Motion video signal processing for recording or reproducing – Local trick play processing – With randomly accessible medium
Reexamination Certificate
1999-12-23
2002-05-07
Tran, Thai (Department: 2615)
Motion video signal processing for recording or reproducing
Local trick play processing
With randomly accessible medium
C348S220100, C348S345000, C348S352000
Reexamination Certificate
active
06385393
ABSTRACT:
BACKGROUND OF THE INVENTION:
1. Field of the Invention:
The present invention relates to a magnetic recording type of photographic apparatus capable of effecting motion-image recording and still-image recording.
2. Description of the Related Art:
In the field of magnetic recording, a demand for high-density recording has recently been increasing. To meet such a demand, there is provided, for example, a video tape recorder (VTR) of the type which is capable of effecting magnetic recording of high density by transporting a magnetic tape at a reduced speed. However, a VTR provided with a fixed head for recording an audio signal has the disadvantage that if an audio signal is recorded while simply transporting a magnetic tape at a reduced speed, no large relative speed is obtained and the quality of reproduced sound is degraded. For this reason, a method has been adopted in which the length of each track scanned by a rotary head is extended with respect to the track length used in the conventional art and an audio signal which is compressed along its time axis is sequentially recorded in the additional portion of each extended track.
By way of example, such a method will be explained with reference to a VTR of the rotary 2-head helical scan type. As shown in
FIG. 1
, a magnetic tape
1
is wrapped around a rotary cylinder
2
through an angle of (180+&thgr;) degrees or more and, as shown in
FIG. 2
, a video signal recording area
5
and a PCM audio signal recording area
6
are traced by a rotary head
3
or
4
during the rotation of the rotary cylinder
2
through 180 degrees and during the rotation of the same through &thgr; degrees, respectively. A PCM audio signal which is compressed along its time axis is recorded in the PCM audio signal recording area
6
.
A method of recording a still image in a digital signal recording area has been proposed as an applied example of the aforesaid method of recording a digital signal in one area while recording a video signal in another area. Since the amount of information carried by a still image is comparatively small, it is possible to record the entire still-image information in the PCM audio signal recording area
6
on the magnetic tape
1
by scanning a number of PCM audio signal recording areas
6
. According to this method, not only is it possible to realize still-image photography utilizing a photographic apparatus and a recording medium which are identical to those used for motion-image photography, but it is also possible to provide a high-quality still image. The quality of this still image is higher than that of a still image obtainable by repeatedly reproducing a video signal from the same track on a magnetic tape in a VTR while keeping the magnetic tape in a temporarily stopped state.
In such a magnetic recording type of photographic apparatus capable of recording a motion image and a still image, it is possible to perform automatic exposure control similar to that of a conventional camera for motion-image photography.
One example of automatic exposure control used in the conventional camera for motion-image photography will be described below with reference to FIG.
3
.
FIG. 3
shows an example of a camera for motion-image photography capable of performing automatic exposure control based solely on an automatic iris control.
Light which has passed through an optical system
601
is conducted to an exposure adjustment mechanism (iris)
602
, and the amount of the light is adjusted by the iris
602
. The light is then made incident on an image sensor
603
such as a CCD and is converted into an electrical signal by the image sensor
603
. The electrical signal from the image sensor
603
is subjected to processing such as gamma correction and separated into a luminance signal and a chrominance signal, by a camera signal processing circuit
604
. The luminance and chrominance signals are converted into a standardized television video signal which conforms to, for example, the NTSC system, by a camera encoder
605
.
In the meantime, a luminance signal Y which has not been subjected to gamma correction in the camera signal processing circuit
604
is supplied to an integrator
606
, where the luminance signal Y is subjected to integration processing. An arithmetic device
607
calculates the difference between the output of the integrator
606
and a reference value to generate a difference signal. The arithmetic device
607
supplies the difference signal to a driver
609
as an exposure control signal. The driver
609
causes the actuator
610
to control the aperture size of the iris
602
on the basis of the exposure control signal, thereby keeping constant the relationship between the output of the integrator
606
and the predetermined reference value.
Another example of automatic exposure control used in the conventional camera for motion-image photography will be described below with reference to FIG.
4
.
FIG. 4
shows an example of a camera for motion-image photography capable of performing automatic exposure control based on an automatic iris and automatic level control.
Light from a subject passes through a lens
702
and an iris
703
and is made incident on an image sensor
704
, where the incident light is converted into an electrical signal. The iris
703
is controlled by the automatic iris circuit
705
on the basis of the electrical signal from the image sensor
704
. In the meantime, the signal from the image sensor
704
is supplied to a voltage-controlled amplifier (VCA)
706
, where the level of the signal is controlled. An automatic gain control (AGC) circuit which is a constituent element of the VCA
706
is controlled by an AGC control circuit
707
in accordance with the output of the VCA
706
. A signal processing circuit
708
separates the output signal of the VCA
706
into a chrominance signal and a luminance signal and performs predetermined processing to output a standard video signal (according to the NTSC or PAL system).
Such a camera for motion-image photography is required to complete automatic exposure control in a short time since the state of a subject to be photographed varies temporally continuously during motion-image photography. However, if the speed of the automatic exposure control is excessively fast, the amount of exposure may exceed a desired amount exposure or an exposure control operation may be repetitively performed. As a result, the photographed subject may be reproduced as a continuous image of insufficient image quality. For this reason, it is desirable that the automatic exposure control be performed with smoothness rather than at a high speed.
On the other hand, still-image photography is achieved by freezing instantaneously the motion of a subject to be photographed. Accordingly, to prevent a shutter opportunity from being missed, high-speed automatic exposure and rapid control free from error are desired. As a result, if automatic exposure control similar to that used for the motion-image photography is performed during the still-image photography, no good exposure is achieved.
In the magnetic recording type of photographic apparatus as shown in
FIG. 1
, it is possible to utilize AF control similar to that of a motion-image photographic apparatus. Since the state of a subject to be photographed varies temporally continuously during motion-image photography, it is desired that the focusing time required for AF in the motion-image photographic apparatus be made short. However, if an object other than a subject being photographed passes across the scene, excessively fast AF will respond to the object abnormally sensitively, and the photographed subject may be reproduced as a continuous image of insufficient image quality. For this reason, it is desirable to take account of smoothness rather than high-speed response with respect to the performance of AF.
A so-called hill climbing system is known as one automatic focus adjusting method to meet the above-described demand. In the hill climbing system, a high-frequency component is extracted from a video signal o
Canon Kabushiki Kaisha
Robin Blecker & Daley
Tran Thai
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