JPH10304377A - Picture encoding method/device and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of picture quality in other ranges, and to reduce a working time by re-calculating bit distribution for each coded picture designated in a customized designation process. SOLUTION: An MPEG encoder controller 23, i.e., a control means, preliminarily calculates bit distribution, including reserve data amount, for each coded picture whose customized range is designated for picture quality adjustment according to the operation of a user, and re-calculates bit distribution for each coded picture within a customized designated range by using the reserve data amount. At the time of customization by the re-distribution calculation, the range of customization from stock bits to bits to be used for the bit re-distribution at the time of customization is obtained, and bit amount obtained by adding preliminarily stocked bits to the total sum of bit amount distributed at the time of the initial bit distribution calculation are supplied to a range designated as the range of customization. Thus, the bit amount of a part outside the customized range remains changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image encoding method, apparatus, and recording medium for improving the image quality by re-encoding the video information when the image quality of the video information compressed by encoding is deteriorated. About.

[0002]

2. Description of the Related Art When video information is stored on a package medium such as a digital video disk (DVD) or a video CD, an encoding system for performing an encoding process for compressing the video information firstly stores the material. Measure the encoding difficulty (DIFFICULTY) of the image,
Based on the encoding difficulty level, encoding is performed by performing a bit allocation process for each frame of each piece of video information so as to be within a given number of bits within the recording capacity of the package medium.

For example, FIG. 9 shows a specific example of a video encoding system for encoding video information for a DVD.

In FIG. 9, a video encoding controller 20 for controlling video encoding is connected via a network to a supervisor controller 1 for managing the entire system.

The supervisor controller 1 is a controller for executing a supervisor which is a program for monitoring the operation of the entire system and for controlling efficiently, among programs constituting the operating system,
In this video encoding system, the entire DVD authoring system is managed, encoding conditions are given to each encoding system such as video, audio, subtitles, and menus, and a report of the encoding result is received.

For a specific example of this video encoding system, video encoding conditions are specified by, for example, a file named v.enc. Then, from the video encode controller 20 side, the bit stream of the encoded result is a RAID (Redundant Arrays of Inexpensive Diske) in which a plurality of hard disk drives (HDDs) are connected in parallel to improve the recording capacity and transfer speed performance.
s) Report the address v.adr written on 16 and the data (vxxx.aui) required when the encoded bit stream is multiplexed with sub-pictures such as audio, subtitles, and menus. I have.

The video encoding controller 10 has a graphical user interface (Graphical User I).
GUI) 11, a bit allocation calculation unit 12 storing a bit allocation calculation program (BIT_ASSIGN) described later, and an MPEG encoder controller 13 for executing the bit allocation calculation processing program inside the bit allocation calculation unit 12. , DVTR controller 14.

The user uses the GUI 11 to execute a bit allocation calculation processing program provided in the bit allocation calculation unit 12,
The MPEG encoder controller 13 can be managed. In addition, the DVTR controller 14 can be managed.

[0009] The MPEG encoder controller 13 comprises:
It executes the bit allocation calculation processing program provided in the bit allocation calculation unit 12 and controls the MPEG encoder 15. In addition, the DVTR controller 14
The VTR 17 is controlled. The DVTR 17 is connected to the MPEG encoder 15, and the MPEG encoder 15
Is connected to the monitor 18 for displaying the encoded result. Further, the MPEG encoder 15 is also connected to the RAID 16 for recording an encoding result.

The MPEG encoder 15 removes the redundancy in the time direction by motion compensation prediction. Also,
The MPEG encoder 15 converts an intra-frame encoded image encoded only within a frame into an I-picture (Intra Code
d), an inter-frame forward prediction coded image coded by predicting the present from a past screen is coded by predicting the present from a P-picture (Predictive Coded), a picture in both past and future directions. A bidirectional predictive coded image is converted to a B-picture (Bidirectionaly Predictive Co
ded) to compress and encode the video information. Here, a group of pictures including one I picture is always a GOP (Group of Pictures) as shown in FIG. In FIG. 10, the number of frames N of the GOP
Is 15, and the head of the GOP in the display order shown in (A) in the figure is the B picture next to the P or I picture before the I picture. The end of the GOP is the first P picture before the next I picture. Also, the GOP in the coding order shown in (B) in the figure has the I picture at the top. The operation of the video encoding system will be described with reference to the flowchart of FIG. First, in step S101,
An encoding condition v.enc such as a total bit amount and a maximum rate to be assigned to video via the network 2 is given from the supervisor controller 1.

