CN111447438B - Rapid intra-frame prediction mode judgment method for universal video coding - Google Patents
Rapid intra-frame prediction mode judgment method for universal video coding Download PDFInfo
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Abstract
The invention discloses a fast mode judgment method for universal video coding, which utilizes a rough mode judgment method (RMD) to acquire context information; predicting the coding rate R from a mathematical perspective based on the probability distribution of the residuals e The method comprises the steps of carrying out a first treatment on the surface of the Predicting coding distortion D by combining context information in the pixel domain e The method comprises the steps of carrying out a first treatment on the surface of the According to the rate distortion cost J e An intra-prediction mode is determined from the candidate mode set. Experimental results show that the method for judging the fast intra-frame mode of the universal video coding can reduce the coding complexity by about 29% under the condition of less influence on the coding efficiency.
Description
Technical Field
The invention belongs to the technical field of video coding, and particularly relates to a fast intra-frame prediction mode judgment method for universal video coding.
Background
With the rapid development of network technology, the video coding technology is mature and perfect, the transmission technology is continuously improved, and the video service is widely applied. How to better realize efficient video coding is always a research hotspot in the video field. The new generation video coding standard VVC (general video coding) aims at the point of 'large data volume of high definition/ultra high definition video', and by means of advanced coding tools, abundant video contents are effectively represented by a more flexible means, so that a large amount of storage space and transmission bandwidth are saved, and the capability of coping with new service challenges is provided.
To further exploit spatial correlation to remove redundancy of video content, VVC introduces 67 intra prediction modes, including multi-angle mode, planar mode, and DC mode. An optimal mode is selected from a plurality of modes to maximize intra coding efficiency of VVC by using intra prediction mode decision according to texture characteristics of video. The method is realized mainly by means of Lagrange optimization technology, each mode obtains coding code rate and coding distortion through the steps of prediction, transformation, quantization, entropy coding, inverse quantization, inverse transformation, pixel reconstruction and the like, rate distortion cost is calculated, and the optimal prediction mode is determined by comparing the rate distortion cost.
In VVC, the intra prediction mode decision algorithm is divided into two parts, coarse mode decision (RMD) and Rate Distortion Optimization (RDO). The sum of absolute errors after Hadamard transformation is firstly used as D in the RMD module s Calculating a rate distortion cost J of an intra-prediction mode for a distortion measure s ：
J s ＝D s +λ s ·R s ， (1)
Wherein lambda is s R is Lagrangian factor s Representing the number of bits consumed to encode the intra prediction mode. According to the result of equation (1), M (m=6) most likely to be the optimal intra prediction modes are selected to constitute the most probable mode set. Then each intra prediction mode in the most probable mode set is encoded in RDO, and the rate-distortion cost J is selected e The smallest mode is taken as the optimal intra prediction mode:
J e ＝D e +λ e ·R e . (2)
parameter lambda e Represents the Lagrangian factor, R e D is the sum of the number of coded bits of the intra prediction mode and the number of coded bits of the prediction residual e Is the sum of the mean square errors.
Although multiple modes can well capture video information in any direction in a frame, overload operand and long processing time delay are brought to an encoder, which is extremely unfavorable for the expansion of the multimedia service based on the VVC. Jamali et al use transform domain residuals to predict rate distortion costs, excluding prediction modes that cannot be optimal to reduce coding complexity (see Jamali M, COULOMBE s.fast HEVC intra mode decision based on RDO cost prediction [ J ]. IEEE Transactions on Broadcasting, 2018:1-14); tariq predicts the rate-distortion cost of the current block according to the dynamic change of the rate-distortion cost of the adjacent block, and determines the optimal prediction mode by minimizing the rate-distortion cost (see Tariq j.rd-cost as statistical inference for early intra mode decision in HEVC [ J ]. Multimedia Tools and Applications,2019,78 (12): 16783-16801); in addition, by means of intelligent optimization algorithm, a new objective function of new optimal prediction mode decision can be established by analyzing and researching the characteristics of intra-frame prediction mode decision (see TARIQ J, ARMGHAN A, IJAZ A, ASHRAF I.Pure intra mode decision in HEVC using optimized firefly algorithm [ J ]. Journal of Visual Communication and Image Representation,2020, vol.68). The method is mainly used for optimizing 35 kinds of intra-frame prediction mode decisions in High Efficiency Video Coding (HEVC), and has low accuracy and coding efficiency so as to be unsuitable for being applied to the latest video coding VVC. It is therefore necessary to establish a fast intra mode decision method for a suitable VVC.
