JP7441638B2 - Encoding device, decoding device, and program - Google Patents

Description

The present invention relates to an encoding device, a decoding device, and a program.

Research is being conducted on video encoding methods to compress the amount of data when transmitting and storing still images and moving images. In recent years, ultra-high resolution videos such as 8K-SHV have become increasingly popular, and AVC/H. 264 and HEVC/H. Encoding systems such as H.265 are known.

The evaluation software (VTM) for VVC, which is a next-generation video coding system jointly standardized by MPEG and ITU, uses intra prediction that uses spatial correlation within a frame (for example, (See Patent Document 1).

In intra prediction, the encoding device selects the optimal mode from a total of 67 prediction modes, including planar prediction, DC prediction, and 65 types of directional prediction, using decoded reference pixels around the block to be encoded. is selected and the information is sent to the decoding device.

In addition, since the prediction modes used in the block to be encoded and its surrounding blocks have a high correlation, the prediction modes used in the blocks to the left and above the block to be encoded, and the predictions in the direction close to those prediction modes. It is possible to apply a priority intra prediction mode (MPM: Most Probable Modes) in which modes are prioritized and a relatively small amount of data is allocated relative to other prediction modes.

In HEVC, for a block to be encoded of a predetermined size, the scan order indicating the encoding and decoding order during binarization of transform coefficients is switched according to the intra prediction mode. Specifically, it is possible to improve the encoding efficiency by adaptively switching the scan order using statistical bias in the distribution of prediction residuals depending on the intra prediction mode.

JVET-O2001 Versatile Video Coding (Draft 6)

As described above, statistical bias occurs in the distribution of prediction residuals depending on the intra prediction mode. For example, when the intra prediction mode is a nearly vertical directional prediction mode, there is a high possibility that a large value transform coefficient will appear at the top of the block. In that case, efficiency can be improved by scanning horizontally from the bottom to the top of the block.

However, with conventional encoding methods, when it is necessary to identify the intra prediction mode during streaming syntax analysis, the next syntax analysis process cannot be continued at that point, resulting in a reduction in throughput on the decoding device side. be.

Therefore, an object of the present invention is to provide an encoding device, a decoding device, and a program that can improve encoding efficiency while suppressing reduction in throughput on the decoding device side.

The encoding device according to the first aspect is an encoding device that performs encoding in units of blocks constituting an image, and the encoding device performs encoding on a block-by-block basis that constitutes an image, and performs intra prediction using decoded pixels surrounding the encoding target block. an intra prediction unit that generates a prediction block corresponding to the block; a transformation/quantization unit that performs transformation processing and quantization processing on a prediction residual representing a difference between the encoding target block and the prediction block; - An entropy encoding unit that encodes the transform coefficients output by the quantization unit, and when the entropy encoding unit encodes the transform coefficients according to a syntax indicating the intra prediction mode used for the intra prediction. a scan control unit that determines the scan order from among a plurality of scan order candidates, the scan control unit determining the scan order from the syntax without specifying the intra prediction mode from the syntax. The gist is to make decisions directly.

The decoding device according to the second aspect is a decoding device that performs decoding in units of blocks constituting an image, and by decoding the encoded stream, a syntax indicating an intra prediction mode used for intra prediction of the block to be decoded is provided. and an entropy decoding unit that outputs a transform coefficient of the block to be decoded, and a scan order in which the entropy decoder decodes the transform coefficient is determined from among a plurality of scan order candidates according to the syntax. an intra prediction unit that generates a prediction block corresponding to the block to be decoded by intra prediction using decoded pixels surrounding the block to be decoded; an inverse quantization/inverse transform unit that performs an inverse quantization process and an inverse transform process to restore a prediction residual, and combines the restored prediction residual and the prediction block to restore the decoding target block. The scan control unit directly determines the scan order from the syntax without specifying the intra prediction mode from the syntax.

The gist of the program according to the third aspect is to cause a computer to function as the encoding device according to the first aspect.

The gist of the program according to the fourth aspect is to cause a computer to function as the decoding device according to the second aspect.

According to the present invention, it is possible to provide an encoding device, a decoding device, and a program that can improve encoding efficiency while suppressing reduction in throughput on the decoding device side.

FIG. 1 is a diagram showing the configuration of an encoding device according to an embodiment. FIG. 3 is a diagram showing a scan order according to an embodiment. It is a figure showing an example of a non-MPM mode number concerning an embodiment. FIG. 3 is a diagram showing intra prediction mode candidates according to the embodiment. FIG. 3 is a diagram showing association information according to an embodiment. FIG. 1 is a diagram showing the configuration of a decoding device according to an embodiment. FIG. 3 is a diagram showing the operation of the scan control unit according to the embodiment.

