JPH11205787A - Picture communication method and its equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of a picture even when the bit rate varies largely in real time at the time of using a data transmission line generating large errors such as a radio line. SOLUTION: An error control means 3 restores a communication error by resending erroneous data when a picture data communication error is generated. In addition the means 3 informs a successive picture control means 7 of a bit rate obtained as the result of error control. The means 7 decides a parameter to use for encoding a picture through the use of an encoding parameter set in a coding parameter set in a coding parameter table 7a based on the reported bit rate and informs an encoder 6 of it. The encoder 6 generates picture data by encoding video data through the use of the designated encoding parameter to generate such picture data for reproducing an optimum picture in spite of the variation of a bit rate to transmit to an opposite terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image communication method and an image communication apparatus used for a communication path having a high probability of occurrence of a communication error such as a radio line.

[0002]

2. Description of the Related Art In recent years, high-speed data communication over a wireless line has been realized with the start of a PHS service, so that a moving image such as a videophone, which has been conventionally realized using a wired line such as an ISDN or a public network. Application of communication applications to wireless lines has been required.

Conventionally, a moving image communication apparatus generally has an error control means. This error control means adds header information necessary for an automatic retransmission request (ARQ) to the encoded image data and transmits the data to the partner terminal.

Further, data for use is always stored again in the transmission buffer, and when a retransmission of data is requested from the partner terminal due to a communication error, the designated data is taken out from the transmission buffer and transmitted again. As a result, image data transmission without communication errors becomes possible.

Since the number of retransmissions changes depending on the degree of occurrence of a communication error, the error control means 3 performs an operation every certain time to control the bit rate which changes successively in image data transmission. Notify the means.

[0006] The image quality control means instructs the encoder to use parameters for encoding so as to generate image data at substantially the same rate as the bit rate of the image data sent from the transmission buffer.

As a control method at this time, for example, a method of fixing the Q value and controlling the frame rate in accordance with the change of the bit rate and the input image, or a method of setting the target value to the frame rate and setting the bit rate and the input image There has been a method of controlling the Q value in accordance with the change of. In this manner, an image communication device that is prepared for a communication error is realized.

[0008]

However, in the conventional image coding system and the image communication apparatus using the same, a large bit error or a large bit error occurs when a large communication error occurs on a line. There is a problem that image quality is deteriorated such as image reproduction.

It is an object of the present invention to provide an image communication method and an image communication apparatus which ensure good image quality even with a bit rate fluctuation in such an image communication apparatus.

[0010]

In order to solve the above problem, the present invention uses a parameter (Q
Value / frame rate) control range is set in advance for each predetermined bit rate width, and image quality control is performed using a method of performing encoding using parameters in a parameter control range corresponding to a change in bit rate. .

According to the present invention, good image quality can be ensured even if the bit rate fluctuates due to the occurrence of a communication error.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the first aspect of the present invention, a parameter control range for image coding such as a quantization step and a frame rate corresponding to each bit rate range is stored in a table for each bit rate. Having, and to encode the video data using the parameters of the parameter control range corresponding to the bit rate according to the change of the bit rate for image communication,
This has the effect of performing image coding using optimal coding parameters to reproduce good images for each bit rate.

According to a second aspect of the present invention, there is provided a line interface for controlling data communication with a partner terminal through a line, and in the case of multimedia communication, voice / data and images are multiplexed and the data is transmitted to the line interface as one data. When a multiplexing unit that transmits and separates the image, audio, and data from the data received from the partner terminal and a communication error is detected in the data communicated through the line interface and the multiplexing unit and an error is found. 2. An error control unit that recovers an error, an image quality control unit that controls encoding using the method according to claim 1, according to a bit rate notified by the error control unit, and an instruction from the image quality control unit. An encoder for encoding video data to be input using parameters, and an image encoded by the encoder And a transmission buffer for temporarily storing data and transmitting the data to an error control means. It has the effect of generating and transmitting data.

According to a third aspect of the present invention, a bit rate range for setting a parameter control range is set so as to partially overlap an adjacent bit rate range, and two coding parameter ranges exist for the bit rate. Is to use the current parameter control range,
There is an effect that the switching of the coding parameter control range has hysteresis.

(Embodiment 1) FIG. 1 is a functional block diagram of an image communication apparatus according to an embodiment of the present invention, and FIG. 2 is a conceptual diagram showing the relationship between codes for each bit rate and a parameter control range. Hereinafter, the operation of the image communication apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, reference numeral 1 denotes a communication line such as a PHS service. A line interface 2 enables data communication through the communication line 1. Reference numeral 4 denotes a multiplexing unit that multiplexes image data, audio data, and data into one serial data when necessary. 3
Is a communication error control means for taking appropriate measures against a communication error occurring in image data exchanged with the partner terminal and recovering the communication error.

Reference numeral 6 denotes an encoder that performs compression processing on input video input data using a predetermined algorithm to generate encoded image data. Reference numeral 5 denotes a transmission buffer for temporarily storing the image data generated by the encoder 6. Reference numeral 7 denotes an image quality control unit that controls parameters such as a quantization step (hereinafter, Q value) and a frame rate used when encoding video data. 7a is an encoding parameter table that defines an encoding parameter control range for each bit rate.

The operation of the image communication apparatus configured as described above will be described below.

The line interface 2 establishes a data communication channel at a constant communication speed when connected to the partner terminal through the communication line 1. In the case of multimedia communication, the error control means 3 multiplexes the image and audio / data and transmits the multiplexed image. The error control means 3 adds header information necessary for an automatic retransmission request (ARQ) to the encoded image data and transmits the data to the partner terminal.

