JP7449253B2 - Encoding device, decoding device and program - Google Patents

Description

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

In the video encoding system represented by H.265/HEVC (High Efficiency Video Coding), there are two methods: inter prediction using temporal correlation between frames and intra prediction using spatial correlation within frames. It is configured to perform prediction while switching types of prediction to generate a residual signal, then perform orthogonal transformation processing, loop filter processing, and entropy encoding processing and output the resulting stream.

In intra prediction in HEVC, a total of 35 types of intra prediction modes are available, including planar prediction, DC prediction, and directional prediction.Intra prediction is performed using adjacent decoded reference pixels according to the intra prediction mode determined by the encoder. is configured to do so. Hereinafter, unless otherwise specified, the term "reference pixel" indicates a decoded reference pixel.

Here, in intra prediction in HEVC, a specified value (10 If it is a moving image of bits, it is configured to create a reference pixel to be used when generating a predicted image by filling in "512").

Furthermore, in conventional HEVC, since encoding processing is performed in raster scan order starting from the upper left, reference pixels may not have been decoded yet. In such a case, the predicted image is generated using a zero-order extrapolated value of the nearest decoded reference pixel.

In particular, in intra prediction in conventional HEVC, reference pixels located at the lower left or upper right of the CU are often not decoded due to encoding processing in raster scan order. If directional prediction is performed from the direction in which , there is a problem that prediction accuracy decreases and encoding efficiency decreases.

In order to solve this problem, in intra prediction, raster scan order (for example, Z-type) is used as the encoding processing order for a plurality of transform blocks (hereinafter referred to as "TU: Transform Unit") existing in a CU. In addition, a technique is known that aims to improve prediction accuracy by giving a degree of freedom to the encoding order of U type, X type, etc. (see Non-Patent Document 1).

In addition, intra prediction used in HEVC is prediction using spatially adjacent reference pixels on the upper or left side, and the accuracy of predicted pixels near the reference pixel is high, while the prediction at positions far from the reference pixel is Pixel accuracy tends to decrease (see FIG. 10).

In addition, in the figures of this specification, the arrow indicating the direction of the intra prediction mode (prediction direction) is assumed to be directed from the pixel to be intra-predicted to the reference pixel, as described in the HEVC standard (the same applies hereinafter). .

Conventional HEVC utilizes this property to perform Discrete Sine Transform (DST) or Discrete Cosine Transform (DCT) in the horizontal and vertical directions from the left side and above where the reference pixel is located. orthogonal transformation processing is applied to reduce the entropy of the residual signal.

In particular, as shown in FIG. 11, the shape of the DST impulse response is asymmetrical, with one end point being closed and the other end point widening. By applying DST in accordance with the signal strength of the residual signal, entropy can be effectively reduced.

By the way, Non-Patent Document 2 describes a technique for increasing the types of orthogonal transform processing bases that can be selected in addition to the orthogonal transform processing (DCT-II, DST-VII) employed in conventional HEVC. .

According to the technique described in Non-Patent Document 2, encoding efficiency can be improved by selecting the optimal orthogonal transformation process that concentrates the energy of the residual signal more (capable of reducing entropy). .

On the other hand, there is a problem in that increasing the types of bases for orthogonal transformation processing increases the amount of information required to transmit and store flag information indicating which orthogonal transformation processing has been applied.

In order to prevent such problems, the technique described in Non-Patent Document 2 is configured to select orthogonal transformation processing for the residual signal obtained by intra prediction, depending on the intra prediction mode.

The reason for this is that there is a statistical bias in the tendency of the energy distribution of the residual signal depending on the direction in which intra prediction is performed. It is possible to reduce the amount of information required for transmitting and storing flag information indicating the basis of the applied orthogonal transformation process.

Mochizuki et al., “Applied intra prediction method based on average value coordinates”, Information Processing Society of Japan Research Report, vol. 2012-AVM-77, No. 12. X.ZHAO, J.CHEN, M.KARCZEWICZ, "MODE-DEPENDENT NON-SEPARABLE SECONDARY TRANSFORM", ITU-T SG16/Q6 DOC. COM16-C1044, October 2015

However, in the technique described in Non-Patent Document 2, the basis group of orthogonal transformation processing (orthogonal transformation processing group).

