JP3203612B2 - Image encoding / decoding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
V: high-density television) In a high-efficiency encoding method in which a high-sampling-rate signal such as an image is divided into a plurality of standard TV-size small images and processed in parallel, the characteristics of the divided small images are significantly different. However, the present invention relates to an image encoding method capable of allocating an appropriate amount of information and obtaining a decoded image with high image quality as a result.

[0002]

2. Description of the Related Art When a signal sampled at a high frequency such as a high-definition image (HDTV image) is encoded with high efficiency, a parallel processing method is used to operate hardware in real time.

As shown in FIG. 4, consider a case where an HDTV signal is spatially divided into four to make a small image of a standard TV size and encoding processing is performed in parallel. In FIG. 4, 101 is H
DTV images, 102A, 102B, 102C, 102D
Is a standard TV size small image.

FIG. 5 is a block diagram showing a functional configuration of an apparatus for spatially dividing the HDTV signal into four parts to make a small image of a standard TV size and performing an encoding process in parallel.
1 is an input terminal, 202 is an HDTV signal, 203 is an image dividing unit, 204 to 207 are small images of a standard TV size, 20
8 to 211 are an information compression unit, 212 to 215 are buffer memory units, 216 to 219 are coded outputs, 220 is a multiplexing unit, 221 is coded output data, and an output terminal 222.

[0005] In FIG. 5, when the HDTV signal is spatially divided into four to make a small image of a standard TV size and the encoding process is performed in parallel, first, on the transmission side, the input terminal 20 is used.
The HDTV signal 202 input from the
3 and 4 standard TV size small images 204 to 20
Divide into seven. The divided small images 204 to 207 of the standard TV size are respectively divided into information compression units 208 to 21.
1 and subjected to an encoding process. The encoded output is
Feedback control is performed so that the data is input to the buffer memory units 212 to 215 and the output becomes a constant information amount. Encoded outputs 216 to 21 each having a constant information amount
9 is input to the multiplexing unit 220, is combined into one encoded output data 221, and is transmitted to the transmission path via the output terminal 222.

Considering the characteristics of the HDTV signal as an input, which one of the four small images is naturally different in the screen part in each frame, It is difficult to specify whether or not is easy to encode. Therefore, when the information amount of R (bit / s) is assigned to the entire HDTV signal, the information amount assigned to each small image is equal to 1 / 4R (bit / s) for every small image. It is usual to do.

[0007]

SUMMARY OF THE INVENTION However, HDT
Considering a case where a V image is encoded with R (bit / s) without being divided (it may be considered that ideal information is allocated in a screen), depending on the image, a small image to be divided may be used. Are not necessarily the same in the four areas corresponding to.

For example, as shown in FIGS. 6 and 7, at first, there is a very fine and rapidly moving area in one part (a) of the screen, and the other parts (b), (c), (d) ) Is relatively flat, and a case is considered where this fine area gradually moves to the part (b) with time. Initially, the parts (b), (c) and (d) are 1 / 4R (bit
/ S) can be encoded with much less information than
Here, the surplus information amount is reduced to the part (a) where it is difficult to encode with small information, so that the part (a) is reduced to 1/4.
Encoding is performed by applying a larger amount of information than R (bit / s). After that, a fine area where much information is to be used gradually moves to (b), so that the information amount allocated to (a) is gradually allocated to (b).

By the way, in the coding of the division type, if the coding process is performed on the assumption that the characteristics of the four divided small images are the same as in the conventional method, the 1 / 4R
(Bit / s) is used and coding is performed by forcibly suppressing the area to be coded by spending more information than ＲR (bit / s). As a result, the image quality of the decoded image is deteriorated. I will. Conversely, a region where a decoded image of sufficiently high image quality can be obtained with an information amount smaller than 1 / 4R (bit / s) may be encoded by 1 / 4R (bit / s),
In this case, wasteful information is being sent.

