JP2023101760A - Image encoding device, image encoding method, image encoding program, image decoding device, image decoding method and image decoding program - Google Patents

Abstract

To provide an image encoding device which improves encoding efficiency by performing block division suitable for image encoding and image decoding.SOLUTION: An image encoding device 100 which divides an image into blocks and performs encoding on a divided block basis comprises: a luminance signal block dividing unit for generating 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 for generating a color difference signal block by dividing a color difference signal of an image into rectangles in a predetermined size; and a prediction image generating unit including a luminance signal predicting section for predicting a luminance signal and a color difference signal predicting section for predicting a color difference signal. The luminance signal block and the color difference signal block are each independently divided in the case of intra-prediction and divided together in the case of inter-prediction. The color difference signal predicting section is capable of performing luminance/color difference intra-prediction, in which the color difference signal is predicted from the decoded luminance signal, and in a case where a size of the luminance signal block is equal to or larger than the predetermined size, use of the luminance/color difference intra-prediction is inhibited.SELECTED DRAWING: Figure 1

Description

The present invention relates to a technique of dividing an image into blocks and performing encoding and decoding on a block-by-block basis.

In image coding and decoding, an image is divided into blocks, each of which is a set of a predetermined number of pixels, and the blocks are coded and decoded. Appropriate block division improves the coding efficiency of intra-prediction and inter-prediction. Also, in intra prediction, encoding efficiency is improved by predicting the secondary signal from the decoded image of the primary signal.

JP 2013-90015 A

However, when the secondary signal is predicted from the decoded image of the primary signal, the amount of processing increases and the dependency relationship between the processing for the primary signal and the processing for the secondary signal occurs, making parallel processing difficult.

The present invention has been made in view of such circumstances, and its object is to provide a technique for improving coding efficiency by performing block division suitable for image coding and decoding.

In order to solve the above-described problems, an image coding apparatus according to one aspect of the present invention is an image coding apparatus that divides an image into blocks and performs coding in units of divided blocks, the image coding apparatus comprising: a luminance signal block division unit that divides a luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks; a color difference signal block division unit that divides the color difference signals of the image into rectangles of a predetermined size to generate color difference signal blocks; a luminance signal prediction unit that predicts the luminance signal; , the luminance signal block and the chrominance signal block are divided independently in the case of intra prediction, and divided together in the case of inter prediction, the chrominance signal prediction unit is capable of luminance chrominance intra prediction for predicting the chrominance signal from the decoded luminance signal, and prohibits the use of the luminance chrominance intra prediction when the size of the luminance signal block is equal to or larger than a predetermined size.

Another aspect of the present invention is an image coding method. This method is an image coding method for dividing an image into blocks and performing coding in units of divided blocks, comprising: a luminance signal block division step of dividing a luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks; a chrominance signal block division step of dividing the chrominance signals of the image into rectangles of a predetermined size to generate chrominance signal blocks; a luminance signal prediction step of predicting the luminance signal; In the case of tiger prediction, they are divided independently, and in the case of inter prediction, they are divided together, and the chrominance signal prediction step is capable of luminance chrominance intra prediction that predicts the chrominance signal from the decoded luminance signal, and if 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.

Yet another aspect of the present invention is an image decoding device. This apparatus is an image decoding apparatus that performs decoding in block units obtained by dividing an image, and includes a luminance signal block division unit that divides the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a color difference signal block division unit that divides the color difference signals of the image into rectangles of a predetermined size to generate color difference signal blocks, a luminance signal prediction unit that predicts the luminance signal, and a color difference signal prediction unit that predicts the color difference signals. It is divided independently, and in the case of inter prediction, it is divided together, the chrominance signal prediction unit is capable of luminance chrominance intra prediction for predicting the chrominance signal from the decoded luminance signal, and prohibits the use of the luminance chrominance intra prediction when the size of the luminance signal block is equal to or larger than a predetermined size.

Yet another aspect of the present invention is an image decoding method. This method is an image decoding method in which decoding is performed in block units obtained by dividing an image, and includes a luminance signal block division step of dividing a luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks, a chrominance signal block division step of dividing the chrominance signals of the image into rectangles of a predetermined size to generate chrominance signal blocks, a luminance signal prediction step of predicting the luminance signal, and a chrominance signal prediction step of predicting the chrominance signals. Separated independently and jointly in the case of inter prediction, the chrominance signal prediction step is capable of luminance chrominance intra prediction for predicting a chrominance signal from a decoded luminance signal, and prohibiting the use of the luminance chrominance intra prediction when the size of the luminance signal block is equal to or greater than a predetermined size.

Any combination of the above constituent elements, and conversion of expressions of the present invention into methods, devices, systems, recording media, computer programs, etc. are also effective as aspects of the present invention.

According to the present invention, block division suitable for image encoding and decoding becomes possible, encoding efficiency is improved, and image encoding and decoding with a small amount of processing can be provided.