An encoding device and a decoding device according to an embodiment will be described with reference to the drawings. The encoding device and the decoding device according to the embodiment encode and decode moving images represented by MPEG, respectively. In the description of the drawings below, the same or similar parts are designated by the same or similar symbols.

<Configuration of encoding device>
First, the configuration of the encoding device according to this embodiment will be explained. FIG. 1 is a diagram showing the configuration of an encoding device 1 according to this embodiment.

As shown in FIG. 1, the encoding device 1 includes a block division section 100, a subtraction section 110, a transform/quantization section 120, an entropy encoding section 130, a scan control section 131, and an inverse quantization/inverse It includes a converting section 140, a combining section 150, a memory 160, and a predicting section 170.

The block division unit 100 divides an original image, which is an input image in units of frames (or pictures) constituting a moving image, into a plurality of image blocks, and outputs the image blocks obtained by the division to the subtraction unit 110. The size of the image block is, for example, 32×32 pixels, 16×16 pixels, 8×8 pixels, or 4×4 pixels. The shape of the image block is not limited to a square, but may be rectangular (non-square). The image block is a unit that is encoded by the encoding device 1 (that is, a block to be encoded), and is a unit that is decoded by the decoding device (that is, a block to be decoded). Such an image block is sometimes called a CU (Coding Unit).

For example, the block division unit 100 outputs a luminance block and a chrominance block by performing block division on a luminance signal and a chrominance signal that constitute an image. The division may be independently controllable for the luminance signal and the color difference signal. When a luminance block and a chrominance block are not particularly distinguished, they are simply referred to as encoding target blocks.

The subtraction unit 110 calculates a prediction residual representing the difference (error) between the current block to be encoded output from the block division unit 100 and the prediction block obtained by predicting the current block to be encoded by the prediction unit 170. Specifically, the subtraction unit 110 calculates a prediction residual by subtracting each pixel value of the prediction block from each pixel value of the block, and outputs the calculated prediction residual to the conversion/quantization unit 120.

The conversion/quantization unit 120 performs conversion processing and quantization processing on a block-by-block basis. The conversion/quantization unit 120 includes a conversion unit 121 and a quantization unit 122.

The transformer 121 performs transform processing on the prediction residual output from the subtracter 110 to calculate transform coefficients, and outputs the calculated transform coefficients to the quantizer 122 . The transformation processing refers to, for example, discrete cosine transform (DCT), discrete sine transform (DST), Karhunenloeb transform (KLT), or the like. However, the conversion process may include a conversion skip that adjusts the pixel domain signal by scaling or the like without converting the pixel domain signal to a frequency domain signal. The transform unit 121 outputs information regarding the transform process applied to the block to be encoded to the entropy encoder 130.

The conversion unit 121 may use MTS that switches between a plurality of conversion bases in encoding the luminance signal. Specifically, the conversion unit 121 may apply a conversion base (conversion type) selected from among DCT-2, DST-7, and DCT-8 in each of the horizontal direction and the vertical direction.

The quantization unit 122 quantizes the transformation coefficients output from the transformation unit 121 using a quantization parameter (Qp) and a quantization matrix, and subjects the quantized transformation coefficients to an entropy encoding unit 130 and inverse quantization/inverse transformation. 140.

The entropy encoding unit 130 performs entropy encoding on the transform coefficients output from the quantization unit 122, performs data compression to generate encoded data (bitstream), and transmits the encoded data to the encoding device 1. Output to the outside of. For entropy encoding, a Huffman code, CABAC (Context-based Adaptive Binary Arithmetic Coding), or the like can be used.

Specifically, the entropy encoding unit 130 reads out the two-dimensionally arranged transform coefficients in a predetermined scanning order and encodes them in sub-block units. FIG. 2 is a diagram showing the scan order according to this embodiment.

In FIG. 2, the encoding target block has a size of 8 pixels in the horizontal direction and 8 pixels in the vertical direction (that is, 8 × 8 pixels), and each sub-block SB1 to SB4 has a size of 4 pixels in the horizontal direction and 8 pixels in the vertical direction. An example having a size of 4 pixels (ie, 4×4 pixels) is shown.

As shown in FIG. 2, there are three scan order candidates: diagonal scan, vertical scan, and horizontal scan. As shown in FIG. 2A, the diagonal scan is a scan order in which scanning is performed diagonally from the high frequency side to the low frequency side within each sub-block. As shown in FIG. 2B, the vertical scan is a scan order in which scanning is performed in the vertical direction from the high frequency side to the low frequency side within each subblock. As shown in FIG. 2C, the horizontal scan is a scan order in which scanning is performed in the horizontal direction from the high frequency side to the low frequency side within each subblock.

