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BACKGROUND OF THE INVENTION
1. Field of the Application
This invention relates to a magnetic recording device such as a video tape
recorder (VTR), and more particularly to a magnetic recording device
simple in arrangement which is capable of recording still pictures with
high picture quality.
2. Description of the Prior Art
Recently, a so-called "camera recorder" has been popularly used which is
formed by combining a video camera and a VTR in an eight mm video cassette
recorder (hereinafter referred to as "an 8-mm video cassette recorder") or
a VHS-C.
A specific feature of the camera recorder is that it is small in size and
lightweight. Therefore, the camera recorder is suitable for a person to
carry while travelling or to a particular event such as an athletic
meeting, and has been sufficiently improved in picture quality to a degree
which is acceptable for ordinary use.
For instance, the image pickup tube or image pickup element which is the
most essential component in a video camera has been improved in
sensitivity and in resolution. Especially in the case of a CCD
(charge-coupled device), the number of picture elements has been increased
to about 250,000, so that the resolution has been increased by about 30%,
and the occurrence of smear and moire phenomena has been suppressed.
With respect to the circuitry, the emphasis circuit and the comb type
filter have been improved to increase the S/N ratio. Furthermore, the
camera recorder has an advantage inherent therein that, since the camera
is coupled directly to the VTR, a circuit for mixing a luminance signal
and color signal and a circuit for separating these signals can be
omitted, so that it is unnecessary to compress the band of the luminance
signal and the color signal, which thus improves the resolution and the
color reproducibility.
In general, with a video camera, a motion picture of moving persons or
scenes is taken, but a still picture is rarely taken. However, often a
single frame of the motion picture is reproduced as a still picture for
observation.
In reproduction of a still picture with a VTR, the resultant picture often
suffers from blur and noise. This difficulty is attributed to a tracking
error which is caused when the magnetic head does not accurately trace the
video track where a picture to be reproduced has been recorded. However, a
recent VTR has been equipped with a magnetic head for reproducing still
pictures only, to lessen the effect of the blur or noise.
On the other hand, recently a video printer for providing a video image as
a hard copy has been proposed, and therefore it can be considered that it
will become popular to print a still picture from a video signal for
enjoyment.
Problems to be Solved by the Invention
In the case of a still picture, the data of the picture which are
invariable with time are observed as visual data. Therefore, a still
picture must be much higher in picture quality than a motion picture.
Therefore, if the reproducing video signal includes jitter or dropout,
then the resultant picture may suffer from swing, distortion, color
irregularity and noise; sometimes the picture quality is so greatly
lowered that the still picture is no longer observable. The picture
quality thus lowered becomes more significant when such still picture is
provided as a hard copy.
Although the video camera, and especially the camera recorder has come into
wide use, its picture quality is much lower than the photographic picture.
Therefore, the user commonly employs a camera recorder or a portable
separable camera for taking a motion picture, and a photographic picture
still camera for taking a still picture. Sometimes he is forced to carry
both a video camera and a still camera with him.
The video system can be divided into an image pickup system, a recording
system, and a hard copy system. For the image pickup system, the
development of a CCD having 400,000 picture elements is in progress, and
the CCD will be realized soon. For the hard copy system, recently the
picture quality has been markedly improved, and it will soon reach a
practically useful level. Therefore, the remaining recording system is
important; however, while a variety of signal processing circuits for
improving a picture quality have been proposed, no still picture which is
high enough to enjoy has been obtained.
SUMMARY OF THE INVENTION
In view of the foregoing, an object of this invention is to provide a
magnetic recording device in which, while a motion picture is being
recorded, a unitary part of the motion picture is extracted to perform a
still picture recording operation with high picture quality.
Merely adding a still picture recording function to a video camera can be
readily achieved by combining a still picture recording device with the
latter since a variety of still picture recording devices have been
proposed in the art. Such approaches have been tried in various manners
with the result that the devices produced are heavy in weight and high in
manufacturing cost and are not well balanced. In order to popularize the
video camera having a still picture recording function, it goes without
saying that it must be sufficiently high in picture quality, and it is
also essential that it is lightweight; that is, it should be such that no
heavy mechanisms are included. Furthermore, the video camera should be low
in manufacturing cost. However, no magnetic recording device which
satisfies the above-described requirements has yet been proposed.
