TWI886550B - Determination method for chroma intra prediction mode and image encoding device - Google Patents

Abstract

A determination method for chroma intra prediction mode includes: performing simple RDO calculations to luminance values of each of pixels of an image block to obtain multiple luminance candidate modes; determining multiple chroma candidate modes according to one of the luminance candidate modes and a chroma simple RDO result generated by performing simple RDO calculations to chroma values of each of pixels of the image block; performing full RDO calculations of the luminance candidate modes to the luminance values of each of pixels of the image block to select a luminance target mode; performing full RDO calculations of the chroma candidate modes to the chroma values of each of pixels of the image block to obtain chroma full RDO results; determining chroma target mode according to the luminance target mode and the chroma full RDO results. Prediction modes of the chroma values and the luminance values of the pixels of the image block are determined in stages, such that the chroma acquires the luminance target mode timely to determine whether to use the DM mode for encoding. The simple RDO calculations to the chroma values and the luminance values of each of pixels of the image block are performed in parallel.

Description

Method for determining chroma intra-frame prediction mode and image coding device

This case relates to the field of video coding technology, and more particularly to a method for determining a chroma intra-frame prediction mode and an image coding device.

The High Efficiency Video Coding (HEVC) standard defines 35 luma intra-frame prediction modes (including Planar mode, DC mode, and 33 different angle modes) and 5 chroma intra-frame prediction modes (Planar mode, DC mode, horizontal mode, vertical mode, and luma derived (DM) mode). The DM mode indicates a mode in which the same intra-frame prediction mode as the luma component's intra-frame prediction mode is applied as the chroma component's intra-frame prediction mode. In the DM mode, the chroma intra-frame prediction mode is set to be equal to the luma optimal intra-frame prediction mode. Using the DM mode for chroma encoding can improve coding efficiency and reduce the amount of bits transmitted for the encoded video. However, in actual encoding, luma and chroma are usually encoded in parallel, which makes it impossible for chroma to obtain the optimal mode of luma in time, so the DM mode cannot be used.

The purpose of this application is to provide a method for determining a chroma intra-frame prediction mode and an image coding device to improve the above-mentioned problem.

In some embodiments, the method for determining the chrominance intra-frame prediction mode includes: performing a simple RDO calculation on the luminance value of each pixel of an image block to obtain a plurality of luminance candidate modes; determining a plurality of chrominance candidate modes according to one of the plurality of luminance candidate modes and a chrominance simple RDO result obtained by performing a simple RDO calculation on the chrominance value of each pixel of the image block; performing a complete RDO calculation corresponding to the plurality of luminance candidate modes on the luminance value of each pixel of the image block; RDO calculation is performed to select a luminance target mode; a complete RDO calculation corresponding to a plurality of chrominance candidate modes is performed on the chrominance value of each pixel of the image block to obtain a chrominance complete RDO result; and a chrominance target mode is determined according to the luminance target mode and the chrominance complete RDO result; wherein the simple RDO calculation is performed on the luminance value of each pixel of the image block and the simple RDO calculation is performed on the chrominance value of each pixel of the image block in parallel.

In some embodiments, the image encoding device includes: a luminance candidate mode circuit, a chrominance candidate mode circuit, a luminance target mode circuit, a chrominance full RDO calculation circuit, and a chrominance target mode circuit. The luminance candidate mode circuit obtains the luminance value of each pixel of an image block from a memory, performs a simple RDO calculation on the luminance value of each pixel of the image block to obtain multiple luminance candidate modes; the chrominance candidate mode circuit obtains the chrominance value of each pixel of the image block from the memory, and determines multiple chrominance candidate modes according to one of the multiple luminance candidate modes and the chrominance simple RDO result obtained by performing a simple RDO calculation on the chrominance value of each pixel of the image block; the luminance target mode circuit performs a corresponding RDO calculation on the luminance value of each pixel of the image block. The invention discloses a method for selecting a luminance target mode by performing full RDO calculations of multiple luminance candidate modes; a chrominance full RDO calculation circuit performs full RDO calculations corresponding to multiple chrominance candidate modes on the chrominance value of each pixel of the image block to obtain a chrominance full RDO result; a chrominance target mode circuit determines a chrominance target mode according to the luminance target mode and the chrominance full RDO result; wherein the simple RDO calculations on the luminance value of each pixel of the image block and the simple RDO calculations on the chrominance value of each pixel of the image block are performed in parallel.

The method for determining the chroma intra-frame prediction mode and the image coding device provided in this case perform simple RDO calculation on the brightness value of each pixel of the image block in parallel with simple RDO calculation on the chroma value of each pixel of the image block. In this way, the prediction mode of the chroma value of the pixel is determined by calculating the rate-distortion cost of the chroma component and the luminance component in parallel in steps, thereby improving the coding performance.

The features, implementation and effects of this case are described in detail below with reference to the accompanying drawings.

The technical terms used in the following description refer to the customary terms in this technical field. If this manual explains or defines some of the terms, the interpretation of those terms shall be based on the explanation or definition in this manual.

