JPH0851630A - Movement compensation predicting encoder - Google Patents

Abstract

PURPOSE:To improve the encoding efficiency of a movement compensation predicting encoder. CONSTITUTION:This encoder is constituted of a precise MV detector 8 for obtaining a motion vector by accuracy higher than transmission accuracy (a transmission standard,) a precise movement compensator 9 for performing movement compensation by the obtained motion vector and obtaining prediction signals by the accuracy higher than the transmission accuracy, an MV value rounding device 14 and an MV encoder 15 for rounding the obtained motion vector to the transmission accuracy and encoding it and predictive encoding means (2-5) for encoding a prediction residual and the movement compensation is performed by the accuracy higher than the transmission accuracy on an encoding side. By not encoding an error by the accuracy limit of a movement compensation processing not provided with correlation between frames and encoding the essential change of pictures provided with correlation between the frames more faithfully for that, the next inter-frame prediction efficiency is improved and the general encoding efficiency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is a high-efficiency coding apparatus for digitizing an image with a smaller amount of information by using interframe and interfield prediction in a system for recording, reproducing and displaying image information. In particular, the present invention relates to a device that performs motion compensation processing.

[0002]

[Prior art]

<Motion Compensation Predictive Coding Device> In high-efficiency coding of a moving image, inter-frame prediction is performed by utilizing high correlation between frames and fields (hereinafter, represented by frames). Particularly in recent years, motion-compensated inter-frame prediction has become common, in which a signal of a frame used for prediction is spatially moved according to the motion of an image and then inter-frame prediction is performed.

Such motion-compensated interframe prediction (hereinafter,
FIG. 4 shows an example of an encoding device that performs motion compensation prediction. The image signal input from the image input 1 is given to the predictive subtractor 2 and the motion vector (hereinafter abbreviated as MV) detector 23. In the prediction subtractor 2, the inter-frame prediction signal given from the motion compensator 24 is subtracted from the input image signal,
The prediction residual signal is provided to DCT3. 8 for DCT3
Two-dimensional discrete cosine transform (D
CT) is performed, and the transformed prediction residual signal (DCT coefficient) is given to the quantizer 4. The quantizer 4 quantizes the signal with a predetermined step width, and the fixed-length code is given to the inverse quantizer 13 and the variable-length encoder 5.

In the variable-length encoder 5, the fixed-length code is variable-length-encoded into a compressed code, which is given to the multiplexer 6. A concrete method of variable-length coding is to convert a two-dimensional array of DCT into a one-dimensional array signal string by zigzag scanning, in which a non-zero value is the value, and 0 is the continuous number (run length) of the Huffman code. Turn into. The multiplexer 6 multiplexes the code of the prediction residual and the code of the MV information provided from the MV encoder 15, and outputs the code string from the code output 7.

On the other hand, in the inverse quantizer 13, the fixed length code is replaced with the representative value and given to the inverse DCT 12. Reverse D
The inverse transform of DCT3 is performed in CT12, and the reproduced prediction residual signal is given to the adder 11. In the adder 11, the inter-frame prediction signal given from the motion compensator 24 is added to the prediction residual signal to be a reproduced image signal, which is given to the image memory 10. The image memory 10 stores images used for inter-frame prediction, and if necessary, MV
It is provided to the detector 23 and the motion compensator 24.

The MV detector 23 determines the MV between the input image signal and the reproduced image signal stored in the image memory 10 and used for prediction. The obtained MV is calculated by the motion compensator 24 and M
It is provided to the V encoder 15. The MV encoder 15 encodes the information of the MV value required for motion compensation in the decoding device, and gives the code to the multiplexer 6. Motion compensator 24
Is a reproduction image signal stored in the image memory 10,
It is spatially moved according to the value and is given to the prediction subtractor 2 and the adder 11 as an inter-frame prediction signal.

The operation of the MV accuracy and motion compensator 24 is
Since the motion compensation processing is the same as that of the decoding device (that is, the accuracy on the decoding device side), it is set to match the transmission accuracy (that is, transmission standard). As a transmission standard, an international standard such as MPEG is generally used, and the MV accuracy in that case is a unit of 1/2 pixel. For MV detection with 1/2 pixel accuracy, MV is calculated once with pixel accuracy, and only 1 around the MV is 1
Recalculate again with 2 pixel accuracy. In addition, how to create a pixel at the 1/2 pixel position in the motion compensator 24 is also defined, and it is created by simple addition (Bi-Linear) of adjacent pixels.
Such MV detection and motion compensation processing are performed in units of 16 × 16 pixel macroblocks in which four DCT blocks are connected.

