JP2000244928A - Image decoder and method for restoring image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image decoder and a method for restoring an image by which an error of supplied picture data can be compensated and the resulting data can be decoded without the need for a re-transmission request even when the error is detected in the supplied picture data. SOLUTION: An error compensation control section 20 of the image decoder 10 applies selection control to an image data prediction section 26, a selector section 22 and a decoding data storage section 24 in response to error information from a system multiplex decoder 12, allows the selector section 22 to supply decoded image data to the decoded data storage section 24 only when the image data are normal, allows the selector section 22 to supply the decoded image data to the image data prediction section 26, where image data of an erroneous field are predicted based on the supplied image data to compensate the image data with the error when the image data are in error. When the image data are normal, the decoder 10 outputs the data as they are, re-transmission of the erroneous image data is avoided and the decoder 10 always output the normal image data or the image data whose error is compensated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image decoding apparatus and an image restoration method in which image data encoded on a transmission side is transmitted to a decoding side via a communication channel, and the decoding side restores the image data. Even if an error occurs due to transmission, it is possible to compensate for a visual effect that appears when the display is performed, and is suitable for use in, for example, a receiving device.

[0002]

2. Description of the Related Art When an image is transmitted as a digital signal and transmitted, generally, a digitized image signal, that is, image data is encoded and transmitted to a receiving side, and the receiving side decodes and displays the encoded image data. It is displayed on a device or a printer. Image coding is performed by first applying a discrete cosine transform (Discrete Cosine Transform:
Hereinafter, processing such as DCT), quantization, motion compensation, and bidirectional prediction are performed to compress the information amount of the image data. This information-compressed code is called an information source code. Second, the encoded information is encoded according to the data format to be transmitted. This encoding converts the information into a transmittable bit stream. This coding includes, for example, hierarchical structure coding, variable length coding, and the like.

[0003] Image data to be transmitted includes a still image and a moving image. When transmitting the latter video,
Before performing the above-described encoding, a difference between a temporally previous image and a current image is obtained. Encoding of an image in a moving image is performed using the difference result. As a result, further information compression is performed as compared with the above-described information compression.

When decoding image data which has been subjected to such compression processing, the procedure is exactly the reverse of the processing performed in the previous information compression, that is, extraction (cutout) of compressed data and expansion of the extracted compressed data). Is performed. When transmitting the information-compressed image data, the compressed data may be erroneous in the transmission path for some reason such as noise. At this time, when the image data is decoded, the decoding process is performed in correspondence with the above-described various types of encoding.
In many cases, the effect of this error extends to other image data. An example of this effect is a moving image. In this case, since the difference between the temporally previous image and the current image is transmitted as image data, an error propagates also in the time axis direction.

[0005] A method of requesting retransmission has been proposed to avoid the propagation of this error. In this method, an error detection code is added when encoding is performed in advance on the transmission side, and transmission is performed. When an error is detected on the decoding side, a request is made to the transmission side for retransmission of erroneous image data. It is to display a missing image. The function of requesting retransmission is included in, for example, a system multiplex decoding unit that separates image data and various data into another medium. When an error is detected, other normal data is temporarily stored in a buffer until image data is retransmitted. The data stored in this buffer is processed after processing the retransmitted image data. MPEG2 (MovingPicture Expe
In the rts Group 2 (hereinafter simply referred to as MPEG2) standard, one frame of image data (that is, one frame) is divided into two fields on the transmitting side, and each is encoded and transmitted to the decoding side. Therefore, on the decoding side, the above-described series of decoding processing is performed on the image data supplied from the transmission side for each field. At this time, error detection is also performed for each field on the decoding side, and a retransmission request is also output based on the error detection result.

[0006]

By the way, when a retransmission request is made in response to an error in image data, first, a normal one-time request is made.
Clearly, the data amount due to retransmission of the image data increases as compared with the time of transmitting the data for the number of sheets. When communication is performed in real time, the delay time of each data becomes a problem. For this reason, the transmission rate of image data must be reduced in accordance with data having a long delay time. In order to satisfy these two points, since the amount of data passing through the transmission path is a predetermined amount, image data must be highly compressed with respect to other data. When such highly-compressed image data is transmitted, the decoded image has an image quality of a coarse resolution, and the image deteriorates with respect to the original image.