An object of the present invention is to divide a signal having a high sampling rate such as an HDTV image into a plurality of small images of a standard TV size. It is an object of the present invention to provide a technique capable of allocating an appropriate amount of information even when properties of divided small images are greatly different in a high-efficiency encoding method that performs parallel processing.

Another object of the present invention is to provide an image coding method capable of obtaining a decoded image having good image quality.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0013]

The outline of a typical invention among the inventions disclosed in the present application will be briefly described as follows.

On the transmitting side, an image to be encoded is divided into a plurality of small images, and the divided small images are subjected to high-efficiency encoding in parallel and transmitted. An image coding and decoding method for decoding encoded data for a plurality of divided small images and then combining the decoded data to obtain an original image .
Variance and motion features within a frame, which are spatial features.
The sum of the variances of the inter-frame difference values
The information amount assigned to the image of
It is characterized in that it is proportionally divided into the divided small images, and in encoding each small image, control is performed so that the encoded output information amount becomes the distributed information amount.

[0015]

[0016]

According to the above-mentioned means, by using a feature amount that responds to the difficulty of encoding, it is possible to determine whether each of the divided small images is easy or difficult to encode. Since it is possible to predict in advance whether image quality can be obtained or high image quality cannot be obtained unless a large amount of information is allocated, when encoding is performed at R (bit / s) as a whole, even if information is small, R '(bit / s) for a small image determined to provide high image quality
Control is performed so that information of (R ′ <R) is assigned, and R ″ (bit / s) (R ″) is assigned to a small image for which it is determined that high image quality cannot be obtained unless a large amount of information is assigned. >
Control can be performed so as to allocate the information of R).

[0017] This makes it possible to allocate information to the entire image based on the feature amount of the input image.
The image quality of the decoded image can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image encoding / decoding method according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) In an image encoding / decoding method according to Embodiment 1 of the present invention, an image to be encoded is divided into a plurality of small images on a transmitting side, and each divided small image is divided into a plurality of small images. On the other hand, high efficiency coding is performed in parallel and transmitted.
On the receiving side, an image encoding / decoding method for decoding encoded data for a plurality of transmitted small images and then combining the decoded data to obtain an original image, wherein a feature amount of each divided small image Is calculated, and the amount of information allocated to the entire image is allocated to each of the divided small images based on the obtained characteristic amount. When each small image is encoded, the encoded output information amount is The control is performed so that the information amount is distributed.

FIG. 1 is a block diagram showing a functional configuration of an apparatus (computer comprising a computer) for implementing the image encoding / decoding method according to the first embodiment.
2 is an HDTV signal, 403 is an image division unit, 404 to 40
7 is a standard TV size small image, 408 to 411 are feature amount calculation units, and 412 to 415 are feature amounts in each small image.
16 is an information allocating unit, 417 to 420 are information amounts allocated to each small image, 421 to 424 are information compressing units,
Reference numerals 25 to 428 denote buffer memory units, reference numerals 429 to 432 denote encoded outputs, reference numeral 433 denotes a multiplexing unit, reference numeral 434 denotes encoded output data, and reference numeral 435 denotes an output terminal.

The apparatus according to the first embodiment appropriately determines the amount of information to be allocated to each small image based on the characteristic amount of each small image calculated prior to encoding. , Is configured as shown in FIG.

In the operation of this embodiment, as shown in FIG. 1, first, an HDTV signal 402 is input to an input terminal 401. The input HDTV signal 402 is divided into four standard TV size small images 404 to
407. The divided small images of the standard TV size are respectively calculated by the feature amount calculation units 408 to 411.
And the feature amounts 412 to 415 in each small image are obtained. The information allocating unit 41 uses the obtained feature amount.
6, the information amount 417-42 allocated to each small image
0 is calculated. Here, the sum of the information amounts 417 to 420 assigned to the respective small images is controlled so as to be equal to the information amount assigned to the entire image.

