Abstract:
A multichannel image compression device comprises recording means for storing digital images on a plurality of channels in frames channel by channel into memories, control means for performing control in such a manner that the digital images stored by the recording means into the memories increase in number on a specific channel, and compression means for subjecting the digital images recorded by the recording means into the memories to compression coding by correlating frames channel by channel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-370996, filed Dec. 27, 1999, the entire contents of which are incorporated herein by reference.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a digital image compression device, and more particularly to a multichannel image compression device for compressing digital images on a plurality of channels and to its method.  
           [0003]    As is generally known, when images are recorded to keep watch with a camera or the like, a recording medium with a large capacity is required to record the images as they are, because the recording is usually done for many hours.  
           [0004]    Since images in such watching are not necessarily recorded continuously, they are often recorded intermittently to reduce the recording capacity. This type of video recording is sometimes called time lapse video recording.  
           [0005]    In use for watching, there are often a plurality of watch points. In such a case, the watch points are photographed intermittently in sequence and the multichannel intermittent images are transmitted or recorded.  
           [0006]    On the other hand, with recent advances in digital technology, images have been processed in digital form. To obtain digital images, it is necessary to record a tremendous volume of information.  
           [0007]    To decrease the amount of information, image compression techniques for compressing images by correlating images, including the JPEG (Joint Photographic Experts Group) and MPEG (Moving Picture Image Coding Experts Group) techniques, have rapidly been popularized.  
           [0008]    When time lapse video recording of a plurality of places is effected using such digital techniques, the images can be compressed making use of the correlation between images. In this case, time lapse video recording using the JPEG standard is known as image compression means.  
           [0009]    Since the JPEG standard is a compression method disadvantageous in that the compression ratio is not very high.  
           [0010]    On the other hand, use of MPEG techniques makes it possible to correlate frames. In the case of a multichannel, however, since the images in front of and behind the channel to be switched come from other watch points, correlating the frames without any modification leads to the disadvantage of failing to perform efficient image compression.  
           [0011]    To overcome these problems, the applicant has filed Japanese Patent Application No. 11-276922, which has disclosed an image compression device which has an image buffer memory for each channel and correlates frames channel by channel, thereby effecting coding and compression according to, for example, the MPEG standard.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    The object of the present invention is to provide not only a multichannel image compression device by further improving the above-described image compression device to make the device suitable for a case where more careful watch is required on the image on a predetermined specific channel or on a specific channel giving a warning that an abnormality has occurred, but also its method.  
           [0013]    The foregoing object is accomplished by providing a multichannel image compression device comprising: recording section for storing digital images on a plurality of channels in frames channel by channel into memories; control section for performing control in such a manner that the digital images stored by the recording section into the memories increase in number on a specific channel; and compression section for subjecting the digital images recorded by the recording section into the memories to compression coding by correlating frames channel by channel.  
           [0014]    The foregoing object is further accomplished by providing a multichannel image compression method comprising: a recording step of storing digital images on a plurality of channels in frames channel by channel into memories; a control step of performing control in such a manner that the digital images stored in the memories in the recording step increase in number on a specific channel; and a compression step of subjecting the digital images recorded in the memories in the recording step to compression coding by correlating frames channel by channel.  
           [0015]    With the above configuration and method, because control is performed in such a manner that, when digital images on a plurality of channels are stored in memories in frames channel by channel, the digital images stored in the memories increase in number on a specific channel, more careful watch can be kept on the image on a predetermined specific channel or on a specific channel giving a warning that an abnormality has occurred.  
           [0016]    Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0017]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.  
         [0018]    [0018]FIG. 1 is a block diagram to help explain a multichannel image compression device and its method according to a first embodiment of the present invention;  
         [0019]    [0019]FIGS. 2A to  2 F are illustrations to help explain the operation of the first embodiment;  
         [0020]    [0020]FIG. 3 is a block diagram to help explain a multichannel image compression device and its method according to a second embodiment of the present invention; and  
         [0021]    [0021]FIGS. 4A to  4 G are illustrations to help explain the operation of the second embodiment.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    Hereinafter, referring to the accompanying drawings, a first embodiment of the present invention will be explained. FIG. 1 shows an image recording device  10 , which will be explained in the first embodiment. The first embodiment illustrates a case where places needing more careful watch have been predetermined. In this case, it is assumed that there are four watch points and, of these places, the first place has to be watched more carefully than the others.  
         [0023]    The image recording device  10  of FIG. 1 comprises cameras  11   a,    11   b,    11   c,  and  11   d  provided in four places needing watch, a selector circuit  12  for selecting one of the images picked up by these cameras  11   a  to  11   d,  buffer memories  13   a,    13   b,    13   c,  and  13   d  for storing the image selected by the selector circuit  12  temporarily frame by frame in such a manner that the selected image corresponds to each channel or each of the cameras  11   a  to  11   d,  a selector circuit  14  for selecting one of the images stored in the buffer memories  13   a  to  13   d,  an MPEG coding device  15  for coding the image on the channel selected by the selector  14  according to the MPEG standard, a recording device  16  for recording the image MPEG-coded by the MPEG coding device  15  in a DVD (Digital Versatile Disc) or another type of recording medium that enables recording and reproduction of data, and a control circuit  17  for supervising control of the selector circuits  12 ,  14 , buffer memories  13   a  to  13   d,  MPEG coding device  15 , and recording device  16 .  
         [0024]    The image on each channel compressed and recorded in the recording device  16  is selectively subjected to an MPEG decoding process at an MPEG decoding device  18 . The resulting image is displayed on an display unit  19 .  
         [0025]    The operation of the image recording device  10  with the aforementioned configuration will be explained by reference to FIGS. 2A to  2 F. FIG. 2A shows the channel numbers of the images selected by the selector circuit  12 . In this case, the images obtained from the cameras  11   a  to  11   d  are allocated the channel numbers  1  to  4 .  
         [0026]    [0026]FIG. 2B shows the frame numbers of the images selected by the selector circuit  12 . In this case, the image for each frame obtained from the selector circuit  12  is allocated a frame number in sequence, regardless of the cameras  11   a  to  11   d,  or the channels.  
         [0027]    [0027]FIGS. 2C to  2 F show the frame numbers of the images stored in the buffer memories  13   a  to  13   d.  Under each frame number, the type (B, P, or I) of the pictures has been written which constitute a GOP (Group Of Picture), a unit of encoding, in subjecting the images stored in the buffer memories  13   a  to  13   d  to MPEG coding.  
         [0028]    The common terminal on the right side of the selector circuit  12  is making the rounds repeatedly in such a manner that the terminal is switched so as to touch the individual contacts on the left side, starting from the top to the bottom sequentially and, when it reaches the bottom contact, then returns to the top and is switched so as to touch them from the top to bottom in sequence again.  
         [0029]    As a result, the selector circuit  12  is switched in such a manner that it selects the image from the camera  11   a  every other frame. Then, the image from the camera  11   a  selected by the selector circuit  12  is stored in the buffer memory  13   a.    
         [0030]    Specifically, in the case of frame number  1 , the selector circuit  12  comes to select the image on channel number  1  and the image photographed by the camera  11   a  is stored in the buffer memory  13   a.  In the case of frame number  2 , the selector circuit  12  comes to select the image on channel number  2  and the image photographed by the camera  11   b  is stored in the buffer memory  13   b.    
         [0031]    Next, in the case of frame number  3 , the selector circuit  12  comes to select the image on channel number  1  again and the image photographed by the camera  11   a  is stored in the buffer memory  13   a.  In the case of frame number  4 , the selector circuit  12  comes to select the image on channel number  3  and the image photographed by the camera  11   c  is stored in the buffer memory  13   c.    
         [0032]    Then, in the case of frame number  5 , the selector circuit  12  comes to select the image on channel number  1  again and the image photographed by the camera  11   a  is stored in the buffer memory  13   a.  In the case of frame number  6 , the selector circuit  12  comes to select the image on channel number  4  and the image photographed by the camera  11   d  is stored in the buffer memory  13   d.    
         [0033]    Then, in the case of frame number  7 , the selector circuit  12  comes to select the image on channel number  1  again and the image photographed by the camera  11   a  is stored in the buffer memory  13   a.  In the case of frame number  8 , the selector circuit  12  comes to select the image on channel number  2  and the image photographed by the camera  11   b  is stored in the buffer memory  13   b.    
         [0034]    Similarly, from this time on, the images photographed by the individual cameras  11   a  to  11   d  are stored in the respective buffer memories  13   a  to  13   d.  In this case, the images with frame numbers  1 ,  3 ,  5 ,  7 ,  9 ,  11 ,  13 , . . . are stored in the buffer memory  13   a.  That is, as shown in FIGS. 2C to  2 F, the number of the images stored in the buffer memory  13   a  is triple as many as that in each of the buffer memories  13   b  to  13   d.    
         [0035]    Then, the selector circuit  14  supplies the images stored in the buffer memories  13   a  to  13   d  to the MPEG coding device  15 , which subjects the images to MPEG coding. In this case, it is assumed that the number N of pictures constituting one GOP, a unit of MPEG coding, is  15 . For example, for channel number  1 , the pictures B 0 , B 1 , I, B 2 , B 3 , P 0 , B 4 , . . . are obtained as written under the respective frame numbers in FIG. 2C.  
         [0036]    For each of the other channel numbers  2  to  4 , the pictures B 0 , B 1 , I, . . . are obtained as written under the respective frame numbers in FIGS. 2D to  2 F.  
         [0037]    Consequently, if the number of pictures constituting one GOP is the same on each channel, the image on channel number  1  will be MPEG-coded at a speed three times as fast as the image on each of the other channels  2  to  4 . That is, the degree of watch on the channel with channel number  1  can be increased as compared with the channels with the other channel numbers  2  to  4 .  
         [0038]    In the first embodiment, explanation has been given about the case where the channel on which the degree of watch needs to be increased has been determined beforehand. With the present invention, however, the channel on which the degree of watch needs to be increased may be changed appropriately according to the conditions.  
         [0039]    [0039]FIG. 3 shows a second embodiment of the present invention which keeps close watch on the place, because one of the places being under watch has given a warning.  
         [0040]    The image recording device  30  of FIG. 3 comprises cameras  31   a,    31   b,    31   c,  and  31   d  provided in four places needing watch, a selector circuit  32  for selecting one of the images picked up by these cameras  31   a  to  31   d,  buffer memories  33   a,    33   b,    33   c,  and  33   d  for storing the image selected by the selector circuit  32  temporarily frame by frame in such a manner that the selected image corresponds to each channel, or each of the cameras  31   a  to  31   d,  a selector circuit  34  for selecting one of the images stored in the buffer memories  33   a  to  33   d,  an MPEG coding device  35  for coding the image on the channel selected by the selector  34  according to the MPEG standard, a recording device  36  for recording the image MPEG-coded by the MPEG coding device  35 , a control circuit  37  for supervising control of the selector circuits  32 ,  34 , buffer memories  33   a  to  33   d,  MPEG coding device  35 , and recording device  36 , warning devices  38   a,    38   b,    38   c,  and  38   d  provided near the four cameras  31   a  to  31   d  respectively, and a warning signal sensing circuit  39  for sensing the warning signal issued from these warning devices  38   a  to  38   d  and sending information on the channel issuing the warning signal and other information to the control circuit  37 .  
         [0041]    The image on each channel compressed and recorded in the recording device  36  is selectively subjected to an MPEG decoding process at an MPEG decoding device  40 . The resulting image is displayed on an display unit  41 .  
         [0042]    The operation of the image recording device  30  with the aforementioned configuration will be explained by reference to FIGS. 4A to  4 G. In the normal state, the selector switch  32  is connected to the cameras  31   a  to  31   d  sequentially and the images picked up by the cameras  31   a  to  31   d  are stored in the buffer memories  33   a  to  33   d,  respectively.  
         [0043]    When the images obtained from the cameras  31   a  to  31   d  are allocated channel numbers  1  to  4  as shown in FIG. 4A and the images selected by the selector circuit  32  are allocated consecutive frame numbers as shown in FIG. 4B, the images with channel numbers  1  to  4  are selected by the selector circuit  32  sequentially as shown in FIGS. 4C to  4 F and stored as the images with frame numbers  1  to  4  in the buffer memories  33   a  to  33   d.    
         [0044]    Next, the images with channel numbers  1  to  4  are selected by the selector circuit  32  sequentially and are stored as the images with frame numbers  5  to  8  in the buffer memories  33   a  to  33   d.  Similarly, from this point on, the images with channel numbers  1  to  4  are stored in the buffer memories  33   a  to  33   d,  respectively.  
         [0045]    Here, it is assumed that the number N of pictures constituting one GOP, a unit of coding in MPEG- 2 , is  15 . In this case, when 15 images with frame numbers  1 ,  5 ,  9 , . . . have been stored in the buffer memory  33   a,  they are read via the selector circuit  34  into the MPEG coding device  35 , which subjects these images to MPEG coding, producing I, B, and P pictures. These resulting pictures are stored in the recording device  36 .  
         [0046]    The images stored in the buffer memories  33   b  to  33   d  are also read via the selector circuit  34  similarly into the MPEG coding device  35 , which codes the images channel by channel. The resulting pictures are stored in the recording device  36 .  
         [0047]    As described above, the images on the individual channels are normally subjected to MPEG coding uniformly and then the resulting pictures are stored. When one of the warning devices  38   a  to  38   d  has given a warning signal that indicates the occurrence of an abnormality, the operation changes.  
         [0048]    Specifically, as shown in FIG. 4G, it is assumed that the warning device  38   b  gives a warning signal at the time when, for example, the selector circuit  32  has selected the image with frame number  61 . Then, the warning signal sensing circuit  39  senses the warning signal from the warning device  38  and informs the control circuit  37  that it has received the warning signal from the warning device  38   b.    
         [0049]    From this time on, the control circuit  37  controls the selector circuit  32  and buffer memories  33   a  to  33   d  in such a manner that it causes the image picked up by the camera  31   b  to be stored in the buffer memory  33   b  at a rate of one out of two operations of storing the image selected by the selector circuit  32  into the buffer memories  33   a  to  33   d.    
         [0050]    As a result, the image with the next frame number  62  is stored in the buffer memory  33   b  and the image with frame number  63  is stored in the buffer memory  33   c.  The image with the next frame number  64  is stored in the buffer memory  33   b  again.  
         [0051]    Similarly, the image with the frame number  65  is stored in the buffer memory  33   d,  the image with frame number  66  is stored in the buffer memory  33   b,  and the image with the frame number  67  is stored in the buffer memory  33   a.    
         [0052]    Similarly, from this point on, the image photographed by the camera  31   b  is stored in the buffer memory  33   b  at a rate of one out of two operations of storing the image selected by the selector circuit  33  into the buffer memories  33   a  to  33   d.    
         [0053]    When the number of the images stored in the buffer memories  33   a  to  33   d  has reached 15, they are read via the selector circuit  34  into the MPEG coding device  35 , which codes them according to the MPEG standard. The resulting pictures are stored in the recording device  36 .  
         [0054]    Specifically, after the warning device  38   b  has given a warning signal, the speed at which the image obtained from the camera  31   b  is stored in the buffer memory  33   b  is three time as fast as the speed at which the images obtained from the other cameras  31   a,    31   c,    31   d  are stored in the buffer memories  33   a,    33   c,    33   d,  which increases the frequency of one GOP being coded.  
         [0055]    When the recorded images are reproduced, the recording device  36  is connected to the MPEG decoding device  40 . The MPEG decoding device  40  is connected to the display unit  41 . The image on the selected channel is decoded according to the MPEG standard and the MPEG-decoded picture is displayed on the display unit  41 .  
         [0056]    In this case, since the images obtained from the camera  31   b  and stored in the buffer memory  33   b  are three times as many as those obtained from each of the other cameras  31   a,    31   c,    31   d  and stored in the buffer memories  33   a,    33   c,  and  33   d,  the degree of watch on the channel with channel number  2  after the issue of the warning signal is increased.  
         [0057]    The second embodiment has the advantage that an abnormality is sensed even without any watchman and watch on the abnormality with the cameras  33   a  to  33   d  is intensified automatically.  
         [0058]    While in the second embodiment, the warning devices  38   a  to  38   d  are provided for the cameras  33   a  to  33   d  respectively and the channel on which the degree of watch is increased is determined automatically, such a channel may be determined manually.  
         [0059]    Although in the first and second embodiments, the images are coded according to the MPEG standard, the present invention is not limited to MPEG coding and may be applied to any other compression coding as long as it uses frame correlation.  
         [0060]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.