JP2003299091A - Image encoder and image encoding method, image recorder, and image transmitter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image encoder and an image encoding method which can prevent overflow or underflow of an occupied amount of a VBV (video buffering verifier) buffer due to the amount change of a generated code bit amount by compositing in a split image encoder, and to provide an image recorder and an image transmitter. <P>SOLUTION: The upper limit and lower limit are set for the occupation amount of the VBV buffer controlled by each split image encoder, or the upper limit is set for the occupied amount of the VBV buffer controlled by each split image encoder to adjust an initial value of the occupation amount of the composited VBV buffer. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, an HDTV.
Image coding apparatus and method for compressing and coding a moving image signal such as (High Definition TeleVision) signal, image recording apparatus for recording the coded signal, and image transmission apparatus for transmitting the coded signal Regarding

[0002]

2. Description of the Related Art MPEG2 is used as a moving image coding system.
The standard (ISO / IEC13818) is widespread. In this MPEG2, the concept of a profile that mainly defines the classification of functions (difference in syntax) and a level that defines the difference in the amount of processing such as image size is introduced, and the coding performance that can be supported is classified into classes. ing. For example, 720 x 480 pixels, 60 fields /
For the image of ITU-R601 of second, MP @ ML (Mai
n Profile at Main Level) is 1920 x 1080 pixels and M for HDTV images with 60 fields / sec.
P @ HL (Main Profile at High Level) is normally used.

An encoder of the MPEG2 standard uses a so-called VBV buffer that is conceptually connected to the output of the encoder to control the buffer state at the time of reception on the decoder side. The encoder side controls the data amount of the bitstream by preventing both overflow and underflow. In order to perform accurate control, it is necessary to accurately obtain the bit amount (input bit amount) input to the VBV buffer during one picture period, the VBV buffer occupation amount calculated by the input bit amount, and the like.

On the other hand, an apparatus for encoding a moving picture signal having a screen configuration with a large number of pixels such as an HDTV signal, for example, MP.
A device that executes @HL encoding requires very high-speed processing, and thus is difficult to realize and is a very expensive device. On the other hand, a device that executes MP @ ML encoding and decoding may be smaller and have a lower operation speed than a device of MP @ HL, and it is widely used because it has already been integrated into an LSI. Therefore, it can be used very inexpensively. Therefore, for example, in the moving picture coding or decoding apparatus disclosed in Japanese Patent Laid-Open No. 10-234043 or 2001-346201, a moving picture signal having a screen configuration with a large number of pixels, such as an HDTV signal, is generated. A method of performing MP @ HL encoding or decoding by dividing into a plurality of screens, encoding or decoding the signals of each divided screen with an MP @ ML device, and integrating the processing results is known. Has been.

As described above, one image signal is divided,
In an image encoding device that encodes using a plurality of encoders, a target generated code bit amount is appropriately allocated to each encoder in order to obtain high image quality. For example, in the moving picture coding apparatus described in Japanese Patent Laid-Open No. 10-234043, coding is controlled so that the code amount generated in each divided image area is uniform. Also,
In Japanese Patent Laid-Open No. 2001-346201, the bit rate of each encoder is set according to the complexity of each divided image, and the sum of the output bit rates of each encoder is made to match the target bit rate of the integrated bit stream. Doing things.

In such an image coding apparatus having a plurality of encoders, the bit rate assigned to each encoder and the target generated code bit amount change depending on the picture, depending on the complexity of the image. Therefore, in such an image coding device, when the plurality of encoders divide and control the generated code bit amount by the VBV buffer, the input bit rate and the input of picture unit of the VBV buffer controlled by each encoder are input. The bit amount also changes for each picture. In order to appropriately control the amount of generated code bits in the encoding process by the VBV buffer, it is necessary to be able to cope with the case where the bit rate and the input bit amount change in picture units.

When a bit stream of a plurality of divided images is combined into one integrated bit stream, a part of the header data value in each bit stream is rewritten according to the MPEG standard, and the code bit amount of the header data is changed. Change. Therefore, the total bit amount of the combined bitstream and the total bit amount of each of the pre-combined bitstreams do not match. As a result, the value of the input bit amount of the VBV buffer and the value of the VBV buffer occupation amount are different before and after combination.

[0008]

Further, since the increase / decrease amount of the generated code bit amount due to the combination of the bit streams differs depending on the picture type, the code bit amount of the combined bit stream and the VBV buffer input bit amount are Each time, the amount of change greatly varies by that amount, which causes the variation width of the VBV buffer occupancy of the combined bitstream after combining to be larger than that before combining. As a result, before combining, VBV
Even if the buffer occupancy is controlled so as not to overflow or underflow, overflow or underflow may occur after composition.

The present invention has been made in view of the above problems. A first object of the present invention is to determine the amount of change in the generated code bit amount due to synthesis when one image signal is divided into a plurality of images and encoded. An object of the present invention is to provide an image encoding device and an image encoding method capable of preventing the overflow or underflow of the post-combination VBV buffer occupation amount.
A second object of the present invention is to provide an image recording device using the above image encoding device and image encoding method. A third object of the present invention is to provide an image transmission device using the above image encoding device and image encoding method.

[0010]

In order to solve the above-mentioned problems, an image coding apparatus according to the present invention codes N divided image signals obtained by dividing an input image signal to generate N bit streams. Then, the N first-type VBVs (vide) that virtually buffer the N bit streams are provided.
buffering verifier) N divided image encoding means including a buffer, integrating means for integrating the N bitstreams into one bitstream, and virtually buffering the integrated bitstreams. A VBV buffer of two types, and a combined change amount that is a change amount of a code bit amount of each picture of the integrated bitstream that occurs when the N bitstreams are integrated into one bitstream. The N number of the varied bitstreams of the combined bitstream in the second type VBV buffer are set to fall within the maximum and minimum occupancy of the second type VBV buffer. The variation range of the occupancy of each type 1 VBV buffer is limited.

Specifically, the occupied amount of the second type VBV buffer which is changed by the combined change amount is equal to the second occupied amount.
The upper limit of the occupancy of each of the N first-type VBV buffers is set so as not to exceed the maximum occupancy of the second VBV buffer of the second type, and the upper limit of the occupancy of each of the N first-type VBV buffers is changed. The occupancy is the same as the second type V
Do not become smaller than the minimum occupancy of the BV buffer,
A lower limit is set for the occupancy of each of the N first-type VBV buffers.

Alternatively, the occupancy of the second type VBV buffer, which is changed by the combined change amount, does not become larger than the maximum occupancy of the second type VBV buffer. An upper limit is set on the occupancy of each VBV buffer, and the occupancy of the second type VBV buffer that is changed by the combined change amount is the second type VBV buffer.
The initial value of the occupancy in the second type VBV buffer is adjusted so as not to become smaller than the minimum occupancy of the V buffer.

In order to solve the above-mentioned problems, the image coding method of the present invention divides an input image signal into N divided image signals and encodes the N divided image signals to obtain N divided image signals. An image encoding method for generating a bitstream and integrating the N bitstreams into one bitstream, wherein each of the N bitstreams is represented by N
Virtual buffers in each of the VBV buffers of the first type, the integrated bitstreams in the VBV buffers of the second type, and the N bitstreams in one bit. Occupancy of the integrated bitstream in the VBV buffer of the second type, which is changed by a combined change amount that is a change amount of the code bit amount of each picture of the integrated bitstream that occurs when the integrated bitstream is integrated. To
The fluctuation range of the occupancy of each of the N first-type VBV buffers is limited so that the occupancy of the second VBV buffer is within the maximum and minimum occupancy ranges.

Specifically, the occupancy of the second type VBV buffer, which is changed by the combined variation, is
The upper limit of the occupancy of each of the N first-type VBV buffers is set so as not to exceed the maximum occupancy of the second VBV buffer of the second type, and the upper limit of the occupancy of each of the N first-type VBV buffers is changed. The occupancy is the same as the second type V
Do not become smaller than the minimum occupancy of the BV buffer,
A lower limit is set for the occupancy of each of the N first-type VBV buffers.

