JP3465316B2 - Video signal encoding method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal coding system, and more particularly to a video signal quantization control system.

[0002]

2. Description of the Related Art FIG. 6 shows, for example, ISO-IEC / JTC1 / SC29 / WG11 M.
FIG. 9 is a schematic block diagram showing a conventional video signal encoding system shown in PEG 92 / N0245 Test Model 2. In the figure,
The digitized video signal 1101 input from the input terminal 101a is supplied to the first input of the subtractor 9, the first input of the motion compensation prediction circuit 16 and the second input of the quantization circuit 11. The output 1102 of the subtractor 9 is the DCT
It is supplied to the first input of the quantizing circuit 11 via the circuit 10. The output 1104 of the quantization circuit 11 is given to the input of the transmission buffer 19 via the variable length coding circuit 18, and is given to the first input of the adder 14 via the dequantization circuit 12 and the IDCT circuit 13. To be Adder 1
4 is provided to a first input of the memory circuit 15, and an output 1108 of the memory circuit 15 is provided to a second input of the motion compensation prediction circuit 16 and a first input of the switching circuit 17.
Given to the input of. The second output of the memory circuit 15 is provided with the first output 1111 of the motion compensation prediction circuit 16. On the other hand, the zero signal is given to the second input of the switching circuit 17, and the second output 1110 of the motion compensation prediction circuit 16 is given to the third input of the switching circuit 17. The output 1109 of the switching circuit 17 is the subtractor 9
And the second input of adder 14. On the other hand, the second output 1113 of the transmission buffer 19 is supplied to the third input of the quantization circuit 11, and the transmission buffer 1
The first output 1114 of 9 is output from the output terminal 2d.

FIG. 7 shows, for example, ISO-IEC / JTC1 / SC29 / WG11 MPE.
FIG. 9 is a schematic block diagram showing an example of a quantization control method in the conventional video signal coding method shown in G 92 / N0245 Test Model 2. In the figure, the first generated code amount 1201 input from the input terminal 101d is the complexity calculation circuit 2
0a of the first average quantization step parameter 1202 given to the first input of the input terminal 101e.
Is given to the second input of the complexity calculation circuit 20a. The first complexity 1203, which is the output of the complexity calculation circuit 20a
Is supplied to the first input of the target bit amount calculation circuit 4e. The second generated code amount 1204 input from the input terminal 101f is given to the first input of the complexity calculation circuit 20b, and the second average quantization step parameter 1205 input from the input terminal 101g is the complexity calculation. It is applied to the second input of the circuit 20b. Complexity calculation circuit 20
The second complexity 1206 which is the output of b is given to the second input of the target bit amount calculation circuit 4e. Third generated code amount 1207 input from input terminal 101h
Is given to the first input of the complexity calculating circuit 20c, and the average quantization step parameter 1208 in the previous B picture inputted from the input terminal 101i is given to the second input of the complexity calculating circuit 20c. Complexity calculation circuit 20
The third complexity 1209, which is the output of c, is given to the third input of the target bit amount calculation circuit 4e.

The fourth input of the target bit amount calculation circuit 4e is the first remaining number 1 from the input terminal 101j.
210 has a second input from the input terminal 101k for the fifth input.
1211 is input. The sixth input has a constant Kp1212, which is the output of the constant generating circuit 21a.
However, the constant Kb1213, which is the output of the constant generation circuit 21b, is input to the seventh input. Further, the remaining code amount 1214 is input to the eighth input from the input terminal 101l. A picture type 1215 is input to the ninth input from the input terminal 101m.

The target bit amount 1217, which is the output of the target bit amount calculation circuit 4e, is given to the first input of the virtual buffer selection circuit 22a. The generated code amount input from the input terminal 101c is input to the second input of the virtual buffer selection circuit 22a. A picture type 1215 is input to the third input from the input terminal 101m. The target bit amount 1218, which is the first output of the virtual buffer selection circuit 22a, is input to the first input of the first virtual buffer remaining amount calculation circuit 5e, and the generated code amount 1219 up to the current macroblock which is the second output. Is the first
Is input to the second input of the virtual buffer remaining amount calculation circuit 5e. The target bit amount 1220 that is the third output of the virtual buffer selection circuit 22a is generated at the first input of the second virtual buffer remaining amount calculation circuit 5f up to the current macroblock in the current picture that is the fourth output. Code amount 12
21 is input to the second input of the second virtual buffer remaining amount calculation circuit 5f. The fifth of the virtual buffer selection circuit 22a
The target bit amount 1222, which is the output of the third virtual buffer remaining amount calculation circuit 5g, is input to the first input of the third virtual buffer remaining amount calculation circuit 5g, and the generated code amount 1223, which is the sixth output, It is input to the second input.

The output 1224 of the first virtual buffer remaining amount calculating circuit 5e is supplied to the first input of the virtual buffer selecting circuit 22b and the output 1224 of the second virtual buffer remaining amount calculating circuit 5f.
25 is a second input of the virtual buffer selection circuit 22b,
Output 1226 of the third virtual buffer remaining amount calculation circuit 5g
Is applied to the third input of the virtual buffer selection circuit 22b. For the fourth input of the virtual buffer selection circuit 22b,
The picture type 1215 is input from the input terminal 101m. The output 1227 of the virtual buffer selection circuit 22b is
The reference quantization step parameter 1228 that is given to the quantization step parameter calculation circuit 6e and is the output of the quantization step parameter calculation circuit 6e is given to the first input of the adaptive quantization circuit 7e. The adaptive quantization coefficient 1229 is applied to the second input of the adaptive quantization circuit 7e from the input terminal 101n. The quantization step parameter 1230 output from the adaptive quantization circuit 7e is output to the output terminal 2
It is output from e.

