Image coding device, image coding method, image decoding device, and image decoding method

Abstract

To provide an image coding device capable of improving a coding efficiency by performing a block division that is adopted to a coding and a decoding of an image.SOLUTION: An image coding device 100 that divides an image into blocks and performs encoding on a divided block basis comprises: a luminance signal block dividing unit that generates a luminance signal block by dividing a luminance signal of an image into rectangles in a predetermined size; a color difference signal block dividing unit that generates a color difference signal block by dividing a color difference signal of an image into rectangles in a predetermined size; and a prediction image generation unit that includes a luminance signal prediction part for predicting a luminance signal and a color difference signal prediction part for predicting a color difference signal. The luminance signal block and the color difference signal block are each divided independently in the case of an intra prediction, and is divided together in the case of an inter-prediction. The color difference signal prediction part can perform luminance / color difference intra-prediction for predicting the color difference signal from the decoded luminance signal, and inhibits use of the luminance / color difference intra-prediction in the case where a size of the luminance signal block is a predetermined size or larger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for dividing an image into blocks and performing encoding and decoding in units of the divided blocks.

Background Art

[0002] In image encoding and decoding, an image is divided into blocks, which are sets of a predetermined number of pixels, and encoding and decoding are performed in units of the blocks. By performing appropriate block division, the encoding efficiency of intra prediction (intra-frame prediction) and inter prediction (inter-frame prediction) is improved. Also, in intra prediction, the encoding efficiency is improved by predicting a secondary signal from the decoded image of a primary signal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when predicting a secondary signal from the decoded image of a primary signal, the processing amount increases, and a dependency relationship occurs between the processing for the primary signal and the processing for the secondary signal, making parallel processing difficult.

[0005] The present invention has been made in view of such a situation, and an object thereof is to provide a technique for improving encoding efficiency by performing block division suitable for image encoding and decoding.

Means for Solving the Problems

[0006] In order to solve the above problems, an image encoding apparatus according to an aspect of the present invention is an image encoding apparatus that divides an image into blocks and performs encoding in units of the divided blocks, and includes a luminance signal block dividing unit that divides the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a chrominance signal block dividing unit that divides the chrominance signal of the image into rectangles of a predetermined size to generate chrominance signal blocks, a luminance signal prediction unit that predicts a luminance signal, and a chrominance signal prediction unit that predicts a chrominance signal. The luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction and are divided together in the case of inter prediction. The chrominance signal prediction unit is capable of luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal, and when the size of the luminance signal block is equal to or larger than a predetermined size, the use of the luminance-chrominance intra prediction is prohibited.

[0007] Another aspect of the present invention is an image encoding method. This method is an image encoding method that divides an image into blocks and performs encoding in units of the divided blocks, and includes a luminance signal block dividing step of dividing the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a chrominance signal block dividing step of dividing the chrominance signal of the image into rectangles of a predetermined size to generate chrominance signal blocks, a luminance signal prediction step of predicting a luminance signal, and a chrominance signal prediction step of predicting a chrominance signal. The luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction and are divided together in the case of inter prediction. The chrominance signal prediction step is capable of luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal, and when the size of the luminance signal block is equal to or larger than a predetermined size, the use of the luminance-chrominance intra prediction is prohibited.

[0008] Yet another aspect of the present invention is an image decoding apparatus. This apparatus is an image decoding apparatus that performs decoding in units of blocks obtained by dividing an image. The apparatus includes a luminance signal block dividing unit that divides the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a chrominance signal block dividing unit that divides the chrominance signal of the image into rectangles of a predetermined size to generate chrominance signal blocks, a luminance signal predicting unit that predicts a luminance signal, and a chrominance signal predicting unit that predicts a chrominance signal. The luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction, and are divided together in the case of inter prediction. The chrominance signal predicting unit is capable of luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal, and when the size of the luminance signal block is equal to or larger than a predetermined size, use of the luminance-chrominance intra prediction is prohibited.

[0009] Yet another aspect of the present invention is an image decoding method. This method is an image decoding method that performs decoding in units of blocks obtained by dividing an image. The method includes a luminance signal block dividing step of dividing the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a chrominance signal block dividing step of dividing the chrominance signal of the image into rectangles of a predetermined size to generate chrominance signal blocks, a luminance signal predicting step of predicting a luminance signal, and a chrominance signal predicting step of predicting a chrominance signal. The luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction, and are divided together in the case of inter prediction. The chrominance signal predicting step is capable of luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal, and when the size of the luminance signal block is equal to or larger than a predetermined size, use of the luminance-chrominance intra prediction is prohibited.

[0010] Note that any combination of the above components, as well as those obtained by converting the expression of the present invention among a method, an apparatus, a system, a recording medium, a computer program, etc., are also effective as aspects of the present invention.

Advantages of the Invention

[0011] According to the present invention, block division suitable for image encoding and decoding becomes possible, improving the encoding efficiency and enabling image encoding and decoding with a small processing amount.

Brief Description of the Drawings

[0012]

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Embodiments for Carrying Out the Invention

[0013] Embodiments of the present invention provide an image encoding technique for dividing an image into rectangular blocks and encoding / decoding the divided blocks.

[0014] (First Embodiment) The image encoding device 100 and the image decoding device 200 according to Embodiment 1 of the present invention will be described.

[0015] FIG. 1 is a configuration diagram of an image encoding apparatus 100 according to the first embodiment. Here, FIG. 1 shows only the data flow related to the image signal. For additional information other than the image signal, such as motion vectors and prediction modes, each component supplies it to the encoded bit string generation unit 105 to generate corresponding encoded data, but the data flow related to the additional information is not shown.

[0016] The block division unit 101 divides the image into encoding target blocks that are the processing units for encoding, and supplies the image signal within the encoding target blocks to the residual signal generation unit 103. Further, the block division unit 101 supplies the image signal of the encoding target block to the predicted image generation unit 102 in order to evaluate the degree of match of the predicted image.

[0017] The block division unit 101 recursively divides the image into rectangles of a predetermined size to generate encoding target blocks. The block division unit 101 includes a four-division unit that divides the target block in the recursive division into four blocks by dividing it horizontally and vertically, and a two-division unit that divides the target block in the recursive division into two blocks by dividing it horizontally or vertically. The detailed operation of the block division unit 101 will be described later.