In addition to such scan processing and encoding processing of transform coefficients, the entropy encoding section 130 encodes information regarding the transformation processing output from the transformation section 121 and information regarding the prediction processing output from the prediction section 170. Also performs encoding.

Here, the information regarding the prediction process includes syntax (hereinafter referred to as "intra prediction mode syntax") indicating the intra prediction mode used by the prediction unit 170 for intra prediction of the current block to be encoded. Examples of intra prediction mode syntax indicating an intra prediction mode for a luminance block include intra_luma_mpm_flag, intra_luma_not_planar_flag, intra_luma_mpm_idx, and intra_luma_mpm_remainder.

intra_luma_mpm_flag is a flag indicating whether the intra prediction mode used for intra prediction is included in a plurality of priority intra prediction modes (hereinafter referred to as "MPM mode"). When intra_luma_mpm_flag is “1”, it indicates that the intra prediction mode is included in the MPM mode. On the other hand, when intra_luma_mpm_flag is "0", the intra prediction mode is not included in the MPM mode, that is, the intra prediction mode is included in multiple non-priority intra prediction modes (hereinafter referred to as "non-MPM mode"). shows.

intra_luma_not_planar_flag is a flag indicating whether the intra prediction mode is the planar mode when the intra_luma_mpm_flag is “1”. When intra_luma_not_planar_flag is “1”, it indicates that the intra prediction mode is not Planar mode. On the other hand, when intra_luma_not_planar_flag is "0", it indicates that the intra prediction mode is Planar mode.

intra_luma_mpm_idx is an index indicating which MPM the intra prediction mode is when the intra_luma_not_planar_flag is “1”. Note that intra_luma_mpm_idx indicates any number from MPM1 to MPM5 using Truncated Unary encoding.

intra_luma_mpm_remainder is a non-MPM mode number indicating any non-MPM intra prediction mode when intra_luma_mpm_flag is “0”. FIG. 3 is a diagram showing an example of non-MPM mode numbers according to the present embodiment.

As shown in FIG. 3, intra_luma_mpm_remainder indicates any number among 61 modes using Truncated binary encoding. The 61 modes represent 61 intra prediction modes other than the MPM mode by assigning reference directions in ascending order from the lower left to the upper right.

The scan control unit 131 controls the scan order when the entropy encoding unit 130 encodes transform coefficients. Specifically, the scan control unit 131 determines a scan order from among a plurality of scan order candidates according to the intra prediction mode syntax indicating the intra prediction mode used for intra prediction of the block to be encoded. The entropy encoding unit 130 is controlled according to the scan order. In this embodiment, as shown in FIG. 2, the plurality of scan order candidates are assumed to be three: diagonal direction scan, vertical direction scan, and horizontal direction scan. Details of the scan control unit 131 will be described later.

The inverse quantization/inverse transform unit 140 performs inverse quantization processing and inverse transform processing on a block-by-block basis. The inverse quantization/inverse transformation section 140 includes an inverse quantization section 141 and an inverse transformation section 142.

The dequantization unit 141 performs dequantization processing corresponding to the quantization processing performed by the quantization unit 122. Specifically, the dequantization unit 141 restores the transform coefficients by dequantizing the transform coefficients output from the quantization unit 122 using a quantization parameter (Qp) and a quantization matrix. The obtained transform coefficients are output to the inverse transform section 142.

The inverse transform unit 142 performs an inverse transform process corresponding to the transform process performed by the transform unit 121. For example, if the transform unit 121 performs a discrete cosine transform, the inverse transform unit 142 performs an inverse discrete cosine transform. The inverse transform unit 142 performs inverse transform processing on the transform coefficients output from the inverse quantization unit 141 to restore the prediction residual, and outputs the restored prediction residual, which is the restored prediction residual, to the synthesis unit 150. do.

The combining unit 150 combines the restored prediction residual output from the inverse transform unit 142 with the prediction block output from the prediction unit 170 on a pixel-by-pixel basis. The combining unit 150 decodes (reconfigures) the current block by adding each pixel value of the restored prediction residual and each pixel value of the prediction block, and outputs the decoded block to the memory 160. Note that the decoded block is sometimes called a reconstructed block.

The memory 160 stores the decoded blocks output from the combining unit 150, and accumulates the decoded blocks as decoded images in frame units. The memory 160 outputs the stored decoded blocks or decoded images to the prediction unit 170. Note that a loop filter may be provided between the synthesis section 150 and the memory 160.

The prediction unit 170 performs prediction processing on a block-by-block basis. The prediction unit 170 includes an inter prediction unit 171, an intra prediction unit 172, and a switching unit 173.