Alternatively, the occupancy of the second type VBV buffer, which is changed by the combined change amount, does not become larger than the maximum occupancy of the second type VBV buffer. An upper limit is set on the occupancy of each VBV buffer, and the occupancy of the second type VBV buffer that is changed by the combined change amount is the second type VBV buffer.
The initial value of the occupancy in the second type VBV buffer is adjusted so as not to become smaller than the minimum occupancy of the V buffer.

In order to solve the above-mentioned problems, the image recording apparatus of the present invention encodes N divided image signals obtained by dividing an input image signal to generate N bit streams, N divided image coding means including N first type VBV buffers for virtually buffering each bit stream, and integrating means for integrating the N bit streams into one bit stream. A second type VBV buffer that virtually buffers the integrated bitstream and a recording unit that records the integrated bitstream on a recording medium, and one of the N bitstreams. Fluctuated by the combined change amount that is the change amount of the code bit amount of each picture of the integrated bitstream that occurs when the image is integrated into the other bitstream. The N first type buffers are arranged so that the combined bitstream occupancy of the second type VBV buffers falls within the maximum and minimum occupancy ranges of the second type VBV buffers. Limit the range of variation of the occupancy of each VBV buffer.

In order to solve the above problems, the image transmission apparatus of the present invention encodes N divided image signals obtained by dividing an input image signal to generate N bit streams, N divided image coding means including N first type VBV buffers for virtually buffering each bit stream, and integrating means for integrating the N bit streams into one bit stream. A second type VBV buffer for virtually buffering the integrated bitstream, and a transmission means for transmitting the integrated bitstream, wherein the N bitstreams are one bitstream The integration is changed by a combined change amount that is a change amount of the code bit amount of each picture of the integrated bitstream that occurs at the time of integration. The occupancy of the second type of the VBV buffer of the bit stream, the second type of VB
The variation range of the occupancy of each of the N first-type VBV buffers is limited so that the V buffer occupies the maximum occupancy and the minimum occupancy.

According to the present invention described above, when one image signal is divided into a plurality of divided images and encoded, the total amount of input bits for each picture is calculated in the VBV buffer of the bit stream of each divided image. Then, the divided images are allocated to the encoding process according to the image complexity. As a result, the value of the input bit amount of the VBV buffer can be changed for each picture, and the VBV of the bit stream of each divided image can be changed.
You can control the buffer occupancy so that it does not overflow or underflow. As a result, the VBV buffer occupancy of the combined bitstream is constant on average in GOP units or in a wider range, and
Appropriate coding can be performed without an average increase or decrease. Further, the variation range of the occupied amount of the VBV buffer of the bit stream of each divided image is limited, and the post-combination VBV resulting from the increase / decrease in the generated code bit amount due to the combination
Prevents buffer occupancy overflow and underflow.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image coding apparatus and an image coding method of the present invention, and an image recording apparatus and an image transmission apparatus using the same will be described below with reference to the accompanying drawings. First Embodiment In the image coding apparatus according to the present embodiment, a picture of a VBV buffer controlled by each divided image coding apparatus according to an externally set bit rate, for example, a bit rate written in a sequence header. The total amount of input bits for each of the divided images is calculated and allocated to each divided image encoding device according to the image complexity of the divided image, the occupied amount of each VBV buffer is obtained, and the encoding bit rate of the divided image encoding device is calculated. Appropriate control. However, the variation range of the post-combination VBV buffer occupation amount is wide due to the increase / decrease in the generated code bit amount due to the combination, and overflow or underflow may occur. In order to prevent this, the variation range of the occupied amount of the VBV buffer controlled by each divided image coding device is limited. For example, the VBV buffer occupancy amount has predetermined upper and lower limits.

[Structure of Moving Image Encoding Device] FIG. 1 is a block diagram showing the structure of a moving image encoding device 101 as one embodiment of the image encoding device of this embodiment. The moving picture coding device 101 includes a screen dividing device 110, first to fourth
The divided image coding devices 120-1 to 120-4, the bitstream integration device 150, and the control device 170. The screen dividing device 110 divides each picture of the input moving image signal into four image signals for each predetermined image area, and each of the first to fourth divided image encoding devices 120-1.
To 120-4. As shown in FIG. 2, the moving image signal input to the moving image encoding apparatus 101 is an HDTV video signal, and the luminance signal is 1920 horizontal pixels × 1080 vertical pixels.
The line and color difference signals are an interlace signal of 960 horizontal pixels × 1080 vertical lines in a 4: 2: 2 format. The frame rate is 30 frames / second.

The screen dividing device 110 first converts a luminance signal into 1440 pixels in the horizontal direction and a color difference signal into 720 pixels in the horizontal direction by a filtering process. In the vertical direction, MP
Since it is determined by the EG2 standard that the interlaced image must be a multiple of 32 lines, dummy data of 8 lines is added below the image for both the luminance signal and the color difference signal to make 1088 lines. Then, the screen division device 110 divides the image whose size has been converted in this way into four areas A, B, C, and D as shown in FIG. It is output to the fourth divided image encoding devices 120-1 to 120-4. For example, the luminance signal is divided into four signals of horizontal 720 pixels × vertical 544 lines.

First to fourth divided image coding devices 120-
1-120-4 (divided image coding devices A, B, C, D)
Encodes the image signal of each divided area input,
Generate an MPEG2-MP @ ML bitstream,
Output to the bitstream integration device 150. In the bit stream output from the divided image encoding device 120-i (i = 1 to 4), the independent values of the image size and the frame rate are within the range of MP @ ML, but they are related to each other. The sample rate (number of pixels per second) slightly exceeds that range and is not exactly MP @ ML. Here, for the sake of simplicity, MP @ M is used for convenience.
The expression L is used. FIG. 3 illustrates an example of the configuration of the divided image coding device 120-i (i = 1 to 4) by taking the divided image coding device 120-1 (divided image coding device A) as an example. For example, the divided image coding device 120-i
Each of (i = 1 to 4) is a processor 130-i (i =
1 to 4) and output buffer 131-i (i = 1 to 4)
Have. In order to control the state of the output buffer at the time of receiving on the decoder side, the VBV buffers 132-i (i = 1 to 4), which are input buffers of the virtual decoder, are respectively encoders 130-i (i = 1 to 4). , Is connected conceptually. The encoders 130-i (i = 1 to 4) are
The code bit amount Sa, n, Sb, n, Sc, n, Sd, n generated for each picture for calculating the VBV buffer occupancy is V
Input to the BV buffer 132-i (i = 1 to 4).

The processors 130-i (i = 1 to 4) are
It is a general MPEG2-MP @ ML encoder,
The input image signal is encoded by MPEG2. Further, the generated bit stream is output to the output buffer 131-i (i = 1 to 4) on a picture-by-picture basis. The four encoders 130-i (i = 1 to 4) apply VBV buffers 132-i (i) to the input divided image signals.
= 1 to 4) and the target value of the code bit amount instructed by the control device 170, the bit rate and the generated code bit amount are controlled, and for example, for each divided image of the previous picture. Variable-rate encoding according to complexity is performed, and an MPEG2-MP @ ML bit stream is output to the buffers 131-i (i = 1 to 4). Further, each encoder 130-i (i = 1 to 4) has an amount related to the complexity of the encoded divided image, for example, the code bit amount Sa, n, Sb, n, Sc, n generated for each picture.
Sd, n, average quantizer scale code (quantizer scale c
The average value of ode) Qa, n, Qb, n, Qc, n, Qd, n (n is a picture number) is calculated and transferred to the control device 170.