1 is a configuration diagram of an image encoding device according to a first embodiment; FIG. 1 is a configuration diagram of an image decoding device according to a first embodiment; FIG. Fig. 4 is a flow chart illustrating splitting into treeblocks and splitting inside treeblocks; FIG. 4 is a diagram showing how an input image is divided into treeblocks; FIG. 4 is a diagram for explaining z-scan; It is the figure which divided the treeblock into four horizontally and vertically. It is the figure which divided the treeblock into two in the horizontal direction. It is the figure which divided the treeblock into two in the vertical direction. FIG. 10 is a flowchart for explaining the processing of each divided block when the treeblock is divided into four in the horizontal direction and the vertical direction; FIG. FIG. 10 is a flowchart for explaining processing of each divided block when a treeblock is horizontally divided into two; FIG. FIG. 10 is a diagram showing how a divided block is re-divided when a treeblock is horizontally divided into two. FIG. 10 is a flowchart for explaining processing of each divided block when a treeblock is vertically divided into two; FIG. FIG. 10 is a diagram showing how a divided block is re-divided when a treeblock is vertically divided into two; FIG. 4 is a diagram showing an example of syntax regarding block division according to the first embodiment; FIG. It is a figure explaining intra prediction. It is a figure explaining inter prediction. FIG. 4 is a diagram for explaining a color difference format; It is a figure explaining luma-chrominance intra prediction. 10 is a flow chart illustrating luma-chrominance intra prediction; FIG. 4 is a diagram illustrating a case where the size of a chrominance block is larger than the size of a luminance block; FIG. 4 is a diagram illustrating a case where the size of a chrominance block is smaller than the size of a luminance block; FIG. 10 is a diagram illustrating an example of syntax of intra color difference prediction mode; FIG. 10 is a diagram illustrating an example of limiting intra color difference prediction by replacing peripheral pixels; FIG. 10 is a diagram illustrating luminance/chrominance intra prediction based on a difference in luminance block size;

Embodiments of the present invention provide an image coding technique that divides an image into rectangular blocks and encodes/decodes the divided blocks.

(First embodiment)
An image encoding device 100 and an image decoding device 200 according to Embodiment 1 of the present invention will be described.

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

The block division unit 101 divides an image into blocks to be encoded, which are processing units for encoding, and supplies image signals in the blocks to be encoded to the residual signal generation unit 103 . In addition, the block dividing 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 matching of the predicted images.

A block division unit 101 recursively divides an image into rectangles of a predetermined size to generate encoding target blocks. The block dividing unit 101 includes a 4-dividing unit that horizontally and vertically divides the target block in the recursive division into 4 blocks to generate 4 blocks, and a 2-dividing unit that generates 2 blocks by horizontally or vertically dividing the target block in the recursive division into 2 blocks. A detailed operation of the block dividing unit 101 will be described later.

The predicted image generation unit 102 performs intra-picture prediction (intra prediction) or inter-picture prediction (inter prediction) based on the prediction mode from the decoded image signal supplied from the decoded image memory 108 to generate a predicted image signal. The image signal in the encoding target block supplied from the block division unit 101 is used for evaluation of intra prediction and inter prediction. In intra prediction, a predictive image signal is generated using the image signal of the block to be coded supplied from the block division unit 101 and the image signal of the coded blocks in the same picture as the block to be coded supplied from the decoded image memory 108 and adjacent to the block to be coded. In inter-prediction, the image signal of the block to be coded supplied from the block division unit 101 is stored in the decoded image memory 108 before or after the picture (coded picture) including the block to be coded in time series as a reference picture, and block matching such as block matching is evaluated between the coded picture and the reference picture, a motion vector indicating the amount of motion is obtained, motion compensation is performed from the reference picture based on the amount of motion, and a predicted image signal is generated. The predicted image generator 102 supplies the predicted image signal thus generated to the residual signal generator 103 .

The residual signal generation unit 103 performs subtraction between the image signal to be encoded and the prediction signal generated by the prediction image generation unit 102 to generate a residual signal, and supplies the residual signal to the orthogonal transformation/quantization unit 104 .

The orthogonal transformation/quantization unit 104 orthogonally transforms/quantizes the residual signal supplied from the residual signal generation unit 103, and supplies the orthogonal transformation/quantized residual signal to the encoded bit string generation unit 105 and the inverse quantization/inverse orthogonal transformation unit 106.

The coded bit string generation unit 105 generates a coded bit string for the orthogonally transformed and quantized residual signal supplied from the orthogonal transforming/quantizing unit 104 . Also, the coded bit string generation unit 105 generates coded bit strings corresponding to additional information such as motion vectors, prediction modes, and block division information.

The inverse quantization/inverse orthogonal transformation unit 106 inversely quantizes/inverse orthogonally transforms the orthogonally transformed/quantized residual signal supplied from the orthogonal transformation/quantization unit 104, and supplies the inversely quantized/inverse orthogonally transformed residual signal to the decoded image signal superimposing unit 107.

The decoded image signal superimposing unit 107 superimposes the predicted image signal generated by the predicted image generating unit 102 and the residual signal inversely quantized and inverse orthogonally transformed by the inverse quantization/inverse orthogonal transformation unit 106 to generate a decoded image, and stores it in the decoded image memory 108. The decoded image may be stored in the decoded image memory 108 after being subjected to filtering processing for reducing block distortion or the like due to encoding.

FIG. 2 is a configuration diagram of the image decoding device 200 according to Embodiment 1. As shown in FIG. Here, FIG. 2 shows only the data flow related to the image signal, and additional information other than the image signal such as the motion vector and prediction mode is supplied to each component by the bit string decoding unit 201 and used for the corresponding processing, but the data flow related to the additional information is not shown.

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

The block division unit 202 determines the shape of the decoding target block based on the decoded block division information, and supplies the orthogonal transform/quantized residual signal of the determined decoding target block to the inverse quantization/inverse orthogonal transform unit 203.

The block division unit 202 recursively divides the image into rectangles of a predetermined size based on the decoded block division information to generate decoding target blocks. The block dividing unit 202 includes a 4-dividing unit that horizontally and vertically divides the target block in the recursive division into 4 blocks to generate 4 blocks, and a 2-dividing unit that generates 2 blocks by horizontally or vertically dividing the target block in the recursive division into 2 blocks. A detailed operation of the block dividing unit 202 will be described later.