FIG. 8 is a conceptual diagram of the refresh system which is one of the prominent properties of the hybrid coding system.

Next, the operation will be described. As one of high-efficiency coding schemes for coding a video signal, there is a hybrid coding scheme in which inter-picture predictive coding using motion compensation prediction and intra-picture transform coding are combined. This conventional example also employs the above hybrid coding method. In this case, the digitized input signal is subjected to DCT in the spatial axis direction by taking the difference between the images using motion compensation prediction in order to reduce the redundancy in the time axis direction. The transformed coefficients are quantized, variable-length coded, and then transmitted through a transmission buffer.

The basic concept of quantization control will be described below. Generally, in a video signal encoding system, the transmission rate is fixed, so that a method for converging the generated code amount to the transmission rate is required. The concept of the method of converging the generated code amount to the fixed transmission rate is shown below. In general, the converted coefficient cannot always be expressed with a finite number of digits. Representing this coefficient with a finite number of digits is called quantization, a discrete value by quantization is called a quantization level, and an interval between quantization levels is called a quantization step. Also, the difference between the coefficient before quantization and the quantization level after quantization is called quantization noise. If the quantization step is made smaller, the quantization noise will be reduced, but the generated code amount will be increased.If the quantization step is made larger, the quantization noise will be increased, but the generated code amount will be reduced. Become. Controlling the quantization step in this way is called quantization control. That is, the quantization control makes it possible to converge the generated code amount to the transmission rate. At this time, it is an important subject to converge to a fixed rate while maintaining good image quality. In this conventional example, a quantization step parameter is used as an index similar to the quantization step. The function of the quantization step parameter may be considered to be equivalent to the quantization step.

The following two are defined as units for performing quantization control. Standard fixed rate period Standard control period

The reference fixed rate period means a unit or period in which the generated code amount is determined to be a fixed rate. For example, the sum of the generated code amounts in a certain number of screens may be a fixed rate, or the generated code amount in one screen may be a fixed rate.
If this fixed rate period is large, the tolerance of fluctuations in the generated code amount within that period increases. For example, in a moving image, the generated code amount changes for each picture as the image moves. Therefore, in order to continuously obtain stable image quality, it is effective that the fixed rate period is large.
However, in order to increase the tolerance of fluctuations in the generated code amount,
A large capacity buffer is required. A large capacity buffer means an increase in delay time in the encoding / decoding system. On the other hand, if the fixed rate period is small, the admissibility of the generated code amount becomes low. For example, a fraction of the screen
If the degree is set as a fixed rate period, it is not possible to sufficiently allow the fluctuation of the generated code amount in the screen. For example, in a moving image, there is often a case where only one part in the screen is moving. In such a case, the degree of image quality deterioration in the screen varies greatly depending on the position in the screen. there is a possibility. However, in this case, the buffer capacity may be small, which means that the delay time in the coding / decoding system is small.

The reference control period is defined as follows. Basically, the quantization control is to check the state of the generated code amount every certain period, verify whether or not it matches the desired generated code amount, and change the quantization step parameter if it does not match. That is the work. The above period is defined as the standard control period. If this reference control period is large, the code amount becomes excessively large or small, which easily causes a buffer overflow or underflow. If this reference period is short, overflow or underflow is unlikely to occur, but a high degree of accuracy is required to predict the desired generated code amount. Uncertain prediction of the desired amount of generated code causes unnecessary fluctuation of the quantization step parameter,
This causes local deterioration of image quality.

In describing the quantization control method in this conventional example, the hierarchical structure of the video signal in this conventional example will be defined, and one property of the hybrid coding related to the hierarchical structure will be described below.

The hierarchical structure of the video signal in this conventional example is outlined as follows. Sequence: Consists of one or more consecutive GOPs. GOP: Composed of a plurality of consecutive pictures (screens). Picture: One screen, which is composed of multiple slices. Slice: It consists of one or more macroblocks. Macro block: It consists of four luminance blocks and a color difference block at the same position on the screen. Block: One block is composed of 8 × 8 pixels. In this conventional example, three types of pictures are defined. There are three types: I picture that does not perform inter-picture predictive coding but only intra-picture conversion coding, P picture that predicts from only one direction, and B picture that predicts from both directions.

Next, one of the prominent properties of the hybrid coding system is listed below. In this conventional example, inter-picture predictive coding using motion compensation prediction is performed. this is,
Since it is basically time-domain predictive coding, it is necessary to set an initial value. Further, in order to prevent the propagation of an error that occurs accidentally after encoding, it is necessary to set the initial value at an appropriate cycle. This periodic initial value setting operation is generally called periodic refresh. The periodic refresh in the case of the hybrid method using inter-picture predictive coding using motion compensation prediction and intra-picture transform coding is specifically intra-picture transform coding without motion-compensated prediction.
Generally, as a refresh method, there are a method of collectively performing screens and a method of performing divided screens. The system referred to in the conventional embodiment is the former, and its refresh screen is called an I picture. In the case of the screen division refresh method, for example, the screen is divided into several areas, and one area is refreshed for each screen. FIG. 8 shows a conceptual diagram of the refresh method. In general, intra-picture transform coding has a larger amount of generated code than inter-picture predictive coding, and therefore, when performing periodic refresh in screen units, a large reference fixed rate period of about several pictures is adopted. This means that the delay time in the encoding / decoding system is large.