If the reproduced image signal is deteriorated in the MV detection, an appropriate MV may not be obtained. Therefore, the input image signal of the same frame used in the prediction is stored in another image memory. , It may be used instead of the reproduced image signal.

<Decoding Device> Next, a decoding device corresponding to the coding device of FIG. 4 will be described. FIG. 5 is a block diagram showing an example of the decoding apparatus. The image data given from the code input 51 is separated by the demultiplexer 52 into the code of the prediction difference and the code of the MV information. The code of the prediction difference is input to the variable length decoder 53 and the code of the MV value is MV decoded. Given to the container 55. In the variable length decoder 53, the variable length code is returned to the fixed length, and the obtained fixed length code is given to the inverse quantizer 13. The MV decoder 55 decodes the MV information, and the obtained MV value is given to the motion compensator 24.

In the inverse quantizer 13, the quantized representative value corresponding to the fixed length code is obtained and given to the inverse DCT 12. The inverse DCT 12 performs the inverse transformation process of the DCT 3 of FIG. 4, and the prediction residual signal reproduced by this is added by the adder 11
Given to. In the adder 11, the inter-frame prediction signal given from the motion compensator 24 is added, and the reproduced image signal is outputted from the image output 54 and the image memory 1
Given to 0. Reproduced images used for inter-frame prediction are stored in the image memory 10 and output to the motion compensator 24 as needed. In the motion compensator 24, the reproduced image is MV
Motion compensation is performed according to the value to create an inter-frame prediction signal, which is provided to the adder 11. The same MV value as that of the encoding device is used, and the inter-frame prediction signal becomes the same as that of the encoding device.

[0011]

In motion-compensated predictive coding, the prediction residual component is coded so that the decoded image is closer to the input signal. The prediction residual component includes not only an essential image change in which the pattern itself changes from frame to frame but also an error due to the accuracy limit that occurs because the motion compensation process is not necessarily ideal. Since the essential change of the image gradually changes for each frame, by faithfully encoding, the prediction error of the next frame can be reduced. However, since the error due to the accuracy limit of the motion compensation process changes for each frame, even if the coding is performed, the fidelity of the frame is improved, and it does not contribute to the prediction of the next frame. This is because the essential change of the image is correlated between frames, but the error due to the accuracy limit is not correlated between frames.

The present invention has been made by paying attention to the above points. By performing motion compensation with a higher accuracy than transmission accuracy, an error due to the accuracy limit of motion compensation processing is not coded, and accordingly, it is essential. It is an object of the present invention to provide a motion-compensated predictive coding device that improves the next inter-frame prediction efficiency and the overall coding efficiency by more faithfully coding changes in images.

[0013]

According to the present invention, when a moving picture is inter-picture predictively coded, a motion vector between an input picture signal and a picture signal used for prediction is obtained with higher accuracy than transmission accuracy, and Motion compensation that performs interframe predictive coding with a motion-compensated signal of the image signal used for prediction according to the motion vector, rounds the obtained motion vector to transmission accuracy, and encodes the motion vector value that has become transmission accuracy for transmission. This is a predictive coding device.

Further, when the moving picture is subjected to inter-picture predictive coding, a motion vector between the input picture signal and the picture signal used for prediction is obtained with transmission accuracy, and the picture signal used for prediction is motion-compensated according to the motion vector. Obtains an inter-frame prediction signal with transmission accuracy, obtains a small motion vector between the inter-frame prediction signal and the input image signal with a higher accuracy than the transmission accuracy, and accurately calculates the prediction signal or the input image signal according to the small motion vector. Is a motion-compensated predictive coding apparatus that performs inter-frame predictive coding with a signal whose motion is compensated in 1. and uses a predictive signal of transmission accuracy in local decoding corresponding to this coding.

