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Claims  |
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What is claimed is:
1. A method of recording image data in successive tracks on a rotatable
medium driven at substantially constant linear velocity, comprising:
receiving successive image frames of said image data; encoding said image
frames by converting a first image frame of image data to an intraframe
code signal and converting (n-1) succeeding image frames of image data to
(n-1) interframe code signals, wherein n is the maximum number of image
frames recordable in an innermost track of said medium driven at
substantially constant linear velocity; and recording at least one
intraframe code signal and at least (n-1) interframe code signals in each
track.
2. The method of claim 1 wherein the step of recording comprises recording
(n-1) interframe code signals between successive intraframe code signals.
3. The method of claim 2 wherein said successive tracks comprise a spiral
track of successive turns and the intraframe and interframe code signals
are recorded in said spiral track.
4. The method of claim 1 wherein each track is comprised of a number of
data frames, and the step of recording comprises recording an intraframe
code signal in plural data frames and recording (n-1) interframe code
signals in less than (n-1) data frames.
5. The method of claim 1 wherein the step of recording comprises recording
intraframe code signals at locations adjacent each other in successive
tracks.
6. The method of claim 1 wherein the step of recording comprises recording
more than (n-1) interframe code signals between successive intraframe code
signals as the radius of the track in which said interframe code signals
are recorded increases.
7. The method of claim 6 wherein the step of recording further comprises
recording only one intraframe code signal in a track.
8. The method of claim 7 wherein said successive tracks comprise a spiral
track of successive turns.
9. The method of claim 8 wherein the step of recording comprises recording
an integral number of encoded image frames in an equal number of data
frames, with said intraframe code signal being recorded in plural data
frames in a turn and the remaining data frames in that turn having
recorded therein interframe code signals which follow said intraframe code
signal.
10. The method of claim 1 wherein the step of converting an image frame of
image data to an interframe code signal comprises comparing one frame of
image data to a preceding frame of image data and encoding the differences
therebetween such that said interframe code signal represents said
differences.
11. A method of reproducing image data from successive turns on a rotatable
record medium driven at substantially constant linear velocity, wherein
said image data has been recorded as an intraframe code signal
representing an image frame followed by a number of successive interframe
code signals representing an equal number of successive image frames, with
said number of interframe code signals in a turn being at least as large
as the capacity of interframe code signals recordable in an innermost
turn, said method comprising: reproducing the intraframe and interframe
code signals in each turn; coupling the reproduced code signals to an
intraframe decoder to recover image data therefrom; coupling the
reproduced code signals to an interframe decoder to recover image data
therefrom; sensing if an intraframe or interframe code signal is
reproduced; and changing over the reproduced code signals between the
intraframe decoder and the interframe decoder as a function of whether the
intraframe or interframe code signal is sensed as being reproduced.
12. The method of claim 11 wherein a predetermined number of interframe
code signals had been recorded between successive intraframe code signals,
and wherein the step of changing over the reproduced code signals between
the intraframe decoder and the interframe decoder comprises changing over
the reproduced code signals from the interframe decoder to the intraframe
decoder after said predetermined number of code signals has been
reproduced and changing over the reproduced code signals from the
intraframe decoder to the interframe decoder after an intraframe code
signal has been reproduced.
13. The method of claim 12 wherein each turn is comprised of several data
frames, with each intraframe code signal recorded in plural data frames
and the predetermined number of interframe code signals recorded in
next-following data frames.
14. The method of claim 13 wherein said predetermined number of interframe
code signals is recorded in less than said predetermined number of data
frames.
15. The method of claim 11 wherein the number of interframe code signals
recorded between successive intraframe code signals varies with the radius
of the turn in which said interframe code signals are recorded, and
wherein the step of changing over the reproduced code signals between the
intraframe decoder and the interframe decoder includes the step of
controlling the change-over as a function of the radius of the turn from
which the code signals are reproduced.
16. The method of claim 15 wherein the number of interframe code signals
recorded between successive intraframe code signals increases as the
radius of the turn in which said interframe code signals are recorded
increases, and wherein the step of controlling the change-over comprises
changing over the reproduced code signals from the interframe decoder to
the intraframe decoder after a variable number of interframe code signals
has been reproduced, said variable number being determined by the radius
of the turn from which the interframe code signals are reproduced.