Here, the characteristics of the residual signal obtained by intra prediction using the right or lower reference pixels are different from the characteristics of the residual signal obtained by intra prediction using the upper or left reference signal.

Therefore, in the technique described in Non-Patent Document 2, when intra prediction is performed using reference pixels on the right side or the lower side, if the orthogonal transformation processing group that can be selected only in the intra prediction mode is switched, The orthogonal transformation processing to be applied has to be selected from among options that are not statistically highly effective in entropy reduction, which poses a problem in that entropy may instead increase and encoding performance may deteriorate.

Therefore, the present invention has been made to solve the above-mentioned problems, and provides an encoding device, a decoding device, and a program that can efficiently reduce entropy and improve encoding performance in intra prediction. The purpose is to provide.

A first feature of the present invention is an encoding device configured to divide an original image in units of frames constituting a moving image into blocks to be encoded and encode the blocks, using an intra prediction mode. an intra prediction unit configured to generate a predicted image; and a residual signal configured to generate a residual signal based on a difference between the predicted image generated by the intra prediction unit and the original image. and a generation unit that generates a residual signal generated by the residual signal generation unit in at least one of the horizontal and vertical directions when the position of the reference pixel used to generate the predicted image includes at least one of the right side and the bottom side. an inversion unit configured to invert one side; and an orthogonal transformation processing group configured to perform orthogonal transformation processing from among a predefined orthogonal transformation processing group according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. The present invention further comprises an orthogonal transform unit configured to select a transform process and perform the selected orthogonal transform process on the residual signal inverted by the inverter.

A second feature of the present invention is a decoding device configured to divide an original image in units of frames constituting a moving image into blocks to be encoded and decode the predicted image using an intra prediction mode. an intra prediction unit configured to generate a quantized transform coefficient; an inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient; and an intra prediction unit configured to generate the intra prediction mode and the predicted image. Select an inverse orthogonal transform process to be applied from a predefined group of inverse orthogonal transform processes according to the position of the reference pixel used for generation of an inverse orthogonal transform unit configured to perform the selected inverse orthogonal transform process; and a signal output from the inverse orthogonal transform unit when the position of the reference pixel includes at least one of the right side and the bottom side; and a reversing section configured to reverse the image in at least one of the horizontal direction and the vertical direction.

A third feature of the present invention is an encoding device that is configured to divide an original image in units of frames constituting a moving image into encoding target blocks and encode them, using an intra prediction mode. an intra prediction unit configured to generate a predicted image; and a residual signal configured to generate a residual signal based on a difference between the predicted image generated by the intra prediction unit and the original image. a generation unit, and is configured to select an orthogonal transformation process to be applied from a predefined orthogonal transformation process group according to the intra prediction mode and the position of a reference pixel used for generating the predicted image. and an orthogonal transform unit, wherein the orthogonal transform unit transforms the residual signal generated by the residual signal generating unit when the position of the reference pixel includes at least one of the right side and the bottom side. On the other hand, the gist is that the selected orthogonal transformation processing is performed after inverting at least one of the bases in the horizontal direction and the vertical direction.

A fourth feature of the present invention is a decoding device configured to divide an original image in units of frames constituting a moving image into blocks to be coded and decode the predicted image using an intra prediction mode. an intra prediction unit configured to generate a quantized transform coefficient; an inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient; and an intra prediction unit configured to generate the intra prediction mode and the predicted image. and an inverse orthogonal transform unit configured to select an inverse orthogonal transform process to be applied from a predefined group of inverse orthogonal transform processes according to the position of a reference pixel used for generation of the inverse orthogonal transform unit. and the inverse orthogonal transformation unit transforms the signal output from the inverse quantization unit in at least one of the horizontal direction and the vertical direction when the reference pixel includes at least one of the right side and the bottom side. The gist is that the selected inverse orthogonal transform process is performed after inverting the basis of .

A fifth feature of the present invention is a program for causing a computer to function as the encoding device described in the first and third features.

A fifth feature of the present invention is a program for causing a computer to function as the decoding device described in the second and fourth features.