[0018] The prediction image generation unit 102 performs intra-picture prediction (intra prediction) or inter-picture prediction (inter prediction) based on the prediction mode on the decoded image signal supplied from the decoded image memory 108, and generates a prediction image signal. The image signal within the encoding target block supplied from the block division unit 101 is used for the evaluation of intra prediction and inter prediction. In intra prediction, a prediction image signal is generated using the image signal of the encoding target block supplied from the block division unit 101 and the image signals of the surrounding encoded blocks adjacent to the encoding target block existing in the same picture as the encoding target block supplied from the decoded image memory 108. In inter prediction, the image signal of the encoding target block supplied from the block division unit 101 is used with the encoded picture stored in the decoded image memory 108 that is before or after in the time series of the picture (encoded picture) including the encoding target block as the reference picture. Block matching degree evaluation such as block matching is performed between the encoded picture and the reference picture to obtain a motion vector indicating the amount of motion. Motion compensation is performed from the reference picture based on this amount of motion, and a prediction image signal is generated. The prediction image generation unit 102 supplies the prediction image signal thus generated to the residual signal generation unit 103.

[0019] The residual signal generation unit 103 subtracts the prediction signal generated by the prediction image generation unit 102 from the image signal to be encoded to generate a residual signal, and supplies it to the orthogonal transform / quantization unit 104.

[0020] The orthogonal transform / quantization unit 104 orthogonally transforms and quantizes the residual signal supplied from the residual signal generation unit 103, and supplies the orthogonally transformed and quantized residual signal to the encoded bit sequence generation unit 105 and the inverse quantization / inverse orthogonal transform unit 106.

[0021] The encoded bit sequence generation unit 105 generates an encoded bit sequence for the orthogonally transformed and quantized residual signal supplied from the orthogonal transform / quantization unit 104. Also, the encoded bit sequence generation unit 105 generates corresponding encoded bit sequences for additional information such as motion vectors, prediction modes, and block division information.

[0022] The inverse quantization and inverse orthogonal transformation unit 106 inverse quantizes and inverse orthogonally transforms the orthogonally transformed and quantized residual signal supplied from the orthogonal transformation and quantization unit 104, and supplies the inverse quantized and inverse orthogonally transformed residual signal to the decoded image signal superposition unit 107.

[0023] The decoded image signal superposition unit 107 superimposes the predicted image signal generated by the predicted image generation unit 102 and the residual signal inverse quantized and inverse orthogonally transformed by the inverse quantization and inverse orthogonal transformation unit 106 to generate a decoded image, and stores it in the decoded image memory 108. Note that filtering processing for reducing block distortion and the like due to encoding may be performed on the decoded image and then stored in the decoded image memory 108.

[0024] FIG. 2 is a configuration diagram of the image decoding apparatus 200 according to Embodiment 1. Here, FIG. 2 shows only the data flow related to the image signal. For additional information other than the image signal such as motion vectors and prediction modes, the bit string decoding unit 201 supplies it to each component for use in corresponding processing, but the data flow related to the additional information is not shown.

[0025] The bit string decoding unit 201 decodes the supplied encoded bit string and supplies the orthogonally transformed and quantized residual signal to the block division unit 202.

[0026] The block division unit 202 determines the shape of the block to be decoded based on the decoded block division information, and supplies the orthogonally transformed and quantized residual signal of the determined block to be decoded to the inverse quantization and inverse orthogonal transformation unit 203.

[0027] The block division unit 202 recursively divides the image into rectangles of a predetermined size based on the decoded block division information to generate blocks to be decoded. The block division unit 202 includes a four-division unit that divides the target block in the recursive division into four blocks by dividing it horizontally and vertically, and a two-division unit that divides the target block in the recursive division into two blocks by dividing it horizontally or vertically. The detailed operation of the block division unit 202 will be described later.

[0028] The inverse quantization and inverse orthogonal transformation unit 203 performs inverse orthogonal transformation and inverse quantization on the supplied orthogonal-transformed and quantized residual signal to obtain an inverse orthogonal-transformed and inverse-quantized residual signal.

[0029] The predicted image generation unit 204 generates a predicted image signal from the decoded image signal supplied from the decoded image memory 206 and supplies it to the decoded image signal superposition unit 205.

[0030] The decoded image signal superposition unit 205 generates a decoded image signal by superimposing the predicted image signal generated by the predicted image generation unit 204 and the residual signal that has been inverse orthogonal-transformed and inverse-quantized by the inverse quantization and inverse orthogonal transformation unit 203, outputs it, and stores it in the decoded image memory 206. Note that filtering processing for reducing block distortion and the like due to encoding may be performed on the decoded image and stored in the decoded image memory 206.

[0031] The operation of the block division unit 101 of the image encoding apparatus 100 will be described in detail. FIG. 3 is a flowchart for explaining the division into tree blocks and the division inside the tree blocks.

[0032] First, the input image is divided into tree blocks of a predetermined size (S1000). For example, the tree block is 128 pixels x 128 pixels. However, the tree block is not limited to 128 pixels x 128 pixels, and any size and shape may be used as long as it is rectangular. Also, the size and shape of the tree block may be set to a fixed value between the encoding apparatus and the decoding apparatus, or the encoding apparatus may determine it, record it in the encoded bitstream, and the decoding apparatus may use the recorded block size. The state of dividing the input image into tree blocks is shown in FIG. 4. The tree blocks are encoded and decoded in raster scan order, that is, from left to right and from top to bottom.

[0033] The interior of the tree block is further divided into rectangular blocks. The interior of the tree block is encoded and decoded in the z-scan order. Fig. 5 shows the order of the z-scan. In the z-scan, encoding and decoding are performed in the order of top left, top right, bottom left, and bottom right. The interior of the tree block can be divided into four parts or two parts. The four-way division is performed horizontally and vertically. The two-way division is performed horizontally or vertically. Fig. 6 is a diagram of the tree block divided into four parts horizontally and vertically. Fig. 7 is a diagram of the tree block divided into two parts horizontally. Fig. 8 is a diagram of the tree block divided into two parts vertically.

[0034] Referring to Fig. 3 again, it is determined whether to divide the interior of the tree block into four parts horizontally and vertically (S1001).