On the other hand, each small image is processed by an information compression unit 421.
To 424 and subjected to an encoding process. The encoded output is input to the buffer memory units 425 to 428,
Each of them is feedback-controlled so that the output becomes the information amount 417 to 420 determined by the information allocating unit 416. Encoded outputs 42 each having a constant information amount
9 to 432 are input to the multiplexing unit 433, are combined into one encoded output data 434, and are transmitted to the transmission path via the output terminal 435.

As can be seen from the above description, the present embodiment 1
According to the above, by using a feature amount that responds to the difficulty of encoding, whether each divided small image is easy or difficult to encode, that is, whether high quality can be obtained even with a small amount of information , Or if a large amount of information is not assigned, it is possible to predict in advance whether a high image quality will not be obtained. Therefore, when encoding is performed at R (bit / s) as a whole, a high image quality can be obtained even if the information is small. Is controlled so that information of R '(bit / s) (R'<R) is assigned to the small image, and high image quality cannot be obtained unless a large amount of information is assigned. It is possible to control such that the information of R ″ (bit / s) (R ″> R) is assigned to the small image.

[0025] This makes it possible to allocate information to the entire image based on the features of the input image, thereby improving the image quality of the decoded image.

(Embodiment 2) An image encoding / decoding method according to Embodiment 2 of the present invention considers a case where an HDTV signal is divided into four small images of a standard TV size and processed. It is assumed that the variance within a frame as a quantity and the variance between frame differences as a motion feature quantity are used. It is assumed that a discrete cosine transform is used as an information compression method. In this case, when the information of R (bit / s) is assigned as a whole, the information amount assigned to each small image is calculated as follows.

First, the input HDTV signal is divided into four standard TVs.
The image is divided into small images of a size, and each of the divided four small images is divided into 16 × 16 small blocks.
The pixel value in the small block is represented by B (k, l) [(k, l) = 0,
1, 2,..., 15], and the difference between the small block and the small block one frame before is D (k, l) [(k, l) =
0, 1, 2,..., 15], and the _intra- frame variance σ ² _intra and _inter- frame variance σ ² _inter of each small block are obtained according to the following equation (1).

[0028]

(Equation 1)

Here, B bar and D bar represent B bar
It is the average value of (k, l) and D (k, l).

Next, for each of the four small images, the calculated σ ² _intra and σ ² _inter are averaged within the small image, and the average _intra- frame variance σ ² _intra bar and the average inter-frame variance for the small image Find σ ² _inter bar. Using these two values, a spatio-temporal feature amount is obtained as a feature amount F of the small image as shown in the following Expression 2.

[0031]

(Equation 2)

In general, the average _intra- frame variance σ ² _intra bar increases when the screen includes many high-definition areas, and when high information cannot be obtained unless a large amount of information is used. . Also, the average _inter- frame variance σ ² _inter bar becomes large when the motion is intense. Similarly, when a large amount of information is not used, high image quality cannot be obtained. Therefore, the value of F is difficult to encode, that is, indicates a large value when high image quality cannot be obtained unless a large amount of information is used, and indicates a small value otherwise. It can be used as an indicator of the difficulty of conversion.

Therefore, using the spatiotemporal feature values Fm (m = 1, 2, 3, 4) obtained for the four small images, the information amount Rm, (m = 1 , 2,
3, 4) is calculated by the following equation (3).

[0034]

(Equation 3)

In this way, the value of Rm for the small image which is relatively difficult to encode among the four small images is set to a large value, and when the encoding of each small image is executed, the Rm value is assigned. By performing the encoding control so as to obtain the information amount, it is possible to perform the bit allocation according to the difficulty of encoding each small image. Further, the information amount of the entire HDTV image can be controlled to be represented by the following equation (4).

