JPH09312847A - Coding method for dynamic image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the coding method for a dynamic image in which the effect of disturbance of an image is eliminated in a short time even on the occurrence of a transmission error in the transmission of a coded dynamic image. SOLUTION: Each of a series of frames forming a dynamic image is divided into a plurality of macro blocks and the dynamic image is coded in the unit of each macro block. In the dynamic image coding method, an INTER/INTRA mode management section 15 is added to a coding control section 7 having an INTER/INTRA mode identification function. As to frames at a prescribed interval in a series of the frames, macro blocks forming part of the frames are forcibly intraframe-coded. That is, as to frames of a prescribed period in a series of the frames forming a dynamic image, all macro blocks being components of the frames are forcibly intraframe-coded and even on the occurrence of a transmission error in a frame, the effect of the transmission error is eliminated by the frame.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of coding a moving image by mixing intra-frame coding and inter-frame coding, and more particularly, to a predetermined interval for a series of frames constituting the moving image. The present invention relates to a method of forcibly encoding all macroblocks of a frame for each frame.

[0002]

2. Description of the Related Art Conventionally, in order to reduce the amount of transmission when transmitting a moving image, the MPEG system or the H.264 standard is used. 261
A moving image is encoded by various methods such as a method. For example, H. The H.261 system uses an I
This is a standardized encoding method for video conferences using SDN. For information source encoding, interframe encoding that reduces redundancy in the time axis direction and intraframe encoding that reduces spatial redundancy in each frame are performed. An encoding method combining and is adopted.

Such H.264 An apparatus that performs the H.261 system encoding process has a configuration as shown in FIG. 4, for example, and inputs input moving image data (video input).
Interframe coding (INTER mode) and intraframe coding (INTRA mode) are switched for each frame for coding. The INTRA mode is mainly executed by the discrete cosine transform unit (DCT transform unit) 1 and the quantization unit 2. Here, the inter-frame coding (that is, the predictive coding) is performed by using the luminance component 1 for each frame forming the moving image.
It is performed for each macroblock (hereinafter, abbreviated as MB) of 6 × 16 pixels and two types of color difference components 8 × 8 pixels.
The CT is performed for each block of 8 × 8 pixels, the DCT transform unit 1 performs the discrete cosine transform for each block of 8 × 8 pixels, and the quantization unit 2 for the MB intra-coded by the DCT transform unit 1. Linear quantization is performed with the same step size except for the DC component.

On the other hand, the INTER mode is mainly executed by the inverse quantization unit 3, the inverse DCT conversion unit 4, the image memory 5 and the subtractor 6. Inverse quantizer 3 and inverse DCT transformer 4
Decodes the coded image data, the image memory 5 holds the decoded image data (frame) as variance value comparison image data with the next frame, and the subtractor 6 is held in the image memory 5. The difference between the frame and the next frame is calculated and input to the DCT conversion unit 1. INT like this
The ER mode and the INTRA mode are switched by the mode switching units 8 and 9 controlled by the encoding control unit 7, and either mode is determined by comparing the variance values of the original signal and the prediction error signal, for example. It Specifically, for example, when the scene of the moving image is switched, INTR
The frame is encoded in the A mode.

Numeral 10 is an adder, 11 is an in-loop filter, and INTER output from the encoding controller 7
/ INTRA identification flag, transmission / non-transmission identification flag, quantization characteristics, quantized output index output from the quantization unit 2, motion vector output from the image memory 5, filter ON output from the in-loop filter 11 OF
The F signal is input to a multiplexing unit (not shown). In addition, the multiplexing unit converts the encoded image data from the H.264 standard. A packet having a format according to a hierarchical structure such as 261 is generated, and a process of adding an error correction code such as BCH to each packet is performed.

