Chroma intra prediction method and apparatus, and computer storage medium

Abstract

A chroma intra prediction method, a decoder and a computer storage medium are provided. The chroma intra prediction method comprises: obtaining a DM corresponding to a current chroma block from code stream data corresponding to the current chroma block (101); if the DM is a direct current (DC) mode or a planar (Planar) mode, obtaining a chroma prediction mode set according to an optimization candidate mode (102); and using the chroma prediction mode set to perform chroma reconstruction on the current chroma block (102).

Description

[0001] This application is a divisional application of PCT International Patent Application No. PCT / CN2019 / 070148, filed on January 2, 2019, entitled "Chroma Intra Prediction Method and Device, and Computer Storage Medium", which entered the Chinese national phase as Chinese Patent Application No. 201980062647.8. TECHNICAL FIELD

[0002] Embodiments of the present application relate to the intra prediction technology in the field of video coding, in particular to a chroma intra prediction method and device, and computer storage medium. BACKGROUND

[0003] In the next generation video coding standard H.266 or Versatile Video Coding (VVC), the independent division of blocks for coding is supported for both luma and chroma, and one chroma block can correspond to multiple luma blocks. However, the existing Direct Mode (DM) can only reflect the local texture features of the center region of the current chroma block. When one chroma block corresponds to multiple luma blocks at the same position, it is unreasonable to directly use a single DM for chroma prediction. For example, when the DM is Direct Current (DC) mode or Planar mode, the current chroma block can be considered as flat and smooth. However, if the corresponding multiple luma blocks are not flat, the chroma intra prediction by DM only will greatly reduce the accuracy of intra prediction, thereby reducing the coding efficiency. Although there are horizontal and vertical directions as default alternatives in the chroma prediction mode, in this case, the chroma blocks that conform to the overall horizontal and vertical prediction directions are also very few, thereby wasting the alternative positions and being not conducive to improving the coding efficiency. SUMMARY

[0004] Embodiments of the present application provide a chroma intra prediction method, a decoder and a computer storage medium, which can effectively improve the accuracy of intra prediction and improve the coding efficiency.

[0005] The technical solutions of the embodiments of the present application are implemented as follows:

[0006] The embodiments of the present application provide a chroma intra prediction method, which comprises the following steps:

[0007] Obtaining a direct mode (DM) corresponding to the current chroma block from code stream data corresponding to the current chroma block.

[0008] If the DM is a direct current (DC) mode or a planar mode, obtaining a chroma prediction mode set according to an optimized alternative mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block.

[0009] The embodiment of the present application provides a decoder, the decoder comprises an acquisition part,

[0010] The acquisition part is used for acquiring DM corresponding to the current chroma block from code stream data corresponding to the current chroma block, and acquiring a chroma prediction mode set according to an optimized candidate mode if the DM is a direct current DC mode or a planar Planar mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block.

[0011] The embodiment of the present application provides a decoder, the decoder comprises a processor, a memory in which instructions executable by the processor are stored, a communication interface, and a bus used for connecting the processor, the memory and the communication interface, and when the instructions are executed, the processor performs the chroma intra prediction method.

[0012] The embodiment of the present application provides a computer readable storage medium, a program is stored in the computer readable storage medium, and the program is applied to a decoder and is executed by a processor to implement the chroma intra prediction method.

[0013] The embodiment of the present application provides a chroma intra prediction method, a decoder and a computer storage medium, the decoder acquires DM corresponding to a current chroma block from code stream data corresponding to the current chroma block; if the DM is a direct current DC mode or a planar Planar mode, a chroma prediction mode set is acquired according to an optimized candidate mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block. It can be seen that in the embodiment of the present application, after the decoder acquires the DM from the code stream data of the current chroma block, if the DM is the DC mode or the Planar mode, the chroma prediction mode set can be constructed by using the optimized candidate mode, and then the current chroma block is reconstructed according to the chroma prediction mode set, so that the problem of low chroma intra prediction accuracy when the DM is the DC mode or the Planar mode can be solved, and the coding efficiency can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is an intra prediction schematic diagram;

[0015] Figure 2 It is a 67 intra prediction mode schematic diagram;

[0016] Figure 3 It is an intra prediction method schematic diagram;

[0017] Figure 4 It is a vertical prediction schematic diagram;

[0018] Figure 5 It is a horizontal prediction schematic diagram;

[0019] Figure 6 An illustration of a set of chroma intra prediction modes;

[0020] Figure 7 An illustration of a chroma block and a luma block Figure 1 ;

[0021] Figure 8 An illustration of a chroma block and a luma block Figure 2 ;

[0022] Figure 9 An illustration of a video encoding process;

[0023] Figure 10 An illustration of a video decoding process;

[0024] Figure 11 An illustration of an implementation process of a chroma intra prediction method proposed by embodiments of the present application;

[0025] Figure 12 An illustration of establishing an optimal candidate mode Figure 1 ;

[0026] Figure 13 An illustration of establishing an optimal candidate mode Figure 2 ;

[0027] Figure 14 An illustration of establishing an optimal candidate mode Figure 3 ;

[0028] Figure 15 An illustration of establishing an optimal candidate mode Figure 4 ;

[0029] Figure 16 An illustration of establishing an optimal candidate mode Figure 5 ;

[0030] Figure 17 An illustration of a composition structure of a decoder proposed by embodiments of the present application Figure 1 ;

[0031] Figure 18 An illustration of a composition structure of a decoder proposed by embodiments of the present application Figure 2 . DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. It can be understood that the specific embodiments described herein are only used to explain the related application, but not to limit the application. In addition, it should be noted that, for the convenience of description, only the parts related to the application are shown in the drawings.

[0033] In video coding, a prediction value of a current processing block is constructed by using a reconstructed image in space or time, and only the difference between the real value and the prediction value is transmitted to reduce the amount of data transmission. In the intra prediction, the spatial correlation within a picture or a region of the picture is utilized. The intra prediction of the current processing block can be performed by relying on the pixels in the neighboring processing blocks that have been processed, for example, by using the upper row and the left column of the current processing block to construct the prediction value of the current processing block, Figure 1 As shown in the schematic diagram of the intra prediction, Figure 1 each pixel point of the current processing block is predicted by using the pixels of the neighboring processing blocks.