[0035] If it is determined that the interior of the tree block is to be divided into four parts (S1001: Yes), the interior of the tree block is divided into four parts (S1002), and each process of the blocks divided into four parts horizontally and vertically is performed (S1003). The re-division process of the divided blocks will be described later (Fig. 9).

[0036] If it is determined that the interior of the tree block is not to be divided into four parts (S1001: No), it is determined whether to divide the interior of the tree block into two parts (S1004).

[0037] If it is determined that the interior of the tree block is to be divided into two parts (S1004: Yes), it is determined whether the direction of the two-way division is the horizontal direction (S1005).

[0038] If it is determined that the direction of the two-way division is the horizontal direction (S1005: Yes), the interior of the tree block is divided into two parts horizontally (S1006), and each process of the blocks divided into two parts horizontally is performed (S1007). The re-division process of the blocks divided into two parts horizontally will be described later (Fig. 10).

[0039] When it is determined that the direction of the 2-way split is the vertical direction instead of the horizontal direction (S1005: No), the inside of the tree block is split into two in the vertical direction (S1008), and each process of the blocks split in the vertical direction is performed (S1009). The re-splitting process of the blocks split in the horizontal direction will be described later (Fig. 11).

[0040] When it is determined not to split the inside of the tree block (S1004: No), the block splitting process is terminated without splitting the inside of the tree block (S1010).

[0041] Subsequently, the processing of each of the divided blocks when the tree block is divided into four in the horizontal and vertical directions will be described using the flowchart of Fig. 9.

[0042] It is determined whether to split the inside of the block into four again in the horizontal and vertical directions (S1101).

[0043] When it is determined to split the inside of the block into four again (S1101: Yes), the inside of the block is split into four again (S1102), and each process of the blocks split in the horizontal and vertical directions is performed (S1103).

[0044] When it is determined not to split the inside of the block into four again (S1101: No), it is determined whether to split the inside of the block into two (S1104).

[0045] When it is determined to split the inside of the block into two (S1104: Yes), it is determined whether the direction of the 2-way split is the horizontal direction (S1105).

[0046] When it is determined that the direction of the 2-way split is the horizontal direction (S1105: Yes), the inside of the block is split into two in the horizontal direction (S1106), and each process of the blocks split in the horizontal direction is performed (S1107).

[0047] When it is determined that the direction of the 2-way split is the vertical direction instead of the horizontal direction (S1105: No), the inside of the block is split into two in the vertical direction (S1108), and each process for the block split into two in the vertical direction is performed (S1109).

[0048] When it is determined not to split the inside of the block (S1104: No), the block split process is terminated without splitting the inside of the block (S1110).

[0049] The process shown in the flowchart of FIG. 9 is executed for each of the blocks divided into four. The inside of the divided blocks is also encoded and decoded in the z-scan order.

[0050] Subsequently, the processing of each of the divided blocks when the tree block is split into two in the horizontal direction will be described using the flowchart of FIG. 10.

[0051] When the tree block is split into two in the horizontal direction, each of the two divided blocks first determines whether to divide the inside of the block into four in the horizontal and vertical directions (S1201).

[0052] When it is determined to divide the inside of the block into four (S1201: Yes), the inside of the block is divided into four (S1202), and each process for the block divided into four in the horizontal and vertical directions is performed (S1203).

[0053] When it is determined not to divide the inside of the block into four (S1201: No), it is determined whether to divide the inside of the block into two again (S1204).

[0054] When it is determined to divide into two again (S1204: Yes), the inside of the block is divided in the vertical direction (S1205), and each process for the block divided into two in the vertical direction is performed (S1206).

[0055] When it is determined not to divide into two again (S1204: No), the block split process is terminated without re-splitting the inside of the block (S1207).

[0056] Fig. 11 shows the state of re - division of the divided blocks when the tree block is divided into two in the horizontal direction. Here, when the tree block, which is the parent block, is divided into two in the horizontal direction, in the re - division of the divided blocks, only division into two in the vertical direction is allowed, and it is automatically divided into two in the vertical direction. Also, when the tree block, which is the parent block, is divided into two, it is also possible to completely prohibit four - division in the child blocks. As a result, it is possible to prohibit blocks from being divided in the same direction as the parent block, so that block division into a more horizontally elongated rectangle can be prevented, and the encoding / decoding process becomes easier.

[0057] The process shown in the flowchart of Fig. 10 is executed for each block divided into two in the horizontal direction. The inside of the divided block is also encoded and decoded in the order of top and bottom.

[0058] Subsequently, the processing of each divided block when the tree block is divided into two in the vertical direction will be described using the flowchart of Fig. 12.

[0059] When the tree block is divided into two in the vertical direction, each of the divided blocks first determines whether to divide the inside of the block into four in the horizontal and vertical directions (S1301).

[0060] If it is determined that the inside of the block is to be divided into four (S1301: Yes), the inside of the block is divided into four (S1302), and each process of the block divided into four in the horizontal and vertical directions is performed (S1303).

[0061] If it is determined that the inside of the block is not to be divided into four (S1301: No), it is determined whether to divide the inside of the block into two again (S1304).

[0062] If it is determined to divide into two again (S1304: Yes), the inside of the block is divided in the horizontal direction (S1305), and each process of the block divided into two in the horizontal direction is performed (S1306).

[0063] When it is determined not to perform the second division again (S1304: No), the block division process ends without further dividing the inside of the block (S1307).

[0064] Fig. 13 shows the state of re - division of the divided blocks when the tree block is divided vertically into two parts. Here, when the tree block, which is the parent block, is divided vertically into two parts, for the re - division of the divided blocks, only division in the horizontal direction is allowed and it is automatically divided horizontally. Also, when the tree block, which is the parent block, is divided into two parts, it is also possible to completely prohibit four - division in the child blocks. Thereby, since it is possible to prohibit the blocks from being divided in the same direction as the parent block, it is possible to prevent block division into a more vertically elongated rectangle, making the encoding / decoding process easier.

[0065] The process shown in the flowchart of Fig. 12 is executed for each block divided vertically into two parts. The inside of the divided block is also encoded and decoded in the order of left and right.