The inverse quantization/inverse orthogonal transform unit 203 performs inverse orthogonal transform and inverse quantization on the supplied orthogonal transform/quantized residual signal to obtain an inverse orthogonal transform/inverse quantized residual signal.

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 superimposing unit 205 .

The decoded image signal superimposition unit 205 superimposes the predicted image signal generated by the predicted image generation unit 204 and the residual signal inversely orthogonally transformed and inversely quantized by the inverse quantization/inverse orthogonal transformation unit 203 to generate a decoded image signal, output it, and store it in the decoded image memory 206. The decoded image may be stored in the decoded image memory 206 after being subjected to filtering processing for reducing block distortion or the like due to encoding.

The operation of the block dividing section 101 of the image encoding device 100 will be described in detail. FIG. 3 is a flow chart illustrating the partitioning into treeblocks and the partitioning within the treeblocks.

First, an input image is divided into tree blocks of a predetermined size (S1000). For example, assume that the treeblock is 128 pixels by 128 pixels. However, the treeblock is not limited to 128 pixels×128 pixels, and any rectangular size and shape may be used. Also, the size and shape of the treeblock may be fixed values between the encoding device and the decoding device, or may be determined by the encoding device and recorded in the encoded bitstream, and the decoding device may use the recorded block size. FIG. 4 shows how an input image is divided into treeblocks. The treeblocks are encoded and decoded in raster scan order, left to right, top to bottom.

The interior of the treeblock is further divided into rectangular blocks. The inside of the treeblock is encoded/decoded in z-scan order. FIG. 5 shows the order of z-scans. The z-scan encodes and decodes in the order top left, top right, bottom left, bottom right. The division inside the treeblock can be divided into 4 or 2, and the 4 division is divided in the horizontal direction and the vertical direction. The split into two is split horizontally or vertically. FIG. 6 is a diagram of a treeblock divided into four horizontally and vertically. FIG. 7 is a diagram of a treeblock horizontally divided into two. FIG. 8 is a diagram of a treeblock vertically divided into two.

Refer to FIG. 3 again. It is determined whether the inside of the treeblock is to be divided horizontally and vertically into four (S1001).

When it is determined that the inside of the treeblock is to be divided into four (S1001: Yes), the inside of the treeblock is divided into four (S1002), and each block divided horizontally and vertically is processed (S1003). The re-division processing of the blocks divided into four will be described later (FIG. 9).

If it is determined not to divide the inside of the treeblock into four (S1001: No), it is determined whether to divide the inside of the treeblock into two (S1004).

If it is determined that the inside of the treeblock is to be divided into two (S1004: Yes), it is determined whether the direction of division into two is the horizontal direction (S1005).

If it is determined that the direction of division into two is the horizontal direction (S1005: Yes), the inside of the treeblock is horizontally divided into two (S1006), and each process of the two horizontally divided blocks is performed (S1007). The re-division processing of the blocks divided into two in the horizontal direction will be described later (FIG. 10).

If it is determined that the direction of division into two is not the horizontal direction but the vertical direction (S1005: No), the inside of the treeblock is vertically divided into two (S1008), and the vertically divided blocks are processed (S1009). The re-division processing of the horizontally divided blocks will be described later (FIG. 11).

If it is determined not to split the inside of the treeblock into two (S1004: No), the block splitting process ends without splitting the inside of the treeblock into blocks (S1010).

Next, the processing of each divided block when the treeblock is horizontally and vertically divided into four will be described with reference to the flowchart of FIG.

It is determined whether or not the inside of the block is to be divided into four again in the horizontal and vertical directions (S1101).

If it is determined that the inside of the block is to be divided into four again (S1101: Yes), the inside of the block is again divided into four (S1102), and the blocks divided into four horizontally and vertically are processed (S1103).

If it is determined not to divide the inside of the block into four again (S1101: No), it is determined whether to divide the inside of the block into two (S1104).

If it is determined that the inside of the block is to be divided into two (S1104: Yes), it is determined whether the direction of division into two should be the horizontal direction (S1105).

When it is determined that the direction of division into two is the horizontal direction (S1105: Yes), the inside of the block is horizontally divided into two (S1106), and each process of the two horizontally divided blocks is performed (S1107).

If it is determined that the direction of division into two is not the horizontal direction but the vertical direction (S1105: No), the inside of the block is vertically divided into two (S1108), and the vertically divided blocks are processed (S1109).

If it is determined not to divide the inside of the block into two (S1104: No), the block division processing ends without dividing the inside of the block into blocks (S1110).

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

Next, the processing of each divided block when the treeblock is horizontally divided into two will be described with reference to the flowchart of FIG.

When the treeblock is horizontally divided into two blocks, each divided block first determines whether the inside of the block is to be divided into four horizontally and vertically (S1201).

When it is determined that the inside of the block is to be divided into four (S1201: Yes), the inside of the block is divided into four (S1202), and the blocks divided horizontally and vertically are each processed (S1203).

If 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).

If it is determined to divide into two again (S1204: Yes), the inside of the block is vertically divided (S1205), and each process of the vertically divided two blocks is performed (S1206).

If it is determined not to divide into two again (S1204: No), the block dividing process is terminated without redividing the inside of the block (S1207).

FIG. 11 shows how the divided block is re-divided when the treeblock is horizontally divided into two. Here, when the tree block, which is the parent block, is divided into two in the horizontal direction, the re-divided block into two is allowed to be divided into two only in the vertical direction, and is automatically divided into two in the vertical direction. Also, when a tree block, which is a parent block, is split into two, it is possible to completely prohibit splitting into four child blocks. As a result, it is possible to prevent a block from being split in the same direction as the parent block, thereby preventing block splitting into a rectangle that is elongated in the horizontal direction, thereby facilitating the encoding/decoding process.