[0034] In the intra prediction, the selection of the prediction direction is also important. Specifically, when the pixels of the neighboring coding blocks are used to construct the prediction value of the current processing block, a plurality of prediction directions can be adopted. For example, Figure 2 As shown in the schematic diagram of the 67 intra prediction modes, Figure 2 of the 67 intra prediction modes, specifically, 65 prediction directions with index numbers 2-66, a Planar mode with index number 0 and a DC mode with index number 1 are included.

[0035] In the embodiments of the present application, the above-mentioned Figure 2 , Figure 3 As shown in the schematic diagram of the intra prediction method, Figure 3 when the prediction value of each pixel point is constructed by using the index number 66 of the prediction direction, the pixel points with numbers 0-16 are the upper row data of the current processing block. Each pixel of the current processing block is filled according to the pixel on the upper right diagonal line.

[0036] In the embodiments of the present application, the Planar mode is mainly used in the region where the image texture is relatively smooth and has a relatively gradual change process, and the prediction method thereof is to use the pixel value of the reconstructed neighboring processing block corresponding to the current processing block as a reference pixel value, and then perform linear interpolation and average calculation.

[0037] Compared with the Planar mode, the DC mode is mainly used in the region where the image is flat, the texture is smooth, and there is no much gradual change, and the specific prediction method is to predict according to the last row of the reference pixels above the current processing block and the rightmost column of the reference pixels on the left side of the current processing block. It can be seen that in the intra prediction, the Planar mode and the DC mode are both relatively flat prediction block construction methods, and the DC mode is to fill the entire chroma block by using the average value of the last row and the leftmost column of the reference pixels, and the Planar mode is to fill the chroma block by using the gradual change method.

[0038] In the above-mentioned Figure 2There are two special direction modes: the VER mode (vertical prediction) with a prediction direction index number of 50 and the HOR mode (horizontal prediction) with a prediction direction index number of 18.

[0039] Figure 4 This is a schematic diagram of vertical prediction. Figure 5 This is a schematic diagram of horizontal prediction, such as... Figure 4 and 5 As shown, if the prediction direction is vertical, then vertical prediction can be performed based on the pixel values ​​of the vertically corresponding pixels in the previous row; if the prediction direction is horizontal, then horizontal prediction can be performed based on the pixel values ​​of the horizontally corresponding pixels in the left column.

[0040] When performing intra-frame prediction of brightness, it can be done as described above. Figure 2 The system performs predictions on 0-66 modes, then selects the prediction direction with the smallest difference from the current processing block (i.e., the best match) to construct the predicted value. The encoder writes the difference and prediction direction into the bitstream. The decoder parses the bitstream to obtain the prediction direction index number, then calculates the luminance prediction value. This value is added to the difference signal parsed from the bitstream to obtain the reconstructed luminance value.

[0041] However, chroma intra-frame prediction differs from luma intra-frame prediction. To reduce encoding and decoding complexity, only a portion of the prediction direction is extracted for processing during chroma intra-frame prediction. For example, in VVC, the chroma intra-frame candidate mode set can include one or more chroma intra-frame prediction modes, such as Linear Model Prediction (LM), with LM_T mode on the left and LM_L mode on the right, as well as DC mode, Planar mode, vertical VER mode, and horizontal HOR mode, etc.

[0042] Figure 6 This is a schematic diagram of the chroma intra-frame candidate mode set, such as... Figure 6 As shown, the chroma intra-frame candidate mode set can include different modes. Existing technologies can perform chroma intra-frame prediction by selecting one of the different modes. For example, DM can represent the prediction mode of the corresponding luma center block, while Cross-component Linear Model Prediction (CCLM) represents the construction of the prediction signal using the scheme of (a*luminance value + b), where a and b are both natural numbers. When DM is any of the DC mode, Planar mode, VER mode, or HOR mode, this mode can be replaced with the angle mode with the prediction direction index number 66.

[0043] Further, if the coding framework supports separate partitioning of luma and chroma, i.e. the two partitioning can be inconsistent, thus there is a phenomenon that one chroma block can correspond to multiple luma blocks, Figure 7 An illustration of chroma block and luma block Figure 1 , Figure 8 An illustration of chroma block and luma block Figure 2 As shown in Figure 7 and 8 , the chroma block in Figure 7 corresponds to the luma block in Figure 8 includes five parts separately coded (represented by different gray levels). Since the CR under DM can only reflect the local texture features of the chroma block, when the chroma block corresponds to multiple co-located luma blocks, it is unreasonable to directly use a single DM prediction, for example, shown in Figure 7 When the prediction mode of the luma center block is selected as the DC mode or the Planar mode, it needs to be considered that the current block is flat, however Figure 7 the current luma block in may not be flat. Although there are horizontal and vertical directions as default options in the chroma prediction mode, in this case, the chroma block that overall conforms to the horizontal and vertical prediction directions is also rare, thereby wasting the option position and being not conducive to improving the coding efficiency.

[0044] In the embodiments of the present application, the above-mentioned chroma intra prediction method can be applied to the intra prediction part in the video coding hybrid framework, in addition to being applicable to VVC, it can also be applied to any other video coding hybrid framework, and the present application is exemplarily described but not limited by VVC. Specifically, the above-mentioned chroma intra prediction method can simultaneously act on the encoding end and the decoding end. For example, Figure 9 An illustration of video coding process, as shown in Figure 9 , video coding can include intra estimation, intra prediction, motion compensation and other specific steps, wherein the chroma intra prediction method proposed by the present application can be applied to the intra prediction part; Figure 10 An illustration of video decoding process, as shown in Figure 10 , video decoding can include filtering, intra prediction, motion compensation and other specific steps, wherein the chroma intra prediction method proposed by the present application can be applied to the intra prediction part.

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application.

[0046] In an embodiment, the present application provides a chroma intra prediction method, Figure 11 An implementation process schematic diagram of a chroma intra prediction method proposed by the present application is shown in Figure 11As shown, in the embodiments of the present application, the method for the decoder to perform chroma intra prediction can include the following steps:

[0047] Step 101, obtaining the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block.

[0048] In the embodiments of the present application, the decoder can obtain the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block.

[0049] It should be noted that, in the embodiments of the present application, the decoder can first receive the video bit stream, and then obtain the code stream data corresponding to the current coding block from the received video bit stream.

[0050] In the embodiments of the present application, after obtaining the code stream data corresponding to the current coding block, the decoder can further obtain the residual data corresponding to the current chroma block from the code stream data.