The buffer 131-i (i = 1 to 4) temporarily stores the encoded bit stream input from the encoder 130-i (i = 1 to 4), and the control device 170.
It is output to the bitstream integration device 150 at the bit rate instructed by. Therefore, from the first to fourth divided image coding devices 120-1 to 120-4,
An MPEG2-MP @ ML bit stream is output. The format of the moving image signal input to the moving image encoding apparatus 101 is 4: 2: 2, but since it is converted to the 4: 2: 0 format in the divided image encoding apparatus 120-i,
The bit stream output from the divided image coding device 120-i is a bit stream of a moving image signal in the 4: 2: 0 format.

The bitstream integration device 150 has a first
~ Fourth divided image coding device 120-i (i = 1 to 4)
The four MPEG2-MP @ ML bit streams output from are combined to generate an MPEG2-MP @ HL bit stream. That is, four MPEG2-
One MPEG2-MP @ HL bit stream is obtained by decomposing the MP @ ML bit stream in slice units and reconstructing them into one bit stream. FIG. 4 is a diagram for explaining the arrangement of bit streams decomposed in slice units in the present embodiment.

The control device 170 controls the moving picture coding device 10.
Each component is controlled so that 1 performs a desired operation. The control device 170 uses the post-combination VBV buffer calculation unit 171,
The control unit 172 is included. Post-combination VBV buffer operation unit 17
1 calculates the VBV buffer occupancy after combining. Specifically, the post-combination VBV buffer operation unit 171 outputs the generated code bit amount Sa, n, Sb, n, Sc, n for each picture output from the divided image encoding device 120-i (i = 1 to 4).
The generated code bit that is extracted by decoding the image data of the integrated bit stream in the virtual VBV buffer using Sd, n and the combined change amount ΔT that is the increase / decrease amount of the code bit amount due to the combination described later. The total amount Sn is calculated, and the input bit amount IBn to the VBV buffer of the integrated bit stream is calculated according to the bit rate R set from the outside, thereby calculating the VBV buffer occupation amount Bn of the integrated bit stream. . FIG. 5 is a block diagram showing an example of the configuration of the post-combination VBV buffer operation unit 173. As shown in FIG. 5, the post-combination VBV buffer operation unit 173 includes a generated code bit amount operation unit 165, an input bit amount operation unit 167, and an occupation amount operation unit 168.

The generated code bit amount adding unit 165 generates the generated code bit amount Sa, n, Sb, n for each picture transferred from each divided image coding device 120-i (i = 1 to 4).
Add Sc, n and Sd, n. In the present embodiment, as an example, four values are simply summed. And to that total,
A change amount, which is a change in the code bit amount due to composition of each picture, is added. As will be described later, in the present embodiment, -1032 bits are added for I pictures, and +1200 bits are added for P pictures and B pictures, respectively.

The input bit amount calculation unit 167 inputs the input bit amount I for each picture into the VBV buffer of the integrated bit stream based on the bit rate R set from the outside.
Find Bn. To cancel the accumulation of the error of the input bit amount, the difference between the theoretically correct input bit amount and the actually input bit amount was actually input for each picture number for which the theoretical input bit amount is an integer value. Add to the bit amount. For example, the picture rate P is 30 Hz and the bit rate R
Is 10 Mbps, the theoretical value of the input bit amount IBn for each picture is IBn = R / 10/3 = 3333.
33.33333333, the sum of the input bit amounts for each of the three pictures is 3 × IBn = 3 × R / P = R / 10 = 100.
It becomes 0000. The actually input bit amount per picture is 333333, and 0.333333 ... Is discarded. This error gradually accumulates. Therefore, in the input bit amount calculation unit 162, if 1 is added to the actual input bit amount for every 3 pictures, the actually input bit amount is 3 × 333333 + 1 = 10000.
00, a correct bit amount can be obtained without accumulating errors. In this way, the input bit amount IBn for each picture is obtained.

The occupancy calculation unit 168 calculates, for example, the generated code bit amount based on the input generated code bit amount for each combined picture and the input bit amount for each picture by VB.
The VBV buffer occupancy is obtained by subtracting from the buffer occupancy held by the V buffer and adding the input bit amount to the VBV buffer occupancy.

The control unit 172 controls the moving picture coding apparatus 101.
Controls each component so as to perform a desired operation. For example, the control unit 172 controls each divided image coding device 120-i (i = 1 according to the bit rate set from the outside.
~ 4) control the VBV buffer 132-i (i = 1 to 1)
4) The total amount of input bits for each picture is accurately calculated, and is allocated to each divided image coding device 120-i (i = 1 to 4) according to the image complexity of each divided image. As shown in FIGS. 1 and 3, the control unit 172 controls the V for each picture.
BV buffer input bit amount IBa, n, IBb, n, IBc,
n and IBd, n are the divided image coding devices 120-i, respectively.
(I = 1 to 4).

In addition, for example, the control unit 172 controls the GOP
The generated code bit amount of the remaining pictures is allocated to each divided image coding device 120-i (i = 1 to 4) for each picture according to the image complexity of each divided image, and the generated code bit for each picture is assigned. Indicate the target value of quantity. Based on that, each divided image coding device 120-i (i = 1 to 4)
Performs variable rate coding on the input image signal.

The input bit amounts IBa, n, IBb, n, IBc, n, IBd, n and the generated code bit amounts Sa, n, Sb, n, Sc, n, Sd, n input from the control unit 172 are Originally, the encoder 130-i (i = 1 to 4) sets the generated code bit amount to V
Subtract from the buffer occupancy held by the BV buffer,
The occupancy amount Ba, n, Bb, n, Bc, n, Bd, n of the VBV buffer 132-i (i = 1 to 4) is calculated by adding the input bit amount to the occupancy amount of the VBV buffer. The VBV buffer 132-i (i = 1 to 4) overflows,
Encoder 130-i so as not to underflow
(I = 1 to 4) controls the encoding bit rate and the generated code bit amount. Each encoder 130-i (i = 1
VBV buffer 132-i (i.
= 1 to 4), the VBV buffer occupation amount of the combined bitstream is controlled by controlling the encoding bit rate, and the bit rate and the code bit amount are appropriately adjusted.

In order to accurately calculate the amount of generated code bits after combining, the total amount of input bits before combining, or the like, or
The target code bit amount such as the generated code bit amount of the remaining pictures in the GOP is set to the divided image coding device 120-i (i = 1.
4) to 4), it is necessary to correct the increase / decrease in the code bit amount (composition change amount) due to image division and combination. Next, the increase / decrease of the code bit amount (composite change amount) due to image division and combination will be described, and then the code bit amount of the post-combination bit stream, the VBV buffer input bit amount, and the VBV buffer due to the combination change amount. The fluctuation of the occupancy will be described. Then, a method of preventing the breakdown of the VBV buffer due to the fluctuation will be described.

[Increase / Decrease of Code Bit Amount by Compositing] In the plurality of moving picture coding apparatuses 101 of the present embodiment, when one bitstream is composed from a plurality of bitstreams, it is included in each stream in order to comply with the standard. Some of the existing header data has a changed value and needs to be rewritten. Due to this change, the bit amount of the bitstream after combining usually increases or decreases, and becomes different from the total bit amount of the plurality of bitstreams before combining. For example, as shown in FIG. 4, four MPEG2-MP
Decompose @ML bitstream in slice units and
Reconstructed into one bitstream and one MPEG2-
When synthesizing the MP @ HL bit stream, only one sequence, GOP, picture-level header data, extension data, and user data higher than the slice unit is required. Divided image coding apparatus 120-1 (divided image coding apparatus A)
Using only the bitstream output from the first to fourth divided image coding devices 120-2 to 120-4 (divided image coding devices B to D).

More specifically, the bitstream integration device 150 includes the first to fourth divided image coding devices 120-
1 to 120-4, after starting encoding, in each of the four bit streams output from the four divided image coding devices 120-1 to 120-4, until the first slice start code appears, Only the bit stream output from the first divided image coding device 120-1 (divided image coding device A) is output, and the second to fourth divided image coding devices 120-2 to 120-1 are output.
20-4 (divided image encoding devices B to D) discards the bitstream output. This reduces the bit amount of header data and the like to 1/4 after combining. In this embodiment, in order to make the reduction amount the same for each picture type, the encoding such that the length of the header data is changed is not performed, and the sequence header is added for each GOP. Make the length of evenings constant.

