Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1998-02-06
2001-09-18
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C386S349000, C386S349000, C386S349000
Reexamination Certificate
active
06292622
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for low-speed reproducing in a video cassette recorder (VCR). More particularly, it relates to a method for low-speed reproducing in a video cassette recorder (VCR) capable of reproducing a continuous time varying image in which a noise, or an unstable vibration of the screen is prevented when reproducing at a low speed of ⅔, ½, etc. of the normal speed in the VCR.
2. Description of the Related Art
Generally, a video cassette recorder (VCR) is an apparatus for recording and reproducing a video and an audio signal recorded on a recording medium, i.e., a video cassette tape. The VCR can reproduce the recorded video signal at a normal, low or high speed, or can stop reproducing the signal.
The servo system of the VCR is divided into a drum servo which controls the rotation of a head, and a capstan servo which controls the track and maintains the running speed of the recording medium. Specifically, the capstan servo controls the phase and speed of the capstan motor so that the head which is allotted to each channel can accurately reproduce the video signal of the relevant channel. The capstan servo also regularly maintains the running speed of the recording medium when reproducing or recording. The rotation speed of the capstan motor is controlled by obtaining a capstan speed error voltage from a capstan frequency generator (CFG) signal corresponding to the running speed of the recording medium. In the case of a low-speed reproducing, a temporary stop, a classifying operation, etc., a slow step signal outputted from the microcomputer is applied to the capstan motor.
The phase of the capstan motor is controlled by adding the capstan speed control voltage to a capstan phase error voltage which is obtained by comparing the frequency of a control signal with a reference frequency when reproducing.
In the case of a conventional 2-head VCR, a first head (channel
1
) and a second head (channel
2
) are arrayed at the periphery of the head drum facing each other apart by 180 degrees. Moreover, in order to enhance the recording density in the conventional recording medium, a method for obliquely recording the video signal in the recording medium per unit of field is applied. Here, the video signal is recorded in alternating turns in a first field (field
1
) corresponding to channel
1
and in a second field (field
2
) corresponding to channel
2
. The signals recorded in field
1
and field
2
are recorded using an Azimuth recording method in order to prevent the signals from disturbing each other.
When the recording medium is run at a predetermined speed by the capstan motor and the head drum is rotated at a predetermined speed by a spindle motor, the first head reproduces the video signal recorded in field
1
(channel
1
) and the second head reproduces the video signal recorded in field
2
(channel
2
) according to the head switching pulse signal. By composing the signals recorded in fields
1
and
2
, it is possible to reproduce the video signal of one frame.
In addition, in the conventional low-speed reproducing method, a stopped (paused) screen is continuously reproduced irregularly by simply rotating the capstan motor with the slow step method. In this case, the reproduced screen is stopped once per a predetermined period.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a method for low-speed reproducing in a video cassette recorder (VCR) capable of reproducing a continuous time varying image of high quality and without noise by generating a pseudo head switching pulse signal for determining a switching period of a main head and an additional head.
It is another object of the present invention to provide a method for low-speed reproducing in a video cassette recorder capable of reproducing a time varying image which is always stable by controlling the generation of a control pulse which controls the tracing position of a head when performing low-speed reproducing in the VCR.
Yet another object of the present invention is to provide a method of low-speed reproducing in a video cassette recorder capable of preventing unstable vibration of the reproduced image on the screen which is caused when a vertical synchronization is not detected on the section of the recording medium when reproducing signals in the VCR at a low speed, or when the vertical synchronization signal is detected from different positions.
According to one aspect of the present invention, a period which is regularly and repeatedly performed is detected from an envelope waveform of a video signal generated by the main head. The pseudo head switching pulse signal for switching the operation state of the main head and the additional head is generated according to the detected period, and the voltage level of the envelope waveform detected by the main head is compared with the voltage level of the envelope waveform detected by the additional head. According to the compared result, a reproducing signal is detected from one head which has the envelope waveform having a high voltage level.
Here, the period indicates the number of the head switching pulse corresponding to the least common multiple of the speed to be reproduced.
According to another aspect of the present invention, the period which is regularly and repeatedly performed is detected from the envelope waveform of the video signal which is reproduced by the main head. The pseudo head switching pulse signal for switching the operation state of the main head and the additional head is generated according to the detected period, and a control signal is moved to a section where the level of the envelope waveform is high in the positive and negative sections of the pseudo head switching signal, thereby searching for a position where the varying amount of the envelope waveform arrives at its maximum. It is possible to automatically control the tracking within the section of the head switching pulse signal corresponding to the searched position.
According to another aspect of the present invention, the period which is regularly and repeatedly performed is detected from the envelope waveform of the video signal which is reproduced by the main head. The pseudo vertical synchronization signal corresponding to the head switching pulse signal is generated at a position which is delayed by a predetermined period from each edge part of the head switching pulse signal. The position of the pseudo vertical synchronization signal is variably set in the section where the additional heads are operated. In addition, the position of the pseudo vertical synchronization signal is variably and fixedly set in alternating turns in the section where the main heads are operated.
Here, initial positions of each pseudo vertical synchronization signal are set to 6.5H, 6.75H, 6H, 5H, 5.25H and 6.75H, when reproducing at a low speed of ⅔ of normal speed.
The pseudo vertical synchronization signal can vary the position within a range of 5H to 8H.
The pseudo vertical synchronization signal is set so that its position can be varied based on the 0.25H.
REFERENCES:
patent: 5319499 (1994-06-01), Kim et al.
patent: 5539589 (1996-07-01), Yamamoto
patent: 5684916 (1997-11-01), Hong
patent: 5966265 (1999-10-01), Takayama
patent: 6014493 (2000-01-01), Shimoda
patent: 6078724 (2000-06-01), Kawase
patent: 6173111 (2001-01-01), Kwon et al.
Lee Jong-gyu
Son Gyu-yeong
Dilworth & Barrese LLP
Samsung Electronics Co,. Ltd.
Tran Thai
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