CN114666585A - A rate control method and device based on visual perception - Google Patents

Abstract

The invention discloses a code rate control method based on visual perception, which comprises the following steps: step S10: and calculating the gradient amplitude of the texture rich area inside the LCU, and taking the calculation result as a texture perception factor of the LCU. Step S20: and calculating the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU, and taking the calculation result as the motion perception factor of the LCU. The steps S10 and S20 are performed in sequence, either before or simultaneously. Step S30: and calculating the bit distribution weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and further calculating the target coding bit number of the LCU. The invention has the technical effects that the target bit distribution of the LCU in the image frame is more in line with the characteristics of subjective perception of human eyes, improves the subjective visual quality of the human eyes and is suitable for being realized by hardware.

Description

A rate control method and device based on visual perception

technical field

The present invention relates to a video coding technology, in particular to a code rate control method and device suitable for hardware implementation based on visual perception.

Background technique

Video coding is a technique to characterize video information by compressing redundant components in video images and using as little data as possible. HEVC (High Efficiency Video Coding, also known as H.265) is a new generation of video coding standards. Compared with the previous generation of video coding standard AVC (Advanced Video Coding, also known as H.264), under the premise of achieving the same video coding quality, HEVC can reduce the coding bit rate by about 50%, and the video compression performance is improved compared with AVC. about double. Due to the large computational load of the video coding algorithm, in order to improve the video coding speed, it has become a common practice in the industry to use an application specific integrated circuit (ASIC) to perform hardware acceleration on the video coding process.

Video coding techniques use image blocks as basic coding units. In HEVC, a basic coding unit is a CU (Coding Unit, coding unit). The CU may be an image block of 64 pixels×64 pixels, 32 pixels×32 pixels, 16 pixels×16 pixels, or 8 pixels×8 pixels. The image block of 64 pixels×64 pixels is also called LCU (Largest Coding Unit, largest coding unit).

In practical applications, the bandwidth capacity of the channel used to transmit compressed video is limited. If the encoding bit rate of the compressed video is too high and exceeds the capacity of the channel bandwidth, it will cause video transmission congestion or even packet loss. If the encoding bit rate of the compressed video is too low, the channel bandwidth will not be fully utilized, and higher video quality cannot be obtained. Therefore, it is necessary to use rate control (Rate Control) technology to control the output code rate of the video encoder to match the channel bandwidth capacity.

The purpose of the bit rate control technology is to adjust the encoding parameters of the video encoder to make the output bit rate of the video encoder equal to the preset target bit rate, and at the same time reduce encoding distortion as much as possible to improve the video encoding quality. Currently, in the HEVC reference encoder HM (HEVC Test Model, HEVC test model), the rate control algorithm adopted is based on the JCTVC-K0103 proposal. The JCTVC-K0103 proposal establishes a mathematical relationship model between the encoding bit rate R and the Lagrange multiplier λ (that is, the R-λ model), and realizes the rate control task through two links: target bit allocation and target bit control.

In the JCTVC-K0103 proposal, target bit allocation is performed at three levels, namely GOP (Group Of Pictures, a group of pictures, that is, a set of temporally continuous picture frames) level, picture frame level, and basic coding unit level. In order to reduce the computational complexity, in the target bit allocation at the basic coding unit level, the LCU is generally selected as the basic unit of the target bit allocation. Therefore, the target bit allocation at the basic coding unit level is also commonly referred to as the LCU level target bit allocation.

其中，T_{LCU_curr}为当前待编码LCU分配的目标编码比特数，T_Pic为当前待编码视频帧(视频帧也称图像帧)分配的目标编码比特数，Bit_H为事先预估的视频帧头信息需要的比特数，Coded_Pic为当前待编码视频帧中已编码的LCU的实际编码比特数，ω_{LCU_curr}为当前待编码LCU的比特分配权重，ω_LCU表示不特指某一个LCU的比特分配权重，∑_{{AllNotCodedLCUs}}ω_LCU为当前待编码视频帧中所有未编码LCU的比特分配权重之和。After the target bit allocation at the GOP level and the image frame level, the target number of encoded bits of the current video frame to be encoded is determined, and the next step is to perform the LCU level target bit allocation to determine the current video frame. The bit allocation of each LCU weight, and allocate the target number of coded bits to each LCU according to the bit allocation weight of each LCU. In the JCTVC-K0103 proposal, LCU-level bit allocation is performed according to the following formula.

Among them, T _{LCU_curr} is the target coding bit number allocated by the LCU to be encoded currently, T _Pic is the target coding bit number allocated by the current video frame to be encoded (video frame is also called image frame), Bit _H is the pre-estimated video frame header information The number of bits required, Coded _Pic is the actual number of encoded bits of the LCU encoded in the current video frame to be encoded, ω _{LCU_curr} is the bit allocation weight of the current LCU to be encoded, ω _LCU indicates the bit allocation weight that does not specifically refer to a certain LCU, ∑ _{{AllNotCodedLCUs}} ω _LCU is the sum of the bit allocation weights of all uncoded LCUs in the video frame currently to be coded.

It can be found from the above formula that the core of LCU-level bit allocation is the bit allocation weight ω LCU of the _LCU . After calculating the bit allocation weights of all LCUs in the current to-be-coded video frame, the sum of the bit allocation weights of all uncoded LCUs in the current frame can be obtained by accumulating the bit allocation weights of each uncoded LCU. Then, according to the proportion of the bit allocation weight of each LCU in the sum of the bit allocation weights of all uncoded LCUs in the current frame, the target number of encoded bits of each LCU can be calculated to complete the target bit allocation at the LCU level.

其中，ω_LCU为LCU的比特分配权重，MAD_LCU为LCU在前一编码帧中的同位LCU的预测误差MAD值。

其中，N_pixels为LCU中像素点的数目，∑_{{AllPixelsInLCU}}是对LCU中的所有像素点进行累加，P_org为原始像素点的亮度值，P_pred为预测像素点的亮度值。In the JCTVC-K0103 proposal, the bit allocation weight ω _LCU of the LCU is calculated according to the prediction error MAD value (Mean Absolute Differences, Mean Absolute Differences) of the LCU in the same position (ie the same position) of the previous coded frame, and the calculation formula is as follows.

Among them, ω _LCU is the bit allocation weight of the LCU, and MAD _LCU is the prediction error MAD value of the LCU of the same position in the previous coded frame of the LCU.

