KR100233835B1 - Bit rate control method for divided screen encoding - Google Patents

Abstract

A bit rate control method for dividing screen bit rate control that can be effectively applied to a video encoder that divides and encodes a high definition TV screen in a bit rate control for generating coded data at a constant bit rate in a coder while preventing rapid deterioration of picture quality .

Description

Bit rate control method for split-screen coding

FIG. 1 is a block diagram illustrating a principle of a general bit rate control method. FIG.

FIG. 2 is a flow chart illustrating a conventional bit rate control method. FIG.

FIG. 3 is a flowchart for explaining a bit rate control method according to the present invention; FIG.

DESCRIPTION OF THE REFERENCE NUMERALS

1: image input unit 2: encoding unit

3: Buffer unit 4: Bit rate control unit

The present invention relates to a bit rate control method for a split-screen coding, and more particularly, to a video encoder for dividing a relatively large screen such as a high-definition TV and encoding in parallel, prevents encoded video data at a constant bit rate while preventing a sudden change in picture quality .

Generally, in view of the processing speed of the hardware that can be used when designing an encoder that encodes a video image and a relatively large screen such as a high-definition TV, the screen is divided and processed in parallel. In order to maintain a constant image quality in encoding a moving picture, the amount of bits generated in the encoder must be variable according to the characteristics of the screen. In addition, the bit rate should be effectively controlled in order to output the coded moving image data constantly through a limited transmission channel and to maintain a constant image quality.

FIG. 1 is a block diagram for explaining the principle of a general bit rate control method. When an image is inputted through the image input unit 1, the image input from the encoding unit 2 is encoded. In the buffer unit 3, And then output the encoded bit stream at a constant bit rate to the outside. At this time, the bit rate control unit 4 adjusts the amount of bits generated by the encoding unit 2 using the buffer state of the buffer unit 3.

The most widely known bit rate control method known in the video coding is the method disclosed in the already known ISO / ICE JTC1 / SC29 / WG11 MPEG (Moving Picture Experts Group) -2 (Test Model) As shown in FIG.

FIG. 2 is a flow chart for explaining a conventional bit rate control method. In step 101, a new picture group (a certain number of pictures of a moving picture to be coded, hereinafter referred to as a screen group or GOP Pictures) is started, the process proceeds to step 102 to calculate a usable bit amount according to a limited data rate, and then proceeds to step 103. [ However, if the new picture group unit encoding is not started in step 101, the process proceeds to step 103 immediately. In step 103, if a new picture unit encoding is started, the process proceeds to step 104, and a bit amount of each picture is calculated according to the order of pictures to be coded considering the picture characteristics for each picture, and then the process proceeds to step 105 And if the encoding of the new picture unit is not started, the process directly proceeds to the step 105. If it is determined in step 105 that encoding of a new coded block has not been started, the process returns to step 101 to determine whether to start coding on a screen group basis. In step 105, The virtual buffer fullness is calculated using a value obtained by dividing the bit allocation value for the screen by the number of encoding blocks and a bit amount generated by actually encoding each encoding block, and then the process proceeds to step 107. In step 107, a quantization parameter value is calculated for each coded block using the calculated virtual buffer fullness, and the process proceeds to step 108. In step 108, the calculated quantization parameter value is transmitted to the encoding unit 2 to adjust the amount of bits generated.

Such a conventional bit rate control method performs three levels of hierarchical bit rate control in a bit rate control in units of a GOP, a picture, and a macroblock. Such a bit rate control method can be effectively used when coding a single screen, but has a problem that it can not be used as it is when a relatively large screen such as a High Definition TeleVision screen is divided and encoded in parallel.

Therefore, the present invention can effectively apply the present invention to a video encoder that divides and categorizes a high-definition TV screen in bit rate control for generating coded data at a constant bit rate in the coder while preventing sharp deterioration of image quality. And to provide a bit rate control method for a split screen bit rate control.

According to another aspect of the present invention, there is provided a method for encoding a bitstream, the method comprising: calculating a usable bit rate in accordance with a limited data rate on a per screen group basis; Allocating a bit amount differentially to each divided screen by using the calculated bit allocation amount and characteristic information of a screen generated in each divided screen; Calculating a virtual buffer fullness by using a value obtained by dividing the allocation value by the number of encoding blocks and a bit amount generated by actually encoding; calculating a quantization parameter value for each encoding block using the calculated virtual buffer fullness; And transmitting the calculated quantization parameter value to the encoding unit to adjust a bit amount generated .

