US007 1581.67B1
`
`(12) United States Patent
`Yerazunis et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,158,167 B1
`Jan. 2, 2007
`
`(54) VIDEO RECORDING DEVICE FOR A
`TARGETABLE WEAPON
`
`(75) Inventors: William S. Yerazunis, Acton, MA
`(US); Darren L. Leigh, Belmont, MA
`US (US)
`(73) Assignee: Mitsubishi Electric Research
`Laboratories, Inc., Cambridge, MA
`(US)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`5,845,165 A * 12/1998 McMahan ................... 396/426
`5,845,240 A * 12/1998 Fielder ..........
`... 704/201
`5,930,493 A * 7/1999 Ottesen et al. ................ 725/92
`
`(Continued)
`FOREIGN PATENT DOCUMENTS
`4127534 A1 * 2, 1993
`
`DE
`
`(Continued)
`Primary Examiner Mehrdad Dastouri
`(74) Attorney, Agent, or Firm—Andrew J. Cartin; Dirk
`Brinkman
`
`(21) Appl. No.: 09/150,360
`
`(57)
`
`ABSTRACT
`
`(22) Filed:
`
`Sep. 9, 1998
`O
`O
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 08/906,493,
`filed on Aug. 5, 1997.
`
`(51) Int. Cl.
`(2006.01)
`H04N 7/8
`(2006.01)
`GIB 5/00
`(52) U.S. Cl. ............................................. 348/61; 360/5
`(58) Field of Classification Search .................. 348/61,
`348/143, 151: 360/5, 6: 386/46, 117
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`4,348,277
`4,630,911
`4,835,621
`4,955,812
`5,026,158
`5,294,978
`5,342,054
`5,400,185
`5.499,049
`5,546,124
`5,815,205
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`ck
`
`9, 1982 Cowlin et al. .............. 209/705
`12/1986 Paul ........................... 396/426
`5, 1989 Black ...
`... 386,118
`9, 1990 Hill .........
`... 434/16
`6, 1991 Golubic ...................... 356,252
`3/1994 Katayama ....
`... 375,240.12
`8/1994 Chang ........................ 473,156
`3/1995 Scerbo .......................... 360.5
`3/1996 Esfandiari ................... 348/143
`8/1996 Scerbo ....................... 348,158
`9, 1998 Hashimoto .................. 348/373
`
`A compact video image recording device which is mount
`able to a gun and useful for recording video images before
`and after the firing of the gun. The recording device includes
`a camera comprising a lens and a video image sensor. The
`Video recording device is mounted on the gun Such that the
`viewing area of the camera includes the target area of the
`gun. The video image sensor generates an electronic signal
`representative of a video image impinging the respective
`sensor. The output of the image sensor is processed and
`generally employed to produce frame data which are suc
`cessively stored in successive frame locations of a semicon
`ductor memory organized as a circular buffer memory while
`the video recording device is in an active state. Upon the
`firing of the gun, additional frames are stored in the buffer
`memory for a short period of time and a portion of the buffer
`memory is employed to preserve a video record of the
`shooting both before and after the event. Additional frames
`are successively stored in the unused portion of the buffer
`memory. In the event of a further firing of the gun, an
`additional portion of the buffer memory is dedicated to
`preserving the image data associated with Subsequent firing
`incident. This process may be repeated until the buffer
`memory is full in the event the gun is repeatedly fired. A
`Video record is thus generated which documents the circum
`stances preceding and following the firing of the gun.
`
`38 Claims, 11 Drawing Sheets
`
`Samples
`
`1
`
`2
`
`3.
