CN114286097A

CN114286097A - Coding block quantization increment parameter optimization method in secondary video coding rate control

Info

Publication number: CN114286097A
Application number: CN202111580986.0A
Authority: CN
Inventors: 戴伟; 刘振宇
Original assignee: Nantong Chaohui Information Technology Co ltd
Current assignee: Nantong Chaohui Information Technology Co ltd
Priority date: 2021-12-22
Filing date: 2021-12-22
Publication date: 2022-04-05
Anticipated expiration: 2041-12-22
Also published as: CN114286097B

Abstract

The invention relates to the technical field of video coding compression, in particular to a quantization increment parameter optimization method in a secondary coding rate control application scene. In the rate control algorithm, a frame is equally divided into 16x16 image blocks, where the Quantization Parameter (QP) of the ith 16x16 coding unit_i) Is based on frame-level basic quantization parameters

And its quantization parameter delta (Δ QP)_i) Specifically, QP_iIs the sum of the base quantization parameter and its quantization parameter increment. The invention is applied to a secondary coding algorithm: coding the same video sequence twice, and pre-coding the target video sequence according to the code rate limiting condition and the interframe information correlation degree in the first codingProcessing; the second coding adopts an enhanced related inter-frame information transfer estimation algorithm according to the statistical analysis of the quantization parameter of each coding block in the first coding, and further performs quantization increment parameter (delta QP) of the 16x16 coding block_i) And (6) optimizing. By adopting the quantization increment parameter optimization algorithm, the code rate cost can be reduced under the same coding image quality.

Description

Coding block quantization increment parameter optimization method in secondary video coding rate control

Technical Field

The invention relates to the technical field of video compression, in particular to a quantization increment parameter optimization method in a secondary coding rate control application scene.

Background

The rate control algorithm in video coding, in which a frame is equally divided into 16x16 image blocks with Quantization Parameters (QP) of the ith 16x16 coding unit, is the core technology of encoder design_i) Is based on frame-level basic quantization parameters

And its quantization parameter delta (Δ QP)_i) Determining, specifically, QP_iBy addition of a base quantization parameter to its quantization parameter increment, i.e.

The code rate control algorithm in video coding is realized by adjusting QP_iThe minimum rate-distortion cost is achieved at the specified channel bandwidth. It is formally expressed as

Wherein, QP_iIs the quantization parameter of the ith 16x16 image block, D_i(QP_i) And R_i(QP_i) Taken as QP_iDistortion and code rate at λ lagrange factor, R_CFor the target code rate, I is the number of 16x16 image blocks within the code rate control sliding window.

In the traditional quantization increment parameter optimization method, pre-motion prediction calculation is carried out on an undersampled image of a source image, the inter-frame block particle size information correlation degree is estimated, and then quantization increment parameters of 16x16 image blocks are adjusted quantitatively. Compared with the traditional method, the invention is a method for optimizing the quantization increment parameter of the coding unit based on the application scene of the secondary coding rate control, namely the parameter delta QP in the formula (1)_iThe optimization method of (1).

Disclosure of Invention

The invention is in the second encodingMotion vector, quantization parameter, intra prediction coding cost (C) of coding block obtained by first encoding_intra) And inter-frame prediction coding cost (C)_inter) And optimizing the quantization increment parameter of the coding block in the secondary coding process.

The quantitative algorithm for quantifying the parameter increment relies on an accurate estimate of the amount of inter-frame information propagation. The first point of the invention is to use the motion vector, quantization parameter and intra-frame prediction coding cost (C) obtained by the first coding_intra) And inter-frame prediction coding cost (C)_inter) To improve the estimation accuracy of the 16x16 block granularity interframe information propagation quantity (PI). In this process, we have invented the concept of the information gain factor (α).

When a mapping relation between PI and quantization parameter increment is constructed, we invent a dynamic intensity parameter s definition method based on the current 16x16 block quantization step size, namely s ═ min (1, max (0, τ · (QP-30))), wherein a variable τ ∈ [0.01, 0.1 ]. Under the environment of low-code-rate coding, the performance of the algorithm is further improved.

Drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:

fig. 1 is a schematic flow chart of a quantization increment parameter optimization method in a secondary coding rate control application scenario according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the delivery of 16x16 pieces of granularity information between related frames according to an embodiment of the present invention; in the figure, the nth frame is a predicted frame, the nth frame takes the (n-1) th frame as a reference frame, each frame comprises 3x3 image blocks of 16x16, and a small square represents a 16x16 image block; shaded block in nth frame is CU₁₁The intra prediction cost, the inter prediction cost and the input information amount of the block of the position are represented as C_intra、C_interAnd PI; the output information amount is

The output information amount after gain PO' is alpha PO, wherein

Q is the quantization step size of the shaded block, σ²Predicting a variance for the shadow block; the 16x16 shadow blocks in the n-1 th frame are the reference areas corresponding to the shadow blocks in the n-1 th frame; PO' is split into its input information amount in equal proportion according to the overlapping area of the reference area and the adjacent 16x16 blocks; for example, if CU₀₁The area overlapping the reference region is 25 luminance pixels,

is subject to CU₀₁The input information of (1).

Detailed Description

The technical solution of the present invention will now be further explained in detail with reference to the accompanying drawings and examples.

Fig. 1 is a schematic flowchart illustrating a method for optimizing quantization increment parameters in a secondary coding rate control application scenario in this embodiment, where the method includes:

s1, dividing each frame image into 16x16 blocks, and obtaining the motion vector, quantization parameter and intra-frame prediction coding cost (C) of each 16x16 block in each frame image of the video according to the first coding result_intra) And inter-frame prediction coding cost (C)_inter) The aforementioned motion vector, quantization parameter, and intra prediction coding cost (C)_intra) And inter-frame prediction coding cost (C)_inter) Is used in the second encoding to readjust the quantization increment parameter of each 16x16 block to improve the image quality of the second encoding.

