JP3167914B2 - Image decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image decoding apparatus capable of automatically judging and decoding encoded moving images and still images.

[0002]

2. Description of the Related Art When transferring an image via a transmission line, the image is encoded. In addition, images can be transferred to magnetic disks, CD-
Images are also encoded when stored in a storage medium such as a ROM. If the image is encoded in this way,
When displaying an image, the image must be decoded by the image decoding device.

[0003] There are moving images and still images as images. A moving image is an image frame sequence in which a plurality of image frames are arranged on the time axis as shown in FIG. 8, and a still image is an image frame sequence composed of only one image frame as shown in FIG. M
In image coding standards such as PEG-1 and MPEG-2,
Both images are standardized so that they can be encoded,
It is desirable that both can be decoded as an image decoding device.

Here, attention is paid to the case of decoding a moving image.
In order to obtain a smooth reproduced image, it is necessary to always display image frames at a constant time interval.
However, when an encoded image signal is received via a transmission path, fluctuations occur during the time when the image signal arrives at the image decoding device due to factors such as jitter in the communication network and signal transmission speed jitter on the transmission side. Occurs. Also, when an image is read from a storage medium such as a magnetic disk, fluctuations in the access time and fluctuations in the time when an image signal is input to the image decoding device due to a bus neck or the like occur. Since such fluctuations become obstacles for displaying image frames at fixed time intervals, a technique of providing a buffer in the image decoding device and absorbing the fluctuation by the buffer has been conventionally used. Note that a configuration using a buffer has also been used when reading an encoded image signal from a storage medium such as a magnetic disk instead of a transmission path.

FIG. 10 shows a conventional image decoding apparatus for decoding an encoded image signal received via a transmission line. The transmission interface unit 1001 receives a signal from the transmission side via a transmission path. Since the signal from the transmitting side is usually also multiplexed with an audio signal or the like, the signal is separated by the demultiplexing unit 1002 for each medium. Hereinafter, only the image signal will be described, and the description of the signal processing of other media will be omitted. The image signal separated by the demultiplexing unit 1002 is temporarily stored in the buffer unit 1003. The buffer unit 1003 always keeps a certain signal amount in a processing waiting state, so that the image decoding unit 1006 does not fall into a state where there is no image signal when trying to read an encoded image signal. As a result, the image decoding unit 1006 is not affected by the fluctuation of the arrival time of the encoded image signal, and can always reproduce the image frame at a constant time interval. As described above, in order for the buffer unit 1003 to always wait for a certain amount of signal to be processed, the image decoding unit 1006 is stopped for a while after the image signal starts to arrive at the buffer unit 1003, and a predetermined period is set. When the signal amount exceeding the threshold value is accumulated in the buffer unit 1003, the operation of the image decoding unit 1006 is started. That is, the buffering counting unit 1004
03, the signal amount temporarily stored is monitored, and when the signal amount exceeds the threshold value, the decoding start control unit 1005 is notified, and the decoding start control unit 1005 starts the operation of the image decoding unit 1006. After that, a substantially constant amount of image signals accumulates in the buffer unit 1003 while absorbing the fluctuation of the arrival time of the signal received from the transmission path.

FIG. 11 shows a buffering counting section 1004.
FIG. 7 is a diagram for explaining a temporal change of an image signal amount temporarily stored in the image decoding unit and an operation state of the image decoding unit 1006. As described above, in the related art, the fluctuation of the arrival time of the image signal is absorbed by using the buffer, and the smooth reproduction of the moving image is realized.

[0007]

However, there is a problem that when a conventional image decoding apparatus configured as described above attempts to decode a still image, the image decoding operation is not started.

FIG. 12 is a diagram for explaining this problem.
As shown in FIG. 12, when the decoding start control unit 1005 has a smaller total image signal amount of still images than a threshold value instructing the operation start of the image decoding unit 1006, the operation of the image decoding unit 1006 does not start, The image signal remains stored in the buffer unit 1003. Of course, if the threshold value is reduced, a still image with a small signal amount can be decoded. However, when the threshold value is reduced, the amount of image signals constantly stored in the buffer unit 1003 in the case of a moving image decreases, so that fluctuations in the arrival time of image signals cannot be completely absorbed.