[0036]

(Equation 4)

FIG. 2 shows an example of a change in the spatiotemporal feature value Fm and a change in the allocation information amount Rm accompanying the change. In this example,
Until time t ′, the spatio-temporal features of each small image are almost equal,
Thereafter, the spatio-temporal feature amount of the small image 1 gradually increases,
The feature amounts of the small images 3 and 4 are reduced, and at time t ″, the ratio of the spatiotemporal feature amounts is F ₁ : F ₂ : F ₃ : F ₄ = 7: 4: 3:
It becomes 2. On the other hand, when information is allocated to each small area by the above-described method, R ₁ : R ₂ :
R ₃ : R ₄ = 1: 1: 1: 1, and the same 1 /
4R (bit / s) information is allocated. On the other hand, after time t ′, the allocation state gradually changes according to the change in the spatiotemporal feature amount. At time t ″, R ₁ : R ₂ :
R ₃ : R ₄ = 7: 4: 3: 2. The information allocation at time t "is as follows: small image 1 has 7 / 16R (bit / s), small image 2 has 4 / 16R (bit / s), and small image 3 has 3 / 16R (bit / s).
R (bit / s), 2 / 16R (bit / s
s).

FIG. 3 is a block diagram showing a functional configuration of an apparatus (computer-based apparatus) for implementing the image encoding / decoding method according to the second embodiment.
2 is an HDTV signal, 603 is an image dividing unit, 604 to 60
7 is a small image of a standard TV size, 608 to 611 are intra-frame variance calculation units, 612 to 615 are inter-frame variance calculation units, 616 to 619 are spatio-temporal feature amount calculation units, and 620 to 6
Spatial feature amount time _{23 F 1, F 2, F} 3, F 4, 624 is information assigning unit, 625 to 628 is information amount R ₁ assigned to each small _{image, R 2, R 3, R} 4, 629~ 632 is a discrete cosine transform unit, 633 to 636 are quantization units, and 637 to 6
Numeral 40 is a code allocating unit, 641 to 644 are buffer memory units, 645 to 648 are coded outputs, 649 is a multiplexing unit, 650 is coded output data, and 651 is an output terminal.

As shown in FIG. 3, the operation of the apparatus according to the second embodiment is as follows. First, the HDTV signal 602 is input to the input terminal 601.
Is entered. The input HDTV signal 602 is divided into four standard TV size images 604 to 604 by an image dividing unit 603.
607. The divided small images 604 to 607 of the standard TV size are respectively subjected to intra-frame variance calculators 608 to 611 and inter-frame variance calculator 61.
Is input to 2-615, average frame variance sigma ² _intra bars and the average inter-frame variance sigma ² _{i NTER} bars in each small image is determined, the space-time feature quantity calculator 61 using these
6 to 619, the spatio-temporal features F ₁ ,
_{F 2, F 3, F 4} (620~623) is obtained.

The calculated spatiotemporal feature Fm (m = 1,
The information allocating unit 624 uses the information amounts R ₁ , R ₂ , R ₃ , and R ₄ (625) to be assigned to each small image using ( ₂ , ₃ , ₄ ).
６628) is calculated.

On the other hand, each of the small images 604 to 607 is input to the discrete cosine transform units 629 to 632, subjected to discrete cosine transform, and then input to the quantization units 633 to 636. The quantization unit quantizes the discrete cosine transform coefficients, and codes are assigned by the code assignment units 637 to 640, and then sent to the buffer memory units 641 to 644. In the buffer memory units 641 to 644, the quantizing units 63 are set so that the outputs thereof become the information amounts 625 to 628 determined by the information allocating unit 624, respectively.
Apply feedback control to 3-636. The coded outputs 645 to 648 each having a constant information amount
The data is input to the input terminal 49, is collected into one encoded output data 650, and is transmitted to the transmission path via the output terminal 651.

In the first and second embodiments, the case of dividing into four parts has been described. However, the case of dividing into plural parts can be considered in the same manner. Further, as the feature amount, another feature amount that can predict the difficulty of encoding can be used.

