JPH08280031A - MOVING PICTURE ENCODING DEVICE AND DECODING DEVICE THEREOF - Google Patents

Abstract

(57) An object of the present invention is to provide an excellent moving picture coding apparatus and moving picture decoding apparatus with improved image quality. SOLUTION: A moving picture coding apparatus is provided with means 31 for obtaining a quantization step size of a block which has been subjected to inter-frame predictive coding from a residual amount of a buffer 19, and a quantization step size from the obtained quantization step size. Means for obtaining the quantization step size of the different intra-frame coded blocks, and quantization means 14 for performing the quantization with either of the two quantization step sizes based on the signal instructing the intra-frame coding. Prepare This gives different quantization step sizes between the inter-frame prediction coded block and the intra-frame coded block, and can be determined in consideration of the influence on the visual sense at the time of quantization. It is possible to improve the image quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture coding apparatus and a decoding apparatus for use in a video conference system, a video telephone and the like.

[0002]

2. Description of the Related Art A moving picture coding apparatus is used in a video apparatus such as a video conference system or a videophone which handles moving pictures. A conventional example of such a moving picture coding apparatus is shown in FIG. There is one shown in. FIG. 4 shows the overall configuration of a conventional moving image coding apparatus. In this figure, reference numeral 1 is a subtractor, and input image signal 2
The inter-frame prediction signal 3 and the prediction error signal 4 are output. A refresh control unit 5 receives the timing signal 6 and outputs a refresh instruction signal 7. Reference numeral 8 denotes an inter-frame / in-frame selecting unit, which receives the input image signal 2, the prediction error signal 4 and the refresh instruction signal 7 and outputs the switching control signal 9. Reference numeral 10 denotes an inter-frame / intra-frame changeover switch, which is a prediction error signal 4,
The input image signal 2 and the switching control signal 9 are input,
The orthogonal transform unit input signal 11 is output.

Reference numeral 12 is an orthogonal transform unit, which receives the orthogonal transform unit input signal 11 and outputs a transform coefficient 13. A quantizer 14 receives the transform coefficient 13 and the quantization step size 15 as inputs, and outputs a quantized transform coefficient 16. Reference numeral 17 denotes an encoding unit, which is a quantized transform coefficient 1
Input 6 and output code 18. Reference numeral 19 denotes a transmission buffer unit, which receives the code 18, and outputs a transmission signal 20 and a residual buffer amount 21. Reference numeral 22 is a quantization control unit, which inputs the residual buffer amount 21 and outputs a quantization step size 15. An orthogonal inverse transform unit 23 receives the quantized transform coefficient 16 as an input and outputs a reproduced signal 24. An adder 25 receives the reproduced signal 24 and the inter-frame prediction signal / zero signal 26 as an input,
7 is output. 28 is a variable delay frame memory,
The decoded signal 27 and the input image signal 2 are input, and the inter-frame prediction signal 3 is output. Reference numeral 29 denotes an inter-frame / intra-frame changeover switch, which receives the inter-frame prediction signal 3 and the switching control signal 9 and outputs the inter-frame prediction signal / zero signal 26.

Next, the operation of the above conventional example will be described.
In FIG. 4, the input image signal 2 is an interframe prediction signal (or a motion compensation interframe prediction signal) in the subtractor 1.
The difference with 3 is calculated and output as the prediction error signal 4. The refresh control unit 5 generates a refresh instruction signal 7 from the timing signal 6. Here, the refresh is used as a countermeasure against a difference in calculation accuracy between the moving image encoding device on the transmitting side and the decoding device on the receiving side and a transmission error. Various operations are taken. It is determined whether or not refresh is performed for each block composed of M pixels × N lines, and the refresh control unit 5 outputs the refresh instruction signal 7 for the block to be refreshed between the frames / inside selection unit 8
Output to. Normally, refreshing is performed at a rate of several blocks in one frame, and all blocks in the entire screen are operated in about 10 seconds to complete the screen. This cycle is called a refresh cycle.

