JP3029914B2 - Image hierarchical encoding / decoding device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hierarchical image encoding / decoding apparatus for hierarchically encoding / decoding an image, especially a moving image. In recent years, realization of a unified encoding algorithm for applications having different image formats has been desired. At the same time, compatibility with a low-rate coding algorithm (a coding algorithm used for a TV conference system or a storage medium) which has already been standardized is strongly desired. Therefore, various hierarchical encoding / decoding schemes are currently being studied to fulfill these requirements.

[0002]

2. Description of the Related Art In a video communication network, when a high-resolution terminal and a low-resolution terminal coexist in the network, it is necessary to provide compatibility between the high-resolution terminal and the low-resolution terminal. For this reason, in such a network, image data is hierarchically encoded / decoded for high-resolution and low-resolution, so as to be compatible with a low-rate encoding algorithm.

[0003] In this method, on the encoding side, a high-resolution input image is down-sampled to produce a low-resolution image, and this image is encoded by a low-rate standardized encoding method. And On the other hand, as the encoded data of the higher hierarchy, the encoded data of the lower hierarchy is decoded to obtain a decoded image. And encodes the difference to obtain encoded data in a higher hierarchy. On the decoding side, when the decoder is a low-rate standardized decoder, a decoded screen is obtained using only the coded data in the lower layer. If the decoder can handle the higher layer, in addition to generating a decoded screen from the coded data in the lower layer, it also decodes the coded data in the higher layer and adds the decoded screen obtained in the lower layer to the upsampled image. Thus, a high-resolution decoded screen is obtained.

FIGS. 5 and 6 show examples of the configuration of an apparatus for performing such hierarchical encoding / decoding. Here, FIG.
Shows the configuration on the encoding device side, and FIG. 6 shows the configuration on the decoding device side.

[0005] The encoding apparatus has resolution conversion means 41 for converting an input image into n types of resolutions. Where n is 2
In the above integers, the resolution decreases as n increases,
It is assumed that 1 ≦ i <j <n. The resolution converting means 41 converts the image having the lower resolution j into an image having a lower resolution j, for example, by thinning the image having the resolution i.

The encoding means 42 encodes an image having a resolution j, and the encoded data is sent to the receiving side and input to the decoding means 3 to be decoded into a decoded image having the resolution j. . The resolution conversion means 44 is a circuit for converting the decoded image having the resolution j into an image having a higher resolution i by, for example, interpolating the decoded image. The subtraction unit 45 calculates a difference between the input image of the resolution i and the screen of the resolution i converted by the resolution conversion unit 44. The encoding means 46 encodes the difference data to generate encoded data and transmits it to the receiving side.

[0007] On the decoding device side on the receiving side, the decoding means 4
7 decodes the received encoded data of the resolution j to generate a decoded image of the resolution j. This decoded image is input to the resolution conversion means 49 and is converted into an image of resolution i. On the other hand, the decoding means 48 decodes the received coded data and outputs difference data for the image of the resolution i. The adding means 50 'adds the difference data and the image from the resolution converting means 49 to generate a decoded image having the resolution i.

With the above configuration, when the receiving side is a low resolution terminal, a low resolution decoded image is reproduced, and when the receiving side is a terminal capable of handling high resolution, a high resolution decoded image is reproduced. Can be compatible

[0009]

In consideration of compatibility between high resolution and low resolution, it is necessary to encode / decode images hierarchically as described above. However, when both the encoder side and the decoder side can handle high resolution, low-resolution images are not displayed, so it is not necessary to perform hierarchical coding. /
Can be decrypted.

On the other hand, in general, in order to obtain an image of the same image quality, the amount of information required for encoding is smaller in single-layer encoding than in hierarchical encoding, and therefore, in terms of encoding efficiency. It is preferable to perform encoding / decoding in a single layer. Therefore, the conventional hierarchical encoding / decoding scheme is:
It can be said that coding efficiency is sacrificed in order to emphasize compatibility.