`
`4
`
`5
`
`6
`
`7
`
`8
`
`9
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`10
`
`Seconds -- 0
`
`2
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`3
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`4 p is
`
`7
`
`
`
`s
`
`... O
`
`

`

`US 7,158,167 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`5.991,043 A * 11/1999 Andersson et al. ......... 356,400
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`JP
`
`287964 A * 10, 1988
`O 156944 A 10, 1997
`09 OO4999
`1, 1997
`
`O 215 130 A
`
`3, 1987
`
`* cited by examiner
`
`

`

`U.S. Patent
`U.S. Patent
`
`
`
`Jan. 2, 2007
`Jan. 2, 2007
`
`Sheet 1 of 11
`Sheet 1 of 11
`
`
`
`US 7,158,167 B1
`US 7,158,167 B1
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`
`Motorola v. Stellar
`
`Motorola Exhibit 1017
`Page 003
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 2, 2007
`Jan. 2, 2007
`
`Sheet 2 of 11
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`US 7,158,167 B1
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`Jan. 2, 2007
`Jan. 2, 2007
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`Sheet 3 of 11
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`US 7,158,167 B1
`US 7,158,167 B1
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`U.S. Patent
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`Jan. 2, 2007
`Jan. 2, 2007
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`U.S. Patent
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`Jan. 2, 2007
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`Jan. 2, 2007
`Jan. 2, 2007
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`Sheet 8 of 11
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`US 7,158,167 B1
`US 7,158,167 B1
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`Motorola v. Stellar
`
`Motorola Exhibit 1017
`Page 010
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 2, 2007
`Jan. 2, 2007
`
`Sheet 9 of 11
`Sheet 9 of 11
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`US 7,158,167 B1
`US 7,158,167 B1
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`Motorola Exhibit 1017
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`
`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 2, 2007
`Jan. 2, 2007
`
`Sheet 10 of 11
`Sheet 10 of 11
`
`US 7,158,167 B1
`US 7,158,167 B1
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`
`
`Motorola v. Stellar
`
`Motorola Exhibit 1017
`Page 012
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`

`

`U.S. Patent
`U.S. Patent
`
`Jan. 2, 2007
`Jan. 2, 2007
`
`Sheet 11 of 11
`Sheet 11 of 11
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`US 7,158,167 B1
`US 7,158,167 B1
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`
`
`

`

`US 7,158,167 B1
`
`1.
`VIDEO RECORDING DEVICE FOR A
`TARGETABLE WEAPON
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`Continuation-in-part of application Ser. No. 08/906,493,
`filed Aug. 5, 1997
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`10
`
`Not Applicable
`
`BACKGROUND OF THE INVENTION
`
`15
`
`2
`For the above reasons, a video recording device would be
`desirable which could record video frames on a continuing
`basis and capture a video record of circumstances Surround
`ing a triggering event occurring at an unpredictable time. It
`would further be desirable for such a device to be compact,
`lightweight, cost effective and avoid the aforementioned
`deficiencies of prior art video recording devices employing
`mechanical transports.
`
`BRIEF SUMMARY OF THE INVENTION
`
`In accordance with the present invention, a video record
`ing device is disclosed which is contained within a com
`pactly sized housing. One or more video image sensors are
`mounted to the housing. Alternatively, one or more video
`image sensors are provided which are electrically coupled to
`the housing via wires so as to permit the image viewing area
`to be selected freely via suitable mounting of the sensors by
`a user. The video recording device records video frames
`Successively in at least one circular buffer memory orga
`nized as a continuous loop overwriting the oldest frame
`within the respective buffer memory with a more recently
`received frame. Upon receipt of a triggering event, a pre
`determined number of additional frames are recorded within
`the circular buffer memory at which point recording ceases.
`A plurality of circular memory buffer groups may be pro
`vided to extend the overall recording time for the device by
`selectively storing video data samples to the respective
`buffer groups. The foregoing video recording device can be
`fabricated as a compact transportable unit which employs no
`moving parts and which has relatively low power consump
`tion facilitating battery operation in certain embodiments.