Here, it can be said that the refresh period is set to a plurality of frames, the entire specific frame of the plurality of frames is refreshed, and the other frames are not refreshed. In that case, all the blocks of the specific frame are selected within the frame.

If the refresh instruction signal 7 indicates a refresh, the inter-frame / intra-frame selecting section 8 selects the inside of the frame. When the refresh is not instructed, the inter-frame / in-frame selecting unit 8 selects the inter-frame or the intra-frame based on the input image signal 2 and the prediction error signal 4. Input image signal 2 if within frame
Is output as a switching control signal 9 so as to select the prediction error signal 4 in the case of interframe. The inter-frame / intra-frame switching switch 10 receives the switching control signal 9 and outputs either the input image signal 2 or the prediction error signal 4 as the orthogonal transform unit input signal 11. The orthogonal transformation unit input signal 11 is orthogonally transformed by the orthogonal transformation unit 12 and becomes a transformation coefficient 13. The transform coefficient 13 is quantized in the quantizer 14 by the linear quantizer having the quantization step size 15 given from the quantization controller 22, and is output as the quantized transform coefficient 16.

The quantized transform coefficient 16 is encoded by the encoding unit 17.
Is converted into a code 18 and temporarily stored in the transmission buffer unit 19 and then output as a transmission signal 20 in accordance with the line speed. The quantization control unit 22 uses the transmission buffer unit 19
It receives the buffer residual amount 21 from the above, determines the quantization step size, and outputs it as the quantization step size 15. The orthogonal inverse transform unit 23 performs orthogonal inverse transform on the quantized transform coefficient 16 and outputs it as a reproduction signal 24. The reproduced signal 24 is added to the inter-frame prediction signal / zero signal 26 in the adder 25, and is accumulated in the variable delay frame memory 28 as a decoded signal 27. Here, the selection of the inter-frame prediction signal / zero signal 26 is selected by the inter-frame / inside change-over switch 29 by the switching control signal 9. In the case of inter-frame, the inter-frame prediction signal 3 and the zero signal in the frame are selected. The decoded signal accumulated in the variable delay frame memory 28 is compared with the input image signal 2 to detect a motion vector, and the motion compensation prediction value compensated by the vector is output as the following inter-frame prediction signal 3.

As shown in FIG. 5, the quantization controller 22
A quantization step size selection ROM 30 is provided, and the remaining buffer amount 21 is input to the quantization step size 1
5 is output. As shown in FIG. 6, the quantization step size 15 is represented by a step function proportional to the buffer residual amount 21. Quantization step size selection R in FIG.
The OM 30 is doing this conversion.

As described above, even in the above-described conventional moving picture coding apparatus, the quantization step size can be controlled by obtaining the quantization step size from the buffer residual amount.

[0010]

However, in the above-described conventional moving picture coding apparatus, the quantization step size is constant regardless of whether or not the block to be quantized is a refresh block. There is a problem that the image quality is conspicuous and it takes time to converge to a constant image quality on the entire screen.

The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent moving picture coding apparatus and a decoding apparatus therefor for improving image quality.

[0012]

In order to achieve the above object, the present invention provides a moving picture coding apparatus for obtaining a quantization step size of a block coded by inter-frame prediction coding from a buffer residual amount, Means for obtaining a quantization step size of an intra-coded block different from the quantization step size obtained from the obtained quantization step size, and the two quantizations based on a signal instructing the intra-frame encoding. The gist is to have a quantizing means for quantizing with any of the step sizes.

The present invention also provides, as a method of encoding a moving image, a step of obtaining a quantization step size of a block which has been subjected to interframe predictive encoding from a buffer residual amount,
From the quantization step size obtained in the step, a step of obtaining a quantization step size of an intra-frame coded block different from the quantization step size, and the step 2 based on a signal instructing the intra-frame coding
The present invention provides a processing procedure with a step of quantizing with any one of four quantization step sizes.

