KR20050076245A - Method for controlling transmission bit-rate - Google Patents

Abstract

The present invention relates to a bit rate control method for transmitting variable bits generated by MPEG video encoding as fixed bits. In particular, the present invention detects a scene change by using the complexity of the encoded picture at the scene change time point without a separate scene change detection device. The complexity of the picture to be encoded after the scene change is calculated by referring to the picture after the scene change, thereby minimizing image quality deterioration and minimizing hardware complexity, computation amount, and delay after the scene change occurs. In particular, the overflow of the bit buffer can be prevented. In addition, since the scene change detection device is not used, hardware is simplified and the amount of computation is not large, thereby minimizing delay and reducing costs.

Description

Method for controlling transmission bit-rate}

The present invention relates to a bit rate control method for transmitting variable bits generated by MPEG video encoding as fixed bits.

Since a lot of resources are required for storing and transmitting a video, a technique for compressing, storing, and transmitting the video is required.

A widely used standard for this purpose is the Moving Picture Experts Group (MPEG). In other words, the MPEG encoder for compressing and encoding a video is largely based on a discrete cosine transform (DCT) quantization, a motion estimation and compensation technique, and a variable length encoding based on a code occurrence probability, and includes bit rate control for transmission of a fixed bit rate. Included.

At this time, the algorithm mainly used in the MPEG coder is the material of MPEG-2 under international standardization in IS / IEC JTC1 / SC29 / WG11, which is an organization of ISO (International Organization for Standardization) (document number AVC-491, TEST MODEL 5) This is the suggested method.

FIG. 1 is a block diagram illustrating a general MPEG encoder, and includes an encoder 100, a bit rate controller 200, and an MC controller 300 that controls motion compensation of the encoder 100.

That is, the subtractor 101 outputs the difference data with the motion-compensated data from the motion compensation unit 109 to the DCT unit 102 if the input data is an I picture or the P or B picture. The DCT unit 102 DCTs the input data and outputs the quantized unit to the quantization unit 103.

Here, the DCT unit 102 removes the correlation of data through two-dimensional axis transformation. To this end, after dividing the picture into block units, the DCT unit 102 transforms each block according to the DCT scheme. The axially transformed data tends to converge in one direction (lower frequency side). Only the collected data are quantized by the quantization unit 103 and then output to the variable length coding (VLC) unit 104. The VLC unit 104 outputs the frequently-valued values to the buffer 110 after reducing the total number of bits by displaying a small number of bits and a rare value to a large number of bits. The buffer 110 temporarily stores the VLC data and outputs the data for transmission or storage. The buffer 110 calculates the fullness of the buffer and outputs the buffer to the bit rate controller 200.

In addition, the DCT coefficients quantized by the quantization unit 103 are input to the IQ unit 105 again, dequantized, and then output to the IDCT unit 106. The IDCT unit 106 IDCTs the inverse quantized DCT coefficients and outputs them to the adder 107. The adder 107 adds the IDCT value and the motion compensated value to restore the complete image, which is the final pixel value, and then stores the result in the memory 108 for motion compensation. The motion compensator 109 performs motion compensation using the previous frame read from the memory 108 according to the MC controller 300 and then outputs the motion compensation to the subtractor 101 and the adder 107.

On the other hand, the MPEG standard uses variable length coding (VLC) as described above. For this reason, the bits generated by the encoder are also variable. Therefore, the bit rate control unit 200 controls bit rate for use in applications requiring fixed bit rate transmission or the size of an encoded image.

The bit rate controller 200 adjusts the generation amount of data by varying the step size of the quantization unit 103 mainly according to the buffer fullness of the buffer 110. That is, if the number of bits generated is greater than or equal to the reference value, the amount of data to be filled in the buffer 110 is increased. Therefore, the quantization step size is increased to reduce the number of bits to be generated later. The number of bits is increased to adjust the state of the buffer 110 as a whole. The generation bit is controlled by the quantization step. The image quality is greatly influenced by the bit rate control.

At this time, referring to TM5, the bit rate controller 200 performs the following three steps.

First, the first step is a bit allocation step, in which the complexity is predicted and the target bit is allocated. That is, bits are allocated in GOP (Group Of Picture) units according to the transmission bit rate, and bits to be allocated to each picture in the GOP are determined according to the complexity of each picture (I, P, B frame). In other words, bits are allocated on a picture-by-picture basis by picture type and complexity in the GOP.

In this case, after the I, P, and B pictures are encoded by the encoding unit 100, the complexity X of each of the I, P, and B pictures is obtained as shown in Equation 1 below.

here, Are the amount of bits generated after encoding the previous I, P, and B pictures, respectively. Is the average quantization parameter computed by averaging the actual quantization values used during encoding of all macroblocks of each picture.

