KR20090049108A - Bit rate control advice and method using quantization coefficient property - Google Patents

Abstract

      The present invention relates to bit rate control of an image compression apparatus. More particularly, the present invention relates to a quantization coefficient characteristic for adjusting a quantization coefficient by dividing a bit amount according to a quantization coefficient in intervals so as to obtain an optimal image quality for an image service. A bit rate control method and apparatus are provided.

      As the motion change of the image and the complexity of the screen appear in various ways, the variation in the amount of bits output from the image compression encoder is severe.

      In the prior art, a method of determining the quantization coefficient according to the bit amount allocated to one frame and approaching the target bit amount by considering only the overflow or shortage of the buffer is used, so that the bit amount required for overflow or the remaining frame is processed. There is a problem that underfloor occurs due to lack of.

     According to the present invention, in order to generate the same bit amount, the quantization coefficient is adjusted differently according to the quantization characteristics of the video encoder to reach the target bit amount, so that image quality can be effectively improved and efficient bit rate management can be achieved. will be.

Quantization, bit rate

Description

Bit rate control advice and method using quantization coefficient property

      The present invention relates to bit rate control of an image compression apparatus. More particularly, the present invention relates to a quantization coefficient characteristic for adjusting a quantization coefficient by dividing a bit amount according to a quantization coefficient in intervals so as to obtain an optimal image quality for an image service. The present invention relates to a bit rate control method.

      Data networks providing video services have a limited amount of data that can be transmitted.

      As the video service is limited in the capacity of the network, a bit rate control method is required to efficiently allocate the optimal video quality within the capacity of a given network.

      Most video compression standards use a method of removing information that is redundant in time and space.

      For temporal deduplication, data is reduced by using only the difference image from the previous scene using motion compensation, and spatial deduplication is used to reduce duplication by using color information or frequency characteristics of the image.

      Since the amount of data generated in each frame has a variable amount of data of a general video service, a bit rate control method is required to provide a fixed bit rate service corresponding to a given network capacity.

      The present invention relates to such a bit rate control method.

      As described above, the bit rate control method of adjusting the quantization coefficient according to whether the buffer overflows or underflows is used.

      1 is a flowchart illustrating a bit rate control process using a quantization coefficient.

      The process will be described with reference to FIG. 1 as follows.

      When the buffer size is calculated, the quantization coefficient for the current frame is determined according to the buffer size. The quantization coefficient of the current frame is determined using an error (SAD) value of the difference image from the previous frame.

      In this case, since the first frame (I frame) does not exist in the previous image frame, the set initial quantization coefficient is set to perform the encoding.

      Then, after encoding is performed, the state of the buffer, that is, overflow or underflow of the buffer is determined, and the determined result thereof is used to determine the quantization coefficient of the next frame.

      If overflow is generated using the error value (SAD) of the difference image of the previous frame, the quantization coefficient is increased by a fixed value to reduce the data bit. When an underfloor is generated, the quantization coefficient is fixed by the fixed value. Lower the number of data bits to determine the quantization coefficient.

      As described above, the conventional bit rate control method uses a method of determining the quantization coefficient according to the bit amount allocated to one frame in consideration of the overflow or lack of the buffer and approaching the target bit amount.

      As the movement of the image and the complexity of the screen vary, it can be seen that the variation in the amount of bits output from the image compression encoder varies significantly according to the quantization coefficient. Only the overflow or lack of the conventional buffer is considered as described above. According to the bit rate control method, the number of output bits of each coded image is much larger than the target bit amount, or a lack of bit amount required to process the remaining frame appears.

      As a result, the image quality of successive frames generally becomes more and more deteriorated, and the overflow of the buffer becomes large.

      The present invention has been made to solve the problems of the prior art, and in consideration of the fact that the instantaneous slope of each section of the quantization coefficient is different in the amount of change in the amount of data bits according to the quantization coefficient, the target bit amount allocated to the frame In determining the quantization coefficient of the frame to be encoded according to the quantization coefficient level of the previous frame and the overflow of the buffer so as to be as close as possible, the determined value is adjusted differently for each section of the quantization coefficient so that the buffer overflow phenomenon and the image quality The purpose of the present invention is to provide a method of effectively controlling the bit rate while preventing degradation of the chip.

      The bit rate control device of the present invention,

      An initial value calculator for setting an initial value for bit rate control and encoding, a buffer amount measurer for measuring a buffer amount based on the initial value set in the initial value calculator, and a buffer amount measurer Quantization coefficient calculation unit for calculating the quantization coefficient according to the buffer amount, and quantization coefficient adjustment for determining the quantization coefficient by the quantization coefficient adjustment value set for each section based on the quantization value and the buffer measurement amount calculated according to the measured buffer amount And an encoder and a parameter updater to encode an image based on the quantization coefficient determined by the quantization coefficient controller and to update a buffer parameter based on the encoded and output bitstream.

       In the prior art, the bit rate is controlled by using a method of determining a quantization coefficient according to the bit amount allocated to one frame and approaching the target bit amount by considering only the overflow or lack of the buffer. Considering that the instantaneous slope is different for each section in the quantization coefficient and the amount of change in the data bits, it is possible to effectively control the bit rate by dividing the quantization coefficient according to the section.