Further, the present invention provides a method for coding a moving image signal by selecting intra-frame coding and inter-frame predictive coding in block units, and in this coding method, inter-frame predictive coding is performed. The block is quantized by obtaining the quantization step size from the buffer residual amount, and the intra-coded block is quantized with a quantization step different from the quantization step size of the normal block. .

Further, the present invention has as its gist a decoding device for receiving and decoding a signal encoded as described above.

The present invention having the above-described structure has the following operations. That is, in the refresh control unit, the quantization step size of the block subjected to the inter-frame predictive coding is obtained from the residual buffer amount, and then the intra-frame code different from the quantization step size is obtained from the quantization step size obtained in the step. The quantization step size of the converted block is obtained. After that, quantization is performed in one of the two quantization step sizes based on the signal instructing the intraframe coding. Since this is done, it is possible to give different quantization step sizes to the blocks that are inter-frame predictive coded and the blocks that are intra-frame coded, and it is possible to improve image quality.

As another operation of the present invention, intra-frame coding and inter-frame predictive coding are selected in block units to code a moving image signal. In this encoding operation, the inter-frame predictive coded block is quantized by obtaining the quantization step size from the buffer residual amount, and the intra-frame coded block is quantized with a quantization step size different from the normal block quantization step size. Quantize by size. With such an operation, different quantization step sizes can be given to the block that has been subjected to inter-frame predictive coding and the block that has been subjected to intra-frame coding, and the image quality can be improved.

The decoding device receives and decodes the signal encoded as described above.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention comprises means for obtaining a quantization step size of an inter-frame predictive encoded block from a buffer residual amount in a moving picture encoding device, and the obtained means. Any one of the two quantization step sizes based on a signal instructing the intra-frame encoding, a means for obtaining a quantization step size of an intra-frame encoded block different from the quantization step size from the quantization step size. And a quantizing means for quantizing. By this means, it is possible to give different quantization step sizes to the blocks coded with inter-frame predictive coding and the blocks coded with intra-frame, which has the effect of improving the image quality.

According to a second aspect of the present invention, as a moving picture coding method, a step of obtaining a quantization step size of a block that has been subjected to interframe predictive coding from a buffer residual amount, and the obtained quantization step The step of obtaining a quantization step size of an intra-frame coded block different from the quantization step size from the size, and the step 2 based on a signal instructing the intra-frame coding.
And a step of quantizing with one of four quantization step sizes. By this means, it is possible to give different quantization step sizes to the blocks coded with inter-frame predictive coding and the blocks coded with intra-frame, and the image quality is improved.

According to a third aspect of the present invention, an interframe predictive coded block is used as a method of coding a moving image signal by selecting intraframe coding and interframe predictive coding in block units. Quantizes the quantization step size from the buffer remaining amount and quantizes it, and the intra-coded block is quantized with a quantization step different from the quantization step size of the normal block. By this, it is possible to give different quantization step sizes between the inter-frame predictive coded block and the intra-frame coded block, and the intra-frame coded block has the quantization step size of the normal block. Since the image is quantized in a quantization step different from the size, the image quality is improved.

According to a fourth aspect of the present invention, in the moving picture coding method according to the second or third aspect, the quantization step size of the intra-frame coded block is inter-frame predictive coded. A non-linear quantization step is taken so as to be smaller than the block quantization step size.

According to a fifth aspect of the present invention, as a moving picture decoding device, a signal output from the moving picture coding device according to the first aspect is received and decoded.

The invention according to claim 6 of the present invention is a moving picture decoding device, which receives and decodes a signal coded by the moving picture coding method according to any one of claims 2 to 3. It was done like this.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the overall configuration of an embodiment of the present invention. Since the configuration is similar to that of the conventional example shown in FIG. 4 except for the quantization controller, the same reference numerals are given to the same elements. Duplicate description is omitted. In this embodiment, in addition to the buffer remaining amount 21 being input to the quantization controller 31, the refresh instruction signal 7 and the static / moving information 32 when motion vector detection is performed by the variable delay frame memory 28 are input. , The quantization step size 33 is output.