Accordingly, an object of this invention is to provide a magnetic recording
device which is well balanced in arrangement and can be conveniently used.
More specifically, an object of the invention is to provide a magnetic
recording device which is lightweight and low in manufacturing cost and
which can record still pictures with high quality.
Another object of the invention is to provide a magnetic recording device
which can record a still picture with high picture quality and record an
audio signal with high sound quality.
A further object of the invention is to provide a magnetic recording device
in which a still picture is completely recorded, when it is instructed to
stop a motion picture recording operation for recording a necessary still
picture.
A still further object of the present invention is to provide a magnetic
reproducing device capable of reproducing still pictures high in picture
quality.
The foregoing objects of the invention have been achieved by the provision
of a magnetic recording device of a helical scanning system in which a
magnetic tape is transported while being obliquely wound on a cylinder
through a predetermined angle, which is provided with rotary magnetic
heads, and whenever the magnetic heads scan the magnetic tape obliquely,
an analog video signal of a motion picture is recorded as well as a
unitary picture component such as a frame or field, in which, according to
the invention, PCM still picture recording means for carrying out a PCM
still picture recording operation in a time division manner in a scanning
period of the magnetic heads is provided, the PCM still picture recording
means comprising: means for converting the analog video signal of the
motion picture into a digital video signal; means for receiving the
digital video signal for the unitary picture component and subjecting the
digital video signal thus received to time axis expansion; and means for
converting the digital video signal for the unitary picture component into
a PCM signal which is recorded over a plurality of continual head scanning
periods of time with a predetermined period.
In the magnetic recording device of the invention, whenever the magnetic
heads scan the magnetic tape, a motion picture and a still picture are
recorded in a time division manner. The motion picture is recorded in the
form of an analog video signal similarly as in the case of the
conventional magnetic recording device, while the still picture is
recorded in the form of a PCM signal.
Such a still picture is a unitary part of a motion picture, i.e., one frame
which is extracted out of the motion picture at a predetermined period.
The digital video signal of the unitary picture component thus extracted,
after being time-axis expanded at a predetermined rate, is recorded as a
predetermined portion, in the form of a PCM signal, during a head scanning
period. A plurality of head scanning periods of time are used for
recording one unitary picture component.
After the PCM still picture recording operation is accomplished in this
manner, the operation of extracting a unitary picture component out of the
motion picture is carried out again, the unitary picture component
together with the motion picture is PCM-recorded as a still picture on the
same magnetic tape with the same magnetic head in a time division manner.
That is, while a motion picture is being recorded, parts of the motion
pictures (frames) are PCM-recorded as still pictures at predetermined
intervals.
A still picture reproduced by the PCM still picture recording in the
invention is not affected by a time base error caused by jitter in the PCM
recording operation and is free from dropout; that is, it is less affected
by these factors. Therefore, the resultant still picture is high enough in
picture quality to enjoy and can be stored for a long period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings;
FIG. 1 is an explanatory diagram showing the arrangement of tracks on a
magnetic tape in an 8-mm video format;
FIG. 2 is an explanatory diagram showing a tape winding angle in the 8-mm
video format;
FIG. 3 is a block diagram showing the arrangement of essential components
of an 8-mm video cassette recorder which is the first embodiment of this
invention;
FIG. 4, (A)-(C), is a diagram for a description of a PCM still picture
recording operation in the embodiment shown in FIG. 1;
FIG. 5 is a diagram showing modification examples of a specification for
the PCM still picture recording operation in the invention;
FIG. 6 is a block diagram showing the second embodiment of the present
invention;
FIGS. 7 to 9 are diagrams for a description of a PCM still picture
recording operation in the second embodiment of FIG. 6;
FIG. 10, (A)-(E), is an explanatory diagram for a description of the third
embodiment of the present invention;
FIG. 11 is a block diagram showing a detail of the fourth embodiment of the
present invention;
FIG. 12, (A)-(E), is an explanatory diagram for a description of the fourth
embodiment of FIG. 11;
FIG. 13 is a block diagram showing the fifth embodiment of the present
invention;
FIG. 14 A-C and 15(A)-(D) are explanatory diagrams for a description of the
fifth embodiment of FIG. 13;
FIG. 16 is a block diagram showing a sixth embodiment of the present
invention;
FIG. 17 (A)-(F) and 18 (A)-(F) are explanatory diagrams for a description
of the sixth embodiment of FIG. 16;
FIG. 19 is a block diagram showing a seventh embodiment of the present
invention;
FIG. 20, (A)-(G), is an explanatory diagram for description of the seventh
embodiment of FIG. 19;
FIG. 21 is a block diagram showing an embodiment of a magnetic reproducing
device of the present invention; and
FIG. 22, (A)-(D) is an explanatory diagram for a description of the
embodiment of FIG. 21.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of this invention applied to an 8 mm video cassette recorder
will be described with reference to FIGS. 1 through 5.
