JPH06276512A - Picture communication equipment - Google Patents

Abstract

PURPOSE:To obtain the picture communication equipment able to reproduce a smooth moving picture even in a communication network at a low speed rate by decreasing transmission quantity of picture data and increasing number of transmission frames. CONSTITUTION:The picture communication equipment is provided with a difference processing means 3 calculating a difference of block data between a current frame and a preceding frame, a quantization means 5 quantizing the data, and a variable length coding means 9 applying variable length coding to the data, and a coding judging means 8 judging data of the remaining number of a block to be zero when variable length coding is applied to data of a number of part of the block and commanding the end of variable length coding processing of the data of the block. The data required to be sent as to one block are data subjected to variable length coding till the coding judging means 8 commands the end of variable length coding and a code representing that the remaining data of the block are all zero.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image communication apparatus for compressing and transmitting image data such as a moving image and a still image, and more particularly to reducing the encoded data amount of one frame so that many frames It enables transmission.

[0002]

2. Description of the Related Art In recent years, CCITT (International Telegraph and Telephone Advisory Committee) has officially made a recommendation of video coding system, still image coding system, multiplexing system, communication procedure, etc. for audiovisual services, which is followed by each company. To CCI
Image communication devices such as a video conference system and a video phone that comply with the TT recommendation are on sale.

Since the amount of image data is enormous,
Data compression processing is required to reduce the amount of data to be transmitted.

As one process for reducing the amount of data, one frame of data has a certain size, for example, 8 ×.
It is performed by dividing the block into blocks of 8 pixels, comparing each block with a block having a high correlation in the immediately preceding frame (previous frame), and taking the difference. A block having a high correlation in the previous frame is searched for in a range including the block at the same position and its periphery, for example, 24 × 24 pixels around 8 × 8 pixels. Such a process of obtaining a difference between frames is called a process in the interframe mode.

The processing in the interframe mode cannot be used for the first frame or the initial frame (scene change frame) when the scene is changed. In these cases, use the block data as is,
Processing in the in-frame mode is performed.

As shown in FIG. 2, the conventional image communication apparatus has an intra-frame for determining whether to process data of an input block (for example, 8 × 8 pixels) in the intra-frame mode or the inter-frame mode. / Interframe determination unit 1,
A motion compensation processing unit 2 that detects a block (referred to as a “search block”) that has the highest correlation with an input block from the previous frame when processing in the interframe mode, and an input block and a search block detected by the motion compensation processing unit 2. And a difference processing unit 3 that performs a difference calculation (this result is referred to as a “difference block”) with the input block in the intra-frame mode, and a difference block calculated by the difference processing unit 3 in the inter-frame mode. Is converted by a conversion method such as discrete cosine transform (DCT conversion) to reduce the amount of information, and quantization is performed to approximate the block data converted by the conversion processor 4 to discrete values. A processing unit 5,
An inverse quantization processor 6 that inversely quantizes the block data quantized by the quantization processor 5 and an inverse discrete cosine of the block data inversely quantized by the inverse quantization processor 6. Inverse conversion is performed by a conversion method such as conversion (inverse DCT conversion) and is output to the frame memory 11, and the data of the blocks quantized by the quantization processing unit 5 are sequentially read, and zero (RUN) is set. A variable length coding processing unit 9 for coding block data by a combination of the number of data (referred to as ".") And a non-zero data value following zero (called LEVEL), and control for connecting to a communication network. In addition, it is provided with a network interface processing unit 10 for transmitting the block data coded by the variable length coding processing unit 9 to the partner device.

In this image communication apparatus, the following operation is performed in order to compress and transmit moving image data.

First, the network interface processing unit 10 controls the connection of the communication channel with the partner device via the communication network, and sets the state in which communication is possible. After that, the data of one frame is input as an image to the intra-frame / inter-frame determination unit 1 for each block of 8 × 8 pixels.

In the intra-frame / inter-frame judging section 1, for each input block, the block data in the first frame, the block data in the scene change frame, the number of blocks processed in the inter-frame mode, etc. It is determined whether the processing is performed in the intra-frame mode or the inter-frame mode according to the judgment criterion of No. 1. When processing is performed in the intra-frame mode, the input block data is transferred to the conversion processing unit 4. When processing in the inter-frame mode, the input block data is transferred to the motion compensation processing unit 2.

In the motion compensation processing unit 2, when block data is input from the intra-frame / inter-frame determination unit 1,
From the data stored in the frame memory 11,
The data of the input block and the block of the same value and the block around it (24x24 pixels around 8x8 pixels) are taken in, and the calculation of minimum difference absolute value sum etc. The block having the highest correlation (search block) is detected, and the change in position (motion vector) between the search block and the input block is obtained.

The difference processing unit 3 performs a difference calculation between the input block and the search block detected by the motion compensation processing unit 2, and transfers the difference block of the calculation result to the conversion processing unit 4. Since the data in this difference block is the difference between the input block and the search block having a very high correlation, a large amount of data concentrated near zero will be included.