`More specifically, a video camera is provided which
`contains a lens and a video image sensor. The lens is
`employed to focus a video image on a video image sensor
`Such as a charge coupled device sensor or an artificial retina
`as hereinafter discussed. The output of the video image
`sensor comprises an analog signal which is coupled to one
`or more A/D converters. The A/D converter(s) is sampled to
`generate a digital representation of the video image sensor
`analog output signal. A predetermined number of digital
`samples comprise one video frame. The digitized output
`signal(s) from the A/D converter(s) is coupled to a central
`controller in the form of a microprocessor or any other
`Suitable controller. The microprocessor compresses the digi
`tized frame data and stores the compressed frame data in the
`next sequential location of the circular buffer. In one
`embodiment, the digitized frame data is encrypted prior to
`storing the same in the buffer so as to prevent unauthorized
`access to Such data. The circular frame buffer comprises a
`semiconductor memory such as DRAM or any other suitable
`high speed semiconductor memory.
`Upon detection of a trigger event, the video recording
`device records a predetermined number of additional frames
`and then ceases to record further frame data. In this manner,
`a video event record is obtained which commences prior to
`the triggering event and extends in time after the triggering
`event. Triggering events may include an accelerometer out
`put signal crossing a predetermined threshold, a signal
`employed to initiate airbag deployment in an automobile, a
`signal representing a recognized change in a video image or
`acoustic signal, a signal indicative of a security or fire alarm
`condition, a button actuated by a user, or any other Suitable
`activation signal known in the art. Further, an activation
`button is provided which permits a user to take a single
`frame “snap shot' which is retained within the buffer
`memory until purged upon user activation of a purge button.
`
`The present invention relates to video recording devices
`and more particularly to a video recording device which is
`adapted to store video images corresponding generally to the
`area Surrounding the sighting area of a targetable weapon
`Such as a gun.
`Numerous applications exist in which it is desirable to
`retain a video record for evidentiary or historical purposes.
`For example, in an automobile, or on a bicycle or motor
`cycle, it would be desirable to record a video image of the
`circumstances existing immediately prior to and after an
`accident. Additionally, in security applications, it would be
`highly desirable to be able to record a video image of the
`circumstances existing immediately prior to an event trig
`gering an alert condition and following the triggering of
`Such a condition.
`Another example in which it would be desirable to have
`a recorded video image for evidentiary purposes involves
`the firing of a lethal or non-lethal targetable weapons such
`as a gun, TAZER(TM) or mace. In the event an individual is
`injured or killed, for example, by a police officer acting in
`the line of duty, lawsuits are sometimes filed against the
`officer and the municipality in which it is asserted that the
`shooting of the victim was without justification and unlaw
`ful. Such suits are typically accompanied by large damage
`claims. In these circumstances, it would be desirable to have
`a video record which would show the scene as viewed by the
`police officer at the time the gun was fired.
`Additionally, in numerous other applications it would be
`desirable to be able to create a video record of circumstances
`existing both before and after a triggering event.
`A number of image recording devices are well known in
`the art. In time lapse photography a series of still pictures are
`taken over a period of time. Such pictures are typically taken
`with a periodically actuated still or a motion picture camera
`and employ photographic film. The cameras are loaded with
`a limited supply of film and the camera must be reloaded
`when the Supply of film is exhausted. Accordingly, Such
`devices are not well suited for applications in which it is
`desired to record images over a long period of time when
`only a very short period of time is of interest and the
`particular period of interest cannot be predicted.
`In Security applications, a video camera is often employed
`to record a video image on magnetic tape on a continuous
`basis. When the tape is exhausted it must be replaced.
`Both photographic cameras employing photographic film
`and video cameras utilizing magnetic tape as the recording
`media employ mechanical transport mechanisms which are
`susceptible to failure when subjected to shock and vibration.
`Accordingly, Such devices are ill Suited for use in applica
`tions and environments in which shock and vibration are the
`O.
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`US 7,158,167 B1
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`10
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`3
`A serial output channel is provided to permit recorded
`frame data to be downloaded to a computer for viewing.