The present invention has been made in view of the above circumstances, and an object of the present invention is to perform hierarchical coding and single-layer coding in accordance with the resolutions of a transmitting side encoder and a receiving side decoder. And to improve the coding efficiency as much as possible.

[0012]

FIGS. 1 and 2 are explanatory diagrams of the principle according to the present invention. As shown in FIG. 1, a hierarchical encoding apparatus for an image according to the present invention, as shown in FIG. 1, converts resolution of an input image into images of a plurality of layers having different resolutions, A first encoding unit 22, a decoding / resolution conversion unit 23 that decodes the encoded data encoded by the first encoding unit 22 and converts the resolution into an image of a higher resolution hierarchy; A subtracting unit 24 for calculating a difference between the image converted by the resolution converting unit 23 and the input image of the higher resolution hierarchy
And second encoding means 25 for encoding the difference data of the subtraction means 24, and when the decoding device can decode the encoded data encoded by the second encoding means, Instead, it has a control means 26 for controlling so as to encode the input image of the higher resolution hierarchy as it is.

The control means 26 inputs "0" data to the subtraction means 24 in place of the image converted by the decoding / resolution conversion means 23, and outputs the output of the subtraction means 24 to the second encoding means 25. Can be configured to be encoded.

The control means may input the input image of the higher resolution hierarchy to a third encoding means (not shown) as it is, or may replace the differential data from the subtracting means 24 with the second encoding means. 25 can be configured.

FIG. 2 is a block diagram showing a hierarchical decoding apparatus for an image according to the present invention.
As shown in (1), the first decoding means 31 decodes the received encoded data of a certain layer of resolution, and decodes the received encoded data of a layer having a higher resolution than the received layer. A second decoding unit 32, a first resolution conversion unit 33 that converts the decoded image decoded by the first decoding unit into an image of a higher resolution hierarchy,
An adding unit 34 for adding the image converted by the resolution converting unit 33 and the decoded value decoded by the second decoding unit 32 to generate a decoded image of the second resolution; and a second decoding unit 32
And a control means 35 for controlling the decoded value of (i) as a decoded image as it is.

The control means 35 can be configured to input "0" data to the adding means 34 in place of the decoded image decoded by the first decoding means 31.

The control means 35 includes an addition means 34
, The output of the second decoding unit 32 can be taken out as it is to obtain a decoded image.

[0018]

On the coding device side, the coding of the low-resolution image coded by the first coding means 22 and the difference data of the high-resolution image coded by the second coding means 25 are usually performed. Hierarchical encoding is performed by transmitting encoded data, but if it is known that the receiving side has high resolution, the control means 26 encodes the high-resolution input image as it is and sends it to the receiving side. I will send it. Thereby, single-layer encoding can be performed.

There are various methods for encoding the high-resolution input image as it is by the control means 26. For example, the image data input from the decoding / resolution conversion means 23 to the subtraction means 24 is converted to "0" data to obtain a high-resolution image. May be passed substantially as it is through the subtraction means 24, or switching may be performed such that a high-resolution input image is directly input to the second encoding means 25 without passing through the subtraction means 24. Alternatively, a high-resolution input image may be encoded by a third encoding unit different from the second encoding unit 25 and sent to the receiving side.

On the receiving side, when the transmitting side is performing hierarchical coding, if the receiving side has a low resolution, the decoding means 31
To reproduce and display the low-resolution decoded image. On the other hand, if the receiving side has high resolution, the adding means 34 performs high-resolution decoding based on the low-resolution decoded image and the differential data decoded by the decoding means 32. And reproduces and displays the decoded image.