The processing shown in the flowchart of FIG. 10 is executed for each block divided horizontally. The inside of the block divided into two is also encoded and decoded in order from the top to the bottom.

Next, the processing of each divided block when the treeblock is vertically divided into two will be described with reference to the flowchart of FIG.

When the treeblock is vertically divided into two, each divided block first determines whether the inside of the block is to be divided into four horizontally and vertically (S1301).

When 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 the blocks divided into four horizontally and vertically are processed (S1303).

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

If it is determined to divide into two again (S1304: Yes), the inside of the block is horizontally divided (S1305), and each process of the horizontally divided two blocks is performed (S1306).

If it is determined not to divide into two again (S1304: No), the block dividing process is terminated without redividing the inside of the block (S1307).

FIG. 13 shows how the divided block is re-divided when the treeblock is vertically divided into two. Here, when the tree block, which is the parent block, is vertically divided into two, the re-divided block into two is allowed to be divided into two only horizontally, and is automatically divided into two horizontally. Also, when a tree block, which is a parent block, is split into two, it is possible to completely prohibit splitting into four child blocks. As a result, it is possible to prevent blocks from being divided in the same direction as the parent block, thereby preventing block division into elongated rectangles in the vertical direction, thereby facilitating encoding/decoding processing.

The processing shown in the flowchart of FIG. 12 is executed for each block divided vertically. The inside of the block divided into two is also encoded and decoded in order of left and right.

Although re-division of a divided block when a treeblock is divided has been described, the parent block need not be a treeblock. For example, when a treeblock (128×128) is divided into 4 and the 4-divided block (64×64) is further divided into 4 or 2, the above processing is also applied to division of the re-divided blocks.

Next, the operation of the block dividing section 202 of the image decoding device 200 will be described. The block division unit 101 of the image encoding device 100 divides blocks according to the same processing procedure as the block division unit 101 of the image coding device 100, but the block division unit 101 of the image coding device 100 selects a block division pattern and outputs the selected block division information. is different in that it has a syntax structure in which information without options is not transmitted in the bitstream.

FIG. 14 shows an example of syntax (code bitstream syntax rules) regarding block division in the first embodiment. For division inside the treeblock, first, a flag (4_division_flag) indicating whether to divide into four is transmitted and received. When dividing into four (4_division_flag is 1), the treeblock is divided into four and the process ends. After that, the inside of the four-divided block is re-divided according to the syntax shown in FIG. When not dividing into 4 (4_division_flag is 0), a flag (2_division_flag) indicating whether to divide into 2 is transmitted/received. When dividing into two (2_division_flag is 1), a flag (2_division_direction) indicating the direction of division into two is further transmitted and received. If 2_division_direction is 1, it indicates division in the vertical direction, and if 2_division_direction is 0, it indicates division in the horizontal direction. After that, the inside of the block divided into two is redivided by the syntax shown in FIG. 14 again. If the treeblock is not divided into two (2_division_flag is 0), the process ends without dividing the treeblock.

Here, processing for re-dividing the inside of a block divided into four or two will be described. The syntax shown in FIG. 14 is also used for the process of re-dividing the inside of a block, but it differs from the case of dividing a treeblock in that there are restrictions on the direction of division when dividing into two. In other words, when the treeblock is divided into two, when redividing the inside of the two-divided block, it is prohibited to divide the treeblock in the same direction as the direction in which the treeblock was divided into two. This prevents the divided blocks from becoming longer and narrower rectangles, and prevents an increase in memory bandwidth required for intra prediction and inter prediction. The details of preventing an increase in memory bandwidth will be described later.

Further, it is of course possible to limit the division in the same direction when the number of divisions in the same direction is counted and the number exceeds a predetermined number. For example, although division into two in the same direction is permitted up to two times, division into two in the same direction is prohibited from the third time.

In FIG. 14, 4-division is selected preferentially, and the syntax is such that the information on whether to divide into 4 is transmitted and received prior to the information on whether to divide into 2 or not. On the other hand, when the division into two is selected preferentially, it is also possible to have a syntax in which the information on whether to divide into two is transmitted and received prior to the information on whether to divide into four. This is because the amount of code to be transmitted as a bit stream is reduced by transmitting/receiving events that are more likely to occur probabilistically first. In other words, the syntax may be such that it is presumed which of the four divisions and the two divisions is likely to occur, and the division information that is more likely to occur is transmitted and received first. For example, by transmitting/receiving whether to give priority to division into 4 or division into 2 in the header information of the image, the coding device adaptively determines the priority division number with high coding efficiency, and the decoding device can divide the inside of the tree block with the syntax based on the selected priority division number.

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.

An example of intra prediction is shown in FIGS. 15(a) to 15(d). FIGS. 15A and 15B show prediction directions and mode numbers of intra prediction. In intra prediction, as shown in FIGS. 15(c) and 15(d), by copying pixels from encoded/decoded pixels close to the encoding/decoding target block, a prediction image of the encoding/decoding target block is generated. In intra prediction, since prediction image generation and encoding/decoding pixel generation are repeated in units of blocks, the processing order is sequential in units of blocks, and the smaller the inside of the block is divided, the greater the overall processing load. Also, as the shape of the block becomes a long and narrow rectangle, the process of copying pixels from the memory becomes large. In addition, since orthogonal transformation of residual signals is performed for encoding/decoding, the more types of rectangular sizes are required, the more types of orthogonal transformations are required, resulting in an increase in circuit size. Therefore, when dividing the inside of a block into two, by restricting the division into two in the same direction as the method of dividing the parent block, it is possible to prevent an increase in the memory bandwidth required for intra prediction.