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a flowchart for explaining a bit rate control method for dividing screen bit rate control according to the present invention. The present invention performs a bit rate control function in the order of a GOP, a picture, a sub-picture, and a macroblock as a hierarchical control method in four steps. The bit rate control function of the divided picture units is added. The bit rate control in units of a picture group (GOP) and a sub-picture unit performs total bit rate control by collectively collecting information generated in each divided screen, and the bit rate control in a coding block unit is performed independently Bit rate control. The bit rate control method for the divided screen vith ratio control will now be described in detail with reference to FIG. 3.

If coding of a certain number of moving pictures to be newly encoded is started in step 201 from the start signal, the flow advances to step 202 to calculate a usable bit amount according to a limited transmission rate, and then proceeds to step 203 do. However, if it is determined in step 201 that the encoding of a new picture group has not been started, the process directly proceeds to step 203. In step 203, if a new screen unit encoding is started, the process proceeds to step 204, and a bit amount of each before-split screen is calculated according to the order of a screen to be coded considering image characteristics for each screen, . In step 205, a bit amount is separately allocated to each divided screen using the calculated bit allocation amount and characteristic information of a screen generated in each divided screen, and then the process proceeds to step 206. If the new screen unit encoding is not started in step 203, the process directly proceeds to step 206. In step 206, if the encoding of the new encoding block is not started, the process proceeds to step 206 immediately. In step 206, if the encoding of a new encoding block is not started, the process returns to step 201, where it is determined whether to start encoding on a per screen group basis. When encoding is performed on a per encoding block basis, The process proceeds to step 207 where the virtual buffer fullness is calculated using a value obtained by dividing the bit allocation value for the divided arc plane by the number of coding blocks and a bit amount generated by actually encoding each coding block and then proceeds to step 208 . In step 208, a quantization parameter value is calculated for each encoding block using the calculated virtual buffer fullness, and then the process proceeds to step 209. In step 209, the calculated quantization parameter value is transmitted to the encoding unit 2 to control the amount of bits generated.

An example of the bit allocation step 205 of each divided screen is as follows.

The bit rate control method is a method of controlling the bit rate by receiving information generated in the previous coding process. The bit rate is controlled by the number of bits allocated to the entire screen before division, and T Th screen and the average quantization parameter values are denoted by Sn and Qrn, respectively, and the number of divided screens is N, the complexity X of the screen in the full screen before division is calculated by summing the sum of Sn and Qrn (2), and the complexity Xn of the screen in the nth divided screen is expressed as the product of the average of Sn and Qrn (Equation 3). The number of bits Tn allocated to the divided screen is represented by a value obtained by multiplying the complexity Xn of the screen in the divided screen with the complexity X in the whole screen by the number of bits T allocated to the entire screen. This bit allocation method can be expressed as follows.

As described above, according to the present invention, there is provided a bit rate control method for dividing and encoding a moving picture, the method comprising the steps of: dividing a moving picture into a plurality of pictures, There is an excellent effect that a more uniform image quality can be provided without a large difference in image quality between divided screens.

Claims (2)

Calculating a usable bit amount in accordance with a limited transmission rate in units of picture groups, calculating an allocation amount for each screen according to a sequence of pictures to be encoded in consideration of image characteristics for each screen, A step of allocating a bit amount differentially to each divided screen by using the allocation amount and the characteristic information of the screen generated in each divided screen, a step of dividing the bit allocation value for each divided screen by the number of encoded blocks, Calculating a quantization parameter value for each coded block by using the calculated virtual buffer fullness, calculating a quantization parameter value for each coded block by using the calculated virtual buffer fullness, And transmitting the divided bit rate to the encoding unit. The bit rate control method. 2. The bit rate control method according to claim 1, wherein a bit amount for each divided screen is differentially assigned according to the following equation. Tn: Number of bits allocated to full screen before segmenting Sn, and Qrn: the number of bits generated as a result of division in the n-th divided screen from the screen of the same type as the previous screen, and the average quantization parameter value N: Number of split screens X: Complexity of the screen before full screen Xn: Complexity of screen in nth divided screen Tn: Number of bits allocated to the split screen