Patent Publication Number: US-9906789-B2

Title: Encoding or decoding method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/294,498, filed on Oct. 14, 2016, which is a continuation of U.S. patent application Ser. No. 14/750,608, filed on Jun. 25, 2015, now U.S. Pat. No. 9,503,729, which is a continuation of U.S. patent application Ser. No. 14/317,083, filed on Jul. 25, 2014, now U.S. Pat. No. 9,325,993, which is a continuation of U.S. patent application Ser. No. 14/102,186, filed Dec. 10, 2013, now U.S. Pat. No. 8,804,827, which is a continuation of International Patent Application No. PCT/CN2012/080334, filed Aug. 20, 2012, which claims priority to Chinese Patent Application No. 201210018818.7, filed Jan. 20, 2012. All of the afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
     This application is related to U.S. patent application Ser. No. 14/839,626, filed on Aug. 28, 2015, now U.S. Pat. No. 9,351,001, and U.S. patent application Ser. No. 14/317,040, filed on Jun. 27, 2014, now U.S. Pat. No. 9,124,900. This application, U.S. patent application Ser. No. 14/839,626 and U.S. patent application Ser. No. 14/317,040 share a common domestic claim to U.S. patent application Ser. No. 14/102,186, filed Dec. 10, 2013, now U.S. Pat. No. 8,804,827. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the video image processing field, and in particular, to an encoding or decoding method and apparatus. 
     BACKGROUND 
     An existing encoding or decoding technology of video images includes an intra coding technology and an inter coding technology. The intra coding refers to a technology of compressing and encoding an image content merely by using a spatial correlation within an image that is being encoded currently. The inter coding refers to a technology of compressing and encoding a current image by using a temporal correlation between the image that is being encoded currently and an encoded image. In order to improve efficiency of image intra coding, the H.264/AVC (Advanced Video Coding, advanced video coding) standard first introduced an intra prediction technology to remove a spatial information redundancy between the image block that is being encoded currently and a neighboring encoded image block. As a result, unlike earlier intra coding technologies, H.264/AVC needs to perform spatial transformation and entropy encoding only on a prediction differential signal instead of an original image signal, so as to improve the intra coding efficiency. 
     A video image signal generally includes one luma component and two chroma components. The HEVC (High Efficiency Video Coding, high efficiency video coding) solution is a new generation video encoding standardized solution that the International Organization for Standardization is currently working on. It inherits the intra prediction encoding technology of the H.264/AVC standard, and introduces a new intra prediction mode, the LM mode, regarding the chroma components. When the LM mode is used, a chroma component predicted value of an image block is obtained by calculation using a linear model based on a reconstruction value of resampling a luma component of a corresponding block. Therefore, the LM mode is different from a conventional directional intra prediction mode. It uses a correlation between a luma component and a chroma component of an image, and is a method of predicting a chroma component value by using a luma component value. 
     The HEVC solution inherits and extends the intra prediction encoding technology in the H.264/AVC standard. All available intra prediction modes for chroma components of an image block form a prediction mode set, which includes the following six prediction modes: 
     DM mode: performs prediction by using an intra prediction mode of a luma component of a current block as a prediction mode of a chroma component; 
     LM mode: calculates a predicted value of a chroma component by using a value of a luma component of a sampling point based on a linear model, where a parameter of the linear model is obtained by calculation based on a luma component value and a chroma component value of a sampling point adjacent to a current block; 
     DC mode: uses an average value of chroma component values of a sampling point adjacent to a current block as a predicted value of a chroma component of the current block; 
     Planar (Planar) mode: calculates a predicted value of a sampling point of a current block based on an assumption of a spatially linear smooth change in a value of the sampling point; 
     Horizontal mode: uses a chroma component value of an adjacent sampling point to the left as a predicted value of a chroma component of all sampling points within the same row of a current block; and 
     Vertical mode: uses a chroma component value of an adjacent above sampling point as a predicted value of a chroma component of all sampling points within the same column of a current block. 
     In a related technology, the foregoing chroma prediction modes use a TU (Truncated Unary, truncated unary) code solution to perform encoding or decoding, where the encoding or decoding are highly complex, and decoding efficiency is low. 
     SUMMARY 
     Embodiments of the present invention provide an encoding or decoding method and apparatus which can reduce encoding or decoding complexity in video image processing and improve decoding efficiency. 
