JP2647229B2 - Image coding device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding device for encoding and transmitting an input image signal.

[Prior Art] FIG. 2 is a schematic diagram of an image packet encoding device including a conventional image encoding device and an image packet decoding device including a conventional image decoding device (Nomura et al., “DCT Of Cell Loss and Its Countermeasure in Interframe Coding Using CDMA, "1988 Image Coding Symposium, pp85
-86).

FIG. 2A shows an encoding device. In FIG. 2A, an image signal s input from an input terminal 21 is shown.
Is divided into blocks of several n × n pixels for each frame, and then divided into discrete cosine transformers (DCT converters) 22.
Is subjected to discrete cosine transform in block units. From the obtained discrete cosine coefficients, a frame memory is
The discrete cosine coefficient of the corresponding block one frame before stored in 24 is subtracted, and these difference values d are selected. The difference value d is converted into a code i by the quantizer 25 and output to the scanner 26.

This code i is sent to an inverse quantizer 27 having the inverse characteristic of the quantizer 25, and after being inversely quantized, the adder 20 outputs the discrete value one frame before used to obtain the difference value d. The signal is added to the cosine coefficient, converted to a locally reproduced discrete cosine coefficient, and output to the frame memory 24. This locally reproduced discrete cosine coefficient is used for encoding the next frame.

With such a processing system, a code i obtained by predictively coding the discrete cosine coefficient is obtained.

As shown in FIG. 3, the scanner 26 sequentially scans the input code i while repeatedly reciprocating diagonally in block units. FIG. 3 shows the scanning order of the code i of the block of 8 × 8 pixels. At this time, the scan is divided into the low frequency component iL and the high frequency component iH by two.
The code i is hierarchized by division. The hierarchized code components iL and iH are respectively the corresponding variable length encoders.
After being sent to 28 and 29 and subjected to run-length Huffman coding, the packet assembling section 210 hierarchizes them into priority cells and non-priority cells, assembles them into packets (cells) of the same type, and sends them to the transmission path. Is done.

That is, information indicating priority / non-priority is added to each cell as header information. Introduce a hierarchical structure with priority to the network, against cell discards that occur at the time of network congestion, without discarding priority cells containing low-frequency elements important for image signals,
Non-priority cells are discarded, and image quality deterioration due to discarding is minimized.

FIG. 2 (B) shows the configuration of the decoding device. Second
In FIG. 2B, a cell sent from the encoding device is decomposed by a packet decomposing unit 211 and is divided into encoded image data and parameters required for decoding. The coded image data (data for the low-band code iL and data for the high-band code iH) which constituted the priority cell and the non-priority cell are run-length / Huffman-coded by the corresponding variable-length decoding units 212 and 213, respectively. Decrypted. After that, the image code (low-band code iL, high-band code iH) that has been divided into priority / non-priority by the data synthesis unit 214 is reconstructed. The reproduction code iS is obtained.

The reproduced code iS is subjected to inverse quantization, which is the inverse processing of the quantizer 25, by the inverse quantizer 215, and then the frame memory 216
Is added by the adder 217 to the reproduced discrete cosine coefficient of the corresponding block one frame before stored in the corresponding block, and is converted into the reproduced discrete cosine coefficient. An inverse DCT transformer 218 performs an inverse transform of the discrete cosine transform on the reproduced discrete cosine coefficient, and the obtained reproduced image signal sS is output to an output terminal 219.
And is stored in the frame memory 216 for processing of the next frame.

[Problems to be Solved by the Invention] By the way, an asynchronous transfer mode (AT
M) The net is being considered. It is known that cell discarding due to network congestion occurs as a signal deterioration factor in the asynchronous transfer mode network.

In the image packet encoding / decoding device described above, the cells are given priority according to the importance of the data in the cells, and the network is also provided with hierarchical lines such as priority channels / non-priority channels. Is assumed. In this way, the high-priority cells are protected from being discarded to suppress image quality deterioration, but the control configuration and the like for that purpose have been complicated.

In addition, although the priority concept is introduced, the capacity of the priority channel may be insufficient, and the priority cell may be discarded. The effect on the reproduced image quality at this time is very large.