[0051] It should be noted that, in the embodiments of the present application, when the encoder performs the selection of the luma intra prediction mode, it can perform prediction according to multiple modes respectively, for example, it can perform prediction according to the 0-66 modes in the above-mentioned Figure 2 However, when the encoder performs the selection of the chroma intra prediction mode, it does not perform prediction on all the 0-66 modes, but only extracts part of the prediction directions to perform prediction and selection. Therefore, after obtaining the code stream data, the decoder can further construct a chroma intra candidate set corresponding to the current chroma block from the code stream data, i.e., the chroma prediction mode set corresponding to the current chroma block.

[0052] In the embodiments of the present application, the chroma prediction mode set can include at least one chroma intra prediction mode, for example, the chroma prediction mode set can include the DM, LM, LM_T, LM_L, DC, Planar, and other directional prediction modes.

[0053] In the embodiments of the present application, the current chroma block can be a square chroma block or a rectangular chroma block, and the embodiments of the present application do not make specific limitations.

[0054] Step 102, if the DM is the DC mode or the Planar mode, obtaining the chroma prediction mode set according to the optimization candidate mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block.

[0055] In an embodiment of the present application, after the decoder obtains the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block, if the DM is in the DC mode or the Planar mode, the decoder can obtain the chroma prediction mode set according to the optimization alternative mode. The chroma prediction mode set can be used for intra-chroma prediction of the current chroma block.

[0056] It should be noted that, in an embodiment of the present application, the chroma prediction mode set is used for chroma prediction. Specifically, the decoder can perform chroma prediction on the current chroma block through the chroma prediction mode set, so as to reconstruct the chroma corresponding to the current chroma block.

[0057] In an embodiment of the present application, after the decoder obtains the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block, the decoder can determine whether the DM is in the DC mode or the Planar mode.

[0058] It should be noted that, in an embodiment of the present application, if the decoder determines that the DM is in the DC mode or the Planar mode, the encoder can add the mode according to the optimization alternative mode, so as to obtain the chroma prediction mode set.

[0059] In an embodiment of the present application, after the decoder determines the DM corresponding to the current chroma block from the code stream data, the decoder can first analyze the DM, so as to determine whether the DM is in the DC mode or the Planar mode.

[0060] It should be noted that, in an embodiment of the present application, since the Planar mode and the DC mode are both relatively flat construction prediction block modes, when the DM is in the DC mode or the Planar mode, it can be considered that the luminance block is flat. However, the actual situation is not like this. For example, in VVC, luminance and chroma are independently divided into blocks for encoding, and one chroma block can correspond to multiple luminance blocks. Therefore, the DM can only reflect the local texture features of the center region, that is, there is a possibility that the luminance block is not flat. That is, in the case where the DM is in the Planar mode or the DC mode, if a single DM is directly used for prediction, the accuracy will be reduced. Although the horizontal and vertical directions are also default alternatives in the chroma prediction mode, in this case, the chroma block that conforms to the horizontal and vertical prediction directions as a whole is also rare, thereby wasting the alternative position and being not conducive to improving the coding efficiency.

[0061] It should be noted that in the implementation of the present application, Table 1 is the initial state of the intra prediction direction design table, as shown in Table 1, when the DM is in the DC mode or the Planar mode, the initial state of the prediction direction is the DC mode or the Planar mode; Table 2 is the subsequent state of the intra prediction direction design table, as shown in Table 2, when the corresponding luminance center block is in the Planar mode or the DC mode, if the entire luminance block adopts one intra prediction direction, it indicates that the current block is likely to be flat, in order to ensure the efficiency of the flat block, another flat mode will be filled. Among them, since the DM and the CCLM are important coding tools, they need to be prioritized.

[0062] Table 1

[0063]

[0064] Table 2

[0065]

[0066] Since the current DC mode or Planar mode flat information can only be obtained through the luminance block. In fact, at this time, the corresponding chrominance block may cover multiple luminance block regions, which contain texture information with direction, and the direction of these texture information has different probability distribution.

[0067] On the other hand, in the prior art, when the DM is in any one of the DC mode, the Planar mode, the VER mode or the HOR mode, the mode can be replaced with the angle mode of the prediction direction index number 66.

[0068] However, in actual application, the VER mode and the HOR mode with the prediction direction index numbers 18 and 50 have a large proportion, but the probability of the texture penetrating through the entire chrominance block is very small. In contrast, the diagonal angle modes with the prediction direction index numbers 34, 66 and 2 and the direction modes near them can accurately predict the chrominance block with a larger probability.

[0069] Therefore, since the DM can only reflect the local texture characteristics of the chrominance block, when the chrominance block corresponds to multiple co-located luminance blocks, it is unreasonable to directly use a single DM prediction and supplement with the horizontal, vertical and diagonal mode corresponding to the prediction direction index number 66 to construct the chrominance prediction mode set. Therefore, the decoder needs to optimize the construction of the chrominance prediction mode set according to the optimized candidate mode. At the same time, since in actual application, the diagonal angle modes with the prediction direction index numbers 34, 66 and 2 and the direction modes near them can accurately predict the chrominance block with a larger probability, these prediction direction modes can be used to replace the original horizontal and vertical prediction direction modes, and further supplement the DM.

[0070] In embodiments of the present application, if the DM is DC mode or Planar mode, the decoder can further obtain the set of chroma prediction modes for chroma prediction according to the optimized candidate modes.

[0071] It should be noted that in embodiments of the present application, the decoder can pre-set at least one mode as a candidate mode, i.e., the decoder is pre-set with the optimized candidate modes.

[0072] In embodiments of the present application, the diagonal angle modes with prediction direction index numbers of 34, 66 and 2 are more frequently used for prediction in the small blocks of the corresponding luma region of the current chroma block, and thus the modes with prediction direction index numbers of 34, 66 and 2 can be stored in the optimized candidate modes. For example, if the current chroma block is a square chroma block, i.e., the diagonal angle mode of the current chroma block is the mode with prediction direction index number of 34, 66 or 2, the decoder can add the mode with prediction direction index number of 34 to the set of chroma prediction modes first, and then add one of the other diagonal angle modes, i.e., the mode with prediction direction index number of 66 or 2, to the set of chroma prediction modes when obtaining the set of chroma prediction modes according to the optimized candidate modes.