In addition, four MPEG2-MP @ ML bit streams are decomposed into slices to obtain one MPE.
When synthesizing G2-MP @ HL bitstream,
In the combined MPEG2-MP @ HL bit stream header data, a parameter that needs to be rewritten, for example, the horizontal pixel size (HS) of the sequence layer
V: Horizontal Size Value), vertical pixel size (VS
V: Vertical Size Value), aspect ratio information (AR
I: Aspect Ratio Information), bit rate (BR
V: Bit Rate Value), VBV buffer size (VBS
V: VBV Buffer Size Value). For these parameters, the bitstream integration device 150
According to the instruction from the control unit 172 of the control device 170,
Alternatively, each divided image encoding device 120-i (i = 1 to 1
4) Rewrite each value of the bit stream output from 4) to the value calculated. It should be noted that the F code (F-code) representing the search range of the motion vector is the first to fourth divided image coding devices 120-i (i = 1 to 1).
In 4), if an attempt is made to rewrite the same value on a picture-by-picture basis, conversion and rewriting of the motion vector value are also required, which is a complicated process. Therefore, before encoding each picture, the control unit 172 causes each divided image coding device to rewrite. 120-i
It is desirable to set the same value to (i = 1 to 4) in advance.

The bitstream integrating device 150 decomposes the bitstream after the slice start code into slice units, and as shown in FIG. 4, A1, B1, A2, B2, ..., A34, B34, C.
1, D1, C2, D2, ..., C34, D34 are rearranged in this order and output. At this time, the value of the slice header indicating the vertical position information of the slice is rewritten to a correct value as necessary. In addition, a macroblock address increment (MBAI: macroblock address increment) that represents horizontal position information in the first macroblock of a slice.
nt) is also rewritten to the correct value if necessary. The bitstream integration device 150 outputs the bitstream of the slice D34 and then outputs the divided image coding device 120-i (i =
1 to 4) to a sequence end code (SEC: sequence)
If a ce end code) is output, one sequence end code is output from the bitstream integration device 150, and synthesis is completed or the next sequence header code (SHC: sequence header code) is input. If the sequence end code is not output, the next picture start code (PSC: picture start co
de), or until the sequence header attached to each GOP is output, the bitstream integration device 150
Repeats the same process.

By rewriting the header data such as the MBAI of the slice, the bit amount of the combined bit stream increases or decreases so much that it cannot be ignored compared to before the combining. In the header data that requires rewriting of the bitstream, the macroblock address increment (MBA) of the first macroblock of the slice, which is variable-length coded, is used.
I: macroblock address increment). MBAI
Represents horizontal position information in the first macroblock of the slice. When the screen is divided by vertical dividing lines as in the present embodiment, the image regions B and D in FIG. 2, that is, the image region B is included in the bit stream obtained by encoding the screen on the right side of the dividing line. Since the horizontal position of the first macroblock (left end) of the slices (B1, ..., B34 and D1, ..., D34) in D is not at the left end of the screen compared to before the synthesis, the first macro of all slices It is necessary to rewrite the MBAI of the block with a new value. Since MBAI is variable length header data,
The rewriting changes the MBAI bit amount.

More specifically, as shown in FIGS. 4 and 6, before combining, the first macroblocks of all the slices of the image areas B and D are both at the left end of the screen, so that the MPEG
According to the two standards, the value of MBAI is 1. That is, MBA
When “1” is written in I and this bit stream having a bit length of 1 bit is combined, there are image areas A and C on the left side of the slices of image areas B and D, and in this embodiment, 720 There are image data of pixels, that is, 45 macroblocks. That is, in the slices of the image areas B and D, the horizontal position of the first macroblock is 46 macroblocks, and therefore the bitstream integration device 150 rewrites so that the value of MBAI represents 46. In MPEG2, "MBAI = 46"
"Macroblock Escape (MBESC: macroblock
escape) ”+“ MBAI = 13 ”. M
The BESC value is 33, and the MBAI value 13 represented by a fixed length of “0000 0001000” of 11 bits is “0000 1000” of 8 bits. That is, as shown in FIG. 6, the data MBAI having a length of 1 bit is rewritten to the data having a length of 19 bits.

Further, in order to obtain byte alignment,
That is, in order to align the start code with the 8-bit unit position, in the present embodiment, the bit stream integration device 150 adds 6-bit zero “000000” as stuffing data at the end of each slice data. That is, as shown in FIG. 6, the data representing the horizontal position of the first macroblock in each slice of the image areas B and D is rewritten to 25-bit data. Therefore, in the image areas B and D, (19 + 6) -1 = 24 bits increase per slice.
As shown in FIG. 4, in the present embodiment, there are 68 such slices per picture in the image areas B and D, so 24 × 68 = 163 per picture.
2 bits increase. This is constant regardless of the picture type.

In this embodiment, the bit amount of the header data above the slice layer per bit stream is 888 bits for I picture and 144 bits for P picture and B picture, respectively. In addition, the total bit amount of header data above the slice layer is 4 × 888 bits for I pictures and 4 × 144 bits for P and B pictures. As described above, after combining, the bit amount of the header data above the slice layer is reduced to 1/4. Therefore, the increase / decrease value of the generated code bit amount by combining is + 1632−3 × 888 = −1032 bits in the case of I picture, and + 1632−3 × 144 = in the case of P picture and B picture.
It becomes +1200 bits. Further, in this embodiment, GO
The so-called N value of P = 15 and M value = 3. Ie 1
There are one I picture, four P pictures, and ten B pictures in the GOP. Therefore, the increase / decrease value of the generated code bit amount for one GOP due to the bitstream synthesis is 14 × 1200-1032 = + 15768 bits, which is constant for each GOP.

As described above, the four MPEG2-MP @ M
When the L bit stream is decomposed in slice units and one MPEG2-MP @ HL bit stream is combined, the generated code bit amount for one GOP is increased by 15768 bits after the combination before the combination. Therefore, the simple sum of the code bit amount of each divided image encoding device does not match the code bit amount of the combined bit stream. In the present embodiment, for example, the generated code bit amount calculation unit 165 of the post-combination VBV buffer calculation unit 171 shown in FIG.
Accurately calculates the amount of generated code bits after combining,
The generated code bit amount Sa, n for each picture transferred from each divided image encoding device 120-i (i = 1 to 4),
It is necessary to add the increase / decrease amount of the generated code bit amount due to the combination (referred to as the combined change amount) to the total of Sb, n, Sc, n and Sd, n. Also, to calculate the total amount of input bit amount before combining from the specified bit rate accurately, from the input bit amount after combining calculated from the specified bit rate,
The synthetic variation must be subtracted. Further, when assigning the target code bit amount to each of the divided image coding devices 120-i (i = 1 to 4), the bit rates of the four bit streams before the synthesis are accurately determined as the target bit rates after the synthesis. In the case of matching with, it is also necessary to correct the combined change amount.

[Fluctuation of VBV Buffer Occupancy of Post-Combining Bitstream] As described above, the code bit amount of the post-combining bitstream is determined by the increase / decrease amount of the generated code bit amount (combining change amount) due to the combining. Since this is different from the sum of the code bit amounts of the four bit streams, the input bit amount of the VBV buffer and the VBV buffer occupancy amount of the combined bit stream also fluctuate from those before the combining. In particular, since the combined change amount varies depending on the picture type, the fluctuation range of the VBV buffer occupancy amount of the combined bitstream becomes larger than that before the combination. As a result, even if the occupancy of the VBV buffers 132-i (i = 1 to 4) in each divided image coding device 120-i (i = 1 to 4) is controlled so that overflow or underflow does not occur. , Overflow and underflow may occur after composition.