First, the 8-mm video format will be described with reference to FIGS. 1
and 2.
As is well known in the art, the 8-mm video system has been standardized by
the "8-mm Video Social Gathering", and is significantly different from the
conventional VHS system or beta system in that the tape width is much
smaller, both in the audio signal recording system and in the tracking
system.
FIG. 1 shows the arrangement of tracks on the magnetic tape in the 8-mm
video system. The tape has a width of 8 mm, and is a metal tape of coating
or vacuum deposition tape. Similarly as in the conventional system, the
tracks are formed obliquely on the tape by helical scanning. A PCM track
TR.sub.p corresponding to a head scan of 36.degree. is formed on the
extension of each of video tracks TR.sub.v corresponding to a head scan of
180.degree.. In the video tracks TR.sub.v, video signals (Video) are
recorded similarly as in the conventional system, and FM audio signals
(AFM) and tracking pilot signals (TPS) are recorded in a frequency
multiplex mode. On the other hand, in the PCM tracks TR.sub.p,
time-compressed audio signals are recorded by PCM (hereinafter referred to
as "PCM-recording", and tracking pilot signals (TPS) are recorded in a
superposition mode. The PCM recording is optional; that is,
after-recording can be employed.
As shown in FIG. 2, the PCM track TRP is obtained by increasing the drum
winding angle, which is usually 180.degree., by 36.degree.. As is apparent
from the arrangement of video heads in FIG. 2, when one video head CH-1
accomplishes the recording of a video track TR.sub.V, the other video head
CH-2 starts the PCM recording of the succeeding PCM track TR.sub.P.
Referring back to FIG. 1, a cue track TR.sub.Q for recording cue signals
and an audio track TR.sub.A for recording audio signals are provided on
both sides of the tracks TR described above, respectively. These tracks
TR.sub.Q and TR.sub.A are optional.
The tracking pilot signals TPS are provided according to the automatic
track finding (ATF) system. Four tracking pilot signals f1 through f4
different in frequency from one another are successively recorded on the
tracks TR. In reproduction, tracking servo is effected in such a manner
that tracing is carried out with high accuracy by detecting the frequency
difference between adjacent tracking pilot signals. Accordingly, in the
8-mm video system, control tracks of the stationary head type are not
employed.
In the embodiment of the invention, as described later, part of a motion
picture is PCM-recorded, as a still picture, in the pCM tracks TRP, and
the PCM still picture recording is carried out substantially in the same
PCM format as the PCM audio recording. Thus, a PCM encoder for PCM audio
recording is also used for recording a still picture.
Constitution of the Embodiment
FIG. 3 shows the arrangement of essential components of an 8-mm video
cassette recorder according to the embodiment of the invention.
In FIG. 3, light from an object is applied through a lens 10 to a CCD
(charge-coupled device) 12 so that the image of the object is formed on
the image pickup surface of the CCD 12. In the CCD 12, the image formed
thereon is converted into electrical signals which are accumulated, and
horizontal and vertical scanning operations are carried out with the aid
of a drive circuit 14 to output video signals. The video signals thus
output are supplied to camera process circuit 16, so as to be subjected to
signal processing such as noise reduction and gamma correction.