When a retransmission of data is requested from the partner terminal due to the occurrence of a communication error, the designated data is again taken out from the transmission buffer and transmitted. As a result, image data transmission without communication errors becomes possible. In such a retransmission method, the number of retransmissions changes depending on the degree of occurrence of a communication error, so that the effective bit rate of image data transmission changes. The error control unit 3 notifies the image quality control unit 7 of the bit rate that changes sequentially by performing the calculation every certain time.

For video input, an image in a predetermined format is input at a constant period (for example, CIF format: 352 × 288 [dot], 30 every / second). The encoder 6 has a predetermined coding symbol (for example, ITU-T Recommendation H.263).
Is used to encode video data to generate image data.

The picture quality control means 7 refers to the coding parameter table 7a corresponding to the bit rate notified from the error control means 3 and instructs the coding unit 6 on the parameters to be used for coding. 5 so as to generate image data at substantially the same rate as the bit rate of the image data sent out.

At this time, in the coding parameter table 7a, for example, as shown in FIG. 2, the control range of each coding parameter is previously determined according to three bit rate ranges (N ₁ = N ₂ , M ₁ = M ₂ ). Is set. In general, the larger the bit rate, the larger the frame rate and the smaller the quantization step, the greater the amount of image data that can be encoded. The frame rate relates to the temporal resolution of the image, and the quantization step relates to the spatial resolution of the image, while the image quality depends on a combination of both the temporal resolution and the spatial resolution.

The coding parameter control range defined for each bit rate in FIG. 2 is represented as a set of combinations of temporal resolution and spatial resolution at which the image quality is optimized for each bit rate. At this time, it goes without saying that the characteristics of the coding parameter control range need not be rectangular as shown in FIG. 2, but may be other shapes.

In the example of FIG. 2, 0 <bit rate ≦ N
1 for Q₁<Q value <Q_TwoAnd FR _Two<Frame rate
<FR₁Use values in the range of as encoding parameters
(Characteristic A). Also, N_Two<Bit rate ≦ M₁Then Q '
₁<Q value <Q '_TwoAnd FR '_Two<Frame rate <F
R '₁Use values in the range of as encoding parameters
(Characteristic B). Also, M₁<Q "at bit rate₁<Q
Value <Q ”_TwoAnd FR " _Two<Frame rate <FR ”₁
Use values in the range of
C). The image data stored in the transmission buffer 5 is error-free.
It is extracted from the control unit 3 and sent to the partner terminal.

(Embodiment 2) The parameter table per bit rate in Embodiment 1 is defined as M ₁ > N ₁ > N ₂ ,
It is configured such that M ₁ > M ₂ > N ₂ . At this time, two parameter tables correspond to the bit rates in the range of N ₁ > bit rate N ₂ and M ₁ > bit rate> M ₂ .

When N2 ≦ bit rate <N1 from the state of bit rate <N2, the parameter table of the characteristic A is continuously used, and after the bit rate ≧ N1, the parameter table of the characteristic B is used.

Conversely, when N2 ≦ bit rate <N1 from the state of M2> bit rate ≧ N1, the table of the characteristic B is continuously used, and after the bit rate <N2, the parameter table of the characteristic A is used. Use

In this way, it is possible to prevent the parameter table to be referred from being switched due to a small change in the bit rate at the boundary of the parameter table, and to prevent the deterioration of the image quality.

[0030]

As described above, according to the present invention, an image is encoded and data is encoded so that the image has high error resilience even on a line having a large communication error and reproduces an optimal image even with a change in bit rate. Can be transmitted.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an image communication device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of a coding parameter control range for each bit rate of the image communication device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Communication line 2 Line interface 3 Error control means 4 Multiplexing means 5 Transmission buffer 6 Encoder 7 Picture quality control means

Claims (4)

[Claims] 1. A table having a parameter control range for image coding such as a quantization step and a frame rate corresponding to each bit rate range as a table for each bit rate, and according to a change in the bit rate for image communication. An image communication method, wherein video data is encoded using a parameter in the parameter control range corresponding to a bit rate. 2. A line interface for controlling data communication with a partner terminal through a communication line. In the case of multimedia communication, voice / data and images are multiplexed and data is sent out as one data to the line interface. A multiplexing unit that separates the data received from the terminal into video, audio, and data, and whether there is a communication error in the data communicated through the line interface and the multiplexing unit is checked. An error control unit for recovering, an image quality control unit for controlling encoding using the method according to claim 1 according to a bit rate notified from the error control unit, and a parameter specified by the image quality control unit. An encoder for encoding the input video data, and temporarily storing the image data encoded by the encoder. Product image communication apparatus characterized by being composed of the transmission buffer to be sent to the error control means. 3. A bit rate range for setting a parameter control range is set so as to partially overlap an adjacent bit rate range. If two coding parameter ranges exist for the bit rate, the current parameter control range is set. 2. The image communication method according to claim 1, wherein a range is used. 4. A line interface for controlling data communication with a partner terminal via a communication line, and in the case of multimedia communication, multiplexing voice / data and image, sending data to the line interface as one data, and A multiplexing unit that separates the data received from the terminal into video, audio, and data, and whether there is a communication error in the data communicated through the line interface and the multiplexing unit is checked. An error control unit for recovering, an image quality control unit for controlling encoding using the method according to claim 1 according to a bit rate notified from the error control unit, and a parameter specified by the image quality control unit. An encoder for encoding the input video data, and temporarily storing the image data encoded by the encoder. A transmission buffer for sending to the accumulation error control means, a bit rate range for setting a parameter control range is set so as to partially overlap an adjacent bit rate range, and two coding parameter ranges are set for the bit rate. An image communication device characterized by using a current parameter control range if it exists.