SUMMARY OF THE INVENTION It is an object of the present invention to automatically enable reproduction of a still image in an image decoding apparatus which reproduces a smooth moving image by absorbing fluctuations in the arrival time of an image signal using a buffer. is there.

[0010]

Therefore, in order to achieve the above object, the image decoding apparatus of the present invention has a buffer means for temporarily storing an encoded image signal, and a code storage means for storing the encoded image signal in the buffer means. Measuring the data amount of the coded image signal, and when the coded image signal reaches a predetermined first threshold value, a buffering measurement unit that outputs a decoding start, and a value of the buffering measurement unit, Measuring the time from the time when it becomes constant, and when the measured time reaches a predetermined second threshold value, forcibly decoding determination means for outputting decoding start; and the buffering measurement means or the forcible decoding determination. Decoding start control means for supplying a decoding start signal to the image decoding means upon any decoding start output from the means.

[0011] In the above image decoding apparatus, the communication network is configured to have a transmission interface means for inputting an encoded image signal received through the communication network to a buffer means. It is suitable in that it can correspond to various image communication systems realized through the communication.

In the above image decoding apparatus, the data storage means for storing at least information including the coded image signal is connected to the data storage means directly or via a communication means. Transfer control means for taking out the coded image signal and inputting it to the buffer means is preferable in that the moving image and the still image can be stored and provided in the data storage means without distinction. .

According to the present invention, the time from when the measured value of the buffering counting means no longer changes is measured by time measurement, and when the measured value reaches a predetermined threshold, a compulsory decoding start signal is generated. The image decoding device includes a decoding determination unit. Then, the image decoding apparatus starts the decoding process triggered by two cases, that is, when the measured value of the buffering counting unit reaches a predetermined threshold value and when the forced decoding start signal is generated.

When the image decoding means reads out the image signal, the buffering amount of the buffer means decreases, and when the transmission interface means or the transfer control means inputs the image signal, the buffering amount increases. When decoding a moving image, the reading speed and the writing speed from the buffer means cannot be completely balanced. Therefore, the buffering amount in the buffer means frequently changes, and the measured value of the buffering counting means also frequently changes. Therefore, the measured value in the time measurement by the forced decoding determination means is not frequently reset and becomes constant, and the forced decoding determination means does not generate the forced decoding start signal.

On the other hand, in the case of decoding a still image, since the subsequent image signal is not sent after receiving one image signal, the buffering amount of the buffer means does not change thereafter, and Becomes Therefore, the measurement value of the time measurement by the forced decoding determination unit that measures the time from when the buffering amount becomes constant increases monotonously,
Eventually, a predetermined threshold is reached. At this time, the forced decoding determination means generates a forced decoding start signal, and the decoding operation of the image decoding means is forcibly started. Thus, in the present invention,
The decoding operation can be automatically started even for a still image.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

[Embodiment 1] This embodiment is an example in which the present invention is applied to an image decoding apparatus that decodes an encoded image signal received from an image transmitting side via a transmission path.

FIG. 1 is a diagram showing the configuration of this embodiment. The transmission interface unit 101 receives a signal from the image transmission side from the transmission path and sends the signal to the demultiplexing unit 102. Since signals of various media are multiplexed in the signal, the demultiplexing unit 102 separates the multiplexed signal into signals for each medium such as an audio signal and an image signal. Hereinafter, in the present embodiment, the description of the processing related to the signal of the medium other than the image is omitted. When the signal from the transmitting side is not media-multiplexed and is composed of only an image signal, the demultiplexing unit 102 is unnecessary.