Among them, N _pixels is the number of pixels in the LCU, ∑ _{{AllPixelsInLCU}} is the accumulation of all pixels in the LCU, P _org is the brightness value of the original pixel, and P _pred is the brightness value of the predicted pixel.

When viewing video images, the human eye is affected by subjective perception, and pays more attention to the areas with complex texture and rich details in the video images, and pays less attention to the flat areas with insignificant texture features in the images. At the same time, when viewing a video image, the human eye also pays more attention to the areas in the video image with violent motion and rich changes, and pays less attention to the static area in the image. In other words, in video images, motion-rich regions and texture-rich regions are more likely to attract human visual attention. Based on this visual perception feature of the human eye, it is necessary to allocate more target codes to the LCUs in the motion-rich areas and texture-rich areas in the image frame when the target coding bit rate of the image frame is fixed during the video coding process. The number of bits to improve the visual quality of the subjective perception of the human eye. In order to achieve this purpose, the rate control algorithm of video coding is required to be able to detect motion-rich areas and texture-rich areas, and calculate the LCU-level bit allocation weight accordingly, so that more target coding bits are allocated to people located at the human level. In the LCU in the eye attention area, the visual quality of the subjective perception of the human eye is improved.

The research on the HEVC rate control technology based on the JCTVC-K0103 proposal can find that the bit allocation weight at the LCU level is calculated based on the prediction error MAD value of the same LCU in the previous coded frame. It only calculates pixels from the perspective of signal processing. The brightness difference between the points does not take into account the subjective visual perception characteristics of the human eye, and cannot achieve the purpose of allocating more target coding bits to the area of interest of the human eye. Therefore, it is necessary to improve the LCU-level target bit allocation method in the HEVC rate control technology, and select factors that can represent the visual perception of the human eye to calculate the LCU-level bit allocation weights. The LCU allocates more target coding bits to achieve the purpose of improving the visual quality of the subjective perception of the human eye. The visual perception factor mentioned here needs to be able to represent the degree of subjective attention of the human eye to the image content, and it needs to meet the following characteristics: (1) For areas of human eye attention, such as motion-rich areas and texture-rich areas, the value of the visual perception factor larger; and the greater the motion range and texture complexity, the greater the value of the visual perception factor. (2) For areas that the human eye does not pay attention to, such as areas with sparse motion and simple textures, the value of the visual perception factor is smaller; and the smaller the motion amplitude and the simpler the texture, the smaller the value of the visual perception factor;

At present, there have been some technical solutions to improve the HEVC rate control technology, so as to achieve the purpose of improving the subjective perception visual quality of human eyes. Most of these schemes also start from finding factors that can characterize the visual perception of the human eye, and use the visual perception factor to calculate the bit allocation weight at the LCU level, and allocate more target coding bits to the LCU within the human eye's attention area. However, these existing technical solutions generally have the following problems.

The first type of prior art solution needs to preprocess the whole frame of image before encoding the current frame. The purpose of preprocessing is to calculate the bit allocation weight of each LCU in the current frame according to the selected visual perception factor, and then accumulate the sum of the bit allocation weights of all LCUs in the current frame, and then pass the bit allocation weight of each LCU in the current frame. Calculate the target number of coded bits of each LCU according to the proportion occupied in each LCU. This kind of technical solution needs to add a preprocessing stage before image encoding to calculate the bit allocation weights of all LCUs in the whole frame of image, and then the target number of encoded bits of each LCU can be calculated. In this kind of technical solution, the preprocessing of the whole frame image takes a lot of time, and the larger the resolution of the image frame is, the longer the preprocessing time is, which will introduce a large frame-level coding delay. At the same time, since the preprocessing of the whole frame image is performed separately from the image encoding, the image content needs to be read from the memory separately for the preprocessing and encoding, which consumes a lot of extra bus bandwidth. Therefore, this type of technical solution is suitable for software encoder implementation, but not for hardware encoder implementation.

The second type of prior art solution utilizes the correlation between video frames, and uses the bit allocation weight of each LCU in the previous frame as the bit allocation weight of the co-located LCU in the current frame. In this type of scheme, when encoding the previous frame, in the process of encoding each LCU, the bit allocation weight corresponding to this LCU is simultaneously calculated according to the visual perception factor. When the encoding of the previous frame is completed, the bit allocation weights of each LCU on the previous frame are also calculated simultaneously. The bit allocation weight of each LCU in the current frame adopts the bit allocation weight of the co-located LCU in the previous frame. For such technical solutions, although there is no need to add additional preprocessing stages, the real-time performance is good, and additional bus bandwidth is not consumed, but since the bit allocation weight of the LCU on the current frame is completely calculated from the image content of the previous frame It can be seen that when the frame-to-frame variation is large, the bit allocation weight of the LCU on the current frame does not match the subjective visual sensitive area of the human eye, and the LCU bit allocation error is large.

In addition to the above problems, the algorithms for visual perception factors selected by many prior art solutions are very complex, require a large amount of computation, consume a lot of computing resources and bandwidth resources, and are not suitable for hardware implementation.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to propose an HEVC code rate control method and device suitable for hardware implementation based on human subjective visual perception.

In order to solve the above technical problems, the present invention proposes a rate control method based on visual perception, which includes the following steps: Step S10: Calculate the gradient magnitude of the texture-rich area inside the LCU, and use the calculation result as the texture perception factor of the LCU. Step S20: Calculate the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU, and use the calculation result as a motion perception factor of the LCU. The sequence of the step S10 and the step S20 is either one of the preceding steps, or performed simultaneously. Step S30: Calculate the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculate the target number of encoded bits of the LCU.

Further, the texture perception factor of the LCU represents the visual sensitivity of the human eye to the texture feature of the LCU; the larger the value of the texture perception factor of the LCU, the richer the texture inside the LCU is, and the more subjective vision of the human eye is concerned; The smaller the value of the texture perception factor of the LCU, the flatter the texture inside the LCU is, and the less the subjective vision of the human eye is concerned.

Further, the motion perception factor of the LCU represents the visual sensitivity of the human eye to the motion feature of the LCU; the larger the value of the motion perception factor of the LCU, the richer the motion inside the LCU, and the more concerned about the subjective vision of the human eye; The smaller the value of the motion perception factor of the LCU is, the lighter the motion inside the LCU is, and the less the subjective vision of the human eye is concerned.