After setting the encoding conditions, in step S102, the MPEG encoding controller 10 measures the encoding difficulty of the encoded material. here,
The DC value and the motion vector amount ME of each pixel are also read. Then, a file is created based on these measurement results.

The actual measurement of the encoding difficulty is performed as follows. Video information to be encoded is DVTR17
Is recorded as a master on a digital video cassette, and this master is used as the DVTR controller 1
In step 4, the reproduction is performed while controlling the DVTR 17, and the encoding difficulty of the encoded material is measured.

Here, the amount of generated bits is measured under the condition that the number of quantization steps is set to a fixed value at the time of encoding. The amount of generated bits is large in an image having many motions and large high frequency components, and the generated bit amount is small in a still image or an image having many flat portions. The magnitude of this generated bit amount is defined as the image encoding difficulty.

Next, in Step S103, Step S
Based on the encoding conditions set in step 101, step S
The bit allocation calculation unit 22 executes the bit allocation calculation processing calculation program in accordance with the degree of encoding difficulty of each picture measured in 2 and performs allocation calculation of the allocated bit amount (target amount: TARGET).

The user is made to determine whether or not to execute encoding using the result of the bit allocation calculation in step S103, based on the image quality of the output of the local decoder built in the MPEG encoder 15.

Actually, in step S104, the user checks the image quality by performing a preview mode (Preview) in which an arbitrary processing range can be designated without outputting the bit stream based on the bit allocation to the RAID 16.

If there is no problem in the image quality in the image quality evaluation in step S105, the process proceeds to step S106, and the encoding process is executed. After performing customization work for image quality adjustment, such as raising the filter level or adjusting the filter level, step S109 is performed.
Then, the bit allocation calculation processing program inside the bit allocation calculation unit 22 is executed again to perform the bit redistribution calculation.

Thereafter, the process returns to step S104, where the customized portion is previewed, and the image quality is confirmed in step S105.
6, the entire encoding is performed by the MPEG encoder 25.
To run. In step S107, the bit stream that is the encoding result is a SCSI (Small Computer Sys
The data is directly written to RAID 16 via the tem interface.

After the encoding in step S106, the video encode controller 10 reports the above-described encoding result information to the supervisor controller 1 via the network.

In the flowchart of FIG. 11, steps S102, S104 and S10
The processing of each step except for 6 means offline processing.

Hereinafter, the bit allocation calculation process in the bit allocation calculation unit 12 executed in step S103 will be described in detail. First, the total amount of bits (QTY_BYTES) from the disk capacity from the supervisor controller 1
And the maximum bit rate (MAXRATE) is specified, the MPEG encoder controller 13 responds
Calculate the total number of bits (USB_BYTES) that is limited so that it is less than the maximum bit rate (MAXRATE), and from this value GO
Number of bits required for P header (GOP_HEADER) (TOTAL_HEADER)
DER) minus the number of supply bits (SUPPLY_BYT) that is the target value of the total number of targets from the total number of frames.
ES).

The number of supply bits (SUPPLY_B
The bit allocation calculation processing program inside the bit allocation calculation unit 22 is executed so as to be within the size of (YTES), and the bit amount (TARGET) allocated to each picture is allocated. FIG. 12 is a flowchart showing details of the bit allocation calculation process in step S103.

First, in step S201, as described above, the total bit amount (QTY_BYTES) sent from the supervisor controller 1 and the maximum bit rate (MAXRA)
Upon input of (TE), the MPEG encoder controller 13 supplies the number of supply bits (SUPPLY_BYT) as described above.
ES).

Next, the measurement file created by the measurement of the encoding difficulty in step S102 in FIG. 10 is read as it is in step S202, and when the encoding difficulty is measured, each of the images measured together is measured. From the DC value and the amount of change of the parameter of the magnitude of the motion vector amount ME, step S2
03 finds the point where the scene changes.

The scene change detection / processing in this step S203 has already been disclosed by the present applicant in Japanese Patent Application No. 8-27409.
"Video signal processing device" disclosed in the specification 4 and the drawings
Is a process of detecting a scene change point in accordance with.

This "video signal processing apparatus" detects the DC level of each frame of the video signal, and detects the frame of the scene change of the video signal from the error value obtained by approximating the DC level with a curve. , Clarify the scene change point.

Next, in step S204, a chapter (CH
APTER) Perform boundary processing. At the time of a chapter search in a DVD playback device, a jump is performed from an unspecified picture. To change. That is,
Change P picture to I picture.

Steps S204 and S
As a result of the series of operations at 205, the picture type (I,
(P, B picture) is changed, the picture type at the time of measuring the coding difficulty is changed. Therefore, in step S206, interpolation / correction is performed to the value of the coding difficulty corresponding to the changed picture type. I do.