FIG. 16 shows an example of inter prediction. In inter-prediction, a prediction image of a block to be encoded/decoded is generated by copying pixels in block units from pixels included in an encoded/decoded image. In inter-prediction, when copying pixels from a reference image in units of blocks, it is often the case that the configuration of the apparatus requires acquisition of memory management units that include necessary pixels. Therefore, the smaller the block is divided or the longer the block is in the rectangular shape, the greater the overall processing load. In addition, when performing decimal-precision motion compensation using an interpolation filter on a reference image, it is necessary to copy pixels in which several pixels are added to the pixels contained in the block. Therefore, when dividing the inside of a block into two, by restricting the division into two in the same direction as the dividing direction of the parent block, it is possible to prevent an increase in the memory bandwidth required for inter prediction.

Next, the relationship between the luminance signal and the color difference signal in intra prediction will be described. 4:2:0, 4:2:2, 4:4:4, etc. are conventionally known as formats between luminance signals and color difference signals. In the 4:2:0 format shown in FIG. 17A, two pixels of the luminance signal are sampled both horizontally and vertically, while one pixel of the color difference signal is sampled both horizontally and vertically. Since the human eye can perceive the luminance signal more sensitively than the color difference signal, the information amount of the color difference signal is reduced rather than the luminance signal. In the 4:2:2 format shown in FIG. 17B, two pixels of the luminance signal are sampled in the horizontal direction, while one pixel of the color difference signal is sampled in the horizontal direction. In the vertical direction, two pixels of the luminance signal are sampled in the vertical direction, while two pixels of the color difference signal are sampled in the vertical direction. In the 4:4:4 format shown in FIG. 17C, two pixels of the luminance signal are sampled horizontally and vertically, while two pixels of the color difference signal are sampled both horizontally and vertically.

This embodiment will be described by taking the 4:2:0 format, which is 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 luminance blocks and a chrominance block division unit that divides the chrominance signal of the image to generate chrominance blocks, and independently divides the luminance signal and the chrominance signal into blocks in intra prediction. That is, in intra prediction, the size of the luminance block and the size of the chrominance block are determined independently. In intra prediction, each of the luminance signal and the color difference signal copies the pixel value from the surrounding pixels. Therefore, the prediction efficiency is improved by independently dividing the luminance signal and the color difference signal into blocks. In inter prediction, on the other hand, luminance signals and color difference signals are treated together and divided into blocks. That is, in inter prediction, the size of the luminance block and the size of the chrominance block are the same. This is because inter prediction does not need to distinguish between luminance and color difference in motion compensation.

The predicted image generation units 102 and 204 include a luminance signal prediction unit that predicts the luminance signal and a color difference signal prediction unit that predicts the color difference signal. The color difference signal prediction unit performs luminance color difference intra prediction that predicts the color difference signal from the encoded/decoded pixels of the luminance signal in order to increase the prediction efficiency of the color difference signal in intra prediction. In luminance/chrominance intra prediction, the primary signal is coded/decoded before the secondary signal, and the secondary signal is predicted using the coded/decoded primary signal. Here, in the 4:2:0 format and 4:2:2 format, since the information amount 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, the luminance signal and the color difference signal have the same amount of information, but in accordance with other formats, it is common to use the luminance signal as the primary signal and the color difference signal as the secondary signal.

FIG. 18 is a diagram explaining luminance/chrominance intra prediction, and FIG. 19 is a flowchart explaining luminance/chrominance intra prediction.

As shown in FIG. 18, the luminance/chrominance intra prediction is performed based on the degree of correlation between the encoded/decoded neighboring pixels 12a and 12b of the luminance block 10 and the encoded/decoded neighboring pixels 16a and 16b of the color difference block 14. Since the luminance/chrominance intra prediction predicts the color difference signal, the surrounding pixels for which the degree of correlation is to be calculated are specified based on the surrounding pixels of the color difference block to be encoded/decoded. In other words, the peripheral pixels of the luminance block located at the same position as the peripheral pixels determined for the chrominance block are the targets for calculating the degree of correlation.

First, the degree of correlation between the peripheral pixels of the encoded/decoded luminance signal and the peripheral pixels of the color difference signal is calculated (S1901). Subsequently, the encoded/decoded luminance signal of the encoding/decoding target block is down-sampled (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 and a plurality of filter types may be selected, or filters with different numbers of filter taps may be prepared and a plurality of filter types may be selected. The filter type may be automatically selected using the degree of correlation between surrounding pixels, or the filter type may be encoded/decoded in the bitstream and transmitted. Unless the degree of correlation between neighboring pixels is used to determine the down-sampling filter for the luminance signal of the block to be encoded/decoded, the processing of steps S1901 and S1902 can be performed in any order, and steps S1901 and S1902 can be processed in parallel.

Finally, a color difference signal is predicted from the downsampled luminance signal based on the degree of correlation between surrounding pixels (S1903). Down-sampling is 1/2 horizontally/vertically for 4:2:0 format. For 4:2:2 format, it is halved horizontally and not downsampled vertically. In the case of 4:4:4 format, downsampling is not performed in both the horizontal and vertical directions.

In the luminance/color difference intra prediction, the prediction process of the color difference signal can be started after the coding/decoding of the luminance signal of the encoding/decoding target block is completed. Therefore, the timing at which prediction processing of the chrominance block can be started depends on the size of the luminance block and the size of the chrominance block.