[0015]

In the encoding apparatus of the present invention, motion compensation is performed with a higher precision than the transmission precision, so errors due to the precision limit are reduced. Therefore, the code conventionally used for coding the error is unnecessary, and the code can be used for coding the original change of the image. However, since the motion compensation on the decoding side can be performed with the same precision as the transmission precision, the error due to the precision limit is the same as in the conventional case, and since it is not coded, the fidelity becomes poor.

As a result, in the prediction residual component, the essential image change is more faithfully encoded, and the error due to the accuracy limit is not faithfully encoded. The error due to the accuracy limit does not affect the inter-frame prediction of the next image, while the more faithful coding of the essential image changes contributes to improved prediction efficiency, which leads to overall prediction efficiency. Be improved.

[0017]

【Example】

<Encoder 1> FIG. 1 is a block diagram showing the first embodiment of the encoder. The same parts as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals. The configuration is different from the conventional example of FIG. 4 in that a fine MV detector 8 and a fine motion compensator 9 are provided instead of the MV detector 23 and the motion compensator 24, and that an MV value rounder 14 is further provided. In FIG. 1, the difference from the conventional example in FIG. 4 in operation lies in the inter-frame prediction processing, and the coding operation of the prediction residual is the same as in the conventional example.

The predictive subtractor 2 subtracts the inter-frame predictive signal supplied from the fine motion compensator 9 from the image signal input from the image input 1 to provide a predictive residual signal to the DCT 3. DCT 3, quantizer 4, variable length encoder 5, multiplexer 6, inverse quantizer 13, inverse DCT 12, adder 1
1. The operation of the image memory 10 is the same as the conventional example.

On the other hand, the fine MV detector 8 and the fine motion compensator 9
The configuration and operation of the MV detector 23 are basically the same as those of the conventional MV detector 23,
The motion compensator 24 is the same as the motion compensator 24, but its accuracy is different. The accuracy of the motion vector (MV) is 1/2 pixel accuracy which is the transmission accuracy (accuracy of the transmission standard) in the conventional example.
In this embodiment, the accuracy is 1/6 pixel, which is higher than the transmission accuracy (transmission standard). This is shown in FIG. 1/6
In the pixel-accurate MV detection, the MV is obtained once with the pixel precision, and only the periphery of the MV is obtained again with the 1/6 pixel precision. The high precision MV information obtained by the fine MV detector 8 is given to the fine motion compensator 9 and the MV value rounder 14.

In the fine motion compensator 9, the precision of the MV is made finer in accordance with the fine MV detector 8, and the method of forming pixels at positions other than the original pixels is also made highly precise. In particular,
As shown in FIG. 7, in the conventional example, Bi using only adjacent pixels is used.
-Linear (simple quadratic linear interpolation) ((A) in the figure), but it is also created by high-precision (high-order) re-sampling processing that also uses peripheral pixels ((B) in the figure). ).

The MV value rounding unit 14 discards (rounds) lower information in order to match a highly accurate motion vector value with the transmission accuracy (transmission standard) to reduce the accuracy, and as a motion vector value with the same accuracy as the transmission accuracy. , MV value encoder 15. Specifically, nine MVs with 1/6 pixel precision surrounded by a broken line in FIG. 6 are regarded as the same MV with 1/2 pixel precision. The MV value encoder 15 encodes the MV value as in the conventional example.

In this embodiment, the motion compensation operation differs between the encoding device and the decoding device. Since inter-frame prediction is a cyclic operation, the differences between the coding device and the decoding device are cumulative. Therefore, it is necessary to prevent the error due to the rounding of the MV value from being biased to one side, and this is the reason why the precision is set to 1/6 pixel, which is a precision that is an even multiple of the transmission precision.
If 1/6 pixel precision is rounded to 1/2 pixel precision, 1
Even-numbered 1/6 pixel points between the / 2 pixel precisions are divided into two to have the 1/2 pixel precision on both sides, and the error is balanced. Since this error has no correlation between frames, it does not cause a big problem even if accumulated.

In addition to the unidirectional prediction, the motion compensation method includes bidirectional prediction (B-pict) used in MPEG and the like.
ure) is the same.

<Encoding Device 2> FIG. 2 shows the second encoding device.
It is a block diagram which shows the Example of. The same parts as those in the conventional example shown in FIG. 4 are denoted by the same reference numerals. Smaller M than the conventional example of FIG.
The configuration is different in that there is a V detector 21 and a small motion compensator 22. In the figure, what is different from the conventional example in operation is only the minute MV detector 21 and the minute motion compensator 22, and the MV detector 23,
The configuration and operation of other parts including the motion compensator 24 are the same as those of the conventional example.