[0006]

When a moving image is coded and transmitted through a low bit rate transmission line such as wireless, for example, p × 64 Kbps (where, p = 1 to 3 is used).
0) which is compatible with a relatively low bit rate. 26
One method is adopted. This H. The H.261 system is a system premised on the use of ISDN for the transmission path, and copes with transmission errors by adding a BCH code to the packet. Here, for example, 10 ^-4 to 1 like wire transmission
When the probability of error occurrence is relatively low, such as 0 ^-5 , the BCH code has an improvement efficiency of 10 ^-7 to 10 ^-8 with respect to the occurrence of a transmission error, and can be sufficiently used in practice. However, when a transmission path with relatively low transmission quality such as radio is used, fading may occur and the transmission packet itself may be lost. With respect to such a dropout, if there is still image transmission, there is no temporal concept between images, and therefore a retransmitting process can be performed, but for moving image transmission, retransmitting cannot be adopted.

Therefore, in moving image transmission, an error generated in a certain frame is carried over as it is, and since inter-frame coding is used as a coding method, the influence of the error also affects subsequent frames. It was out of order.
That is, the decoding side (reception device side) takes measures to prevent decoding of an erroneous frame, outputs a still image by the previous frame until a normal frame is received, and when a normal frame is received, The moving image will be output again. However, when the normal frame received first after the error occurs is the INTER mode frame, only the MB part in the INTER mode is updated, resulting in an uncomfortable image.

For example, as shown in FIG. 5, when the first frame a1 is decoded as a frame in INTRA mode on the decoding side without transmission error, a highly reproducible image a3 can be obtained, but the second frame b1 is obtained. If a transmission error occurs in the third frame c1 and the first frame a3 in which there is no transmission error is the still image (b3, c3).
Will be displayed as And the fourth frame d
When 1 is normally received, since the difference data of the second frame b1 and the third frame c1 is not prepared, the first frame data a2 is updated with the fourth frame data d2. Image d that should be originally obtained
The image d3 different from 1 is output. This situation is especially the case with H. H.261 is remarkable, and H.264 is notable. In the H.261 system, since the timing of inserting the intra-coded frame in the series of frames to be transmitted is not specified, it is not guaranteed when the original image is obtained.

The present invention has been made in view of the above-mentioned conventional circumstances, and can eliminate the influence of image disturbance within a short time even when a transmission error occurs in the transmission of an encoded moving image. It is an object of the present invention to provide a moving image encoding method capable of performing the following.

[0010]

In order to achieve the above object, a moving picture coding method according to the present invention divides each frame into a plurality of macroblocks for a series of frames constituting the moving picture. In the moving picture coding method in which each macroblock is coded as a unit, all the macroblocks are forcibly intraframe-coded with respect to the frames at predetermined intervals in the series of frames. That is, for a frame having a predetermined cycle in a series of frames forming a moving image, all the macroblocks forming the frame are forcibly intraframe-coded. Thus, even if a transmission error occurs in a certain frame, the influence of the transmission error can be eliminated by the frame.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A moving image coding method according to an embodiment of the present invention will be described with reference to the drawings. The method of the present embodiment is implemented by an encoding processing device having a configuration similar to that shown in FIG. 4, and in the encoding processing device of the present embodiment, the encoding control unit 7 having the INTER / INTRA mode identification function. The INTER / INT having the configuration shown in FIG.
The RA mode management unit 15 is added. In FIG. 1, the DCT transform unit 1 and the quantization unit 2 are collectively shown as an information source coding unit 16.

INTER / INTRA mode management unit 15
Includes a timer 17 that measures time, an INTRA mode frame activation processing unit 18 that detects the timing of the INTRA mode based on the time counting by the timer 17, and all macro blocks that are activated by the activation processing unit 18 to form a frame. INT for turning on the INTRA frame forced insertion flag for forcibly intraframe coding
RA frame forced insertion flag unit 19, INTRA mode frame flag unit 20 for turning on the INTRA mode frame flag for intra-frame coding of macroblocks, INTRA frame forced insertion flag and INT
And an INTRA mode frame creation section 21 for synthesizing an INTRA mode identification flag into a normal identification signal based on the RA mode frame flag and outputting it to the multiplexing section.