The camera process circuit 16 supplies a luminance signal Y with a
synchronizing signal S, and a color signal C to a modulating/recording
circuit 18. In the circuit 18, the luminance signal Y is subjected to FM
modulation, while the color signal C is subjected to frequency conversion,
from 3.58 MHz to about 743 KHz, and to phase shifting (PI). As a result,
the modulating/recording circuit 18 outputs a video signal Video which is
obtained by mixing an FM luminance signal YFM and a low frequency
conversion color signal Co. The video signal Video is applied to a mixer
circuit 24, where it is mixed with an FM audio signal AFM output by an FM
modulator 22. The output of the mixer circuit 24 is applied through
changeover switches 25 and 26 to magnetic heads 28 and 30 alternately with
the field period. In FIG. 3, reference numeral 20 designates a microphone
to supply an audio signal AU to the FM modulator 22.
The magnetic heads 28 and 30 are fitted in a slit formed substantially in
the middle of a cylinder 32 which is rotated by a spindle motor 34 at a
speed of thirty revolutions per second which is equal to the frame
frequency. A magnetic tape 36 obliquely wound on the cylinder 32 is
advanced at a predetermined speed by a tape running mechanism such as a
capstan, so that the magnetic tape 36 is obliquely scanned alternately by
the magnetic heads 28 and 30 to record analog signals such as the video
signals Video on the video tracks TR.sub.V.
The cylinder 32 has a magnet piece and a stationary head (not shown) which
produces a pulse PG representing the rotational phase of the magnetic
heads 28 and 30. The pulse PG is applied to a servo circuit 38. In the
servo circuit 38, the pulse PG is compared with a reference pulse PS
produced by a synchronizing signal generating circuit 40. That is, the
servo circuit 38 controls the spindle motor 34 so that the rotation of the
heads is synchronous with the reference pulse PS, and also controls a
capstan motor 42 so that the speed of running the magnetic tape 36 is
maintained constant. The servo circuit 38 further operates to apply switch
change-over signals SW1 and SW2 respectively to the switches 25 and 26.
The above-described components are commonly provided for the 8-mm video
cassette recorder, being substantially similar to the video cassette
recorder of VHS or beta system.
Now, the PCM still picture recording system of the embodiment will be
described. The camera process circuit 16 outputs the luminance signal Y
and color difference signals R-Y and B-Y. These analog signals Y, R-Y and
B-Y are converted into digital signals YD, (R-Y)D and (B-Y)D by a
change-over switch 50 and A/D (analog-to-digital) converters 52 and 54
with sampling frequencies, for instance, in a ratio of 4:1:1 according to
the component coding system, respectively. In the component encoding in
the ratio of 4:1:1, in the change-over switch 50, the armature is tripped
over the terminals 50a and 50b once while the luminance signal Y is
sampled four times, so that the color difference signals R-Y and B-Y are
each selected once in that period. This operation of the change-over
switch 50 is effected in response to a change-over signal SQ from the
synchronizing signal generator 40. The synchronizing signal generator 40
supplies a clock signal CL for sampling and A/D conversion to the A/D
converters 52 and 54.
In the A/D conversion, the sampling frequency and the quantizing bit number
greatly affect the picture quality, and therefore they must be higher than
certain values; in other words, they should be at least in the Nyquist
band. The sampling frequency should be higher than 2 MHz, preferably
higher than 3 MHz. The quantizing bit number is at least five (bits) for
the luminance signal Y+S, and three for the color difference signals R-Y
and B-Y. In this connection, it should be taken into consideration that,
as the quantizing bit number increases, the processing circuit becomes
more intricate, and the manufacturing cost also increases. In the
embodiment, the quantizing bit number is set to eight (bits) because the
digital data in the 8-mm video format are of 8-bits. For instance in the
case where the still picture quality is such that (1) th frequency
characteristic curve of the luminance signal Y is substantially flat up to
4.2 MHz and (2) the frequency characteristic curves of the color
difference signals R-Y and B-Y are substantially flat up to 1.0 MHz, and a
filter the ratio of "end of passband"/"start of stopband" of 1:1.3 is
used, the sampling frequency is set to at least to 10.92 MHz:
4.2.times.1.3.times.2=10.92 MHz (1)
In the 8-mm video system, the quantity of data bits per field, that is, the
quantity of data bits written in each PCM track TR.sub.P, is set to 1050
words (one word being eight bits). Accordingly, if, in the PCM still
picture recording operation of the embodiment, 1H part of the video signal
is PCM-recorded in each PCM track TR.sub.P, then in the case of the
component coding in the ratio of 4:1:1, the sampling frequency fs for the
luminance signal is set to 700 fH (.apprch.11.01 MHz) according to the
following equation (2):
8(3/2.times.fs/fH)=8.times.1050 (2).