Further, on the decoding side, it is necessary to temporarily store other data from which an error has been detected in a memory such as a buffer until transmission by a retransmission request is completed.
If error detection occurs frequently or a plurality of times, it is necessary to provide a memory having a large data capacity not only on the decoding side but also on the transmission side to cope with this occurrence.

[0008] The retransmission request does not immediately respond to the request, but takes time. In particular, for example,
In the case of performing satellite communication or retransmission a plurality of times, on the decoding side, the total amount of time required for each of the retransmission request and the retransmission becomes a delay time, and a very long time is required.

Furthermore, when this retransmission request is made in real-time communication, it is not possible to wait until correct image data is supplied. The number of retransmissions is limited due to problems such as the relationship. Further, there is no guarantee that the image data supplied by the retransmission request is always accurate.

The present invention solves the above-mentioned drawbacks of the prior art, and provides an image decoding system capable of compensating for and decoding an error in the supplied image data without making a retransmission request even if an error is detected in the supplied image data. It is an object to provide an apparatus and an image restoration method.

[0011]

According to the present invention, there is provided an image decoding apparatus for receiving encoded image data supplied on a field basis and decoding the received image data. The apparatus includes a field detection unit that detects which field the received image data is, an error detection unit that detects an error in the image data, and further includes a decoding result storage unit that stores normally decoded image data. Selecting means for supplying normally decoded image data to the decoding result storage means and selecting an output destination of the decoded image data from the decoding result storage means or an input destination of supplied information; and Image prediction means for predicting image data of an erroneous field based on image data stored in the decoding result storage means via the Error compensation control means for performing selection control on the prediction means, selection means, and decoding result storage means in accordance with error information from the error detection means, and performing compensation control on the erroneously decoded image data in the image prediction means. And characterized in that:

The error compensation control means includes an error information storage means for storing error information supplied from the error detection means, and a control means for controlling the decoding result storage means and the image prediction means according to the information in the error information storage means. And a selection control unit for performing selection control of the selection unit. As a result, the image decoding apparatus performs compensation control of image data according to the presence or absence of an error.

The selection means includes a first selection means for supplying the decoded image data from the decoding result storage means only when it is normal, an image prediction means for supplying the decoded image data from the decoding result storage means to the image prediction means, and It is desirable to include a second selection unit for selecting either one of the outputs or one of the decoded image data and the motion information from the decoding result storage unit supplied. This allows
Either the image data in which the decoded image data is normal or the image data in which the decoded image data has been compensated is output from this device, and the input information is selected.

The image prediction means may use image data of another field corresponding to the field in which an error has been detected, as prediction data. This makes it possible to perform complicated error correction and eliminate the need to retransmit erroneous image data.

It is preferable that the image prediction means predicts the prediction data for the erroneous image data by using the image data of one field before and / or one field after in time. Since the image data to be used tends to have a strong correlation with the image data of the erroneous field, sufficient prediction can be made.

Further, the image prediction means supplies a filter processing means for performing a filtering process to the image data used for the prediction data, and supplies a filter coefficient and a filtering procedure to the filtering processing means, and controls the operation of the filtering processing means. May be included.
As a result, the image data of the erroneous field is subjected to a filtering process on the image data of another field, thereby enabling more accurate prediction.

When decoding a field, the image decoding apparatus stores motion information, which is the amount of motion of a moving object in an image with the passage of time, as well as the amount of motion between the same fields of different frame images. And a motion information storage unit that outputs the calculated motion information.The image prediction unit uses one of the motion information storage unit for the image data of the field and the output information supplied from the decoding result storage unit. It is desirable to predict image data. Even if the time of the two fields is shifted and the image data of one of the fields has an error, the prediction is performed in consideration of the motion information, so that appropriate prediction can be performed for the erroneous image data.

In addition to the prediction based on the motion information, it is desirable that the image predicting unit performs the prediction using the image data obtained by the filter processing unit and the filter control unit. This allows for more accurate predictions.

It is preferable that the error detecting means be supplied with an error detection code used for error detection together with the supplied image data.