The inter prediction unit 171 performs inter prediction using correlation between frames. Specifically, the inter prediction unit 171 uses the decoded image stored in the memory 160 as a reference image, calculates a motion vector by a method such as block matching, predicts a target block for inter prediction, and performs inter prediction. A block is generated, and the generated inter prediction block is output to the switching unit 173. Here, the inter prediction unit 171 selects the optimal inter prediction method from among inter prediction using multiple reference images (typically, bi-prediction) and inter prediction using one reference image (unidirectional prediction). Inter prediction is performed using the selected inter prediction method. The inter prediction unit 171 outputs information related to inter prediction (motion vectors, etc.) to the entropy encoding unit 130.

The intra prediction unit 172 performs intra prediction using spatial correlation within a frame. Specifically, the intra prediction unit 172 generates an intra prediction block by referring to decoded pixels around the target block for intra prediction among the decoded images stored in the memory 160, and generates an intra prediction block. The block is output to the switching unit 173. The intra prediction unit 172 selects an intra prediction mode to be applied to the target block of intra prediction from among the plurality of intra prediction modes, and predicts the target block using the selected intra prediction mode. Intra prediction section 172 outputs intra prediction mode syntax indicating the selected intra prediction mode to entropy encoding section 130.

FIG. 4 is a diagram showing intra prediction mode candidates according to this embodiment. As shown in FIG. 4, there are 67 intra prediction mode candidates from 0 to 66 for the luminance block. Mode "0" of the intra prediction mode is planar prediction, mode "1" of the intra prediction mode is DC prediction, and modes "2" to "66" of the intra prediction mode are directional prediction. In directional prediction, the direction of the arrow indicates the reference direction, the starting point of the arrow indicates the position of the pixel to be predicted, and the end point of the arrow indicates the position of the reference pixel used to predict the pixel to be predicted. There are two modes: mode "2", which is an intra prediction mode that refers to the lower left direction, and mode "66", which is an intra prediction mode that refers to the upper right direction, as the reference direction parallel to the diagonal line passing through the upper right and lower left vertices of the block. , mode numbers are assigned clockwise from mode "2" to mode "66" for each predetermined angle.

The switching unit 173 switches between the inter prediction block output from the inter prediction unit 171 and the intra prediction block output from the intra prediction unit 172, and outputs one of the prediction blocks to the subtraction unit 110 and the combination unit 150.

In this way, the encoding device 1 according to the present embodiment includes an intra prediction unit 172 that generates a prediction block corresponding to the current block to be encoded by intra prediction using decoded pixels surrounding the current block, and a A transformation/quantization unit 120 that performs transformation processing and quantization processing on the prediction residual representing the difference between the target block and the prediction block, and an entropy code that encodes the transformation coefficients output by the transformation/quantization unit 120. The entropy encoding unit 130 determines the scan order when encoding the transform coefficients from among a plurality of scan order candidates according to the encoding unit 130 and the intra prediction mode syntax indicating the intra prediction mode used for intra prediction. A scan control unit 131 is provided.

In this embodiment, the encoding device 1 prioritizes prediction modes used in blocks to the left and above the block to be encoded and prediction modes in a direction close to these prediction modes, and selects other prediction modes. MPM is applied to allocate a relatively small amount of data to.

Specifically, the intra prediction unit 172 according to this embodiment includes an MPM determination unit 1721 and a syntax generation unit 1722. The MPM determining section 1721 corresponds to a priority mode determining section.

The MPM determining unit 1721 selects a plurality of priority intra prediction modes (MPM modes) to be preferentially applied to the block to be encoded, and a plurality of priority intra prediction modes (MPM modes) to be preferentially applied to the block to be encoded, based on intra prediction modes applied to blocks surrounding the block to be encoded. A plurality of non-priority intra prediction modes (non-MPM modes) other than the intra prediction mode are determined. The MPM determining unit 1721 generates a list consisting of the determined MPM modes. Such a list is sometimes called an MPM list. For example, the MPM list consists of six preferred intra prediction modes.

The syntax generation unit 1722 generates intra prediction mode syntax indicating the intra prediction mode used by the intra prediction unit 172 for intra prediction of the current block to be encoded, and transmits the generated intra prediction mode syntax to the entropy encoding unit 130 and It is output to the scan control section 131. As described above, the intra prediction mode syntax indicating the intra prediction mode for the luminance block includes intra_luma_mpm_flag, intra_luma_not_planar_flag, intra_luma_mpm_idx, and intra_luma_mpm_remainder.