17. The method of claim 16 wherein only one intraframe code signal is
recorded in a turn, and wherein the step of changing over the reproduced
code signals between the intraframe decoder and the interframe decoder
further includes changing over the reproduced code signals from the
intraframe decoder to the interframe decoder after an intraframe code
signal is reproduced.
18. The method of claim 11 wherein the intraframe code signal and/or the
interframe code signal includes identifying data; wherein the step of
sensing comprises detecting said identifying data; and wherein the step of
changing over the reproduced code signals comprises coupling said
reproduced code signals to said intraframe decoder or to said interframe
decoder in response to the detected identifying data.
19. A method of recording image data in successive turns on a rotatable
medium driven at substantially constant linear velocity, comprising:
receiving successive image frames of said image data; converting a first
of said image frames of image data to an intraframe code signal;
converting m succeeding image frames of image data to m interframe code
signals, wherein m is a variable integer depending upon the particular
turn in which the intraframe and interframe code signals are recorded; and
recording the intraframe code signal and m interframe code signals on said
medium.
20. The method of claim 19 wherein the step of recording includes recording
intraframe code signals at locations proximate each other in successive
turns.
21. The method of claim 20 wherein the step of recording further includes
recording only one intraframe code signal in each turn.
22. The method of claim 19 wherein the step of converting m succeeding
image frames of image data to m interframe code signals includes data
compressing said m image frames of image data such that each interframe
code signal is of a length less than a data frame; and wherein the step of
recording includes recording said m interframe code signals in less than m
data frames.
23. The method of claim 22 wherein the step of recording further includes
recording an intraframe code signal in plural data frames in a turn.
24. The method of claim 19 wherein said successive turns comprise
successive circular tracks on said record medium.
25. The method of claim 19 wherein said successive turns comprise a spiral
track on said record medium.
26. A method of reproducing image data from successive turns on a rotatable
record medium driven at substantially constant linear velocity, wherein
said image data has been recorded on said medium as an intraframe code
signal representing an image frame followed by a m successive interframe
code signals representing m successive image frames and wherein m is a
variable integer depending upon the particular turn in which the
intraframe and interframe code signals are recorded, said method
comprising: reproducing the intraframe and interframe code signals from
each turn; selectively coupling the reproduced code signals to an
intraframe decoder to decode an intraframe code signal reproduced from a
turn and then to an interframe decoder to decode m successive interframe
code signals reproduced from said turn, thereby to recover image data from
intraframe and interframe code signals reproduced from a turn; sensing
when an intraframe or interframe code signal is reproduced; and
controlling the selective coupling of said reproduced code signals as a
function of whether intraframe or interframe code signals are sensed as
being reproduced.
27. The method of claim 26 wherein the step of controlling the selective
coupling comprises sensing the turn from which the intraframe and
interframe code signals are reproduced, detecting when m interframe code
signals have been reproduced, and coupling the reproduced code signals to
said intraframe decoder after m interframe code signals have been
reproduced.
28. The method of claim 27 wherein each turn is comprised of several data
frames, with each intraframe code signal recorded in a predetermined
number of data frames; and wherein the step of controlling the selective
coupling comprises detecting when said intraframe code signal has been
reproduced from said predetermined number of data frames and coupling the
reproduced code signals to said interframe decoder.
29. The method of claim 28 wherein only one intraframe code signal is
recorded in each turn.
30. The method of claim 26 wherein intraframe code signals are recorded at
locations proximate each other in successive turns.
31. The method of claim 26 wherein the intraframe code signal and/or the
interframe code signal includes identifying data; and wherein the step of
controlling the selective coupling comprises detecting said identifying
data in the reproduced code signals and coupling said reproduced code
signals to said intraframe decoder or to said interframe decoder in
response to the detected identifying data.