Preferably, the error detecting means uses a syntax error for error detection when decoding the supplied image data.

Preferably, the decoding result storing means stores the number of each field of the image data together with the decoded image data.

According to the image decoding apparatus of the present invention, the error compensation control means performs selection control on the image prediction means, the selection means and the decoding result storage means according to the error information from the error detection means. The decoded image data is supplied to the decoding result storage means via the selection means, and the erroneous image data is discarded. If there is an error in the image data, the normal image data from the decoding result storage means is selected. Is supplied to the image predicting unit via the image predicting unit. The image predicting unit predicts image data of an erroneous field based on the supplied image data, compensates for the erroneous image data, and performs normal decoding. In this case, by directly outputting the image data from the device, retransmission of erroneous image data can be avoided, and either normal image data or image data in which the influence of errors is suppressed can be avoided. Or is always output as the restored image.

The present invention also relates to an image restoration method for receiving encoded image data supplied in units of fields and decoding the received image data. This method detects which field is the received image data. An error detecting step for detecting an error in the image data, further comprising a field detecting step, and an error generating a control signal for performing compensation control on the image data which has been erroneously decoded according to the detection result of the error detecting step. The compensation control step and the supply of the normally decoded image data and the selection of the output destination of the supplied decoded image data or the input destination of the supplied information are respectively performed by the control signal obtained in the error compensation control step. A selecting step, and an image predicting step of predicting image data of an erroneous field based on the image data decoded by the selecting step Hints, in the selection process, already and outputs any one of image data predicted by the supplied have decoded image data or the image predictive process.

According to the image restoration method of the present invention, the field of the received image data and the presence or absence of an error in the image data are detected, and a control signal is generated in accordance with the presence or absence of the error. The destination of the image data is selected accordingly, and prediction is performed on the image data in the erroneous field based on the normal decoded image data, and the predicted image data or the decoded image data already supplied is By outputting either of them, it is possible to always output the image data in which the influence of the error is suppressed, which is restored.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image decoding apparatus and an image restoration method according to the present invention will be described in detail with reference to the accompanying drawings.

The image decoding apparatus according to the present invention is built in, for example, a receiver and used for restoring received transmission data.
In the present embodiment, an image decoding apparatus 10 mounted on such a receiver will be described with reference to FIGS.
As shown in FIG. 1, the image decoding device 10 includes a system multiplex decoder 12, a standby buffer unit 14, a video signal multiplex decoding unit.
16, information source decoding unit 18, error compensation control unit 20, selector unit 2
2, a decoded data storage unit 24 and an image data prediction unit 26 are provided.

Among them, the system multiplex decoder 12, the standby buffer unit 14, the video signal multiplexing decoding unit 16 and the information source decoding unit 18 have the configuration included in the conventional image decoding apparatus. The system multiplex decoder 12 separates a multiplexed signal, which is a multiplexed bit string supplied via a transmission path (not shown), for each medium. The multiplexed signal includes not only a video signal but also various signals corresponding to respective media such as, for example, an audio signal and data used for teletext. The system multiplex decoder 12 separates the signal and detects an error of the signal.
For error detection, for example, a syntax error or the like is used. Heretofore, when an error is detected, the system multiplex decoder 12 outputs a retransmission signal to the signal transmitting side so that the image data in which the error has occurred is retransmitted, and the retransmitted image data is normally transmitted. Do not output until transmitted.
When the normal image data is supplied, the separated data is output to the standby buffer unit 14 for the first time. However, in the present embodiment, information on error detection is output to the error compensation control unit 20 without outputting the retransmission signal. The error compensation control unit 20 will be described later.

The standby buffer section 14 is a system multiplex decoder.
This is a buffer memory for waiting for data supplied from 12. The waiting data here is performed only for the image. The standby buffer unit guarantees the decoding processing time for the received data. The input and output of data relating to this guarantee are timing-controlled by a system control unit (not shown) or the like.

The video signal multiplexing decoding section 16 cuts out image data from the standby buffer section 14. This image data is data compressed by, for example, hierarchical structure coding or variable length coding. Video signal multiplexing decoding section 16
Performs hierarchical structure decoding, variable length decoding, and the like by extracting this image data.