FIG. 2 shows a concrete configuration of the quantization control section 31. In FIG. 2, the quantization step size selection ROM 34 receives the buffer residual amount 21 as an input, and outputs the quantization step size 35 of a normal block. The moving area ROM 36 receives the quantization step size 35 of the normal block as an input, and outputs the quantization step size 37 for the refresh block and the moving area. The static area ROM 38 has a normal block quantization step size 35.
Is input, and the quantization step size 39 in the case of the refresh block and the static region is output. The selector 40 receives the quantization step size 37 in the case of the refresh block and the moving area, the quantization step size 39 in the case of the refresh block and the still area, and the moving information 32, and inputs the quantization step size 41 of the refresh block. Is output. The selector 42 receives the quantization step size 35 of the normal block, the quantization step size 41 of the refresh block and the refresh instruction signal 7 and outputs the quantization step size 33.

Next, the quantization controller 31 in the above embodiment.
The operation of will be described. The quantization step size 35 of the normal block is obtained by the quantization step size selection ROM 34 as a function of the buffer residual amount 21. In order to have different quantization step sizes for the refresh blocks, the normal block quantization step size 35 is input to the moving area ROM 36 and the still area ROM 38, and the moving area and still area quantization step sizes 37 and You get 39.

ROM for moving area and ROM for static area
As 38, for example, a quantization step size conversion table in the normal case and the refresh case as shown in FIG. 3 is provided. In the example (a), a downward convex function is used, and the quantization step size Qr of the refresh block is set to a value smaller than the quantization step size Qn in the normal case. In the example (b), the minimum value Qmin of the quantization step size is set as the quantization step size Qr of the refresh block. Q in example (c)
r is set to be Qn multiplied by a constant a, or the larger of the minimum value Qmin of the quantization step size. In the example (d), Qr has a value obtained from the downwardly convex function f (Qn) in the case of the static region, and takes a value obtained from the downwardly convex function g (Qn) in the case of the moving region. f (Qn) <g (Qn). This is because the visual spatial resolution is reduced, and it is not noticeable even if a large quantization step size is used in the moving region as compared with the static region. In the example (e), the minimum value Qmin of the quantization step size is taken in the static region as Qr and the value Qmov larger than Qmin is taken in the moving region. Example (f)
Then, as Qr, the larger one of Qmin and Qmin is multiplied by Qa multiplied by a constant a <1 in the static region, and Qm is multiplied by a constant b b <1 in the dynamic region and Qmi.
I try to take the larger of the n. However, a
<B.

Quantization step size 3 in the case of the moving region and the static region of the refresh block thus obtained
7, 39, based on the static / moving information 32, the quantizing step size of the moving area in the case of the moving area and the quantizing step size of the static area in the case of the static area are respectively selected by the selector 40 in the refresh block. It is selected as the quantization step 41. Based on the refresh instruction signal 7, the selector 42 sets the normal block quantization step size 35 in the case of a normal block and the refresh block quantization step size 41 in the case of a refresh block as the quantization step size 33. Output.

As described above, in the above embodiment, the quantization step sizes 37 and 39 of the refresh blocks of the moving area and the static area are obtained from the quantization step size 35 of the normal block, and the static information 32 and the refresh instruction signal are further obtained. Since one quantization step size is selected from three cases based on 7, there is an effect that the image quality can be controlled by the property of the block and the image quality can be improved.

By executing the reverse processing of the above encoding processing operation, it is possible to realize a moving image decoding apparatus which receives the encoded signal generated as described above and reproduces a moving image. it can.

[0032]

As is apparent from the above embodiment, the present invention obtains the quantization step size of a block that has been subjected to interframe predictive coding from the buffer residual amount, and the quantization step size is obtained from the obtained quantization step size. Since the quantization step size of the intra-frame coded block that is different from the step size is obtained and then the quantization is performed with one of these quantization step sizes, the inter-frame prediction coded block and the intra-frame It is possible to improve the image quality because different quantization step sizes can be given to the encoded blocks and the determination can be made in consideration of the influence on the visual sense at the time of quantization.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing the overall configuration of a moving picture coding apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram showing a configuration of a quantization control unit that is a main part of the present invention.