其中使用前一帧的LCU内部纹理丰富区域的梯度幅值的最大值作为当前帧中LCU内部纹理丰富区域的梯度幅值的归一化的基准；归一化值

即为LCU的纹理感知因子。步骤S14：使用当前帧的像素梯度均值计算下一帧纹理丰富像素的梯度判定阈值Grad_Thr。Further, calculating the texture perception factor of the LCU in the step S10 specifically includes the following steps. Step S11: Calculate the gradient magnitude Grad _x,y of each pixel inside the LCU, and judge whether each pixel inside the LCU is a texture-rich pixel based on the gradient determination threshold of the texture-rich pixel obtained from the gradient information of the previous frame; The area composed of texture-rich pixels is the texture-rich area inside the LCU. Step S12: Calculate the gradient magnitude Grad _{LCU of the texture-rich area inside the LCU} ; when calculating the Grad _LCU of each LCU in the current frame, record the maximum value G _max among them. Step S13: Normalize the gradient amplitude Grad _LCU of the texture-rich area inside the LCU to obtain

The maximum value of the gradient amplitude of the texture-rich area inside the LCU of the previous frame is used as the normalization benchmark for the gradient amplitude of the texture-rich area inside the LCU in the current frame; the normalized value

It is the texture perception factor of LCU. Step S14: Calculate the gradient determination threshold Grad _Thr of the texture-rich pixels in the next frame by using the mean value of the pixel gradients of the current frame.

Further, in the step S11, if Grad _x,y >Grad _Thr is satisfied, it is determined that the pixel belongs to the texture-rich pixel, otherwise it is determined that the pixel does not belong to the texture-rich pixel; Grad _Thr is the texture-rich pixel obtained from the gradient information of the previous frame. Gradient decision threshold for pixels.

Grad_x,y>Grad_Thr；其中，M是LCU的水平宽度，N是LCU的垂直高度，Grad_LCU是LCU内部所有纹理丰富像素的梯度幅值之和。Further, in the step S12,

Grad _x,y >Grad _Thr ; where M is the horizontal width of the LCU, N is the vertical height of the LCU, and Grad _LCU is the sum of the gradient magnitudes of all texture-rich pixels inside the LCU.

其中，G_max是前一帧中各个LCU的Grad_LCU的最大值；

的取值在[0,ZZ]之间并且为整数，使用0到ZZ之间的整数来代表0至1的归一化范围，ZZ代表归一化后的最大值。Further, in the step S13,

Among them, G _max is the maximum value of the Grad _LCU of each LCU in the previous frame;

The value of is between [0, ZZ] and is an integer. An integer between 0 and ZZ is used to represent the normalized range from 0 to 1, and ZZ represents the normalized maximum value.

其中，W是当前图像帧的水平宽度，H是当前图像帧的垂直高度。Further, in the step S14, Grad _Thr =Grad _avg +Grad _offset or Grad _Thr =α×Grad _avg ; wherein, Grad _offset is the gradient threshold adjustment deviation, α is the gradient threshold adjustment multiplier, and Grad _avg is the current frame pixel gradient mean;

Wherein, W is the horizontal width of the current image frame, and H is the vertical height of the current image frame.

其中使用前一帧的LCU内部运动丰富区域的帧差幅值的最大值来作为当前帧中LCU内部运动丰富区域的帧差幅值与面积占比的乘积的归一化的基准；归一化值

即为LCU的运动感知因子。步骤S25：使用当前帧的帧差幅值均值计算下一帧的运动丰富像素的帧差判定阈值Diff_Thr。Further, calculating the motion perception factor of the LCU in the step S20 specifically includes the following steps. Step S21: Calculate the frame difference amplitude Diff _x,y of each pixel inside the LCU and the corresponding pixel of the LCU in the previous frame, and use the frame difference judgment threshold of the motion-rich pixels obtained from the frame difference information of the previous frame to judge the frame difference within the LCU. Whether each pixel is a motion-rich pixel; the area composed of motion-rich pixels inside the LCU is the motion-rich area within the LCU. Step S22: Calculate the frame difference amplitude Diff _{LCU of the motion-rich area within the LCU} ; when calculating the Diff _LCU of each LCU in the current frame, record the maximum value D _max among them. Step S23: Calculate the area ratio Area LCU of the motion-rich area inside the _LCU . The sequence of the step S22 and the step S23 can either be preceded or be performed simultaneously. Step S24: Calculate the normalized value of the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU

The maximum value of the frame difference amplitude of the motion-rich area within the LCU in the previous frame is used as the normalization benchmark for the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU in the current frame; value

It is the motion perception factor of LCU. Step S25: Calculate the frame difference determination threshold Diff _Thr of the motion-rich pixels of the next frame by using the frame difference amplitude mean value of the current frame.

Further, in the step S21, if Diff _x,y >Diff _Thr is satisfied, it is determined that the pixel belongs to a motion-rich pixel, otherwise it is determined that the pixel does not belong to a motion-rich pixel; Diff _Thr is the motion obtained from the frame difference information of the previous frame. The frame difference judgment threshold for rich pixels.

Diff_x,y>Diff_Thr；其中，M是LCU的水平宽度，N是LCU的垂直高度，Diff_LCU是LCU内部所有运动丰富像素的帧差幅值之和。Further, in the step S22,

Diff _x,y > Diff _Thr ; where M is the horizontal width of the LCU, N is the vertical height of the LCU, and Diff _LCU is the sum of the frame difference amplitudes of all motion-rich pixels inside the LCU.

其中，Area_LCU的取值在[0,ZZ]之间并且为整数，对应面积占比0％至100％；M是LCU的水平宽度，N是LCU的垂直高度；

其中，若像素为运动丰富像素，则其对应的Mov_x,y取值为1，否则取值为0。Further, in the step S23,

Among them, the value of Area _LCU is between [0, ZZ] and is an integer, and the corresponding area accounts for 0% to 100%; M is the horizontal width of the LCU, and N is the vertical height of the LCU;

Among them, if the pixel is a motion-rich pixel, its corresponding Mov _{x, y} takes the value of 1, otherwise it takes the value of 0.

其中，

的取值在[0,ZZ]之间并且为整数，使用0到ZZ之间的整数来代表0至1的归一化范围，ZZ代表归一化后的最大值；D_max是前一帧中各个LCU的Diff_LCU的最大值。Further, in the step S24,

in,

The value of is between [0, ZZ] and is an integer, using an integer between 0 and ZZ to represent the normalized range from 0 to 1, ZZ represents the normalized maximum value; D _max is the previous frame The maximum value of the Diff LCUs of each _LCU in .