The information source decoding section 18 subjects the output signal from the video signal multiplexing decoding section 16 to decompression processing. The supplied signal is the information that is still compressed. Information source decoding unit 18
Performs decompression of compressed information by performing a process reverse to that of the information source coding. The reverse processing includes, for example, motion compensation, inverse quantization, and inverse DCT processing. These series of decompression processes are performed to restore image data.

With these configurations alone, when erroneous image data is supplied, it takes a long time before the target image data is retransmitted, which is a serious problem when real-time processing is required, for example. . Therefore, without performing this retransmission, the erroneous image data is compensated for by the processing on the decoding side. To realize this, the image decoding apparatus 10 of the present embodiment includes, in addition to the conventional configuration, the error compensation control unit 20, the selector unit 22, the decoded data storage unit 24, and the image data prediction unit 26, as described above. Is provided.

The error compensation control unit 20 includes an error information storage unit 20
a and a selector control unit 20b. The error information storage unit 20a is a memory for storing information based on the result of error detection performed in the system multiplex decoder 12. The error information storage unit 20a performs input and output of this information under the control of a system control unit (not shown). The error information storage unit 20a temporarily stores the information and supplies this information to the selector control unit 20b. The selector control unit 20b generates a control signal for controlling the selection of the selector unit 22 according to whether the supplied information is normal or incorrect. Also, an error compensation control unit
Numeral 20 controls the image data prediction unit 26 and the decoded data storage unit 22 to perform compensation according to the respective errors, and performs data input / output control. The above control may be performed by the system control unit.

The selector section 22 is provided with selectors 22a and 22b. The selector 22a selects whether to supply the decoded image data from the information source decoding unit 18 to the decoded data storage unit 24. When normal image data is supplied, a decoded data storage unit (not shown) according to a control signal is provided.
The side supplying 24 is selected. Further, when erroneous image data is supplied, also in this case, though not shown, the side that discards the image data is selected according to the control signal.

The selector 22b selects an output destination of the image data read from the decoded data storage unit 24. A control signal is supplied from the selector control unit 20b of the error compensation control unit 20 according to the presence or absence of an error in the image data supplied to the selector 22b. The selector 22b selects an output destination of the image data depending on whether or not there is an error in outputting from the device 10 via the image data prediction unit 26 or the output terminal according to the control signal. The decoded data storage unit 24 is a memory that stores only normally decoded image data. Decryption data storage
In the field 24, together with the image data decoded by the information source decoding unit 18, a field number indicating which line of which field is stored is stored.

The image data prediction unit 26 uses a plurality of prediction memories when image data having a field structure (not shown) is supplied. In the image data prediction unit 26, the image data from the decoded data storage unit 24 is supplied to the prediction memory that supplies the supplied erroneous image data through the selector 22b. Here, as the supplied image data, although the field is different, the vicinity of the line of the erroneous field, that is, the adjacent line is used. The image data thus predicted is stored in the information storage unit 18 as a reference image and a device.
These are output as output image data from 10 respectively.

With such a configuration, the data stored in the image decoding apparatus 10 can be used as prediction data without causing the transmitting side to output a retransmission request to the image data having an error. The output from the device can be obtained. As a result, it is possible to suppress an increase in the capacity of the standby buffer for temporarily waiting for the received data. Such an increase in capacity does not output a retransmission request, so that the capacity of the buffer on the transmission side can be reduced.

Next, the operation of the image decoding apparatus 10 will be described with reference to FIG. The image decoding apparatus 10 inputs a multiplexed bit sequence obtained by encoding an image from a transmission side via an input terminal. The input multiplexed bit string is data having a field structure. The multiplexed bit string is output to the system multiplex decoder 12.
Is separated for each medium. The separated data includes:
The system multiplex decoder 12 uses a CRC (Cyclic Redundancy Checker)
k: Cyclic redundancy check). This check determines whether an error exists in the received data. The system multiplex decoder 12 uses this check result as an error compensation control unit.
20 error information storage unit 20a. Further, the system multiplex decoder 12 outputs the received data to the standby buffer unit 14.