Furthermore, when an error occurs in the transmission path such as cell discard, the contents of the frame memory 24 used for inter-frame coding and the frame memory 216 used for inter-frame decoding become inconsistent and cannot be decoded properly. There is also a problem that this state propagates for a long time.

The present invention proposes an image coding apparatus that performs coding without assuming the use of a hierarchical network and that can prevent a large adverse effect from being propagated for a long time even when an error occurs in a transmission system. Is what you do.

[Means for Solving the Problems] The present invention provides an image encoding apparatus, comprising: an intra-frame encoding unit that intra-frame encodes a low-frequency component of an input image signal; And an inter-frame encoding unit for encoding. Further, the intra-frame encoding unit includes an average value calculation unit that calculates an average value of the low-frequency component for each block, and an encoder that encodes the low-frequency component subtracted from the average value. After that, the coded low band component and the coded other band component are transmitted, and the average value is transmitted as a parameter necessary for the decoding process.

[Operation] In the present invention, a low-frequency component of an input image signal is intra-frame encoded by an intra-frame encoding unit, and other band components are inter-frame encoded by an inter-frame encoding unit. The low-frequency component of the input signal is encoded and transmitted after being subtracted from the average value of the low-frequency component for each block, and the average value is also transmitted as a parameter necessary for the decoding process.

Embodiment Overall Image Packet Encoding Apparatus Prior to description of an image packet decoding apparatus incorporating an image decoding apparatus according to an embodiment of the present invention, a corresponding image packet encoding apparatus will be described.

FIG. 4 shows the structure of the image packet coding apparatus, and FIGS. 5 and 6 show the detailed structures of the intra-frame coding unit and the inter-frame coding unit, respectively.

In FIG. 4, an image signal input from an input terminal 41 is QMF (Quadrature) as a two-dimensional band division filter.
The Mirror Filter) unit 42 divides each frame into two bands of a high frequency component and a low frequency component in each of the horizontal direction and the vertical direction, and divides the entire frame into signal components of four bands in a two-dimensional spatial frequency domain. You.

The image signal components of the four bands obtained by the division are respectively assigned to the corresponding decimation units (thinning units) 43, 44, 4
5 and 46, the image signal components SLL, SLU, SUL, and SUU (subscripts are horizontal, In the vertical order, L indicates a low-frequency component and U indicates a high-frequency component).

An image signal component SLL, which is a low-frequency component in both the horizontal direction and the vertical direction, is provided to an intra-frame encoding unit 47 having a detailed configuration shown in FIG. 5, and other image signal components SLU, SUL,
The SUUs are respectively supplied to the corresponding motion compensation interframe coding units 48, 49 and 410 whose detailed configuration is shown in FIG. Each of the encoding units 47, 48, 49, and 410 encodes the given image signal component, and supplies its encoded value iLL, iLU, iUL, iUU to the corresponding variable length encoding unit 411, 412, 413, 414. .

Each of the variable-length encoding units 411, 412, 413, and 414 has an input code value
The iLL, iLU, iUL, and iUU are, for example, run-length / Huffman-coded and output to the MUX unit (multiplexing unit) 415.

The MUX unit 415 multiplexes the input code into one series of signals and supplies the multiplexed signal to the packet assembling unit 416. The packet assembling unit 416 assembles this into cells of a certain length and transmits the cells to, for example, an ATM transmission network. At this time, the type of information in the cell (such as which band the signal is in) as the header information and the parameters (block average value h and motion vector MV L
U, MV UL, MV UU) are added.

Here, the reason why the intra-frame coding is used only for the image signal component SLL which is a low-frequency component in both the horizontal direction and the vertical direction is because such an image signal component SLL is an important component for an image. , This image signal component S
It is not good that LL is unstable for a long time due to cell discarding, etc., because the influence of cell discarding was kept in that frame by adopting intra-frame coding and it did not affect the next frame .

Details of Intra-Frame Encoding Unit Next, an intra-frame encoding unit that encodes an image signal component SLL that is a low-frequency component in both the horizontal and vertical directions.
47 will be described.