     That is, according to the present invention, in order to generate the same bit amount, the quantization coefficient is adjusted differently in each section according to the quantization characteristic of the video encoder to reach the target bit amount, so that the image quality can be effectively improved and the effective bit rate management can be achieved. It would be.

      When the present invention is described with reference to the embodiments shown in Figures 2 to 4 as follows.

      The bit rate control device of the present invention,

      An initial value calculator 210 for setting an initial value for bit rate control and encoding, a buffer amount measurer 220 for measuring a buffer amount based on an initial value set by the initial value calculator 210, and The quantization coefficient calculator 230 calculates a quantization coefficient according to the buffer amount measured by the buffer amount measuring unit 220, and each section based on the quantization value and the buffer measurement amount calculated according to the measured buffer amount. A quantization coefficient adjusting unit 240 determines a quantization coefficient based on a set quantization coefficient adjusting value, and encodes an image based on the quantization coefficient determined by the quantization coefficient adjusting unit 240, and then encodes an image based on the encoded bitstream. And an encoding unit and a parameter updating unit 250 for updating the buffer parameters.

      In the present invention having such a configuration,

      The initial value calculator 210 is a means for calculating an initial value required for bit rate control by receiving a required bit rate and a frame rate per second of an image to be encoded.

      The buffer amount measuring unit 220 is a means for calculating the overflow or deficiency of the buffer in the buffer amount based on the initial value of the quantization coefficient calculated by the initial value calculating unit 210.

The quantization coefficient calculator 230 is a means for calculating quantization coefficients by receiving parameters for calculating the quantization coefficients.

      The quantization coefficient control unit 240 is for determining the quantization coefficient according to the quantization coefficient adjustment value set for each section in consideration of the amount of change of the data bits according to the quantization coefficient, the quantization coefficient calculated by the quantization coefficient calculator 230 Is a means for finally setting the quantization coefficient to be used for encoding.

      The quantization coefficient control unit 240 is configured as a means for adjusting the quantization coefficient calculated by the quantization calculator in consideration of the fact that the slope of each section is different in the quantization characteristics, that is, the amount of change in the amount of data bits according to the quantization coefficient. will be.

      The quantization coefficient adjustment value is a value that is statistically determined as test data through an iterative encoding process by taking into account the amount of change in the data bits according to the quantization coefficient, and the lookup table in the quantization coefficient control unit 240 in the form of data. It can be set and saved in the form of (Look-up table).

      3 is a graph showing the amount of data bits according to the quantization coefficients according to the present invention.

      Referring to FIG. 3, the amount of change in the amount of data bits according to the quantization coefficient is described as follows.

      The shape of the graph is shown in inverse curve curve according to the variation amount of each section.

      According to the graph, as the quantization coefficient increases, the data bit amount decreases rapidly, and the slope of the graph starts rapidly, then gradually, and then becomes flat. The data bit amount according to the quantization coefficient value is an instantaneous slope for each section. It can be seen that appears differently.

      Looking back, this means that the change in the quantization coefficient and the change in the bit amount are not the change of the same value.

      In other words, in order to generate the same bit amount, it means that the target bit amount can be adjusted by adjusting the quantization coefficient differently according to when the value of the quantization coefficient is small and large.

     For example, if the buffer overflow or deficiency is 10% overflow or deficiency as in general bit rate control, if the quantization coefficient is uniformly increased or decreased by the same value, that is, ΔQP, as shown in FIG. The amount of bit generated is different.

      Therefore, increasing or decreasing the buffer overflow or deficiency by 10% to a uniform quantization size results in inefficient buffer control.

      Therefore, the quantization coefficient adjusting unit 240 according to the present invention intends to adjust the quantization coefficient calculated by dividing the data bit change amount according to the quantization coefficient value into each section as shown in Equation 1 below.

      The interval of the quantization coefficient may be arbitrarily divided and processed according to the quantization characteristic of the video encoder. In the embodiment of Equation 1, the interval of the quantization coefficient is divided into three intervals.

      The quantization coefficient is determined as in Equation 1 below.

     [Equation 1]

If (QP <T ₁ )

{Adjustment of Quantization Coefficient for Buffer State in T ₁ Interval}

Else if (T ₁ <QP <T ₂ )

{Adjust Quantization Coefficient for Buffer State in Interval Between T ₁ and T ₂ }

Else if (T _M <QP)

{Adjustment of Quantization Coefficient for Buffer State in T _M Period}

      The calculated quantization coefficient QP represents a quantization control value set according to a corresponding section.

      The encoder and the parameter updater 250 are means for outputting a coded bitstream so that the input image is close to the target number of bits using the finally determined quantization coefficient, and updating the parameter.

      Looking at the operation of the bit rate control apparatus according to the quantization coefficient of the present invention having such a configuration as follows.

      4 is a flowchart illustrating a method of controlling a bit rate according to a quantization coefficient.