FIG. 3 is a graph showing an example of conversion for obtaining a quantization step size of a refresh block from a quantization step size of a normal block and static information in the same embodiment.

FIG. 4 is a schematic block diagram showing the overall configuration of a conventional moving image encoding device.

FIG. 5 is a schematic block diagram of a conventional quantization controller.

FIG. 6 is a graph showing an example of selecting a quantization step size in a conventional example.

[Explanation of symbols]

1 Subtractor 2 Input image signal 3 Inter-frame prediction signal 4 Prediction error signal 5 Refresh control section 6 Timing signal 7 Refresh instruction signal 8 Inter-frame / inside selection section 9 Switching control signal 10 Inter-frame / inside switching switch 11 Orthogonal conversion section input Signal 12 Orthogonal transform unit 13 Transform coefficient 14 Quantization unit 15 Quantization step size 16 Quantized transform coefficient 17 Encoding unit 18 Code 19 Transmission buffer unit 20 Transmission signal 21 Buffer residual amount 22 Quantization control unit 23 Orthogonal inverse transformation Part 24 Reproduced signal 25 Adder 26 Inter-frame prediction signal / Zero signal 27 Decoded signal 28 Variable delay frame memory 29 Inter-frame / inside switch 31 Quantization control unit 32 Static information 33 Quantization step size 34 Quantization step size selection ROM 35 Normal block Quantizer step size 36 ROM for moving area 37 quantization step size for refresh block and moving area 38 static area ROM 39 quantization step size for refresh block and still area 40 selector 41 refresh block Quantizer step size 42 selector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Clearcose Joseph, New Jersey, USA 08543-5300, Princeton, CNR 5300 David Sanoff Research Center, Inc. (72) Inventor Masahiro Wakamori Tsunashima, Kanagawa-ku, Yokohama, Kanagawa Prefecture 4th-3rd Higashi Matsushita Communication Industrial Co., Ltd. (72) Inventor Tsuyoshi Takeshi 3rd-1st 3rd Tsunashima East Tsunashima, Kohoku Ward, Yokohama City, Kanagawa Matsushita Communication Industry Co., Ltd.

Claims (6)

[Claims] 1. A means for obtaining a quantization step size of an inter-frame predictive-coded block from a buffer residual amount, and an intra-frame encoding different from the obtained quantization step size to the quantization step size. A moving image comprising means for obtaining a quantization step size of a block, and quantization means for performing quantization with one of the two quantization step sizes based on a signal instructing intraframe coding. Encoding device. 2. A step of obtaining a quantization step size of a block subjected to interframe predictive encoding from a buffer residual amount, and an intraframe encoding different from the quantization step size obtained from the quantization step size obtained in the step. A moving picture code, which comprises a step of obtaining a quantization step size of the generated block and a step of quantizing with one of the two quantization step sizes based on a signal instructing intra-frame coding. Method. 3. A method for encoding a moving image signal by selecting intra-frame encoding and inter-frame predictive encoding in block units, wherein the inter-frame predictive encoded block is quantized from a buffer residual amount by a quantization step. A moving picture coding method, wherein a size is quantized and quantized, and an intra-coded block is quantized with a quantized step size different from a quantized step size of a normal block. 4. A non-linear quantization step is taken so that a quantization step size of an intra-frame coded block is smaller than a quantization step size of an inter-frame predictive coded block. Claim 2
Alternatively, the moving picture coding method described in 3 above. 5. A moving picture coding apparatus for receiving and decoding a signal output from the moving picture coding apparatus according to claim 1. 6. A moving picture decoding apparatus for receiving and decoding a signal coded by the moving picture coding method according to any one of claims 2 to 4.