In FIG. 5, an input image signal component SLL is provided to a block dividing section 51. The block division unit 51 divides the image signal into several blocks each including n × n pixels on a frame basis, and supplies an image signal component of each block to the average value calculation unit 52 and the subtractor 53. The average value calculation unit 52 calculates the average value h in the block and supplies it to the subtractor 53. The subtractor 53 subtracts the average value h in the block from the image signal component to obtain a difference value.
The dLL is provided to an orthogonal transform unit 54 composed of, for example, a discrete cosine transformer. The orthogonal transformer 54 orthogonally transforms the difference value dLL and supplies the result to the quantizer 55. The quantizer 55 quantizes the orthogonal transform coefficient to obtain an output code iLL.

The average value h in the block obtained by the average value calculation unit 52
Are transmitted to the image packet decoding device as parameters necessary for the decoding process, as described above.

Next, the image signal components SLU and SLU other than the image signal component SLL
UL, SUU interframe coding units 48, 49, 410
Will be described.

In FIG. 6, the input image signal component SLU, SUL or S
UU is provided to the block dividing unit 61. Block division unit 61
Divides an input image signal component into several blocks each composed of n × n pixels on a frame basis and supplies the block to a subtractor 62. The subtractor 62 subtracts the predicted value of the signal component given from the motion compensator 63 from the signal component, and calculates a difference value dL.
U, dUL or dUU is given to an orthogonal transform unit 64 composed of, for example, a discrete cosine transform unit. The orthogonal transform unit 64 orthogonally transforms the difference value dLU, dUL or dUU for each block, and provides the result to the quantizer 65.
The quantizer 65 quantizes the orthogonal transform coefficients, and obtains the obtained code iL.
Output U, iUL or iUU.

The code iLU, iUL or iUU is given to an inverse quantization unit 66, and the inverse quantization unit 66 performs inverse processing of the quantization unit 65 to convert the code into local reproduction orthogonal transform coefficients. Given to. The inverse orthogonal transform unit 67 performs an inverse process of the orthogonal transform unit 64 on the local reproduction orthogonal transform coefficient, obtains a local reproduction difference value, and supplies the difference value to the adder 68. The adder 68 is supplied with the motion-compensated local reproduction orthogonal transform coefficient (prediction value) one frame before output from the motion compensator 63, and the adder 68 calculates the local reproduction orthogonal transform coefficient and the prediction value. The values are added to obtain a local reproduction image signal component, and the local reproduction image signal component is supplied to the leakage unit 69. The leakage part 69
After multiplying the image signal component of the local reproduction by a leak coefficient α (smaller than 1), the image signal component is given to the frame memory 610 and stored.

The image signal components stored in the frame memory 610 are used for processing of the next frame, and
And is given to the subtractor 62 as a predicted value as described above.

The motion compensator 63 is provided with an image signal component from the block divider 61 although signal lines are not shown, and the motion compensator 63 and the image signal component stored in the frame memory 610 one frame before , A motion vector (for example, a pair of horizontal and vertical motion vectors) is detected, and motion compensation is performed based on the motion vector. As described above, this motion vector information
The MV LU, MV UL, and MV UU are transmitted to the image packet decoding device as parameters necessary for the decoding process.

Next, an image packet decoding apparatus incorporating the image decoding apparatus according to an embodiment of the present invention will be described.

FIG. 1 shows the configuration of the image packet decoding apparatus, and FIGS. 7 and 8 show the detailed configurations of the intra-frame decoding unit and the inter-frame decoding unit, respectively.

In FIG. 1, a cell from a transmission line is a packet decomposing unit.
Decomposed given to 11. The packet decomposing unit 11 also detects a cell discard position. The data decomposed by the packet decomposing unit 11 is supplied to a DEMUX unit (demultiplexing unit) 12.

The DEMUX unit 12 divides this into encoded image information and parameters (such as motion vectors) required for decoding,
The signal components are divided into signal components of each band, and provided to the corresponding variable length decoding units 13, 14, 15, and 16, respectively.

The variable-length decoding units 13, 14, 15, and 16 perform inverse processing of the above-described variable-length encoding units 411, 412, 413, and 414 to reproduce the reproduced codes YLL, YLU, YUL, and YUU (iLL, iLU, iUL, respectively). , IUU
(Corresponding to the above) and gives the result to the corresponding decoding units 17, 18, 19, 110. The reproduction code YLL relating to the image signal components in the low band in both the horizontal direction and the vertical direction is supplied to the intra-frame decoding unit 17 shown in detail in FIG. 7, and the other reproduction codes YLU, YUL, Y
The UU is an inter-frame decoding unit 18 whose detailed configuration is shown in FIG.
19, given to 110.