Disclosure of Invention
The invention aims to provide a fast intra-frame prediction mode judging method for general video coding, which has lower coding complexity and higher coding efficiency.
The technical scheme adopted by the invention is that a fast intra-frame prediction mode judgment method for universal video coding specifically comprises the following steps:
step 1, first, M (m=6) candidate modes most likely to be the optimal intra prediction mode are selected from among the intra prediction modes in 67 using RMD method. And secondly, respectively calculating the coding code rate and the coding distortion of the M candidate modes according to the step 2 and the step 3, obtaining the total cost of each candidate mode, and selecting the prediction mode with the minimum total cost from the total cost as the optimal intra-frame prediction mode of the coding block.
Step 2, the residual error of the transform domain can be described as zero-mean gaussian distribution, and the sum of mean square errors is used as a distortion measure, and the quantized theoretical rate distortion model is as follows:
where x represents the residual error, δ is the standard deviation of the residual error, and e is a natural constant. At high bit rate or low distortion, the coding rate R and log 2 δ Proportional, and thus residual, coding rate is aboutThe method comprises the following steps:
R r ≈α·log 2 σ , (4)
wherein α is 0.5. The number of coded bits for the intra prediction mode can be obtained by the RMD module:
R m ＝R s . (5)
the total number of coded bits R e ：
R e ≈R m +R r .(6)
In step 3, since VVC coding uses scalar quantization technique, the pixel cannot be restored to the original value after being de-coded, resulting in distortion. According to the intra coding principle, the pixel distortion d at the (i, j) position can be expressed as the difference between the original pixel value p and the reconstructed pixel value p':
wherein p is p Is the pixel predicted value obtained by adopting a certain intra-frame prediction mode, p e Representing the difference, p, between the original pixel value and the predicted pixel value e ' represents the difference between the reconstructed pixel value and the predicted pixel value. Considering that the current pixel has a strong correlation with the reference pixel and all use the same quantization parameter, the coding distortion of the current pixel can be determined by means of the coding distortion d (r) i ,r j ) And (3) predicting:
total distortion D of final encoded block e ：
The present invention is also characterized in that,
the method for calculating the parameter delta in the formula (9) in the step 2 is as follows:
for residual block coefficients r with the size of N multiplied by N, a transformation matrix T is obtained after DCT transformation:
where A is the DCT matrix, then:
wherein [] u,u The coefficient values in the matrix at the (u, u) position are represented, and the symbol R' is defined as:
the parameter ρ is used to measure the correlation between pixel values in the horizontal direction and the vertical direction, and its value is set to 0.6; parameter delta p For representing the standard deviation of pixels within the residual block, this value can be approximated by means of the mean absolute difference MAD:
compared with the prior art, the invention has the following advantages:
(1) The invention predicts the coding rate from the angle of the rate distortion theory and has high accuracy.
(2) The invention predicts the coding distortion from the angle of the rate distortion theory and has high accuracy.
(3) The fast intra-frame prediction mode judging method provided by the invention considers the characteristics of video content and has better coding efficiency.
(3) The method for judging the fast intra-frame prediction mode considers the VVC coding technology and has better coding efficiency.
(4) The present invention determines the optimal intra prediction mode by using the predicted rate-distortion cost, and the encoding complexity can be reduced by about 30% compared to the existing method.