In step S207, according to the encoding difficulty obtained by interpolation / correction of the encoding difficulty in step S206 and the total number of supply bits (SUPPLY_BYTES), the number of bits allocated to each picture in step S207 (TARG
ET).

Then, in step S208, RAID 16
After calculating the address at the time of writing the bit stream of the encoding result to step S209, the process proceeds to step S209.
Create a control file for the encoder.

For example, as a specific example of the bit allocation calculation,
First, a case will be described in which a bit amount is allocated in GOP units, and then bit allocation is performed in each GOP according to the encoding difficulty of each picture. Here, the GOP at the time of encoding is determined according to the sum of the encoding difficulty levels (GOP_DIFF) for each GOP.
The unit bit allocation amount (GOP_TARGET) is allocated. The sum of the encoding difficulty for each GOP (GOP_DIFF) and G
FIG. 13 shows an example of the simplest function for converting the bit allocation amount (GOP_TARGET) in OP units.

In this example, an evaluation function of Y = AX + B is used, where the vertical axis Y is the bit allocation amount (GOP_TARGET) in GOP units, and the horizontal axis X is the sum of the encoding difficulty levels for each GOP (GOP_DIFF). Note that the sum of the encoding difficulty levels of all the pictures (DIFFICULTY_SUM) is calculated in advance.

First, the total number of bits (USB_BYTES) limited so as to be equal to or less than the maximum bit rate is determined by the total bit amount (QTY_BYTE) given from the supervisor controller 1.
USB_BYTES = min (QTY_BYTES, MAXRATE × KT × TOTAL_FRAME_NUMBER) using S) and the maximum bit rate (MAXRATE).

Here, in the case of NTSC, KT = 1/8 (bits) / 30 (H
z), 1/8 (bits) / 25 (Hz) for PAL. Also, TOTAL_F
RAME_NUMBER is the total number of frames of the material to be encoded, min
(s, t) is a function that selects the smaller one of s, t.

The number of supply bits (SUPPLY_BYTES)
Is the limited total number of bits (USB_
BYTES) to the number of bits required for the GOP header (TOTAL_H
EADER) and SUPPLY_BYTES = USB_BYTES-TOTAL_HEADER (2)

The sum of the encoding difficulty of all pictures (DIFFICULTY_SUM) can be expressed as DIFFICULTY_SUM = ΣDIFFICULTY (3).

Also, the bit allocation amount (GO
The minimum value (GOP_MINBYTES) of (P_TARGET) is set to B = GOP_MINBYTES (4) as in the following equation (4).

Then, Σy = A × Σx + B × n as in the evaluation function shown in FIG. 12 is obtained.

Where Σy = SUPPLY_BYTES, Σx = D
IFFICULTY_SUM, n is the total number of GOPs.

Therefore, A = (SUPPLY_BYTES-B × n) / DIF
FICULTY_SUM. Then, the bit allocation amount (GOP_TARGET) for each GOP can be expressed as GOP_TARGET = A × GOP_DIFF + B (5).

Thereafter, bits are allocated in each GOP according to the degree of difficulty of encoding each picture. When the distribution of each picture in the GOP is proportional to the magnitude of the encoding difficulty, the target amount of each picture is obtained by the following equation (6).

Target (k) = GOP_TARGET × diffuculty (k) / GOP_diff (6) (1 ≦ k ≦ the number of pictures in GOP) A control file created using the target amount obtained in this manner Performs variable bit rate encoding according to the difficulty of the material image.

The quality of the encoded output image is shown in FIG.
When confirming by preview in step S104, it may be found that there is a problem with the image quality at a specific position. In such cases, customization (customiz
According to e), the image quality can be improved by increasing the target bit amount at the above position.

Here, it is assumed that the parameter change over time is customized to improve the image quality. As an example of the time information of this parameter, as shown in FIG.
Examples include those defined in the customization control file (weight.txt).

In the figure, ENCU_nb indicates the number of the role to be encoded, Filter indicates the strength of the filter, D_weight indicates the weighting factor at the time of bit allocation, and CS_enb indicates the customization enable. Here, the time information of the change point of the parameter is represented as a time code (Timecode).

The file (weig
ht.txt), the bit allocation is recalculated.
As a result of the recalculation of the bit allocation, a control file reflecting the customization is created.