The encoding method of the present embodiment is carried out by the apparatus having the above-mentioned configuration in accordance with the procedure shown in FIGS. The MB is forcibly intra-coded. For example, every two frames (a first frame, a fourth frame, a seventh frame, ...) Of a series of frames are configured by forcibly intra-coding all MBs, and regarding the remaining frames. Is INTE
It is composed of MB coded according to the R / INTRA identification flag. The process of forcibly creating a frame of only intra-coded MBs is interrupted at intervals of, for example, 1 second based on the time measured by the timer 17, and INT
The RA frame forced insertion flag is turned on (step S
1). That is, according to this cycle, frames at a predetermined interval in the series of frames are selected as targets of the forced processing.

In the encoding control process for encoding the MB in the frame, it is judged whether the BM currently executing the process is the last BM in the frame (step S11) and the last B is determined.
If it is M, the processing in the INTRA mode is unnecessary, so the INTRA mode frame flag is set to OFF (step S12). Next, it is determined whether the BM that is currently executing the process is the first BM in the frame (step S13), and further it is determined whether the INTRA frame forced insertion flag is ON (step S14).

As a result, it is not the first BM or INT
If the RA frame compulsory insertion flag is not turned on, normal encoding processing according to the INTER / INTRA identification flag is performed (step S15). On the other hand, the first B
If it is M and the INTRA frame forced insertion flag is ON, the INTRA mode frame flag is set to O.
N to force the INTRA mode encoding to be executed (step S16), and all the BMs forming the frame are intra-frame encoded. Therefore, by performing the compulsory processing in the INTRA mode based on the interrupt of the predetermined cycle as described above, all the BMs are intermittently included in the frames in which the BMs are intra-coded in the series of frames forming the moving image. Becomes

For example, first frame, fourth frame, 7
When an error occurs in the second frame in the transmission of the frame in which all MBs are forcibly intra-coded for the first frame, ..., the receiving device (encoding side) redisplays the first frame. Then, when the third frame is received without error, the third and subsequent frames are decoded and displayed. Here, since the second frame does not exist, the correlation between the frames is lost, and the third frame is an image that is greatly affected by the transmission error. However, 4 received immediately after this
Since all BMs in the frame are intra-coded in the frame, the image disturbance based on the third frame is immediately resolved, and the images in the fifth and subsequent frames having inter-frame correlation are also clear. Become. The cycle of forcibly executing the INTRA mode as described above is preferably as short as possible in order to quickly eliminate transmission errors, but the amount of transmission data increases as the INTRA mode is executed. It can be arbitrarily set as required in consideration of the above.

[0017]

As described above, according to the moving picture coding method of the present invention, all the macroblocks forming a frame are forcibly forced with respect to a frame at a predetermined interval in a series of frames. Since the intra-frame coding is performed, it is possible to eliminate the influence of the image disturbance due to the transmission error in a short time.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a main part of an apparatus for implementing an encoding method according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a procedure of interrupt processing according to an embodiment of the present invention.

FIG. 3 is a flowchart showing a procedure of encoding control processing according to an embodiment of the present invention.

FIG. 4 is a configuration diagram showing a main part of an apparatus for performing an encoding method.

FIG. 5 is a conceptual diagram for explaining the influence of transmission error.

[Explanation of symbols]

1 ... DCT conversion unit, 2 ... Quantization unit, 7 ...
-Encoding control unit, 17 ... timer, 18 ... IN
TRA mode frame activation processing unit, 19 ... INTR
A frame forced insertion flag section, 21 ... INTRA mode frame creation section,

Claims (1)

[Claims] 1. A method of encoding a moving image, wherein each frame is divided into a plurality of macroblocks for a series of frames forming the moving image, and each macroblock is encoded as a unit. The method for encoding a moving image is characterized in that all the macroblocks are forcibly intraframe-encoded with respect to frames having a predetermined interval.