In particular, the syntax generation unit 1722 generates intra prediction mode syntax having intra_luma_mpm_flag, which is a flag indicating whether the intra prediction mode used for intra prediction is included in the MPM mode or the non-MPM mode. Furthermore, when the intra prediction mode used for intra prediction is included in a non-MPM mode, the syntax generation unit 1722 generates an intra prediction mode syntax that further includes intra_luma_mpm_remainder, which is a non-MPM mode number indicating the intra prediction mode used for intra prediction. Generate taxes.

In the present embodiment, the scan control unit 131 determines a scan order from among a plurality of scan order candidates according to an intra prediction mode syntax indicating an intra prediction mode used for intra prediction of a block to be encoded. Here, the scan control unit 131 directly determines the scan order from the intra prediction mode syntax indicating the intra prediction mode, without specifying the intra prediction mode from the intra prediction mode syntax indicating the intra prediction mode.

Specifically, when the intra_luma_mpm_flag indicates that the intra prediction mode used for intra prediction is included in the non-MPM mode, that is, when the intra_luma_mpm_flag is "0", the scan control unit 131 uses the intra prediction mode indicating the intra prediction mode. Determine scan order directly from prediction mode syntax.

For example, when intra_luma_mpm_flag indicates that the intra prediction mode used for intra prediction is included in a non-MPM mode, the scan control unit 131 performs intra prediction using association information that associates each non-MPM mode number with a scan order candidate. A scan order candidate corresponding to the non-MPM mode number (intra_luma_mpm_remainder) included in the intra prediction mode syntax indicating the mode is determined as the scan order.

FIG. 5 is a diagram showing association information according to this embodiment.

As shown in FIG. 5, 61 non-MPM modes (non-MPM modes) other than the six MPM modes are represented by assigning numbers in ascending order from the lower left to the upper right in the reference direction. Each non-MPM mode number is associated with a scan order candidate (scan).

Specifically, the non-MPM mode numbers are grouped into first to third groups. The first group is a directional prediction mode, and is a group associated with an intra prediction mode in which the prediction direction is closer to the horizontal direction than the vertical direction. The second group is a directional prediction mode, and is a group associated with an intra prediction mode in which the prediction direction is closer to the vertical direction than the horizontal direction. The third group is a group other than the first group and the second group.

In FIG. 5, non-MPM mode numbers "9" to "20" correspond to the first group, non-MPM mode numbers "39" to "52" correspond to the second group, and other non-MPM mode numbers Corresponds to the third group. The association information associates the first group with vertical scan (scan=1), the second group with vertical scan (scan=2), and the third group with diagonal scan (scan=0). Match.

Here, the range is set so that no matter what intra prediction mode is selected as the MPM mode, a non-MPM mode that is somewhat close to the horizontal or vertical direction is included in scan=1 or scan=2. Further, this range is not fixed to the example shown in FIG. 5, but is variable.

When the intra_luma_mpm_flag indicates that the intra prediction mode is included in the non-MPM mode, the scan control unit 131 uses a table (correlation information) as shown in FIG. 5 to select the non-MPM mode included in the intra prediction mode syntax. Since the number (intra_luma_mpm_remainder) can be converted into a scan order number (any one of "0", "1", and "2"), the scan order can be directly determined from the non-MPM mode number.

<Decoding device configuration>
Next, the configuration of the decoding device according to the present embodiment will be mainly described with respect to the differences from the encoding device 1. FIG. 6 is a diagram showing the configuration of the decoding device 2 according to this embodiment.

As shown in FIG. 6, the decoding device 2 includes an entropy decoding section 200, a scan control section 201, an inverse quantization/inverse transformation section 210, a combining section 220, a memory 230, and a prediction section 240.

The entropy decoding unit 200 parses the encoded data generated by the encoding device 1, acquires an intra prediction mode syntax indicating the intra prediction mode used by the encoding device 1 for intra prediction, and uses the acquired intra prediction. The mode syntax is output to the scan control section 201 and the prediction section 240. Intra prediction mode syntax for the luminance block includes intra_luma_mpm_flag, intra_luma_not_planar_flag, intra_luma_mpm_idx, and intra_luma_mpm_remainder.

In decoding the intra prediction mode syntax, the entropy decoding unit 200 decodes intra_luma_mpm_flag, and in the case of "1", decodes intra_luma_not_planar_flag which indicates whether or not the intra prediction mode is Planar mode. When intra_luma_not_planar_flag is “0”, Planar mode is specified as the intra prediction mode. Further, if the intra_luma_not_planar_flag is "1", the entropy decoding unit 200 next decodes the intra_luma_mpm_idx and identifies the number of the MPM. On the other hand, when the intra_luma_mpm_flag is "0", the entropy decoding unit 200 decodes the intra_luma_mpm_remainder and identifies which intra prediction mode not included in the MPM is the one.

Further, the entropy decoding unit 200 acquires information regarding the transformation process, and outputs the acquired information to the inverse quantization/inverse transformation unit 210.