Drawings
Fig. 1 is a flowchart of a fast intra mode decision method for general video coding according to the present invention.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The invention is directed to a fast intra mode decision method for general video coding, the specific calculation flow is shown in figure 1,
step 1, using the sum of absolute errors D after Hadamard transformation s Calculating a rate distortion cost J of an intra-prediction mode for a distortion measure s ：
J s ＝D s +λ s ·R s ， (1)
Wherein lambda is s R is Lagrangian factor s Representing the number of bits consumed to encode the intra prediction mode. According to the result of equation (1), M (m=6) most likely to be the optimal intra prediction modes are selected to constitute the most probable mode set. Step 2, calculating a parameter delta under the i (i epsilon M) th candidate mode:
for residual block coefficients r with the size of N multiplied by N, a transformation matrix T is obtained after DCT transformation:
where A is the DCT matrix, then:
wherein [] u,u The coefficient values in the matrix at the (u, u) position are represented, and the symbol R' is defined as:
the parameter ρ is used to measure the horizontal and vertical directionsCorrelation between upward pixel values, the value of which is set to 0.6; parameter delta p For representing the standard deviation of pixels within the residual block, this value can be approximated by means of the mean absolute difference MAD:
step 3, calculating the coding rate under the i (i epsilon M) candidate modes:
calculating the coding rate of the residual error:
R r ≈α·log 2 σ , (4)
wherein α is 0.5. The coding rate for the intra prediction mode can be obtained by the RMD module:
R m ＝R s . (5)
the total code rate R e ：
R e ≈R m +R r . (6)
Step 4, calculating the coding distortion in the ith (i E M) candidate mode
According to the intra coding principle, the pixel distortion d at the (i, j) position can be expressed as the difference between the original pixel value p and the reconstructed pixel value p':
wherein p is p Is the pixel predicted value obtained by adopting a certain intra-frame prediction mode, p e Representing the difference, p, between the original pixel value and the predicted pixel value e ' represents the difference between the reconstructed pixel value and the predicted pixel value. Considering that the current pixel has a strong correlation with the reference pixel and all use the same quantization parameter, the coding distortion of the current pixel can be determined by means of the coding distortion d (r) i ,r j ) And (3) predicting:
total distortion D of final encoded block e ：
And 5, calculating the rate distortion cost under the ith (i epsilon M) candidate mode according to the formula (2).
And 6, selecting a prediction mode with the minimum rate distortion cost from the candidate mode set as an optimal intra prediction mode of the coding block.
The effects of the present invention are further illustrated by experiments.
The VVC intra-frame coding performance under different application scenes with different resolutions is tested through experiments. The statistical result shows that the average coding time of the invention is reduced by 31.2%, and the average coding bit number is increased by 1.53%. When facing new video service characteristics and new coding technology, the method can compress rich video content more quickly by applying a quick intra-frame prediction mode judgment method of general video coding, save the coding time of a system, improve the capability of coping with new service challenges in video playing, and enable more and more users to participate in video application, thereby feeling the unique charm brought by high-definition/ultra-high-definition video on the spot.
Claims (2)
1. The fast intra mode judging method for the universal video coding is characterized by comprising the following steps:
step 1, selecting M candidate modes which are most likely to become the optimal intra-frame prediction mode from 67 intra-frame prediction modes by using a rough mode judgment method;
step 2, calculating the standard deviation delta of the transform domain residual error in the ith (i epsilon M) candidate mode; the method for calculating the parameter delta comprises the following steps:
for residual block coefficients r with the size of N multiplied by N, a transformation matrix T is obtained after DCT transformation:
where A is the DCT matrix, then:
wherein [] u,u The coefficient values in the matrix at the (u, u) position are represented, and the symbol R' is defined as:
the parameter ρ is used to measure the correlation between pixel values in the horizontal direction and the vertical direction, and its value is set to 0.6; parameter delta p For representing the standard deviation of pixels within the residual block, which value is approximated by means of the mean absolute difference MAD:
step 3, calculating the coding rate of the ith (i epsilon M) candidate mode; the method for calculating the coding rate specifically comprises the following steps:
calculating the coding rate of the residual error:
R r ≈α·log 2 δ (4) Where α is 0.5, the coding rate for the intra prediction mode is obtained by the RMD module:
R m ＝R s (5)
the total code rate R e ：
R e ≈R m +R r (6)；
Step 4, calculating coding distortion under the i (i epsilon M) candidate modes; the specific method for calculating the coding distortion is as follows:
according to the intra coding principle, the pixel distortion d at the (i, j) position is expressed as the difference between the original pixel value p and the reconstructed pixel value p':
wherein p is p Is the pixel predicted value obtained by adopting a certain intra-frame prediction mode, p e Representing the difference, p, between the original pixel value and the predicted pixel value e ' represents the difference between the reconstructed pixel value and the predicted pixel value; considering that the current pixel has a strong correlation with the reference pixel and all use the same quantization parameter, the coding distortion of the current pixel is thus determined by the coding distortion d (r i ,r j ) And (3) predicting:
total distortion D of final encoded block e ：
Step 5, calculating the rate distortion cost under the i (i epsilon M) candidate mode;
and 6, selecting a prediction mode with the minimum rate distortion cost from the candidate mode set as an optimal intra prediction mode of the coding block.
2. The fast intra mode decision method for general video coding according to claim 1, wherein in step 1, M takes a value of 6.
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