     In one aspect, an encoding or decoding method is provided, including: extracting first information in a bitstream; determining a chroma component intra prediction mode according to the first information; when the chroma component intra prediction mode cannot be determined according to the first information, extracting second information in the bitstream; and determining the chroma component intra prediction mode according to the second information, where the first information includes information for indicating whether the chroma component intra prediction mode is a DM mode or an LM mode, the second information is used to indicate a remaining mode as the chroma component intra prediction mode, and the remaining mode is one of available chroma component intra prediction modes other than a mode that may be determined according to the first information. 
     In another aspect, an encoding or decoding apparatus is provided, including a first extracting unit, a first determining unit, a second extracting unit, and a second determining unit, where the first extracting unit is configured to extract first information in a bitstream; the first determining unit is configured to determine a chroma component intra prediction mode according to the first information extracted by the first extracting unit; the second extracting unit is configured to, when the first determining unit cannot determine the chroma component intra prediction mode according to the first information, extract second information in the bitstream; and the second determining unit is configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit, where the first information includes information for indicating whether the chroma component intra prediction mode is a DM mode or an LM mode, the second information is used to indicate a remaining mode as the chroma component intra prediction mode, and the remaining mode is one of available chroma component intra prediction modes other than a mode that may be determined according to the first information. 
     The foregoing technical solutions may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To illustrate the technical solutions in the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments of the present invention. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic flowchart of an encoding or decoding method according to an embodiment of the present invention; 
         FIG. 2  is a schematic flowchart of an encoding or decoding method according to another embodiment of the present invention; 
         FIG. 3  is a schematic flowchart according to an embodiment of the present invention; 
         FIG. 4  is a schematic flowchart according to another embodiment of the present invention; 
         FIG. 5  is a schematic block diagram of an encoding or decoding apparatus according to an embodiment of the present invention; and 
         FIG. 6  is a schematic block diagram of another encoding or decoding apparatus according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following clearly describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     The wording “and/or” in this document merely describes an association between associated objects, indicating that three relationships may exist, for example, A and/or B may indicate three situations: only A exists, A and B exist at the same time, and only B exists. In addition, the character “/” in this document usually represents that the former and later associated objects are in a “or” relationship. 
     A chroma component in an embodiments of the present invention may refer to any chroma component of two chroma components. ADC mode, a vertical mode, a horizontal mode, and a planar mode in a chroma component intra prediction mode set of HEVC are the same as corresponding modes in the H.264/AVC standard in terms of a basic principle, but are different in specific implementation methods. An LM mode and a DM mode are two newly added modes. Besides the prediction modes mentioned above, there is a replacement mode. If the DM mode is the same as one of the remaining prediction modes in a prediction mode set, the replacement mode is used to replace the chroma prediction mode that is the same as the DM mode, so as to make a new prediction mode set. The DM mode performs prediction by using an intra prediction mode of a luma component of a current block as a prediction mode of a chroma component. Therefore, the method may also equivalently determine whether an intra prediction mode of a luma component is the same as a remaining prediction mode in the prediction mode set. The replacement mode may be a prediction mode that is different from all the modes in the chroma component prediction mode set. 
     The chroma component prediction mode set may be different in different embodiments of the present invention. One usable chroma component prediction mode set includes a DM mode, an LM mode, a DC mode, a vertical mode, a horizontal mode, and a planar mode. Another usable chroma component prediction mode set includes a DM mode, a DC mode, a vertical mode, a horizontal mode, and a planar mode. Another usable chroma component prediction mode set includes a DM mode, an LM mode, and a default mode. Another usable chroma component prediction mode set includes a DM mode and a default mode. 
     The LM mode in the modes mentioned above is an optional technology in the existing HEVC solution. Under an HE (High Efficiency, high efficiency) encoding configuration condition, the LM mode is included in available modes for the chroma component intra prediction mode. In such cases, the prediction mode set includes six prediction modes. However, under an LC (Low Complexity, low complexity) encoding configuration condition, the LM mode is not included in available modes for the chroma component intra prediction mode. In such cases, the prediction mode set includes five prediction modes. In the existing HEVC solution, whether the LM mode is an available mode is determined according to a binary flag (flag) in a bitstream. 