The image signal input from the image input 1 is given to the predictive subtractor 2, the minute MV detector 21 and the MV detector 23. The predictive subtractor 2 subtracts the inter-frame predicted image that has been subjected to highly accurate motion compensation from the input image, and provides the prediction residual to the DCT 3. DCT 3, quantizer 4, variable length encoder 5, multiplexer 6, MV encoder 15, inverse quantizer 13, inverse DCT 12, adder 11, image memory 1
0, the operation of the MV detector 23 is the same as the conventional example. The operation of the motion compensator 24 is also the same as the conventional example, but the inter-frame prediction signal from the motion compensator 24 is given to the minute MV detector 21 and the minute motion compensator 22 instead of the predictive subtractor 2.

The minute MV detector 21 obtains a minute movement difference between the inter-frame prediction signal and the input signal as a minute MV. Here, since the inter-frame prediction signal has already been motion-compensated with 1/2 pixel precision of the transmission precision, the minute MV becomes finer than that, and the precision is made finer than the transmission precision. If the specific accuracy is 1/6 pixel accuracy as in the first embodiment, MV is -2/6 and -1 in the horizontal and vertical directions.
Five kinds of values of / 6, 0, +1/6 and +2/6 are set, and MV is selected from 25 kinds of 5 × 5 vectors.

The minute motion compensator 22 is a minute MV detector 21.
The motion compensation is performed by the high-order resampling as in the first embodiment with the precision of the minute MV given by As described above, this embodiment is based on the fine MV detector 8 and the fine motion compensator 9 of the first embodiment.
In the processing performed in (1), the processing portion having higher precision than the transmission precision is separated and applied only to the predictive subtractor 2. In this case, since the inter-frame prediction signal from the motion compensator 24 is input to the adder 11, the locally decoded image becomes the same as in the conventional example, and the error between the encoding device and the decoding device does not occur. .

<Encoding Device 3> FIG. 3 shows the third encoding device.
It is a block diagram which shows the Example of. The same parts as those in the second embodiment shown in FIG. 2 are designated by the same reference numerals. In FIG. 3, the insertion position of the small motion compensator 22 is different from that of the second embodiment in structure.

The image signal input from the image input 1 is given to the minute motion compensator 22, the minute MV detector 21, and the MV detector 23. In the minute motion compensator 22, the minute MV detector 2
In accordance with the minute MV value given from 1, the minute motion compensation of one pixel or less is performed as in the case of FIG. 2, and the result is given to the predictive subtractor 2. The prediction subtractor 2 subtracts the inter-frame prediction image from the input image that has been subjected to the slight motion compensation instead of the input image as it is, and the prediction residual is DC.
Given to T3. DCT 3, quantizer 4, variable length encoder 5, multiplexer 6, MV encoder 15, inverse quantizer 1
3, inverse DCT 12, adder 11, image memory 10, MV
The operations of the detector 23 and the motion compensator 24 are the same as those in the second embodiment.

The minute MV detector 21 is basically the same as the case of FIG. 2, but since the MV for moving the input image signal is calculated with the predicted signal as a reference, the input is reversed. In this embodiment, as in the second embodiment, the locally decoded image is the same as in the conventional example, and no error occurs between the encoding device and the decoding device. Furthermore, there is an advantage that the frequency characteristics can be balanced by applying the resample processing to both the prediction signal and the input signal. With respect to the frequency characteristic deterioration caused by the re-sampling process of motion compensation, this occurs only in the prediction signal in the conventional example and the first embodiment.
This is because what was likely to be a mismatch is balanced by being applied to both the prediction signal and the input signal.

Further, since the aliasing distortion component independently present in each signal is suppressed due to the deterioration of the frequency characteristics of both signals, the error component which is not the original motion of the image is reduced, and for the purpose of this embodiment. It becomes a suitable treatment.

<Decoding Device> The decoding device corresponding to the motion compensation predictive coding device shown in FIGS. 1 to 3 is the same as the conventional example shown in FIG. 4, and a new decoding device is not required. Absent.