The flow of the bit reallocation calculation at the time of customization is performed according to a series of procedures shown in FIG. In step S301, the range for customizing the image is set to a customization start point (KSATART) and a customization end point (KEND), and the subsequent step S302.
Specifies the customization level (D_WEGHT [k]). Then, in the next step S303, a customization control file (weight.txt) is created. Here, the customization level (D_WEGHT
Set the customization enable (CS_ENB [k]) in the range where the value of [k]) is not the initial value to 0. Then, a series of steps for setting the customization parameters is completed.

When encoding video of video information,
The image quality of the entire image is confirmed by preview based on the control file. If there is no problem in the image quality, the entire encoding is executed.

As described above, in order to improve the image quality at a specific position, there are cases where it is desired to increase the bit rate by increasing the number of target bits, which is the number of bits allocated by customization.

As described above, the calculation for customizing by bit reallocation is performed in step S4 as shown in FIG.
It is executed by a series of steps including steps from 01 to S407. The calculation of the bit redistribution is performed by a bit allocation calculation processing program provided in the bit allocation calculator 22 of the video encoding controller 20.

In step S401, the encoding conditions for this bit redistribution calculation are input, and in step S402
Specifies the range of customization. In step S403, the control parameters of the first bit allocation calculation result are input, and in step S404, the customization parameters are input using a customization control file (weight.txt).

In step S405, the number of target bits is calculated by the above-described method, and in step S4
At 06, an address for storing the customized data is calculated. Then, in step S407, an encoder control file is created, and this series of procedures ends.

[0053]

However, when the bit rate is improved by increasing the number of target bits allocated to the customization range R1 by bit reallocation, the total number of bits is fixed as shown in FIG. Therefore, the number of bits in the other range R2 is reduced in order to compensate for the bit increase in the range R1.

For this reason, there is a possibility that the image quality of other parts may be newly deteriorated due to the reduction in the number of bits. When the image quality is newly deteriorated, the image quality check and the encoding process may need to be performed again for the entire range.

Further, when the customization of the image quality and the image quality confirmation and encoding processing are repeatedly executed,
Work time T required for customization, Sourc the length of the material
If e_length and the number of customizations are CN, the product of the length of the material and the number of customizations, that is, T = Source_length × C
Given by N. Therefore, the length of the material Source_lengthd
Is large, the work time T becomes very long.

Further, if a specific position of an image is improved by customization, the image quality of other parts is repeatedly deteriorated, and there is a possibility that the operation of improving the image quality may not be converged.

The present invention has been made in view of the above-mentioned circumstances, and does not degrade the image quality of the other range in which the image quality is improved, reduces the working time, and improves the image quality. It is an object of the present invention to provide an image encoding method, an apparatus, and a recording medium for completing an operation in a predetermined number of steps.

[0058]

In order to solve the above-mentioned problems, an image encoding method according to the present invention comprises an intra-frame encoded image, an inter-frame forward predicted encoded image, and a bidirectional predicted encoded image. In an image encoding method for encoding a video material by an image encoding group including a predetermined number, a bit allocation step of calculating a bit allocation for each of the encoded images and securing a reserve data amount, A customization specifying step of specifying customization for image quality adjustment with respect to the bit allocation in the bit allocation step, and for each of the encoded images specified in the customization specifying step using the preliminary data amount, And a bit redistribution step of calculating the bit allocation again.

An image encoding apparatus according to the present invention encodes a video material by an image encoding group including a predetermined number of intra-frame encoded images, inter-frame forward predicted encoded images, and bidirectional predicted encoded images. In the image encoding apparatus to be customized, a customization designating unit that designates a customization range for image quality adjustment according to a user operation, and the above-mentioned encoded images for which the customization range is designated by the customization designating unit, Bit allocation means for calculating the bit allocation while securing the spare data amount, and for each of the encoded images within the customization range using the spare data amount, the bit allocation means for calculating the bit allocation again. is there.

[0060] A recording medium according to the present invention stores video material encoded by an image encoding group including a predetermined number of intra-coded images, inter-frame forward predicted coded images, and bidirectional predicted coded images. In the recording medium on which recording is performed, a spare data amount is secured at the time of the first bit allocation calculation for each of the encoded images, and the above spare is used when performing customization designation processing for image quality adjustment on the image after the first bit allocation. The bit allocation is calculated again for each of the encoded images specified in the customization specifying process using the data amount, and the video material is recorded.

[0061]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an image encoding method, apparatus and recording medium according to the present invention will be described below.
This will be described in detail with reference to the drawings.

The image encoding apparatus is a video encoding system for encoding a video material recorded on a digital video cassette tape for DVD, for example, and has a configuration as shown in FIG.