     The chroma encoding solution uses a TU (Truncated Unary) code to binarize mode information of a current block, and then performs entropy encoding on a binary flag after the binarization by using a CABAC (Context-Adaptive Binary Arithmetic Coding) technology. For example, under an HE configuration condition, the six modes, namely, DM, LM, vertical, horizontal, DC, and planar modes may be presented by a TU code word 0, 10, 110, 1110, 11110, and 11111, respectively; under an LC configuration condition, the five modes, namely, DM, vertical, horizontal, DC, and planar modes may be represented by a TU code word 0, 10, 110, 1110, and 1111, respectively. A decoding end determines a prediction mode for a chroma component of a current block according to the TU code word obtained by parsing. 
     In fact, the TU code word may be regarded as a group of binary flags in series. In an entropy encoding or entropy decoding process, whether to continue to encode or decode the following binary flags is determined according to a value of each binary flag one by one. In addition, each binary flag in the TU code word represents a binarized determination. For example, under an LC encoding configuration condition, a TU code having a maximum value 5 is used. That is, the TU code includes a maximum of four binary flags. The first binary flag is used to determine whether a mode of a current block is a DM mode; the second binary flag is used to determine whether the chroma component prediction mode of the current block is a vertical mode; the third binary flag is used to determine whether the chroma component prediction mode of the current block is a horizontal mode; and the fourth binary flag is used to determine whether the chroma component prediction mode of the current block is a DC mode. If the chroma component prediction mode of the current block is not among the four modes described above, it must be a planar mode. 
     When the TU code word is used to encode and decode chroma component intra prediction mode information, a value of a previous binary flag is the basis for determining whether to encode or decode a next binary flag. This conditional encoding or decoding increases complexity of entropy encoding or entropy decoding. 
     The DM mode is used with a high probability, which reduces importance of other modes than the DM mode. Moreover, it is possible that the DM mode is the same as the planar mode, the DC mode, the horizontal mode, or the vertical mode, indicating that a large redundancy exists in a set of available modes, where the redundancy affects efficiency of compressing video images. 
     There are many available modes, where six modes are available under an HE condition, and five modes are available under an LC condition. This increases calculation complexity in a process for an encoding end to select a mode. 
     An embodiment of the present invention provides an encoding or decoding method to solve the above problem. 
       FIG. 1  is a schematic flowchart of an encoding or decoding method  10  according to an embodiment of the present invention, including the following content. 
       11 . Extract first information in a bitstream. 
     The first information includes information for indicating whether a chroma component intra prediction mode is a DM mode or an LM mode. 
       12 . Determine a chroma component intra prediction mode according to the first information. 
       13 . When the chroma component intra prediction mode cannot be determined according to the first information, extract second information in the bitstream. 
       14 . Determine the chroma component intra prediction mode according to the second information. 
     The second information is used to indicate a remaining mode of the chroma component intra prediction mode, where the remaining mode is one of available chroma component intra prediction modes other than a mode that may be determined according to the first information. 
     The remaining mode may be one of modes in a chroma component intra prediction mode set other than a mode that may be determined according to the first information. For example, if the first information is used to determine whether the chroma component intra prediction mode is a DM mode or an LM mode, the remaining mode may be one of the modes in the chroma component intra prediction mode set other than the DM mode and the LM mode. 
     When a luma component intra prediction mode is the same as the chroma component intra prediction mode in use, a replacement mode may be used to replace the chroma component intra prediction mode, where the replacement mode is one of modes that are different from the modes in the chroma component intra prediction mode set. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
       FIG. 2  is a schematic flowchart of an encoding or decoding method  20  according to another embodiment of the present invention, including the following content. 
       21 . Extract first information in a bitstream. 
     The first information includes information for indicating whether a chroma component intra prediction mode is a DM mode or an LM mode. The first information may include one or two pieces of sub-information carried by a binary flag. The first information may also be carried by a TU code having a maximum value 2. 
       22 . Determine whether a chroma component intra prediction mode is a DM mode according to the first information. 
     When the chroma component intra prediction mode is determined as the DM mode, that is, a result is “yes”, step  23  is performed and the DM mode is used as the chroma component intra prediction mode. 