In the conversion processing unit 4, the input block from the intra-frame / inter-frame determination unit 1 in the intra-frame mode, and the difference between the input block and the search block from the difference processing unit 3 in the inter-frame mode. The blocks are transferred, the conversion processing unit 4 performs conversion processing for reducing the amount of information on these blocks by a method such as DCT conversion, and the quantization processing unit 5 performs conversion processing on the blocks converted by the conversion processing unit 4. Converts data into discrete values for transmission over digital networks.

In the inverse quantization processing unit 6 and the inverse conversion processing unit 7, since the data required for the motion compensation processing unit 2 to detect the search block is stored in the frame memory 11, the quantization processing unit 5 operates. For quantized blocks,
Inverse quantization processing and inverse transformation processing are performed, and in the case of the intra-frame mode, the block subjected to the above processing is directly
Further, in the case of the inter-frame mode, the block obtained by adding the block subjected to the above processing and the search block is
Output to the same value as the input block in the frame memory 11.

In the variable length coding processing unit 9, the data of the blocks quantized by the quantization processing unit 5 are LE in a fixed order.
Read until VEL appears, number of RUN and LEV
Variable length coding is performed in combination with EL, and the above variable length coding is repeated until all the data in the block is processed.

3 and 4 show the block data (8 × 8 pixels) after the quantization processing and the reading order in the variable length coding processing in the case of 8 × 8 pixels. This block data is characterized in that RUN appears more frequently as the horizontal frequency and the vertical frequency become higher.

The compressed image coded data output from the variable length coding processing unit 9 is transmitted to the partner device via the network interface processing unit 10.

By repeating such a series of operations for a plurality of blocks, one frame of compressed encoded data is transmitted to the partner device.

[0018]

However, in the data compression in the conventional image communication apparatus, the reduction of the data amount is not always sufficient for utilizing the communication network having a low transmission rate. Therefore, when transmitting data through a low transmission rate communication network, the number of frames that can be transmitted is limited, and many frames cannot be transmitted.
It becomes difficult to reproduce a smooth image.

The present invention solves the above-mentioned conventional problems, and further reduces the amount of image data to be transmitted, thereby increasing the number of frames that can be transmitted and smoothing moving images even under a low-rate communication network. It is an object of the present invention to provide an image communication device capable of reproducing a video.

[0020]

Therefore, in the present invention, difference processing means for calculating the difference between the data of blocks between the current frame and the previous frame, and quantization means for quantizing the data of the blocks subjected to difference processing are provided. In an image communication apparatus including variable length coding means for variable length coding the quantized block data, the variable length coding means performs variable length coding on a partial number of data in the block. At this time, the value of the remaining number of data in the block is determined to be zero, and an encoding determination means for instructing the variable length encoding means to end the variable length encoding processing of the data in this block is provided. It is provided.

Further, the encoding determination means sets a time point for instructing the end of the variable length encoding processing of the subsequent blocks based on the appearance state of zero data in the variable length encoding of a plurality of blocks. Is configured.

Further, in the variable length coding of the data of the block, when the fixed number of data is continuously zero, the coding judging means instructs the variable length coding means to change the variable length of the data of the block. The end of the encoding process is instructed.

[0023]

Therefore, the data that needs to be transmitted with respect to one block is the data that has been variable-length coded by the encoding determination means until the end of variable-length coding is issued, and the remaining data of that block. Since it is only a code indicating that the data is all zero, the time required for variable length coding is shortened compared to the case where all the data of the block is variable length coded and transmitted, and the coded data to be transmitted The amount decreases.

Therefore, the number of frames to be transmitted can be increased, and even when a low-rate communication network is used,
A smooth moving image can be reproduced on the receiving side.

[0025]

(First Embodiment) In an image communication apparatus according to an embodiment of the present invention, as shown in FIG. 1, variable length coding is performed between a quantization processing unit 5 and a variable length coding processing unit 9. An encoding determination unit 8 for instructing the end of is provided. The coding determination unit 8 sequentially reads the block data quantized by the quantization processing unit 5, transfers the number of RUNs and LEVEL to the variable-length coding processing unit 9, and also transfers a fixed number of blocks. When the variable length coding of data is performed, the variable length coding processing unit 9 is instructed to end the variable length coding processing of the block.

Other configurations and operations of the image communication apparatus are the same as those of the conventional apparatus (FIG. 2).

In this apparatus, when the quantized block data is transferred from the quantization processing section 5 to the coding determination section 8, the coding determination section 8 processes the data in the block in the order shown in FIG. The read, the number of RUNs and the LEVEL are transferred to the variable length coding processing unit 9. Further, a variable length coding end command is sent to the variable length coding processing unit 9 at the time when a predetermined number of data are processed while reading the data in this block.

For example, when the predetermined number is 18, the variable length coding processing unit 9 is terminated when the variable length coding processing up to 18 of the data shown in FIG. 4 is completed. Order. This is equivalent to determining that all the data in blocks 19 to 64 are RUN.