Furthermore, the entropy decoding unit 200 performs scan processing according to the scan order in the multi-value processing of the transform coefficients after the arithmetic decoding processing has been performed on the encoded data, so that the transform coefficients ( Specifically, the quantized transform coefficients are output to the inverse quantization/inverse transform section 210.

Scan control section 201 determines the scan order in which entropy decoding section 200 decodes transform coefficients from among a plurality of scan order candidates, according to the intra prediction mode syntax output from entropy decoding section 200. Specifically, the scan control unit 201 determines a scan order from among a plurality of scan order candidates according to the intra prediction mode syntax to be used for intra prediction of the block to be decoded, and sets the entropy code according to the determined scan order. control unit 130. As described above, there are three scan order candidates: diagonal scan, vertical scan, and horizontal scan. Details of the scan control unit 201 will be described later.

The inverse quantization/inverse transformation unit 210 performs inverse quantization processing and inverse transformation processing on a block-by-block basis. The inverse quantization/inverse transformation section 210 includes an inverse quantization section 211 and an inverse transformation section 212.

The dequantization unit 211 performs dequantization processing corresponding to the quantization processing performed by the quantization unit 122 of the encoding device 1. The dequantization unit 211 restores the transform coefficients of the block to be decoded by dequantizing the quantized transform coefficients output from the entropy decoding unit 200 using a quantization parameter (Qp) and a quantization matrix. , the restored transform coefficients are output to the inverse transform unit 212.

The inverse transform unit 212 performs an inverse transform process corresponding to the transform process performed by the transform unit 121 of the encoding device 1. The inverse transform unit 212 performs inverse transform processing on the transform coefficients output from the inverse quantization unit 211 to restore the prediction residual, and outputs the restored prediction residual (restored prediction residual) to the synthesis unit 220. do.

The combining unit 220 decodes (reconfigures) the original block by combining the prediction residual output from the inverse transform unit 212 and the prediction block output from the prediction unit 240 pixel by pixel. Output the block to memory 230.

The memory 230 stores the decoded blocks output from the combining unit 220, and accumulates the decoded blocks as decoded images in units of frames. The memory 230 outputs the decoded block or decoded image to the prediction unit 240. Furthermore, the memory 230 outputs the decoded image in units of frames to the outside of the decoding device 2 . Note that a loop filter may be provided between the synthesis section 220 and the memory 230.

The prediction unit 240 performs prediction on a block-by-block basis. The prediction unit 240 includes an inter prediction unit 241, an intra prediction unit 242, and a switching unit 243.

The inter prediction unit 241 performs inter prediction using correlation between frames. Specifically, the inter prediction unit 241 performs inter prediction using the decoded image stored in the memory 230 as a reference image based on information regarding inter prediction (for example, motion vector information) output from the entropy decoding unit 200. The prediction target block is predicted to generate an inter prediction block, and the generated inter prediction block is output to the switching unit 243.

The intra prediction unit 242 performs intra prediction using spatial correlation within a frame. Specifically, the intra prediction unit 242 uses the intra prediction mode according to the information regarding intra prediction output from the entropy decoding unit 200 (i.e., the intra prediction mode syntax) to generate the decoded data stored in the memory 230. An intra prediction block is generated by referring to decoded pixels around the target block for intra prediction in the image, and the generated intra prediction block is output to the switching unit 243.

In the present embodiment, the decoding device 2 prioritizes the prediction modes used in the left and upper blocks of the block to be encoded and the prediction modes in the direction close to these prediction modes, and MPM is applied to allocate a relatively small amount of data.

Specifically, the intra prediction unit 242 according to this embodiment includes an MPM determination unit 2421. The MPM determining unit 2421 corresponds to a priority mode determining unit.

The MPM determining unit 2421 determines an MPM mode to be preferentially applied to the block to be decoded and a non-MPM mode other than the MPM mode, based on the intra prediction modes applied to blocks surrounding the block to be decoded. The MPM determining unit 2421 generates a list (MPM list) consisting of the determined MPM modes. For example, the MPM list consists of six preferred intra prediction modes.

The intra prediction unit 242 specifies Planar mode as the intra prediction mode when intra_luma_mpm_flag is "1" and when intra_luma_not_planar_flag is "0". Further, when intra_luma_not_planar_flag is “1”, the intra prediction unit 242 next decodes the intra_luma_mpm_idx and identifies the number of the MPM determined by the MPM determination unit 2421. On the other hand, when intra_luma_mpm_flag is "0", the intra prediction unit 242 identifies which intra prediction mode is not included in MPM based on intra_luma_mpm_remainder.