[0073] In embodiments of the present application, since the modes with prediction direction index numbers of 66 and 2 belong to two directions of the same slope, the decoder can adjust the mode with prediction direction index number of 2 by one angle clockwise to be an optimized candidate mode, e.g., the mode with prediction direction index number of 6. Meanwhile, the decoder can also adjust the mode with prediction direction index number of 66 by one angle counterclockwise to be an optimized candidate mode, e.g., the mode with prediction direction index number of 61. Further, the decoder can also adjust the modes with prediction direction index numbers of 66 and 2 by one angle to be optimized candidate modes.

[0074] In embodiments of the present application, in addition to the diagonal angle modes being more frequently used for prediction, other derived angles near the diagonal angle modes are also more frequently used for prediction, and thus the modes with prediction direction index numbers of 32, 64 and 4 can be included in the optimized candidate modes. For example, the decoder can add the mode with prediction direction index number of 32 to the set of chroma prediction modes first, and then add one of the modes with prediction direction index numbers of 64 and 4 to the set of chroma prediction modes when obtaining the set of chroma prediction modes according to the optimized candidate modes.

[0075] In the embodiments of the present application, the decoder can determine at least one diagonal angle mode as the optimization candidate mode when establishing the optimization candidate mode, or can determine the derived angle mode of the at least one diagonal angle mode as the optimization candidate mode, or can determine the at least one diagonal angle mode and the derived angle mode of the at least one diagonal angle mode as the optimization candidate mode. The decoder can first determine the derived angle, specifically, the decoder can first determine the index number M corresponding to the DM, where M is an integer greater than 0; then the decoder can obtain the transform parameter N, and finally determine the index number corresponding to the derived angle mode according to M and N, so as to obtain the derived angle mode; where N is an integer greater than 0.

[0076] In the embodiments of the present application, when the decoder determines the index number corresponding to the derived angle mode according to M and N, the M and the N can be subjected to addition operation or subtraction operation, and finally the index number corresponding to the derived angle mode is obtained. Wherein, N can take values of 3, 5 or 7, but is not limited to these values. For example, the index number M corresponding to the DM is 1 (i.e. the DM is the DC mode), then the decoder can obtain the angle direction of 1+5 or 1-5 as the index number corresponding to the derived angle mode. Since the prediction mode generally cannot be represented by a negative number, a specific mapping method can be used to map the calculated value to the effective representation range. For example, the specific calculation formula can be (M+62-N) % 64+2, and the result obtained is 60.

[0077] In the embodiments of the present application, for the wide angle mode of the non-square block, one of the modes with the prediction direction index numbers of 66 and 2 can be selected as a candidate according to the effective prediction direction range thereof, and the angle corresponding to the other index number is adjusted as a candidate.

[0078] In the embodiments of the present application, after the decoder obtains the chroma prediction mode set according to the optimization candidate mode, i.e. after step 102, the method for the decoder to perform chroma intra prediction can further include the following steps:

[0079] Step 103, performing decoding processing according to the chroma prediction mode set to perform chroma reconstruction on the current chroma block.

[0080] In the embodiments of the present application, after the decoder obtains the chroma prediction mode set according to the optimization candidate mode, the decoder can perform decoding processing according to the chroma prediction mode set to perform chroma reconstruction on the current chroma block.

[0081] In the embodiments of the present application, after obtaining the chroma prediction mode set, the decoder can further decode the current chroma block by using the chroma prediction mode set, so as to reconstruct the current chroma block.

[0082] It should be noted that, in the embodiments of the present application, since the decoder obtains the code stream data corresponding to the current coding block from the received video bit stream, and obtains the DM from the code stream data, the decoder can also obtain the residual data corresponding to the current chroma block from the code stream data.

[0083] In the embodiments of the present application, after obtaining the chroma prediction mode set according to the optimization candidate mode, and obtaining the residual data corresponding to the current chroma block from the code stream data, the decoder can perform chroma intra prediction decoding on the residual data based on the chroma prediction mode set, so as to reconstruct the current chroma block.

[0084] The chroma intra prediction method provided in the embodiments of the present application includes: obtaining, by a decoder, DM corresponding to a current chroma block from code stream data corresponding to the current chroma block; and obtaining, by the decoder, a chroma prediction mode set according to an optimization candidate mode, if the DM is a direct current (DC) mode or a planar (Planar) mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block. It can be seen that, in the embodiments of the present application, after obtaining the DM from the code stream data of the current chroma block, if the DM is the DC mode or the Planar mode, the decoder can construct the chroma prediction mode set by using the optimization candidate mode, and then reconstruct the current chroma block according to the chroma prediction mode set, so as to solve the problem of low chroma intra prediction accuracy when the DM is the DC mode or the Planar mode, and further improve the coding efficiency.

[0085] Based on the above embodiments, in another embodiment of the present application, after obtaining the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block, if the DM in the DM is the DC mode or the Planar mode, the decoder can consider that the chroma prediction mode set needs to be obtained according to the optimization candidate mode, so as to improve the decoding accuracy.

[0086] It should be noted that, in the implementation of the present application, since the Planar mode and the DC mode are both relatively flat construction prediction block modes, when the luminance center block is selected as the DC mode or the Planar mode, it can be considered that the luminance block is flat during DM. However, the actual situation is not like this. In VVC, luminance and chrominance are independently divided into blocks for encoding, and one chrominance block can correspond to multiple luminance blocks. Therefore, DM can only reflect the local texture characteristics of the center area, that is, there is a possibility that the luminance block is not flat. That is, in the case of DM being the Planar mode or the DC mode, it is unreasonable to directly use a single DM for prediction, which can reduce accuracy. Although there are horizontal and vertical directions as default options in the chrominance prediction mode, in this case, the overall chrominance block conforming to the horizontal and vertical prediction directions is also very few, thereby wasting the option position and being not conducive to improving the coding efficiency. Therefore, it is necessary to obtain a chrominance prediction mode set according to the optimized option mode. Specifically, before obtaining the chrominance prediction mode set according to the optimized option mode, the decoder also needs to obtain the linear mode LM corresponding to the current chrominance block from the code stream data.

[0087] In the implementation of the present application, the method for the decoder to obtain the chrominance prediction mode set according to the optimized option mode can specifically include the following steps:

[0088] Step 201, filling DM and LM into the chrominance prediction mode set.

[0089] Step 202, filling the chrominance prediction mode set according to the optimized option mode.

[0090] In the embodiment of the present application, the decoder can first add DM and LM to the chrominance prediction mode set, so that two modes in the above chrominance prediction mode set can be determined. Then, the above decoder can continue to fill the above chrominance prediction mode set according to the optimized option mode, and finally obtain the chrominance prediction mode set.