The image signal separated by the demultiplexing unit 102 is sent to a buffer unit 103, where it is temporarily stored. The amount of the image signal temporarily stored in the buffer unit 103 is measured by the buffering counting unit 104. When a new image signal is input to the buffer unit 103, the buffering counting unit 104 increases the count value by that amount,
When the temporarily stored image signal is extracted and sent to the image decoding unit 108, the count value is reduced by that amount. Every time the count value in the buffering counting unit 104 changes, the time count value of the timer unit 105 is reset and the time measurement is restarted. The forced decryption determination unit 106 includes a timer unit 10
When the time count value of 5 exceeds the threshold value 1, the decoding start control unit 1
07, a forced decoding start signal is sent. The decoding start control unit 107 performs one of the following: 1) when the count value of the buffering counting unit 104 exceeds a predetermined threshold value 2; or 2) when the forced decoding determination unit 106 sends a forced decoding start signal. In this case, a decoding start signal is sent to the image decoding unit 108. Upon receiving the decoding start signal, the image decoding unit 108 sequentially extracts and decodes the image signals temporarily stored in the buffer unit 103, and displays them on the image display unit 109.

In the present embodiment, the image decoding unit 108 is configured to, once receiving the decoding start signal, continue the operation until there is no more image signal waiting to be processed in the buffer unit 103. I do. Further, the configuration is such that the rate at which the image decoding unit 108 extracts image signals from the buffer unit 103 and the rate at which the demultiplexing unit 102 enters image signals into the buffer unit 103 averagely match.

FIG. 2 is a diagram for explaining the processing flow of the forced decoding determination unit 106. The forced decoding determination unit 106 monitors the time count value A of the timer unit 105, and sends a forced decoding start signal to the decoding start control unit 107 when it exceeds the threshold value 1.

FIG. 3 is a diagram for explaining the timing at which the forced decoding determination unit 106 generates a forced decoding start signal. As shown in FIG. 3, while the amount of image signal temporarily stored in the buffer unit 103 is fluctuating, the time count value of the timer unit 105 is frequently reset, and does not reach the threshold value 1. However, when the amount of image signals on the buffer unit 103 does not change, the time count value of the timer unit 105 monotonically increases, and eventually reaches the threshold value 1. Forced decryption determination unit 10
6 generates a forced decoding start signal at this time. In addition,
In FIG. 3, the forced decoding start signal is a pulse signal. However, other signals, for example, a step signal may be used.

FIG. 4 is a diagram for explaining the processing flow of the decoding start control unit 107. The decoding start control unit 107 monitors the count value B of the buffering counting unit 104, and sends a decoding start signal to the image decoding unit 108 when the count value B exceeds the threshold value 2. Further, the decoding start control unit 107 determines whether the forced decoding
Also, when the forced decoding start signal is received from 06, the decoding start signal is sent to the image decoding unit 108.

Next, the operation of this embodiment will be described along the time axis.

FIG. 5 is a diagram showing an example of a change over time of the count value of the buffering counting unit 104 and a change in the operation state of the image decoding unit 108 when the image sent from the transmission side is a moving image.

In this moving image example, the buffer unit 10
Reference numeral 3 indicates that no image signal is stored in the initial state. In the case of FIG. 5, the count value of the buffering counting unit 104 reaches the threshold value 2 at time 1. The image decoding unit 108 is in a stopped state until time 1, but when time 1 is reached, the decoding start control unit 107 sends a decoding start signal to the image decoding unit 108 according to the processing flow described in FIG. The image decoding unit 108 that has received the decoding start signal starts operation, and sequentially extracts and decodes image signals from the buffer unit 103. Note that, as shown in FIG. 5, a slight delay occurs between the time when the count value of the buffering counting unit 104 reaches the threshold value 2 and the time when the image decoding unit 108 actually starts operating.

In the above description, the value of the threshold value 2 is set so that the buffer unit 103 does not cause underflow.
As described above, the image decoding unit 108
Since the rate at which the image signal is extracted from the multiplexing unit 102 and the rate at which the multiplexing / demultiplexing unit 102 inputs the image signal are configured to be on average, if the threshold value 2 is set appropriately, the threshold value 2 Is temporarily stored, and no underflow occurs.

Although the timer unit 105 and the forced decoding determination unit 106 are operating even in the case of a moving image, the time count value in the moving image is constant because the amount of image signal in the buffer unit 103 constantly changes as shown in FIG. Is constantly repeated, and if the threshold 1 is appropriately selected, the forced decoding determination unit 1
06 does not generate a forced decoding start signal. Also,
In FIG. 5, for simplicity, the buffering counting unit 1
Although the case where the count value of 04 changes linearly is illustrated, it is not necessary to be linear.

