KR19980029969A - Bit allocation method when switching scenes - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

Bit allocation method when switching scenes

2. The technical problem to be solved by the invention

Calculate bits used for encoding in picture units and improve encoding performance using scene change information.

3. Summary of Solution to Invention

A first step of calculating, by the bit rate controller, a usable bit amount according to a limited bit rate in units of a screen group of a video to be encoded, and calculating bit allocation amounts of each screen in the order of pictures to be encoded according to the type of screen; A second step of increasing the bit amount calculated in the first step at a predetermined rate when a scene change occurs in the prediction screen; And if the scene change occurs in the previous prediction screen or the intra screen or the scene change occurs in the previous prediction screen or the intra screen, the bit amount calculated in the first step is determined by a predetermined ratio. And a third step of reducing it.

4. Important uses of the invention

Applied to a video encoding method including a bidirectional prediction screen (B).

Description

Bit allocation method when switching scenes

According to the present invention, in the moving picture expert group (MPEG) video encoding method, which is one of the moving picture encoding methods, the scene change occurs among the bit rate control methods used to maintain a constant picture quality. The present invention relates to a bit allocation method in scene switching for performing bit rate control without delay.

In general, the amount of bits generated by the encoder varies according to the characteristics of the screen in order to maintain a constant image quality in encoding a video.In order to maintain constant image quality while simultaneously outputting video encoded data through a limited transmission channel, The control method is essential.

1 is a block diagram illustrating a general bit rate control apparatus, in which 11 is an image input unit, 12 is an encoding unit, 13 is a buffer unit, and 14 is a bit rate controller.

As shown in the figure, a general bit rate control apparatus encodes an image input by the encoder 12 when an image is input from the image input unit 11, and stores the encoded value in the buffer unit 13 at a constant bit rate. The coded bit string is output to the outside.

At this time, in order to keep the bit amount output from the buffer unit 13 constant, the bit rate controller 14 adjusts the generated bit amount of the encoder 12 using the buffer state of the buffer unit 13.

Accordingly, the most widely known conventional method for controlling bit rate in video encoding performed by the bit rate control unit 14 is ISO / IEC JTC1 / SC29 / WG11 Moving Picture Experts Group (MPEG) -2 TM (Test Model). This method mainly works as shown in FIG.

FIG. 2 is a flowchart of a general bit rate control, in which the bit rate controller 14 calculates a usable bit amount according to a limited bit rate in units of GOPs (group of pictures) of a video to be encoded ( 201 and 202, bit allocations are calculated for each screen in the order of the screens encoded according to the type of the screen in consideration of the image characteristics of each screen (203 and 204).

The virtual buffer fullness is calculated using the value obtained by dividing the bit allocation value for the screen by the number of coding blocks and the amount of bits generated while encoding the coding block (205 and 206). Using the calculated virtual buffer fullness, a quantization parameter is calculated for each coding block (207), and the value is transmitted to the encoder 12 (208) to adjust the amount of bits generated.

In this method, the bit rate control is performed by hierarchical bit rate control in three stages in units of GOP, picture units, and macroblocks, so that coding similar to the previous screen is continuously input. Poetry has excellent performance, but has a disadvantage in that the picture quality is severely degraded when the nature of the screen is completely changed, that is, when a scene change occurs.

Accordingly, the present invention devised to overcome the above-described problems of the prior art calculates the bits to be used for encoding in units of screens, and then increases or decreases the screen unit allocation bits calculated using scene change information at a constant rate. It is an object of the present invention to provide a bit allocation method for scene change to improve encoding performance.

1 is a block diagram illustrating a general bit rate control apparatus;

2 is a general bit rate control flowchart;

3 is a flowchart of bit allocation process at the time of scene change according to the present invention;

* Explanation of symbols for the main parts of the drawings

11: video input unit

12: encoder

13: buffer

14: bit rate control unit

In accordance with an aspect of the present invention, there is provided a bit allocation method for scene change, the encoder encoding an image input from an image input unit, and a bit string encoded at a constant bit rate after storing the encoded value. A bit allocation method during scene change, which is applied to a bit rate control device having a buffer unit for outputting and a bit rate control unit for maintaining a constant bit amount output from the buffer unit, wherein the bit rate control unit is a screen group of a video to be encoded. A first step of calculating a usable bit amount according to a limited bit rate by a unit and calculating bit allocation amounts of each screen in the order of a picture to be encoded according to the type of picture; A second step of increasing the bit amount calculated in the first step at a predetermined rate when a scene change occurs in the prediction screen; And if the scene change occurs in the previous prediction screen or the intra screen or the scene change occurs in the previous prediction screen or the intra screen, the bit amount calculated in the first step is determined by a predetermined ratio. It characterized in that it comprises a third step of reducing to.