[0033]

In the encoding apparatus of the present invention, motion compensation is performed with a higher precision than the transmission precision (transmission standard), so essential changes in the image are more faithfully encoded in the prediction residual component. , The error due to the accuracy limit is not faithfully encoded.
Errors due to accuracy limits do not affect the inter-frame prediction of the next image, while essential frame changes are more faithfully coded to improve inter-frame prediction and improve overall prediction efficiency. To do. Since the prediction efficiency is improved, the prediction residual to be coded is reduced, and the coding efficiency is improved.

On the other hand, in each frame, an increase in the error due to the accuracy limit causes a spatial displacement, but if the motion compensation accuracy of the transmission accuracy (transmission standard) is 1/2 pixel, it is visually Subjective image quality is also desirable because it is less of a problem and the fidelity of essential image changes is improved. As a result, it becomes possible to obtain the required reproduction image quality with a smaller code amount.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration example of an encoding device that is a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of an encoding device which is a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of an encoding device which is a third embodiment of the present invention.

FIG. 4 is a diagram showing a configuration example of a conventional encoding device.

FIG. 5 is a diagram showing a configuration example of a conventional decoding device.

FIG. 6 is a diagram showing a fine motion vector and a state of rounding processing thereof.

FIG. 7 is a diagram showing a state of resample processing in a conventional example and an example.

[Explanation of symbols]

1 ... Image input, 2 ... Predictive subtractor, 3 ... DCT, 4 ... Quantizer, 5 ... Variable length encoder, 6 ... Multiplexer, 7 ... Code output, 8 ... Fine MV detector, 9 ... Fine Motion compensator, 10 ... Image memory, 11 ... Adder, 12 ... Inverse DCT, 13 ... Inverse quantizer, 14 ... MV rounder, 15 ... MV encoder, 21
... micro MV detector, 22 ... micro motion compensator, 23 ... MV detector, 24 ... motion compensator, 51 ... code input, 52 ... demultiplexer, 53 ... variable length decoder, 54 ... image output, 55 ...
MV decoder.

Claims (3)

[Claims] 1. An apparatus for performing motion compensation inter-picture predictive coding of a moving image, means for obtaining a motion vector between an input image signal and an image signal used for prediction with a higher accuracy than transmission accuracy, and the motion vector. Motion compensating means for motion-compensating an image signal used for prediction in accordance with the above, and obtaining a prediction signal with higher accuracy than transmission accuracy; and means for rounding the motion vector to transmission accuracy and encoding a motion vector value with transmission accuracy. A motion compensation predictive coding apparatus, comprising: a predictive coding means for coding a residual obtained by subtracting the predictive signal from an input image signal. 2. An apparatus for motion-compensated inter-picture predictive coding of a moving picture, a means for obtaining a motion vector between an input image signal and a reproduced image signal used for prediction with transmission accuracy, and predicting according to the motion vector. Between the input image signal and the prediction signal of the transmission accuracy, a small motion vector with a precision higher than the motion vector and smaller than or equal to the pixel interval is provided between the motion compensation means for motion-compensating the image signal to be used and obtaining the prediction signal of the transmission accuracy. Means for obtaining, a motion compensation means for re-sampling the predicted signal of the transmission accuracy according to the minute motion vector to obtain a minute motion compensated predicted signal, and a residue obtained by subtracting the minute motion compensated predicted signal from an input image signal. A predictive coding unit for coding the difference and a predicted image signal of the transmission accuracy are used to perform a decoding process corresponding to the predictive coding unit to perform a reproduction image signal. Motion compensated predictive coding apparatus characterized by comprising a local decoding means for obtaining. 3. An apparatus for performing motion compensation inter-picture predictive coding of a moving image, a means for obtaining a motion vector between an input image signal and an image signal used for prediction, and a motion of the image signal used for prediction according to the motion vector. Motion compensation means for compensating to obtain a prediction signal, and means for obtaining a minute motion vector having a pixel interval or less with a higher accuracy than the motion vector between the input image signal and the prediction signal obtained by the motion compensation means, A small motion compensating unit that obtains a small motion compensation signal by performing motion compensation on an input image signal according to the small motion vector, and a predictive encoding unit that encodes a residual obtained by subtracting the prediction signal from the small motion compensation signal. A motion-compensated predictive coding device comprising: