JP3871217B2 - Video receiver - Google Patents

Description

  The present invention relates to an apparatus for receiving and reproducing an encoded and transmitted image signal, and particularly to an apparatus for low transfer rate transmission in which it is difficult to transmit a moving image with good image quality.

<Image transmission>
In recent years, transmission of image signals has become a significant part of the communication field. For image transmission, digital systems are considered advantageous, and international standard systems such as H.261, H.262 (MPEG-2), H.263, etc. are defined. When these methods are used, low-rate transmission such as 64 kbps or 384 kbps is also possible when limited to target images with little motion such as video conference images and video phone images. However, it is considered that an image with a normal motion requires about 500 k to 1 Mbps even when the resolution is lowered, and 4 to 8 Mbps at a normal resolution.

  FIG. 10 shows an example of a conventional configuration of such a moving image encoding / transmission apparatus and moving image receiving apparatus. The moving image coming from the moving image input 1 is encoded by the moving image encoder 2 by an encoding method such as the H.262 standard to form a data string. This data string is transmitted after being multiplexed with voice data or the like coming from another information input 91 by the multiplexer 5. On the receiving side, after other information is separated (as other information output 92) by the demultiplexer 22, it is decoded by the video decoder 25 conforming to the standard, and a reproduced image is output. On the other hand, still image transmission using the JPEG method or the like can be transmitted at a low transfer rate if the time for transmitting one image is lengthened. For example, when an image of 720 × 480 pixels is encoded without impairing the image quality, it has an information amount of about 500 kbit, but can be transmitted at 32 kbps if it takes about 15 seconds.

  When an image is encoded and transmitted, if the line transfer rate is low, a moving image with good image quality cannot be transmitted even if high-efficiency encoding is used. On the other hand, in the case of a still image, it is possible to transmit an image with good image quality by taking time, but since the state of movement of the subject is not known, information that can be grasped from the image in disaster prevention and crime prevention is limited. The present invention has been made paying attention to the above points, and a data sequence encoded by inter-frame predictive coding in which independent frames are provided at a predetermined cycle is selected and transmitted only at a part of GOPs. It is an object of the present invention to provide a moving image receiving apparatus that can display a moving image having a good quality although it is a part by reproducing a still image or a moving image repeatedly in real time.

  The present invention is an apparatus that receives and reproduces a moving image code string, separates each GOP data string from an input data string, and intermittently extracts the GOP data string from a buffer that outputs at a higher transfer rate than the input. This is a moving image receiving apparatus that decodes the data sequence to obtain a moving image while the data sequence comes in, and holds and outputs the decoded image as a still image when there is no incoming data sequence. Further, the data string of each GOP is separated from the input data string, the GOP data string is intermittently extracted from the buffer that outputs at a transfer rate higher than the input, and the GOP unit data string is held in the ring buffer. This is a moving picture receiving apparatus that repeatedly decodes the data of the same GOP until a data string of the same arrives to obtain and output a moving picture.

In the present invention, a data sequence encoded by inter-frame predictive coding in which independent frames are provided at a predetermined cycle is selected and transmitted only for some GOPs (with GOP as a unit of selection, two or more of 1 GOP cycle) (Only a part of the GOP data string is selected and transmitted periodically at an integer multiple cycle) , and the data missing GOP is replaced with a still image or a repetitive moving image of the sent GOP on the receiving side and reproduced, A time corresponding to a plurality of GOPs is spent for transmission of 1 GOP, and the substantial transfer rate can be increased several times for the moving image of the selected GOP. In addition, by using an image buffer for GOP before encoding and reducing the encoding target signal, it is possible to reduce the processing speed of moving image encoding while performing real-time transmission. Furthermore, by setting the encoding to a variable rate and changing the GOP length and the selected GOP according to the generated code amount, it is possible to keep the reproduction image quality constant even on a line with a fixed transfer rate.

  In the present invention, a data sequence encoded by inter-frame predictive coding in which independent frames are provided at a predetermined cycle is selected and transmitted only for a part of GOPs, and data missing GOP is a still image or sent GOP on the receiving side. By substituting and replaying with the repeated moving image, it becomes possible to multiply the substantial transfer rate of the moving image several times, and it is possible to obtain a moving image with a good quality although it is a part in real time. It becomes possible. As a result, even in a system using a low-rate line, both image quality (resolution) and movement can be achieved, and necessary information can be effectively transmitted for disaster prevention and crime prevention.