Accordingly, the present invention controlled as described above is a screen obtained by using a conventional bit rate control method when a scene change occurs in the bit rate control method of video encoding including a bidirectionally predictive-coded picture before and after By increasing or decreasing the number of bits for encoding, a better encoding performance is obtained.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

FIG. 3 is a flowchart of bit allocation processing during scene change according to the present invention, in which only a portion 204 for calculating a bit allocation amount in each screen of the known bit rate control method of FIG. 2 is changed.

First, in step 203 of determining whether to start the screen of FIG. The bit quota is calculated at 301.

Thereafter, it is determined whether a scene change has occurred without using it as it is (302), and if it is a prediction (P: predictive-coded) screen where the scene change has occurred (303), the calculated value is increased at a constant rate (304), If a scene change has not occurred in a bidirectionally predicted-coded (B) screen (305), it is determined whether a scene change has occurred in a previous prediction (P) screen or an intra screen (306).

As a result of the determination, if a scene change occurs in the previous prediction (P) screen or the intra (I) screen, the calculated value 301 is reduced by a certain ratio (307), and the previous prediction (P) screen or intra is displayed. If the scene change has not occurred in the screen (I), it is determined whether the scene change has occurred in the previous previous prediction (P) or intra (I) screen (308).

In this case, when a scene change occurs in a previous prediction (P) or intra (I) screen, the calculated value 301 is reduced at a predetermined ratio (309).

Referring to the process of the present invention treated as described above with a specific example as follows.

Input screen is

I1, B2, B3, P4, B5, B6, P7, B8, B9, P10, B11, B12, I13, B14, B15, P16, B17, B18, P19, B20, ...

Is the encoding order

I1, P4, B2, B3, P7, B5, B6, P10, B8, B9, I13, B11, B12, P16, B14, B15, P19, B17, B18, P22, ...

If a scene change occurs in P7, when the value obtained using the existing screen allocation method is Tp7 ', the bit allocation value Tp7 of the last screen unit according to the present invention is

In B5 and B6, since the scene change occurred in the previous prediction (P) screen, the bit allocation value of the screen unit is modified by the following Equation (2) and (Equation 3), and B8 and B9 Since the scene transition has occurred in the previous prediction (P) screen, the bit allocation value of the screen unit is modified by the following Equations (4) and (5).

In the above equations, a, b1, and b2 are zero or positive constants for increasing or decreasing the bit allocation value of the screen unit obtained by the conventional method during scene change.

The present invention described above is capable of various substitutions, modifications, and changes within the scope without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains, and thus is limited to the above-described embodiments and drawings. It is not.

According to the above, the present invention can be easily implemented by performing some additional bit allocation process according to scene change in the existing bit allocation method, and can provide better image quality than the existing bit rate control method.

In addition, when the video encoding process includes the bi-prediction (B) screen, only scene change information is used without a separate screen delay, thereby facilitating implementation.

Claims (6)

An encoding unit encoding an image input from an image input unit, a buffer unit storing the encoded value and outputting a bit string encoded at a constant bit rate to the outside, and maintaining a constant amount of bits output from the buffer unit. In the bit allocation method at the time of scene change to be applied to a bit rate control device having a bit rate control unit, A first step of calculating, by the bit rate controller, a usable bit amount according to a limited bit rate in units of a screen group of a video to be encoded, and calculating bit allocation amounts of each screen in the order of pictures to be encoded according to the type of screen; A second step of increasing the bit amount calculated in the first step at a predetermined rate when a scene change occurs in the prediction screen; And It is determined whether the scene change has occurred in the previous prediction screen or the intra screen, or the scene change has occurred in the previous prediction screen or the intra screen. And a third step of reducing. The method of claim 1, The second step, A fourth step of determining whether a scene change has occurred; A fifth step of increasing the already calculated value at a predetermined ratio if the scene change has occurred; And And a sixth step of determining whether a scene change has occurred in a previous prediction screen or an intra picture if the scene change has not occurred in the bidirectional prediction screen. The method of claim 1, The third step, A fourth step of reducing the calculated value by a predetermined ratio when a scene change occurs in a previous prediction screen or intra screen; A fifth step of determining whether a scene change occurs in the previous prediction or intra screen when the scene change does not occur in the previous prediction screen or the intra screen; And And a sixth step of reducing the calculated value by a predetermined ratio if a scene change has occurred in a previous previous prediction or intra screen. The method of claim 2, The fifth step, In the 7th prediction screen, a scene change occurs and the bit allocation calculated in the first step is In this case, the bit allocation value (Tp7) of the final screen unit is And a is 0 or a positive constant. The method of claim 3, wherein The fourth step, Since the fifth sixth bidirectional prediction screen has a scene change in the previous prediction screen, And Bit allocation value in units of a screen is modified, and b is 0 or a positive constant. The method of claim 3, wherein The sixth step, Since the 8th 9th bidirectional prediction screen has a transition in the previous prediction screen, And Bit allocation value in units of a screen is modified, and b is 0 or a positive constant.