As can be seen from the above description, the present embodiment 2
According to FIG. 2, as shown in FIG. 2, the spatio-temporal feature amount of each small image is substantially equal until time t ′, and then the small image 1
At the time t ″, the ratio of the spatio-temporal feature amounts becomes
F ₁ : F ₂ : F ₃ : F ₄ = 7: 4: 3: 2 On the other hand, when the information is allocated to each small area by the above-described method, R ₁ : R ₂ : R ₃ : R ₄ = 1: 1: 1 until time t ′.
1: 1, the same 1 / 4R (bit / s) for every small image
Information is assigned. On the other hand, after time t ′, the allocation state gradually changes according to the change of the spatiotemporal feature amount. At time t ″, R ₁ : R ₂ : R ₃ : R ₄ = 7: 4: 3:
It becomes 2. The information allocation at time t ″ is 7
/ 16R (bit / s), 4 / 16R (bi
t / s), 3 / 16R (bit / s) for small image 3, and 2 / 16R (bit / s) for small image 4.

Thus, information can be assigned to the entire image based on the feature amount of the input image.
The image quality of the decoded image can be improved.

As described above, the present invention has been specifically described based on the embodiments. However, it is needless to say that the present invention is not limited to the above-described embodiments, and various changes can be made without departing from the gist of the present invention.

[0046]

The effects obtained by the typical ones disclosed in the present application will be briefly described as follows.

It is possible to predict in advance how much information should be allocated to each of the divided small images prior to encoding. Therefore, by controlling the information generation amount of the divided small image based on the predicted value, it is possible to efficiently allocate the information amount as compared to the fixed allocation, and as a result, the image quality of the decoded image is improved. Can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a functional configuration of an apparatus (computer comprising a computer) for implementing an image encoding / decoding method according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a change in a spatio-temporal feature amount Fm and a change in a corresponding allocation information amount Rm according to the second embodiment of the present invention.

FIG. 3 is a block diagram illustrating a functional configuration of an apparatus (an apparatus including a computer) for performing the image encoding / decoding method according to the second embodiment.

FIG. 4 is a diagram for explaining a case where a conventional HDTV signal is spatially divided into four to make a small image of a standard TV size and encoding processing is performed in parallel.

FIG. 5 is a block diagram showing a functional configuration of a conventional apparatus that spatially divides an HDTV signal into four parts to make a small image of a standard TV size and performs encoding processing in parallel.

FIG. 6 is a diagram for explaining a problem of a conventional image encoding / decoding method.

FIG. 7 is a diagram for explaining a problem of a conventional image encoding / decoding method.

[Explanation of symbols]

201, 401, 601 ... input terminals, 202, 402,
602 ... input HDTV signal, 203, 403, 603 ...
Image division unit, 204 to 207, 404 to 407, 604
~ 607 ... divided standard TV size small image, 208 ~
211, 421 to 424 ... information compression unit, 212 to 21
5,425-428,641-644... Buffer memory section, 216-219... Coded output, 220,433,6
49: multiplexing unit, 221, 434, 650: multiplexed encoded data, 222, 435, 651 ... output terminal,
408 to 411: feature amount calculation unit; 412 to 415: obtained feature amount, 416, 624: information allocation unit, 41
7 to 420, 625 to 628... Allocated information amount,
429 to 432 ... encoded output data, 608 to 611 ...
Intra-frame variance calculator, 612 to 615: Inter-frame variance calculator, 616 to 619: Spatio-temporal feature amount calculator, 62
0-623: Spatio-temporal feature amount, 629-632: Discrete cosine transform unit, 633-636: Quantization unit, 637-64
0: code assignment unit.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7/68 H04N 1/41-1/419

Claims (1)

(57) [Claims] 1. A transmitting side divides an image to be coded into a plurality of small images, performs high efficiency coding on each of the divided small images in parallel, and transmits the divided small images. An image encoding / decoding method for decoding encoded data for a plurality of transmitted small images and then combining the decoded data to obtain an original image, wherein a spatial feature amount is calculated for each of the divided small images .
Differences between frames, which are the variances and motion features in the frames
Find the sum of the variances of the minute values and assign them to the entire image.
The allocated information amount is distributed to each divided small image in proportion to the added value, and in encoding each small image,
An image encoding / decoding method, characterized in that control is performed so that each encoded output information amount becomes a distributed information amount.