Next, FIG. 6 shows an example of a time change of the count value of the buffering counting unit 104 and an operation state change of the image decoding unit 108 when the image sent from the transmission side is a still image.

In this still image example, the buffer unit 103 does not store any image signal in the initial state. If the image is a still image, the total image signal amount is equal to the threshold 2
The following cases are possible. FIG. 6 is an example, and the count value of the buffering counting unit 104 does not exceed the threshold value 2. When all the image signals for one still image enter the buffer unit 103, the buffering counting unit 104
No longer changes. The time when the count value of the buffering counting unit 104 does not change is referred to as time 2. Here, focusing on the count value of the timer unit 105, the count value of the timer unit 105 is repeatedly reset until time 2, but after the time 2, the count value of the timer unit 105 is not reset, and with the passage of time. To increase. Then, when the time count value reaches the threshold value 1, the forced decoding determination unit 106 sends a forced decoding start signal to the decoding start control unit 107. Upon receiving the forced decoding start signal, the decoding start control unit 107 sends a decoding start signal to the image decoding unit 108, and
The operation of the image decoding unit 108 is started. Note that there is a slight delay between the time when the time count value of the timer unit 104 reaches the threshold value 1 and the time when the image decoding unit 108 actually starts operating, as shown in FIG.

The image decoding unit 108 which has started operation sequentially takes out image signals from the buffer unit 103 and decodes them, as in the case of a moving image. Then, when there is no image signal waiting to be processed in the buffer unit 103, the image decoding unit 108 stops operating. Although FIG. 6 illustrates a case where the count value of the buffering counting unit 104 changes linearly for simplicity, the count value does not necessarily need to be linear.

Here, in order to make the explanation easy to understand, the present embodiment has been described by dividing the image sent from the transmitting side into a moving image or a still image. But,
The point of this embodiment is that it is automatically determined whether the image is a still image or a moving image. That is, it is not necessary to explicitly specify whether the received image is a still image or a moving image. If the received image is a still image,
A forced decoding start signal is provided to the decoding start control unit 107 by the functions of the buffering counting unit 104, the timer unit 105, and the forced decoding determination unit 106, and the image decoding unit 108 starts operating. On the other hand, when a moving image is received, the forced decoding start signal is not generated because the image signal amount in the buffer unit 103 constantly changes, and the function of the decoding start control unit 107 that monitors the count value of the buffering counting unit 104 is performed. Accordingly, the image decoding unit 108 starts operating.

[Embodiment 2] This embodiment is an example in which the present invention is applied to an image decoding apparatus which decodes an encoded image signal stored in a data storage device such as a magnetic disk or a CD-ROM. .

FIG. 7 is a diagram showing the configuration of this embodiment. The transfer control unit 701 sequentially takes out the signals stored in the data storage device 710 and sends them to the demultiplexing unit 702. Since signals of various media are multiplexed in the signal, the demultiplexing unit 702 separates the multiplexed signal into signals for each medium such as an audio signal and an image signal. Hereinafter, in the present embodiment, the description of the processing related to the signal of the medium other than the image is omitted. If the signals stored in the data storage device 710 are not media-multiplexed and are composed only of image signals, the demultiplexing unit 7
02 is unnecessary.

The image signal separated by the demultiplexing unit 702 is sent to a buffer unit 703, where it is temporarily stored. The amount of the image signal temporarily stored in the buffer unit 703 is measured by the buffering counting unit 704. When a new image signal is input to the buffer unit 703, the buffering counting unit 704 increases the count value by that amount,
When the temporarily stored image signal is extracted and sent to the image decoding unit 708, the count value is reduced by that amount. Every time the count value in the buffering counting section 704 changes, the time count value of the timer section 705 is reset and the time measurement is restarted. The forced decryption determination unit 706 includes a timer unit 70
When the time count value exceeds the threshold 1, the decoding start control unit 7
07, a forced decoding start signal is sent.

The decoding start control unit 707 performs the following operations: 1) when the count value of the buffering counting unit 704 exceeds a predetermined threshold value 2, or 2) when the forced decoding determination unit 706 sends a forced decoding start signal. In either case, a decoding start signal is sent to the image decoding unit 708. Upon receiving the decoding start signal, the image decoding unit 708
Are sequentially extracted and decoded, and displayed on the image display unit 709.