其中，W是图像帧的水平宽度，H是图像帧的垂直高度。Further, in the step S25, Diff _Thr =Diff _avg +Diff _offset or Diff _Thr =β×Diff _avg ; wherein, Diff _offset is the motion threshold adjustment deviation, β is the motion threshold adjustment multiplier, and Diff _avg is the current frame Frame difference amplitude average value;

where W is the horizontal width of the image frame and H is the vertical height of the image frame.

Further, in the step S30, the formula for calculating the bit allocation weight of the LCU according to the texture perception factor K _T of the LCU and the motion perception factor K _M of the LCU is as follows: ω _LCU = μ _T ×K _{T +} μ _M ×KM ; Among them, ω _LCU is the bit allocation weight of LCU, and its value is between [0, ZZ] and is an integer, and an integer between 0 and ZZ is used to represent 0 to 1; μ _T is the weight coefficient of LCU texture perception factor , μ _M is the weight coefficient of the LCU motion perception factor, both of which satisfy μ _T + μ _M =1 and 0<μ _T <1 and 0<μ _M <1.

进而计算出LCU的目标编码比特数；

Further, in the step S30, after calculating the bit allocation weight ω _LCU of the LCU in the current frame, use the sum of the LCU bit allocation weights of the previous frame statistics to replace the sum of the bit allocation weights of the LCU in the current frame, real-time Calculate the proportion of the bit allocation weight of the LCU in the current frame in the entire image frame

Then calculate the target number of encoded bits of the LCU;

Preferably, the value of ZZ is one of 127, 255, 511, or 1023.

The present application also proposes a code rate control device based on visual perception, including a texture perception factor calculation module, a motion perception factor calculation module and an LCU bit allocation module. The texture perception factor calculation module is used to calculate the gradient magnitude of the rich texture area inside the LCU, and use the calculation result as the texture perception factor of the LCU. The motion sensing factor calculation module is used to calculate the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU, and use the calculation result as the motion sensing factor of the LCU. The LCU bit allocation module calculates the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculates the target coding bit number of the LCU.

The technical effect achieved by the present invention is to make the target bit allocation of the LCU in the image frame more in line with the characteristics of subjective perception of the human eye, improve the subjective visual quality of the human eye, and is suitable for hardware implementation.

Description of drawings

FIG. 1 is a schematic flowchart of a rate control method proposed by the present invention.

FIG. 2 is a schematic structural diagram of a code rate control device proposed by the present invention.

FIG. 3 is a schematic diagram of a specific flow of calculating the texture perception factor of the LCU in step S10.

FIG. 4 is a schematic diagram of a specific flow of calculating the motion perception factor of the LCU in step S20.

Reference numerals in the figure indicate: 10 is a texture perception factor calculation module, 20 is a motion perception factor calculation module, and 30 is an LCU bit allocation module.

Detailed ways

Referring to FIG. 1 , the rate control method proposed by the present invention includes the following steps.

Step S10: Calculate the gradient magnitude of the rich texture area inside the LCU, and use the calculation result as the texture perception factor of the LCU. The texture perception factor represents the visual sensitivity of human eyes to LCU texture features.

Step S20: Calculate the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU, and use the calculation result as a motion perception factor of the LCU. The motion perception factor represents the visual sensitivity of the human eye to the motion feature of the LCU. This step uses the product of the frame difference amplitude and the area ratio of the LCU motion-rich region to calculate the motion perception factor of the LCU, which is an innovation of the present invention. The inventor found through experiments that if only the frame difference amplitude of the motion-rich area inside the LCU is used to represent the motion richness of the LCU, this method is more sensitive to small-area motion, and is easily affected by sensor noise, resulting in inaccurate determination results. If only the area ratio of the motion-rich area inside the LCU is used to characterize the motion richness of the LCU, this method is very sensitive to the subtle changes in the illumination and shadow of the local area of the image caused by the foreground motion, which does not conform to the characteristics of human eyes. Using the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU to characterize the motion-richness of the LCU can overcome the shortcomings of the single method above, and can more accurately reflect the visual attention of the human eye to the motion area.

The sequence of the step S10 and the step S20 is not strictly limited, and either one can be performed before or simultaneously.

Step S30: Calculate the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculate the target number of encoded bits of the LCU.

By adopting the code rate control method proposed by the present invention, the bit allocation of the LCU in the image frame can be more in line with the characteristics of the subjective perception of the human eye, and the subjective visual quality of the human eye can be improved.

Referring to FIG. 2 , the rate control device proposed by the present invention includes a texture perception factor calculation module 10 , a motion perception factor calculation module 20 and an LCU bit allocation module 30 , which generally correspond to the rate control method shown in FIG. 1 . Among them, the texture perception factor calculation module 10 is used to calculate the gradient magnitude of the rich texture area inside the LCU, and use the calculation result as the texture perception factor of the LCU. The motion sensing factor calculation module 20 is configured to calculate the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU, and use the calculation result as the motion sensing factor of the LCU. The LCU bit allocation module 30 calculates the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculates the target number of encoded bits of the LCU.

Referring to FIG. 3 , the calculation of the texture perception factor of the LCU in the step S10 specifically includes the following steps.

Step S11: Calculate the gradient magnitude Grad _x,y of each pixel in the LCU, and determine whether each pixel in the LCU is a texture-rich pixel based on the gradient determination threshold of the texture-rich pixel obtained from the gradient information of the previous frame. If Grad _x,y > Grad _Thr is satisfied, the pixel is determined to be a texture-rich pixel, otherwise it is determined that the pixel is not a texture-rich pixel. Grad _Thr is the gradient determination threshold of the texture-rich pixels obtained from the gradient information of the previous frame, as detailed in the subsequent step S14. The area composed of texture-rich pixels inside the LCU is the texture-rich area inside the LCU.

Grad_x,y>Grad_Thr。其中，M是LCU的水平宽度，N是LCU的垂直高度，单位均为像素数量。Grad_LCU是LCU内部所有纹理丰富像素的梯度幅值之和，反映了LCU内部纹理丰富区域的梯度幅值大小。在计算当前帧中各个LCU的Grad_LCU时，记录下其中的最大值G_max，供计算下一帧的LCU的Grad_LCU的归一化值

时使用。Step S12: Calculate the gradient magnitude Grad _LCU of the texture-rich area inside the LCU, and the calculation formula is as follows.