Embodiments of the image receiving apparatus according to the present invention will be described below with reference to the drawings.
<Image encoding transmission apparatus 1>
First, a first example of an image encoding / transmission apparatus suitable for the moving picture receiving apparatus of the present invention will be described. FIG. 1 is a configuration diagram of an image encoding transmission apparatus. The moving image signal coming from the moving image input 1 is given to the moving image encoder 2. The moving image encoder 2 is an H.264 format. This is based on the H.262 (MPEG-2) standard and the like, and its frame structure is shown in FIG. In the figure, I, P, and B are frame types, which are an intra-frame independent encoding frame, a unidirectional prediction frame, and a bidirectional prediction frame, respectively. An I frame is inserted about once every 0.5 to 3 seconds.

  A frame group from the I frame to the front of the next I frame is a GOP (Group Of Picture), and each GOP can be handled as an independent data string. For frame type continuity, the B frame may be inserted before the I frame. In response to a scene change or the like, an I frame may be inserted irregularly in the GOP.

  The moving image encoder 2 outputs information indicating the GOP switching timing and the GOP number together with the data string that is the encoding result. The data string is supplied to the data switch 3 that is opened and closed by a control signal supplied from the selection controller 8. Here, only the data string selected by opening / closing the switch 3 is applied to the data buffer, and the remaining data strings are discarded. The selected data is supplied to the next data buffer 4. The data buffer 4 stores intermittently incoming data strings and outputs them at a lower transfer rate than the input. That is, a high-rate bursty data string is smoothed to a low uniform-rate data string. The data string output from the data buffer 4 is multiplexed with the information of the selected GOP by the next multiplexer 5 and output from the code output (terminal) 6.

On the other hand, the selection controller 7 selects and passes 1 GOP through the data switch 3 in a predetermined cycle in units of GOP based on the information indicating the GOP switching timing and the GOP number. The selection ratio is about once every 3 to 10 times. This control information is given to the multiplexer 5. Since the output GOP decreases in this way, the encoding rate of the moving picture encoder 2 is increased accordingly. For example, if the GOP is selected once every five times and the transfer rate of the code output 6 is 100 kbps, the encoding rate of the moving picture encoder 2 is 500 kbps, which is five times 100 kbps. Therefore, the smaller the selection ratio of GOPs to be selected and transmitted, the higher the transfer rate and the better the image quality.
<Image receiving apparatus 1>
An image receiving apparatus according to the first embodiment of the present invention is shown in FIG. The code signal coming from the code signal input 21 is given to the demultiplexer 22. In the demultiplexer 22, the information of the selected GOP is separated from the data string, and the data string is given to the data buffer 23. The data buffer 23 corresponds to the data buffer 4 of the image encoding / transmission apparatus of FIG. 1, stores data strings inputted at a uniform low rate, and outputs them in a burst form at a high rate.

  A data string is output from the data buffer 23 only when the data switch 24 is connected to the output of the data buffer 24, and is provided to the moving picture decoder 25 via the data switch 24. The opening / closing of the switch 24 is controlled by the selection controller 27 according to the information of the selection GOP. In the moving image decoder 25, the data string is decoded and converted into a moving image, which is output from the image signal output (terminal) 26.

  Here, when the data switch 24 is disconnected and the data string is not input to the moving image decoder 25, the moving image decoder 25 outputs the final image of the moving image as a still image. It should be noted that since there is time before the start of the next moving image, the final still image and the subsequently reproduced moving image are discontinuous.

  On the other hand, it is possible to continuously reproduce up to the first I frame of the next GOP. In this case, a still image is the first I frame of the next GOP. However, when encoded with MPEG, the first I frame is encoded so as to have a relatively good image quality, so that the image quality is good. This is advantageous because the images are displayed continuously as still images. In this case, the end of the moving image and the still image are discontinuous. FIG. 3 shows the processing timing from the image encoding / transmission apparatus of FIG. 1 to the receiving apparatus of FIG. The numbers are GOP numbers. Only one GOP is selected out of five, and only the data string is transmitted. The reproduction method is shown in reproduction a.