     When it is determined that the chroma component intra prediction mode is not a DM mode, that is, a result is “no”, alternatively, step  24  is performed to determine whether a chroma component intra prediction mode set includes an LM mode, where the determining method is the same as the prior art. 
     When it is determined that the set includes the LM mode, that is, a result is “yes”, step  25  is performed. 
       25 . Determine whether the chroma component intra prediction mode is an LM mode according to the first information. 
     When the chroma component intra prediction mode is determined as the LM mode, that is, a result is “yes”, step  26  is performed and the LM mode is used as the chroma component intra prediction mode. 
     When it is determined that the chroma component intra prediction mode is not an LM mode, that is, a result is “no”, step  27  is performed. 
     After step  24  is performed, step  27  may also be performed if it is determined that the set does not include the LM mode, that is, a result is “no”. 
       27 . Extract second information in the bitstream. 
       28 . Determine a remaining mode by using the second information, and use the remaining mode as the chroma component intra prediction mode. 
     The remaining mode may be one of modes in a chroma component intra prediction mode set other than a mode that may be determined according to the first information. For example, in the embodiment, the first information is used to determine whether the chroma component intra prediction mode is a DM mode or an LM mode; then, the remaining mode may be any of four modes in the chroma component intra prediction mode set other than the DM mode and the LM mode. The second information may carry encoding information indicating which one the remaining mode specifically is. The encoding information of the four modes may be carried by using an FL code, where a corresponding relationship is established between each mode and an FL code. 
     Step  29 : Determine whether the chroma component intra prediction mode determined in the previous step is the same as a luma component intra prediction mode. 
     If they are the same, that is, a result is “yes”, step  30  is performed to determine to use a replacement mode as the chroma component intra prediction mode. The replacement mode is one of modes that are different from the modes in the chroma component intra prediction mode set. 
     If they are different, that is, a result is “no”, step  31  is performed to determine to keep the chroma component intra prediction mode unchanged. 
     As an implementation method, step  32  may replace steps  27  and  28 . 
     As another implementation method, step  29  is optional, and step  31  may be directly performed after step  32  or step  28 . 
       32 . Use a default mode as the chroma component intra prediction mode, where the default mode is one of predefined luma component intra prediction modes. 
     In the above technical solutions, with respect to different technologies that are used, for example, a method for carrying information, multiple steps described above may be combined, or one step may be divided and completed in multiple steps. The present invention sets no limit thereto. The implementation methods shall fall within the protection scope of the present invention. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
     Both the chroma component intra prediction mode and the luma component intra prediction mode are about the current block. Therefore, in the following embodiments, they are respectively referred to as a current block chroma mode and a current block luma mode for short, which generally may also be respectively referred to as a chroma mode and a luma mode for short. In a standard, generally, there are more modes in a luma component intra prediction mode set than modes in a chroma component intra prediction mode set. 
       FIG. 3  is a schematic flowchart according to an embodiment  300  of the present invention. 
     In the embodiment of the present invention, a binary flag is used to carry first information. The first information may include information for indicating whether a current block chroma mode is a DM mode by using a binary flag, which is expressed as DM information. 
     The first information may also include information for indicating whether a current block chroma mode is an LM mode by using a binary flag, which is expressed as LM information. If the LM mode is not an available mode in chroma component intra prediction mode set, a bitstream contains no LM information, and an encoding end and a decoding end perform no encoding or decoding operation on LM information. 
     The second information is used to indicate a remaining mode of the chroma component intra prediction mode, where the remaining mode is one of available chroma component intra prediction modes other than a mode that may be determined according to the first information. An FL (Fix Length, fixed-length) code word having a length of 2 may be used to represent the second information. The remaining modes may be four modes, that is, vertical, horizontal, DC, and planar modes. For example, FL code words 00, 01, 10, and 11 may be used to represent the four modes, respectively. 
     When entropy decoding is performed on the DM information, it is allowed to use no context model or use one context model, and a context model may be selected from multiple context models according to encoding information of adjacent blocks. 
     When entropy decoding is performed on the LM information, it is allowed to use no context model or use one context model, and a context model may be selected from multiple context models according to encoding information of adjacent blocks. 