FIG. 7 exemplifies a change in the VBV buffer occupancy before and after the synthesis. The variation in the VBV buffer occupancy in the bitstream after the synthesis increases due to the synthesis variation, and overflow or underflow occurs. Is likely to occur. FIG. 7A is a simple sum of changes in the occupancy of the VBV buffers 132-i (i = 1 to 4) controlled by the divided image encoding device 120-i (i = 1 to 4). And FIG. 7 (b) is
This figure shows the change in the VBV buffer occupancy of the integrated bitstream obtained by combining the bitstreams output from the divided image coding devices 120-i (i = 1 to 4). In FIGS. 7A and 7B, in order to show the possibility of underflow, theoretically all the divided image coding devices 120-i (i = 1 to 4) have the lowest occupied amount. This is the case when it changes in. Further, in FIGS. 7A and 7B, the initial value B0 of the occupancy of the VBV buffer before and after the synthesis, that is, immediately before the encoding of the first I picture (the generated code bit amount is subtracted) is performed. The occupancy is set equal.

As shown in FIG. 7A, first, the divided image is V of the divided image encoding device 120-i (i = 1 to 4).
The occupancy of the BV buffers 132-i (i = 1 to 4) is set to zero, and the total VBV buffer occupancy before combining, which is the total, is also zero. The encoded image data of each divided image of the first I picture in one GOP is the VBV buffer 132-i.
The sum of the code bit amounts input to (i = 1 to 4) during one picture period is IB, that is, the input bit amount for each picture of the VBV buffer before combining is IB.
Is. Immediately before encoding the I picture, VB before combining
The occupancy of the V buffer is the initial occupancy value B0, that is, B0 = IB. Each divided image of the first I picture is encoded by the divided image encoding device 120-i (i = 1 to 4), and each divided image encoding device 120-i (i =
Let S be the total of the code bit amounts generated in 1 to 4). Here, it is assumed that the code bit amount S generated by the encoding is equal to the input bit amount IB. That is, the S bit is subtracted from the VBV buffer occupation amount B0 before combining due to the encoding of the I picture, and the occupation amount after encoding becomes zero. Subsequently, the encoded image data of the next B picture is input and 1
The total input bit amount during the picture period is also IB, and the total code bit amount generated by the encoding is S, so that the VB immediately after the encoding of the B picture is performed.
The V buffer occupancy is zero. The same applies to subsequent pictures. Thus, the VB before the synthesis shown in FIG.
The V buffer occupancy is obtained.

In FIG. 7A, the VBV occupation amount becomes zero after the picture is encoded before the combining,
Underflow has not occurred. However, the situation changes after combining the four uncombined bitstreams. In the present embodiment, the increase / decrease amount of the generated code bit amount by combining the bit streams is I picture: −1032 bits,
P picture: +1200 bits, B picture: +120
The number of generated code bits during 1 GOP increases or decreases by +15768 bits, and the input bit amount to the VBV buffer after combining is more average than the input bit amount to the VBV buffer before combining. +15768/15
= + 1051.2 bits increase. Due to the increase / decrease amount due to the combination, the VBV buffer occupation amount after the combination gradually decreases.

Specifically, as shown in FIG. 7B, the first I picture is encoded, and the occupancy after the combination is changed to S.
Only -1032 bits are subtracted, and the occupied amount after encoding is 1
It becomes 032 bits. Further, since the input bit amount between each picture is IB + 1051.2, which is increased by 1051.2 bits, the occupied amount after combining is 1051.2 for each picture.
It gets higher bit by bit. Therefore, immediately before the next B picture is encoded, the occupation amount is S + 1032 + 1051.2 = S.
+2083.2 bits, that is, 2083.2
A bit higher. Since the B picture and the P picture are encoded from the next onward, the value subtracted as the generated code bit amount is S + 1200, which increases by 1200 bits for each picture. That is, the occupancy of each picture decreases by 1200 bits. On the other hand, since the increase in the input bit amount between each picture is 1051.2 bits, as a result, the occupancy amount after each picture is encoded is 1032 bits immediately after the I picture is encoded, and the occupancy amount is calculated for each picture. 120
0-1051.2 = decreased by 148.8 bits, GO
When the P last picture is coded and the generated code bit amount is subtracted, the occupancy becomes the lowest and 1032-14 ×
(1200−1051.2) = − 1051.2 bits. That is, there is 1051.2 bits of underflow.

The above is all of the divided image coding devices 120.
-I (i = 1 to 4), the occupancy is changed in the lowest state. FIG. 8 shows a case in which all divided image coding apparatuses 120-i (i = 1 to 4) change in a state in which the occupancy is the highest, that is, VB before and after combining.
When the initial value B0 of the occupancy of the V buffer is the same as the buffer size, the change in the occupancy before and after the synthesis is shown. Similar to FIG. 7, FIG. 8A shows the divided image encoding device 1
20-i (i = 1 to 4) VBV buffer 132-i
It is simply the sum of the occupation amounts of (i = 1 to 4),
FIG. 8B shows a divided image coding device 120-i (i = 1.
4) shows changes in the VBV buffer occupancy of the integrated bitstream obtained by combining the bitstreams output from FIG. In FIG. 8B, the initial value B of the VBV buffer occupancy is calculated by encoding the first I picture.
S-1032 bits are subtracted from 0, and the occupied amount after encoding is B0-S + 1032 bits. The input bit amount between each picture is IB + 1051.2, which is 10
This increases by 51.2 bits, and the occupancy is (B0-S + 1032) + (IB + 1) immediately before the next B picture is encoded.
051.2) = B0 + 2083.2 bits. That is, it is +2083.2 bits higher than the buffer size, and the overflow is 2083.2 bits.

[Limitation of Occupancy of Divided Image Device VBV Buffer] In order to prevent overflow and underflow due to fluctuations in the occupied amount of VBV buffer after combining, each divided image encoding device 120-i (i = 1 to 4) A state in which the variable range of the VBV buffer occupancy of the VBV buffer 132-i (i = 1 to 4) to be controlled is limited and the occupancy is the lowest in the divided image coding device 120-i (i = 1 to 4). , Also, try not to reach the highest level. In the present embodiment, as shown in FIG. 7B, underflow of the post-combination VBV buffer occurs when the VBV buffer occupation amount controlled by the divided image encoding device 120-i (i = 1 to 4) is the lowest. Has a maximum amount of 1051.2 bits, and V controlled by the divided image encoding device 120-i (i = 1 to 4)
When the BV buffer occupancy is the highest, the post-combination VBV
The maximum amount of buffer overflow is 2083.2 bits. Split image coding device 120-i (i = 1 to 1
Since the total variation range of the VBV buffer occupancy controlled by 4) is from zero to the post-combination VBV buffer size, that is, the variation range of the post-combination VBV buffer occupancy is a total of 1051 .2 + 2083.
2 = 3134.4 bits wide.

In order to make the fluctuation range of the post-combination VBV buffer occupancy the same as the post-combination VBV buffer size, the fluctuation range of the pre-combination occupancy, that is, the size of the pre-combination VBV buffer is 313.4 bits. It should be small. In the present embodiment, the combined VBV buffer size is 7340032 bits, which is the maximum value of MP @ H-14. Usually, each divided image coding device 120-i
(I = 1 to 4) VBV buffer 132-i (i = 1 to 1)
The size of 4) is 1 / the size of the VBV buffer size after synthesis.
4 and becomes 7340032/4 = 1835008 bits. The size of the VBV buffer before combining is the sum of the sizes, which is the same as the size of the VBV buffer after combining.

The size of the VBV buffer before composition is set to 313.
In order to reduce the bit size by 4.4 bits, the size of the VBV buffer of each divided image coding device 120-i (i = 1 to 4) may be reduced by 334.4 / 4 = 783.6 bits. Therefore, in this embodiment, the size of the VBV buffer 132-i (i = 1 to 4) controlled by each divided image encoding device 120-i (i = 1 to 4) is 7340.
032 / 4-783.6 = 1834234.4 bits.