`Alternatively, any appropriate data transfer link and protocol
`may be employed.
`The above described apparatus thus provides a video
`recording device which has high reliability, is compact, cost
`effective and suitable both for consumer and commercial
`applications.
`In one application, a video recording device as described
`above is mounted to a targetable weapon, such as a gun. The
`Video recording device is aligned so as to record images
`generally surrounding the line of fire of the weapon. When
`employed in conjunction with a gun, the video recording
`device may be mounted to the barrel of the gun, may be
`piggy-backed on a laser targeting device mounted to the gun,
`or may be combined with a laser targeting device within a
`single housing. The video recording device commences the
`recording of video frames upon the removal of the gun from
`a holster. Video frames are recorded successively in the
`circular buffer memory. A gun firing signal is generated upon
`discharge of the gun. The gun firing signal may be generated
`by an accelerometer or a microphone or alternatively, may
`comprise a signal generated upon actuation of the trigger of
`the gun, in which case an interface between the gun and the
`video recording device, is provided. Upon detection of the
`firing signal, the video recording device stores additional
`frames within the circular buffer memory for a short period
`of time. Upon a firing event, specified frame data associated
`with that firing event both before and after the event is
`preserved and cannot be overwritten as a result of further use
`of the gun or Subsequent firing events. Frame data associated
`with each subsequent firing events is stored within an
`unused portion of the circular buffer memory. In a preferred
`embodiment of the invention, fewer video frames are stored
`for each Subsequent firing event.
`
`4
`FIG. 7 is a table illustrating an alternative storage tech
`nique for storage of video data in the semiconductor
`memory buffer;
`FIG. 8 is a table illustrating a further alternative storage
`technique for storage of video data in the semiconductor
`memory buffer;
`FIG. 9 is a pictorial view illustrating the use of a gun
`having a video recording device in accordance with the
`present invention mounted thereto;
`FIG. 10A comprises a side view of a gun having a video
`recording device in accordance with the present invention
`mounted below the barrel of the gun:
`FIG. 10B is a frontal view of the gun and video recording
`device of FIG. 9A;
`FIG. 11A is a side view of a gun having a laser target
`designator and a video recording device in accordance with
`the present invention mounted below the barrel of the gun:
`FIG. 11B is a frontal view of the gun, laser target
`designator and video recording device of FIG. 10A:
`FIG. 12A is a side view of a gun having a housing
`containing a laser target designator and a video recording
`device mounted below the barrel of the gun:
`FIG. 12B is a frontal view of the gun and housing of FIG.
`11A:
`FIG. 13 is a side view illustrating the gun, laser target
`designator and video recording device of FIG. 10A disposed
`within a holster; and
`FIG. 14 is a block diagram illustrating a video recording
`device in accordance with the present invention for use with
`a gun.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`An application of a video recording device 2 in accor
`dance with the present invention is illustrated in FIG. 1. The
`recording device 2 is mounted within a first vehicle 4 which
`has come to a stop behind a second vehicle 6 at an inter
`section. Vehicle 6 has also come to a stop at the intersection,
`however, it has backed up so as to impact vehicle 4 causing
`damage to vehicle 4. It would be highly desirable for the
`driver of vehicle 4 to have an evidentiary record which
`establishes that the accident was caused by vehicle 6 since
`it would normally be presumed in Such a circumstance that
`the driver of vehicle 4 was the cause of the accident. The
`Video recording device 2 in accordance with the present
`invention generates such a record by continually recording
`video frames in a circular buffer at a predetermined frame
`rate. In response to a trigger event, Such as an air bag
`activation signal or a button activated by the driver, the
`video recording device records a predetermined number of
`additional frames before ceasing to record further frames. In
`the foregoing manner, the driver of vehicle 4 can establish
`the true cause of the accident. The foregoing example is
`provided solely as an illustration of the operation of the
`video recording device 2 of the present invention.