Next, the quantization control method in the conventional example will be described. FIG. 7 is a diagram for explaining an example of the quantization control method in the conventional example. In this conventional example, basically, 1 GOP period is adopted as the reference fixed rate period and 1 macroblock period is adopted as the reference control period. The quantization control is performed in the following procedure. Estimate the bit amount (target bit amount) that can be used in the encoding of the next picture. The reference value of the quantization step parameter for each macroblock is set based on the estimated target bit amount and the actually generated code amount. The reference value of the quantization step parameter is changed according to the feature of the image for each macroblock, and the final quantization step parameter for each macroblock is determined.

The details will be described below. As the first procedure, the amount of bits that can be used in encoding the next picture is estimated. Introducing the concept of complexity in this work.
In this conventional example, complexity is defined for each picture type. Also, the complexity is updated every time one picture is encoded. In reality, since the coded picture has a certain picture type, one complexity will be updated each time one picture is coded. Immediately before encoding the f-th picture of the g-th GOP, the complexity Xi (g, f) of the I picture and the complexity Xp of the P picture
The complexity Xb (g, f) of (g, f) and B picture is defined as follows. Xi (g, f) = Si (s, x) × Qi (s, x) Xp (g, f) = Sp (t, y) × Qp (t, y) Xb (g, f) = Sb (u , z) × Qb (u, z)

At this time, Si (s, x) is the actual amount of generated code in the xth picture of the sGOP, which is the I picture that existed in the closest past, and Sp (t, y) is in the closest past. Sb (u, z) is the actual amount of generated code in the y-th picture of the t-th GOP, which is the P-picture, and is the actual amount of generated code in the z-th picture of the u-th GOP, which is the closest B picture that existed in the past. . (At this time, one of the above three pictures should correspond to the f-1th picture of the gGOP.) Also, Qi (s, x), Qp (t, y), Qb
(u, z) is the average value of the actual quantization step parameters in the above three pictures.

Based on the complexity, the target bit amount T (g, f) of the f-th picture of the g-th GOP is estimated as follows.

[0020]

[Equation 1]

[0021] R (g, f) is the total number of remaining bits allocated to the g-th GOP immediately before the f-th picture of the g-th GOP is coded, and is updated as follows after the coding of each picture. R (g, f) = R (g, 1)-{S (g, 1) + S (g, 2) +… + S (g, f-
1)} Here, S (g, f-1) represents the actual generated code amount in the (f-1) th picture of the gth GOP. Further, the following calculation is performed before the head picture of the GOP is encoded. R (g + 1,1) = G + R (g, f + 1) G = BIT_RATE × (F / PICTURE_RATE) At this time, F is the number of pictures per GOP, and R (1, 1) = G Further, Fp (g, f) and Fb (g, f) are the number of pictures of the P picture and the B picture that remain unencoded in the current GOP immediately before encoding the fth picture of the gth GOP. Show.

Next, as the second procedure, the reference value of the quantization step parameter for each macroblock is set based on the estimated target bit amount and the actual generated code amount. A virtual buffer is assumed when setting the reference value.
The virtual buffer is a buffer that roughly stores the difference between the target bit amount and the actual generated code amount. A virtual buffer is assumed for each picture. That is, if the picture is an I picture, the virtual buffer for the corresponding I picture is, if the picture is a P picture, the virtual buffer for the corresponding P picture is, and if the picture is a B picture, the corresponding B picture is Is used, and the buffer occupancy of the virtual buffer is changed. For example, if the picture type of the f-th picture of the g-th GOP is an I-picture, the occupation ratio di (g, f, m immediately before encoding the m-th macroblock of the f-th picture of the g-th GOP of the virtual buffer for I-pictures. ) Is defined as follows. di (g, f, m) = di (g, f, 1) + B (g, f, 1) + B (g, f, 2) +…
+ B (g, f, m-1)-{T (g, f) × ((m-1) / MB_cnt)} where MB_cnt is the number of macroblocks per picture, and B (g, f, m-1) f, m-1) is the actual generated code amount in the m-1th macroblock of the fth picture of the gth GOP. For di (g, f, 1), the buffer occupancy ratio di (a, b, MB_cnt + 1) in the b-th picture of the a-th GOP, which is the picture of the same type that existed in the closest past, is adopted. Further, the occupancy rate dp (g, f, m) of the virtual buffer for the P picture and the occupancy rate db (g, f, m) of the virtual buffer for the B picture are similarly updated according to the picture type.

The virtual buffer occupancy ratios di (g, f, m), dp (g,
Based on f, m) and db (g, f, m), the reference value Qr (g, f, m) of the quantization step parameter of the m-th macroblock of the f-th picture of the g-th GOP is calculated as follows. It If (the f-th picture of the g-th GOP is an I-picture) Then Qr (g, f, m) = (di (g, f, m) / VB) × 31 If (the f-th picture of the g-th GOP is a P-picture) Then Qr (g, f, m) = (dp (g, f, m) / VB) × 31 If (the f-th picture of the g-th GOP is a B-picture) Then Qr (g, f, m) = (db (g, f , m) / VB) × 31 At this time, VB: virtual buffer capacity.