     A GOP buffer size calculation process for calculating the buffer size, a quantization coefficient calculation process for calculating a quantization coefficient for the first frame (I frame) when the calculated buffer size is set, and the set initial quantization coefficient to the target bit number of the image. A process of encoding to approximate, a process of determining a buffer state (overflow or underflow), a process of calculating a quantization coefficient of the next frame based on the result of the determined buffer state, and a calculated quantization Checking the coefficients, adjusting the quantization coefficients according to the quantization coefficient adjustment values set in each section, adjusting the quantization coefficients to determine the final quantization coefficients used for encoding, encoding the image using the determined quantization coefficients, and Updating a parameter for encoding; determining a buffer state for the updated parameter; It is characterized in that it is made to repeat the process of calculating the quantization coefficient in consideration of the buffer state.

      A detailed description of the operation of the present invention is as follows.

      The initial value calculator 210 receives the required bit rate and the frame rate of the image to be encoded, calculates an initial value necessary for bit rate control, and transmits the calculated initial value to the buffer amount measuring unit 220. do.

      In general, the initial value calculation is performed only once at the start of encoding.

      The buffer amount measurer 220 receives an input from the initial value calculator 210, receives parameters for measuring the buffer amount from the encoding and parameter updater 250, measures a buffer amount, and then calculates the quantization coefficient calculator 230. To send.

      Buffer amount measurement is a process of calculating the overflow or underflow of the buffer (overflow / underflow) is determined as shown in Equation 2 below.

     [Equation 2]

       overflow = (RealBitSum-IdealBitSum) / IdealBitSum

       RealBitSum: Sum of the number of output bits of previously coded frames

       -IdealBitSum: Sum of target bits of previously coded frames

      The quantization coefficient calculator 230 receives the input from the buffer amount measuring unit 220 and receives the parameters for calculating the quantization coefficient from the encoding and parameter updating unit 250 to determine the quantization coefficient.

      The quantization coefficient adjusting unit 240 receives the overflow or deficiency of the buffer determined by the buffer amount measuring unit 220 and the quantization coefficient determined from the quantization coefficient calculating unit 230, and quantizes the quantization coefficient according to the quantization coefficient adjustment value set for each section. As shown in Equation 1, which is a formula for determining the coefficient, the quantization coefficient is adjusted by the method of adjusting the quantization coefficient for each buffer state and transmitted to the encoder and the parameter updater 250.

      The encoder and the parameter updater 250 output the encoded bitstream so that the input image approaches the target bit number using the quantization coefficient determined by the quantization coefficient adjuster 240 and update the parameter.

      The buffer state is determined from the updated parameters, the buffer state of the next frame is taken into account, the quantization coefficient is calculated, and iteratively proceeds to complete encoding for all frames.

1 is a flow chart showing a conventional bit rate control apparatus

2 is a flowchart illustrating a bit rate control apparatus according to a quantization coefficient characteristic according to the present invention.

3 is a graph showing the amount of data bits according to the quantization coefficient according to the present invention.

4 is a block diagram illustrating a method of controlling a bit rate according to characteristics of a quantization coefficient according to the present invention.

Claims (3)

      An initial value calculator for setting an initial value for bit rate control and encoding, a buffer amount measurer for measuring a buffer amount based on the initial value set in the initial value calculator, and a buffer amount measurer Quantization coefficient calculation unit for calculating the quantization coefficient according to the buffer amount, and quantization coefficient adjustment for determining the quantization coefficient by the quantization coefficient adjustment value set for each section based on the quantization value and the buffer measurement amount calculated according to the measured buffer amount And a coding unit and a parameter updating unit for encoding an image based on the quantization coefficient determined by the quantization coefficient adjusting unit and updating a buffer parameter based on the encoded and output bitstream. Bit rate control device according to characteristics.       The method of claim 1, wherein the quantization coefficient adjusting unit is the following equation, If (QP <T ₁ ) {Adjustment of Quantization Coefficient for Buffer State in T ₁ Interval} Else if (T ₁ <QP <T ₂ ) {Adjust Quantization Coefficient for Buffer State in Interval Between T ₁ and T ₂ } Else if (T _M <QP) {Adjustment of Quantization Coefficient for Buffer State in T _M Period} Bit rate control apparatus according to the quantization coefficient characteristics, characterized in that for adjusting the quantization coefficient calculated by the quantization coefficient calculation unit for each section of the change value of the data bit according to the quantization coefficient as in.       In the bit rate control method for adjusting the quantization coefficient by dividing the bit amount according to the quantization coefficient for each section,       Determining the buffer state, that is, overflow or underflow of the buffer, calculating the quantization coefficient of the next frame based on the result of the determined buffer state, checking the calculated quantization coefficient, and A quantization coefficient adjustment process of determining a final quantization coefficient used for encoding by adjusting the quantization coefficient according to the quantization coefficient adjustment value set in each section, encoding a video using the determined quantization coefficient, and encoding parameters And updating the data and determining the buffer state of the updated parameter and calculating the quantization coefficient in consideration of the buffer state of the next frame.

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