According to the present invention, it is possible to provide an encoding device, a decoding device, and a program that can efficiently reduce entropy and improve encoding performance in intra prediction.

FIG. 1 is a diagram showing an example of functional blocks of an encoding device 1 according to the first embodiment. FIG. 2 is a diagram showing an example of functional blocks of the orthogonal transform/quantization unit 14c of the encoding device 1 according to the first embodiment. FIG. 3 is a diagram illustrating an example of the direction of the intra prediction mode used in the first embodiment. FIG. 4 is a diagram illustrating an example of a method for generating a predicted image in the first embodiment. FIG. 5 is a diagram illustrating an example of a predicted image generation method in the first embodiment. FIG. 6 is a flowchart illustrating an example of the operation of the encoding device 1 according to the first embodiment. FIG. 7 is a diagram showing an example of functional blocks of the decoding device 3 according to the first embodiment. FIG. 8 is a diagram showing an example of functional blocks of the inverse quantization/inverse transform section 33b of the decoding device 3 according to the first embodiment. FIG. 9 is a flowchart showing an example of the operation of the decoding device 3 according to the first embodiment. FIG. 10 is a diagram for explaining the prior art. FIG. 11 is a diagram for explaining the prior art. FIG. 12 is a diagram for explaining the prior art.

(First embodiment)
The encoding device 1 and decoding device 3 according to the first embodiment of the present invention will be described below with reference to FIGS. 1 to 9.

Here, the encoding device 1 and the decoding device 3 according to this embodiment are configured to support intra prediction in a video encoding method such as HEVC. Note that the encoding device 1 and the decoding device 3 according to this embodiment are configured to be compatible with any video encoding method as long as it performs intra prediction.

The encoding device 1 according to this embodiment is configured to divide an original image in units of frames constituting a moving image into CUs and encode them. Furthermore, the encoding device 1 according to this embodiment may be configured to be able to divide a CU into a plurality of TUs. In the following, the present embodiment will be explained using an example in which a CU is divided into a plurality of TUs, but the present invention does not divide a CU into a plurality of TUs, and the position of the reference pixel of the CU is It is also applicable to cases involving the side or right side.

In addition, in this embodiment, for a CU to be encoded where there is no adjacent decoded reference pixel, such as a CU located at the upper left corner in a frame, a specified value ("512" for a 10-bit video image) is set. Since it is configured to create reference pixels to be used when generating a predicted image by filling in the CU, it is assumed that all pixels adjacent to the left side of the CU to be encoded can be used as reference pixels.

As shown in FIG. 1, the encoding device 1 according to the present embodiment includes an intra prediction mode determination unit 11, a TU division determination unit 12, a coding order control unit 13, a sequential locally decoded image generation unit 14, It includes a memory 15 and an entropy encoding section 16.

The intra prediction mode determining unit 11 is configured to determine the optimal intra prediction mode to be applied to the CU.

The TU division determining unit 12 is configured to determine whether or not to divide a CU into a plurality of TUs. In addition, in this embodiment, as a method of dividing a CU into a plurality of TUs, a four-division case is explained as an example, but the number of divisions and the shape of division when dividing a CU into a plurality of TUs are , but is not limited to such cases.

The encoding order control unit 13 is configured to determine the encoding order of TUs within a CU based on the intra prediction mode (for example, the direction of the intra prediction mode).

For example, when the TU division determination unit 12 determines to divide a CU into a plurality of TUs, the encoding order control unit 13 determines that the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 is from the lower left. When the direction is toward the upper right (that is, when direction prediction is performed from the lower left to the upper right), the encoding order of the TUs in the CU is not the conventional raster scan order, but the lower left TU in the CU→ The encoding order is lower right TU in the CU → upper left TU in the CU → upper right TU in the CU, or lower left TU in the CU → upper left TU in the CU → lower right TU in the CU → It may be configured to adopt a predefined coding order among the coding orders of the upper right TU in the CU.

The sequential locally decoded image generation unit 14 is configured to generate locally decoded images (decoded images for each TU) based on the encoding order determined by the encoding order control unit 13 and the method of dividing the CU into TUs. ing.