Next, as the third procedure, the above Qr (g, f,
Based on m), the final quantization step parameter for each macroblock is determined. In the present embodiment, the adaptive quantization coefficient K (g, f,
m) is obtained, and the final quantization step parameter Q (g, f, m) for each macroblock is calculated as follows. Q (g, f, m) = Qr (g, f, m) × K (g, f, m)

[0025]

The quantization control method in the conventional video signal coding method is mainly intended for the case where the screen is collectively refreshed periodically.
It is not optimized for the case of dividing the screen and performing periodic refresh. Moreover, the calculation method of the complexity and the quantization step parameter is not quantitatively optimal.

The present invention has been made to solve the above problems, and an object thereof is to obtain a quantization control method suitable for the screen division refresh method and a quantization control method based on quantitative properties. .

[0027]

According to a first aspect of the present invention, there is provided a video signal coding method, wherein an image composed of a plurality of blocks is subjected to either intra-picture transform coding or inter-picture predictive coding for each block. of a video signal encoding method for encoding by applying an encoding method, image signal power represent the complexity of the image of the picture, and pre-Symbol both inter-image signal power representing the complexity of the motion block For each of the blocks to which the intra-picture transform coding of the current frame is applied,
The image obtained one frame before for the block
The complexity is predicted using the internal signal power, and the
For blocks to which inter-picture predictive coding is applied,
The inter-image signal pattern obtained one frame before
Using word to predict the complexity of predicted complexity Ichikaku
The sum of face areas and the single or multiple blocks
On the basis of the ratio of the predicted complexity of each region within one screen that, with the estimated amount of bits available in each area, the estimated amount of bits actually generated code amount of the current frame it is for setting the quantization step in each region of the current frame based on the difference.

Further, the area where the block are mixed to apply image transform coding and inter-picture predictive coding,
The complexity of each block included in the area, and
Intra-picture transform coding and inter-picture transform coding in the domain
The complexity is predicted based on the number of blocks to which the optimization is applied .

[0029]

[0030]

The video signal coding method according to claim 1 of the present invention is the complexity predicted for each region based on the previous image.
The amount of bits available in each region
Based on the difference between the amount of bits generated and the amount of codes actually generated
Then, the quantization step of each area is set.

In the video signal coding method according to the second aspect of the present invention, an area in which blocks to which intra-picture transform coding and inter-picture predictive coding are applied coexist is set in the area.
The complexity of each included block, and the area
To apply intra-picture transform coding and inter-picture transform coding.
Predict complexity based on the number of blocks

[0032]

[0033]

【Example】

Example 1. The first embodiment of the present invention will be described below. FIG. 2 is a schematic block diagram for explaining an example of the quantization control system in the first embodiment of the present invention. In the figure, the average inter-image signal power 201 input from the input terminal 1a is the first input of the target complexity calculation circuit 3a, and the average intra-image signal power 202 input from the input terminal 1b is the target complexity calculation The reference quantization step parameter 203 input from the input terminal 1c to the second input of the circuit 3a is the target complexity calculation circuit 3a.
The type identification signal 204 input from the input terminal 1d is input to the third input of the target complexity calculation circuit 3a.
The generated code amount 205 independent of the quantization input from the input terminal 1e is input to the target complexity calculation circuit 3
provided to the fifth input of a. The output 206 of the target complexity calculation circuit 3a is the target bit amount calculation circuit 4
The buffer remaining amount 207 input from the input terminal 1f to the first input of a is supplied to the second input of the target bit amount calculation circuit 4a. Target bit amount calculation circuit 4
The target bit amount 208 that is the output of a is the first input of the virtual buffer remaining amount calculation circuit 5a, and the generated code amount 209 that is input from the input terminal 1g is the second input of the virtual buffer remaining amount calculation circuit 5a. Given to. The output 210 of the virtual buffer remaining amount calculation circuit 5a is given to the input of the quantization step parameter calculation circuit 6a. The reference quantization step parameter 211, which is the output of the quantization step parameter calculation circuit 6a, is given to the first input of the adaptive quantization circuit 7a. The adaptive quantization coefficient 212 is given to the second input of the adaptive quantization circuit 7a from the input terminal 1h. The quantization step parameter 213 for each macroblock, which is the output of the adaptive quantization circuit 7a, is output to the output terminal 2
It is output from a.

FIG. 3 is a diagram showing a schematic relationship between the complexity referred to in the quantization control method and the generated code amount in the first embodiment of the present invention.

The operation will be described below. In recent years, the development of high-efficiency coding apparatus for video signals has been shifting to the development of high-resolution systems including HDTV signals. At this time, the high-resolution system inevitably requires high-speed processing. Generally, by adopting parallel processing, high speed performance is supplemented.

FIG. 1 is a diagram showing a main hierarchical structure of a video signal in the first embodiment. FIG. 1B is the same as FIG.
FIG. 7 is a diagram in which a picture in is vertically divided into S pieces.
At this time, each of the S divided areas is called a sub-picture, and each sub-picture becomes a unit for performing parallel processing.
It should be noted that the divided area of the sub-picture is not limited to this example. FIG. 1C is a diagram in which each sub-picture is further divided into L pieces. At this time, in each sub-picture, each of the L divided areas is GOB (Gro).
Up of Block). It should be noted that the GOB division area does not follow only this example. Also, FIG. 1 (d)
Such as GOB that exists in the same position in each sub-picture
Are collectively called a slice. As in the conventional example, there are macroblocks and blocks as lower layers of GOB.