[0091] It should be noted that, in the embodiment of the present application, when the decoder adds DM and LM to the chrominance prediction mode set, specifically, the prediction direction index number of the mode corresponding to DM and the prediction direction index number of the mode corresponding to LM are added to the prediction mode set. For example, if DM is the DC mode and the prediction direction index number of the mode corresponding to LM is 15, the decoder can first add the prediction direction index numbers 1 and 15 to the chrominance prediction mode set, and then fill the chrominance prediction mode set according to the optimized option mode. Specifically, since DM is the DC mode, the decoder will supplement the prediction direction index number 0 of the Planar mode to the chrominance prediction mode set during the process of filling the chrominance prediction mode set according to the optimized option mode.

[0092] It should be noted that in the embodiments of the present application, when the decoder fills the chroma prediction mode set according to the optimization candidate mode, the following steps can be specifically included:

[0093] Step 202a, when the DM is the DC mode, the Planar mode and the optimization candidate mode are filled into the chroma prediction mode set.

[0094] In the embodiments of the present application, if the DM corresponding to the current chroma block is the DC mode, the decoder does not need to modify and replace the Planar mode, and therefore the Planar mode and the optimization candidate mode can be filled into the chroma prediction mode set, and the order can not be distinguished when the number of bits allocated is the same.

[0095] It should be noted that in the embodiments of the present application, when the decoder adds the Planar mode and the optimization candidate mode to the chroma prediction mode set, the prediction direction index number corresponding to the Planar mode and the prediction direction index number corresponding to the other optimization candidate modes are added to the prediction mode set. For example, if the prediction direction index numbers corresponding to the other optimization candidate modes are 32 and 61, the decoder can add the prediction direction index numbers 0, 132 and 61 to the chroma prediction mode set, respectively.

[0096] Step 202b, when the DM is the Planar mode, the DC mode and the optimization candidate mode are filled into the chroma prediction mode set.

[0097] In the embodiments of the present application, if the DM corresponding to the current chroma block is the Planar mode, the decoder does not need to modify and replace the DC mode, and therefore the DC mode and the optimization candidate mode can be filled into the chroma prediction mode set, and the order can not be distinguished when the number of bits allocated is the same.

[0098] It should be noted that in the embodiments of the present application, when the decoder adds the DC mode and the optimization candidate mode to the chroma prediction mode set, the prediction direction index number corresponding to the DC mode and the prediction direction index number corresponding to the other optimization candidate modes are added to the prediction mode set. For example, if the prediction direction index numbers corresponding to the other optimization candidate modes are 2 and 60, the decoder can add the prediction direction index numbers 1, 2 and 60 to the chroma prediction mode set, respectively.

[0099] In the embodiments of the present application, further, the method for the decoder to add the optimization candidate mode to the chroma prediction mode set can include the following steps:

[0100] Step 301, determining the priority of at least one mode in the optimization candidate mode.

[0101] In the embodiments of the present application, the decoder can first determine the priority of at least one mode in the optimization candidate mode.

[0102] It should be noted that in the embodiments of the present application, the optimization candidate mode can be at least one mode, and specifically, the prediction direction index numbers of the at least one mode are all different.

[0103] It should be noted that in the embodiments of the present application, the decoder can determine the priority according to the size of the actual use probability of the at least one mode.

[0104] Step 302, add the optimization candidate mode to the chroma prediction mode set in the order from high to low priority.

[0105] In the embodiments of the present application, after the decoder determines the priority of at least one mode in the optimization candidate mode, the decoder can further add the optimization candidate mode to the chroma prediction mode set in the order from high to low priority.

[0106] In the embodiments of the present application, in the process of adding the optimization candidate mode to the chroma prediction mode set, the decoder can first add the optimization candidate mode with the highest priority, and then select the next optimization candidate mode in the order from high to low priority to construct the chroma prediction mode set.

[0107] It should be noted that in the embodiments of the present application, when the decoder adds the optimization candidate mode to the chroma prediction mode set, the decoder specifically adds the prediction direction index number corresponding to the optimization candidate mode to the prediction mode set.

[0108] That is, if the decoder can construct the chroma prediction mode set according to the preset optimization candidate mode, the accuracy of prediction can be improved.

[0109] The chroma intra prediction method proposed in the embodiments of the present application, the decoder obtains the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block; if the DM is a direct current DC mode or a planar Planar mode, the chroma prediction mode set is obtained according to the optimization candidate mode; wherein the chroma prediction mode set is used for chroma reconstruction of the current chroma block. As can be seen, in the embodiments of the present application, after the decoder obtains the DM from the code stream data of the current chroma block, if the DM is a DC mode or a Planar mode, the decoder can construct the chroma prediction mode set by using the optimization candidate mode, and then reconstruct the current chroma block according to the chroma prediction mode set, so as to solve the problem of low accuracy of chroma intra prediction when the DM is a DC mode or a Planar mode, and further improve the coding efficiency.

[0110] In embodiments of the present application, the current chroma block includes a square chroma block and a non-square chroma block. On this basis, the decoder can determine at least one diagonal angle mode as the optimization candidate mode when establishing the optimization candidate mode, or determine a derived angle mode of the at least one diagonal angle mode as the optimization candidate mode, or determine the at least one diagonal angle mode and the derived angle mode of the at least one diagonal angle mode as the optimization candidate mode.

[0111] In embodiments of the present application, the decoder can determine at least one diagonal angle mode as the optimization candidate mode. Specifically, if the current chroma block is a square chroma block, i.e., the diagonal angle mode of the current chroma block is a mode with a prediction direction index number of 34, 66 and 2, the diagonal angle mode with the prediction direction index number of 34, 66 and 2 is more used for prediction. Figure 12 For establishing the optimization candidate mode Figure 1 As shown in Figure 12 , the decoder can first determine a diagonal angle prediction mode with a prediction direction index number of 34 as the optimization candidate mode, and then determine any one of the modes with a prediction direction index number of 66 and 2 as the optimization candidate mode.

[0112] In embodiments of the present application, the decoder can also determine a derived angle mode of at least one diagonal angle mode as the optimization candidate mode. Specifically, if the current chroma block is a square chroma block, i.e., the diagonal angle mode of the current chroma block is a mode with a prediction direction index number of 34, 66 and 2, in addition to the diagonal angle mode being more used for prediction, other derived angles near the diagonal angle mode are also more used for prediction. Figure 13 For establishing the optimization candidate mode Figure 2 As shown in Figure 13 , the decoder can first determine a derived angle prediction mode with a prediction direction index number of 32 as the optimization candidate mode, and then determine any one of the modes with a prediction direction index number of 66 and 2 as the optimization candidate mode.