As will be described later, each of the decoding units 17, 18, 19, 110 decodes the reproduced codes YLL, YLU, YUL, YUU, and obtains the reproduced image signal components S'LL, S'LU,
S′UL and S′UU are given to corresponding interpolation sections (sample interpolation sections) 111, 112, 113 and 114, respectively.

Each of the interpolation units 111, 112, 113, and 114 receives a given reproduced image signal component S'LL, S'LU,
S'UL and S'UU are up-sampled twice in the horizontal and vertical directions, that is, four times in total, and provided to the QMF section 115. QMF part 1
15 filters up-sampled image signal components, then synthesizes signals of four bands and outputs them.
The reproduction image signal is output from 116.

Details of Intra-Frame Decoding Unit Next, details of the above-described intra-frame decoding unit 17 that decodes the reproduction code YLL will be described.

In FIG. 7, the reproduced code YLL is given to a switch circuit 71, and is selected by the switch circuit 71 and given to the inverse quantization unit 72 except when the cell is discarded. This reproduction code YLL is
In the inverse quantization unit 72, the inverse processing of the quantization unit 55 (FIG. 5) is performed, converted to a reproduction orthogonal transform coefficient, and provided to the inverse orthogonal transform unit 73. The inverse orthogonal transform unit 73 performs an inverse process of the orthogonal transform unit 54 on the reproduced orthogonal transform coefficient, obtains a reproduced difference value d′ LL, and supplies the difference value d′ LL to the adder 74. The adder 74 is provided with the average value h output from the average value calculation unit 52 of the encoding device and given to the decoding device. The adder 74 calculates the reproduction difference value d′ LL and the average value h is added to obtain a reproduced image signal component S′LL, and the reproduced image signal component S′LL is output to the interpolation unit 111.

In this manner, the intra-frame decoding process during normal reception is performed.

At the time of cell discard detection, the above-described switch circuit 71 is switched to the other input terminal side, and the block information (reproduction code) lost due to cell discard is set to 0. At this time,
Since the difference value given from the inverse orthogonal exchanger 73 to the adder 74 also becomes 0, the average value h is output as it is as the compensated reproduced image signal component S'LL, and the minimum reproduced image quality is secured.

Details of Interframe Decoding Unit Next, details of the interframe decoding unit 18, 19, or 110 for the reproduced code YLU, YUL, or YUU will be described.

In FIG. 8, the reproduced code YLU, YUL or YUU is supplied to a switch circuit 81, and is selected by the switch circuit 81 and supplied to an inverse quantization unit 82 except when the cell is discarded. The reproduced code YLU, YUL or YUU is quantized by the inverse quantization
The inverse processing of 65 (FIG. 6) is performed to convert the data into reproduced orthogonal transform coefficients, which are provided to the inverse orthogonal transform unit 83. Inverse orthogonal transform unit 83
Performs an inverse process of the orthogonal transform unit 64 on the reproduced orthogonal transform coefficient to obtain a reproduced difference value d′ LU, d′ UL or d′ UU, and gives the value to the adder 84. Based on the motion vector information MV LU, MV UL, or MV UU output from the motion compensator 63 of the encoding device and given to the decoder, the adder 84 performs 1 motion compensation by the motion compensator 85. The reproduction orthogonal transform coefficient (predicted value) before the frame is given. The adder 84 adds the reproduced difference value d'LU, d'UL or d'UU to the predicted value to obtain a reproduced image signal component S'LU, S'UL or S'UU. The component S′LU, S′UL or S′UU is output to the interpolation unit 112, 113 or 114.

The reproduced image signal components S'LU, S'UL or S'UU are provided to the leakage section 86. The leakage unit 86 multiplies the reproduced image signal component S'LU, S'UL, or S'UU by a leak coefficient α equal to the leak coefficient in the encoding device, and supplies the multiplied result to the frame memory 87 for storage.