Even in the case of parallel processing, in order to prevent deterioration of image quality depending on the position on the screen, the quantization control needs to treat all sub-pictures collectively, that is, as a picture. At this time, basically, when GOBs existing at the same position in each sub-picture are processed at the same time, the quantization control is processed in slice units. It should be noted that the slice is for the purpose of collectively processing the regions processed at the same time, and the divided regions do not follow only this example.

FIG. 2 is a diagram for explaining an example of the quantization control method in the first embodiment of the present invention. In this embodiment, basically, one picture period is used as a reference fixed rate period, One slice period is adopted as the control period, and the quantization control is performed according to the following procedure based on the main hierarchical structure. Estimate the bit amount (target bit amount) that can be used for encoding each slice of the next picture. The reference value of the quantization step parameter for each macroblock is set based on the estimated target bit amount and the actually generated code amount. The reference value of the quantization step parameter is changed according to the feature of the image for each macroblock, and the final quantization step parameter for each macroblock is determined.

In this embodiment, the case of performing parallel processing or the case of dividing a screen and performing periodic refreshing is also considered. Therefore, in this embodiment, GOB will be described as a basic unit.

The details will be described below. As the first procedure, the amount of bits that can be used for encoding each slice of the next picture is estimated. For this work, in this embodiment,
For each GOB, a pattern target complexity and a motion target complexity are defined. The pattern target complexity is
The target complexity is defined based on the intra-image signal power, and the motion target complexity is the complexity defined based on the inter-image signal power.

The image signal power Eint is defined as follows, for example, in macroblock units. When the macroblock size is P (pixels) × Q (lines) and the signal value of the (p, q) component of the macroblock is V (p, q), P, Q: represents the size of the macroblock Constants p and q: variables that represent positions within the macroblock

[0042]

[Equation 2]

It is assumed that The in-image signal power Eint does not have to comply with the above definition as long as it is an index indicating the complexity of the pattern of the input image. For example, the absolute value sum or the absolute value sum of squares of the conversion coefficients excluding the DC component after the input signal is subjected to the conversion coding and the specific quantization is performed for each conversion coefficient may be used.

The inter-picture signal power Emc is defined as follows, for example, in macroblock units. The macroblock size is P × Q, and (p,
When the signal value of the q) component is V (p, q) and the signal value of the (p, q) component of the motion compensation prediction block of the macroblock is R (p, q),

[0045]

[Equation 3]

It is assumed that The inter-image signal power Emc does not have to comply with the above definition as long as it is an index representing the complexity of the movement of the input image. For example, the sum of absolute values or the sum of absolute values squared after transform-encoding the signal after motion compensation prediction and performing specific quantization for each transform coefficient may be used.

[0047] The s sub-picture of the picture target complexity Yint of the h slice of the f picture (f, h, s) and the motion target complexity Ymc (f, h, s) is a function fint and functions fm
It is defined as follows using c. Yint (f, h, s) = fint (GOBaverage_Eint (f-1, h, s), Q (f,
h, s)) Ymc (f, h, s) = fmc (GOBaverage_Emc (f-1, h, s), Q (f,
h, s), Sv (f-1, h, s)) At this time, GOBaverage_Eint (f-1, h, s) and GOBaverage
_Emc (f-1, h, s) is the average Eint and the average Emc of the s-th sub-picture of the h-th slice of the (f-1) -th picture, and Q
(f, h, s) is the average value of the quantization step parameters actually used in the s-th sub-picture of the h-th slice of the f-th picture, and Sv (f-1, h, s) is the f-1 picture number
This is a code amount that does not depend on quantization among the code amounts actually generated in the s-th sub-picture of the h slice. Sv (f, h, s)
Indicates the code amount of information that is not quantized, such as the address of a macroblock, the quantization step parameter, and the information of a motion vector in motion compensation. In addition, Sv
As the approximate value of (f, h, s), only the code amount of the motion vector in motion compensation may be used. If GOBaverage_Eint (f-1, h, s) or GOBaverage_Emc (f-1, h, s) or Sv (f-1, h, s) cannot be used due to the delay due to the hardware configuration, Is defined as Yint (f, h, s) = fint (GOBaverage_Eint (f-2, h, s), Q (f,
h, s)) Ymc (f, h, s) = fmc (GOBaverage_Emc (f-2, h, s), Q (f,
h, s), Sv (f-2, h, s))

In the above definition, the functions fint and fmc are
It is defined as follows. 3 (a) shows, GOBaverage_Eint of the s sub-picture of the first h slice of the f picture
It is a figure which shows the schematic relationship of (f, h, s) and the generated code amount Sint (f, h, s) when the said GOB is intra-coded. As is clear from the figure, from GOBaverage_Eint (f, h, s) and Q (f, h, s)
It is possible to estimate Sint (f, h, s). This estimated generated code amount is the pattern target complexity Yint. 3B and 3C show GOBaverage_Emc (f, h, s) of the s-th sub-picture of the h-th slice of the f-th picture and the above G.
It is a figure which shows the schematic relationship of the generation | occurrence | production code amount Smc (f, h, s) at the time of encoding OB between images. FIG. 3B shows the generated code amount Sm.
Of c (f, h, s), the proportion of the code amount Sv (f, h, s) that does not depend on the quantization step parameter Q (f, h, s) such as the motion vector code amount in motion compensation is small. FIG. 3C shows a case where the code amount Sv (f, h, s) independent of the quantization occupies a large proportion of the generated code amount Smc (f, h, s). . Therefore, Smc (f, h, s) is GOBaverage_Emc (f, h, s
s), Q (f, h, s) and Sv (f, h, s), and the estimated generated code amount is the motion target complexity Ymc. Function f
int and fmc are defined based on the above quantitative properties.