     No context model is used when entropy decoding is performed on the second information. In other words, a by-pass (equiprobability) mode is used to perform entropy decoding on a bitstream to obtain an FL code word having a length of 2, and determine the corresponding mode described according to the FL code word. This can improve throughput for entropy decoding. The by-pass mode is a binary entropy encoding or entropy decoding mode which does not use a probability model. In other words, the by-pass mode assumes an equal probability for a binary flag as 0 or 1 where entropy encoding or entropy decoding is currently performed. 
     It should be noted that it is the prior art to decode a binary flag without using a context model, that is, the by-pass mode in the CABAC technology. It is the prior art to decode a binary flag by using one context model. For example, in a luma intra mode encoding or decoding solution of HEVC, this entropy decoding method is performed for a first binary flag. It is the prior art to select a context model from multiple context models according to the encoding information of adjacent blocks. For example, in the HEVC solution, this entropy decoding method is used for a skip mode flag (skip flag). Therefore, details of the above three entropy decoding methods may not be described. 
     The embodiment  300  includes the following content. 
       310 . Extract DM information from a bitstream by using the entropy decoding method described above. If a current block chroma mode is determined as a DM mode according to the DM information, end the mode determining procedure; otherwise, perform step  320 . 
       320 . Extract LM information from the bitstream by using the entropy decoding method described above. If the current block chroma mode is determined as an LM mode according to the LM information, end the mode determining procedure; otherwise, perform step  330 . 
     It should be noted that, if the LM mode is not included in available modes for chroma component intra prediction, there is no LM information in the bitstream. A decoding end does not need to perform a parsing operation and this step may be skipped. The prior art may be used to determine whether the LM mode is included in the available modes for chroma component intra prediction. 
       330 . Extract second information from the bitstream by using the entropy decoding method described above. The second information is an FL code word having a length of 2. 
       340 . Determine remaining mode information according to the second information, and use a remaining mode as a current block chroma mode. 
     The current block chroma mode is determined according to a corresponding relationship between the FL code word and the remaining mode. One available corresponding relationship is described above. 
     Alternatively, if a current block luma mode is the same as the current block chroma mode determined in the remaining modes according to the above method, a replacement mode is used to replace the current block chroma mode used in step  340 . A mode which is different from modes in a chroma component intra prediction mode set may be selected as the replacement mode. For example, a directional prediction mode from upper-right to lower-left may be used as the replacement mode. When the current block luma mode is not the same as the current block chroma mode determined from the remaining modes according to the above method, the current block chroma mode used in step  340  remains unchanged. 
     After the current block chroma mode is determined, the mode determining procedure may be ended. 
     In addition, in order to remove a redundancy in available prediction modes for a chroma component, alternatively, the set of available prediction modes for the chroma component includes only three chroma component prediction modes, that is, a DM mode, an LM mode, and a default mode. In such cases, step  360  may be used to replace steps  330  and  340 , where other steps remain unchanged. In such cases, it is known according to the previous steps that the current block chroma mode is neither the DM mode nor the LM mode. The default mode may be one of predefined luma component intra prediction modes. 
       350 . If the current block luma mode is the same as the current block chroma mode, use a replacement mode to replace the current block chroma mode. 
       360 . Use a default mode as the current block chroma mode. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
       FIG. 4  is a schematic flowchart according to another embodiment  40  of the present invention. The difference from the embodiment  300  lies in that a TU code word having a maximum value 2 is used to carry first information, which is used to indicate whether a current block chroma mode is a DM mode or an LM mode. The TU code word may be 0, 10, and 11. The three code words may respectively indicate that the current block chroma mode is a DM mode, that the current block chroma mode is an LM mode, and that the current block chroma mode is neither the DM mode nor the LM mode, that is, the current block is one in a remaining mode set. It should be noted that if the LM mode is not included in available modes for chroma component intra prediction, the TU code word may be rolled back to a binary flag, where the binary flag indicates whether the current block chroma mode is a DM mode. 
     Similarly, an FL (Fix Length, fixed-length) code word having a length of 2 is used to carry second information to represent a remaining mode in a chroma prediction mode. Other aspects, for example, an entropy decoding method, are the same as the embodiment  300 . 
       41 . Determine a current block chroma mode by extracting a TU code word indicating whether the current block chroma mode is a DM mode or an LM mode. 