The disclosed content of this case includes a method for determining a chroma frame prediction mode and an image encoding device. Part or all of the process of the method for determining a chroma frame prediction mode of this case can be in the form of software and/or firmware, and can be executed by the image encoding device of this case.

FIG1 is a schematic diagram of the functional modules of the image coding device of the present invention. The image coding device 10 may be a system on chip (SoC) image coding chip, and the image coding device 10 includes a memory 100, an intra-frame prediction circuit 200, a calculation circuit 300, and a coding circuit 400. The memory 100 is a static random access memory (SRAM), and its first storage area 100A stores the original pixels of the image block to be coded, and its second storage area 100B stores the reference pixels of the image block to be coded. The second storage area 100B is also used to store the reconstructed pixels of the image block to be coded. In the embodiment of the present case, both the original pixel and the reference pixel include the brightness value and the chrominance value of the pixel. The intra-frame prediction circuit 200 predicts a to-be-encoded image block of the same frame according to a prediction mode using the reconstructed pixels (i.e., reference pixels) of the adjacent to-be-encoded image block to be encoded to generate the predicted pixels of the image block. The calculation circuit 300 generates the reconstructed pixels and encoding parameters of the to-be-encoded image block according to the pixels of the to-be-encoded image block and the predicted pixels. The encoding circuit 400 generates a bit stream according to the pixels of the to-be-encoded image block, the predicted pixels, and the encoding parameters. The operations performed by the calculation circuit 300 include all or part of the calculation of residuals, transformation, quantization, inverse quantization, inverse transformation, reconstruction, and filtering. The operating principles of the computing circuit 300 and the encoding circuit 400 are well known to those skilled in the art and will not be described in detail.

In order to ensure coding efficiency, it is necessary to select an appropriate prediction mode. Using the rate-distortion optimization (RDO) algorithm to select the optimal coding parameters is the key to ensuring video coding efficiency. The Lagrangian optimization method is a common optimization tool in video rate distortion. Its rate-distortion mode judgment is to calculate the Lagrangian cost including distortion and bit rate, and select the prediction mode with the smallest cost as the final coding mode. The standard Lagrangian cost formula is as follows:

J=D+λ*R

Among them, J is the Lagrangian cost (i.e., Rate-Distortion Cost, RDO)), D represents the distortion of different coding modes, λ represents the Lagrangian factor, and R represents the number of bits required to use all the information (such as coefficient of variation, mode information, image block division method, etc.) under the current prediction mode.

However, full RDO requires actually encoding each mode once, calculating the Lagrangian cost of each mode, and then selecting the mode with the smallest Lagrangian cost as the actual encoding mode, which is very time-consuming. When the brightness value and the chrominance value of a pixel are encoded in parallel, the best mode for encoding the brightness value of the pixel cannot be known in advance before the encoding process of the chrominance value of the pixel, so that the chrominance value encoding process of the pixel cannot use the DM mode, and it is not conducive to hardware parallel pipeline implementation.

In order to improve the feasibility of encoding the chrominance value of a pixel using the DM mode, the intra-frame prediction circuit 200 calculates the rate-distortion cost RDO of the luminance component and the chrominance component of the image block in a parallel and staged manner, thereby determining the coding mode of the luminance component and the coding mode of the chrominance component more quickly to determine the possibility of using the DM mode to encode the chrominance component. For example, the chrominance component and the luminance component are processed in two stages in parallel. The first stage is to calculate the rate-distortion cost of each prediction mode of the luminance component and the chrominance component through a simple RDO to select their respective candidate prediction modes. The second stage is to calculate the rate-distortion cost of the candidate mode through a full RDO to determine the target prediction mode of the luminance component and the chrominance component, and finally determine whether the chrominance component can be encoded using the DM mode.

Full RDO calculates the rate-distortion cost of the prediction mode according to the standard Lagrangian cost formula. The distortion D is calculated based on the original pixels and reconstructed pixels of the image block. Reconstructed pixels refer to the results of the original pixels predicted by a prediction mode and then processed by transformation, quantization, inverse quantization, inverse transformation, reconstruction, filtering, etc. The R of full RDO is the number of bits actually consumed when encoding according to a certain prediction mode.

In the embodiment of the present case, the simple RDO calculates the rate-distortion cost of the prediction mode according to the adjusted Lagrangian cost formula, and the distortion D is calculated based on the original pixels of the image block and the reference pixels (non-reconstructed pixels) of the image block. In addition, the R of the simple RDO is an estimate of the number of bits that may be consumed when encoding according to a certain mode, not the actual number of bits consumed. Compared with the full RDO, the simple RDO does not use reconstructed pixels, so there is no need for transformation, quantization, dequantization, inversion, reconstruction and other operations. The accuracy is low, but the RDO value of each mode can be quickly estimated.