[0113] In embodiments of the present application, the decoder can first determine at least one derived angle mode. Specifically, the decoder can first determine an index number M corresponding to the DM, where M is an integer greater than 0; then the decoder can obtain a transformation parameter N, and finally determine an index number corresponding to the derived angle mode according to M and N, so as to obtain the derived angle mode; where N is an integer greater than 0.

[0114] In the embodiments of the present application, when the decoder determines the index number corresponding to the derived angular angle mode according to M and N, the decoder can perform addition operation on the M and the N, or perform subtraction operation on the M and the N, and finally obtains the index number corresponding to the derived angular angle mode. Wherein, N can take values of 3, 5 or 7. For example, based on the above Figure 2 When the index number M corresponding to the DM is 0 (i.e. the DM is the Planar mode), the decoder can obtain the index number corresponding to the derived angular angle mode by 0+5 or 0-5. Since the prediction mode generally cannot be represented by a negative number, the calculated value can be mapped to the valid representation range by a specific mapping method. For example, the specific calculation formula can be (M+62-N) % 64+2, and the result is 60. That is, the derived angular angle mode can be the prediction direction angle 5 mode and the prediction direction angle 60 mode at this time.

[0115] In the embodiments of the present application, since the modes with prediction direction index numbers of 66 and 2 belong to two directions of one slope, the decoder can adjust the mode with the prediction direction index number of 2 clockwise by one angle to be an optimization candidate mode, for example, Figure 14 Schematic diagram for establishing optimization candidate mode Figure 3 As shown in Figure 14 , the decoder adjusts the mode with the prediction direction index number of 2 to the mode with the prediction direction index number of 6. Meanwhile, the decoder can also adjust the mode with the prediction direction index number of 66 counterclockwise by one angle to be an optimization candidate mode, for example, Figure 15 Schematic diagram for establishing optimization candidate mode Figure 4 As shown in Figure 15 , the decoder adjusts the mode with the prediction direction index number of 66 to the mode with the prediction direction index number of 61. Further, the decoder can also adjust the mode with the prediction direction index number of 66 and the mode with the prediction direction index number of 2 respectively by one angle to be optimization candidate modes, for example, Figure 16 Schematic diagram for establishing optimization candidate mode Figure 5 As shown in Figure 16 , the decoder adjusts the mode with the prediction direction index number of 66 to the mode with the prediction direction index number of B, and adjusts the mode with the prediction direction index number of 2 to the mode with the prediction direction index number of A.

[0116] It should be noted that in the embodiments of the present application, the decoder can freely combine the diagonal angle modes and the derived angle modes when constructing the chroma prediction mode set according to the optimization candidate modes. For example, if the chroma prediction mode set is to be constructed by 3 optimization candidate modes, one diagonal angle mode and two derived angle modes can be added to the chroma prediction mode set, or two diagonal angle modes and one derived angle mode can be added to the chroma prediction mode set, or three derived angle modes can be added to the chroma prediction mode set, or three diagonal angle modes can be added to the chroma prediction mode set. For example, the decoder can add the prediction direction angle modes 6, 61 and 66 to the chroma prediction mode set, or add the prediction direction angle modes 6, 61 and 34 to the chroma prediction mode set, or add the prediction direction angle modes 6, 61 and 40 to the chroma prediction mode set, and the embodiments of the present application are not limited in this regard.

[0117] In the embodiments of the present application, for the wide angle modes of the long block, one of the modes with the prediction direction index numbers 66 and 2 can be selected as a candidate according to the effective prediction direction range thereof, and the other sequence number corresponding angle is adjusted as a candidate.

[0118] The present application provides a chroma intra prediction method. A decoder obtains a DM corresponding to a current chroma block from code stream data corresponding to the current chroma block. If the DM is a direct current (DC) mode or a planar (Planar) mode, a chroma prediction mode set is obtained according to optimization candidate modes. The chroma prediction mode set is used for chroma reconstruction of the current chroma block. As can be seen, in the embodiments of the present application, after the decoder obtains the DM from the code stream data of the current chroma block, if the DM is the DC mode or the Planar mode, the chroma prediction mode set can be constructed by using the optimization candidate modes, and then the current chroma block is reconstructed according to the chroma prediction mode set, so that the problem of low chroma intra prediction accuracy when the DM is the DC mode or the Planar mode can be solved, and the coding efficiency can be improved.

[0119] Based on the above embodiments, in another embodiment of the present application, Figure 17 The composition structure of the decoder according to the embodiments of the present application is shown in Figure 1 As shown in Figure 17 The decoder 1 according to the embodiments of the present application can include an obtaining part 11, a decoding part 12, a establishing part 13 and a receiving part 14.

[0120] The obtaining part 11 is configured to obtain a DM corresponding to a current chroma block from code stream data corresponding to the current chroma block, and obtain a set of chroma prediction modes according to an optimized candidate mode if the DM is a direct current (DC) mode or a planar (Planar) mode, wherein the set of chroma prediction modes is used for chroma reconstruction of the current chroma block.

[0121] In an embodiment of the present application, the obtaining part 11 is further configured to obtain a linear mode (LM) corresponding to the current chroma block from the code stream data before obtaining the set of chroma prediction modes according to the optimized candidate mode.

[0122] In an embodiment of the present application, the obtaining part 11 is specifically configured to fill the DM and the LM into the set of chroma prediction modes, and fill the set of chroma prediction modes according to the optimized candidate mode.

[0123] In an embodiment of the present application, the obtaining part 11 is further specifically configured to fill the Planar mode and the optimized candidate mode into the set of chroma prediction modes when the DM is the DC mode, and fill the DC mode and the optimized candidate mode into the set of chroma prediction modes when the DM is the Planar mode.

[0124] In an embodiment of the present application, the optimized candidate mode includes at least one mode, wherein a prediction direction index number of the at least one mode is different.

[0125] In an embodiment of the present application, the establishing part 13 is configured to establish the optimized candidate mode before obtaining the set of chroma prediction modes according to the optimized candidate mode.

[0126] In an embodiment of the present application, the establishing part 13 is specifically configured to determine at least one diagonal angle mode as the optimized candidate mode, or determine a derived angle mode of the at least one diagonal angle mode as the optimized candidate mode, or determine the at least one diagonal angle mode and the derived angle mode of the at least one diagonal angle mode as the optimized candidate mode.