FIG. 9 shows each divided image coding device 120-i.
Controlled by (i = 1 to 4), V limited as above
The change in the occupied amount of the BV buffer 132-i (i = 1 to 4) is shown. Each divided image coding device 120-i (i = 1 to 1
In 4), the size of the VBV buffer is VB after synthesis.
Smaller than B1 which is 1/4 of the V buffer size B2,
The difference is represented by a. In this embodiment, as described above, B2 = 7340032 bits and B1 = 18350.
08 bits, a = 783.6 bits, and in each divided image coding device 120-i (i = 1 to 4), the size of the VBV buffer is 18342244.4 bits.

The split image device 120-i shown in FIG.
VBV buffer 132-i (i = 1 to 4) (i
The occupancy of (1) to (4) is obtained as follows, for example. The bit rate R designated by the control unit 172
From this, the input bit amount IBt for each picture is calculated. The control unit 172 is configured to cancel the accumulation of the error of the input bit amount.
Adds the difference between the theoretically correct input bit amount and the actually input bit amount to the actually input bit amount for each number of pictures in which the theoretical input bit amount is an integer value. For example, when the picture rate P is 30 Hz and the bit rate R is 10 Mbps, a correct bit amount can be obtained without accumulating errors by adding 1 to the actual input bit amount every 3 pictures. Since the designated bit rate R is the bit rate of the combined bit stream after combining, the input bit amount IB obtained from the bit rate R is
t is the input bit amount in the state after combining. Control unit 1
Reference numeral 72 subtracts the average combined change amount ΔT, which is the average value of the combined change amount per picture, from this input bit amount IBt, and inputs it to the accurate VBV buffer 132-i (i = 1 to 4) for each picture. The total amount of bits IBn is obtained.

For example, according to the complexity of each divided image of the previous picture, the total amount of input bits IB for each picture IB
Allocation amounts IBa, n, IBb, n, IBc, n, and IBd, n to each divided image coding device 120-i (i = 1 to 4) are calculated, and each divided image coding device 120- Instruct i (i = 1 to 4). Each divided image coding device 120-i (i = 1 to 1
4) uses the input bit amounts IBa, n, IBb, n, IBc, n, and IBd, n allocated from the control unit 172, and the VBV buffer occupancy amounts Ba, n, Bb, n shown in FIG. , Bc, n,
Bd, n is calculated, and the generated code bit amount is controlled based on this. In this way, when the target generated code bit amount and the coding bit rate assigned to each divided image coding device 120-i (i = 1 to 4) and the coding bit rate change for each picture according to the change in the image complexity. Also, for each picture,
An input bit amount is allocated from the external control unit 172, and the coding bit rate can be controlled by the VBV buffer occupation amount.

FIG. 10 shows each divided image coding device 120-.
VB shown in FIG. 9 output from i (i = 1 to 4)
9 shows a change in VBV buffer occupancy of an integrated bitstream obtained by combining four bitstreams having V buffer occupancy. The size of the post-combination VBV buffer is B2. The occupation amount of the combined VBV buffer shown in FIG. 10 is obtained by, for example, the combined VBV buffer calculation unit 171. More specifically, the post-combination VBV buffer operation unit 171 is configured so that the divided image encoding device 120-i (i = 1 to 1
4) Generated code bit amount S for each picture output from 4)
The a, n, Sb, n, Sc, n, Sd, n and the combined variation amount ΔT are added to obtain the generated code bit amount Sn for each picture after the combination. Further, the input bit amount IBn for each picture to the VBV buffer of the integrated bit stream is calculated according to the bit rate R set from the outside. The VBV buffer occupation amount Bn of the integrated bit stream is calculated from the generated code bit amount Sn and the input bit amount IBn.

Split image coding device 120-i (i = 1 to 1
4) VBV buffer 132-i (i = 1 to 1) controlled by
By limiting the size of 4), the size of the variation range of the post-combination VBV buffer occupancy amount is limited to the VBV buffer size or less. Therefore, even when the occupancy becomes the largest, the value is the VBV buffer size. Never exceeds. That is, the VBV buffer does not overflow after synthesis.

However, there is still a possibility that underflow will occur if the variation range of the post-combination VBV buffer occupancy amount is set to the VBV buffer size or less. In order for the occupancy amount to be properly within the VBV buffer size, it is necessary to further manipulate the initial value of the occupancy amount. As shown in FIG. 7, when the initial value of the occupied amount of the VBV buffer after combining is set to be the same as the initial value of the occupied amount before combining, in the present embodiment, the occupied amount decreases by 1051.2 bits after combining, and the maximum value is obtained. 1051.2 bit underflow. In order to prevent the underflow, the occupancy initial value after composition is set higher than that before composition, as shown in FIG. Here, the occupancy initial value after combination is 1051.2
Just add a bit. As a result, even if the occupancy before combining is the smallest, the occupancy after combining is less than that before combining.
Since it is increased by 051.2 bits, the value does not become smaller than zero even if it becomes the smallest occupied amount after the combination. That is, underflow does not occur.

It should be noted that, although the maximum number of bits of overflow or underflow that may occur after combining depends on the picture position in the GOP, changing the limitation for each picture complicates the processing. In this embodiment, the restriction is uniform.

Further, in the present embodiment, the buffer size and the input bit amount are calculated by real numbers, but it is considered that they are generally calculated by integers. In that case, it is desirable to perform rounding toward the condition and further tighten the few-bit limit in consideration of the calculation error due to an integer. That is, it is desirable to set the size of the VBV buffer 132-i (i = 1 to 4) controlled by each divided image coding device 120-i (i = 1 to 4) to an integer value that is smaller by several bits than the above example. . Further, it is desirable to set the initial value of the occupied amount of the VBV buffer after combination to an integer value larger than the above example within a range where overflow does not occur.

In the present embodiment, the variation range of the VBV buffer occupancy controlled by each of the divided image coding devices 132-i (i = 1 to 4) is limited to cause an increase / decrease in the generated code bit amount due to combining. It is possible to prevent overflow and underflow of the VBV buffer after combination, and perform proper encoding.

Second Embodiment The image coding apparatus according to this embodiment has the same configuration as the moving picture coding apparatus 101 according to the first embodiment. However, in the present embodiment, each divided image coding device 120-i (i = 1
~ 4) control the VBV buffer 132-i (i = 1 to 1)
The method 4) of limiting the variation range of the occupation amount is different from that of the first embodiment. In the first embodiment, the size of the VBV buffer 132-i (i = 1 to 4) controlled by each divided image encoding device 120-i (i = 1 to 4) is limited, and the VBV after combining is limited. By operating the buffer occupancy initial value, it is possible to prevent overflow and underflow of the post-combination VBV buffer due to increase / decrease in the generated code bit amount due to the combination. That is, 120-
VBV buffer 132-i controlled by i (i = 1 to 4)
The occupancy of (i = 1 to 4) is VBV limited from zero.
It varies up to the buffer size.

In the present embodiment, each divided image coding device 1
VBV buffer 13 controlled by 20-i (i = 1 to 4)
In the variation range of the occupied amount of 2-i (i = 1 to 4), a lower limit that is not always zero and an upper limit that is irrelevant to the buffer size are set. For example, the occupancy initial values before and after synthesis are the same, and correspondingly, the occupancy of the VBV buffer before synthesis does not fall below 1051.2 bits. Avoid underflow. That is, in the VBV buffers controlled by the VBV buffers 132-i (i = 1 to 4) controlled by the respective divided image encoding devices 120-i (i = 1 to 4), the occupation amount is ¼ of that 262. Set a lower limit so that it does not fall below 8 bits. The upper limit is VBV
The buffer size is, for example, 1/4 of 7340032 bits which is the size after combining, that is, 183500.
Set to 4 bits, but the variation range is the same as the above example 18
Since the number of bits is 34224.4 bits, the lower limit value is 262.8.
Add this value to the bits and add 18342244.4 + 262.
8 = 1834487.2 bits. That is, V controlled by each divided image encoding device 120-i (i = 1 to 4)
The occupation amount of the BV buffer 132-i (i = 1 to 4) is 18
Limit not to exceed 34487.2 bits.