S2, the second encoding uses the same frame structure and reference relationship as the first encoding, and calculates the output information amount PO of the 16x16 block of the predicted frame based on the intra prediction encoding cost and inter prediction encoding cost of the 16x16 block of the predicted frame obtained by the first encoding and the input information amount PI of the 16x16 block. The calculation method comprises the following steps: when C of 16x16 block of a predicted frame_intra、C_interAnd PI is known, the output information amount of 16x16 blocks of the prediction frame

For theA block not to be referred to, whose input information amount PI is 0; .

S3, defining the propagation gain coefficient α of the output information amount PO of the 16x16 block of the predicted frame according to the output information amount PO of the 16x16 block of the predicted frame obtained in step S2, specifically including:

according to the primary coding result, we can obtain the motion vector of the 16x16 block in the prediction frame, the quantization step Q and the variance σ of the prediction residual thereof²Variance σ of prediction residual²Namely, the 16x16 block in the prediction frame is subtracted from the 16x16 block in the reference frame according to the pixel points to obtain the residual value of the 16x16 prediction residual block, and the variance of the residual value is calculated; defining a gain factor of

α · PO is the total amount of input information from the projection of the output information PO of the 16 × 16 block in the predicted frame to the reference frame pointed to by the motion vector. This process is represented by PO' ═ α · PO in fig. 2.

At S4, a 16x16 reference region (e.g., the shaded block of the n-1 frame in fig. 2) in the reference frame is obtained according to the motion vector of the 16x16 block in the predicted frame (e.g., the motion vector of the shaded block of the n-th frame in fig. 2), and any 16x16 block in the reference frame is defined as a related block if there is an overlap with the reference region. If the overlap region contains a number of pixels of the luminance component of s_oThen the amount of information is increased when calculating the PI for the relevant block of 16x16 in this reference frame

Therefore, according to the reference relationship of the first encoding, when the output information amount and the gain coefficient of all the blocks in the predicted frame are known, the PI of all the 16 × 16 blocks in the reference frame can be derived.

S5, deriving the 16x16 block quantization delta Δ QP based on the input information PI of the 16x16 block in the reference frame obtained in step S4, which specifically includes: Δ QP ═ s · log₂(1+ PI) where the strength parameter s is defined as a function of the quantization parameter QP chosen for the current 16x16 block in the primary coding, expressed as s ═ min (1, max (0, τ · (QP-30))), where τ ∈ 0.01, 0.1.

In conclusion, by adopting the quantization increment parameter optimization algorithm, the code rate cost can be reduced under the same coding image quality

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A method for optimizing quantization increment parameters of a coding unit under an application scene based on secondary coding rate control is characterized in that each frame of image is divided into 16x16 blocks, and according to a first coding result, a motion vector, a quantization parameter and an intra-frame prediction coding cost (C) of each 16x16 block in each frame of image of a video are obtained_intra) And inter-frame prediction coding cost (C)_inter) Based on the above information, the quantization increment parameter of the 16x16 block of each frame image is readjusted in the second encoding, so that the image quality of the second encoding is improved.

2. The method of claim 1, wherein the method for optimizing quantization increment parameters of the coding unit under the application scenario of rate control based on secondary coding is characterized by calculating an output information amount PO of a 16x16 block of the predicted frame based on an intra prediction coding cost and an inter prediction coding cost of a 16x16 block of the predicted frame obtained by the first coding and an input information amount PI of the 16x16 block;

when C of 16x16 block of a predicted frame_intra、C_interAnd PI is known, the output information amount of 16x16 blocks of the prediction frame

3. The method of claim 2, wherein the propagation gain α of the output information amount PO of the 16x16 block of the predicted frame is defined according to the output information amount PO of the 16x16 block of the predicted frame, and the total input information amount of the output information amount PO projected to the reference frame pointed by the motion vector is calculated;

defining a gain factor of

Where Q is the quantization step size, σ, of a 16 × 16 block²For the variance of a 16x16 prediction residual block, α · PO is the total amount of input information from the projection of the output information PO of the 16x16 block of the predicted frame to the reference frame pointed to by the motion vector.

4. The method of claim 3, wherein the method for optimizing quantization increment parameters of the coding unit under the application scenario based on the quadratic coding rate control is characterized by calculating an input information amount PI of a related reference block on the reference frame based on the α -PO, and specifically comprises:

obtaining a corresponding 16x16 reference region on the reference frame according to the motion vector of the 16x16 block of the predicted frame, wherein any 16x16 block on the reference frame and the reference region have an overlapping area and are defined as related blocks; the overlapping region includes a number of pixels of a luminance component of s_oThen the amount of information is increased when calculating the PI for this reference frame 16x16 block

According to the reference relation of the first encoding, when the output information amount and the gain coefficient of all the blocks in the predicted frame are known, deriving the PI of all the 16x16 blocks in the reference frame; when a 16x16 block is not referenced, its PI equals 0.

5. The method of claim 4, wherein the calculating the quantization delta Δ QP for the 16x16 block according to the input information PI of the 16x16 block in the reference frame comprises:

ΔQP＝s·log₂(1+ PI) where the intensity parameter s is defined as the selected quantization of the current 16x16 block in one passFunction of parameter QP, expressed as s ═ min (1, max (0, τ · (QP-30))), where τ ∈ [0.01, 0.1 ])]。