The switching unit 243 switches between the inter prediction block output from the inter prediction unit 241 and the intra prediction block output from the intra prediction unit 242, and outputs one of the prediction blocks to the synthesis unit 220.

In this way, by decoding the encoded stream, the decoding device 2 according to the present embodiment obtains the intra prediction mode syntax indicating the intra prediction mode used for intra prediction of the block to be decoded, and the transform coefficients of the block to be decoded. an entropy decoding unit 200 that outputs a transform coefficient, a scan control unit 201 that determines a scan order from among a plurality of scan order candidates when the entropy decoder 200 decodes transform coefficients according to the intra prediction mode syntax; The intra prediction unit 242 generates a prediction block corresponding to the decoded target block by intra prediction using decoded pixels around the target block, and the entropy decoding unit 200 performs inverse quantization processing and inverse transformation on the transform coefficients output. It has an inverse quantization/inverse transform unit 210 that performs processing to restore a prediction residual, and a combination unit 220 that combines the restored prediction residual and the prediction block to restore a block to be decoded.

In this embodiment, the scan control unit 201 directly determines the scan order from the intra prediction mode syntax without specifying the intra prediction mode from the intra prediction mode syntax, similarly to the scan control unit 131 of the encoding device 1. Determine exactly.

Specifically, when the intra_luma_mpm_flag indicates that the intra prediction mode to be used for intra prediction is included in the non-MPM mode, that is, when the intra_luma_mpm_flag is “0”, the scan control unit 201 uses the intra prediction mode indicating the intra prediction mode. Determine scan order directly from prediction mode syntax.

For example, when intra_luma_mpm_flag indicates that the intra prediction mode to be used for intra prediction is included in the non-MPM mode, the scan control unit 201 generates association information (see FIG. 5) that associates each non-MPM mode number with a scan order candidate. The scan order candidate corresponding to the non-MPM mode number (intra_luma_mpm_remainder) included in the intra prediction mode syntax indicating the intra prediction mode is determined as the scan order. The scan control unit 201 can convert the non-MPM mode number (intra_luma_mpm_remainder) to a scan order number (one of "0", "1", or "2"), so it can directly change the scan order from the non-MPM mode number. You can decide.

Thereby, the scan control unit 201 can adaptively switch the scan order in the entropy decoding unit 200 simply by parsing the intra prediction mode syntax. In other words, the scan process can be started without waiting for the intra prediction mode to be specified by the decoding process for the intra prediction mode syntax. Therefore, it is possible to improve encoding efficiency while suppressing reduction in throughput on the decoding device 2 side.

<Operation of scan control unit>
Next, the operations of the scan control units 131 and 201 according to this embodiment will be explained. Since the scan control units 131 and 201 perform similar operations, the operation of the scan control unit 201 will be described here as an example. FIG. 7 is a diagram showing the operation of the scan control unit 201 according to this embodiment.

As shown in FIG. 7, in step S1, the scan control unit 201 determines whether intra_luma_mpm_flag included in the intra prediction mode syntax output by the entropy decoding unit 200 is “0” or “1”. .

When intra_luma_mpm_flag is “0” (step S1: YES), in step S2, the scan control unit 201 generates intra_luma_mpm_remainder included in the intra prediction mode syntax output by the entropy decoding unit 200 and a table as shown in FIG. directly determines the scan order based on the

Specifically, the scan control unit 201 directly determines the scan order from the intra_luma_mpm_remainder by converting the intra_luma_mpm_remainder into a scan order number (one of "0", "1", and "2"). After determining the scan order, the scan control unit 201 controls the entropy decoding unit 200 to perform processing in the determined scan order.

<Other embodiments>
A program that causes a computer to execute each process performed by the encoding device 1 may be provided. A program that causes a computer to execute each process performed by the decoding device 2 may be provided. The program may be recorded on a computer readable medium. Computer-readable media allow programs to be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

The circuits that execute each process performed by the encoding device 1 may be integrated, and the encoding device 1 may be constituted by a semiconductor integrated circuit (chip set, SoC). The circuits that execute each process performed by the decoding device 2 may be integrated, and the decoding device 2 may be constituted by a semiconductor integrated circuit (chip set, SoC).

Although the embodiments have been described above in detail with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the scope of the invention.