This data is supplied from the standby buffer section 14 to the video signal multiplexing decoding section 16 at the same timing. Here, the supplied data is, for example, a video signal in which a plurality of channels are multiplexed and hierarchized, and individual data is compressed by encoding.
The video signal multiplexing / decoding unit 16 separates and decodes the multiplexed and layered video signal, for example, to cut out (or extract) a channel divided into compressed data for each channel. The cut-out data is supplied to the information source decoding unit 18. The information source decoding unit 18 performs motion compensation, inverse quantization and inverse DCT processing on the compressed data to expand the compressed data. The information source decoding unit 18 selects the decompressed image data
Output to 22a. Since this image data has a field structure in the received data (bit string),
This is field data of half of one frame. In each field, one field of the first line in the interlaced scanning is called a top field, and the other field is called a bottom field. It is known that there is a strong correlation between adjacent lines in the first field and the second field, especially between pixels. Therefore, it is considered that adjacent pixels often have similar values. Thus, the two fields are considered to be similar images.

The error information storage unit 20a holds the error check result and outputs the check result to the selector control unit 20b. The selector control unit 20b determines whether the inspection result indicates the presence of an error in the received data. If the error is included in the received data, the selector control unit 20b discards the output from the information source storage unit 18 and the image data prediction unit 26 A control signal for selecting an output to the receiver is generated, and when normal received data is restored, supply of received data from the information source storage unit 18 to the decoded data storage unit 24 and readout from the decoded data storage unit 24 to the outside. A control signal for selecting output of data is generated. Further, the error compensation control unit 20 generates a control signal for controlling operations of the decoded data storage unit 24 and the image data prediction unit 26.

The selector section 22 receives a control signal supplied from the error compensation control section 20 in accordance with the presence or absence of an error.
Output destination of 22a, 22b is selected. By the selection of the selector 22a, the decoded data storage unit 24 always stores normal restored data. Further, the image data prediction unit 26 includes:
Normal restored data is supplied. However, when an error is detected in the received data, the image data of the previous field or the next field is supplied to the image data of the field in which the error has occurred. Further, the supplied image data is preferably a field in the same frame as the field in which the error was detected.
The decrypted data storage unit 24 is configured to maintain such a relationship.
Is controlled by the error compensation control unit 20.

The image data predicting unit 26 predicts a reference image using the supplied image data of the field. When normal decoding is performed, for example, as shown in FIG. 2, eight lines (F-1 to F-8, S-1 to S-8) of a first field (F) and a second field (S) are provided. ) Is used as a transmission line unit, and an image is generated by synthesizing the second field between the lines of the first field. For example,
When a vertically long black square image is transmitted, a 16-line macroblock image shown in FIG. 2A is obtained by normal decoding. By the way, even when comparing the images of the two fields, a visually remarkable difference is often not found. However, as shown in FIG. 2B, an error may occur such that a vertically long black square image is not transmitted in the decoded second field image. At this time, the lines S-1 to S-8 of the erroneous field are requested to be retransmitted to the transmission side.

In the present embodiment, by utilizing the above-described characteristics of the image, the first data which has been decoded normally without performing any complicated arithmetic processing in place of the image data of the second field having an error. The field image data is used as it is. Therefore, of the decoded images, for example, F-
1, F-1, F-2, F-2,..., F-8, F-8 and the image data of the first field are repeated twice to generate one frame as prediction data and output image data. Is done.

When this image is provided as one frame of a moving image, the visual difference between the fields can not be recognized more, so that it is effective error compensation. Such error compensation is effective when the supplied image is applied to an image having no or very little motion, such as a still image. This eliminates the necessity of increasing the capacity of the standby buffer corresponding to the waiting time until the image data is retransmitted and arrives after the conventional retransmission request. Also, by not requesting retransmission, it is possible to prevent a significant delay in decoding and outputting image data. Furthermore, since there is a request that image data must be transmitted and received within a predetermined time while also considering the time of a retransmission request as in the case of real-time communication, the amount of encoded bits tends to be suppressed. However, since there is no retransmission request, a larger amount of the predetermined coded bits can be allocated for this time, so that the image quality can be improved.