FIG. 11 shows each divided image coding device 120-.
The change in the occupancy of the VBV buffer 132-i (i = 1 to 4) controlled as above and controlled by i (i = 1 to 4) is shown. Each divided image coding device 120-i (i = 1 to 1
In 4), the fluctuation range of the VBV buffer occupation amount is
There are upper and lower limits. As a result, the size of the VBV buffer is 1/4 of the post-combination VBV buffer size B2.
(Denoted as B1), and the difference is represented by a. The divided image device 120-i (i = 1) shown in FIG.
VBV buffer 132-i (i = 1 to 4)
The occupancy of 4) is calculated, for example, as in the first embodiment.

FIG. 12 shows each divided image coding device 120-
VB shown in FIG. 9 output from i (i = 1 to 4)
9 shows a change in VBV buffer occupancy of an integrated bitstream obtained by combining four bitstreams having V buffer occupancy. The size of the post-combination VBV buffer is B2. The combined VBV buffer occupancy shown in FIG. 12 is obtained, for example, by the combined VBV buffer operation unit 171.

Divided image coding device 120-i (i = 1 to 1)
4) VBV buffer 132-i (i = 1 to 1) controlled by
By setting the upper limit and the lower limit to the occupancy of 4), the variation range of the post-combination VBV buffer occupancy is limited to the VBV buffer size or less, and therefore even when the occupancy becomes the maximum, the value is the same. It does not exceed the size. That is, the VBV buffer does not overflow after synthesis. Further, the divided image encoding device 120-
VBV buffer 132-i controlled by i (i = 1 to 4)
By setting a lower limit on the occupied amount of (i = 1 to 4),
Since the variation range of the post-combination VBV buffer occupancy amount is limited to the lower limit or more, even the smallest post-combination occupancy amount does not become smaller than zero, so that underflow does not occur.

In the present embodiment, by providing an upper limit and a lower limit to the VBV buffer occupation amount controlled by each divided image encoding device 132-i (i = 1 to 4), it is possible to increase or decrease the generated code bit amount by combining. It is possible to prevent overflow and underflow of the VBV buffer after combination, and perform proper encoding.

Third Embodiment FIG. 13 is a block diagram showing an example of the arrangement of an image recording apparatus 300 of this embodiment. The image recording device 300 has a moving image encoding device 301 and a recording means 302.
The basic configuration of the moving picture coding apparatus 301 is the same as that of the moving picture coding apparatus 101 of the first embodiment, that is, the first to first
The fourth divided image coding devices 120-1 to 120-4, the bitstream integration device 150, and the control device 170 are included, and the control device 170 includes a post-combination VBV buffer operation unit 171 and a control unit 172. Further, the size of the VBV buffer 132-i (i = 1 to 4) controlled by the divided image coding device 120-i (i = 1 to 4) is limited,
In addition, the initial value of the occupancy is adjusted to prevent overflow and underflow due to fluctuations in the post-combination VBV buffer occupancy. Omit detailed explanation.

The recording means 302 is, for example, a video tape recording / reproducing device. In the moving picture coding apparatus 301, four bit streams are time-division multiplexed in picture units to generate one MPEG2-MP @ HL bit stream. MP generated in this way
The bit stream of EG2-MP @ HL is multiplexed with an audio signal as needed, and then recorded on the magnetic tape medium by the video tape recording / reproducing device 302. VB controlled by the divided image coding device 120-i (i = 1 to 4)
By limiting the size of the V buffer 132-i (i = 1 to 4), the variation range of the post-combination VBV buffer occupation amount is limited to the VBV buffer size or less, and the occupation amount is V.
It does not exceed the BV buffer size and does not overflow. In addition, even if the occupancy before combining is the minimum value by setting the occupancy initial value after combining appropriately high,
The occupancy after combining does not become smaller than zero and does not underflow.

According to this embodiment, it is possible to prevent overflow or underflow of the VBV buffer after the synthesis due to the increase or decrease in the generated code bit amount due to the synthesis, and perform the appropriate encoding.

Fourth Embodiment FIG. 15 is a block diagram showing an example of the arrangement of an image transmission device 400 of this embodiment. The image transmission device 400 includes a moving image coding device 401 and a transmission unit 402.
The moving picture coding device 401 has the same configuration as the moving picture coding device 301 of the third embodiment. The size of the VBV buffer 132-i (i = 1 to 4) controlled by the divided image coding device 120-i (i = 1 to 4) is limited, and
The initial value of the occupancy is adjusted to prevent overflow and underflow due to variations in the post-combination VBV buffer occupancy. Omit detailed explanation. In the moving picture coding device 401, four bit streams are time-division multiplexed in picture units to generate one MPEG2-MP @ HL bit stream. M generated in this way
The PEG2-MP @ HL bit stream is multiplexed with an audio signal, if necessary, and then transmitted from the transmission path via the transmission means 402.

Split image coding device 120-i (i = 1 to 1)
4) VBV buffer 132-i (i = 1 to 1) controlled by
By limiting the size of 4), the variation range of the post-combination VBV buffer occupancy amount is limited to the VBV buffer size or less, and the occupancy amount does not exceed the VBV buffer size and does not overflow. In addition, even if the occupancy before combining is the minimum value, the occupancy after combining does not become smaller than zero and underflows by setting the occupancy initial value after combining appropriately high. There is no.

The present embodiment has the same effects as the third embodiment.

Although the present invention has been described above based on the preferred embodiments, the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the gist of the present invention. Is. The image encoding device described in the present embodiment is an example, and various modifications of its configuration are possible. For example, in the embodiment of the present invention, regarding parameters that need to be rewritten as one MPEG2-MP @ HL bit stream such as horizontal pixel size, vertical pixel size, aspect ratio information, bit rate, VBV buffer size, and VBV delay. Is to be rewritten in the bitstream integration device 150. However, from the control unit 172, each divided image encoding device 1
Based on an instruction to 20-i (i = 1 to 4), a bit stream of a value to be rewritten in each divided image coding device 120-i (i = 1 to 4) is generated and output in advance, The bitstream integration device 150 may output the data as it is without any rewriting.

Although the input bit amount is allocated based on the generated code bit amount and the average quantization scale of the image one picture before, for example, the images two pictures before and three pictures before can be referred to. , A plurality of previous images may be referred to. by this,
This is useful because it eliminates the need for high-speed processing required for bit rate control for each picture.

Further, in the above-mentioned embodiment, the number of divisions of the image is four, but it may be a natural number other than four.
In addition, high definition TV (HDTV) signals and standard TV
(SDTV) signal type (eg NTSC signal, P
The AL signal) is not limited at all and may be applied to signals of any standard. Further, the present invention is not limited to the MPEG2 standard, and can be applied to other image compression coding techniques similar to this.

[0076]

According to the present invention, when an image is divided and encoded, overflow or underflow of a VBV buffer after combination due to an increase or decrease in the generated code bit amount due to the combination of bit streams is prevented. , Can be encoded appropriately. Further, in order to realize this, neither an expensive additional device nor complicated arithmetic processing is required.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image coding apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an HDTV video signal input to the image encoding device according to the first embodiment of the present invention and a dividing method thereof.

FIG. 3 is a block diagram showing an example of a configuration of a divided image coding device in the image coding device according to the first embodiment of the present invention.

[Fig. 4] Fig. 4 is a diagram for describing an arrangement of video streams decomposed in slice units in the image encoding device according to the first embodiment of the present invention.

FIG. 5 is a block diagram showing an example of a configuration of a post-synthesis VBV buffer operation unit in the image encoding device according to the first embodiment of the present invention.