[0066] Although the re - division of the divided blocks when the tree block is divided has been described, the parent block does not have to be a tree block. For example, when a tree block (128x128) is divided into four parts and the divided blocks (64x64) are further divided into four parts or two parts, the above - mentioned process is also applied to the division of the re - divided blocks.

[0067] Next, the operation of the block division unit 202 of the image decoding apparatus 200 will be described. The block is divided in the same processing procedure as the block division unit 101 of the image encoding apparatus 100. However, in the block division unit 101 of the image encoding apparatus 100, the block division pattern is selected and the selected block division information is output, while the block division unit 202 of the image decoding apparatus divides the block using the block division information decoded from the encoded bit stream. Also, when decoding the block division information from the encoded bit stream, in a situation where re-division in the same direction is prohibited, the information with no options has a syntax structure that is not transmitted in the bit stream, which is different.

[0068] An example of the syntax (syntax rules of the encoded bit stream) regarding the block division of the first embodiment is shown in FIG. 14. For the division inside the tree block, first, a flag (4_division_flag) indicating whether to perform four-way division is transmitted and received. When performing four-way division (4_division_flag is 1), the tree block is divided into four parts and the process ends. Then, the inside of the block divided into four parts is re-divided again using the syntax shown in FIG. 14. When not performing four-way division (4_division_flag is 0), a flag (2_division_flag) indicating whether to perform two-way division is transmitted and received. When performing two-way division (2_division_flag is 1), a flag (2_division_direction) indicating the direction of two-way division is further transmitted and received. When 2_division_direction is 1, it indicates division in the vertical direction, and when 2_division_direction is 0, it indicates division in the horizontal direction. Then, the inside of the block divided into two parts is re-divided again using the syntax shown in FIG. 14. When not performing two-way division (2_division_flag is 0), the process ends without dividing the tree block.

[0069] Here, a process of re-dividing the inside of a 4-divided or 2-divided block will be described. The process of re-dividing the inside of the block also uses the syntax shown in FIG. 14, but it is different in that there is a limitation in the division direction in the case of 2-division compared to the case of dividing the tree block. That is, when the tree block is 2-divided, when re-dividing the inside of the 2-divided block, it is prohibited to divide in the same direction as the division direction of the 2-divided tree block. This can prevent the divided block from becoming a more elongated rectangle and prevent an increase in the memory bandwidth required for intra prediction and inter prediction. Details of preventing the increase in memory bandwidth will be described later.

[0070] Also, of course, it is possible to limit the division in the same direction when the number of 2-divisions in the same direction is counted and exceeds a predetermined number. For example, 2-divisions in the same direction are permitted up to 2 times, but 2-divisions in the same direction are prohibited from the 3rd time.

[0071] In FIG. 14, a syntax is adopted in which 4-division is preferentially selected and information on whether to perform 4-division is transmitted and received before information on whether to perform 2-division. On the other hand, when 2-division is preferentially selected, it is also possible to adopt a syntax in which information on whether to perform 2-division is transmitted and received before information on whether to perform 4-division. This is because transmitting and receiving the event that is more likely to occur probabilistically first results in a smaller amount of coded data transmitted as a bit stream. That is, it is also possible to adopt a syntax in which it is estimated in advance which of 4-division and 2-division is more likely to occur and the more likely division information is transmitted and received first. For example, by transmitting and receiving whether 4-division or 2-division is prioritized in the header information of the image, the encoding device can adaptively determine the priority division number with high encoding efficiency, and the decoding device can divide the inside of the tree block using the syntax based on the selected priority division number.

[0072] In the image encoding device 100 and the image decoding device 200, intra prediction and inter prediction are performed using the divided blocks. Both intra prediction and inter prediction involve copying pixels from memory.

[0073] Examples of intra prediction are shown in FIGS. 15(a) to 15(d). FIGS. 15(a) and 15(b) show the prediction direction and mode number of intra prediction. As shown in FIGS. 15(c) and 15(d), intra prediction generates a predicted image of an encoding / decoding target block by copying pixels from encoded / decoded pixels adjacent to the encoding / decoding target block. In intra prediction, since the generation of the predicted image and the generation of encoded / decoded pixels are repeated in units of blocks, the processing order is sequential in units of blocks, and the smaller the block is divided internally, the greater the overall processing load becomes. Also, the greater the aspect ratio of the block shape, the greater the pixel copy processing from memory. Also, since orthogonal transformation of the residual signal is performed for encoding / decoding, the greater the variety of rectangle sizes, the greater the variety of orthogonal transformations required, resulting in an increase in circuit scale. Therefore, when dividing a block into two parts, by restricting the division into two parts in the same direction as the division method of the parent block, an increase in the memory bandwidth required for intra prediction can be prevented.

[0074] An example of inter prediction is shown in FIG. 16. Inter prediction generates a predicted image of an encoding / decoding target block by copying pixels in units of blocks from the pixels included in the encoded / decoded image. In inter prediction, when copying pixels in units of blocks from the reference image, the configuration of the device often requires acquisition in units of memory management units that contain the necessary pixels. Therefore, the smaller the block is divided, and the greater the aspect ratio of the block shape, the greater the overall processing load becomes. Also, when performing fractional-precision motion compensation using an interpolation filter on the reference image, copying of pixels obtained by adding several pixels to the pixels included in the block is required, and the smaller the block size, the greater the relative ratio of the additional pixels, resulting in an increase in the overall processing load. Therefore, when dividing a block into two parts, by restricting the division into two parts in the same direction as the division direction of the parent block, an increase in the memory bandwidth required for inter prediction can be prevented.

[0075] Next, the relationship between the luminance signal and the color difference signal in intra prediction will be described. As formats between the luminance signal and the color difference signal, 4:2:0, 4:2:2, 4:4:4, etc. have been conventionally known. In the 4:2:0 format shown in Fig. 17(a), the luminance signal is sampled at 2 pixels both horizontally and vertically, while the color difference signal is sampled at 1 pixel both horizontally and vertically. Since the human eye can perceive the luminance signal more sensitively than the color difference signal, the amount of information of the color difference signal is reduced compared to the luminance signal. In the 4:2:2 format shown in Fig. 17(b), the luminance signal is sampled at 2 pixels horizontally, while the color difference signal is sampled at 1 pixel horizontally. For the vertical direction, the luminance signal is sampled at 2 pixels vertically, while the color difference signal is sampled at 2 pixels vertically. In the 4:4:4 format shown in Fig. 17(c), the luminance signal is sampled at 2 pixels both horizontally and vertically, while the color difference signal is sampled at 2 pixels both horizontally and vertically.