     The entropy decoding method described in the embodiment  300  is used to extract a TU code word having a maximum value 2 from a bitstream. If the current block chroma mode is determined as a DM mode according to the TU code word, end the mode determining procedure; if the current block chroma mode is determined as an LM mode according to the TU code word, end the mode determining procedure; otherwise, the current block chroma mode is determined neither as the DM mode nor as the LM mode according to the TU code word, and step  42  is performed. 
     It should be noted that if the LM mode is not included in available modes for chroma component intra prediction, the TU code word having the maximum value 2 is not parsed from the bitstream; instead, a binary flag is extracted from the bitstream according to the method in the embodiment  300 . If the current block chroma mode is determined as a DM mode according to the binary flag, end the mode determining procedure; otherwise, perform step  42 . 
       42 . Extract second information. 
     Similar to step  330 , the entropy decoding method described in the embodiment  300  is used to extract the second information from the bitstream. The second information is an FL code word having a length of 2. 
       43 . Determine a remaining mode according to the second information, and use the remaining mode as a current block chroma mode. 
     Similar to  340  in the embodiment  300 , the current block chroma mode is determined according to a corresponding relationship between the FL code word and the remaining mode. One available corresponding relationship is described above. 
     Alternatively, in step  44 , if a current block luma mode is the same as the current block chroma mode determined from the remaining modes according to the above method, a replacement mode is used to replace the current block chroma mode used in step  43 . A mode which is different from all modes in a chroma component intra prediction mode set may be selected as the replacement mode. For example, a directional prediction mode from upper-right to lower-left may be used as the replacement mode. When the current block luma mode is not the same as the current block chroma mode determined from the remaining modes according to the above method, the current block chroma mode used in step  43  remains unchanged. 
     After the current block chroma mode is determined, the mode determining procedure may be ended. 
     In addition, similar to the embodiment  300 , in order to remove a redundancy in available prediction modes for a chroma component, alternatively, the set of available prediction modes for the chroma component used in the embodiment may also include only three chroma component prediction modes, that is, a DM mode, an LM mode, and a default mode. Correspondingly, as shown in  FIG. 4 , step  45  may also be used to replace steps  42  and  43  while other steps remain unchanged. In such cases, it is known according to the previous steps that the current block chroma mode is neither the DM mode nor the LM mode. 
       45 . Use a default mode as the current block chroma mode. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
       FIG. 5  is a schematic block diagram of an encoding or decoding apparatus  50  according to an embodiment of the present invention. The apparatus  50  includes a first extracting unit  51 , a first determining unit  52 , a second extracting unit  53 , and a second determining unit  54 . 
     The first extracting unit  51  is configured to extract first information in a bitstream. 
     The first determining unit  52  is configured to determine a chroma component intra prediction mode according to the first information extracted by the first extracting unit  51 . 
     The second extracting unit  53  is configured to, when the first determining unit  51  cannot determine the chroma component intra prediction mode according to the first information, extract second information in the bitstream. 
     The second determining unit  54  is configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit  53 . 
     The apparatus  50  implements methods  20  and  300 , where the specific details are not described repeatedly herein. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
     In addition, alternatively, when the first information extracted by the first extracting unit  51  includes DM information carried by a binary flag, where the DM information is used to indicate whether the chroma component intra prediction mode is a DM mode, the first determining unit  52  is specifically configured to, when the DM information indicates that the chroma component intra prediction mode is a DM mode, use the DM mode as the chroma component intra prediction mode. 
     Alternatively, when the first information extracted by the first extracting unit  51  includes DM information carried by a binary flag, where the DM information is used to indicate whether the chroma component intra prediction mode is a DM mode, the first determining unit  52  is specifically configured to, when the DM information indicates that the chroma component intra prediction mode is not a DM mode, use a default mode as the chroma component intra prediction mode, where the default mode is one of predefined luma component intra prediction modes. 
     Alternatively, when the first information extracted by the first extracting unit  51  includes DM information carried by a binary flag, where the DM information is used to indicate whether the chroma component intra prediction mode is a DM mode, the second extracting unit  53  is specifically configured to, when the first determining unit  52  determines that the DM information indicates that the chroma component intra prediction mode is not a DM mode, extract second information in the bitstream, and the second determining unit  54  is specifically configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit  51 . 