This will satisfy the above-described condition (1). In this case, the
sampling frequency fs/4 for the color difference signals R-Y and B-Y is
set to 175 fH (.apprch.2.75 MHz). On the other hand, 2H part of the video
signal is PCM-recorded every revolution of the cylinder 32. therefore, in
the case where the number of effective scanning lines per frame is 420, a
picture of one frame is PCM-recorded as a still picture in seven (7)
seconds.
The digital signals YD, (R-Y)D and (B-Y)D output by the A/D converters 52
and 54 are inputted for one frame into a frame memory 56 at a write speed
synchronous with the sampling frequency fs. And, in order that, when the
magnetic head 28 or 30 scans the PCM track TR.sub.P, 1H part of the video
signal is PCM-recorded therein, the digital signals YD, (R-Y)D and (B-Y)D
corresponding to the 1H part are output from the frame memory 56 at a
predetermined speed and supplied to a PCM encoder 68 (described later).
Thus, in the frame memory 56, the digital signals YD, (R-Y)-D and (B-Y)D
are read for 1H part during the head scanning period of 36.degree., and
the signals for one frame are read out, for instance, in seven (7)
seconds; that is, the digital signals are subjected to time axis
expansion. The above-described data writing and reading operation of the
frame memory 56 is controlled by a memory controller 58, to which a clock
signal CK and a control signal CT are applied by the synchronizing signal
generating circuit 40 and a system controller 60, respectively.
The PCM encoder 68 is commercially available for the 8-mm video cassette
recorder. In the PCM encoder 68, similarly as in the PCM audio recording
operation, error correction and modulation are carried out. That is, cross
interleave codes of 8-words 2-parities are used as error correcting codes,
and addresses, synchronizing signals and parities are added to data.
Furthermore, error detecting CRC codes are also added. The data include
the video signal, and ID words for indexing. Accordingly, in the case of
the embodiment, the ID words may be utilized, for instance, for detecting
the beginning of a still picture. Furthermore, a biphase modulation which
is a kind of FM modulation is employed for modulation, so that the
recording system following the PCM encoder 68 can be used for both analog
signals and PCM signals.
The digital signals YD, (R-Y)D and (B-Y)D are converted 1H at a time by the
PCM encoder 68 into PCM signals with error correcting codes, which are
applied through the change-over switches 25 and 26 to the magnetic heads
28 and 30 so as to be recorded on the PCM tracks TR.sub.P. The change-over
signals SW1 and SW2 are supplied from the servo circuit 38 to the
change-over switches 25 and 26, so that the switches are closed
alternately every head scanning period. That is, when the tape 36 is
scanned by the magnetic head 28, the switch 25 is closed whereas the
switch 26 is opened. More specifically, in the PCM recording period (or
PCM track scanning period) the armature of the switch 25 is tripped over
to the terminal 25A to supply the PCM signal from the PCM encoder 68 to
the head 28, and in the following motion picture recording period (or
video track scanning period) the armature is tripped over to the terminal
25B to supply the analog video signal Video and the FM audio signal AFM
from the mixer 24 to the head 28. Similarly, when the tape 36 is scanned
with the head 30, the armature of the switch 26 is tripped over to the
terminals 26A and 26B successively, whereas the switch 25 is maintained
opened.
The system controller 60 receives the system clock SC from the
synchronizing signal generating circuit 40 and a head phase pulse PG from
the servo circuit 38, and issues instructions to the memory controller 58
to effect the writing or reading operation of the frame memory 56, and
controls other circuits in the system.
In FIG. 3, a circuit for recording the tracking pilot signal TPS is not
shown.
The PCM still picture recording operation of the embodiment will be
described with reference to FIG. 4.
The part (A) of FIG. 4 shows the fact that pictures picked up by the CCD 12
alter by frame in the order of F1, F2, F3 and so on, thus forming a motion
picture, the frame pictures Fi being recorded in the form of analog video
signals Video on continual video tracks TR.sub.Via, and TR.sub.V,ib of the
magnetic tape 36 as shown in the part (B) Of FIG. 4.