FIG. 6 is a chart showing changes in the bit amount of header data of a bitstream due to synthesis in the image encoding device according to the first embodiment of the present invention.

FIG. 7 is a diagram exemplifying a change in VBV buffer occupancy before and after synthesizing, in which a change in the code bit amount due to synthesizing causes a large variation in the post-synthesizing VBV buffer occupying amount, which may cause underflow. (A) is a simple sum of changes in the VBV buffer occupancy in the divided image encoding device, and (b) is
The change in the VBV buffer occupancy after combining is shown.

FIG. 8 is a diagram exemplifying a change in VBV buffer occupancy before and after synthesizing, in which a change in the code bit amount due to synthesizing causes a large variation in the post-synthesizing VBV buffer occupying amount, which may cause an overflow. And (a) is a simple sum of changes in the VBV buffer occupancy in the divided image coding device, and (b) is
The change in the VBV buffer occupancy after combining is shown.

FIG. 9 is a diagram showing an example of limiting the variation range of the occupancy amount of the VBV buffer of the divided image coding device in the image coding device according to the first embodiment of the present invention.

FIG. 10 is a block diagram of the divided image encoding device in the image encoding device according to the first embodiment of the present invention, following FIG. 9;
If the BV buffer occupancy is limited, VB after synthesis
It is a figure which illustrates the change of the V buffer occupation amount.

[Fig. 11] Fig. 11 is a diagram showing an example of limiting the variation range of the occupancy of the VBV buffer of the divided image coding device in the image coding device according to the second embodiment of the present invention.

FIG. 12 is a view following FIG. 11, in the image encoding device according to the second embodiment of the present invention, when the VBV buffer occupation amount of the divided image encoding device is limited, the V
It is a figure which illustrates the change of the BV buffer occupation amount.

FIG. 13 is a block diagram showing a configuration of an image recording apparatus according to a third embodiment of the present invention.

FIG. 14 is a block diagram showing a configuration of an image transmission device according to a fourth embodiment of the present invention.

[Explanation of symbols]

101 ... Moving picture coding device, 110 ... Screen dividing device, 1
20 ... Divided image encoding device, 130 ... Encoder, 13
1 ... Output buffer, 132 ... VBV buffer, 150 ...
Bit stream integration device, 165 ... Generated code bit amount addition unit, 167 ... Input bit amount calculation unit, 168 ... Occupation amount calculation unit, 170 ... Control device, 171 ... Post-combination VBV buffer calculation unit, 172 ... Control unit, 300 ... Image recording device,
301 ... Moving image coding device, 302 ... Video tape recording / reproducing device, 400 ... Image transmitting device, 401 ... Moving image coding device, 402 ... Transmission means, S ... Generated code bit amount, Q
... Quantization scale code, R ... Bit rate, IB ... Input bit amount, B ... VBV buffer occupation amount, B1 ... Divided image coding device VBV buffer size, B2 ... Post-combination VB
V buffer size, ΔT ... Increase / decrease amount of code bit amount by combining.

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Claims (8)

[Claims] 1. N first divided image signals in which an input image signal is divided are encoded to generate N bit streams, and the N first bit streams are each buffered virtually. Seed VBV (video buffering verifi
er) N divided image encoding means including a buffer, integrating means for integrating the N bitstreams into one bitstream, and a second type for virtually buffering the integrated bitstreams VBV buffer, and is changed by a combined change amount that is a change amount of the code bit amount of each picture of the integrated bitstream that occurs when the N bitstreams are integrated into one bitstream. The first N number of bits so that the occupancy of the combined bitstream in the second type VBV buffer falls within the range of the maximum occupancy and the minimum occupancy of the second type VBV buffer. An image coding apparatus for limiting the variation range of the occupancy of each VBV buffer of a kind. 2. The occupancy of the second type VBV buffer, which is changed by the combined change amount, is equal to the second type VBV buffer.
An upper limit is set on the occupancy of each of the N first-type VBV buffers so as not to become larger than the maximum occupancy of the buffer, and the second-type VBV varied by the combined change amount.
The image code according to claim 1, wherein a lower limit is set to the occupancy of each of the N first-type VBV buffers so that the buffer occupancy does not become smaller than the minimum occupancy of the second-type VBV buffer. Device. 3. The occupancy of the second type VBV buffer which is changed by the combined change amount is the second type VBV buffer occupancy amount.
An upper limit is set on the occupancy of each of the N first-type VBV buffers so as not to become larger than the maximum occupancy of the buffer, and the second-type VBV varied by the combined change amount.
The buffer occupancy is set such that the second type VBV buffer does not become smaller than the second VBV buffer minimum occupancy.
The initial value of the occupation amount in the V buffer is adjusted.
The image encoding device according to 1. 4. An input image signal is divided into N divided image signals, the N divided image signals are encoded to generate N bit streams, and the N bit streams are divided into 1 bits.
An image encoding method for integrating the bitstreams into N bitstreams, wherein each of the N bitstreams is virtually buffered in each of the N first-type VBV buffers. Is virtually buffered in the second type VBV buffer, and is a change amount of the code bit amount of each picture of the integrated bitstream that occurs when the N bitstreams are integrated into one bitstream. The occupancy of the integrated bitstream in the VBV buffer of the second type, which is changed by a certain synthetic variation, is kept within the range of the maximum occupancy and the minimum occupancy of the VBV buffer of the second type. , An image coding method for limiting the variation range of the occupancy of each of the N first-type VBV buffers. 5. The occupancy of the second type VBV buffer which is changed by the combined change amount is the second type VBV buffer occupancy.
An upper limit is set on the occupancy of each of the N first-type VBV buffers so as not to become larger than the maximum occupancy of the buffer, and the second-type VBV varied by the combined change amount.
The image code according to claim 4, wherein a lower limit is set on the occupancy of each of the N first-type VBV buffers so that the buffer occupancy does not become smaller than the minimum occupancy of the second-type VBV buffer. Method. 6. The occupancy of the second type VBV buffer which is changed by the combined change amount is the second type VBV buffer occupancy amount.
An upper limit is set on the occupancy of each of the N first-type VBV buffers so as not to become larger than the maximum occupancy of the buffer, and the second-type VBV varied by the combined change amount.
The buffer occupancy is set such that the second type VBV buffer does not become smaller than the second VBV buffer minimum occupancy.
The initial value of the occupation amount in the V buffer is adjusted.
The image coding method described in. 7. N first divided image signals into which an input image signal is divided are encoded to generate N bit streams, and the N first bit streams are respectively buffered virtually. N divided image encoding means including VBV buffers of a kind, an integration means for integrating the N bitstreams into one bitstream, and a second buffer for virtually buffering the integrated bitstreams A VBV buffer of a kind and a recording means for recording the integrated bitstream on a recording medium, the integrated bitstream of the integrated bitstream occurring when the N bitstreams are integrated into one bitstream. The second type VBV buffer of the integrated bitstream, which is changed by the combined change amount that is the change amount of the code bit amount of each picture. The variable range of the occupancy of each of the N first-type VBV buffers so that the occupancy of the buffer is within the range of the maximum occupancy and the minimum occupancy of the second VBV buffer. Image recording device. 8. N first divided image signals, which are obtained by dividing an input image signal, generate N bit streams, and virtually buffer each of the N bit streams. N divided image encoding means including VBV buffers of a kind, an integration means for integrating the N bitstreams into one bitstream, and a second buffer for virtually buffering the integrated bitstreams A VBV buffer of a kind and a transmission means for transmitting the integrated bitstream, wherein each picture of the integrated bitstream is generated when the N bitstreams are integrated into one bitstream. In the second type VBV buffer of the integrated bit stream, which is changed by the combined change amount that is the change amount of the code bit amount. Image for limiting the fluctuation range of the occupancy amount of each of the N first-type VBV buffers so that the occupancy amount falls within the range of the maximum occupancy amount and the minimum occupancy amount of the second type VBV buffer. Transmission equipment.