     Alternatively, when the DM information of the first information extracted by the first extracting unit  51  indicates that the chroma component intra prediction mode is not a DM mode, and the first information further includes LM information carried by a binary flag, where the LM information is used to indicate whether the chroma component intra prediction mode is an LM mode, the first determining unit  52  is specifically configured to, when it is determined that the LM information indicates that the chroma component intra prediction mode is an LM mode, use the LM mode as the chroma component intra prediction mode. 
     Alternatively, when the DM information of the first information extracted by the first extracting unit  51  indicates that the chroma component intra prediction mode is not a DM mode, and the first information further includes LM information carried by a binary flag, where the LM information is used to indicate whether the chroma component intra prediction mode is an LM mode, the first determining unit  52  is specifically configured to, when it is determined that the LM information indicates that the chroma component intra prediction mode is not an LM mode, use a default mode as the chroma component intra prediction mode, where the default mode is one of predefined luma component intra prediction modes. 
     Alternatively, when the DM information of the first information extracted by the first extracting unit  51  indicates that the chroma component intra prediction mode is not a DM mode, and the first information further includes LM information carried by a binary flag, where the LM information is used to indicate whether the chroma component intra prediction mode is an LM mode, the second extracting unit  53  is specifically configured to extract second information in the bitstream when the first determining unit  52  determines that the LM information indicates that the chroma component intra prediction mode is not an LM mode, and the second determining unit  54  is specifically configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit  53 . 
     Alternatively, when the first extracting unit  51  extracts the first information carried by a truncated unary (TU) code having a maximum value 2, the first determining unit  52  is specifically configured to, when it is determined that the TU code indicates that the chroma component intra prediction mode is a DM mode, use the DM mode as the chroma component intra prediction mode. 
     Alternatively, when the first extracting unit  5  specifically extracts the first information carried by a TU code having a maximum value 2, the first determining unit  52  is specifically configured to, when it is determined that the TU code indicates that the chroma component intra prediction mode is an LM mode, use the LM mode as the chroma component intra prediction mode. 
     Alternatively, when the first extracting unit  51  extracts the first information carried by a TU code having a maximum value 2, the first determining unit  52  is specifically configured to, when it is determined that the TU code indicates that the chroma component intra prediction mode is neither a DM mode nor an LM mode, use a default mode as the chroma component intra prediction mode, where the default mode is one of predefined luma component intra prediction modes. 
     Alternatively, when the first extracting unit  51  extracts the first information carried by a TU code having a maximum value 2, the second extracting unit  53  is specifically configured to extract second information in the bitstream when the first determining unit  52  determines that the TU code indicates that the chroma component intra prediction mode is neither a DM mode nor an LM mode, and the second determining unit  54  is specifically configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit  53 . 
     Alternatively, when the second extracting unit  51  extracts the second information carried by a fixed-length (FL) code, the second determining unit  53  is specifically configured to determine a remaining mode by using the FL code, and use the remaining mode as the chroma component intra prediction mode. The second extracting unit  51  may extract the second information carried by one FL code by using an equiprobability (by-pass) mode. 
       FIG. 6  is a schematic block diagram of another encoding or decoding apparatus  60  according to an embodiment of the present invention. As an implementation manner, the apparatus  60  includes a first extracting unit  61 , a first determining unit  62 , a second extracting unit  63 , a second determining unit  64 , which are the same as or similar to the first extracting unit  51 , the first determining unit  52 , the second extracting unit  53 , and the second determining unit  54  of the apparatus  50 . The difference lies in that the apparatus  60  may further include a third determining unit  65  and/or a fourth determining unit  66 . 
     The first extracting unit  61  is configured to extract first information in a bitstream. 
     The first determining unit  62  is configured to determine a chroma component intra prediction mode according to the first information extracted by the first extracting unit  61 . 
     The second extracting unit  63  is configured to, when the first determining unit  61  cannot determine the chroma component intra prediction mode according to the first information, extract second information in the bitstream, 
     The second determining unit  64  is configured to determine the chroma component intra prediction mode according to the second information extracted by the second extracting unit  63 . 
     The third determining unit  65  is configured to determine whether a chroma component intra prediction mode set includes an LM mode. 