The initial complexity is given by X _i = 160 * bit rate / 115, X _p = 60 * bit rate / 115, X _b = 42 * bit rate / 115, and the bit rate at this time is obtained by the number of bits / second.

That is, each target bit _Ti , T _b , T _{p of} an I, P, or B picture to be encoded is allocated according to Equation 2 below according to the bit rate of the I, P, B picture, which is an image encoding form.

In Equation 2, Kp and Kb are constants depending on the quantization matrix, and Kp = 1.0, Kb = 1.4, and R is the number of bits remaining after encoding previous pictures among the GOP allocated bits. Bit_rate is a channel rate (bit / sec), and picture_rate is the number of pictures decoded per second. At the start of GOP, the R (bit rate) value is set to zero.

For every GOP, R is set to R + GOP_target, and the amount of bits generated for every GOP is subtracted from R, and then this value is updated to R.

Here, G = bit_rate * N / picture_rate, and N is a GOP size. Np, Nb is the number of P, B pictures to be encoded in the current GOP.

The second step is to adjust the rate (i.e., bit rate), and the bit rate control is performed in units of macro blocks. That is, the reference quantization parameter for each macro block is calculated according to the fullness of the virtual buffer 110. The bit rate is controlled so that each picture can be encoded according to the bit allocated in the first step. In this case, the reference quantization parameter for the current macroblock is determined by the virtual buffer fullness by the generation bits up to the previous macroblock.

Here, it is assumed that each picture has an arbitrary virtual buffer, and a method of adjusting the quantization parameter according to the state of the buffer is used.

The third step is an adaptive quantization step, in which an activity of a macroblock to be currently encoded is obtained from an input image, and normalized. At 103, a quantization step to be used for quantization is determined. In other words, adaptive quantization is a method of increasing the subjective picture quality and changing the reference quantization parameter according to the complexity of the current macroblock.

As described above, the bit rate controller 200 should use information of the previous picture to calculate the complexity for bit rate control of the current picture.

That is, in the first step, bit allocation allocates a predetermined bit in GOP units, and bits are allocated in picture units by picture type and complexity in the allocated bits.

In this case, the complexity of the picture to be encoded currently is obtained from a previous picture having the same picture type as the current picture. Thus, this method is fatal when a scene change occurs.

Figure 2 shows how the complexity of the picture currently used for encoding in TM5 is taken from the previous picture.

2, the complexity of the currently encoded picture is obtained from the previous picture of the same picture type. This is the case when transitions are not considered.

Therefore, serious picture quality deterioration occurs when the target bit is allocated in units of pictures after a scene change occurs.

That is, when a scene change occurs, the P picture at the generated time point is encoded as an I picture, and the B picture is encoded as a P picture by unidirectional motion estimation. 2, after the scene change, the P picture 6 is encoded as an I picture, and the B picture 7 is encoded as a P picture. However, the P picture 6 is allocated from the previous P picture 3 and assigned a target bit during encoding.

Thus, more bits are allocated in the allocation of the target bits of the picture compared to the current picture type. This means that bits allocated to other pictures in the GOP are reduced. This is because a certain bit is already allocated in GOP units according to the transmission bit rate.

Therefore, if the encoding is obtained by taking the complexity from the previous picture without considering the scene change in the GOP in which the scene change has occurred, as shown in FIG. 2, the image quality deterioration due to the scene change is severe, and the influence is continuously applied to other pictures in the GOP. This affects the image quality even worse. This may cause an overflow of the bit buffer.

Meanwhile, there is a method of detecting a scene change to solve such a problem and adjusting a bit rate in consideration of the scene change.

That is, the most widely used bit rate control method when a scene change occurs is regarded as a new GOP based on the picture where the scene change occurs. Then, a new bit is allocated to a new GOP, and the picture is encoded into an I (Intra) picture.

However, this method must detect scene transitions in advance. This requires additional frame memory and introduces frame delay. In addition, there is a problem in that the amount of calculation for scene change detection increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a bit rate control method for minimizing complexity when transmitting a variable bit generated by MPEG video encoding as a fixed bit.

In the transmission bit rate control method according to the present invention for achieving the above object, after assigning a predetermined bit in a GOP unit according to the transmission bit rate when encoding a video of MPEG series, the complexity is predicted and predicted for each picture in the GOP In the transmission bit rate control method for assigning a target bit to each picture using the complexity,

Calculating the complexity of a picture to be encoded currently using the complexity of a previous picture having the same picture type as the current picture when encoding pictures in the GOP according to an encoding order; Calculating a complexity of a picture encoded after an I or P picture after the scene change is generated using the complexity of the picture after the scene change when a scene change occurs when encoding a specific picture in the above step; If the scene transition occurs when encoding a specific picture in this step, the complexity of the B picture at the time when the scene transition occurs is calculated using the complexity of the last B picture before the past reference picture.