`A housing 10 for a video recording device 2 in accordance
`with the present invention is depicted in FIG. 2a. The
`housing 10 includes a camera comprising a lens 12 and a
`Video image sensor (not shown) which may comprise a
`charge coupled device (CCD), an artificial retina, or any
`other Suitable optical sensor operative to provide output
`signals when a video image impinges the sensor. By way of
`illustration, the sensor may comprise a model TC241 CCD
`array manufactured by Texas Instruments or an artificial
`retina such as identified and described volume 372, number
`197 NATURE, 1994 which is incorporated herein by refer
`
`25
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`
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`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
`
`The invention will be more fully understood by reference
`to the following Detailed Description of the Invention in
`conjunction with the drawings of which:
`FIG. 1 is a pictorial view illustrating an application for use
`of the video recording device of the present invention;
`FIG. 2a is a pictorial view of a housing for a video
`recording device in accordance with the present invention in
`which a camera comprising a lens and image sensor is
`mounted within the housing:
`FIG. 2b is a pictorial view of an alternative embodiment
`of a housing for the video recording device of FIG. 1 in
`which the camera is disposed external to the housing and in
`electrical communication with video processing circuity
`(not shown) disposed within the housing:
`FIG. 3 is an electrical block diagram of a video recording
`device in accordance with the present invention;
`FIG. 4a is a simplified schematic representation of a
`circular memory buffer employed within the video recording
`device of FIG. 3;
`FIG. 4b is a representation of a semiconductor memory
`buffer employed in the video recording device of FIG. 3 to
`implement a circular memory buffer and associated head and
`tail pointers;
`FIG. 5 is a flowchart illustrating the recording method in
`accordance with the present invention;
`FIG. 6 is a table illustrating one storage technique for
`storage of video data in the semiconductor memory buffer;
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`US 7,158,167 B1
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`ence. The lens 12 is specified to have appropriate optical
`characteristics and is oriented so as to focus a video image
`of the desired field of view on the video image sensor. While
`the housing of FIG. 2a illustrates the use of a single camera,
`multiple cameras may be employed and selectively oriented
`to capture images at desired viewing angles. For example,
`one camera may be positioned at the forward edge 14 of the
`housing 10 and a second camera at the trailing edge 16 of the
`housing 10 to capture images at 180° viewing angles.
`Additionally, by way of example, cameras may be disposed
`on the leading edge 14 and a side edge 17 of the housing 10
`So as to capture video images along orthogonal viewing
`angles. It is further understood that any desired number of
`cameras may be employed.
`Another embodiment of a video recording device assem
`bly in accordance with the present invention is depicted in
`FIG. 2b. The video recording device illustrated in FIG. 2b
`includes a housing 18 and a camera 20 which is disposed
`external to the housing 18. The lens 22 focuses a video
`image on the sensor 24 which, in the preferred embodiment,
`produces an electrical output signal for communication to a
`Video signal processor. The sensor 24 communicates the
`electrical output signal via wires 26 to the video signal
`processor disposed within the housing 18. The wires 26 may
`be coupled to the circuitry (not shown) via a connector or
`alternatively may be hardwired to such circuitry. While a
`single video image sensor 20 is depicted in FIG.2b, as with
`respect to FIG. 2a, the video recording device in accordance
`with the present invention may employ multiple cameras 20
`30
`which may be selectively mounted and positioned at desired
`viewing angles so as to permit a corresponding number of
`Video images to be captured.
`The housings illustrated in FIGS. 2a and 2b may be
`fabricated in a PCMCIA configuration with a PCMCIA
`35
`connector disposed at one end so as to permit the housing to
`be inserted into a laptop computer or any other Suitable
`computer having a PCMCIA interface to permit viewing of
`images captured within the video recording device.