In the present embodiment, the image decoding unit 708 is configured to, once receiving the decoding start signal, continue the operation until there is no image signal waiting to be processed in the buffer unit 703. I do. Further, it is assumed that the rate at which the image decoding unit 708 takes out the image signal from the buffer unit 703 and the rate at which the demultiplexing unit 702 puts the image signal into the buffer unit 703 match on average.

The operation of each unit is the same as that of the first embodiment, and it is automatically determined whether the image extracted from the data storage device 710 is a moving image or a still image, and the decoding is performed.

Although the two embodiments of the present invention have been described with reference to the drawings, it goes without saying that various modifications can be made without departing from the spirit of the invention.

[0040]

As described above, in the image decoding apparatus of the present invention, in the case of a moving image, the fluctuation of the arrival time of the coded image signal is absorbed by the movement of the buffer unit as in the prior art, and the image frame Smooth reproduction is performed.
On the other hand, in the case of a still image, the problem of the related art that the image signal is accumulated in the buffer unit and decoding is not started is solved, and decoding is automatically started. Moreover, since it is automatically determined whether the image signal to be decoded is a moving image or a still image, it is not necessary to give the image type to the image decoding device in advance.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration of a first embodiment of the present invention;

FIG. 2 is a view for explaining a processing flow of a forced decoding determination unit in the first embodiment.

FIG. 3 is a view for explaining the timing at which a forced decoding determination unit in the first embodiment generates a forced decoding start signal;

FIG. 4 is a view for explaining a processing flow of a decoding start control unit in the first embodiment.

FIG. 5 is a diagram for explaining a time change of a count value of a buffering counting unit and a change of an operation state of an image decoding unit when a moving image is received according to the first embodiment.

FIG. 6 is a diagram for explaining a time change of a count value of a buffering counting unit and a change of an operation state of an image decoding unit when a still image is received in the first embodiment.

FIG. 7 is a view for explaining the configuration of a second embodiment of the present invention;

FIG. 8 is a view for explaining the definition of a moving image.

FIG. 9 is a view for explaining the definition of a still image.

FIG. 10 is a diagram illustrating a configuration of a conventional image decoding apparatus.

FIG. 11 is a diagram illustrating a time change of a count value of a buffering counting unit and a change in an operation state of an image decoding unit when a moving image is received by an image decoding device in a conventional example.

FIG. 12 shows a time change of a count value of a buffering counting unit when a still image is received by an image decoding device in a conventional example,
FIG. 7 is a diagram for explaining a change in the operation state of the image decoding unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Transmission interface part 102 ... Demultiplexing part 103 ... Buffer part 104 ... Buffering counting part 105 ... Timer part 106 ... Forced decoding determination part 107 ... Decoding start control part 108 ... Image decoding part 109 ... Image display part 701 ... Transfer control Unit 702 demultiplexing unit 703 buffer unit 704 buffering counting unit 705 timer unit 706 forced decoding determination unit 707 decoding start control unit 708 image decoding unit 709 image display unit 710 data storage device

Claims (3)

(57) [Claims] A buffer means for temporarily storing an encoded image signal, and a data amount of the encoded image signal stored in the buffer means is measured. First
Buffering measuring means for outputting the start of decoding when the threshold value is reached, and measuring the time from when the value of the buffering measuring means becomes constant, and measuring the measured time with a predetermined second threshold value. When a decoding start is reached, a decoding start control means for providing a decoding start signal to the image decoding means by any decoding start output from the buffering measuring means or the forced decoding judgment means An image decoding device, comprising: 2. The image decoding apparatus according to claim 1, further comprising transmission interface means connected to a communication network and for inputting an encoded image signal received via the communication network to a buffer means. 3. A data storage means for storing at least information including a coded image signal, wherein the data storage means is connected to the data storage means directly or via a communication means, and transmits the coded image signal from the data storage means. 2. The image decoding apparatus according to claim 1, further comprising: transfer control means for taking out the data and inputting it to the buffer means.