Grad _x,y > Grad _Thr . Among them, M is the horizontal width of the LCU, N is the vertical height of the LCU, and the unit is the number of pixels. Grad _LCU is the sum of the gradient magnitudes of all texture-rich pixels inside the LCU, which reflects the magnitude of the gradient magnitudes of the texture-rich regions inside the LCU. When calculating the Grad _LCU of each LCU in the current frame, record the maximum value G _max for calculating the normalized value of the Grad _LCU of the LCU of the next frame

when used.

其中使用前一帧的LCU内部纹理丰富区域的梯度幅值的最大值作为当前帧中LCU内部纹理丰富区域的梯度幅值的归一化的基准。归一化值

即为LCU的纹理感知因子，计算公式如下。

其中，

是Grad_LCU的归一化值，

的取值在[0,ZZ]之间并且为整数，方括号表示包含“等于”。G_max是前一帧中各个LCU的Grad_LCU的最大值。在每个具体应用场景中，ZZ是一个固定值。为了方便硬件实现归一化操作，尽可能不引入浮点运算，使用0到ZZ之间的整数来代表0至1的归一化范围，ZZ代表归一化后的最大值。考虑到在保证计算精度的基础上不过大增加计算量，ZZ的优选取值为127、255、511、或1023，以便于硬件实现。Step S13: Normalize the gradient amplitude Grad _LCU of the texture-rich area inside the LCU to obtain

The maximum value of the gradient magnitude of the texture-rich region within the LCU in the previous frame is used as the normalization benchmark for the gradient magnitude of the texture-rich region within the LCU in the current frame. normalized value

It is the texture perception factor of LCU, and the calculation formula is as follows.

in,

is the normalized value of Grad _LCU ,

The value of is between [0, ZZ] and is an integer, and square brackets indicate that "equals" is included. G _max is the maximum value of the Grad _LCU of each LCU in the previous frame. In each specific application scenario, ZZ is a fixed value. In order to facilitate the hardware normalization operation, floating-point operations are not introduced as much as possible, and an integer between 0 and ZZ is used to represent the normalization range from 0 to 1, and ZZ represents the normalized maximum value. Considering that the calculation amount should not be greatly increased on the basis of ensuring the calculation accuracy, the preferred value of ZZ is 127, 255, 511, or 1023, which is convenient for hardware implementation.

Hereinafter, the texture perception factor of the LCU is abbreviated as K _T . The value of K _T is between [0, ZZ]. The larger the value of K _T is, the richer the texture inside the LCU is, and the more the subjective vision of the human eye is concerned; the smaller the value of K _T is, the flatter the texture inside the LCU is, and the less the subjective vision of the human eye pays attention.

其中，W是当前图像帧的水平宽度，H是当前图像帧的垂直高度，单位均为像素数量。Step S14: Calculate the gradient determination threshold Grad _Thr of the texture-rich pixels in the next frame by using the mean value of the pixel gradient of the current frame, and the calculation formula is as follows. Grad _Thr =Grad _avg +Grad _offset or Grad _Thr =α×Grad _avg . Among them, Grad _offset is the gradient threshold adjustment deviation, and α is the gradient threshold adjustment multiplier. The values of these two values can be adjusted according to the user's sensitivity to the image texture area. Grad _avg is the average pixel gradient of the current frame, and the calculation formula is as follows.

Wherein, W is the horizontal width of the current image frame, H is the vertical height of the current image frame, and the unit is the number of pixels.

In the process of calculating the texture perception factor K _T of the LCU, the present invention has the following innovations. (1) Using the correlation of image content between consecutive video frames, the average pixel gradient of the previous frame is combined with the user adjustment parameters as the gradient judgment threshold of the texture-rich pixels in the current frame, and the LCU in the current frame is realized. Adaptive determination of whether the internal pixels belong to texture-rich pixels. (2) Using the correlation of image content between consecutive video frames, the maximum value of the gradient magnitude of the texture-rich region within the LCU counted in the previous frame is used as the normalization of the gradient magnitude of the texture-rich region within the LCU in the current frame. A standardized benchmark to achieve adaptive normalization of the gradient amplitudes in the texture-rich area inside the LCU in the current frame, so that the distribution of the gradient amplitudes of each LCU in the current frame is more reasonable, and the value distribution of K _T is more reasonable. Reasonable.

Referring to FIG. 4 , the calculation of the motion perception factor of the LCU in step S20 specifically includes the following steps.

Step S21: Calculate the frame difference amplitude Diff _x,y of each pixel inside the LCU and the corresponding pixel of the LCU in the same position (ie the same position) of the previous frame, and obtain the frame difference judgment threshold of the motion-rich pixels obtained from the frame difference information of the previous frame. to determine whether each pixel inside the LCU is a motion-rich pixel. The frame difference amplitude value refers to the absolute value of the difference between the luminance values of two corresponding pixel points. In the frame difference (ie, inter-frame difference) method, the luminance values of the corresponding pixels are differentiated, and then the absolute value of the difference needs to be taken as the result to participate in subsequent operations. If Diff _x,y > Diff _Thr is satisfied, the pixel is determined to be a motion-rich pixel, otherwise it is determined that the pixel is not a motion-rich pixel. Diff _Thr is the frame difference determination threshold of the motion-rich pixels obtained from the frame difference information of the previous frame, as detailed in the subsequent step S25. The area inside the LCU composed of motion-rich pixels is the motion-rich area inside the LCU.

Diff_x,y>Diff_Thr。其中，M是LCU的水平宽度，N是LCU的垂直高度，单位均为像素数量。Diff_LCU是LCU内部所有运动丰富像素的帧差幅值之和，反映了LCU运动丰富区域的帧差幅值大小。在计算当前帧中各个LCU的Diff_LCU时，记录下其中的最大值D_max，供计算下一帧中LCU的Diff_LCU与Area_LCU的乘积的归一化值时使用。Step S22: Calculate the frame difference amplitude Diff _LCU of the motion-rich area within the LCU, and the calculation formula is as follows.

Diff _x,y > Diff _Thr . Among them, M is the horizontal width of the LCU, N is the vertical height of the LCU, and the unit is the number of pixels. Diff _LCU is the sum of the frame difference amplitudes of all motion-rich pixels in the LCU, which reflects the frame difference amplitudes of the motion-rich areas of the LCU. When calculating the Diff _LCU of each LCU in the current frame, the maximum value D _max is recorded for use in calculating the normalized value of the product of the Diff _LCU and the Area _LCU of the LCU in the next frame.