Next, a first modification of the embodiment shown in FIG. 1 will be described. A first modification is that the image data prediction unit 26
Is different. The image data prediction unit 26 includes a filter control unit 26a and a filter processing unit 26b. The filter control unit 26a supplies the processing procedure of the filter processing unit 26b, filter coefficients, image data from the selector 22b, and the like to the filter processing unit 26b. The supplied processing procedure includes, for example, a procedure for performing contour enhancement by an edge processing method or the like. Also, the filter processing unit 26b
Is a digital filter composed of delay elements, taps, adders, and the like.

Operations other than the image data prediction unit 26 are exactly the same as those of the above-described embodiment. Therefore, the operation of the first modification will be described by limiting the operation to the image data prediction unit 26. The filter control unit 26a converts the selected image data in response to an error in the selector 22b into a filter processing unit.
Supply 26b. The filter processing unit 26b is supplied with a filter coefficient and a processing procedure from the filter control unit 26a in advance. Using the stored filter coefficients, the filter processing unit 26b performs an operation on image data of a normal field supplied from the filter control unit 26a to perform a desired filter process. The processing result is output to the filter control unit 26
a, and outputs the image data processed in accordance with the control signal from the error compensation control unit 20 via the output terminal. The control from the error compensation control unit 20 controls the filter control unit 26a, particularly when the image data is a moving image, and outputs the obtained image data to the information source decoding unit 18. Information source decoding unit 18
Then, the image data supplied from the image data prediction unit 26 is used as a reference image for decoding the subsequent image data.

As described above, when the prediction for the image data of the erroneous field is performed from the image data of the other fields, including the filtering process, the prediction is performed, so that the prediction in the previous embodiment, that is, the same value is used. It is also possible to perform highly accurate prediction. As a result, even if there is an error, a visually smooth image can be obtained. In particular, the effect is exhibited in an image including an oblique line or the like.

In this embodiment, of the two lines,
Although the average value of two lines using one normal line is used, the present invention is not limited to this number of lines, and image data may be predicted from three or more lines. It goes without saying that a good prediction image can be obtained by using a filter having good frequency characteristics.

Next, a second modification of the embodiment shown in FIG. 1 will be described. In the second modified example, in addition to the configuration of FIG. 1, a motion vector information storage unit 18a is provided so as to be able to better cope with errors in a moving image. The motion vector information storage unit 18a includes a memory function of storing a motion vector used for decoding in the information source decoding unit 18, and between each frame, stores an image using image data of the same field of an adjacent frame. The amount of movement for each of the included moving objects is calculated. The motion vector is information for reflecting the movement amount of the target in the image on the image and smoothly displaying the movement of the target so that the moving image does not have an unnatural feeling. In this case, the selector 22b selects an input destination of information to be supplied to the image data prediction unit 26. That is, one of the motion vector information from the motion vector information storage unit 18a and the normally decoded image data from the decoded data storage unit 24 is selected.

Finally, the operation of the second modification will be briefly described. 4 is basically the same as the operation performed in the configuration of FIG. The selector 22b is supplied with motion vector information from the motion vector information storage unit 18a. The motion vector information storage unit 18a operates according to control from a system control unit (not shown). The selector 22b selects whether to supply either the motion vector information or the normally decoded image data to the image data prediction unit 26 according to the control signal from the error compensation control unit 20. That is, when an error is detected, the selector 22b selects the motion vector information from the motion vector information storage unit 18a, and when it is confirmed that decoding has been normally performed (no error), the decoded data storage unit 24 One from
Select the image data for the field and
Output to 18.

The image data predictor 26 is supplied with the image data of the field decoded correctly in this way. Thus, when a normal operation is performed, the image data prediction unit 26 generates a macroblock by combining the image data of the first field and the image data of the second field as shown in FIG. 5A. The macro block forms a block of 16 lines by combining data of 8 lines each. The normally received image in FIG. 5 is a case where, for example, a target vertically long black square moves in the right and left direction with time. In the images of the first field and the second field, the moving object is displayed at different times, so that the object represented in a straight line in the image of each field is not displayed in a straight line.

