizing signal of the synthesized composite video signal but also a phase of carrier chrominance signal should be synchronized.
In view of the aforesaid aspect, it is an object of this application to provide video signal synchronizing method, circuit and synthesizing apparatus in which an image expressed by a digital video signal and an image expressed by an analog video signal can be synthesized with each other by a simple arrangement.
DISCLOSURE OF INVENTION
According to the present invention, when a continuo
REFERENCES:
patent: 5541666 (1996-07-01), Zeidler et al.
Fukuda Tokuya
Mogi Yasuhide
Yamauchi Etsuro
Frommer William S.
Grant Chris
Sony Corporation
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