Please refer to FIG2, which is a schematic diagram of detailed functional modules of the first embodiment of the intra-frame prediction circuit 200 of FIG1. The intra-frame prediction circuit 200 includes a luminance candidate mode circuit 210, a chrominance candidate mode circuit 220, a luminance target mode circuit 230, a chrominance full RDO calculation circuit 240, and a chrominance target mode circuit 250.

The above circuits are described in detail below with reference to FIG3.

Please refer to FIG. 3, which is a flow chart of a first embodiment of a method for determining a chroma frame coding mode provided by an embodiment of the present invention. The method comprises the following steps:

Step S301: The brightness candidate mode circuit 210 obtains the brightness value of each pixel of the image block from the memory 100, and performs a simple RDO calculation on the brightness value of each pixel of the image block to obtain a plurality of brightness candidate modes. For example, the simple RDO calculation of the DC mode, the Plane mode and at least one angle mode is performed on the brightness value of each pixel of the image block, and a preset number (e.g., 2) of brightness candidate modes are determined based on the simple RDO calculation result.

The at least one angle mode can be obtained from the 33 angle modes in a variety of ways. For example, the first way is to select multiple angle modes as brightness candidate modes based on the simple RDO calculation results obtained by executing the 33 angle modes on the brightness values of each pixel of the image block, for example, sequentially select multiple angle modes corresponding to multiple smaller simple RDO values; the second way is to first select multiple basic angle modes from the 33 angle modes, with a preset number of angle modes between two adjacent basic angle modes; then select a main angle mode based on the simple RDO calculation results obtained by executing the multiple basic angle modes on the brightness values of each pixel of the image block, for example, select a basic angle mode corresponding to the minimum simple RDO value as the main angle mode, and expand the main angle mode to obtain multiple (counted as M) angle modes.

The luminance candidate mode circuit 210 further transmits the selected main angle mode or M angle modes and the plurality of luminance candidate modes to the chrominance candidate mode circuit 220 .

Step S302: The chromaticity candidate mode circuit 220 obtains a plurality of luminance candidate modes from the luminance candidate mode circuit 210 and the chromaticity value of each pixel of the image block from the memory 100, and determines a plurality of chromaticity candidate modes according to one of the plurality of luminance candidate modes and the chromaticity simple RDO result obtained by performing a simple RDO calculation on the chromaticity value of each pixel of the image block. For example, the chromaticity candidate mode circuit 220 performs a simple RDO calculation corresponding to at least one of the Planar mode, the DC mode, the vertical mode, the horizontal mode and the plurality of angle modes on the chromaticity value of each pixel of the image block to obtain a corresponding simple RDO calculation result. A preset number (e.g., 2 or 3) of chromaticity candidate modes are determined based on at least one of the plurality of luminance candidate modes, and the Planar mode, DC mode, vertical mode, horizontal mode, and the simple RDO calculation results corresponding to the plurality of angle modes. In one embodiment, the chromaticity candidate mode circuit 220 obtains the main angle mode from the luminance candidate mode circuit 210, and expands M angle modes based on the main angle mode. In another embodiment, the chromaticity candidate mode circuit 220 directly obtains the M angle modes from the luminance candidate mode circuit 210.

In the embodiment of the present case, the simple RDO calculation for the brightness value of each pixel of the image block in step S301 and the simple RDO calculation for the chrominance value of each pixel of the image block in step S302 are performed in parallel. In this way, by synchronously performing the simple RDO calculation for the chrominance value and the brightness value of the pixel, the overall operation time of the intra-frame prediction circuit 200 can be shortened, and the selection of the chrominance candidate mode is no longer dependent on the brightness candidate mode.

Step S303: The luminance target mode circuit 230 performs a complete RDO calculation corresponding to the multiple luminance candidate modes on the luminance value of each pixel of the image block to select a luminance target mode. Specifically, the complete RDO calculation of each luminance candidate mode is performed on the luminance value of each pixel of the image block, and the mode with the smallest complete RDO value is selected as the luminance target mode. Step S304: The chrominance complete RDO calculation circuit 240 performs a complete RDO calculation corresponding to the multiple chrominance candidate modes on the chrominance value of each pixel of the image block to obtain a chrominance complete RDO result. Specifically, a complete RDO calculation corresponding to each chromaticity candidate mode is performed on the chromaticity value of each pixel of the image block to obtain the complete RDO calculation results corresponding to each chromaticity candidate mode, and the mode corresponding to the minimum RDO value is selected as the chromaticity first pre-target mode, and the mode corresponding to the second minimum RDO value is the chromaticity second pre-target mode. The chromaticity first pre-target mode and the chromaticity second pre-target mode are two modes among the Planar mode, the DC mode, the vertical mode and the horizontal mode, or one mode among the Planar mode, the DC mode, the vertical mode and the horizontal mode and an angle mode.

In step S305, the chroma target mode circuit 250 determines a chroma target mode according to the luma target mode and the chroma complete RDO result.