In the embodiment, the PCM still picture recording operation is carried out
with a constant period TC. In FIG. 4, the PCM still picture recording
operation is performed with a period of 240 frames in the order of F1,
F241 and so forth; i.e., a period of eight (8) seconds.
First, the frame picture F1 is fed into the frame memory 56 as shown in the
part (C) of FIG. 4. That is, the analog video signals Y, R-Y and B-Y
representing the frame picture Fl are converted into digital signals YD,
(R-Y)D and (B-Y)D with the predetermined sampling frequencies and
quantizing bit number, which are inputted into the frame memory 56. This
data inputting operation for one frame is carried out under the control of
the system controller 60.
The frame picture F1 thus fed into the frame memory 56 is recorded in
increments of 1H in the form of PCM signals in a plurality of Continual
PCM tracks TR.sub.Pi and TR.sub.Pj. In the embodiment, the number of
effective scanning lines is 420. Therefore, PCM signals F1.multidot.P1
through F1.multidot.P420 are recorded in 420 PCM tracks TR.sub.P,31a
through TR.sub.P,240b, respectively, and the recording time is seven (7)
seconds. In thirty PCM tracks TR.sub.P,1a through TR.sub.P,30b
(corresponding to one second) before the PCM track TRP,31a, no still
picture data are recorded, but a header HE or control data CD are
recorded.
When the PCM still picture recording of the frame picture Fl has been
accomplished, the next still picture frame cycle TC occurs. In the cycle,
similarly as in the above-described case, the frame picture F241 is
PCM-recorded, as a still picture, on 420 PCM tracks.
As was described above, in the embodiment, while a motion picture is
continuously recorded according to the 8-mm video format, one frame (one
frame picture Fi) of the motion picture is selected with the predetermined
period and PCM-recorded, as a still picture, on the PCM tracks (regions)
in the 8-mm video format.
If the heads 28 and 30 or the reproducing heads are rotated irregularly in
speed or the magnetic tape 36 is expanded or contracted or run
irregularly, then the reproduced signals suffer from jitter. However,
during the PCM reproduction, the jitter is effectively removed from the
PCM signals reproduced from the PCM tracks, and therefore the still
picture reproduced is free from swing and distortion. The still picture is
formed according to a method in which the PCM signals of 1H read from the
420 PCM tracks are combined and subjected to PCM demodulation and D/A
conversion to form a standard analog video signal for one frame.
If, in a VTR (video tape recorder), the magnetic tape or the heads have
scratches or dust, then dropout occurs unavoidably. However, this
difficulty is satisfactorily eliminated by the powerful error correcting
function of PCM. For instance when the redundancy of the error correcting
code is set to 40%, the effect of dropout is substantially eliminated, so
that a satisfactory still picture is reproduced. Furthermore, a variety of
picture quality lowering phenomena accompanying analog recording are
virtually eliminated with the still picture PCM-recorded in the
embodiment. Thus, the invention is excellent in the preservation of record
and in the repeatability of reproduction.
As was described above, in the embodiment, while a motion picture is being
taken, one frame of the motion picture is automatically PCM-recorded with
a predetermined period. Therefore, when the frame thus PCM-recorded is
displayed on the television set or formed into a hard copy through PCM
reproduction, then the resultant still picture is substantially as high in
picture quality as photographic pictures. Furthermore, the frame is
PCM-recorded with the same magnetic heads 28 and 30 and magnetic tape 36
that are used for recording motion pictures, which eliminates not only the
necessity for special mechanisms but also any increase in weight or in
size. Furthermore, the PCM tracks in the 8-mm video system are utilized;
more specifically, a still picture is PCM-recorded in the PCM tracks
according to the PCM format which is substantially the same as that in the
PCM audio recording system, and therefore the PCM encoder for PCM audio
recording operation can be used, as it is, for recording still pictures.
This contributes greatly to reduction of the manufacturing cost.
Thus, the 8-mm video cassette recorder of the invention is a camera
recorder which is lightweight, low in manufacturing cost, high in picture
quality, and has functions of a still camera, and can be conveniently
used.