32. Apparatus for recording image data in successive tracks on a rotatable
medium driven at substantially constant linear velocity, comprising: input
means for receiving successive image frames of said image data; intraframe
encoding means for converting a first image frame of image data to an
intraframe code signal; interframe encoding means for converting (n-1)
succeeding image frames of image data to (n-1) interframe code signals,
wherein n is the maximum number of image frames recordable in an innermost
track of said medium driven at substantially constant linear velocity; and
recording means for recording an intraframe code signal and at least (n-1)
interframe code signals in each track.
33. The apparatus of claim 32 wherein said recording means comprises means
for recording (n-1) interframe code signals between successive intraframe
code signals.
34. The apparatus of claim 33 wherein said recording means records the
intraframe and interframe code signals in a spiral track of successive
turns.
35. The apparatus of claim 32 wherein each track is comprised of a number
of data frames, and said recording means comprises means for recording an
intraframe code signal in plural data frames and for recording (n-1)
interframe code signals in less than (n-1) data frames.
36. The apparatus of claim 32 wherein said recording means comprises means
for recording intraframe code signals at locations adjacent each other in
successive tracks.
37. The apparatus of claim 32 wherein said recording means comprises means
for recording more than (n-1) interframe code signals between successive
intraframe code signals as the radius of the track in which said
interframe code signals are recorded increases.
38. The apparatus of claim 37 wherein said recording means further
comprises means for recording only one intraframe code signal in a track.
39. The apparatus of claim 38 wherein said successive tracks comprise a
spiral track of successive turns.
40. The apparatus of claim 39 wherein said recording means additionally
comprises means for recording an integral number of image frames in an
equal number of data frames by recording said intraframe code signal in
plural data frames in a turn and recording interframe code signals which
follow said intraframe code signal in the remaining data frames in that
turn.
41. The apparatus of claim 32 wherein said interframe encoding means
comprises means for comparing one frame of image data to a preceding frame
of image data and means for encoding the differences therebetween such
that said interframe code signal represents said differences.
42. Apparatus for reproducing image data from successive turns on a
rotatable record medium driven at substantially constant linear velocity,
wherein said image data has been recorded as an intraframe code signal
representing an image frame followed by (n-1) successive interframe code
signals representing (n-1) successive image frames, where n is at least as
large as the capacity of image frame signals recordable in an innermost
turn, said apparatus comprising: playback means for reproducing the
intraframe and interframe code signals in each turn; intraframe decoder
means for recovering image data from the reproduced code signals;
interframe decoder means for recovering image data from the reproduced
code signals; sensing means for sensing if an intraframe or interframe
code signal is reproduced; and coupling means for coupling the reproduced
code signals to the intraframe decoder means or to the interframe decoder
means as a function of whether said intraframe or interframe code signals
are sensed as being reproduced.
43. The apparatus of claim 42 wherein a predetermined number of interframe
code signals is recorded between successive intraframe code signals, and
wherein said coupling means comprises change-over means for changing over
the coupling of the reproduced code signals from the interframe decoder
means to the intraframe decoder means after said predetermined number of
code signals has been reproduced and for changing over the coupling of the
reproduced code signals from the intraframe decoder means to the
interframe decoder means after an intraframe code signal has been
reproduced.
44. The apparatus of claim 43 wherein each turn is comprised of several
data frames, with each intraframe code signal recorded in plural data
frames and the predetermined number of interframe code signals recorded in
next-following data frames.
45. The apparatus of claim 44 wherein said predetermined number of
interframe code signals is recorded in less than said predetermined number
of data frames.
46. The apparatus of claim 42 wherein the number of interframe code signals
recorded between successive intraframe code signals varies with the radius
of the turn in which said interframe code signals are recorded, and
wherein said coupling means includes control means for controlling said
coupling means as a function of the radius of the turn from which the code
signals are reproduced.
47. The apparatus of claim 46 wherein the number of interframe code signals
recorded between successive intraframe code signals increases as the
radius of the turn in which said interframe code signals are recorded
increases, and wherein said control means includes means for changing over
the coupling of the reproduced code signals from the interframe decoder
means to the intraframe decoder means after a variable number of
interframe code signals has been reproduced, said variable number being
determined by the radius of the turn from which the interframe code
signals are reproduced.