Further, the chroma target mode circuit 250 selects a chroma first pre-target mode and a chroma second pre-target mode based on the chroma complete RDO result, and the complete RDO value of the chroma first pre-target mode is less than the complete RDO value of the chroma second pre-target mode. In the present embodiment, at least one of the chroma first pre-target mode and the chroma second pre-target mode includes one of a Planar mode, a DC mode, a vertical mode, and a horizontal mode. The chroma target mode circuit 250 determines the chroma target mode based on the consistency of the luminance target mode and the chroma first pre-target mode. Specifically, the luminance target mode is compared to see whether it is consistent with the chroma first pre-target mode; when they are consistent, the chroma target mode circuit 250 determines that the chroma first pre-target mode is the chroma target mode, and is the DM mode. When the luminance target mode is inconsistent with the first chrominance pre-target mode, one of the Planar mode, DC mode, vertical mode and horizontal mode (with the best performance) is selected as the chrominance target mode from the first chrominance pre-target mode and the second chrominance pre-target mode, that is, when the luminance target mode is inconsistent with the first chrominance pre-target mode and the first chrominance pre-target mode is one of the Planar mode, DC mode, vertical mode and horizontal mode, the first chrominance pre-target mode is used as the chrominance target mode; when the luminance target mode is inconsistent with the first chrominance pre-target mode and the first chrominance pre-target mode is one of the M angle modes, the first chrominance pre-target mode is discarded and the second chrominance pre-target mode is selected as the chrominance target mode.

The following is a detailed description of the chromaticity target mode by taking the chromaticity target mode determination table shown in Table 1 as an example.

Table 1 is a schematic diagram of the determination of the chromaticity target mode Brightness target mode Chroma First Pre-Target Mode Chroma Second Pre-Target Mode Chroma Target Mode DC DC Angle 22 DM (as DC) Angle 22 DC Angle 22 DC Angle 22 Angle 22 DC DM (as Angle 22) Angle 24 Angle 22 DC DC

Please refer to the first and third columns. According to the calculation results of performing the full RDO calculation of the corresponding candidate mode on the chromaticity value of each pixel of the image block, the selected chromaticity first pre-target mode is DC mode and Angle 22 (i.e., angle mode), and the luminance target mode is also DC mode and Angle 22, i.e., the two are consistent, so the chromaticity target mode is DM mode.

Please refer to the second column. According to the calculation result of performing the full RDO calculation of the corresponding candidate mode on the chrominance value of each pixel of the image block, the selected chrominance first prediction target mode is DC mode, but the luminance target mode is Angle 22 mode. The two are inconsistent. Because the DC mode is one of the four intra-frame prediction modes of the chrominance component (i.e., Planar mode, DC mode, horizontal mode, and vertical mode), the chrominance target mode is DC mode.

Refer to the 4th column. According to the calculation result of executing the full RDO calculation of the corresponding candidate mode on the chrominance value of each pixel of the image block, the selected chrominance first pre-target mode is the Angle 22 mode, and the luminance target mode is the Angle 24 mode, which are inconsistent. Since the Angle 22 mode is not one of the 4 standard in-frame prediction modes of the luminance component, the chrominance first pre-target mode (Angel 22 mode) is discarded at this time, and the chrominance second pre-target mode (i.e., the DC mode with the smallest full RDO value among the 4 standard in-frame prediction modes) is selected as the chrominance target mode.

The method for determining the coding mode within the chroma frame can determine the respective coding modes for the brightness value and chroma value of the pixels of the image block in parallel and in stages. For example, step S301 performs a simple RDO calculation on the brightness value of each pixel of the image block, and step S302 performs a simple RDO calculation on the chroma value of each pixel of the image block. The steps S303 and S304 can also be performed in parallel, or steps S301 and S303 form a first pipeline (piple line), and steps S302 and S304 form a second pipeline. The two pipelines can be partially executed synchronously to increase the probability of using the DM mode when encoding the chroma component, thereby improving the efficiency of image encoding.

In order to further improve the encoding speed and determine the candidate modes of the brightness value and chrominance value of the pixels of the image block more quickly, the brightness candidate mode circuit 210 and the chrominance candidate mode circuit 220 can be further split into multiple circuit modules to achieve greater synchronization between step S301 and step S302.

Please refer to FIG. 4, which is a schematic diagram of the detailed functional modules of the intra-frame prediction circuit 200 of FIG. 1 in the second embodiment. Compared with FIG. 2, the difference is that the luminance candidate mode circuit 210 includes a main angle mode circuit 210A, a first mode expansion circuit 210B, a luminance final candidate mode circuit 210C and a first memory 210D; the chrominance candidate mode circuit 220 includes a first chrominance pre-candidate mode circuit 220A, a second mode expansion circuit 220B, a second chrominance pre-candidate mode circuit 220C, a chrominance final candidate mode circuit 220D and a second memory 220E. The first memories 210D and 220E can be different storage areas of the memory 100.

The functions of the luminance candidate mode circuit 210 and the chrominance candidate mode circuit 220 are described in detail below with reference to FIG. 5 and FIG. 6 .