This video encoding system has basically the same configuration as the video encoding system shown in FIG.
The processing performed by the internal MPEG encoder controller 23 is different.

That is, in FIG. 1, in this video encoder system, the GUI encoder 21 controls the MPEG encoder controller 23 as control means for each encoded image in which the customization range for adjusting the image quality is specified according to the operation of the user. Then, the bit allocation is calculated in advance while securing the spare data amount, and the bit allocation is calculated again for each of the coded images within the customization designated range using the spare data amount. Note that the same reference numerals are given to the units performing the same operations as those in FIG. 9 and description thereof is omitted.

In the video encoding system and the image encoding method according to the video encoding system, that is, the bit allocation calculation processing program (BIT_ASSIGN) in the video encoding method, the following bit allocation method is employed. .

That is, in this bit allocation method, a certain number of bits are previously secured as a stock bit number (STC_BYTES) in the range before the reallocation calculation, and when customization is performed by the reallocation calculation, the stock bit number (STC_BYTE) is used.
From S), the bits used for bit redistribution at the time of customization are added to the sum of the amounts distributed at the time of the first bit allocation calculation within the range specified as the range of customization,
Amount (avl_byte
s), and does not change the bit amount of the part outside the customization range. As a result, it is possible to limit the range affected after customization, and the encoding operation time is greatly reduced.

In this bit allocation method, as shown in FIG. 2, the number of bits to be adjusted by customization is adjusted from the number of initially stocked bits (STC_BYTES) and the customization designated range (CS_ENABLE is 0) R1. Supply. In this way, the effect of the customization extends only to the range R1 in which the customization is performed, so that it is not necessary to check the image quality of the other ranges R2 and R3 again.
Therefore, the customizing operation always converges, and need not be repeated endlessly.

However, a problem with this method is that it is difficult to evaluate the number of stock bits (STC_BYTES) to be set first. Stock bits (STC_BYTE
If S) is too large, the overall image quality deteriorates. On the other hand, if it is too small, the range of customization becomes short, and satisfactory correction cannot be performed. Furthermore, if the range for customizing is small, the amount of adjustment of the bit distribution within the specified range increases.

Next, a method for obtaining the number of stock bits (STC_BYTES) will be described with reference to FIG.

FIG. 9A shows the total number of bits of the encoded output (QTY_BYTES) specified by the supervisor controller 1. When the total number of bits (QTY_BYTES) is multiplied by the number of bits of the specified maximum rate (MAXRATE), the total number of limited bits (USB_BYTES) shown in FIG.

The number of supply bits (SUPPLY_BYTES) is, as shown in FIG.
BYTES) minus the number of GOP header bits (GOP_HEADER).

For example, the number of stock bits (STC_BYTES)
In some cases, a stock bit number ratio (STC_RATE) to the supply bit number (SUPPLY_BYTES) may be secured. In this case, the number of stock bits (STC_BYTES)
Is given by the product of the number of stock bits (STC_BYTES) and the ratio of the number of stock bits (STC_RATE) (SUPPLY_BYTES × STC_RATE).

The number of supply bits (SUPPLY_BYTES) is the number of stock bits (STY_BYTES) to be stored for use at the time of reallocation as shown in FIG.
And the number of available bits (AV
L_BYTES).

Here, an example of the distribution of the number of bits in the bit distribution calculation processing executed by the MPEG encoder controller 23 will be described. This bit allocation calculation process is performed by a bit allocation calculation processing program provided in the bit allocation calculation unit 22 of the video encode controller 20 under predetermined control.

Here, the total number of bits (QTY_BYTES) shown in (A), the limited total number of bits (USB_BYTES) shown in (B), and the number of supply bits (S
UPPLY_BUTES), the number of available bits (AVL_BYTES) and the number of stock bits (STC_BYTES) shown in (D) are set, respectively.

Here, the total number of bits (QTY_BYTES), the total number of limited bits (USB_BYTES), and the number of supply bits (S
UPPLY_BUTES), the number of available bits (AVL_BYTES), and the number of stock bits (STC_BYTES) have the following relationship.

That is, the total number of limited bits (USB_BYTE
S) is equal to or less than the total number of bits (QTY_BYTES). Also, the number of bits of the supply bit number (SUPPLY_BYTES) is calculated from the limited total number of bits (USB_BYTES) by using the header (G
OP_HEADER). further,
The number of available bits (AVL_BYTES) is calculated from the number of supply bits (SUPPLY_BYTES) to the number of stock bits (STC_BYTE).
S) excluding the number of bits. These relationships are
It is expressed by the following equation.