[0076] This embodiment will be described by taking the 4:2:0 format most widely used in image coding as an example. The block division units 101 and 202 include a luminance block division unit that divides the luminance signal of the image to generate a luminance block, and a color difference block division unit that divides the color difference signal of the image to generate a color difference block. In intra prediction, the luminance signal and the color difference signal are independently block-divided. That is, in intra prediction, the sizes of the luminance block and the color difference block are independently determined. In intra prediction, since each of the luminance signal and the color difference signal copies the pixel value from the surrounding pixels, the prediction efficiency is increased by independently block-dividing the luminance signal and the color difference signal. On the other hand, for inter prediction, the luminance signal and the color difference signal are handled together for block division. That is, in inter prediction, the sizes of the luminance block and the color difference block are the same. This is because there is no need to distinguish between luminance and color difference in motion compensation in inter prediction.

[0077] The prediction image generation units 102 and 204 include a luminance signal prediction unit that predicts a luminance signal and a color difference signal prediction unit that predicts a color difference signal. The color difference signal prediction unit performs luminance-chrominance intra prediction for predicting a color difference signal from the encoded / decoded pixels of the luminance signal in order to improve the prediction efficiency of the color difference signal in intra prediction. In luminance-chrominance intra prediction, the primary signal is encoded / decoded before the secondary signal, and the secondary signal is predicted using the encoded / decoded primary signal. Here, in the 4:2:0 format or 4:2:2 format, since the amount of information of the luminance signal is larger than that of the color difference signal, the luminance signal is used as the primary signal and the color difference signal is used as the secondary signal. In the 4:4:4 format, although the amount of information of the luminance signal and the color difference signal is the same, it is common to use the luminance signal as the primary signal and the color difference signal as the secondary signal in accordance with other formats.

[0078] FIG. 18 is a diagram for explaining luminance-chrominance intra prediction, and FIG. 19 is a flowchart for explaining luminance-chrominance intra prediction.

[0079] As shown in FIG. 18, luminance-chrominance intra prediction is performed based on the degree of correlation between the encoded / decoded peripheral pixels 12a and 12b of the luminance block 10 and the encoded / decoded peripheral pixels 16a and 16b of the color difference block 14. Since luminance-chrominance intra prediction is for predicting a color difference signal, the peripheral pixels for calculating the degree of correlation are defined based on the peripheral pixels of the color difference block to be encoded / decoded. That is, the peripheral pixels of the luminance block at the same position as the peripheral pixels determined for the color difference block are the targets for calculating the degree of correlation.

[0080] First, calculate the degree of correlation between the peripheral pixels of the encoded / decoded luminance signal and the peripheral pixels of the chrominance signal (S1901). Subsequently, downsample the encoded / decoded luminance signal of the block to be encoded / decoded (S1902). Here, a plurality of filter types for downsampling may be prepared so that the filter type can be selected. For example, filters with different intensities may be prepared to select a plurality of filter types, or filters with different numbers of taps may be prepared to select a plurality of filter types. The filter type may be automatically selected using the degree of correlation between the peripheral pixels, or the filter type may be encoded / decoded and transmitted in the bitstream. Also, if the downsampling filter for the luminance signal of the block to be encoded / decoded is not determined using the degree of correlation between the peripheral pixels, the processing of step S1901 and step S1902 may be in any order, and step S1901 and step S1902 can be processed in parallel.

[0081] Finally, based on the degree of correlation between the peripheral pixels, predict the chrominance signal from the downsampled luminance signal (S1903). For downsampling, in the case of the 4:2:0 format, it is 1 / 2 in the horizontal / vertical directions. In the case of the 4:2:2 format, it is 1 / 2 in the horizontal direction and no downsampling is performed in the vertical direction. In the case of the 4:4:4 format, no downsampling is performed in both the horizontal / vertical directions.

[0082] In luminance-chrominance intra prediction, after the encoding / decoding of the luminance signal of the block to be encoded / decoded is completed, the prediction process of the chrominance signal can be started. Therefore, the timing at which the prediction process of the chrominance block can be started depends on the size of the luminance block and the size of the chrominance block.

[0083] FIGS. 20(a) and 20(b) are diagrams for explaining luminance-chrominance intra prediction when the size of the chrominance block is larger than the size of the luminance block. The number of pixels of the first to fourth luminance blocks 20a, 20b, 20c, 20d divided into four shown in FIG. 20(a) is 16x16, and the number of pixels of the chrominance block 20e shown in FIG. 20(b) is 16x16.

[0084] Here, the comparison of the sizes of the luminance block and the chrominance difference block is a comparison of the areas considering the chrominance difference format, rather than a comparison of the number of pixels within the block. That is, in the 4:2:0 format, since the area occupied by the luminance block is 1 / 2 of the area occupied by the chrominance difference block, when the number of pixels of the luminance block is 16x16 and the number of pixels of the chrominance difference block is 16x16, the size of the luminance block is smaller. In the 4:2:0 format, when the number of pixels of the luminance block is 16x16 and the number of pixels of the chrominance difference block is 8x8, the areas occupied by both blocks are the same, and the luminance block and the chrominance difference block are of the same size.

[0085] To compare the sizes of the luminance block and the chrominance difference block by comparing the number of pixels within the block rather than the area of the block, the number of pixels of the chrominance difference block can be converted to the number of pixels of the luminance block according to the ratio of the luminance signal to the chrominance difference signal in the chrominance difference format. In the case of the 4:2:0 format, since the number of pixels of the luminance signal is twice the number of pixels of the chrominance difference signal, the number of pixels in the vertical and horizontal directions of the chrominance difference block is doubled to convert it to the number of pixels in the vertical and horizontal directions of the luminance block. For example, in the 4:2:0 format, when the size of the luminance block is 16x16 and the size of the chrominance difference block is 16x16, the converted size of the chrominance difference block converted to the number of pixels of the luminance block is 32x32, indicating that the size of the chrominance difference block is larger.