其中，Area_LCU的取值在[0,ZZ]之间，对应面积占比0％至100％。ZZ的含义和优选取值与之前相同，不再赘述。M是LCU的水平宽度，N是LCU的垂直高度，单位均为像素数量。

其中，若像素为运动丰富像素，则其对应的Mov_x,y取值为1，否则取值为0。计算Area_LCU的公式的逻辑意义是，计算LCU内部所有运动像素点的总个数占LCU内部所有像素点的总个数的比例，并将比例归一化。Mov_x,y＝1表示对应像素点为运动像素点，这样对Mov_x,y进行加和，就得到了LCU内部所有运动像素点的总个数。Step S23: Calculate the area ratio Area _LCU of the motion-rich area inside the LCU, and the calculation formula is as follows.

Among them, the value of Area _LCU is between [0, ZZ], and the corresponding area accounts for 0% to 100%. The meaning and preferred value of ZZ are the same as before, and are not repeated here. M is the horizontal width of the LCU, and N is the vertical height of the LCU, in pixels.

Among them, if the pixel is a motion-rich pixel, its corresponding Mov _{x, y} takes the value of 1, otherwise it takes the value of 0. The logical meaning of the formula for calculating the Area _LCU is to calculate the ratio of the total number of motion pixels in the LCU to the total number of pixels in the LCU, and normalize the ratio. Mov _{x, y} = 1 indicates that the corresponding pixel is a moving pixel. In this way, adding Mov _{x, y} to obtain the total number of all moving pixels in the LCU.

The sequence of the step S22 and the step S23 is not strictly limited, and either one can be performed before or can be performed simultaneously.

其中使用前一帧的LCU内部运动丰富区域的帧差幅值的最大值来作为当前帧中LCU内部运动丰富区域的帧差幅值与面积占比的乘积的归一化的基准。归一化值

即为LCU的运动感知因子，计算公式如下。

其中，

的取值在[0,ZZ]之间。ZZ的含义和优选取值与之前相同，不再赘述。D_max是前一帧中各个LCU的Diff_LCU的最大值。Step S24: Calculate the normalized value of the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU

The maximum value of the frame difference amplitude of the motion-rich area within the LCU in the previous frame is used as the normalization reference for the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU in the current frame. normalized value

It is the motion perception factor of the LCU, and the calculation formula is as follows.

in,

The value of is between [0, ZZ]. The meaning and preferred value of ZZ are the same as before, and are not repeated here. _Dmax is the maximum value of the Diff _LCUs of the respective LCUs in the previous frame.

Hereinafter, the motion perception factor of the LCU is abbreviated as K _M . The value of K _M is between [0, ZZ]. The larger the value of _KM , the richer the motion inside the LCU, and the more the subjective vision of the human eye is concerned; the smaller the value of _KM is, the lighter the motion inside the LCU, the less the subjective vision of the human eye pays attention.

其中，W是图像帧的水平宽度，H是图像帧的垂直高度，单位均为像素数量。Step S25: Calculate the frame difference determination threshold Diff _Thr of the motion-rich pixels of the next frame by using the frame difference amplitude average value of the current frame, and the calculation formula is as follows. Diff _Thr = Diff _avg + Diff _offset or Diff _Thr = β×Diff _avg . Among them, Diff _offset is the motion threshold adjustment deviation, and β is the motion threshold adjustment multiplier. The values of these two values can be adjusted according to the user's sensitivity to the image motion area. Diff _avg is the average value of the frame difference amplitude of the current frame, and the calculation formula is as follows.

Among them, W is the horizontal width of the image frame, H is the vertical height of the image frame, and the unit is the number of pixels.

In the process of calculating the motion perception factor KM of the _LCU , the present invention has the following innovations. (1) Using the correlation of image content between consecutive video frames, the average frame difference amplitude value of the previous frame statistics is combined with the user adjustment parameters as the frame difference judgment threshold of the motion-rich pixels in the current frame, so as to realize the detection of the current frame difference. Adaptive determination of whether the pixels inside the LCU in the frame belong to motion-rich pixels. (2) Using the correlation of image content between consecutive video frames, the maximum value of the frame difference amplitude of the motion-rich area within the LCU counted in the previous frame is used as the frame difference amplitude of the motion-rich area within the LCU in the current frame. The benchmark for the normalization of the product of the area ratio, realizes the adaptive normalization of the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU in the current frame, so that the frame difference of each LCU in the current frame is The magnitude distribution is more reasonable, and the value distribution of K _M is more reasonable. (3) Using the product of the frame difference amplitude and the area ratio of the LCU motion-rich area to calculate the motion perception factor of the LCU can more accurately reflect the visual attention of the human eye to the motion area.

In the step S30, the texture perception factor K _T of the LCU and the motion perception factor KM of the _LCU are combined, and the combined result is used as the bit allocation weight of the LCU. The formula for calculating the bit allocation weight of the LCU according to K _T and K _M is as follows. ω _LCU = μ _T ×K _{T +} μ _M ×KM . Among them, ω _LCU is the bit allocation weight of LCU, and its value is between [0, ZZ]. The meaning and preferred value of ZZ are the same as before, and are not repeated here. μ _T is the weight coefficient of the LCU texture perception factor, and μ _M is the weight coefficient of the LCU motion perception factor, both of which satisfy μ _T +μ _M =1 and 0<μ _T <1 and 0<μ _M <1.

进而计算出LCU的目标编码比特数，这属于本发明的一个创新。

的计算公式如下。

Since there is a correlation in the content of consecutive video image frames, for adjacent video image frames, the sum of the bit allocation weights of all LCUs in the frame is also correlated, and the sum of the bit allocation weights of all LCUs in the previous frame can be used. to predict the sum of the bit allocation weights of all LCUs in the current frame. Therefore, in the step S30 of the present invention, after calculating the bit allocation weight of the LCU in the current frame, the correlation on the image content between consecutive video frames will be used, and the LCU bit calculated by the previous frame will be used to allocate the weight. The sum replaces the sum of the bit allocation weights of the LCUs in the current frame, and calculates the proportion of the bit allocation weights of the LCUs in the current frame in the entire image frame in real time

Then, the target coding bit number of the LCU is calculated, which is an innovation of the present invention.

The calculation formula is as follows.