QTY_BYTES> = USB_BYTES SUPPLY_BYTES = USB_BYTES-GOP_HEADER AVL_BYTES = SUPPLY_BYTES-STC_BYTES The number of available bits (AVL_BYTES) is determined by the number of target bits (TARGET_B) assigned to each picture.
YTES) and the remainder of the above allocation (REMAIN). Therefore, the remainder is expressed by the following equation.

REMAIN = AVL_BYTES-TARGET_BYTES The number of out bits (OUT_BYTES) which is the result of this series of bit allocation calculations is the number of target bits (TARGET_BY
TES) and the GOP header (GOP_HEADER). Therefore, the number of out bits is represented by the following equation.

OUT_BYTES = TARGET_BYTES + GOP_HEADER Next, an example of the bit redistribution calculation processing will be described.
This bit redistribution calculation process is also performed by the MPEG encoding controller 23 executing the bit allocation calculation processing program provided in the bit allocation calculation unit 22.

In this bit redistribution calculation processing, the limited total number of bits (USB_BYTES) in the bit allocation calculation processing shown in (A) in FIG. 5 becomes the number of retry bits (RETRY_BYTES) shown in (B). That is, the relationship between these bit numbers is represented by the following equation.

RETRY_BYTES = USB_BYTES The number of bits obtained by removing the number of GOP header bits (GOP_HEADER) from the number of retry bits (RETRY_BYTES) is shown in FIG.
ES). The relationship between these bit numbers is as shown in the following equation.

CHANGE_BYTES = RETRY_BYTES−GOP_HEADER The number of available bits (AVL_BYTES) is, as shown in (D) in the figure, the number of change bits (CHANGE_B
YTES) minus the number of hold bits (HOLD_BYTES). That is, the relationship between these bit numbers is given by the following equation.

AVL_BYTES = CHANGE_BYTES-HOLD_BYTES Here, the number of hold bits (HOLD_BYTES) is a target bit distributed at the time of the first bit distribution outside the range of customization in which the value of a customization enable (CS_ENABLE) described later is 1. This is the sum of the number of bits of the number (TARGET_BYTES).

The number of available bits (AVL_BYTES)
Is used, the number of change target bits (CHANGE_TARGET), which is the number of change bits of the allocation, is set according to the encoding difficulty of each picture specified in the customization range.

Here, since the maximum number of bits given to each picture is limited, as shown in FIG.
The remainder (REMAIN) of allocating the number of change target bits (CHANGE_TARGET) to each picture may occur. The following relationship exists between these bit numbers.

REMAIN = AVL_BYTES-CHANGE_TARGET The number of out bits (OUT_BYTES) which is the sum of the amount of bits output according to the result of this series of bit redistribution calculations
Is the number of bits obtained by combining the number of hold bits (HOLD_BYTES) and the number of change target bits (CHANGE_TARGET). That is, the relationship between these bit numbers is given by:

OUT_BYTES = CHANGE_TARGET + HOLD_BYTES
+ GOP_HEADER Here, an example of a parameter setting method at the time of customization for improving the image quality described above will be described.

If it is found that there is a problem with the image quality of a specific position when checking the image quality of the image of the encoded output by previewing, the target bit amount at the position is increased by customization to improve the image quality. Aim. For example, as a result of the image quality check in the preview, the time T
In some cases, the bit amount in the section from S to time TE is increased.

The video encoder controller 20 of the video encoder system has a GUI 21 through which a user can perform operations related to bit redistribution. Here, the GUI 21 is the monitor 1
8 is a graphical interface that can be set by using a window or the like displayed on the screen 8 and clicking an icon on the screen with a mouse or the like.

The monitor 18 displays at least a first window and a second window. In the first window, as shown in FIG. 6A, the target bit number (TARGET_BYTES), which is the allocated bit number before customization for each picture, is displayed in a time direction.

In the second window, the weight (weight) of the bit rate at the time of customization is displayed in the time direction as shown in (B) in the figure, and the level can be set. I have. Here, in the second window, the section from time TS to time TE has the first weight level W1, and the other sections have the basic level W0.

Customize enable (CS_ENABLE [k])
Is assigned to each frame or picture, and the value is 0
Is a negative logic flag for which the frame is to be customized. This customization enable (CS_ENABL
E [k]) is a basic level W0 for which the weight function (D_WEGHT [k]) of the frame is an initial set value, as shown in FIG.
In this case, the level becomes a high level (1), and in cases other than the basic level W0, the level becomes a low level (0). Here, k is an index for identifying a frame or a picture.