In the variable length coding processing unit 9, variable length coding is performed according to the number of RUNs transferred from the coding judgment unit 8 and the combination of LEVEL, and the data is compressed via the network interface processing unit 10 to the partner device. And transmits the encoded image data. Further, when the variable length coding end command is received from the coding determination unit 8, the code word indicating that the coding of the block is completed is transmitted to the partner device via the network interface processing unit 10.

Therefore, the amount of encoded data for one block is reduced, and the amount of transmission data for one frame is reduced.

(Second Embodiment) The apparatus of the second embodiment is the same as the apparatus of the first embodiment in terms of the hardware configuration, but the criterion for judging the end of variable length coding in the coding judging unit 8 is the same. This is different from the case of the first embodiment.

The coding judgment unit 8 reads the block data transferred from the quantization processing unit 5 in the order shown in FIG.
The variable length coding processing unit 9 sets the number of RUNs and LEVEL.
Transfer to. After performing such processing for a plurality of blocks, the encoding determination unit 8 determines the number of data to be processed in the subsequent blocks based on the appearance status of the RAN in those blocks.

For example, variable length coding processing is performed for all blocks for one frame, and RUs for each block are
The average value of the appearance states of N (how many data in each block are all RUN) is calculated, and this value is set as the number of data to be processed in each block.

As for the block data from the next frame, the variable-length coding processing unit 9 receives the variable-length coding data when the set number of data are processed while the reading processing is performed in the order shown in FIG. Sends an encoding end command. The variable length coding processing unit 9 which has received this instruction executes the same operation as in the first embodiment.

(Third Embodiment) In the device of the third embodiment, when the RUN in the block data continues for a fixed number, the coding judgment unit 8 commands the end of the variable length coding. There is. The other points are the same as those of the apparatus of the first embodiment.

In this image communication apparatus, when the data of the block quantized by the quantization processing unit 5 is transferred to the coding judgment unit 8, the coding judgment unit 8 stores the data in the block in the order shown in FIG. Read data, number of RUNs and LEVE
L is transferred to the variable length coding processing unit 9. Then, the encoding determination unit 8 performs the read process, and when the RUN continuously appears in a predetermined number, the variable length encoding processing unit 9 ends the variable length encoding at that time. Send a command.

For example, when the predetermined number is 7,
When all of the block data 17 to 23 shown in FIG. 4 are RUN, the coding determination unit 8 instructs the variable-length coding processing unit 9 to end the variable-length coding processing, After that, all the data from 19 to 64 are treated as equivalent to RUN. The variable length coding processing unit 9 which has received the end command of the variable length coding processing executes the same operation as in the case of the first embodiment.

As described above, in the devices of the respective embodiments, by utilizing the fact that many RUNs appear in the difference block between the input block and the search block, encoding of block data is omitted on the way, and The amount of coded data of a frame is reduced, and at the same time, the time required for variable length coding processing is shortened.

Therefore, even if the number of frames that can be transmitted is increased and the transmission rate of the communication network used is low, a smooth screen can be reproduced on the receiving side. In addition, the image data can be transmitted quickly.

In each of the embodiments, the case where the moving image data is compressed and transmitted has been described. However, even when the still image data is transmitted by this image communication apparatus, the encoding determination unit 8 and the variable length encoding are used. The processing unit 9 functions to reduce the data amount by the same operation.

[0041]

As is apparent from the above description of the embodiments, in the image communication apparatus of the present invention, the processing speed in the variable length coding processing section can be improved, and the coded data amount of one frame can be improved. Can be reduced. As a result, a large number of frames can be quickly transmitted, and the receiving side can quickly reproduce a smooth moving image even under a low-rate communication network.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an image communication apparatus of the present invention,

FIG. 2 is a block diagram showing a configuration of a conventional image communication device,

FIG. 3 is a diagram showing block data quantized by an image communication device;

FIG. 4 is a diagram showing an order of variable-length coding processing of block data.

[Explanation of symbols]

 1 Intra-frame / inter-frame determination unit 2 Motion compensation processing unit 3 Difference processing unit 4 Transformation processing unit 5 Quantization processing unit 6 Inverse quantization processing unit 7 Inverse conversion processing 8 Encoding determination unit 9 Variable length encoding processing unit 10 Network Interface processing unit 11 Frame memory

Claims (3)

[Claims] 1. A difference processing means for calculating a difference between block data between a current frame and a previous frame, a quantizing means for quantizing difference processed block data, and a variable quantized block data. In an image communication apparatus comprising a variable length coding means for long coding, when the variable length coding means performs variable length coding on a partial number of data in the block, the rest of the block The image determination means for determining the value of the number of data as zero and instructing the variable length encoding means to end the variable length encoding processing of the data of the block is provided. Communication device. 2. The encoding determination means sets a time point for instructing the end of the variable length encoding process of a subsequent block, based on the appearance situation of zero data in variable length encoding of a plurality of blocks. The image communication device according to claim 1. 3. In variable length coding of the data of the block, when a fixed number of data are consecutively zero,
The image communication apparatus according to claim 1, wherein the encoding determination unit instructs the variable length encoding unit to end the variable length encoding process of the data of the block.