Please refer to FIG. 5 , which is a detailed flow chart of step S301 in FIG. 3 , which specifically includes the following steps:

In step S501, the main angle mode circuit 210A performs simple RDO calculations corresponding to multiple basic angle modes on the brightness values of each pixel of the image block to select a main angle mode. The multiple basic angle modes are selected according to a preset number of angle mode intervals in a direction such as the horizontal or/and vertical direction, for example, one basic angle mode is selected every 4 angle modes, so as to select multiple (e.g., 8) basic angle modes from 33 angle modes. The main angle mode circuit 210A performs simple RDO calculations corresponding to the multiple basic angle modes on the brightness values of the pixels of the image block, and selects the basic angle mode corresponding to the minimum simple RDO value as the main angle mode.

The main angle mode circuit 210A stores the selected main angle mode and the simple RDO value obtained by performing simple RDO calculation corresponding to the multiple basic angle modes on the brightness value of the pixels of the image block into the first memory 210D. The main angle mode circuit 210A also sends the main angle mode to the second mode expansion circuit 220B in the chroma candidate mode circuit 220.

In step S502, the first mode expansion circuit 210B selects the same number of angle modes in two symmetrical directions with the main angle mode as the center to expand M angle modes. For example, the M angle modes are centered on the main angle mode and select the same number of angle modes in two symmetrical directions of the main angle mode, such as left and right or up and down. For example, if the main angle mode is mode 29, the first mode expansion circuit 210B selects two modes such as modes 27-28 and modes 30-31 on the left and right sides of mode 29 in sequence, so that 5 angle modes are expanded with mode 29 as the center. There is a preset number of angle modes between two adjacent basic angle modes (such as 4 angle modes per interval as mentioned above), and there is no angle mode between two adjacent angle modes in the M angle modes. The number of angle mode intervals between the main angle mode and an adjacent basic angle mode (for example, the aforementioned interval of 4 angle modes) is greater than the number of angle mode intervals between the main angle mode and an angle mode among multiple angle modes that is farthest away from the main angle mode (for example, the aforementioned interval of 2 angle modes).

In step S503, the final candidate mode circuit 210C performs a simple RDO calculation corresponding to M angle modes, DC mode and Planar mode on the brightness value of the image block to select a plurality of brightness candidate modes.

Specifically, the final candidate mode circuit 210C obtains the simple RDO calculation results by executing the simple RDO calculations corresponding to M angle modes, DC mode and Planar mode according to the brightness values of the pixels of the image block (the simple RDO calculation results of the main angle mode are stored in the first memory 210D, so they can be obtained from the first memory 210D without calculation), and compares the simple RDO calculation results to select the mode corresponding to the preset smaller number of simple RDO calculation results as the brightness candidate mode.

It should be noted that the main angle mode circuit 210A and the final candidate mode circuit 210C have the same circuit structure when they are implemented, or in order to simplify the hardware structure of the brightness candidate mode circuit, the final candidate mode circuit 210C can directly reuse the main angle mode circuit 210A to achieve its function.

Please refer to FIG. 6 , which is a detailed flow chart of step S302 in FIG. 3 , which specifically includes the following steps:

In step S601, the first chroma pre-candidate mode circuit 220A performs a simple RDO calculation corresponding to the Planar mode, DC mode, vertical mode and horizontal mode on the chroma value of each pixel of the image block to select a preset number (e.g., 2 or 3) of winning modes as the first chroma pre-candidate mode.

The winning mode means that the simple RDO value of the mode calculated based on the simple RDO is smaller than the RDO values of other modes. The first chroma pre-candidate mode circuit 220A stores the first chroma pre-candidate mode and its information such as the simple RDO value into the second memory 220E.

In order to increase the encoding speed, step S501 and step S601 can be executed synchronously, that is, when the main angle mode circuit 210A is executing the main angle mode selection, the first chrominance pre-candidate mode circuit 220A synchronously executes to select the first chrominance pre-candidate mode from the Planar mode, DC mode, vertical mode and horizontal mode.

In step S602, the second mode expansion circuit 220B receives the main angle mode and expands M angle modes according to the main angle mode.

The first mode expansion circuit 210B and the second mode expansion circuit 220B can simultaneously obtain the main angle mode from the main angle mode circuit 210A to synchronously perform the angle mode expansion operation, that is, step S502 and step S602 can be executed synchronously. In one embodiment, the second chromaticity pre-candidate mode circuit 220C can receive M angle modes expanded from the main angle from the first mode expansion circuit 210B. In this way, the second mode expansion circuit 220B and step S602 can be omitted.

In step S603, the second chromaticity pre-candidate mode circuit 220C performs a simple RDO calculation corresponding to the M angle modes on the chromaticity value of each pixel of the image block to select a winning mode as the chromaticity angle mode, and determines whether the chromaticity angle mode can be used as the second chromaticity pre-candidate mode based on whether the chromaticity angle mode is the same as one of the multiple brightness candidate modes.