Next, the change in the number of allocated bits (TARGET_BYTES) of each picture before and after the bit redistribution will be described.

As an example of the distribution of the number of allocated bits (TARGET_BYTES) in each picture before bit redistribution,
(A) in FIG. 7 is mentioned. Here, as shown in (B) in the figure, the first picture to the twentieth picture in (A) in the figure are customized. For this purpose, the weight function (D_WEGHT [k]) of this range picture is set to the first weight level W1, and the other pictures are set to the basic level W0. At this time, the value of the customization enable (CS_ENABLE [k]) in the above range is 0, and the value in the other range is 1.

When the bits are redistributed according to the customization range set as described above, the number of bits allocated to the above range, ie, the first to twentieth pictures (TARGET_BYTES), as shown in FIG. Increases, but the number of bits allocated to other pictures (TA
RGET_BYTES) remains at the initial allocation.

Here, the coding difficulty of each picture is the product of the weight function (D_WEIGHT [k]) of the picture and the number of bits generated (GEN_BIT [k]) of the picture when the coding difficulty is measured. Is defined by That is, encoding difficulty (DIFFICULTY)
Is given by the following equation:

DIFFCULTY = D_WEGHT [k] × GEN_BIT [k] A method for obtaining the target amount which is the number of allocated bits will be described. This method uses the encoding difficulty (DI
FFICULTY) and the number of available bits (AVL_BYTES) to obtain an evaluation function, and calculate the target amount (GO
P_TARGET).

As described above, at the time of calculating the bit redistribution, the number of change bits (CHANGE_BYTES) is defined as the number of bits obtained by subtracting the number of bits allocated per GOP (GOP_HEADER) from the limited number of bits (USB_BYTES). The number of available bits (AVL_BYTES) is defined as the number of bytes obtained by subtracting the number of hold bits (HOLD_BYTES) from the number of change bits (CHANGE_BYTES). That is, the relationship between these bit numbers is expressed by the following equation.

CHANGE_BYTES = USB_BYTES-GOP_HEADER AVL_BYTES = CHANGE_BYTES-HOLD_BYTES On the other hand, the total encoding difficulty (DIFICULTY_SUM) is a value for a picture whose customization enable (CS_ENABLE [K]) has a value of 0 and has a weight other than the basic level W0. , Encoding difficulty.

DIFFICULTY_SUM = ΣDIFFICULTY [k] (CS_E
When NABLE [k] is 0), B is the minimum number of bits of a GOP (GOP_MIBUYES),
The sum Σy of y is calculated as the number of available bits (AVL_BY
TES), the sum of xΣx is the sum of the encoding difficulty (DIF
FICULTY_SUM), where n is the total number of GOPs, the following relational expression holds.

Σy = A × Σx + B × n However, the following quantities are used.

B = GOP_MINBYTESΣy = AVL_BYTESΣx = DIFFICULTY_SUM Therefore, A is given by the following equation.

A = (AVL_BYTES−B × n) / DIFFICULTY_SUM And the number of bits allocated in GOP units is (GOP_TARGE
T) is given by the following equation.

GOP_TARGET = A × GOP_DIFF + B Further, the encoding difficulty of each picture (DIFF
Bit allocation according to ICULTY [k]) is performed. The distribution of each picture in a GOP can be proportional to the magnitude of the encoding difficulty. In this case, the number of bits assigned to each picture (TARGET) is obtained by the following equation. Here, k is between 1 and the total number of pictures in the GOP.

TARGET [k] = GOP_TARGET × DIFFICULTY [k] / GOP_DIFF (1 ≦ k ≦ the number of pictures in GOP) Note that the total encoding difficulty (DIFICULTY_SUM) is the value of the customization enable (CS_ENABLE [K]). Is used, the amount of the first bit allocation calculation for the picture whose weight is the basic level W0 is used as it is.

A series of procedures relating to the above-described bit reallocation will be described with reference to a flowchart shown in FIG.

First, in step S1, the encoding conditions for this video redistribution are input, and in the next step S2, the control parameters of the first bit allocation calculation result are input. Then, the process proceeds to the next step S3.

In step S3, a customization designation parameter is input, and in the next step S4,
The total number of redistributed bits (AVL_BYTES) is calculated by adding the stock amount to the sum of the allocation calculation of the initial number of bits in the range to be recalculated. Then, the process proceeds to step S5.

In step S5, the target bit number (TARGET) to be recalculated is calculated for the total redistributed bit number (AVL_BYTES). And step S
Proceed to 6.

In step S6, an address for writing the bit stream of the encoding result in RAID 16 is calculated. Then, in step S7, an encoder control file is created, and this series of steps ends.