Here, if an error in the condition that no object is included in the image of the second field, for example, as shown in the figure, is detected, the image data of the first field is used as in the above-described embodiment. . The first field in this case is image data in the same frame as the previously supplied second field. The image data prediction unit 26 predicts the image data of the second field using the image data and the amount of motion between the first field of the frame supplied next. At this time, a motion vector for the previous image in the field is also used.

This prediction method will be described below with specific examples. In the image of the first field in FIG.
It has moved to the position represented by the dashed rectangle. The image data prediction unit 26 is supplied with motion vector information indicating that the target has moved to this position. The prediction data is encoded from the already supplied image data of the first field and the motion vector.

Further, the image data encoded by halving the value of the motion vector information is replaced with the second image having the error.
The image data of the field is used. The motion vector information is
For example, when a movement of 10 pixels is indicated, the second field is used as a movement of 5 pixels. The reason why the motion vector information (motion amount) can be reduced to half is that the second field is located between the first field in the same frame and the first field in the next frame. The symbol ^* attached to the line of the image of the macroblock in FIG. 5B indicates that it is the second field after prediction. As a result, the same image as shown in FIG. 5A is obtained even if there is an error.

By operating as described above, a correct image can be sufficiently predicted even if an error occurs in one of the fields when transmitting image data having a field structure. In this example, the prediction of the second field is performed from the first field which is temporally consecutive. However, if the first field is incorrect, the prediction can be performed from the second field which is consecutive. Therefore, it can be seen that a field that is temporally successive to the erroneous field may be used. Further, in the second modification, the prediction is performed using the motion vector information. However, the prediction may be performed by performing a filtering process on the images of the same field that are different in time.

With the above arrangement, when image data having a field structure is supplied, even if an error occurs in the image data of one field, it can be sufficiently predicted from the other field. An increase in the waiting time after the request can be suppressed. This allows
The problem of delay in image restoration that occurs is avoided, and the effect is realized in real-time communication. In addition, the suppression of the increase in the waiting time can also suppress the increase in the memory capacity accompanying this, and the device can be simplified. Since a large amount of coded bits can be allocated, it is possible to improve image quality.

[0056]

As described above, according to the image decoding apparatus of the present invention, the error compensation control means performs selection control on the image prediction means, the selection means and the decoding result storage means according to the error information from the error detection means, Only when the image data is normal, the decoded image data is supplied to the decoding result storage means via the selection means, and if the image data has an error,
Based on the supplied image data, the image predictor predicts the image data of an erroneous field based on the supplied image data, compensates for the erroneous image data, and compensates for the erroneous image data. Is output from the apparatus as it is, thereby avoiding retransmission of erroneous image data, and always outputs either normal image data or image data with reduced influence of errors as a restored image. For this reason, for example, the effects of shortening time and improving image quality in real-time communication are exhibited. In addition, the suppression of the increase in the waiting time also enables the simplification of the device by suppressing the increase in the memory capacity accompanying this. Since a large amount of coded bits can be allocated, it is possible to improve image quality. As a result, a device configuration required for retransmission can be simplified.

According to the image restoring method of the present invention, the field of the received image data and the presence or absence of an error in the image data are detected, and a control signal is generated in accordance with the presence or absence of the error. The destination of the image data is selected according to the signal, and prediction is performed based on the normally decoded image data for the image data in the wrong field, and the predicted image data or the decoded image already supplied is By outputting any one of the data and always outputting the restored image data in which the influence of the error is suppressed, it is possible to greatly suppress the increase in the waiting time after the conventional retransmission request. As a result, the problem of delay in image restoration that occurs can be avoided, and the effect can be exhibited in real-time communication.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an image decoding device according to the present invention.

FIG. 2 is a schematic diagram for explaining how to compensate when the image data received in the configuration of FIG. 1 is normal and when there is an error.

FIG. 3 is a block diagram showing a schematic configuration of a first modification of the embodiment in FIG. 1;

FIG. 4 is a block diagram showing a schematic configuration of a second modification of the embodiment of FIG. 1;

FIG. 5 is a schematic diagram illustrating a method of compensating when the image data received in the configuration of FIG. 4 is normal and when there is an error.