The signal component stored in the frame memory 87 is used for processing of the next frame, is motion-compensated through the motion compensating unit 85, and is added as a predicted value as described above.
Given to 84.

Thus, the normal inter-frame decoding process is performed.

At the time of cell discard detection, the above-described switch circuit 81 is switched to the other input terminal side, and the block information (reproduction code) lost due to cell discard is set to 0. At this time,
Since the difference value given from the inverse orthogonal transformer 83 to the adder 84 is also 0, the reproduced image signal component S 'obtained by directly compensating the reproduced image signal component of the previous frame via the motion compensator 85 as it is.
Output as LU, S'UL or S'UU.

In general, when an error occurs during transmission in inter-frame coding, the frame memory 610 in the encoder and the frame memory 87 in the decoder become asynchronous, and there is a problem that the error propagates with time. . Therefore,
In this embodiment, the frame units of the encoder and the decoder can be synchronized with the lapse of time by adding the leakage units 69 and 86 described above. Note that it is conceivable that the addition of the leakage units 69 and 86 increases the prediction error and lowers the coding efficiency. However, the provision of the leakage unit is not limited to the image signal components SLU, SUL or Since the power is relatively small for SUU, there is no practical problem.

Effects of Embodiment Since intra-frame encoding / decoding is applied to a low-frequency component that is an important component on an image, the effect of cell discard can be kept within that frame, and the next frame is affected. Can not be. Further, since the average value is used to compensate for the frame in which the cell is discarded, it is possible to minimize the deterioration of the image quality.

By employing such an encoding / decoding method, it is not necessary to layer each cell, and it is not necessary to perform priority control on a transmission path.

Another embodiment The transmission form from the image encoding device to the image decoding device includes:
It is not limited to packet transmission. For example, a transmission form of recording and reproducing on a recording medium may be used.

Various methods can be applied as a method of transmitting parameters such as a motion vector and a block average value.

Further, a filter other than QMF may be applied as the band division filter, and a one-dimensional band division filter instead of a two-dimensional filter may be applied.

The intra-frame encoding method may be a method using a line correlation or a method using a correlation with an adjacent pixel, in addition to the method of obtaining the average value described above.

[Effects of the Invention] As described above, according to the present invention, the image encoding device
Intra-frame encoding is performed on the low-frequency component of the input image signal, which is the most important in the image, and the encoded image signal output by performing inter-frame encoding on the other band components is output according to each band component. Since decoding is performed appropriately, a high-quality reproduced image can be obtained. For low-frequency components that are targets of intra-frame codes with a large code amount,
The coding amount can be reduced by coding the difference value of the average value of each block of the low-frequency component.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an image packet decoding apparatus according to one embodiment of the present invention, FIG. 2 is a block diagram showing a conventional image packet encoding / decoding apparatus, and FIG. FIG. 4 is an explanatory diagram showing a method of extracting a band component and a high band component, FIG. 4 is a block diagram showing a picture packet encoding apparatus corresponding to the picture packet decoding apparatus according to the above embodiment, and FIG. FIG. 6 is a block diagram showing an inter-frame encoding unit shown in FIG. 4, and FIG. 7 is a block diagram showing an intra-frame decoding unit in the image packet decoding apparatus according to the embodiment. FIG. 8 is a block diagram showing an inter-frame decoding unit. 11: Packet decomposing unit, 12: DEMUX unit, 13 to 16: Variable length decoding unit, 17: In-frame decoding unit, 18, 19, 11
0: Inter-frame decoding unit, 115: QMF unit, 86: Leakage unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenichiro Hosoda 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References 1988 Image Coding Symposium (PCSJ88) 79-80 SPIE Vol. 707 Visual Communications and Image Processing (1986) p. 51-61

Claims (1)

(57) [Claims] 1. An image encoding apparatus, comprising: an intra-frame encoding unit that intra-frame encodes a low-frequency component of an input image signal; and an inter-frame encoding that encodes another band component of the input image signal. An intra-frame encoding unit, wherein the intra-frame encoding unit computes an average value for each block of the low-frequency component, and encoding that encodes the low-frequency component subtracted from the average value. With a container,
An image encoding apparatus for transmitting the low-frequency component encoded after the subtraction and the encoded other band component, and transmitting the average value as a parameter required for a decoding process. .