[0086] Intra prediction enables the prediction processing of subsequent blocks after the decoding process of each block is completed. That is, after the decoding of the first luminance block 20a is completed, the decoding of the second luminance block 20b becomes possible; after the decoding of the second luminance block 20b is completed, the decoding of the third luminance block 20c becomes possible; after the decoding of the third luminance block 20c is completed, the decoding of the fourth luminance block 20d becomes possible.

[0087] When the size of the chrominance block is larger than the size of the luminance block, the peripheral pixels required for the prediction process of the chrominance block 20e exist before the decoding of the four luminance blocks 20a, 20b, 20c, and 20d for both the luminance pixels and the chrominance pixels. Without waiting for the decoding of the four luminance blocks 20a, 20b, 20c, and 20d, it is possible to calculate the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signal in step S1901 of FIG. 19.

[0088] Next, after the decoding of the first luminance block 20a is completed, downsampling of the luminance signal in step S1902 of FIG. 19 is performed. Without waiting for the decoding of the second luminance block 20b to be completed, the pixels of the chrominance block 20e corresponding to the position of the first luminance block 20a can be predicted. Similarly, after the decoding of the second luminance block 20b is completed, downsampling of the luminance signal is performed, and without waiting for the decoding of the third luminance block 20c to be completed, the pixels of the chrominance block 20e corresponding to the position of the second luminance block 20b are predicted. Further, after the decoding of the third luminance block 20c is completed, downsampling of the luminance signal is performed, and without waiting for the decoding of the fourth luminance block 20d to be completed, the pixels of the chrominance block 20e corresponding to the position of the third luminance block 20c are predicted. Finally, after the decoding of the fourth luminance block 20d is completed, downsampling of the luminance signal is performed, and the pixels of the chrominance block 20e corresponding to the position of the fourth luminance block 20d are predicted.

[0089] FIGS. 21(a) and 21(b) are diagrams for explaining the luminance-chrominance intra prediction when the size of the chrominance block is smaller than the size of the luminance block. The number of pixels of the luminance block 21a shown in FIG. 21(a) is 16x16, and the number of pixels of the first to fourth divided chrominance blocks 21b, 21c, 21d, and 21e shown in FIG. 21(b) is 4x4.

[0090] In the 4:2:0 format, since the area occupied by the luminance block is half of the area occupied by the chrominance block, when the number of pixels in the luminance block is 16x16 and the number of pixels in the chrominance block is 4x4, the size of the chrominance block is smaller. To compare the sizes of the luminance block and the chrominance block by comparing the number of pixels in the blocks rather than the area of the blocks, in the case of the 4:2:0 format, the number of pixels in the vertical and horizontal directions of the chrominance block is doubled and converted to the number of pixels in the vertical and horizontal directions of the luminance block. In the 4:2:0 format, when the size of the luminance block is 16x16 and the size of the chrominance block is 4x4, the converted size of the chrominance block converted to the number of pixels in the luminance block is 8x8, and it can be seen that the size of the chrominance block is smaller.

[0091] When the size of the chrominance block is smaller than the size of the luminance block, the peripheral pixels of the first chrominance block 21b can be used from before the decoding of the luminance block 21a for both luminance pixels and chrominance pixels, but the peripheral pixels of the second to fourth chrominance blocks 21c, 21d, 21e cannot be used until the decoding of the luminance block 21a is completed. That is, if the decoding of the luminance block 21a is completed and the decoding of the first chrominance block 21b is not completed, the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signal in step S1901 of FIG. 19 cannot be calculated for the second chrominance block 21c. Similarly, for the third chrominance block 21d, if the decoding of the luminance block 21a is completed and the decoding of the first and second chrominance blocks 21b, 21c is not completed, the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signal cannot be calculated for the third chrominance block 21d. Similarly, for the fourth chrominance block 21e, if the decoding of the luminance block 21a is completed and the decoding of the first to third chrominance blocks 21b, 21c, 21d is not completed, the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signal cannot be calculated for the fourth chrominance block 21e.

[0092] As described above, when the size of the color difference block is smaller than the size of the luminance block, if luminance color difference intra prediction is performed, there is a processing dependency between the luminance block and the color difference blocks and between the color difference blocks in the prediction processing of the color difference block, which is not suitable for parallel processing. Therefore, when the size of the color difference block is smaller than the size of the luminance block, luminance color difference intra prediction is restricted. As methods for restricting luminance color difference intra prediction, there are (1) restricting by syntax, (2) replacing the intra color difference mode, (3) replacing the surrounding pixels, and the like.

[0093] Fig. 22 shows an example of the syntax of the intra color difference prediction mode. When the number of the color difference prediction mode is 0, the same intra prediction mode as the luminance prediction mode is used for the color difference prediction mode. For example, when the luminance prediction mode is the horizontal prediction mode, the color difference prediction mode is also the horizontal prediction mode. When the number of the color difference prediction mode is 1, the average value mode (DC mode) is used. The DC mode performs intra prediction using the average value of the surrounding pixels. When the number of the color difference prediction mode is 2, the luminance color difference intra prediction mode is used.

[0094] As a method for restricting luminance color difference intra prediction, when restricting by syntax, mode 2 is prohibited from being used to represent luminance color difference intra prediction. That is, mode 2 is not transmitted, and the intra color difference mode is selected from mode 0 and mode 1.

[0095] As a method for restricting luminance color difference intra prediction, when replacing the intra color difference mode, when the number of the color difference prediction mode is specified as mode 2, instead of the luminance color difference intra prediction mode, the vertical prediction mode is used. However, the prediction mode to be replaced is not limited to the vertical prediction mode, and other prediction modes may also be used. Also, it is more preferable that the luminance prediction mode of mode 0 and the mode to be replaced by mode 2 are the same and there is no overlap in the modes to be used.

[0096] As a method for restricting the luminance chrominance intra prediction, when replacing the peripheral pixels in (3), replace the peripheral pixels for calculating the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signal in step S1901 of FIG. 19. In the second to fourth chrominance blocks 21c, 21d, and 21e of FIG. 21, the degree of correlation of the peripheral pixels can be calculated without waiting for the decoding of the luminance block 21a.