FIGS. 20(a) and 20(b) are diagrams illustrating 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, and 20d divided into four shown in FIG. 20(a) is 16×16, and the number of pixels of the color difference block 20e shown in FIG. 20(b) is 16×16.

Here, the comparison of the sizes of the luminance block and the chrominance block is not based on the number of pixels in the block, but on the area considering the chrominance format. That is, in the 4:2:0 format, the area occupied by a luma block is half the area occupied by a chroma block, so if the number of pixels in a luma block is 16×16 and the number of pixels in a chroma block is 16×16, then the size of the luma block is smaller. In a 4:2:0 format, if the luminance block has 16×16 pixels and the chrominance block has 8×8 pixels, the area occupied by both blocks is the same, and the luminance and chroma blocks are the same size.

In order to compare the sizes of the luminance block and the chrominance block by comparing the number of pixels in the block instead of comparing the block area, the number of pixels in the chrominance block should be converted to the number of pixels in the luminance block by the ratio of the luminance signal to the chrominance signal in the chrominance format. In the case of the 4:2:0 format, the number of pixels of the luminance signal is twice the number of pixels of the color difference signal, so the number of vertical and horizontal pixels of the color difference block is doubled to convert to the number of vertical and horizontal pixels of the luminance block. For example, in the 4:2:0 format, if the size of the luminance block is 16×16 and the size of the chrominance block is 16×16, the converted size of the chrominance block converted to the number of pixels of the luminance block is 32×32, and it can be seen that the size of the chrominance block is larger.

In intra-prediction, prediction processing of subsequent blocks becomes possible after completion of decoding processing in block units. That is, the second luminance block 20b can be decoded after the decoding of the first luminance block 20a is completed, the third luminance block 20c can be decoded after the decoding of the second luminance block 20b is completed, and the fourth luminance block 20d can be decoded after the decoding of the third luminance block 20c is completed.

When the size of the chrominance block is larger than the size of the luminance block, the peripheral pixels required for prediction processing of the chrominance block 20e exist before the four luminance blocks 20a, 20b, 20c, and 20d are decoded, and 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 can be calculated without waiting for the decoding of the four luminance blocks 20a, 20b, 20c, and 20d. .

Next, after the decoding of the first luminance block 20a is completed, down-sampling of the luminance signal in step S1902 of FIG. 19 is performed. The pixel of the chrominance block 20e corresponding to the position of the first luminance block 20a can be predicted without waiting for the completion of decoding of the second luminance block 20b. Similarly, after the decoding of the second luminance block 20b is completed, the luminance signal is down-sampled, and the pixels of the chrominance block 20e corresponding to the position of the second luminance block 20b are predicted without waiting for the completion of decoding of the third luminance block 20c. Furthermore, after the decoding of the third luminance block 20c is completed, the luminance signal is down-sampled, and the pixels of the chrominance block 20e corresponding to the position of the third luminance block 20c are predicted without waiting for the completion of decoding of the fourth luminance block 20d. Finally, after the decoding of the fourth luminance block 20d is completed, the luminance signal is down-sampled to predict the pixels of the color difference block 20e corresponding to the position of the fourth luminance block 20d.

FIGS. 21A and 21B are diagrams for explaining 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 16×16, and the number of pixels of the first to fourth color difference blocks 21b, 21c, 21d and 21e shown in FIG. 21(b) is 4×4.

In the 4:2:0 format, the area occupied by the luma block is half the area occupied by the chroma block, so if the number of pixels in the luma block is 16×16 and the number of pixels in the chroma block is 4×4, the size of the chroma block is smaller. In order to compare the sizes of the luminance block and the color difference block by comparing the number of pixels in the block instead of comparing the block area, in the case of the 4:2:0 format, the number of vertical and horizontal pixels of the color difference block is doubled and converted into the number of vertical and horizontal pixels of the luminance block. In the 4:2:0 format, when the size of the luminance block is 16×16 and the size of the chrominance block is 4×4, the converted size of the chrominance block converted to the number of pixels of the luminance block is 8×8, and it can be seen that the size of the chrominance block is smaller.

When the size of the chrominance block is smaller than the size of the luminance block, the surrounding pixels of the first chrominance block 21b can be used before the luminance pixel and the chrominance pixel are decoded from the luminance block 21a, but the surrounding pixels of the second to fourth chrominance blocks 21c, 21d, and 21e cannot be used until the decoding of the luminance block 21a is completed. That is, until 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, until the decoding of the luminance block 21a is completed and the decoding of the first and second chrominance blocks 21b and 21c is not completed, the degree of correlation between the peripheral pixels of the luminance signal and the peripheral pixels of the chrominance signals cannot be calculated for the third chrominance block 21d. Similarly, for the fourth chrominance block 21e, unless the decoding of the luminance block 21a is completed and the decoding of the first to third chrominance blocks 21b, 21c, and 21d is not completed, the degree of correlation between the surrounding pixels of the luminance signal and the surrounding pixels of the chrominance signals cannot be calculated for the fourth chrominance block 21e.

In this way, when the size of the chrominance block is smaller than the size of the luma block, performing luma-chrominance intra prediction results in processing dependencies between the luma block and the chrominance block and between the chroma blocks in the prediction processing of the chroma block, making parallel processing unsuitable. Therefore, when the size of the chrominance block is smaller than the size of the luma block, the luma-chrominance intra prediction is restricted. Methods for restricting luma-chrominance intra prediction include (1) restricting by syntax, (2) replacing intra-chroma mode, and (3) replacing peripheral pixels.

FIG. 22 shows an example of the syntax of intra color difference prediction mode. When the color difference prediction mode number 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 color difference prediction mode number is 1, the mean value mode (DC mode) is used. In the DC mode, intra prediction is performed using the average value of surrounding pixels. If the chrominance prediction mode number is 2, then the luma chrominance intra prediction mode is used.