Specifically, the second chromaticity pre-candidate mode circuit 220C receives the selected brightness candidate mode from the brightness final candidate mode circuit 210C, and determines whether the received brightness candidate mode includes an angle mode. If so, the second chromaticity pre-candidate mode circuit 220C compares the chromaticity angle mode and the angle mode in the brightness candidate mode to see if they are consistent. If they are consistent, the selected chromaticity angle mode is used as the second chromaticity pre-candidate mode; otherwise, the chromaticity angle mode is not used as the second chromaticity pre-candidate mode. That is, when the chromaticity angle mode and one of the multiple brightness candidate modes are the same angle mode, the chromaticity angle mode can be used as the second chromaticity pre-candidate mode.

In other embodiments, the second chromaticity pre-candidate mode circuit 220C further determines whether to perform its operation and step S603 according to whether the multiple brightness candidate modes received from the brightness final candidate mode circuit 210C include an angle mode. When the multiple brightness candidate modes received do not include an angle mode, step S603 does not need to be performed. In this way, the calculation time of the chromaticity candidate mode circuit 220 can be saved.

In step S604, the chromaticity final candidate mode circuit 220D determines a plurality of chromaticity candidate modes according to the first chromaticity pre-candidate mode and the second chromaticity pre-candidate mode. The plurality of chromaticity candidate modes at least include the modes in the first chromaticity pre-candidate mode. The chromaticity candidate mode includes the second chromaticity pre-candidate mode only when the angle mode included in the luminance candidate mode is consistent with the angle mode included in the second chromaticity pre-candidate mode.

In conjunction with FIG. 5 and FIG. 6 , step S501 and step S601, step S502 and step S602 can be executed synchronously. In addition, the candidate modes of the luminance pixel and the chrominance pixel can be quickly selected through the simple RDO without the need for transformation, quantization, inverse quantization, inverse transformation, reconstruction and other operations. After that, the complete RDO values of the candidate modes of the luminance value and chrominance value of the pixels of the image block are respectively calculated based on the complete RDO to determine the luminance target mode of the luminance component and the chrominance target mode of the chrominance component, and accordingly determine whether the chrominance pixel can be encoded using the DM mode to improve the encoding speed and save the encoding bit rate.

In summary, this case performs simple RDO calculation on the brightness value of each pixel of the image block in parallel with simple RDO calculation on the chrominance value of each pixel of the image block, thereby realizing staged parallel processing of the prediction modes of the brightness value and chrominance value of the pixels of the image block based on simple RDO and complete RDO. This not only improves the determination speed of the brightness target mode and the chrominance target mode, but also enables the brightness target mode of the brightness value of the pixels of the image block to be obtained in time during the encoding process of the chrominance value of the pixels of the image block to determine whether the chrominance value encoding process can be encoded through the DM mode, thereby improving the encoding performance and efficiency.

Although the embodiments of the present case are described above, the multiple embodiments are not intended to limit the present case. A person with ordinary knowledge in the technical field may modify the technical features of the present case based on the explicit or implicit content of the present case. All such modifications may fall within the scope of patent protection sought by the present case. In other words, the scope of patent protection of the present case shall be subject to the scope of the patent application defined in this specification.

10: Image encoding device 100: Memory 100A: First storage area 100B: Second storage area 200: In-frame prediction circuit 210: Luminance candidate mode circuit 210A: Main angle mode circuit 210B: First mode expansion circuit 210C: Luminance final candidate mode circuit 210D: First memory 220: Chroma candidate mode circuit 220A: First chroma candidate mode circuit 220B: Second mode expansion circuit 220C: Second chroma pre-candidate mode circuit 220D: Chroma final candidate mode circuit 220E: Second memory 230: Luminance target mode circuit 240: Chroma full RDO calculation circuit 250: Chroma target mode circuit 300: Calculation circuit 400: Encoding circuit S301-S305, S501-S503, S601-S604: Steps

FIG1 is a functional module schematic diagram of the image coding device of the present invention; FIG2 is a functional module schematic diagram of the first embodiment of the intra-frame prediction circuit of FIG1; FIG3 is a flow chart of the method for determining the chroma intra-frame coding mode of the first embodiment of the present invention; FIG4 is a functional module schematic diagram of the second embodiment of the intra-frame prediction circuit of FIG1; FIG5 is a detailed flow chart of step S301 in FIG3 in an embodiment; and FIG6 is a detailed flow chart of step S302 in FIG3 in an embodiment.