While the invention has been described with reference to its preferred
embodiment, the invention is not limited thereto or thereby and it will be
obvious to those skilled in the art that various changes and modifications
may be made therein without departing from the invention. For instance,
the sampling period, the quantizing characteristic, and the recording time
mode can be changed when necessary. Such modifications are for instance as
indicated in FIG. 5.
In FIG. 5, Specification A is for the above-described embodiment.
In Specification B, no H blank (horizontal blanking period) is recorded,
and the picture quality is specified high, so that the sampling frequency
is increased as much. However, the effective picture element (PIXEL)
number, the recording PCM track number, and the recording time are the
same as those in Specification A.
In Specification C, the color difference signals R-Y and B-Y are recorded
alternately every 1H, and video signals for 2H are PCM-recorded in one PCM
track under the condition that no H blank is recorded. In Specification C,
the recording PCM track number and the recording time are reduced to half;
however the resultant picture is relatively rough in quality because of
the low sampling frequency.
In Specification D, the conditions are the same as those in Specification
C; however, the sampling frequencies are set to higher values to improve
the picture quality, and therefore the recording PCM track number and the
recording time are slightly increased accordingly.
Only four specifications have been described; however, other specifications
are, of course, available. In the above-described embodiment, the PCM
still picture recording operation is carried out by the frame; however, it
is possible to perform the recording operation by the field.
As is apparent from the above description, the technical concept of the
invention is effectively applied to an 8-mm video cassette recorder;
however, the invention is applicable not only to camera recorders of other
standards but also to portable separable video tape recorders, and to
so-called "fixed video tape recorders" so that television pictures can be
PCM-recorded as still pictures.
As was described above, in the magnetic recording device of the invention,
while a motion picture is being recorded, part of the motion picture which
corresponds to one unit such as one frame or field is extracted and
PCM-recorded as a still picture with a predetermined period. Thereafter,
for instance, in the case of a camera recorder- while a motion picture is
being taken, one frame of the motion picture is PCM-recorded periodically,
and therefore when the frame thus recorded is reproduced on a television
screen or as a hard copy, the resultant still picture is appreciably high
in picture quality.
Furthermore, in the invention, the PCM still picture recording operation is
carried out with the same magnetic heads and magnetic tape that are used
for recording motion pictures, and therefore it is unnecessary to employ
special mechanisms. Accordingly, the magnetic recording device of the
invention is lightweight and low in manufacturing cost and is well
balanced in arrangement. Especially, application of the technical concept
of the invention to an 8-mm video format can be employed as they are.
In order to issue an operation instruction signal to the system controller
60, a still picture recording button 62 may be provided to the outside of
the camera housing as shown in FIG. 6. In the embodiment of FIG. 6, the
writing or reading operation of the frame memory 56 is effected in
response to the operation instruction signal. A still recording indication
lamp 64 is provided in a view finder, so that it is turned on during the
PCM still picture recording operation to thereby indicate that the PCM
still picture recording operation is now being carried out.
In this embodiment, the PCM still picture recording operation is carried
out in response to the operation of the still picture recording button 62.
In FIG. 7, the still picture recording button 62 is depressed at the time
instant t.sub.1. At this instant, the frame picture F3 is being recorded.
In response to the operation of the button, the system controller 60
issues an instruction signal to the memory controller at the time instant
t.sub.2 when recording of the next frame picture F4 starts, so that the
writing operation of the frame memory 56 is effected. The time instant
t.sub.2 when the recording operation is started is based on the head phase
pulse PG from the servo circuit 38. From the time instant t.sub.2 on, the
digital signals YD, (R-Y)D and (B-Y)D representing the frame picture F4
are stored in the frame memory 56. At the same time, the system controller
60 turns on the still picture recording lamp 64.
The digital signals YD, (R-Y)D and (B-Y)D thus stored are recorded by in
increments of 1H, in the form of a PCM signal, in a plurality of continual
PCM tracks TR.sub.P,i and TR.sub.P,j in a predetermined period of time. In
this embodiment, the number of effective Scanning lines is 420. Therefore,
the PCM signals (of 1H) F4.multidot.P1 through F4.multidot.P420 are
recorded in 420 PCM tracks TR.sub.P,34a through TR.sub.P,243b,
respectively, and the recording time is seven (7) seconds. No still
picture data are recorded in the thirty PCM tracks TR.sub.P,4a through
TR.sub.P,33n (corresponding to the lapse of one second) located before the
PCM track TR.sub.P,33a; however, a header HE and a control data CD are
recorded therein.