In this way, real-time calculation of the target coding bit allocation for each LCU in the current frame can be achieved without preprocessing all LCUs in the whole frame before coding, so no frame-level coding delay is introduced. Meanwhile, since the bit allocation weight of the LCU is calculated by the LCU in the current frame, the bit allocation of the LCU is consistent with the subjective visual perception of the human eye on the current frame. If there are a few cases where the image content of the previous and subsequent frames is quite different, the adjustment is performed by the image frame level of the HEVC bit rate control algorithm and the bit allocation algorithm of the GOP level.

The present invention proposes a HEVC code rate control method based on human subjective visual perception and suitable for hardware implementation, and has the following beneficial effects. (1) The rate control method proposed by the present invention can make the bit allocation of the LCU in the image frame more in line with the characteristics of the subjective perception of the human eye, and improve the subjective visual quality of the human eye. (2) The present invention makes full use of the correlation of image content between consecutive video frames in the calculation process of the visual perception factor, so that the determination of the LCU texture-rich area and the motion-rich area can be adaptively completed, and the texture perception factor and The value distribution of the motion perception factor is more reasonable. (3) In the process of calculating the motion perception factor, the present invention uses the product of the frame difference amplitude and the area ratio of the LCU motion-rich area to calculate the motion perception factor of the LCU, which can more accurately reflect the human eye's vision of the motion area. Attention. (4) In the process of LCU bit allocation, the present invention makes full use of the correlation of image content between consecutive video frames, and realizes the real-time calculation of the proportion of the LCU bit allocation weight in the entire image frame, without increasing the image content. In the case of the frame preprocessing stage, the bit allocation of the LCU is made to conform to the subjective visual perception of the human eye on the current frame. (5) The visual perception factor calculation method adopted by the present invention is simple and convenient, the computation amount is small, and the bus bandwidth is occupied less, and is suitable for hardware implementation. (6) In the present invention, the calculation of the LCU texture perception factor and the motion perception factor is performed at the same time as the encoding of the LCU, and there is no need to introduce a preprocessing stage to calculate the visual perception factors of all LCUs in the frame before encoding the entire frame. Frame-level delay, does not need to consume additional bus bandwidth, suitable for hardware implementation.

In order to verify the beneficial effects of the present invention, the present invention selects three YUV video streams Johnny, FourPeople and KristenAndSara in the HEVC standard test sequence ClassE for testing. These three video streams belong to typical video conference scenarios, and the subjective attention area of the human eye is the face part in the video stream. During the experiment, the encoder adopts the constant bit rate control mode, the encoding bit rate of Johnny and KristenAndSara is set to 600kbps, the encoding bit rate of FourPeople is set to 800kbps, the number of encoded frames is 120 frames, the encoding GOP structure is IPPP structure, and the P frame only refers to the previous one. frame. In the experiment, the code rate control algorithm used in HM to calculate the LCU bit allocation weight based on the MAD value is used as a comparison benchmark, and compared with the improved code rate control algorithm based on the subjective visual perception of the human eye proposed by the present invention. The PSNR (Peak Signal-to-Noise Ratio, peak signal-to-noise ratio) of the face region in the YUV video stream encoded image. The unit of PSNR is decibel dB. The higher the PSNR, the smaller the image distortion and the better the image quality. The experimental results are shown in Table 1 below.

Table 1: the test comparison table of the present invention and existing rate control method

In these three YUV video streams, compared with the background region, the face region belongs to both the motion-rich region and the texture-rich region; that is, compared with the background region, the motion feature of the face region is significant, and the texture feature is more significant. As can be seen from Table 1, after applying the code rate control algorithm proposed by the present invention, the PSNR of the face region is improved under the condition that the overall average code rate and average PSNR of the encoded code stream do not change much—Johnny improved by 0.38dB, KristenAndSara The increase of 0.38dB and the increase of FourPeople by 0.42dB effectively enhance the subjective perception visual quality of the human eye.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Various modifications and variations of the present invention are possible for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (18)

1. a code rate control method based on visual perception, is characterized in that, comprises the steps: Step S10: Calculate the gradient magnitude of the rich texture area inside the LCU, and use the calculation result as the texture perception factor of the LCU; Step S20: Calculate the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU, and use the calculation result as the motion perception factor of the LCU; The sequence of the step S10 and the step S20 may be either preceded or performed simultaneously; Step S30: Calculate the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculate the target number of encoded bits of the LCU. 2. The code rate control method based on visual perception according to claim 1, wherein the texture perception factor of the LCU represents the visual sensitivity of the human eye to the LCU texture feature; the texture perception factor of the LCU takes The larger the value, the richer the texture inside the LCU, and the more the subjective vision of the human eye is concerned; the smaller the value of the texture perception factor of the LCU, the flatter the texture inside the LCU, the less the subjective vision of the human eye pays attention. 3. The rate control method based on visual perception according to claim 1, is characterized in that, the motion perception factor of described LCU characterizes the visual sensitivity degree of human eye to LCU motion characteristic; The motion perception factor of described LCU takes The larger the value is, the richer the motion inside the LCU is, and the more attention is paid to the subjective vision of the human eye; the smaller the value of the motion perception factor of the LCU, the lighter the motion inside the LCU, the less the subjective vision of the human eye pays attention. 4. The code rate control method based on visual perception according to claim 1, is characterized in that, calculating the texture perception factor of LCU in described step S10 specifically comprises the following steps; Step S11: Calculate the gradient magnitude Grad _x,y of each pixel inside the LCU, and judge whether each pixel inside the LCU is a texture-rich pixel based on the gradient determination threshold of the texture-rich pixel obtained from the gradient information of the previous frame; The area composed of texture-rich pixels is the texture-rich area inside the LCU; Step S12: Calculate the gradient amplitude Grad _{LCU of the texture-rich area inside the LCU} ; when calculating the Grad _LCU of each LCU in the current frame, record the maximum value G _max therein; Step S13: Normalize the gradient amplitude Grad _LCU of the texture-rich area inside the LCU to obtain

The maximum value of the gradient amplitude of the texture-rich area inside the LCU of the previous frame is used as the normalization benchmark for the gradient amplitude of the texture-rich area inside the LCU in the current frame; the normalized value

is the texture perception factor of LCU; Step S14: Calculate the gradient determination threshold Grad _Thr of the texture-rich pixels in the next frame by using the mean value of the pixel gradients of the current frame. 5. The code rate control method based on visual perception according to claim 4, wherein in the step S11, if Grad _x,y >Grad _Thr is satisfied, it is determined that the pixel belongs to a texture-rich pixel, otherwise it is determined that the pixel is Does not belong to texture-rich pixels; Grad _Thr is the gradient determination threshold of texture-rich pixels obtained from the gradient information of the previous frame. 6. The code rate control method based on visual perception according to claim 4, is characterized in that, in described step S12,