     When the third determining unit  65  determines that the chroma component intra prediction mode set does not include the LM mode, the first information extracted by the first extracting unit  61  includes only information for indicating whether the chroma component intra prediction mode is a DM mode. Alternatively, when the third determining unit  65  determines that the chroma component intra prediction mode set includes the LM mode, the first information extracted by the first extracting unit  61  includes information for indicating whether the chroma component intra prediction mode is a DM mode or an LM mode. 
     The fourth determining unit  66  is configured to, when the determined chroma component intra prediction mode is neither the DM mode nor the LM mode, determine whether a luma component intra prediction mode is the same as the determined chroma component intra prediction mode. 
     When the fourth determining unit  66  determines that the luma component intra prediction mode is the same as the determined chroma component intra prediction mode, a replacement mode is used to replace the determined chroma component intra prediction mode, where the replacement mode is one of modes that are different from the modes in the chroma component intra prediction mode set. Alternatively, when the fourth determining unit  66  determines that the luma component intra prediction mode is not the same as the determined chroma component intra prediction mode, the determined chroma component intra prediction mode remains unchanged. 
     The apparatus  60  implements methods  20  and  300 , where the specific details are not described repeatedly herein. 
     The embodiment of the present invention may reduce the encoding information of a chroma mode and optimize sorting for the information to reduce encoding or decoding steps, thereby reducing encoding or decoding complexity and improving decoding efficiency. 
     A person of ordinary skill in the art may be aware that units and algorithm steps of the examples described with reference to the embodiments disclosed herein may be implemented by using electronic hardware or a combination of computer software and electronic hardware. These functions may be executed in a mode of hardware or software depending on a specific application design constraint condition of the technical solutions. A person skilled in the art may use different methods for each specific application to implement the described functions; however, this implementation shall not be deemed as exceeding the scope of the present invention. 
     A person skilled in the art should clearly understand that, for the convenience and brevity of description, for the specific operation processes of the above system, apparatus, and units, reference may be made to the corresponding processes in the method methods, and details are not described repeatedly here. 
     In the embodiments provided the present application, it should be understood that the system, apparatus, and method disclosed may be implemented in other forms. For example, the apparatus embodiment described above is merely illustrative. For example, the division of units is merely logical functional division, and there are other division forms in real application. For example, multiple units or components may be combined or be integrated to another system, or some features may be ignored or not be executed. In another aspect, the coupling, direct coupling, or communication connection therebetween which is displayed or discussed may be indirect coupling or communication connection of interfaces, apparatuses, or units, and may be electrical, mechanical, or in other forms. 
     The units described as separate components may be or may be not physically separate, and the components displayed as units may be or may be not physical units, and may be located in one place or be distributed on multiple network units. Part or all units may be selected depending on the actual requirements to realize the objectives of the solutions according to the embodiments. 
     In addition, the functional units in embodiments of the present invention may be integrated in one processing unit or exist separately as physical units, or two or more units may be integrated in one unit. 
     The functions may be implemented in a mode of software functional units and sold or used as an independent product, which may be stored in a computer readable storage medium. Based on such understanding, the essence of the technical solutions of the present invention or the part that makes a contribution to the prior art may be implemented in the form of software product. The computer software product is stored in a storage medium, and includes multiple instructions to enable a computer equipment (which may be a personal computer, a server, or a network equipment) to execute all or partial steps of the method described in embodiments of the present invention. The storage medium includes various media which can store program codes such as a USB flash drive, a mobile hard disk, a read-only memory (Read-Only Memory, ROM), a random access memory (Random Access Memory, RAM), a magnetic disk, or an optical disk. 
     The solutions provided by the embodiments of the present invention may be applied in a digital signal processing field, and be implemented by using a video encoder and a decoder. A video encoder and decoder may be widely used in various communication devices or electronic devices, such as a media gateway, mobile phone, wireless device, personal digital assistant (PDA, Personal Data Assistant), hand-held or portable computer, GPS (Global Positioning System, global positioning system) receiver/navigator, camera, video player, video camera, video recorder, and monitoring device. These devices include processor, a storage, and an interface for transferring data. The video encoder and decoder may be implemented directly by using a digital circuit or chip, such as a DSP (Digital Signal Processor, digital signal processor), or be implemented by using software code to drive a processor to execute a procedure in the software code. 
     The foregoing description is merely about the specific embodiments of the present invention, but is not intended to limit the protection scope of the present invention. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.