By the way, in the present embodiment, both the screen batch refresh and the screen division refresh are assumed as the periodic refresh. Further, it is assumed that the screen division refresh area is a slice unit. That is, it may be considered that there are cases where intra-picture coding is performed in slice units.

Based on the above, the final f-th picture
Target Complexity Y (f of the s subpictures h slice,
h, s) is defined as follows depending on whether the slice to which the GOB belongs is an intra-picture encoded slice. If (The slice type to which the GOB belongs is an intra-frame coding slice) Then Y (f, h, s) = Yint (f, h, s) Else Y (f, h, s) = Ymc (f, h , s)

The target complexity of each slice is defined based on the target complexity of each GOB. The f
The target complexity Y (f, h) of the h-th slice of the frame is
It is defined as follows. Y (f, h) = Y (f, h, 1) + Y (f, h, 2) + ... + Y (f, h, S) (S; number of subpictures)

Next, the bit amount (target bit amount) usable in each slice of the next picture is estimated based on the target complexity of each slice and the remaining buffer capacity. Target bit amount of each slice of f-th picture
T (f, h) (1 ≦ l ≦ L) is assumed as follows after the encoding of the f−1th picture is completed. T (f, h) = [Y (f, h) / {Y (f, 1) + Y (f, 2) +… + Y (f, L)}]
× [BIT_RATE / PICTURE_RATE-{BE (f, 1)-BIT_RATE
× TE}] However, in the process of obtaining Y (f, h, s), Q (f,
Q (f-1, L, s) is used instead of h, s). This is because the value of Q (f, h, s) is not yet determined at the time when the target bit amount of each slice of the f-th picture is obtained, that is, immediately before the f-th picture is encoded. In the above equation, BIT_RATE: transmission rate PICTURE_RATE: number of pictures per second TE: reference accumulation time constant, BE (f, h) is the transmission buffer immediately before encoding the h-th slice of the f-th picture. Indicates the remaining amount.

If all Y (f, h) cannot be defined in the initial state immediately after the start of encoding, T (f, h) is defined as follows. T (f, h) = [1 / L] × [BIT_RATE / PICTURE_RATE-(BE
(f, 1) -BIT_RATE x TE}] Further, BE (f, 1) in the initial state is defined as follows, for example. BE (f, h) = BIT_RATE / PICTURE_RATE When BE (f, 1) cannot be used due to the delay due to the hardware configuration, for example, the latest available buffer remaining capacity is used.

Next, as the second procedure, the reference value of the quantization step parameter for each macroblock is set based on the estimated target bit amount and the actually generated code amount. A virtual buffer is assumed when setting the reference value. The virtual buffer is a buffer that roughly stores the difference between the target bit amount and the actual generated code amount. In this embodiment, one virtual buffer is assumed. The occupancy rate d (f, h) of the virtual buffer immediately before encoding the h-th slice of the f-th frame is defined as follows. d (f, h) = {S (1,1) + S (1,2) +… + S (1, L) + S (2,1) + S (2,2) +… + S (2 , L)… + S (f-1,1) + S (f-1,2) +… + S (f-1, L) + S (f, 1) + S (f, 2) +… + S (f, h-1)}-{T (1,1) + T (1,2) +… + T (1, L) + T (2,1) + T (2,2) +… + T (2, L)… + T (f-1,1) + T (f-1,2) +… + T (f-1, L) + T (f, 1) + T (f, 2) + ... + T (f, h-1)} At this time, S (f-1, h) is the actual generated code amount in the h-th slice of the f-th picture.

When S (x, y) cannot be used due to the hardware configuration, S (x, y) is defined as follows, for example. S (x, y) = Y (x, y) The original value of S (x, y) will be applied as soon as it becomes available.

The quantization step parameter is changed by associating the occupation rate of the virtual buffer with the quantization step parameter. For example, if there is no difference between the target bit amount set for each slice and the actual generation amount, the virtual buffer occupancy does not change and the quantization step parameter does not change. If there is a difference between the above two,
The virtual buffer occupancy changes, and the quantization step parameter is modified according to the change. For example, when the generated code amount exceeds the target bit amount,
The difference is the increase amount of the virtual buffer occupation rate. The virtual buffer occupancy corresponds to the quantization step parameter, and an increase in the virtual buffer occupancy leads to an increase in the quantization step parameter. Increasing the quantization step parameter will reduce the subsequent generated code amount.

Based on the virtual buffer occupancy ratio d (f, h),
The reference value Qr (f, h) of the quantization step parameter of the h-th slice of the f-th picture is calculated as follows using the function fq. Qr (f, h) = fq (d (f, h)) function fq is, for example, Qr (f, h) = 31 × {d (f, h) / r}, where r = BIT_RA
TE / PICTURE_RATE or Qr (f, h) = 31 ^{d (f, h) / r} where r = BIT_RAT
E / PICTURE_RATE is possible. Alternatively, it is determined based on the generated code amount and the quantitative property of the quantization step parameter.