Specifically, when the TU division determination unit 12 determines to divide a CU into a plurality of TUs, the sequential locally decoded image generation unit 14 performs the sequential local decoded image generation unit 14 according to the encoding order determined by the encoding order control unit 13. , is configured to sequentially generate locally decoded images.

As shown in FIG. 1, the sequential locally decoded image generation section 14 includes an intra prediction section 14a, a residual signal generation section 14b, an orthogonal transformation/quantization section 14c, and an inverse quantization section/inverse orthogonal transformation section 14d. , and a locally decoded image generating section 14e.

The intra prediction unit 14a is configured to generate a predicted image using the intra prediction mode determined by the intra prediction mode determination unit 11. That is, the intra prediction unit 14a is configured to determine the position of a reference pixel used when generating a predicted image according to the intra prediction mode, and to generate the predicted image using the reference pixel.

Furthermore, the intra prediction unit 14a may be configured to generate a predicted image in the encoding order determined by the encoding order control unit 13.

The residual signal generation unit 14b is configured to generate a residual signal based on the difference between the predicted image generated by the intra prediction unit 14a and the original image.

The orthogonal transformation/quantization unit 14c is configured to perform orthogonal transformation processing and quantization processing on the residual signal generated by the residual signal generation unit 14b, and generate quantized transformation coefficients. .

As shown in FIG. 2, the orthogonal transformation/quantization section 14c includes an inversion section 14c1, an orthogonal transformation section 14c2, and a quantization section 14c3.

The inverting unit 14c1 operates when the position of the reference pixel used to generate the predicted image includes at least one of the right side and the lower side (when generating the predicted image using a reference pixel adjacent to at least one of the right side and the lower side) Furthermore, the residual signal generated by the residual signal generating section 14b is inverted in at least one of the horizontal direction and the vertical direction.

For example, the inverting unit 14c1 is configured to invert the residual signal in the vertical direction when the lower side is included in the position of the reference pixel (when generating a predicted image using reference pixels adjacent to the lower side). You can leave it there.

Alternatively, the inverting unit 14c1 is configured to invert the residual signal in the horizontal direction when the right side is included in the position of the reference pixel (when a predicted image is generated using a reference pixel adjacent to the right side). It's okay.

The orthogonal transform unit 14c2 is configured to perform orthogonal transform processing on the residual signal inverted by the inverter 14c1.

Specifically, the orthogonal transformation unit 14c2 applies an orthogonal transformation processing group from a predefined orthogonal transformation processing group (orthogonal transformation basis group) according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. The inverter 14c1 selects an orthogonal transform process to perform the selected orthogonal transform process, and performs the selected orthogonal transform process on the residual signal inverted by the inverter 14c1.

FIG. 3 shows an example of the intra prediction mode used in this embodiment. As shown in FIG. 3, in this embodiment, intra prediction modes 2 to 9 are classified into category A, intra prediction modes 10 to 26 are classified into category B, and intra prediction modes 27 to 34 are classified into category C. shall be classified as

In this embodiment, an example in which the intra prediction mode in HEVC shown in FIG. 3 is used will be described, but the present invention is also applicable to an example in which other intra prediction modes are used.

Here, the residual signal obtained from the difference between the predicted image and the original image is converted into orthogonal transformation coefficients using orthogonal transformation processing. By concentrating the energy of the residual signal through the orthogonal transform process, it is possible to improve the encoding efficiency in the subsequent entropy encoding process.

In HEVC, DCT and DST are prepared as applicable orthogonal transform processing, and the orthogonal transform processing is performed while switching depending on the block size and prediction mode.

Here, the orthogonal transformation processing is not limited to DST, DCT, etc., but may be any transformation processing applied to the residual signal for the purpose of concentrating energy (including transformation processing that is converted into an integer for speeding up). For example, any conversion process may be used.

By increasing the types of orthogonal transformation processing that can be selected, the possibility of selecting an orthogonal transformation processing that concentrates more energy for residual signals with various energy distributions increases, but on the other hand, which orthogonal The amount of information required to transmit and store flag information indicating whether conversion processing is to be applied increases.