[0127] In an embodiment of the present application, the obtaining part 11 is further configured to determine an index number M corresponding to the DM before establishing the optimized candidate mode, wherein the M is an integer greater than 0, and obtain a transform parameter N and determine an index number corresponding to a derived angle mode according to the M and the N to obtain the derived angle mode, wherein the N is an integer greater than 0.

[0128] In the embodiments of the present application, the obtaining part 11 is specifically configured to add the M and the N to obtain the index number corresponding to the derived angle angle mode; or subtract the M and the N to obtain the index number corresponding to the derived angle angle mode.

[0129] In the embodiments of the present application, the N includes 3, 5 or 7.

[0130] In the embodiments of the present application, the current chroma block includes a square chroma block and a non-square chroma block.

[0131] In the embodiments of the present application, the receiving part 14 is configured to receive a video bitstream to obtain the code stream data before obtaining the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block.

[0132] In the embodiments of the present application, the decoding part 12 is configured to perform decoding processing according to the chroma prediction mode set to perform chroma reconstruction on the current chroma block after obtaining the chroma prediction mode set according to the optimization candidate mode.

[0133] In the embodiments of the present application, the obtaining part 11 is further configured to obtain the residual data corresponding to the current chroma block from the code stream data before performing the decoding processing according to the chroma prediction mode set to perform chroma reconstruction on the current chroma block.

[0134] In the embodiments of the present application, the decoding part 12 is specifically configured to perform chroma intra prediction decoding on the residual data based on the chroma prediction mode set to perform chroma reconstruction on the current chroma block.

[0135] In the embodiments of the present application, the obtaining part 11 is further configured to obtain the chroma prediction mode set according to the optimization candidate mode to perform chroma reconstruction on the current chroma block if there is the same prediction mode in the prediction mode corresponding to the current chroma block obtained from the code stream data after receiving the video bitstream to obtain the code stream data.

[0136] Figure 18 The composition structure of the decoder proposed in the embodiments of the present application Figure 2 As shown in Figure 18 The decoder 1 proposed in the embodiments of the present application can further include a processor 15, a memory 16 storing instructions executable by the processor 15, a communication interface 17, and a bus 18 for connecting the processor 15, the memory 16 and the communication interface 17.

[0137] In the embodiments of the present application, the processor 15 can be at least one of an Application Specific Integrated Circuit (ASIC), a Digital Signal Processor (DSP), a Digital Signal Processing Device (DSPD), a Programmable Logic Device (PLD), a Field Programmable Gate Array (FPGA), a Central Processing Unit (CPU), a controller, a microcontroller, or a microprocessor. It can be understood that, for different devices, the electronic device used to implement the functions of the processor can also be other devices, and the embodiments of the present application are not limited specifically. The device 1 can further include a memory 16, which can be connected with the processor 15, wherein the memory 16 is used to store executable program codes, the program codes including computer operation instructions, and the memory 16 can include a high-speed RAM memory and can also include a non-volatile memory, for example, at least two disk memories.

[0138] In the embodiments of the present application, the bus 18 is used to connect the communication interface 17, the processor 15, and the memory 16, and to realize mutual communication among these devices.

[0139] In the embodiments of the present application, the memory 16 is used to store instructions and data.

[0140] Further, in the embodiments of the present application, the processor 15 is used to acquire a DM corresponding to a current chroma block from code stream data corresponding to the current chroma block; if the DM is a direct current (DC) mode or a planar mode, a chroma prediction mode set is acquired according to an optimization candidate mode; and the chroma prediction mode set is used to perform chroma reconstruction on the current chroma block.

[0141] In practical applications, the memory 16 can be a volatile memory, such as a random-access memory (RAM), or a non-volatile memory, such as a read-only memory (ROM), a flash memory, a hard disk drive (HDD) or a solid-state drive (SSD), or a combination of the above, and provides instructions and data to the processor 15.

[0142] In addition, each functional module in the embodiment can be integrated in one processing unit, or each unit can exist physically independently, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional module.

[0143] If the integrated unit is realized in the form of a software functional module and is not sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiment can be embodied in the form of a software product, the computer software product is stored in a storage medium, and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to execute all or part of the steps of the embodiment method. The foregoing storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0144] The device provided in the embodiment of the present application obtains the DM corresponding to the current chroma block from the code stream data corresponding to the current chroma block; if the DM is a direct current DC mode or a planar Planar mode, the chroma prediction mode set is obtained according to the optimization candidate mode; and the chroma prediction mode set is used for chroma reconstruction of the current chroma block. As can be seen, in the embodiment of the present application, after the DM is obtained from the code stream data of the current chroma block, if the DM is the DC mode or the Planar mode, the chroma prediction mode set can be constructed by using the optimization candidate mode, and then the current chroma block is reconstructed according to the chroma prediction mode set, so that the problem of low chroma intra prediction accuracy when the DM is the DC mode or the Planar mode can be solved, and the coding efficiency can be improved.

[0145] The embodiment of the present application provides a first computer readable storage medium, and a program is stored on the first computer readable storage medium. The program is executed by a processor to implement the chroma intra prediction method.

[0146] Specifically, the program instruction corresponding to the chroma intra prediction method in the embodiment can be stored on a storage medium such as an optical disc, a hard disk, a U disk, etc. When the program instruction corresponding to the chroma intra prediction method in the storage medium is read by an electronic device or executed, the following steps are included.

[0147] The DM corresponding to the current chroma block is obtained from the code stream data corresponding to the current chroma block.

[0148] If the DM is a direct current DC mode or a planar Planar mode, the chroma prediction mode set is obtained according to the optimization candidate mode.

[0149] The chroma prediction mode set is used for chroma reconstruction of the current chroma block.

[0150] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can be in the form of a hardware embodiment, a software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can be in the form of a computer program product implemented on one or more computer usable storage media (including but not limited to magnetic disk storage and optical storage, etc.) containing computer usable program code.

[0151] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks.

[0152] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks.

[0153] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks. Figure 1 The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart or flowsheet block or blocks.

[0154] The above description is only preferred embodiment of the present application, not for limiting the protection range of the present application.