1: Encoding device 2: Decoding device 100: Block division unit 110: Subtraction unit 120: Transformation/quantization unit 121: Transformation unit 122: Quantization unit 130: Entropy encoding unit 131: Scan control unit 140: Inverse quantization - Inverse transform unit 141 : Inverse quantization unit 142 : Inverse transform unit 150 : Combining unit 160 : Memory 170 : Prediction unit 171 : Inter prediction unit 172 : Intra prediction unit 173 : Switching unit 200 : Entropy decoding unit 201 : Scan control unit 210: Inverse quantization/inverse transformation unit 211: Inverse quantization unit 212: Inverse transformation unit 220: Combining unit 230: Memory 240: Prediction unit 241: Inter prediction unit 242: Intra prediction unit 243: Switching unit 1721: MPM determination unit 1722: Syntax generation unit 2421: MPM determination unit

Claims (8)

An encoding device that performs encoding in units of blocks constituting an image,
an intra prediction unit that generates a prediction block corresponding to the current block by intra prediction using decoded pixels surrounding the current block;
a transformation/quantization unit that performs transformation processing and quantization processing on a prediction residual representing a difference between the encoding target block and the prediction block;
an entropy encoding unit that encodes the transformation coefficients output by the transformation/quantization unit;
a scan control unit that determines a scan order from among a plurality of scan order candidates when the entropy encoding unit encodes the transform coefficients according to a syntax indicating an intra prediction mode used for the intra prediction; Equipped with
The encoding device is characterized in that the scan control unit directly determines the scan order from the syntax without specifying the intra prediction mode from the syntax. The intra prediction unit is
A plurality of priority intra prediction modes that are preferentially applied to the block to be encoded based on intra prediction modes applied to blocks surrounding the block to be encoded, and a plurality of priority intra prediction modes other than the plurality of priority intra prediction modes. a priority mode determining unit that determines a non-priority intra prediction mode;
a syntax generation unit that generates the syntax having a flag indicating which of the plurality of priority intra prediction modes and the plurality of non-priority intra prediction modes the intra prediction mode used for the intra prediction is included in; have,
When the flag indicates that the intra prediction mode used for the intra prediction is included in the plurality of non-priority intra prediction modes, the scan control unit may directly determine the scan order from the syntax. The encoding device according to claim 1. When the intra prediction mode used for the intra prediction is included in the plurality of non-priority intra prediction modes, the syntax generation unit further includes a non-priority intra prediction mode number indicating the intra prediction mode used for the intra prediction. generate the syntax;
When the flag indicates that the intra prediction mode used for the intra prediction is included in the plurality of non-priority intra prediction modes, the scan control unit associates each non-priority intra prediction mode number with a scan order candidate. The encoding device according to claim 2, wherein a scan order candidate corresponding to the non-priority intra prediction mode number included in the syntax is determined as the scan order using information. A decoding device that performs decoding in units of blocks constituting an image,
an entropy decoding unit that outputs syntax indicating an intra prediction mode used for intra prediction of the block to be decoded and transform coefficients of the block to be decoded by decoding the encoded stream;
a scan control unit that determines a scan order from among a plurality of scan order candidates when the entropy decoding unit decodes the transform coefficients according to the syntax;
an intra prediction unit that generates a prediction block corresponding to the decoding target block by intra prediction using decoded pixels surrounding the decoding target block;
an inverse quantization/inverse transform unit that performs inverse quantization processing and inverse transform processing on the transform coefficients output by the entropy decoding unit to restore a prediction residual;
a combining unit that combines the restored prediction residual and the prediction block to restore the decoding target block,
The decoding device is characterized in that the scan control unit directly determines the scan order from the syntax without specifying the intra prediction mode from the syntax. The intra prediction unit includes a plurality of priority intra prediction modes that are preferentially applied to the block to be decoded based on intra prediction modes applied to blocks surrounding the block to be decoded, and a plurality of priority intra prediction modes that are preferentially applied to the block to be decoded. a priority mode determination unit that determines a plurality of non-priority intra prediction modes other than
The syntax includes a flag indicating which of the plurality of priority intra prediction modes and the plurality of non-priority intra prediction modes the intra prediction mode used for intra prediction of the block to be decoded is included,
When the flag indicates that an intra prediction mode used for intra prediction of the block to be decoded is included in the plurality of non-priority intra prediction modes, the scan control unit directly determines the scan order from the syntax. The decoding device according to claim 4, characterized in that: When the intra prediction mode used for intra prediction of the block to be decoded is included in the plurality of non-priority intra prediction modes, the syntax further includes a non-priority intra prediction mode number indicating the intra prediction mode used for the intra prediction. death,
When the flag indicates that the intra prediction mode used for the intra prediction is included in the plurality of non-priority intra prediction modes, the scan control unit generates association information that associates each non-priority intra prediction mode number with a scan order candidate. 6. The decoding device according to claim 5, wherein a scan order candidate corresponding to the non-priority intra prediction mode number included in the syntax is determined as the scan order using . A program that causes a computer to function as the encoding device according to any one of claims 1 to 3. A program for causing a computer to function as the decoding device according to any one of claims 4 to 6.

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