48. The apparatus of claim 47 wherein only one intraframe code signal is
recorded in a turn, and wherein said control means further includes means
for changing over the reproduced code signals from the intraframe decoder
means to the interframe decoder means after an intraframe code signal is
reproduced.
49. The apparatus of claim 42 wherein the intraframe code signal and/or the
interframe code signal includes identifying data; and wherein said
coupling means comprises means for detecting said identifying data, and
means for supplying said reproduced code signals to said intraframe
decoder means or to said interframe decoder means in response to the
detected identifying data.
50. Apparatus for recording image data in successive turns on a rotatable
medium driven at substantially constant linear velocity, comprising: input
means for receiving successive image frames of said image data; intraframe
encoding means for converting a first of said image frames of image data
to an intraframe code signal; interframe encoding means for converting m
succeeding image frames of image data to m interframe code signals,
wherein m is a variable integer depending upon the particular turn in
which the intraframe and interframe code signals are recorded; and
recording means for recording the intraframe code signal and m interframe
code signals on said medium.
51. The apparatus of claim 50 wherein said recording means includes means
for recording intraframe code signals at locations proximate each other in
successive turns.
52. The apparatus of claim 51 wherein said recording means further includes
means for recording only one intraframe code signal in each turn.
53. The apparatus of claim 50 wherein said interframe encoding means
includes means for data compressing said m image frames of image data such
that each interframe code signal is of a length less than a data frame;
and wherein said recording means includes means for recording said m
interframe code signals in less than m data frames.
54. The apparatus of claim 53 wherein said recording means further includes
means for recording an intraframe code signal in plural data frames in a
turn.
55. The apparatus of claim 50 wherein said successive turns comprise
successive annular tracks on said record medium.
56. The apparatus of claim 50 wherein said successive turns comprise a
spiral track on said record medium.
57. Apparatus for reproducing image data from successive turns on a
rotatable record medium driven at substantially constant linear, wherein
said image data has been recorded on said medium as an intraframe code
signal representing an image frame followed by m successive interframe
code signals representing m successive image frames and wherein m is a
variable integer depending upon the particular turn in which the
intraframe and interframe code signals are recorded, said apparatus
comprising: playback means for reproducing the intraframe and interframe
code signals from each turn; intraframe decoder means for decoding an
intraframe code signal to recover image data therefrom; interframe decoder
means for decoding m successive interframe code signals to recover image
data therefrom; coupling means for selectively coupling the code signals
reproduced from a turn to said intraframe decoder means or to said
interframe decoder means; and control means for controlling the selective
coupling of said reproduced code signals as a function of whether
intraframe or interframe code signals are reproduced.
58. The apparatus of claim 57 wherein said control means comprises sense
means for sensing the turn from which the intraframe and interframe code
signals are reproduced, detecting means for detecting when m interframe
code signals have been reproduced, and means for coupling the reproduced
code signals to said intraframe decoder means after m interframe code
signals have been reproduced.
59. The apparatus of claim 58 wherein each turn is comprised of several
data frames, with each intraframe code signal recorded in a predetermined
number of data frames; and wherein said control means further comprises
means for detecting when said intraframe code signal has been reproduced
from said predetermined number of data frames and means for coupling the
reproduced code signals to said interframe decoder means in response
thereto.
60. The apparatus of claim 59 wherein only one intraframe code signal is
recorded in each turn.
61. The apparatus of claim 57 wherein intraframe code signals are recorded
at locations proximate each other in successive turns.
62. The apparatus of claim 57 wherein the intraframe code signal and/or the
interframe code signal includes identifying data; and wherein said control
means comprises means for detecting said identifying data in the
reproduced code signals, and means for coupling said reproduced code
signals to said intraframe decoder means or to said interframe decoder
means in response to the detected identifying data. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for recording/reproducing
data on a rotatable record medium and, more particularly, to a technique
by which image data is recorded in data-compressed form but, nevertheless,
can be reproduced when the medium is scanned in a special mode, such as a
high speed search mode, to permit a viewable display of the recorded
images while that medium is scanned.
2. Description of the Prior Art
The recording of image information on a record medium has long been known.