Next, as the third procedure, the above Qr (f, h)
Based on, the final quantization step parameter for each macroblock is determined. In this embodiment, the adaptive quantization coefficient K (f, h, m) is calculated based on the power of the original signal for each macroblock, and the final quantization step parameter Q (f, h ) for each macroblock is obtained as follows. , m) is calculated. Q (f, h, m) = Qr (f, h) × K (f, h, m)

Example 2. The second embodiment of the present invention will be described below. The second embodiment differs from the first embodiment in the target complexity calculation process. In the first embodiment, the GOB is implicitly classified into the two types of intra-picture coding and inter-picture coding, and the target complexity is calculated. (At this time, to be exact, the latter is a hybrid coding of inter-picture coding and intra-picture coding.) However, in reality, one GOB is used.
In some cases, macroblocks for intra-picture coding and macroblocks for inter-picture coding may coexist inside. Based on this, the s sub-picture <br/> target complexity Y of the h slice of the f picture (f, h, s), using function Fintandmc, is defined as follows. Y (f, h, s) = fintandmc (GOBaverage_Eint (f-1, h, s), Ei
nt_num (f-1, h, s), GOBaverage_Emc (f-1, h, s), Emc_num
(f-1, h, s), Q (f, h, s), Sv (f, h, s)) At this time, Eint_num (f-1, h, s): intra-picture coding macro in the GOB Number of blocks Emc_num (f-1, h, s): The number of inter-picture coding macroblocks in the GOB. For example, the function fintandmc is defined based on the quantitative property as in the first embodiment.

Example 3. The third embodiment of the present invention will be described below. This embodiment differs from the first embodiment in the process of calculating the target complexity.

FIG. 4 is a schematic block diagram for explaining an example of the quantization control system in the third embodiment of the present invention. In the figure, the reference quantization step parameter 401 input from the input terminal 1i is the first input of the target complexity calculation circuit 3b, and the generated code amount 402 input from the input terminal 1j is the target complexity calculation circuit 3b. The type identification signal 403 input to the second input of the input terminal 1k from the input terminal 1k is generated by the third input of the target complexity calculation circuit 3b. , Target complexity calculation circuit 3b
Given to the fourth input of. The output 405 of the target complexity calculation circuit 3b is the target bit amount calculation circuit 4b.
The remaining buffer capacity 406 given to the first input of the input terminal 1m of the target bit amount calculation circuit 4
applied to the second input of b. The target bit amount 407 output from the target bit amount calculation circuit 4b is input to the first input of the virtual buffer remaining amount calculation circuit 5b at the input terminal 1
The generated code amount 408 input from n is supplied to the second input of the virtual buffer remaining amount calculation circuit 5b. The output 409 of the virtual buffer remaining amount calculation circuit 5b is given to the input of the quantization step parameter calculation circuit 6b. The reference quantization step parameter 410, which is the output of the quantization step parameter calculation circuit 6b, is given to the first input of the adaptive quantization circuit 7b. The second input of the adaptive quantization circuit 7b is a macroblock-based quantization step parameter 412 output from the adaptive quantization circuit 7b from the input terminal 1o.
Is output from the output terminal 2b.

The operation will be described below. The third embodiment differs from the first embodiment in the process of calculating the target complexity. Similar to the first embodiment, as the first procedure, the bit amount usable in each slice of the next picture is estimated. FIG. 5 is a conceptual diagram of the slice type of the quantization control method in the third embodiment of the present invention, and FIG. 5A shows an example of screen division periodic refresh. In general, the calculation of the target complexity is performed by the GOB in the past picture existing at the same position on the screen as the GOB.
Refer to the information in. At this time, in the case of the screen division periodic refresh, the information of the reference GOB cannot be used as it is. Because G
Depending on the type of slice to which the OB and the reference GOB belong (for example, whether it is an intra-coded slice or not),
For example, the amount of generated code varies greatly. Figure 5 (b)
As described above, in the third embodiment, for example, a combination of three slice types can be considered.

Based on the above, in the third embodiment, for example, three types of target complexity are defined as follows. Intra / non-intra target complexity Yint / mc of the s sub-picture of the first h slice of the f picture (f, h,
s), non-intra / intra target complexity Ymc / int
(f, h, s) and non-intra / non-intra target complexity Ymc / mc (f, h, s) can be calculated as follows using function fint / mc, function fmc / int and function fmc / mc. Is defined. Yint / mc (f, h, s) = fint / mc (S (f-1, h, s), Q (f-1, h, s), Q
(f, h, s), Sv (f-1, h, s)) Ymc / int (f, h, s) = fmc / int (S (f-1, h, s), Q (f-1 , h, s), Q
(f, h, s), Sv (f-1, h, s)) Ymc / mc (f, h, s) = fmc / mc (S (f-1, h, s), Q (f-1 , h, s), Q
(f, h, s), Sv (f-1, h, s)) At this time, S (f-1, h, s) is generated in the sth subpicture of the hth slice of the f-1th picture . Is the code amount,
Q (f-1, h, s) is the s-th slice of the h-th slice of the f-1th picture
The quantization step parameter actually used in the sub-picture, Sv (f-1, h, s) is the h -th picture of the f-1th picture.
The generated code amount does not depend on the quantization in the s-th sub- picture of the slice.