On the other hand, when the transmitting side is performing single-layer encoding, the control unit 35 displays the high-resolution decoded image decoded by the decoding unit 32 as it is. As the method, the image data input from the resolution conversion unit 33 to the addition unit 34 may be set to “0” so that the decoded image of the decoding unit 32 passes through the addition unit 34 substantially as it is. Adding means 34 to the output image of means 32
It may be taken out directly and displayed without passing through.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows the configuration of a hierarchical coding apparatus for an image according to an embodiment of the present invention, and FIG. 3 shows the configuration of the hierarchical decoding apparatus. In this embodiment, the input image is encoded / decoded in two layers. The resolution of the layer is higher than that of the layer, and the image of the layer is obtained by down-sampling the image of the layer. Is obtained.

First, the configuration of the encoding apparatus will be described.
In, the down-sampling unit 1 down-samples (decimates) the input image and performs resolution conversion to a lower-resolution image. The discrete cosine transform unit 2 encodes the resolution-converted low-resolution image by discrete cosine transform. The encoded data is sent to the receiving side and input to the inverse discrete cosine transform unit 3. The inverse discrete cosine transform unit 3 decodes the coded data by the inverse discrete cosine transform to generate a decoded image. The decoded image is input to the up-sampling unit 4 and is subjected to up-sampling (interpolation) to be converted into a high-resolution format image.

The resolution-converted image is input to the subtractor 5 through the selector 7, where a difference from the input image of the original resolution is generated. The data is encoded by cosine transform and sent to the receiving side as hierarchically encoded data. The selector 7 is configured to select and output either the image data from the up-sampling unit 4 or “0” data.

Next, the configuration of the decoding apparatus will be described.
, The inverse discrete cosine transform unit 8 decodes the coded data received in the layer by the inverse discrete cosine transform to generate a decoded image in the layer. On the other hand, the inverse discrete cosine transform unit 9 decodes the coded data received in the hierarchy by the inverse discrete cosine transform, and generates difference data for obtaining a reproduced image having a resolution.

The up-sampling unit 10 up-samples (interpolates) the decoded image generated by the inverse discrete cosine transform unit 8 and converts the resolution into image data in a resolution format. This image data is input to the adder 11 through the selector 12, where it is added to the decoded difference data to obtain a decoded image having a resolution.

The operation of this embodiment will now be described. If the receiving apparatus has not determined whether the resolution is high or low, the same hierarchical encoding / decoding as in the related art is performed for compatibility. That is, the selector 7 on the encoding device side selects the image data from the up-sampling unit 4 and inputs it to the subtractor 5, and the selector 12 on the decoding device side selects and adds the image data from the up-sampling unit 10. Input to the container 11. Thereby, the same hierarchical encoding / decoding as in the related art is performed.

On the other hand, if it is known that the receiving apparatus has high resolution, there is no need to perform hierarchical encoding / decoding, so that single-layer encoding / decoding is performed on the high resolution layer side. To do. That is, the selector 7 on the encoder side selects “0” data and inputs it to the subtractor 5, and the selector 12 on the decoder side selects “0” data and inputs it to the adder 11. Thereby, on the encoding device side,
The input image data of the resolution passes through the subtractor 5 as it is, and is encoded and transmitted by the discrete cosine transform unit 6. On the decoding device side, the encoded data of the image of the resolution is inverse discrete cosine. Decoded by the conversion unit 9,
The decoded image of the decoded resolution passes through the adder 11 as it is, so that single-layer encoding / decoding is performed.

If the resolution of the receiving device is known, the above-described switching of the selector may be performed according to the resolution. If it is not known, the determination as to whether or not the receiving device has a high-resolution function is made, for example, according to CCITT Recommendation H.264. BA of the transmission frame of the communication procedure specified in 242
This can be performed by using S (Bit rate Allocation Signal) to exchange information about each terminal when starting communication between the terminals.

In carrying out the present invention, various modifications are possible. For example, in the above-described embodiment, as means for performing single-layer encoding / decoding, the selectors 7 and 12 select “0” data, and the subtractor 5 and the adder 11 respectively.
However, the present invention is not limited to this. For example, a high-resolution input image is directly input to the discrete cosine transform unit 6 on the transmitting side, and the inverse discrete cosine transform unit is input on the receiving side. Circuit switching may be performed so that the decoded data from 9 is directly extracted without passing through the adder 11. Alternatively, the transmitting side may input a high-resolution input image to a discrete cosine transform unit different from the discrete cosine transform unit 6 and perform encoding.