Magnetic recording permits the re-use of a magnetic medium to record and
reproduce image information several times. For example, image information
is recorded in slant tracks on a magnetic tape or in successive turns on a
magnetic disk, such as the successive turns of a spiral track or in
concentric circular tracks on the disk. Image information also has been
recorded on video disks, such as laser disks in which image data is
represented by pits and lands. Recently, it has been proposed that image
information in the form of video signals be recorded on an optically
readable disk conforming generally in size and physical characteristics to
the so-called audio "compact disk", conventionally referred to as a "CD".
Such information may be recorded in successive turns of a single spiral
track or in consecutive circular tracks.
A compact disk, on which information may be thought of as being permanently
recorded, may be "read" several times. Such a disk functions as a memory
for recorded digital information and often is referred to as a "CD-ROM".
Compact disks and CD-ROM's generally conform to "standards" which tend to
limit the amount of information that can be recorded thereon. Such
standards establish, inter alia, the rotary speed of the disk and the
number and density of the tracks that may be recorded thereon. When
digital video information is recorded, as by digitizing a conventional
videosignal (e.g. an NTSC signal), the CD-ROM conforming to such standards
exhibits a recording capacity on the order of about one hour. Thus, a
video program whose duration does not exceed approximately one hour may be
recorded and played back from such a CD-ROM.
It is appreciated that a larger quantity of data may be recorded on a
CD-ROM if that data is subjected to data compression techniques. For
example, the inherent redundancy in video information suggests that video
signals are favorably susceptible to data compression. An adaptive process
for the coding and decoding of a sequence of pictures by discrete cosine
transformation has been proposed in U.S. Pat. No. 4,707,738. As described
in this patent, video signals may be data compressed by producing
"inter-picture" and "intra-picture" representations of image information.
The inter-picture information, or code, represents the differences between
two successive pictures, or frames. This difference information
constitutes a substantial compression of data, although a video picture
cannot be reproduced from a given inter-picture code signal without a
reference picture or frame to which the difference information may be
combined to reconstitute the encoded picture. However, the intra-picture
information represents substantially all of the information of a given
frame and, thus, constitutes a rather small amount of data compression.
Using the adaptive coding process of the aforementioned patent, intraframe
code signals and interframe code signals may be recorded on a CD-ROM to
extend the effective capacity of that CD-ROM for recording video signals.
This technique is particularly advantageous when highly animated image
data is encoded. Thus, by using intraframe and interframe code signals,
image data which varies rapidly over several frames may be data
compressed. Such encoding of image information into intraframe and
interframe code signals is particularly adapted for compressing the large
amount of information present in a high density television signal.
Typically, a first image frame is encoded as an intraframe code signal and
then, several frames later, another image frame is encoded as an
intraframe code signal. Those image frames which extend between the
successive intraframe encoded frames are encoded as interframe code
signals. When these intraframe and interframe code signals are recorded on
a CD-ROM, such as in successive turns of a spiral track, an intraframe
code signal may be recorded in one turn but the next intraframe code
signal may not be recorded for several turns. This may not present any
difficulties during normal video playback modes because the several
successive interframe code signals which are reproduced are combined with
the information derived from the previously reproduced intraframe code
signal to recover whole frames of image data for display as a conventional
television picture having excellent fidelity. Indeed, several turns of
merely interframe code signals may be reproduced without any noticeable
deterioration in the quality of the displayed picture.
However, when one intraframe code signal followed by several turns of
interframe code signals are recorded, the television picture reproduced
therefrom during special reproducing modes, such as a high speed search
mode, may not be acceptable. In a high speed search mode, the playback
head is moved radially across the record medium at a relatively high
speed. Hence, successive interframe code signals are not reproduced.
Rather, the radial movement of the head during this "track jumping"
operation reproduces selective, individual interframe code signals that
may vary greatly from the previous intraframe code signal that was played
back. Hence, image frames which are derived from these individual
interframe code signals may exhibit less than acceptable quality during
special reproducing modes. Therefore, if image information is to be
recorded on a rotatable medium, such as a CD-ROM, data compression by way
of interframe coding may not permit satisfactory high speed searching.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an improved
technique for recording and reproducing image data on a rotatable record
medium which permits high data compression of the image data yet enables
high quality viewable images to be reproduced therefrom during both normal
and special reproducing modes.