`A block diagram of the video recording device in accor
`dance with the present invention is depicted in FIG. 3. As
`illustrated in FIG. 3, the recording device includes a camera
`40 and video electronics 42. The camera 40 is comprised of
`a lens 44 which is disposed a predetermined distanced from
`the Surface of an image sensor 46. The image sensor 46, as
`described above, may comprise a charge couple device
`array, an artificial retina, or any other Suitable image sensor
`operative to provide an output signal representative of a
`Video image which impinges upon the sensor. In a preferred
`embodiment employing a CCD array as the sensor 46, the
`CCD array produces an analog output signal which is
`electrically coupled to an analog to digital converter 48 via
`a signal path 50. The analog to digital converter may
`comprise a model AD775 A to D converter manufactured by
`Analog Devices, Inc. or any other Suitable analog to digital
`converter. Support electronics 52 are provided which
`include a clock generator which is coupled to the analog to
`digital converter 48 to permit the sensor output 50 to be
`sampled at predetermined intervals and other conventional
`timing circuitry. The analog to digital convertor 48 generates
`60
`a digital representation of the sensor output signal 50. A
`predetermined number of samples of the sensor output
`signal 50 comprise a single video frame. For example, in one
`exemplary embodiment, each frame contains 256 horizontal
`samples by 128 vertical samples yielding an uncompressed
`size of 32,768 bytes. Sixty four such frames can be stored in
`a two (2) megabyte memory.
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`Generally, color images require approximately thirty (30)
`percent more storage space. One could thus store approxi
`mately fifty (50) frames of uncompressed color image
`information in the two (2) megabyte memory.
`For images of the above identified sizes a compression
`ratio of four to one (4:1) is readily achievable. Such would
`permit 256 black and white images or 200 color images to
`be stored in the two (2) megabyte memory. At a recording
`rate of ten (10) frames per second, the two (2) megabyte
`memory will accommodate thus accommodate 25 seconds
`of black and white images or 20 seconds of color images. A
`greater recording interval may be achieved by employing a
`lower sampling rate or by utilizing a larger memory.
`The output of the analog to digital converter is electrically
`coupled to inputs of a central control processor 54 via signal
`path 56 which comprises a parallel signal bus. The central
`control processor 54 in a preferred embodiment, may com
`prise an M32RD microprocessor which is commercially
`available from Mitsubishi Electric, any other suitable micro
`processor, an Application Specific Integrated Circuit (ASIC)
`or any other Suitable implementation of a central control
`processor operative to perform the presently described func
`tions.
`The central control processor 54 is coupled to a semicon
`ductor memory 58 which comprises a DRAMa in preferred
`embodiment. Within the M32RD device referenced above,
`two (2) megabytes of DRAM is incorporated in the com
`mercially available device. Thus the microprocessor 54 and
`the DRAM 58 may be obtained as a single integrated circuit.
`Additional semiconductor memory 60 may be coupled to the
`microprocessor 54 via a bus 62 in the event that it is desired
`to increase the semiconductor memory capacity of the video
`recording device. It may be desired to increase the memory
`capacity of the recording device to permit a greater number
`of frames to be captured or to accommodate the storage of
`Video images received from plural cameras.
`The central control processor 54 executes a control pro
`gram which is stored within a Read Only Memory (ROM).
`The ROM 64 is coupled to the central control processor via
`bus 66. The central control processor 54 may be provided
`with a number of inputs 68 which permit activation of the
`video recording device and control of the device by a user.
`Exemplary inputs comprise, an event sensor 70, a “capture'
`button 72, a “still” button 74 and a “purge” button 76.
`Additionally, the central control processor 54 includes a
`serial output channel 78 which permits stored video images
`to be downloaded to an external video device for viewing.
`In one embodiment, the serial output channel is compatible
`with the well known Xmodem serial protocol. It is appre
`ciated that any Suitable serial channel protocol may be
`employed.