With these processes, the image data string of 500 kbps becomes 100 kbps and can be transmitted through a low-speed line. On the receiving side, a moving image is displayed for 2 seconds, and then a still image is displayed for 8 seconds. Such a display method cannot be used for a general television program or the like, but is effective because a situation in the field can be grasped without always displaying a continuous moving image on a monitoring image or the like. As a result, it becomes possible to know the on-site movement (moving speed of things and people) that could not be grasped only by low-quality continuous moving images and still images.
<Image encoding transmission device 2>
FIG. 5 shows the configuration of a second example of an image encoding / transmission apparatus suitable for the moving picture receiving apparatus of the present invention. The same components as those in FIG. 1 are given the same numbers. The difference in configuration from the first example is that there is an image buffer 52 instead of the data buffer 4, and there is an image switch 51 instead of the data switch 3. That is, an image buffer is provided in place of the data buffer, and the moving image encoding processing speed is reduced. In this case, the output data string is equivalent to that in FIG. 1, and the receiving apparatus is the same. A moving image signal coming from the moving image input 1 is selected by the image switch 51, and only a part of the frames is given to the image buffer 52 in units of the number of frames corresponding to GOP. Information used for this selection is given from the selection controller 54.

  The selection controller 54 controls the image switch 51 at a predetermined GOP length and GOP thinning rate. The concept of the specific timing is the same as in FIG. 1, but in the case of the data string in FIG. 1, the amount of data slightly fluctuates in units of GOPs. Since the rate is completely constant, this is easier than the selection controller 7 of FIG. Information on the selected image is given to the moving image encoder 53 and the multiplexer 5.

  The image buffer 52 inputs an image in real time (30 frames / second) and outputs it to the moving image encoding device 53 at a low speed (6 frames / second). The moving image encoder 53 has the same processing content as that of FIG. 1, but the processing speed is about 1/5. Further, the GOP configuration for encoding is determined according to the selected image information input from the selection controller 54. The data sequence output from the moving image encoder 53 is multiplexed with selected image (GOP) information by the multiplexer 5 as it is.

<Image receiving device 2>
FIG. 7 shows the configuration of the image receiving apparatus according to the second embodiment of the present invention. The same components as those in FIG. 2 are given the same numbers. 2 is different from the first embodiment in that a ring buffer 71 is provided. In FIG. 7, the operations of the code input 21, demultiplexer 22, data buffer 23, and selection controller 27 are the same as those in FIG. The code coming from the code signal input 21 is given to the data switch 24 via the demultiplexer 22 and the data buffer 23.

  As for the output of the data buffer 23, the data string is read and given to the ring buffer 71 only when the data switch 24 is connected to the output of the data buffer 23. The ring buffer 71 is one whose contents are not rewritten except when the data switch 24 is connected to the data buffer 23 and a data string is coming in, and the same data string is repeatedly output.

  The data string output from the ring buffer 23 is decoded by the moving image decoder 25 to become a moving image, which is output from the image output (terminal) 26. Here, the same GOP data string is repeatedly given from the ring buffer 71 to the moving picture decoder 25. In this case, the same moving image for 2 seconds is repeatedly displayed five times. If you want to see the state of movement well, it is more effective than the combination of the moving image and still image display of the first embodiment. The state of this display is shown in reproduction b of FIG.

<Encoding transmission apparatus 3>
FIG. 6 shows the configuration of a third example of an image encoding / transmission apparatus suitable for the moving picture receiving apparatus of the present invention. Elements having the same configuration as in FIG. The operations of the moving image encoder 61, the data buffer 62, and the selection controller 63 are different from the first example of FIG. In the first example of FIG. 1, the moving picture encoder 2 outputs a data string at a fixed rate, and the selection controller 7 operates at a predetermined cycle. However, since the information amount of the moving image greatly depends on the amount of motion and definition of the image, the image quality greatly changes at a fixed rate. In the third example, the output data rate of the moving image encoder 61 is changed, the image quality is made constant, and the transmission time and the number of frames of 1 GOP are made variable.