Note that the energy distribution of the residual signal has a statistical correlation with the distance from the reference pixel used for intra prediction. Therefore, the energy distribution of the residual signal is different between the intra prediction mode using only the left reference pixels and the intra prediction mode using the left and upper reference pixels.

Therefore, the technique described in Non-Patent Document 2 utilizes the correlation between the bias of the energy distribution of the residual signal and the direction of the intra prediction mode to perform orthogonal transformation that can be selected according to the direction of the intra prediction mode. It is configured to switch between processing groups.

Intra prediction mode 2 (intra prediction mode using only the reference pixels located on the left) and intra prediction mode 18 (intra prediction mode using only the reference pixels located on the left) in HEVC are shown in FIGS. 4(a) and 4(b) as examples of the energy distribution of the residual signal. Fig. 3 shows the difference in the energy distribution of the residual signal in the intra prediction mode using the reference pixel located on the upper side).

In this way, the orthogonal transformation processing that has a statistically high entropy reduction effect is different for residual signals having different energy distributions.

Therefore, in the technique described in Non-Patent Document 2, as mentioned above, a group of orthogonal transformation processes that can be selected according to the direction of the intra prediction mode is prepared, and the optimal orthogonal transformation process is selected from among them. It is configured.

According to this technique, by switching the applicable orthogonal transformation processing group according to the direction of the intra prediction mode, the statistical energy distribution of the residual signal can be efficiently concentrated, and the applied orthogonal transformation processing can be It is possible to reduce the information amount of the flag indicating whether the

However, as shown in FIG. 5, when performing direction prediction in intra prediction mode 2 using reference pixels located on the left side and lower side, direction prediction in intra prediction mode 2 is performed using only reference pixels located on the left side. Compared to the case of performing the above, the energy distribution of the residual signal also differs due to the difference in the position of the reference pixel.

The energy distribution of the residual signal resulting from the direction prediction in intra prediction mode 2 using the reference pixels located on the left side and the bottom side (see Fig. 5) is as shown in Fig. 4(b) using the reference pixels located on the left side and the top side. The energy distribution is similar to that obtained by vertically inverting the residual signal resulting from the directional prediction in the intra prediction mode 18.

In other words, when performing directional prediction in intra prediction mode 2, when the left side and bottom side are included as reference pixel positions, the residual signal is vertically inverted and then orthogonal transformation processing is applied. The energy distribution of the orthogonal transform coefficients is calculated when the left side and upper side are included as reference pixel positions when performing direction prediction in intra prediction mode 18, without inverting the residual signal in the horizontal and vertical directions. The energy distribution of orthogonal transformation coefficients obtained when orthogonal transformation processing is applied is similar to that of the orthogonal transformation coefficients (see FIG. 4(b) and FIG. 5).

The energy distribution of the orthogonal transform coefficients obtained by orthogonal transform processing on the residual signal by direction prediction in intra prediction mode 2 differs depending on the position of the reference pixel used for intra prediction. Determining the transform processing group may increase entropy and reduce encoding performance.

Therefore, when inverting the residual signal in at least one of the horizontal direction and the vertical direction depending on the position of the reference pixel in intra prediction, the orthogonal transformation unit 14c2 selects the direction according to the direction of the applied intra prediction mode and the position of the reference pixel. Determine possible orthogonal transformation processing groups.

That is, the orthogonal transformation unit 14c2 is configured to select an orthogonal transformation process to be applied from a predefined orthogonal transformation group according to the direction of the intra prediction mode when the intra prediction mode belongs to category B. may have been done.

For example, when the intra prediction mode is 18, the orthogonal transformation unit 14c2 is configured to select an orthogonal transformation process to be applied from a predefined orthogonal transformation group according to the direction of the intra prediction mode 18. It's okay.

Alternatively, when the intra prediction mode belongs to category A and the lower side is not included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the orthogonal transform that is predefined according to the direction of the intra prediction mode. The orthogonal transformation processing to be applied may be selected from among the transformation group.

For example, when the intra prediction mode is 2 and the lower side is not included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the orthogonal transformation group predefined according to the direction of the intra prediction mode 2. The orthogonal transformation processing to be applied may be selected from among the following.