`The central control processor 54 receives successive
`samples of frame data from the analog to digital converter 48
`and compresses the received frame data in order to reduce
`the storage capacity for the captured video data. One image
`compression technique which may be employed is disclosed
`in U.S. Pat. No. 4,917,812 to Adelson and Simoncelli. While
`any suitable compression technique may be employed, in a
`preferred embodiment of the invention, an asymmetric com
`pression technique (known in the art) is used which mini
`mizes the computational load on the central control proces
`Sor to compress the image data during compression of the
`image data at the expense of greater complexity in the
`decompression algorithm. The use of an asymmetric com
`pression technique thus places greater processing demands
`on the processor which will ultimately perform the decom
`pression which, is likely to comprise a personal computer
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`7
`(PC), a workstation, or some other computer which gener
`ally possesses the necessary processing speed to perform
`Such decompression or which is not burdened by the con
`straint of real time processing. In this manner, the video
`electronics 42 are not burdened with additional cost asso- 5
`ciated with added processing power.
`Following the compression of the frame data, the central
`control processor stores the compressed data within the
`semiconductor memory 58. The semiconductor memory 58
`is structured as a circular memory buffer as illustrated in
`FIG. 4a. Thus, following compression, each compressed
`video frame is stored in the next successive frame buffer
`location and any frame data continued in Such location is
`overwritten. For example, referring to FIG. 4a, if the last
`frame were stored at location 3 of the circular buffer 90, the 15
`subsequent video frame would be stored at location 4 of the
`circular frame buffer. The video recording device, absent
`receipt of some trigger event from the sensor 54 or activation
`of other input by the user, continues to store captured frame
`data in successive locations of the circular buffer, overwrit
`ing previously received frame data stored in respective
`buffer locations with the most recently received frame data.
`The operation of the circular buffer is described with more
`particularity below and with respect to FIG. 4b. The semi
`conductor memory buffer is sized to as to permit the desired
`number of frames to be concurrently stored in the buffer. The
`buffer 100 utilizes a plurality of bytes to store each frame as
`illustrated in frame buffer locations 0 and n. The specific
`number of bytes required for a particular frame is dependent
`upon the resolution of the video image sensor 46, the
`sampling rate of the analog to digital converter 48, and the
`efficiency of the compression algorithm.
`Associated with the semiconductor memory buffer 58
`(and additional buffer memory 60 if such is employed) are
`a tail pointer 102 and a head pointer 104. The head pointer
`points to the address of the frame buffer location for storage
`of the next frame data. Such address is offset in the respec
`tive frame to address the respective byte for the frame data
`being stored. For simplicity, the operation of the buffer is
`explained with respect to the frame addresses recognizing
`that plural locations are utilized within the buffer to store the
`data associated with any given frame.
`The head pointer 104 points to the location for storage of
`the incoming frame data. Thus, if the next frame data is to
`be stored in location 4, the head pointer is set to location 4.
`Once all of the data corresponding to frame 4 has been
`stored in the buffer, in normal operation and in the absence
`of a trigger event, the head pointer is incremented to point
`to frame number 5. As an example, assume a semiconductor
`memory buffer 58 is employed in which n=127; i.e. the
`frame buffer is capable of storing 128 frames of data. It is
`further assumed for purposes of the present example that it
`is desired to have half of the captured frames precede the
`trigger event and half of the frames follow the trigger event.
`The head pointer 104 is incremented following the storing of 55
`each respective frame. In normal operation, the tail pointer
`is incremented each time the head pointer is incremented,
`however, the tail pointer comprises an address which lags
`the head pointer by sixty four. In the circular buffer frame
`address 0 follows frame address n (i.e. 127 in the present
`example).
`Upon detection of a trigger event, the tail pointer ceases
`to increment while frames continue to be stored in subse
`quent frame locations. A test is performed prior to storing
`frame data to determine whether the frame location for the
`data to be stored is one location preceding the tail pointer, in
`which case the frame da