  The moving image signal coming from the moving image input 1 is encoded by the moving image encoder 61. Here, the basic operation of encoding is the same as in FIG. 1, but the output data rate varies greatly depending on the image. The data string is selected by the data switch 3 and applied to the data buffer 62. The operation of the data buffer 62 is basically the same as that in FIG. 1, but the input rate varies. On the other hand, since the output rate is constant, the transition of the accumulated amount is not constant and varies depending on the generated code amount. The accumulated data amount (fullness) is output to the selection controller 63 as information.

  The selection controller 63 observes the buffer fullness and controls the opening / closing timing of the data switch 3. There are two control methods: a method in which the number of GOP frames is fixed and the transmission time of 1 GOP is changed, and a method in which the transmission time of 1 GOP is fixed and the number of GOP frames is changed. When the generated code amount is large and the amount of data accumulated in the buffer is large, the transmission time of 1 GOP is lengthened or the number of frames of 1 GOP is decreased. Conversely, when the amount of generated code is small and the amount of data stored in the buffer is small, the transmission time of 1 GOP is shortened or the number of frames of 1 GOP is increased. A receiving apparatus corresponding to such an encoded transmission apparatus may have the same configuration as the receiving apparatus of the first embodiment of FIG. 2 or the receiving apparatus of the second embodiment of FIG.

  FIG. 8 shows changes in the transmission time of 1 GOP, and FIG. 9 shows changes in the number of frames in 1 GOP. In each figure, playback a corresponds to the receiving device of the first embodiment, and playback b corresponds to the receiving device of the second embodiment. When the GOP transmission time changes, the selected and transmitted GOPs are not at regular intervals. Also, the playback time of 1 GOP on the receiving side is variable. In this case, since the previous GOP that has been transmitted is played back, the transmission time and playback time of each GOP are different.

  On the other hand, when the number of frames in one GOP is changed, since transmission is constant, the reproduction time of each GOP is the same in reproduction. However, since the time of continuous moving images changes in repeated playback, the number of repetitions changes, and in the combined playback of moving images and still images, the respective ratios change.

It is a figure which shows the structure of the 1st example of the image coding transmission apparatus suitable with respect to the moving image receiver of this invention. It is a figure which shows the structure of the image receiver of a 1st Example. It is a figure which shows the 1st process timing of this invention. It is a figure which shows the structure of GOP of this invention. It is a figure which shows the structure of the 2nd example of an image coding transmission apparatus. It is a figure which shows the structure of the 3rd example of an image coding transmission apparatus. It is a figure which shows the structure of the image receiver of a 2nd Example. It is a figure which shows the 2nd process timing of this invention. It is a figure which shows the 3rd process timing of this invention. It is a figure which shows the structure of the image coding transmission apparatus and receiving apparatus of a prior art example.

Explanation of symbols

1 Video input (terminal)
2, 53, 61 Video encoder 3, 24 Data switch 4, 23, 62 Data buffer 5 Multiplexer 6 Code output (terminal)
7, 27, 54, 63 Selection controller 21 Code input (terminal)
22 Demultiplexer 25 Video decoder 26 Image output 51 Image switch 52 Image buffer 71 Ring buffer 91 Other information input (terminal)
92 Other information output (terminal)

Claims (1)

In an apparatus for receiving and playing back a moving image data sequence,
The received moving image data sequence includes a plurality of independent encoded frames obtained by encoding a moving image signal by inter-frame prediction encoding that sets independent encoded frames within a predetermined period. From a continuous data sequence of GOP (Group Of Picture) consisting of a plurality of frames, only a part of the GOP data sequence is selected periodically with a cycle of an integer multiple of 2 or more of the cycle of 1 GOP, using the GOP as a unit of selection. Data sequence of moving images,
Buffer means for inputting the received data string and intermittently outputting at a higher transfer rate than the input;
Selecting means for fetching a GOP data string from the buffer means and providing a GOP unit data string to the ring buffer means;
Ring buffer means for holding the data string and repeatedly outputting the accumulated data string until the next data string arrives;
Image decoding means for decoding the data string output from the ring buffer means to obtain and output a moving image;
A moving image receiving apparatus comprising:

Images