Grad _x,y >Grad _Thr ; where M is the horizontal width of the LCU, N is the vertical height of the LCU, and Grad _LCU is the sum of the gradient magnitudes of all texture-rich pixels inside the LCU. 7. The code rate control method based on visual perception according to claim 4, wherein in the step S13,

Among them, G _max is the maximum value of the Grad _LCU of each LCU in the previous frame;

The value of is between [0, ZZ] and is an integer. An integer between 0 and ZZ is used to represent the normalized range from 0 to 1, and ZZ represents the normalized maximum value. 8. The code rate control method based on visual perception according to claim 4, wherein in the step S14, Grad _Thr =Grad _avg +Grad _offset or Grad _Thr =α×Grad _avg ; wherein, Grad _offset is Gradient threshold adjustment deviation, α is the gradient threshold adjustment multiplier, Grad _avg is the average pixel gradient of the current frame;

Wherein, W is the horizontal width of the current image frame, and H is the vertical height of the current image frame. 9. The code rate control method based on visual perception according to claim 1, wherein calculating the motion perception factor of LCU in the step S20 specifically comprises the following steps; Step S21: Calculate the frame difference amplitude Diff _x,y of each pixel inside the LCU and the corresponding pixel of the LCU in the previous frame, and use the frame difference judgment threshold of the motion-rich pixels obtained from the frame difference information of the previous frame to judge the frame difference within the LCU. Whether each pixel is a motion-rich pixel; the area inside the LCU composed of motion-rich pixels is the motion-rich area within the LCU; Step S22: Calculate the frame difference amplitude Diff _{LCU of the motion-rich area within the LCU} ; when calculating the Diff _LCU of each LCU in the current frame, record the maximum value _Dmax therein; Step S23: Calculate the area ratio Area LCU of the motion-rich area inside the _LCU ; The sequence of the step S22 and the step S23 is either one of the preceding steps, or performed simultaneously; Step S24: Calculate the normalized value of the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU

The maximum value of the frame difference amplitude of the motion-rich area within the LCU in the previous frame is used as the normalization benchmark for the product of the frame difference amplitude and the area ratio of the motion-rich area within the LCU in the current frame; value

is the motion perception factor of LCU; Step S25: Calculate the frame difference determination threshold Diff _Thr of the motion-rich pixels of the next frame by using the frame difference amplitude mean value of the current frame. 10. The code rate control method based on visual perception according to claim 9, wherein in the step S21, if Diff _x,y >Diff _Thr is satisfied, it is determined that the pixel belongs to a motion-rich pixel, otherwise it is determined that the pixel is Does not belong to motion-rich pixels; Diff _Thr is the frame difference determination threshold of motion-rich pixels obtained from the frame difference information of the previous frame. 11. The code rate control method based on visual perception according to claim 9, wherein in the step S22,

where M is the horizontal width of the LCU, N is the vertical height of the LCU, and Diff _LCU is the sum of the frame difference amplitudes of all motion-rich pixels inside the LCU. 12. The code rate control method based on visual perception according to claim 9, wherein in the step S23,

Among them, the value of Area _LCU is between [0, ZZ] and is an integer, and the corresponding area accounts for 0% to 100%; M is the horizontal width of the LCU, and N is the vertical height of the LCU;

Among them, if the pixel is a motion-rich pixel, its corresponding Mov _{x, y} takes the value of 1, otherwise it takes the value of 0. 13. The code rate control method based on visual perception according to claim 9, wherein in the step S24,

in,

The value of is between [0, ZZ] and is an integer, using an integer between 0 and ZZ to represent the normalized range from 0 to 1, ZZ represents the normalized maximum value; D _max is the previous frame The maximum value of the Diff LCUs of each _LCU in . 14. The code rate control method based on visual perception according to claim 9, wherein in the step S25, Diff _Thr =Diff _avg +Diff _offset or Diff _Thr =β×Diff _avg ; wherein, Diff _offset is Motion threshold adjustment deviation, β is the motion threshold adjustment multiplier, Diff _avg is the average frame difference amplitude of the current frame;

where W is the horizontal width of the image frame and H is the vertical height of the image frame. 15. The code rate control method based on visual perception according to claim 1, wherein in the step S30, the bit allocation weight of the LCU is calculated according to the texture perception factor K _T of the LCU and the motion perception factor K _M of the LCU The formula of ω LCU is as follows; ω _LCU = μ _T ×K _T + μ _M ×K _M ; where, ω _LCU is the bit allocation weight of LCU, and its value is between [0, ZZ] and is an integer, using 0 to ZZ The integers between 0 and 1 represent 0 to 1; μ _T is the weight coefficient of the LCU texture perception factor, μ _M is the weight coefficient of the LCU motion perception factor, both satisfy μ _T + μ _M =1 and 0<μ _T <1 and 0 < _μM <1. 16. The code rate control method based on visual perception according to claim 1, wherein, in the step S30, after calculating the bit allocation weight ω _LCU of the LCU in the current frame, use the statistical data of the previous frame. The sum of the LCU bit allocation weights replaces the sum of the bit allocation weights of the LCUs in the current frame, and calculates the proportion of the bit allocation weights of the LCUs in the current frame in the whole image frame in real time

Then calculate the target number of encoded bits of the LCU;

17 . The rate control method based on visual perception according to claim 7 , wherein the value of ZZ is one of 127, 255, 511, or 1023. 18 . 18. A code rate control device based on visual perception, characterized in that it comprises a texture perception factor calculation module, a motion perception factor calculation module and an LCU bit allocation module; The texture perception factor calculation module is used to calculate the gradient magnitude of the texture-rich area inside the LCU, and the calculation result is used as the texture perception factor of the LCU; The motion perception factor calculation module is used to calculate the product of the frame difference amplitude and the area ratio of the motion-rich area inside the LCU, and the calculation result is used as the motion perception factor of the LCU; The LCU bit allocation module calculates the bit allocation weight of the LCU according to the texture perception factor and the motion perception factor of the LCU, and then calculates the target coding bit number of the LCU.

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