Another object is to record data-compressed image information on a
rotatable record medium which may be reproduced and accurately displayed
as a video picture during high speed searching of that medium.
A further object of this invention is to provide a technique for recording
and reproducing image information in the form of data-compressed
intraframe and interframe code signals in successive turns of a rotatable
record medium such that at least one intraframe code signal is recorded in
each turn.
An additional object of this invention is to provide a technique of the
aforementioned type in which the number of interframe code signals which
are recorded between successive intraframe code signals is fixed for all
turns of the record medium.
Still another object of this invention is to provide a technique of the
aforementioned type in which the number of interframe code signals which
are recorded between successive intraframe code signals varies as a
function of the radius of the turn in which they are recorded.
Yet a further object of this invention is to provide a technique in which
image data is recorded on a rotatable record medium as data-compressed
intraframe and interframe code signals, with the intraframe code signals
being recorded at locations proximate each other in successive turns.
Various other objects, advantages and features of the present invention
will become readily apparent from the ensuing detailed description, and
the novel features will be particularly pointed out in the appended
claims.
In accordance with this invention, image data is recorded in successive
turns on a rotatable record medium by converting a first of successive
image frames of image data to an intraframe code signal, converting the
(n-1) next-following frames to (n-1) interframe code signals, and
recording the intraframe and (n-1) interframe code signals on the record
medium. In one embodiment, n is the maximum number of image frames that
can be recorded in the innermost turn of the record medium, n is constant
for all turns and an intraframe and (n-1) interframe code signals are
recorded in all turns. In this embodiment, the same number (n-1) of
interframe code signals separate successive intraframe code signals in all
turns.
In another embodiment, n is a variable and increases as the radius of the
turn in which the code signals are recorded increases. In this other
embodiment, a larger number (n-1) of interframe code signals separate
successive intraframe code signals as the turn radius increases.
As one aspect of this other embodiment, since intraframe code signals are
recorded at locations proximate each other in successive tracks, during a
special reproducing code, such as a high speed search mode, the pick-up
head may be advanced rapidly in the radial direction and may jump from one
intraframe code signal to another from track-to-track to reproduce a video
picture of good fidelity while searching.
In one application of this invention, the successive turns in which the
intraframe and interframe code signals are recorded constitute a spiral
track on the record medium. In another application, the successive turns
constitute consecutive circular tracks. Preferably, the record medium
comprises an optically readable compact disk, such as a CD-ROM; but,
alternatively, the record medium may comprise a magnetic disk.
As another feature of this invention, the recorded image data is recovered
by reproducing the intraframe and interframe code signals and selectively
coupling those code signals either to an intraframe decoder or to an
interframe decoder from which images are reproduced. The selective
coupling is controlled as a function of whether intraframe or interframe
code signals are reproduced. In one embodiment, the intraframe and/or
interframe code signals are provided with identifying data; and this
identifying data is detected and used to couple the reproduced code
signals to one or the other decoder. In another embodiment, a
predetermined number (n-1) of interframe code signals separates successive
intraframe code signals; and the selective coupling of the code signals to
one or the other decoder is controlled as a function of the number of code
signals which are reproduced. In still another embodiment, the number
(n-1) of interframe code signals which separates successive intraframe
code signals varies as the radius of the turn in which those code signals
are recorded. The selective coupling of the reproduced code signals to one
or the other decoder is controlled as a function of the radial position of
the pick-up head used to reproduce those code signals.