[0097] An example of replacing the peripheral pixels is shown in FIG. 23. Normally, the pixels in the first chrominance block 21b are used as the peripheral pixels on the left side of the second chrominance block 21c. However, in order to use the pixels in the first chrominance block 21b, it is necessary to wait for the completion of decoding of the luminance block 21a and the first chrominance block 21b. Therefore, the available area 21f that can be used without waiting for the completion of decoding of the luminance block 21a is used as the peripheral pixels of the second chrominance block 21c. Similarly, for the third chrominance block 21d, the available area 21f that can be used without waiting for the completion of decoding of the luminance block 21a is used as the peripheral pixels of the third chrominance block 21d. Similarly, for the fourth chrominance block 21e, the available area 21f that can be used without waiting for the completion of decoding of the luminance block 21a is used as the peripheral pixels of the fourth chrominance block 21e.

[0098] As described above, in the first embodiment, when performing the luminance chrominance intra prediction, when the size of the chrominance block is smaller than the size of the luminance block, by restricting the luminance chrominance intra prediction, it becomes possible to relax the processing dependency relationship between the luminance block and the chrominance block. As a result, parallel processing of the luminance block and the chrominance block becomes possible, and the amount of encoding / decoding processing can be reduced.

[0099] (Second Embodiment) The second embodiment of the present invention will be described. In the second embodiment, unlike the first embodiment where the luminance chrominance intra prediction is restricted by independently evaluating the sizes of the luminance block and the chrominance block instead of the size relationship between the luminance block and the chrominance block, the other configurations and operations are the same as those in the first embodiment.

[0100] First, the restrictions based on the size of the luminance block will be described. FIGS. 24(a) to 24(c) show the luminance chrominance intra prediction according to the difference in the size of the luminance block. As shown in FIGS. 24(a) and 24(b), the first luminance block 24a corresponds to the position of the first chrominance block 24e, the second luminance block 24b corresponds to the position of the second chrominance block 24f, the third luminance block 24c corresponds to the position of the third chrominance block 24g, and the fourth luminance block 24d corresponds to the position of the fourth chrominance block 24h. Also, the luminance block 24i in FIG. 24(c) corresponds to the positions of the first to fourth chrominance blocks 24e, 24f, 24g, and 24h in FIG. 24(b).

[0101] The dependency between the luminance block and the chrominance block will be described. When the size of the luminance block is small as shown in FIG. 24(a), when the decoding of the first luminance block 24a is completed, the decoding of the first chrominance block 24e becomes possible. When the decoding of the second luminance block 24b is completed, the decoding of the second chrominance block 24f becomes possible. When the decoding of the third luminance block 24c is completed, the decoding of the third chrominance block 24g becomes possible. When the decoding of the fourth luminance block 24d is completed, the decoding of the fourth chrominance block 24h becomes possible.

[0102] On the other hand, when the size of the luminance block is large as shown in FIG. 24(c), the decoding of the first to fourth chrominance blocks 24e, 24f, 24g, and 24h cannot all be made possible unless the decoding of the luminance block 24i is completed.

[0103] When the division of the luminance block and the division of the chrominance block are determined independently, if the absolute size of the luminance block is large, the possibility that the size of the chrominance block becomes smaller than the size of the luminance block increases. Therefore, when the absolute size of the luminance block is equal to or greater than a predetermined size, the luminance chrominance intra prediction of the corresponding chrominance block is restricted.

[0104] Similarly, if the absolute size of the chrominance block is small, the possibility that the size of the chrominance block becomes smaller than the size of the luminance block increases. Therefore, when the absolute size of the chrominance block is equal to or less than a predetermined size, the luminance chrominance intra prediction of the chrominance block is restricted.

[0105] The method for restricting the luminance chrominance intra prediction is the same as that of the first embodiment.

[0106] As described above, in the second embodiment, when the absolute size of the luminance block is larger than the threshold value, or when the absolute size of the chrominance block is smaller than the threshold value, the luminance chrominance intra prediction is restricted. As a result, it is possible to predict the case where the size of the chrominance block becomes smaller than the size of the luminance block, restrict the luminance chrominance intra prediction, and probabilistically relax the processing dependency between the luminance block and the chrominance block.

[0107] (Third Embodiment) The third embodiment of the present invention will be described. In the third embodiment, in the block division unit 101, unlike the first embodiment, when dividing the chrominance block, the chrominance block is divided so that the size of the chrominance block does not become smaller than the size of the luminance block. Other configurations and operations are the same as those of the first embodiment. When dividing the chrominance block, the block division unit 101 prohibits division such that the size of the chrominance block becomes less than the size of the luminance block. As a result, in the luminance chrominance intra prediction, it is possible to avoid the size of the chrominance block becoming smaller than the size of the luminance block, and parallel processing of the luminance block and the chrominance block is always possible.

[0108] The encoded bitstream of the image output by the image encoding device according to the above-described embodiment has a specific data format so that it can be decoded according to the encoding method used in the embodiment, and an image decoding device corresponding to the image encoding device can decode the encoded bitstream of this specific data format.

[0109] When a wired or wireless network is used to exchange the encoded bitstream between the image encoding device and the image decoding device, the encoded bitstream may be converted into a data format suitable for the transmission format of the communication path and then transmitted. In that case, a transmission device that converts the encoded bitstream output by the image encoding device into encoded data in a data format suitable for the transmission format of the communication path and transmits it to the network, and a receiving device that receives the encoded data from the network, restores it to the encoded bitstream, and supplies it to the image decoding device are provided.

[0110] The transmission device includes a memory that buffers the encoded bitstream output by the image encoding device, a packet processing unit that packetizes the encoded bitstream, and a transmission unit that transmits the packetized encoded data via the network. The receiving device includes a receiving unit that receives the packetized encoded data via the network, a memory that buffers the received encoded data, and a packet processing unit that performs packet processing on the encoded data to generate an encoded bitstream and provides it to the image decoding device.

[0111] Also, it is possible to use it as a display device by adding a display unit that displays the image decoded by the image decoding device to the configuration. In that case, the display unit reads out the decoded image signal generated by the decoded image signal superimposing unit 205 and stored in the decoded image memory 206 and displays it on the screen.