If S (f-1, h, s) or Sv (f-1, h, s) cannot be used due to the delay due to the hardware configuration, the following definition is made. Yint / mc (f, h, s) = fint / mc (S (f-2, h, s), Q (f-2, h, s), Q
(f, h, s), Sv (f-2, h, s)) Ymc / int (f, h, s) = fmc / int (S (f-2, h, s), Q (f-2 , h, s), Q
(f, h, s), Sv (f-2, h, s)) Ymc / mc (f, h, s) = fmc / mc (S (f-2, h, s), Q (f-2 , h, s), Q
(f, h, s), Sv (f-2, h, s)) Based on the above, the target complexity Y (f, h, s) of the sth sub-picture of the h-th slice of the final f-th picture Is the f
Slice type SliceType (f, h, s) of the s-th sub-picture of the h-th slice of the picture and the h -th of the f-1th picture
Slice type of slice s sub-picture SliceTyp
It is defined as follows according to e (f-1, h, s). if (SliceType (f-1, h, s) is the intra-picture coding slice) & (SliceType (f, h, s) is the inter-picture coding slice) then Y (f, h, s) = Yint / mc ( f, h, s) if (SliceType (f-1, h, s) is the inter-picture coding slice) & (SliceType (f, h, s) is the intra-picture coding slice) then Y (f, h, s ) = Ymc / int (f, h, s) if (SliceType (f-1, h, s) is the intra-picture coding slice) & (SliceType (f, h, s) is the intra-picture coding slice) then Y (f, h, s) = Ymc / mc (f, h, s)

In the above definition, the function fint / mc, the function fmc
/ int and the function fmc / mc are defined based on the quantitative property as in the first embodiment.

[0066]

According to the video signal coding method of the first aspect of the present invention, the bit amount usable in each area is estimated from the complexity predicted for each area based on the previous image. , Since the quantization step of each area is set based on the difference between the estimated bit amount and the actually generated code amount, it is necessary to appropriately perform the quantization control when different encoding methods are used for each region. You can Moreover, since the predicted complexity based on the encoding side to be performed on each region of the image,
Even if the current image and the previous image have different encoding methods in each region, an appropriate quantization step can be set.

A video signal encoding method according to claim 2
According to the method , for the area to which intra-picture transform coding is applied,
Predicts the complexity based on the signal power in the image, and
Inter-picture signal power for regions to which transform coding is applied
Since the complexity is estimated by using
Proper estimation ensures proper quantization for each region
Steps can be set.

A video signal encoding method according to claim 3
According to the law, the image transform coding, and inter-picture transform coding
In the region based on the number of blocks to which
It predicts complexity, so each region is coded with a different coding method.
Even if there are mixed encoded blocks,
The quantization step can be set. Also, the claims
According to the video signal coding method described in 4, each area of the image
The encoding method applied to the, and suitable for each region of the previous image.
It predicts complexity based on the encoding method used, so
Encoding method in each area between the current image and the previous image
Set the appropriate quantization step, even if
can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a main hierarchical structure of a video signal according to a first embodiment of the present invention.

FIG. 2 is a schematic block diagram for explaining an example of a quantization control method in the first exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a schematic relationship between complexity and a generated code amount referred to in the quantization control method in the first exemplary embodiment of the present invention.

FIG. 4 is a schematic block diagram for explaining an example of a quantization control method in a third exemplary embodiment of the present invention.

FIG. 5 is a conceptual diagram of slice types of a quantization control method according to a third embodiment of the present invention.

FIG. 6 is a schematic block diagram for explaining a conventional video signal encoding system.

FIG. 7 is a schematic block diagram for explaining an example of a quantization control method in a conventional video signal encoding method.

FIG. 8 is a conceptual diagram of a refresh method.

[Explanation of symbols]

1 input terminal 2 output terminals 3 Target complexity calculation circuit 4 Target bit amount calculation circuit 5 Virtual buffer remaining amount calculation circuit 6 Quantization step parameter calculation circuit 7 Adaptive quantization circuit 9 subtractor 10 DCT circuit 11 Quantization circuit 12 Inverse quantization circuit 13 IDCT circuit 14 adder 15 memory circuit 16 Motion compensation prediction circuit 17 Switching circuit 18 Variable length coding circuit 19 send buffer 20 Complexity calculation circuit 21 Constant generation circuit 22 Virtual buffer selection circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takahiro Nakai No. 1 Baba Institute, Nagaokakyo City Video System Development Laboratory, Mitsubishi Electric Corporation (56) Reference JP-A-5-167998 (JP, A) JP-A-4 -51689 (JP, A) JP 5-95536 (JP, A) JP 5-103315 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04N ^7/ 24- 7/68 H04N 1/41

Claims (2)

(57) [Claims] 1. A video signal encoding method for encoding an image composed of a plurality of blocks by applying an encoding method of either intra-picture transform encoding or inter-picture predictive encoding for each block. , before both the inter-picture signal power representing the image signal power represent the complexity of the image of the picture, and the complexity of the motion Symbol block
Found for each click, to apply image transform coding of the current frame the block
For the block, ask for the block one frame before
The signal power in the image is used to predict the complexity, and
On blocks to which Laem inter-picture predictive coding is applied
Is the image obtained for the block one frame before
The inter-image signal power is used to predict the complexity, and a single screen sum of the predicted complexity and one or more of the
On the basis of the ratio of the predicted complexity in each region of Tsu 1 screen consisting click, to estimate the amount of bits available in each region of the current frame, actually occurred and the estimated amount of bits code image signal encoding method characterized by based on the difference between the amount for setting the quantization step in each region of the current frame. 2. Regarding an area in which blocks to which intra-picture transform coding and inter-picture predictive coding are applied are mixed,
The complexity of each block included in the area and the area
Intra-picture transform coding and inter-picture transform coding in
The video signal encoding method according to claim 1, wherein the complexity is predicted based on the number of applied blocks .