In the bit rate control method according to the first embodiment of the present invention, when a scene change occurs between a B picture and a P picture

The complexity of the P picture is calculated using the complexity of the previous P picture,

The complexity of the B picture is calculated using the complexity of the last B picture before the previous B picture,

The complexity of the B picture after the P picture is calculated using a 1/4 times the complexity of the P picture,

The complexity of the P picture after the P picture is calculated using a value of 1 / 2.5 times the complexity of the P picture,

The complexity of the first I picture after the scene change occurs is calculated by using the complexity of the first encoded P picture after the scene change.

In the transmission bit rate control method according to the second embodiment of the present invention, when a scene change occurs between a B picture and a B picture

The complexity of the B picture before the scene change is calculated using the complexity of the previous B picture,

The complexity of the B picture after the scene change is calculated using the complexity of the last B picture before the previous B picture,

The complexity of the P picture after the scene change is calculated using the complexity of the previous P picture,

The complexity of the B picture after the P picture is calculated using a 1/4 times the complexity of the P picture,

The complexity of the P picture after the P picture is calculated using the complexity of the P picture,

The complexity of the first I picture after the scene change occurs is calculated by using the complexity of the first encoded P picture after the scene change.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

In general, in view of the human visual system (HVS), the deterioration of the image quality of the image after the scene change is not sensitive to the human eye.

Therefore, the present invention lowers the image quality of a picture in which a scene change occurs and applies a complexity used in the scene change, thereby minimizing image quality deterioration after the scene change occurs and minimizing hardware complexity, calculation amount, and delay. This prevents the bit buffer from overflowing.

That is, the present invention minimizes the effects of the scene change by newly setting a previous picture to bring the complexity of the picture to be currently encoded when the scene change occurs.

In the case of a P picture, most of the macro blocks are encoded intra if a scene change occurs, and in the case of a B picture, a scene change is encoded by a unidirectional motion vector.

In this case, P or I pictures, which are references to B pictures, are encoded first in encoding order. Therefore, after the encoding of the P or I picture is finished, the B picture is encoded. When scene transition occurs, the complexity of the B picture uses the complexity of the last B picture before the past reference picture.

The complexity of the picture encoded after the I or P picture after the scene change occurs is calculated and used from the value of the complexity obtained from the picture after the scene change.

At this time, the scene change detection apparatus is not used in the present invention. In the present invention, whether to change scenes is determined as the complexity of the encoded picture. That is, if it is determined that the complexity of the encoded picture is larger than the preset threshold, it is determined that a scene change has occurred, and new complexity is applied to subsequent pictures.

3 and 4 illustrate examples of using complexity according to scene change in a bit rate control process according to the present invention.

3 illustrates a case where a scene change occurs immediately before a P picture. Then, the P picture No. 6 will be encoded intra before the No. 4 and No. 5 B pictures according to the encoding order. When encoding the picture 6, it is not known whether the scene has been changed yet, so the picture 6 is intra coded with the complexity from the previous P picture, that is, the P picture 3. In this case, since the picture 6 is encoded intra by taking the complexity from the previous P picture, the complexity after encoding will be larger than the preset threshold. This is because the sixth picture is a P picture, but since the picture is encoded as an I picture, the complexity has the characteristics of the I picture. Therefore, it is determined at this time that a scene change has occurred.

At this point, however, the 4 and 5 pictures have not been encoded yet, so the exact transition time is unknown.

Therefore, picture 4 is then encoded into a P picture taking the complexity of picture 2 B. In this case, the fourth picture is a B picture, but since it is encoded by unidirectional motion compensation, the complexity has the characteristics of the P picture. Therefore, when encoding the B picture 5, the complexity of the picture 2 is used instead of the complexity of the picture 4. That is, the encoding of the B picture 5 uses the complexity of the last B picture (ie, picture 2) before the past reference picture (ie, P picture 4).

This results in deterioration of picture quality but very robust in terms of overflow of the bit stream.

Then, the picture 9 is encoded into the P picture before the pictures 5 and 6 according to the encoding order. In this case, encoding is performed using the complexity obtained from P picture 6, which is the same picture type. However, since the picture 6 is encoded intra by scene change, the complexity has the characteristic of an I picture. Therefore, in this case, picture 9 is encoded into a P picture by using a value 1 / 2.5 times the complexity of picture 6.

Subsequently, pictures 7 and 8 are encoded. In this case, encoding of picture 7 uses a value of 1/4 times the complexity obtained from picture 6 as well. In the subsequent encoding, the same picture type complexity may be used as in TM5.