In the above-described embodiment, the discrete cosine transform / inverse discrete cosine transform is used as the encoding / decoding means. However, the present invention is not limited to this. For example, a prediction coding method or the like may be used. Further, the coding method may be changed according to the hierarchy.

The hierarchical encoding / decoding device according to the present invention is, for example, a T / T device in which high-resolution terminals and low-resolution terminals are mixed.
The present invention can be applied to a multipoint conference device of a V conference system.

[0033]

As described above, according to the present invention, it is possible to select between hierarchical coding / decoding and single-layer coding / decoding according to the resolution of the facing encoder and decoder. Therefore, it is possible to increase the encoding efficiency when encoding a high resolution and improve the image quality of a decoded image.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of an image hierarchical coding apparatus according to the present invention.

FIG. 2 is a diagram illustrating the principle of an image hierarchical decoding apparatus according to the present invention.

FIG. 3 is a diagram illustrating a configuration of an image hierarchical encoding device as one embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of an image hierarchical decoding apparatus as one embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration example of a conventional image hierarchical coding device.

FIG. 6 is a diagram showing a configuration example of a conventional image hierarchical decoding device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Down sampling part 2, 6 Discrete cosine transformation part 3, 8, 9 Inverse discrete cosine transformation part 4, 10 Up sampling part 5 Subtractor 7, 12 Selector 11 Adder 41, 44, 49 Resolution conversion means 42, 46 Coding Means 45 Subtraction means 43, 47, 48 Decoding means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-148279 (JP, A) JP-A-63-73786 (JP, A) JP-A-3-66278 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04N ^7/ 24-7/68 H04N 1/41-1/419 H04N 7/15

Claims (6)

(57) [Claims] 1. A resolution conversion means (21) for converting the resolution of an input image into images of a plurality of hierarchies having different resolutions, a first encoding means (22) for encoding an image of a certain hierarchy resolution, Decoding / resolution conversion means (23) for decoding the coded data coded by the first coding means and converting the resolution into an image of a higher resolution hierarchy, and conversion by the decoding / resolution conversion means Subtraction means (2) for taking the difference between the image and the input image of a higher resolution hierarchy
4), second encoding means (25) for encoding the differential data of the subtraction means, and when the decoding device can decode the encoded data encoded by the second encoding means. Control means (26) for performing control so as to directly encode the input image of the higher resolution in place of the difference data. 2. The control means inputs "0" data to the subtraction means in place of the image converted by the decoding / resolution conversion means, and outputs the output of the subtraction means to the second encoding means. 2. The image hierarchical encoding apparatus according to claim 1, wherein the apparatus is configured to encode the image. 3. The control means inputs the higher resolution hierarchical input image to a third encoding means as it is, or replaces the difference data from the subtraction means with the second encoding means. 2. The image hierarchical encoding apparatus according to claim 1, wherein the apparatus is configured to input the image data to the image. 4. A first decoding means (31) for decoding received coded data of a certain layer resolution, and decoding received coded data of a layer having a higher resolution than the received layer resolution. Second decoding means (32)
First resolution conversion means (33) for converting the resolution of the decoded image decoded by the first decoding means into an image having a higher resolution, and an image converted by the resolution conversion means; Adding means (34) for adding the decoded values decoded by the decoding means to generate a decoded image of the second resolution, and controlling the decoded value of the second decoding means to be the decoded image as it is. An image hierarchical decoding apparatus comprising a control means (35). 5. The image according to claim 4, wherein said control means is configured to input “0” data to said adding means in place of the decoded image decoded by said first decoding means. Decoding device. 6. The image according to claim 4, wherein said control means is configured to take out the output of said second decoding means as it is, instead of outputting from said adding means, and obtain a decoded image. Decoding device.