[Explanation of symbols]

 10 Image decoding device 12 System multiplex decoder 14 Standby buffer unit 16 Video signal multiplexing decoding unit 18 Information source decoding unit 20 Error compensation control unit 22 Selector unit 24 Decoded data storage unit 26 Image data prediction unit 20a Error information storage unit 20b Selector Control unit 22a, 22b selector

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C059 LB16 MA01 MA03 MA23 MA31 ME01 PP04 RF01 RF09 TA08 TA09 TA76 TB04 TB05 TC02 TC22 TD01 UA05 UA33

Claims (12)

[Claims] 1. An image decoding apparatus for receiving coded image data supplied in units of fields and decoding the received image data, the apparatus comprising: field detection means for detecting which field the received image data is And an error detecting means for detecting an error in the image data. The apparatus further comprises: a decoding result storing means for storing normally decoded image data; and a normally decoded image stored in the decoding result storing means. Selection means for supplying data and selecting an output destination of decoded image data from the decoding result storage means or an input destination of information to be supplied; and a selection result stored in the decoding result storage means via the selection means. Image predicting means for predicting image data of an erroneous field based on the image data obtained, the image predicting means, the selecting means, and the decoding Error compensation control means for performing selection control on the result storage means in accordance with error information from the error detection means, and performing compensation control on erroneously decoded image data in the image prediction means. An image decoding device characterized by the following. 2. The apparatus according to claim 1, wherein the error compensation control means stores error information supplied from the error detection means, and an error information storage means for storing error information supplied from the error detection means. An image decoding apparatus, comprising: a selection control unit that controls the decoding result storage unit and the image prediction unit and controls the selection unit. 3. The apparatus according to claim 1, wherein the selection unit supplies the decoded image data from the decoding result storage unit only when the image data is normal. Selecting either one of the image prediction means and the output from the apparatus or selecting one of the decoded image data and the motion information from the supplied decoding result storage means. An image decoding device comprising: a selection unit. 4. The image decoding apparatus according to claim 1, wherein said image prediction means uses image data of another field corresponding to a field in which an error has been detected as prediction data. 5. The apparatus according to claim 4, wherein said image predicting means predicts predicted data for said erroneous image data using image data of one field before and / or one field after in time. An image decoding apparatus characterized in that: 6. The apparatus according to claim 5, wherein the image predicting unit performs a filtering process on the image data used for the prediction data, and the filter processing unit includes a filter coefficient and a filter processing procedure. An image decoding apparatus, comprising: a filter control unit that supplies and controls an operation of the filter processing unit. 7. The apparatus according to claim 5, wherein the apparatus stores, when decoding the field, motion information that is a motion amount of a moving object in an image with the lapse of time, A motion information storage unit that calculates a motion amount between the same fields of different frame images and outputs the calculated motion information, wherein the image prediction unit stores the motion information storage unit and the decoding result storage for the image data of the field. An image decoding apparatus for predicting image data using one of output information supplied from a means. 8. The image decoding apparatus according to claim 7, wherein said image prediction means performs prediction using image data obtained by said filter processing means and said filter control means. 9. The apparatus according to claim 1, wherein an error detection code used for error detection is supplied to the error detection means together with the supplied image data. Image decoding device. 10. The apparatus according to claim 1, wherein said error detection means uses a syntax error for error detection when decoding the supplied image data. Image decoding device. 11. The image decoding apparatus according to claim 1, wherein said decoding result storing means stores the number of each field of the image data together with the decoded image data. 12. An image restoration method for receiving encoded image data supplied in units of fields and decoding the received image data, comprising: a field detecting step of detecting which field of the received image data is detected. An error detection step of detecting an error in the image data, an error compensation control step of generating a control signal for performing compensation control on the image data that has been erroneously decoded according to the detection result of the error detection step, A selection step of supplying the image data normally decoded by the control signal obtained in the error compensation control step and selecting an output destination of the supplied decoded image data or an input destination of the supplied information; An image prediction step of predicting image data of an erroneous field based on the image data decoded in the selection step. 3. The image restoration method according to claim 1, wherein either the decoded image data already supplied or the image data predicted by the image prediction step is output.