As a method of restricting luma-chrominance intra prediction, (1) when restricting by syntax, mode 2 is prohibited because it represents luma-chrominance intra prediction. That is, mode 2 is not transmitted, and the intra color difference mode is selected from mode 0 and mode 1.

As a method of limiting luma-chrominance intra prediction, (2) when replacing intra-chroma mode, if the number of the chroma prediction mode is specified as mode 2, instead of luma-chrominance intra prediction mode, use vertical prediction mode instead. However, the replacement prediction mode is not limited to the vertical prediction mode, and may be another prediction mode. Moreover, it is more preferable that the luminance prediction mode of mode 0 and the mode to be replaced by mode 2 are the same so that the modes to be used do not overlap.

As a method of limiting the luminance/chrominance intra prediction, (3) when replacing the surrounding pixels, the surrounding pixels for calculating the degree of correlation between the surrounding pixels of the luminance signal and the surrounding pixels of the color difference signals in step S1901 of FIG. 19 are replaced. In the second to fourth chrominance blocks 21c, 21d, and 21e in FIG. 21 as well, the degree of correlation of peripheral pixels can be calculated without waiting for the decoding of the luminance block 21a.

FIG. 23 shows an example of replacement of peripheral pixels. The pixels in the first chrominance block 21b are normally used as the peripheral pixels on the left side of the second chrominance block 21c, but in order to use the pixels in the first chrominance block 21b, it is necessary to wait until the decoding of the luminance block 21a and the first chrominance block 21b is completed. Therefore, the usable area 21f is used as the peripheral pixels of the second chrominance block 21c without waiting for the completion of the decoding of the luminance block 21a. Similarly, for the third chrominance block 21d, the available area 21f is used as peripheral pixels of the third chrominance block 21d without waiting for the completion of decoding of the luminance block 21a. Similarly, for the fourth chrominance block 21e, the available area 21f is used as the peripheral pixels of the fourth chrominance block 21e without waiting for the completion of decoding of the luminance block 21a.

As described above, in the first embodiment, if the size of a chrominance block is smaller than the size of a luminance block when performing luminance/chrominance intra prediction, by limiting the luminance/chrominance intra prediction, it is possible to relax the processing dependency between the luminance block and the chrominance block. This enables parallel processing of luminance blocks and chrominance blocks, reducing the amount of processing for encoding and decoding.

(Second embodiment)
A second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in that the size of the luminance block and the size of the chrominance block are independently evaluated instead of the size relationship between the luminance block and the chrominance block to limit the luminance/chrominance intra prediction.

First, the limitation based on the size of the luminance block will be described. FIGS. 24(a) to 24(c) show luma-chrominance intra prediction with different luma block sizes. As shown in FIGS. 24A and 24B, the first luminance block 24a corresponds to the position of the first color difference block 24e, the second luminance block 24b corresponds to the position of the second color difference block 24f, the third luminance block 24c corresponds to the position of the third color difference block 24g, and the fourth luminance block 24d corresponds to the position of the fourth color difference block 24h. Also, the luminance block 24i in FIG. 24(c) corresponds to the positions of the first to fourth color difference blocks 24e, 24f, 24g, and 24h in FIG. 24(b).

Dependencies between luminance blocks and chrominance blocks 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 first chrominance block 24e can be decoded. Once the decoding of the second luminance block 24b is completed, the second chrominance block 24f can be decoded. Once the decoding of the third luminance block 24c is completed, the third chrominance block 24g can be decoded. When the decoding of the fourth luminance block 24d is completed, the fourth chrominance block 24h can be decoded.

On the other hand, when the size of the luminance block is large as shown in FIG. 24(c), all the first to fourth color difference blocks 24e, 24f, 24g, and 24h cannot be decoded until the decoding of the luminance block 24i is completed.

If the luminance block division and the chrominance block division are determined independently, a large absolute size of the luminance block increases the possibility that the size of the chroma block will be smaller than the size of the luminance block. Therefore, when the absolute size of a luminance block is equal to or larger than a predetermined size, the luminance/chrominance intra-prediction of the corresponding chrominance block is restricted.

Similarly, the smaller absolute size of the chroma blocks increases the likelihood that the size of the chroma blocks will be smaller than the size of the luma blocks. 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.

The method of limiting luminance/chrominance intra prediction is the same as in the first embodiment.

Thus, in the second embodiment, luma-chrominance intra prediction is restricted when the absolute size of a luma block is larger than a threshold or when the absolute size of a chrominance block is smaller than a threshold. As a result, in anticipation of the case where the size of the chroma block is smaller than the size of the luma block, it is possible to limit luma-chrominance intra prediction and stochastically relax the processing dependency between the luma block and the chroma block.

(Third Embodiment)
A third embodiment of the present invention will be described. In the third embodiment, the block division unit 101 divides the chrominance blocks so that the size of the chrominance blocks does not become smaller than the size of the luminance blocks. When dividing a chrominance block, the block division unit 101 prohibits division such that the size of the chrominance block is smaller than the size of the luminance block. This prevents the size of the chrominance block from being smaller than the size of the luma block in the luma-chrominance intra prediction, and parallel processing of the luma block and the chroma block is always possible.

The coded bitstream of the image output by the image coding apparatus of the embodiment described above has a specific data format so that it can be decoded according to the coding method used in the embodiment, and the image decoding apparatus corresponding to the image coding apparatus can decode the coded bitstream of this specific data format.