The first I picture, that is, picture 15, that comes after the scene change occurs is encoded using the complexity of the P picture that is first encoded after the scene change, that is, P picture 6.

4 illustrates a case where a scene change occurs between B pictures. Even in this case, the encoding order is the same as that described in FIG.

However, the complexity used for encoding picture 9 is taken from picture 5. This is because picture 5 has been encoded by unidirectional motion compensation due to scene transition, and thus the calculated complexity has the characteristics of P picture.

At this time, the picture 6 is encoded intra intra picture with complexity in the picture 3 because of the scene change. Therefore, the picture number 6 is a P picture, but since it is encoded in intra, the complexity has the characteristics of an I picture.

Therefore, the first I picture, that is, picture 15, that comes after the scene change occurs, is encoded using the complexity of P picture 6 that is first encoded after the scene change.

On the other hand, the terms used in the present invention (terminology) are terms defined in consideration of the functions in the present invention may vary according to the intention or practice of those skilled in the art, the definitions are the overall contents of the present invention It should be based on.

In addition, since the present invention has been described through the preferred embodiment of the present invention, in view of the technical difficulty aspects of the present invention, those having ordinary skill in the art can easily and other embodiments of the present invention. Other variations can be made. Therefore, it is apparent that all of the embodiments and variations cited in the above description belong to the claims of the present invention.

As described above, according to the transmission rate control method according to the present invention, a scene change is detected by using a complexity of an encoded picture at a scene change time without a separate scene change detection device, and then the complexity of a picture to be encoded is newly set. This minimizes picture quality degradation after scene transitions and minimizes hardware complexity, computation, and delay. In particular, the overflow of the bit buffer can be prevented. In addition, since the scene change detection device is not used, hardware is simplified and the amount of computation is not large, thereby minimizing delay and reducing costs.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

1 is a block diagram of a typical MPEG encoder

FIG. 2 is a diagram illustrating a relationship between pictures that result in complexity when encoding respective pictures.

3 is a view showing an embodiment showing a relationship with pictures bringing complexity when encoding pictures of the present invention;

4 is a view showing another embodiment showing a relationship with pictures resulting in complexity when encoding pictures in accordance with the present invention;

Explanation of symbols for main parts of the drawings

100: encoding unit 200: bit rate control unit

300: MC control unit

Claims (9)

In the transmission bit rate control method of assigning a predetermined bit in each GOP unit according to the transmission bit rate when encoding a video of MPEG series, and predicting the complexity for each picture in the GOP and assigning a target bit for each picture using the predicted complexity , Calculating the complexity of a picture to be encoded currently using the complexity of a previous picture having the same picture type as the current picture when encoding pictures in the GOP according to an encoding order; Calculating a complexity of a picture encoded after an I or P picture after the scene change is generated using the complexity of the picture after the scene change when a scene change occurs when encoding a specific picture in the above step; And In this step, when a scene change occurs when encoding a specific picture, the complexity of the B picture at the time when the scene change occurs is calculated using the complexity of the last B picture before the past reference picture. Control method. The method of claim 1, And determining whether a scene change occurs when encoding a specific picture using the complexity of the encoded picture. The method of claim 1, When a transition occurs between the B picture and the P picture The complexity of the P picture is calculated using the complexity of the previous P picture, The complexity of the B picture is calculated using the complexity of the last B picture before the previous B picture, The complexity of the B picture after the P picture is calculated using the complexity of the P picture, The complexity of the P picture after the P picture is calculated using the complexity of the P picture. The method of claim 3, wherein The complexity of the B picture after the P picture is calculated using a value that is 1/4 of the complexity of the P picture. The method of claim 3, wherein The complexity of the P picture after the P picture is calculated using a value 1 / 2.5 times the complexity of the P picture. The method of claim 3, wherein The complexity of the first I picture after the scene change occurs is calculated using the complexity of the first encoded P picture after the scene change. The method of claim 1, When a transition occurs between B picture and B picture The complexity of the B picture before the scene change is calculated using the complexity of the previous B picture, The complexity of the B picture after the scene change is calculated using the complexity of the last B picture before the previous B picture, The complexity of the P picture after the scene change is calculated using the complexity of the previous P picture, The complexity of the B picture after the P picture is calculated using the complexity of the P picture, The complexity of the P picture after the P picture is calculated using the complexity of the P picture. The method of claim 7, wherein The complexity of the B picture after the P picture is calculated using a value that is 1/4 of the complexity of the P picture. The method of claim 7, wherein The complexity of the first I picture after the scene change occurs is calculated using the complexity of the first encoded P picture after the scene change.