S301-S305: Steps

Claims (14)

A method for determining a chroma intra-frame prediction mode, characterized in that the method comprises: performing a simple RDO calculation on the brightness value of each pixel of an image block to obtain a plurality of brightness candidate modes; determining a plurality of chroma candidate modes according to one of the plurality of brightness candidate modes and a chroma simple RDO result obtained by performing a simple RDO calculation on the chroma value of each pixel of the image block; performing a simple RDO calculation corresponding to the plurality of brightness candidate modes on the brightness value of each pixel of the image block; A complete RDO calculation is performed to select a luminance target mode; a complete RDO calculation corresponding to the multiple chrominance candidate modes is performed on the chrominance value of each pixel of the image block to obtain a chrominance complete RDO result; a chrominance target mode is determined according to the luminance target mode and the chrominance complete RDO result; wherein the simple RDO calculation is performed on the luminance value of each pixel of the image block and the simple RDO calculation is performed on the chrominance value of each pixel of the image block in parallel. The determination method as described in claim 1 further includes: selecting a chromaticity first pre-target mode and a chromaticity second pre-target mode based on the chromaticity complete RDO result, wherein the complete RDO value of the chromaticity first pre-target mode is less than the complete RDO value of the chromaticity second pre-target mode; when the chromaticity first pre-target mode is consistent with the luminance target mode, determining the chromaticity first pre-target mode as the chromaticity target mode, and the chromaticity target mode is the DM mode. The determination method as described in claim 2, wherein at least one of the chromaticity first pre-target mode and the chromaticity second pre-target mode includes one of the Planar mode, the DC mode, the vertical mode and the horizontal mode; when the chromaticity first pre-target mode is inconsistent with the luminance target mode, if the chromaticity first pre-target mode is one of the Planar mode, the DC mode, the vertical mode and the horizontal mode, the chromaticity first pre-target mode is determined to be the chromaticity target mode; or, if the chromaticity first pre-target mode is one of a plurality of angle modes, the chromaticity second pre-target mode is determined to be the chromaticity target mode. The determination method as described in claim 1, wherein the simple RDO calculation is performed on the brightness value of each pixel of the image block to obtain the multiple brightness candidate modes, including: performing a simple RDO calculation corresponding to multiple basic angle modes on the brightness value of each pixel of the image block to select a main angle mode, and there is a preset number of angle modes between two adjacent basic angles; taking the main angle mode as the center, sequentially selecting the same number of angle modes in two symmetrical directions to expand M angle modes, and there is no interval angle mode between two adjacent angle modes in the M angle modes; performing a simple RDO calculation corresponding to the M angle modes, DC mode and Planar mode on the brightness value of the image block to select the multiple brightness candidate modes. The determination method as described in claim 4, wherein the determination of multiple chromaticity candidate modes based on one of the multiple luminance candidate modes and the chromaticity simple RDO result obtained by performing simple RDO calculation on the chromaticity value of each pixel of the image block comprises: performing simple RDO calculation corresponding to the Planar mode, DC mode, vertical mode and horizontal mode on the chromaticity value of each pixel of the image block to select a preset number of winning modes as the first chromaticity pre-candidate mode; receiving the main angle mode and expanding the M angle modes according to the main angle mode, or receiving the M angle modes; performing the corresponding RDO calculation on the chromaticity value of each pixel of the image block; Simple RDO calculations of M angle modes are performed to select a winning mode as a chromaticity angle mode, and whether the chromaticity angle mode can be used as a second chromaticity pre-candidate mode is determined based on whether the chromaticity angle mode is the same as one of the multiple luminance candidate modes; the multiple chromaticity candidate modes are determined based on the first chromaticity pre-candidate mode and the second chromaticity pre-candidate mode; wherein the simple RDO calculations corresponding to the multiple basic angle modes are performed on the luminance value of each pixel of the image block, and the simple RDO calculations corresponding to the Planar mode, the DC mode, the vertical mode, and the horizontal mode are performed on the chromaticity value of each pixel of the image block in parallel. The determination method as described in claim 5, wherein when the chromaticity angle mode is the same as one of the multiple brightness candidate modes, the chromaticity angle mode is determined as the second chromaticity pre-candidate mode, so that the multiple chromaticity candidate modes include the first chromaticity pre-candidate mode and the second chromaticity pre-candidate mode; otherwise, when the chromaticity angle mode is different from the multiple brightness candidate modes, the chromaticity angle mode is determined not to be the second chromaticity pre-candidate mode, so that the multiple chromaticity candidate modes only include the first chromaticity pre-candidate mode. The determination method as described in claim 4, wherein the determination of multiple chromaticity candidate modes based on one of the multiple luminance candidate modes and the chromaticity simple RDO result obtained by performing simple RDO calculation on the chromaticity value of each pixel of the image block comprises: performing simple RDO calculation corresponding to the planer mode, DC mode, vertical mode and horizontal mode on the chromaticity value of each pixel of the image block to select a preset number of winning modes as the first chromaticity pre-candidate mode; determining whether the multiple luminance candidate modes include one of the M angle modes; when the multiple luminance candidate modes do not include one of the M angle modes, determining the multiple chromaticity candidate modes according to the first chromaticity pre-candidate mode. An image coding device is characterized in that it includes: a luminance candidate mode circuit, which obtains the