[0112] Also, it is possible to use it as an imaging device by adding an imaging unit to the configuration and inputting the captured image to the image encoding device. In that case, the imaging unit inputs the captured image signal to the block division unit 101.

[0113] The above-described processes related to encoding and decoding can be realized not only as a transmission, storage, and reception device using hardware, but also by firmware stored in a ROM (Read Only Memory), flash memory, etc., or by software such as that of a computer. It is also possible to record the firmware program and software program on a computer-readable recording medium and provide it, provide it from a server through a wired or wireless network, or provide it as data broadcasting of terrestrial or satellite digital broadcasting.

[0114] As described above, the present invention has been described based on the embodiments. It is understood by those skilled in the art that the embodiments are examples, and various modifications are possible for each combination of their respective components and each processing process, and such modifications are also within the scope of the present invention.

Explanation of Signs

[0115] 100 Image Encoding Device, 101 Block Division Unit, 102 Predicted Image Generation Unit, 103 Residual Signal Generation Unit, 104 Orthogonal Transformation / Quantization Unit, 105 Encoded Bit Sequence Generation Unit, 106 Inverse Quantization / Inverse Orthogonal Transformation Unit, 107 Decoded Image Signal Superposition Unit, 108 Decoded Image Memory, 200 Image Decoding Device, 201 Bit Sequence Decoding Unit, 202 Block Division Unit, 203 Inverse Quantization / Inverse Orthogonal Transformation Unit, 204 Predicted Image Generation Unit, 205 Decoded Image Signal Superposition Unit, 206 Decoded Image Memory.

Claims

1. An image encoding apparatus that divides an image into blocks, encodes the divided blocks, and generates a bit stream, comprising: a luminance signal block dividing unit that divides a luminance signal of an image into rectangles to generate luminance signal blocks; a chrominance signal block dividing unit that divides a chrominance signal of an image into rectangles to generate chrominance signal blocks; a luminance signal predicting unit that predicts a luminance signal; a chrominance signal predicting unit that predicts a chrominance signal, wherein the chrominance signal predicting unit is capable of luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal; wherein the luminance signal block dividing unit recursively divides the luminance signal of the image into four in the horizontal and vertical directions or recursively divides it into two in the horizontal or vertical direction; wherein the chrominance signal block dividing unit recursively divides the chrominance signal of the image into four in the horizontal and vertical directions or recursively divides it into two in the horizontal or vertical direction; wherein the luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction, and when the size of the luminance signal block is equal to or greater than a predetermined size, the luminance-chrominance intra prediction is prohibited; wherein the luminance signal blocks and the chrominance signal blocks are divided into blocks of the same size in the case of inter prediction; An image encoding apparatus characterized by the above.

2. An image encoding method that divides an image into blocks, encodes the divided blocks, and generates a bit stream, comprising: a luminance signal block dividing step of dividing a luminance signal of an image into rectangles to generate luminance signal blocks; a chrominance signal block dividing step of dividing a chrominance signal of an image into rectangles to generate chrominance signal blocks; a luminance signal predicting step of predicting a luminance signal; a chrominance signal predicting step of predicting a chrominance signal, wherein in the chrominance signal predicting step, luminance-chrominance intra prediction that predicts a chrominance signal from a decoded luminance signal is possible; wherein the luminance signal of the image is recursively divided into four in the horizontal and vertical directions or recursively divided into two in the horizontal or vertical direction; wherein the chrominance signal of the image is recursively divided into four in the horizontal and vertical directions or recursively divided into two in the horizontal or vertical direction; wherein the luminance signal blocks and the chrominance signal blocks are independently divided in the case of intra prediction, and when the size of the luminance signal block is equal to or greater than a predetermined size, the luminance-chrominance intra prediction is prohibited; When performing inter prediction, the luminance signal block and the chrominance signal block are divided into blocks of the same size. An image encoding method characterized by this. [

3. ] An image decoding apparatus that decodes an image in units of divided blocks, A luminance signal block dividing unit that divides the luminance signal of the image into a rectangle to generate a luminance signal block, A chrominance signal block dividing unit that divides the chrominance signal of the image into a rectangle to generate a chrominance signal block, A luminance signal prediction unit that predicts a luminance signal, A chrominance signal prediction unit that predicts a chrominance signal, The chrominance signal prediction unit is capable of luminance-chrominance intra prediction that predicts a chrominance signal from the decoded luminance signal, The luminance signal block dividing unit recursively divides the luminance signal of the image into four in the horizontal and vertical directions or recursively divides it into two in the horizontal or vertical direction, The chrominance signal block dividing unit recursively divides the chrominance signal of the image into four in the horizontal and vertical directions or recursively divides it into two in the horizontal or vertical direction, In the case of intra prediction, the luminance signal block and the chrominance signal block are divided independently. When the size of the luminance signal block is equal to or greater than a predetermined size, the luminance-chrominance intra prediction is prohibited. When performing inter prediction, the luminance signal block and the chrominance signal block are divided into blocks of the same size. An image decoding apparatus characterized by this. [

4. ] An image decoding method that decodes an image in units of divided blocks, A luminance signal block dividing step of dividing the luminance signal of the image into a rectangle to generate a luminance signal block, A chrominance signal block dividing step of dividing the chrominance signal of the image into a rectangle to generate a chrominance signal block, A luminance signal prediction step of predicting a luminance signal, A chrominance signal prediction step of predicting a chrominance signal, In the chrominance signal prediction step, luminance-chrominance intra prediction that predicts a chrominance signal from the decoded luminance signal is possible, The luminance signal of the image is recursively divided into four in the horizontal and vertical directions or recursively divided into two in the horizontal or vertical direction, The chrominance signal of the image is recursively divided into four in the horizontal and vertical directions or recursively divided into two in the horizontal or vertical direction, In the case of intra prediction, the luminance signal block and the chrominance signal block are divided independently. When the size of the luminance signal block is equal to or greater than a predetermined size, the luminance-chrominance intra prediction is prohibited. The luminance signal block and the chrominance signal block are divided into blocks of the same size in the case of inter prediction. An image decoding method characterized by this. Claim 5 A storage method for storing a bitstream generated according to the image encoding method described in claim 2 in a recording medium. Claim 6 A transmission method for transmitting a bitstream generated according to the image encoding method described in claim 2.

Images