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

The transmission device includes a memory that buffers the encoded bitstream output from 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 packetized encoded data via a network, a memory that buffers the received encoded data, and a packet processing unit that packetizes the encoded data to generate an encoded bitstream and provides it to an image decoding device.

Further, by adding a display section for displaying an image decoded by the image decoding device to the configuration, it is also possible to make a display device. In this case, the display unit reads 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.

Further, by adding an imaging unit to the configuration and inputting the captured image to the image encoding device, it is possible to construct an imaging device. In that case, the imaging unit inputs the image signal of the imaged image to the block dividing unit 101 .

The above encoding and decoding processes can be realized not only as a transmission, storage, and reception device using hardware, but also as firmware stored in a ROM (read only memory), flash memory, etc., or software such as a computer. The firmware program and software program can be recorded on a computer-readable recording medium and provided, provided from a server through a wired or wireless network, or provided as data broadcasting of terrestrial or satellite digital broadcasting.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that the embodiment is an example, and that various modifications can be made to the combination of each component and each treatment process, and that such modifications are within the scope of the present invention.

100 image encoding device 101 block division unit 102 prediction image generation unit 103 residual signal generation unit 104 orthogonal transformation/quantization unit 105 encoded bit string generation unit 106 inverse quantization/inverse orthogonal transformation unit 107 decoded image signal superimposition unit 108 decoded image memory 200 image decoding device 201 bit string decoding unit 202 block division Section 203 Inverse Quantization/Inverse Orthogonal Transformation Section 204 Predicted Image Generation Section 205 Decoded Image Signal Superposition Section 206 Decoded Image Memory.

Claims (8)

An image encoding device that divides an image into blocks and performs coding in units of divided blocks,
a luminance signal block division unit that divides the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks;
a color difference signal block division unit that divides the color difference signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction unit that predicts a luminance signal;
a color difference signal prediction unit that predicts color difference signals;
an encoding unit that encodes the prediction mode to generate a bitstream;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
The chrominance signal prediction unit is capable of performing luminance chrominance intra prediction for predicting a chrominance signal from an encoded luminance signal as part of the prediction mode, and when the size of the luminance signal block is equal to or larger than a predetermined size, prohibits the use of the luminance chrominance intra prediction by not making it part of the prediction mode,
1. An image coding apparatus characterized in that, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size. An image encoding method that divides an image into blocks and encodes each divided block,
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
a color difference signal prediction step of predicting a color difference signal;
encoding the prediction mode to generate a bitstream;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, if luminance chrominance intra prediction for predicting a chrominance signal from an encoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
An image coding method, wherein, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size. An image encoding program that divides an image into blocks and encodes each divided block unit,
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
a color difference signal prediction step of predicting a color difference signal;
causing a computer to perform an encoding step of encoding the prediction mode to generate a bitstream;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, if luminance chrominance intra prediction for predicting a chrominance signal from an encoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
An image coding program characterized in that, in the case of inter prediction, luminance signal blocks and color difference signal blocks are divided into blocks of the same size. An image decoding device that performs decoding in units of blocks obtained by dividing an image,
a decoding unit that decodes the encoded bitstream to obtain a prediction mode;
a luminance signal block division unit that divides the luminance signal of the image into rectangles of a predetermined size to generate luminance signal blocks;
a color difference signal block division unit that divides the color difference signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction unit that predicts a luminance signal;
a color difference signal prediction unit that predicts color difference signals;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
The chrominance signal prediction unit is capable of performing luminance chrominance intra prediction for predicting a chrominance signal from a decoded luminance signal as part of the prediction mode, and when the size of the luminance signal block is equal to or larger than a predetermined size, prohibits the use of the luminance chrominance intra prediction by not making it part of the prediction mode,
An image decoding device characterized in that, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size. An image decoding method for decoding in units of blocks obtained by dividing an image,
a decoding step of decoding the encoded bitstream to obtain a prediction mode;
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
a color difference signal prediction step of predicting the color difference signal;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, when luminance chrominance intra prediction for predicting a chrominance signal from a decoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
An image decoding method, wherein, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size. An image decoding program for decoding in units of blocks obtained by dividing an image,
a decoding step of decoding the encoded bitstream to obtain a prediction mode;
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
causing a computer to execute a color difference signal prediction step of predicting a color difference signal;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, when luminance chrominance intra prediction for predicting a chrominance signal from a decoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
An image decoding program characterized in that, in the case of inter prediction, luminance signal blocks and color difference signal blocks are divided into blocks of the same size. A storage method for dividing an image into blocks and storing a bitstream encoded in units of divided blocks in a recording medium,
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
a color difference signal prediction step of predicting a color difference signal;
an encoding step of encoding the prediction mode to generate a bitstream;
a storing step of storing the bitstream on a recording medium;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, if luminance chrominance intra prediction for predicting a chrominance signal from an encoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
A storage method characterized in that, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size. A transmission method for dividing an image into blocks and transmitting a bitstream encoded in units of the divided blocks,
a luminance signal block division 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 signals of the image into rectangles of a predetermined size to generate color difference signal blocks;
a luminance signal prediction step of predicting a luminance signal;
a color difference signal prediction step of predicting a color difference signal;
an encoding step of encoding the prediction mode to generate a bitstream;
a transmitting step of transmitting said bitstream;
the luminance signal block and the chrominance signal block are split independently for intra prediction and jointly for inter prediction;
In the chrominance signal prediction step, if luminance chrominance intra prediction for predicting a chrominance signal from an encoded luminance signal is possible as part of the prediction mode, and 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 by not making it part of the prediction mode,
A transmission method characterized in that, in the case of inter prediction, a luminance signal block and a color difference signal block are divided into blocks of the same size.

Images