Note that the image encoding method and the image encoding device described in the above embodiments can be similarly applied to a recording medium.

That is, in the recording medium which records the video material encoded by the GOP, as described above,
The number of stock bits (STC_
By using (STC_BYTES), this number of stock bits can be used during bit allocation calculation when customizing to improve image quality without deteriorating image quality outside the customization range. An encoded image with improved image quality in this range can be recorded.

[0114]

In the image coding method, the image coding apparatus and the recording medium according to the present invention, it is possible to specify a range to be subjected to the bit reduction by the bit reallocation at the time of the bit reallocation calculation after the customization. Therefore, the image quality of the portion outside the customized range does not deteriorate. Furthermore, since the range in which the image quality is checked after the bit redistribution is narrowed, the encoding time can be significantly reduced.
Then, the encoded image having the above image quality can be recorded on the recording medium.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of an example of an embodiment of a video encoding system according to an image encoding method, an image encoding device, and a recording medium according to the present invention.

FIG. 2 is a data structure diagram showing the distribution of the number of bits of an encoded image before and after bit redistribution.

FIG. 3 is a data structure diagram showing the distribution of the number of bits of the encoded image.

FIG. 4 is a data structure diagram showing the distribution of the number of bits of the encoded image at the time of bit distribution.

FIG. 5 is a data structure diagram showing the distribution of the number of bits of the encoded image at the time of bit redistribution.

FIG. 6 is a plan view showing first and second windows.

FIG. 7 is a graph showing the number of allocated bits before and after the re-bit allocation of each picture of the coded image and the weight of the customization enable.

FIG. 8 is a flowchart showing a series of steps relating to the bit number redistribution of the encoded image.

FIG. 9 is a block diagram schematically showing a specific example of a conventional video encoder system.

FIG. 10 is a schematic diagram illustrating an example of the structure of a GOP.

FIG. 11 is a flowchart showing a series of steps relating to the operation of the video encoder system.

FIG. 12 is a flowchart showing a series of steps related to a conventional calculation of bit allocation.

FIG. 13 is a graph showing an example of an evaluation function relating to a bit allocation amount in GOP units.

FIG. 14: Customization control file (weig
ht.txt) is a table showing the contents of an example.

FIG. 15 is a flowchart showing a series of steps relating to customization parameter setting.

FIG. 16 is a flowchart showing a series of steps related to a conventional calculation of bit redistribution.

FIG. 17 is a data structure diagram showing an influence on another number of bits by a conventional calculation of bit redistribution.

[Explanation of symbols]

1 Supervisor controller, 16 RAID, 2
0 video encoder controller, 22 bit allocation calculator, 25 MPEG encoder

Claims (6)

[Claims] 1. An image encoding method for encoding a video material by an image encoding group including a predetermined number of intra-frame encoded images, inter-frame forward predictive encoded images, and bidirectional predictive encoded images. A bit allocation step for calculating the bit allocation for each of the encoded images and securing a reserve data amount; and a customization specifying step for specifying customization for adjusting the bit allocation in the bit allocation step. And a bit redistribution step of calculating a bit allocation again for each of the encoded images specified in the customization specifying step using the spare data amount. 2. The image code according to claim 1, wherein said bit allocation step calculates the bit allocation based on the encoding difficulty of each of the encoded images, and secures the spare data amount. Method. 3. The image encoding method according to claim 1, wherein said customization specifying step performs customization specification based on a user operation. 4. An image encoding apparatus for encoding a video material by an image encoding group including a predetermined number of intra-frame encoded images, inter-frame forward predictive encoded images, and bidirectional predictive encoded images. Customization designating means for designating a customization range for adjustment in accordance with a user operation; and a bit allocation and reserve data amount are secured in advance for each of the coded images for which the customization range is designated by the customization designating means. Control means for calculating the bit allocation again for each of the encoded images within the customization range using the spare data amount. 5. The image encoding apparatus according to claim 4, wherein said control means calculates a bit allocation in advance based on the degree of difficulty of encoding each of said encoded images, and secures said spare data amount. Device. 6. A recording medium for recording a video material encoded by an image encoding group including a predetermined number of intra-frame encoded images, inter-frame forward predictive encoded images, and bidirectional predictive encoded images. In the above, reserve the amount of spare data at the time of the first bit allocation calculation for each of the coded images, and use the spare data amount when performing customization designation processing for image quality adjustment on the image after the first bit allocation. A recording medium characterized in that the bit allocation is calculated again for each of the encoded images specified in the customization specifying process, and the video material is recorded.