When the PCM still picture recording operation of the frame picture F4 is
accomplished at the time instant t.sub.3, the system controller 60 turns
off the still picture recording lamp 64, thus notifying the operator of
the fact that the next still picture recording operation can be carried
out; that is, the still picture recording button 62 can be depressed. When
the button 62 is depressed after the lamp 64 has turned off, the frame
picture Fi occurring immediately after the operation of the button 62 is
PCM-recorded as a still picture similar to the case of the frame picture
F4.
When the still picture recording button 62 is depressed while the still
picture recording lamp 64 is on, the depression of the button is made
ineffective by the system controller 60.
As was described above, during the recording operation of a motion picture,
a desired frame of the motion picture can be PCM-recorded by depressing
the still picture recording button 62. Therefore, when the frame thus
PCM-recorded is displayed on the television set or formed into a hard copy
through PCM reproduction, then the resultant still picture is
substantially as high in picture quality as a photographic picture.
Furthermore, the frame is PCM-recorded with the same magnetic heads 28 and
30 and magnetic tape 36 that are used for recording motion pictures, which
eliminates not only the necessity for special mechanisms but also
eliminates any increase in weight or in size. Furthermore, the PCM tracks
in the 8 mm video system are utilized; more specifically, a still picture
is PCM-recorded in the PCM tracks according to the PCM format which is
substantially the same as that in the PCM audio recording operation and
thus can be used, as it is, for recording still pictures. This contributes
greatly to reduction of the manufacturing cost.
Thus, the 8-mm video cassette recorder of the invention is a camera
recorder which is lightweight, low in manufacturing cost, and high in
picture quality, and has function of a still camera, and can be
conveniently used.
In the above-described embodiment, when the still picture recording button
62 is depressed while the still picture recording lamp 64 is kept turned
on i.e., the PCM still picture recording operation is being carried out,
the depression of the button is made ineffective; however, the magnetic
recording device may be so modified that the depression of the button is
accepted during the PCM still picture recording operation. In the
modification, the PCM still picture recording operation is suspended, and
the frame picture Fi occurring immediately after th operation of the
button is PCM-recorded as a still picture. In the PCM still picture
recording operation of the frame picture Fi, data indicating that the
preceding PCM still picture recording operation has been suspended is
included in the header HE.
In the above-described embodiment, the exposure time is equal to that of an
ordinary video camera, 1/30 second or 1/60 second. However, if the device
is provided with a high speed shutter, then a moving object can be
PCM-recorded as a still picture higher in picture quality.
FIG. 8 shows the arrangement of essential components of another embodiment
of the invention provided with a shutter mechanism. Components not shown
in FIG. 8 are equal to those which have been described with reference to
FIG. 6. In FIG. 8, reference numeral 66 designates a programmable shutter
serving also as an aperture blade. The shutter 66 is driven by a shutter
drive section 69 in response to an instruction signal from the system
controller 60. A shutter button 67 corresponds to the still picture
recording button of the above-described embodiment.
FIG. 9 is a time chart for a description of the operation of the shutter 66
in the embodiment (or modification). In FIG. 9, reference characters
t.sub.1, t.sub.2, t.sub.3 and so on designate the start time instant of
frame periods T1, T2, T3 and so on (=1/30 Second), and t.sub.A, the time
instant when the shutter button 67 is depressed. In the frame period T3
occurring immediately after the shutter operation time instant t.sub.A, at
the start time instant t.sub.3 the shutter 66 is closed from its aperture
value Fc in a steady mode, and at the predetermined time instant t.sub.B
the shutter 66 is opened to an aperture value Fn. The aperture value Fn is
determined according to the exposure time t.sub.B -t.sub.4 so that the
total exposure value S3 in the frame period T3 is equal to the exposure
values S1, S2, S4, . . . of the other exposure periods T1, T2, T4, . . . .
. At the end of the frame period T3, the video signal output by the CCD
12, after being digitized, is stored in th | | |