BRIEF DESCRIPTION OF THE DRAWINGS
The following detailed description, given by way of example, will best be
understood in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic representation of a record medium having image
information recorded thereon in accordance with one embodiment of the
present invention;
FIG. 2 is a schematic representation of one embodiment of the recording
format used to record intraframe and interframe code signals;
FIG. 3 is a block diagram of apparatus for reproducing the image
information having the format shown in FIG. 1;
FIG. 4 is a schematic representation of a record medium having image
information recorded thereon in accordance with another embodiment of the
present invention;
FIG. 5 is a schematic representation of the recording format used to record
the image information of FIG. 4;
FIG. 6 is a block diagram of apparatus for recording the image information
on the record medium shown in FIG. 4;
FIG. 7 is a block diagram of apparatus for reproducing the image
information from the record medium shown in FIG. 4;
FIG. 8 is a schematic representation of successive turns of information
recorded on the record medium and is helpful in understanding the
advantages achieved by this invention;
FIGS. 9A-9C are schematic representations of information reproduced from
successive turns during a high speed search operation; and
FIGS. 10A-10C are schematic representations of the manner in which video
pictures are displayed during the high speed search operation.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Before proceeding with a description of the present invention, an
explanation and definition of the terms "intraframe code signal" and
"interframe code signal" are provided. As mentioned above, data
compression is achieved preferably by an adaptive process for coding a
sequence of image frames by discrete cosine transformation. One example of
apparatus for implementing this process to produce both intraframe and
interframe code signals is described in U.S. Pat. No. 4,707,738, and
another example is discussed hereinbelow with respect to FIG. 6. Likewise,
one implementation of the adaptive process for decoding the intraframe and
interframe code signals is described in the aforementioned patent, and
another example of a suitable decoder is described below in conjunction
with FIG. 7. From the aforementioned patent and forthcoming discussion, it
will be recognized that an intraframe code signal contains most of the
information of an original image frame of image data, such as an original
video signal, and although data compression is achieved, the degree of
such compression is substantially less than that attained by an interframe
code signal. The latter is produced using a discrete cosine transformed
signal and represents differences between successive frames of the image
signal. The transformed differences are encoded, as by a variable length
coding arrangement, and the amount of data needed to represent those
differences is far less than the amount of data needed to represent the
entire image frame. Consequently, the interframe code signal exhibits
substantial data compression.
Although the invention described herein preferably uses discrete cosine
transformation of the image data from which intraframe and interframe code
signals are produced, other efficient data compression encoding techniques
can be used. For example, adaptive dynamic range coding which encodes the
image information as a function of the dynamic range of the image data
within discrete blocks of the image frame. Other encoding processes may be
used, if desired.
Turning now to FIG. I, there is illustrated a schematic representation of a
record medium 10 having data compressed image information recorded
thereon. For convenience, the image information is recorded in successive
turns T1, T2, T3, etc. which constitute a spiral track. Alternatively,
turns T1, T2, etc. may comprise discrete circular tracks. Furthermore, it
is assume that record medium 10 is a compact disk, such as a CD-ROM, and
the information recorded in successive turns T1, T2, etc. is digital
information representing image frames. It is appreciated that the CD-ROM
is a copy to be used by a suitable player from which the recorded image
data is reproduced. FIG. 1 also illustrates the track configuration
recorded on a master disk from which a mother is made to produce CD-ROM
copies. Of course, record medium 10 may be a magnetic disk having the
illustrated track configuration.
An understanding of FIG. 1 is best appreciated by referring to the
recording format illustrated in FIG. 2. This recording format represents
six successive image frames F1-F6 which have been encoded into an
intraframe code signal F1 and five succeeding interframe code signals F2,
F3, . . . F6.
Six data frames have been selected for the following reason: Let it be
assumed that record medium 10 is a CD-ROM. When this medium is driven at a
rate conventionally used for compact disk applications, the innermost turn
exhibits a capacity of recording approximately 5.5 image frames, wherein
each frame is a conventional video signal frame. If the medium is driven
with constant linear velocity then, as the recording head or playback head
is driven radially outward, the angular speed of the medium is reduced
such that the linear velocity of each turn is substantially constant. When
recording and reproducing image information at constant linear velocity,
and assuming a recording capacity of approximately one hour, the innermost
turn T1 may record six image frames, provided that data compression is
employed. Thus, six image frames are compressed to "fit" into a turn
capable of storing 5.5 image frames.
As illustrated in FIG. 2, the six image frames constitute a set, and
successive sets of image frames are recorded in successive turns. The
six-frame set is comprised of im | | |