Claims

1. A method for chroma intra prediction, applied to a decoder, characterized in that, The method comprises: parsing code stream data corresponding to a current chroma block, and determining that a prediction mode of the current chroma block is a direct mode DM; obtaining a linear mode corresponding to the current chroma block from the code stream data; determining a chroma prediction mode set according to an optimization candidate mode; wherein when a luma prediction mode corresponding to the direct mode DM is any one of a direct current DC mode, a planar Planar mode, a vertical VER mode or a horizontal HOR mode, the chroma prediction mode set comprises an angle mode with an index number of 66; determining an intra prediction mode of the current chroma block from the chroma prediction mode set, wherein the chroma prediction mode set comprises at least one of the following modes: the DM, the LM, the LM_T and the LM_L; and determining a reconstruction value of the current chroma block according to the intra prediction mode.

2. The method of claim 1, wherein when the luma prediction mode corresponding to the direct mode DM is the DC mode, the chroma prediction mode set is determined according to at least the Planar mode and the optimization candidate mode; when the luma prediction mode corresponding to the direct mode DM is the Planar mode, the chroma prediction mode set is determined according to at least the DC mode and the optimization candidate mode.

3. The method of claim 1, wherein when the luma prediction mode corresponding to the direct mode DM is the DC mode or the Planar mode, a diagonal angle mode with a prediction direction index number of 66 and a diagonal angle mode with a prediction direction index number of 2 are each adjusted by an angle as the optimization candidate mode.

4. A method for chroma intra prediction, applied to an encoder, characterized in that, The method comprises: determining that a prediction mode of a current chroma block is a direct mode DM; determining a chroma prediction mode set according to an optimization candidate mode; wherein when a luma prediction mode corresponding to the direct mode DM is any one of a direct current DC mode, a planar Planar mode, a vertical VER mode or a horizontal HOR mode, the chroma prediction mode set comprises an angle mode with an index number of 66; determining an intra prediction mode of the current chroma block from the chroma prediction mode set, wherein the chroma prediction mode set comprises at least one of the following modes: the DM, the LM, the LM_T and the LM_L; and determining a reconstruction value of the current chroma block according to the intra prediction mode.

5. The method of claim 4, wherein when the luma prediction mode corresponding to the direct mode DM is the DC mode, the chroma prediction mode set is determined according to at least the Planar mode and the optimization candidate mode; when the luma prediction mode corresponding to the direct mode DM is the Planar mode, the chroma prediction mode set is determined according to at least the DC mode and the optimization candidate mode.

6. The method of claim 4, wherein When the luma prediction mode corresponding to the direct mode DM is the direct current DC mode or the planar Planar mode, the diagonal angle mode with a prediction direction index of 66 and the diagonal angle mode with a prediction direction index of 2 are each adjusted by one angle as the optimization candidate mode.

7. An apparatus for chroma intra prediction, applied to a decoder, characterized in that, The apparatus comprises: a module of parsing code stream data corresponding to a current chroma block to determine that a prediction mode of the current chroma block is a direct mode DM; a module of obtaining a linear mode corresponding to the current chroma block from the code stream data; a module of determining a chroma prediction mode set according to optimization candidate modes; wherein when the luma prediction mode corresponding to the direct mode DM is any one of the direct current DC mode, the planar Planar mode, the vertical VER mode or the horizontal HOR mode, the chroma prediction mode set comprises an angle mode with an index sequence number of 66; a module of determining an intra prediction mode of the current chroma block from the chroma prediction mode set, wherein the chroma prediction mode set comprises at least one of the following modes: DM, LM, LM_T and LM_L; and a module of determining a reconstructed value of the current chroma block according to the intra prediction mode.

8. The apparatus of claim 7, wherein, Further comprising: a module of determining the chroma prediction mode set according to at least the planar Planar mode and the optimization candidate mode when the luma prediction mode corresponding to the direct mode DM is the direct current DC mode; a module of determining the chroma prediction mode set according to at least the direct current DC mode and the optimization candidate mode when the luma prediction mode corresponding to the direct mode DM is the planar Planar mode.

9. The apparatus of claim 7, wherein When the luma prediction mode corresponding to the direct mode DM is the direct current DC mode or the planar Planar mode, the diagonal angle mode with a prediction direction index of 66 and the diagonal angle mode with a prediction direction index of 2 are each adjusted by one angle as the optimization candidate mode.

10. An apparatus for chroma intra prediction, applied to an encoder, characterized in that, The apparatus comprises: a module of determining that a prediction mode of a current chroma block is a direct mode DM; a module of determining a chroma prediction mode set according to optimization candidate modes; wherein when the luma prediction mode corresponding to the direct mode DM is any one of the direct current DC mode, the planar Planar mode, the vertical VER mode or the horizontal HOR mode, the chroma prediction mode set comprises an angle mode with an index sequence number of 66; a module of determining an intra prediction mode of the current chroma block from the chroma prediction mode set, wherein the chroma prediction mode set comprises at least one of the following modes: DM, LM, LM_T and LM_L; and a module of determining a reconstructed value of the current chroma block according to the intra prediction mode.

11. The apparatus of claim 10, wherein, Further comprising: a module of determining the chroma prediction mode set according to at least the planar Planar mode and the optimization candidate mode when the luma prediction mode corresponding to the direct mode DM is the direct current DC mode; a module of determining the chroma prediction mode set according to at least the direct current DC mode and the optimization candidate mode when the luma prediction mode corresponding to the direct mode DM is the planar Planar mode. When the luma prediction mode corresponding to the direct mode DM is the planar Planar mode, the module for determining the set of chroma prediction modes according to at least the direct current DC mode and the optimized candidate mode.

12. The apparatus of claim 10, wherein, When the luma prediction mode corresponding to the direct mode DM is the direct current DC mode or the planar Planar mode, a diagonal angle mode with a prediction direction index of 66 and a diagonal angle mode with a prediction direction index of 2 are each adjusted by an angle as the optimized candidate mode.

13. A decoder, characterized by comprising: a memory storing instructions executable by a processor; the processor to execute the instructions to perform the method of any of claims 1-3.

14. An encoder comprising: comprising: a memory storing instructions executable by a processor; the processor to execute the instructions to perform the method of any of claims 4-6.

15. A non-transitory storage medium storing instructions executable by a processor of a decoder, the instructions causing the processor to: the instructions, when executed by the processor, perform the method of any of claims 1-3.

16. A non-transitory storage medium storing instructions executable by a processor of an encoder, the instructions causing the processor to: the instructions, when executed by the processor, perform the method of any of claims 4-6.

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