luminance value of each pixel of an image block from a memory, performs a simple RDO calculation on the luminance value of each pixel of the image block to obtain multiple luminance candidate modes; a chrominance candidate mode circuit, which obtains the chrominance value of each pixel of the image block from the memory, and determines multiple chrominance candidate modes according to one of the multiple luminance candidate modes and the chrominance simple RDO result obtained by performing a simple RDO calculation on the chrominance value of each pixel of the image block; and a luminance target mode circuit, which performs a corresponding RDO calculation on the luminance value of each pixel of the image block. A circuit for calculating the complete RDO of the multiple luminance candidate modes to select a luminance target mode; a circuit for calculating the complete RDO of chrominance to perform the complete RDO calculation corresponding to the multiple chrominance candidate modes on the chrominance value of each pixel of the image block to obtain a chrominance complete RDO result; a chrominance target mode circuit to determine a chrominance target mode according to the luminance target mode and the chrominance complete RDO result; wherein the luminance candidate mode circuit performs the simple RDO calculation on the luminance value of each pixel of the image block in parallel with the chrominance candidate mode circuit performing the simple RDO calculation on the chrominance value of each pixel of the image block. An image coding device as described in claim 8, wherein the chroma full RDO result includes a chroma first pre-target mode and a chroma second pre-target mode, the full RDO value of the chroma first pre-target mode is less than the full RDO value of the chroma second pre-target mode; when the chroma first pre-target mode is consistent with the luminance target mode, the chroma target mode circuit determines that the chroma first pre-target mode is the chroma target mode, and the chroma target mode is the DM mode. An image coding device as described in claim 9, wherein at least one of the chroma first pre-target mode and the chroma second pre-target mode includes one of a Planar mode, a DC mode, a vertical mode, and a horizontal mode; when the chroma first pre-target mode is inconsistent with the luminance target mode, if the chroma first pre-target mode is one of the Planar mode, the DC mode, the vertical mode, and the horizontal mode, the chroma target mode circuit determines that the chroma first pre-target mode is the chroma target mode; or, if the chroma first pre-target mode is one of a plurality of angle modes, the chroma target mode circuit determines that the chroma second pre-target mode is the chroma target mode. The image encoding device as described in claim 8, wherein the brightness candidate mode circuit comprises: a main angle mode circuit, which performs a simple RDO calculation corresponding to a plurality of basic angle modes on the brightness value of each pixel of the image block to select a main angle mode, wherein two adjacent basic angles are separated by a preset number of angle modes; a first mode expansion circuit, which sequentially selects the same number of angle modes in two symmetrical directions with the main angle mode as the center to expand M angle modes, wherein there is no interval angle mode between two adjacent angle modes in the M angle modes; a brightness final candidate mode circuit, which performs a simple RDO calculation corresponding to the M angle modes, DC mode and Planar mode on the brightness value of the image block to select the plurality of brightness candidate modes. An image encoding device as described in claim 11, wherein the chroma candidate mode circuit comprises: a first chroma pre-candidate mode circuit, which performs a simple RDO calculation corresponding to the Planar mode, the DC mode, the vertical mode and the horizontal mode on the chroma value of each pixel of the image block to select a preset number of winning modes as the first chroma pre-candidate mode; a second chroma pre-candidate mode circuit, which performs a simple RDO calculation corresponding to the M angle modes on the chroma value of each pixel of the image block to select a winning mode as the chroma angle mode, and selects a winning mode according to the comparison between the chroma angle mode and the multiple luminance candidate modes. whether one of the chromaticity angle mode is the same to determine whether the chromaticity angle mode can be used as the second chromaticity pre-candidate mode; a chromaticity final candidate mode circuit, based on the first chromaticity pre-candidate mode and the second chromaticity pre-candidate mode, determines the multiple chromaticity candidate modes; wherein the main angle mode circuit performs simple RDO calculations corresponding to multiple basic angle modes on the brightness value of each pixel of the image block and the first chromaticity pre-candidate mode circuit performs simple RDO calculations corresponding to the Planar mode, the DC mode, the vertical mode and the horizontal mode on the chromaticity value of each pixel of the image block in parallel. The image encoding device as described in claim 12, wherein when the chromaticity angle mode is the same as one of the multiple brightness candidate modes, the chromaticity final candidate mode circuit determines the chromaticity angle mode as the second chromaticity pre-candidate mode, so that the multiple chromaticity candidate modes include the first chromaticity pre-candidate mode and the second chromaticity pre-candidate mode; otherwise, when the chromaticity angle mode is different from the multiple brightness candidate modes, the chromaticity final candidate mode circuit determines the chromaticity angle mode not as the second chromaticity pre-candidate mode, so that the multiple chromaticity candidate modes only include the first chromaticity pre-candidate mode. The image encoding device as described in claim 11, wherein the chroma candidate mode circuit includes: a first chroma pre-candidate mode circuit, which performs a simple RDO calculation corresponding to the planer mode, DC mode, vertical mode and horizontal mode on the chroma value of each pixel of the image block to select a preset number of winning modes as the first chroma pre-candidate mode; a second chroma pre-candidate mode circuit, which determines whether the multiple luminance candidate modes include one of the M angle modes; and a chroma final candidate mode circuit, which determines the multiple chroma candidate modes according to the first chroma pre-candidate mode when the multiple luminance candidate modes do not include one of the M angle modes.

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