Alternatively, when the intra prediction mode belongs to category C and the right side is not included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the orthogonal transform that is predefined according to the direction of the intra prediction mode. The orthogonal transformation processing to be applied may be selected from among the transformation group.

For example, when the intra prediction mode is 34 and the right side is not included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the orthogonal transformation group predefined according to the direction of the intra prediction mode 34. The orthogonal transformation processing to be applied may be selected from among the following.

Further, when the position of the reference pixel includes the lower side, the orthogonal transformation unit 14c2 applies orthogonal transformation from among a predefined orthogonal transformation group according to the direction in which the direction of the intra prediction mode is vertically reversed. It may be configured to select a process.

Here, "reversing the direction of intra prediction mode vertically" means converting between the direction of intra prediction modes 2 to 9 and the direction of intra prediction modes 18 to 11, respectively, in the example of FIG. That is, it means converting the direction of each intra prediction mode to the direction of the intra prediction mode having a line-symmetrical positional relationship with respect to the direction of the intra prediction mode 10.

That is, when the intra prediction mode belongs to category A and the lower side is included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the intra prediction mode according to the direction in which the direction of the intra prediction mode is vertically reversed. The orthogonal transformation processing to be applied may be selected from a predefined orthogonal transformation group.

For example, when the intra prediction mode is 2 and the lower side is included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the direction of the intra prediction mode 2 into a direction in which the direction of the intra prediction mode 2 is vertically reversed (the intra prediction mode The orthogonal transformation processing to be applied may be selected from a predefined orthogonal transformation group according to the direction of the direction (18).

Alternatively, when the right side is included in the position of the reference pixel, the orthogonal transformation unit 14c2 applies orthogonal transformation from among a predefined orthogonal transformation group according to the direction in which the direction of the intra prediction mode is horizontally reversed. It may be configured to select a process.

Here, "reversing the direction of intra prediction mode horizontally" means converting between the direction of intra prediction modes 18 to 25 and the direction of intra prediction modes 34 to 27, respectively, in the example of FIG. That is, it means converting the direction of each intra prediction mode to the direction of the intra prediction mode having a line-symmetrical positional relationship with respect to the direction of the intra prediction mode 26.

That is, when the intra prediction mode belongs to category C and the right side is included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the intra prediction mode according to the direction in which the direction of the intra prediction mode is horizontally reversed. The orthogonal transformation processing to be applied may be selected from a predefined orthogonal transformation group.

For example, when the intra prediction mode is 34 and the right side is included as the position of the reference pixel, the orthogonal transformation unit 14c2 converts the direction of the intra prediction mode 34 into a horizontal direction (intra prediction mode The orthogonal transformation processing to be applied may be selected from a predefined orthogonal transformation group according to the direction of the direction (18).

The quantization unit 14c3 is configured to perform quantization processing on the signal output from the orthogonal transformation unit 14c2 and generate quantized transformation coefficients.

The inverse quantization unit/inverse orthogonal transformation unit 14d performs inverse quantization processing and inverse orthogonal transformation processing again on the quantized transform coefficients generated by the orthogonal transformation/quantization unit 14c to generate a residual signal. is configured to generate.

The local decoded image generation unit 14e generates a locally decoded image by adding the predicted image generated by the intra prediction unit 14a to the residual signal generated by the inverse quantization unit/inverse orthogonal transformation unit 14d. It is configured.

The memory 15 is configured to hold the locally decoded images sequentially generated by the locally decoded image generator 14 so that they can be used as reference images.

The entropy encoding unit 16 is configured to perform entropy encoding processing on flag information including the intra prediction mode etc. determined by the intra prediction mode determination unit 11 and quantized transform coefficients, and output the resultant stream. There is.

FIG. 6 shows a flowchart for explaining an example of the operation of the encoding device 1 according to this embodiment.

As shown in FIG. 6, in step S101, the encoding device 1 determines the position of a reference pixel used when generating a predicted image according to the determined intra prediction mode, and generates a predicted image using the reference pixel. A residual signal is generated based on the difference between the predicted image and the original image.

In step S102, the encoding device 1 converts the residual signal generated by the residual signal generation unit 14b in the horizontal direction when the position of the reference pixel used to generate the predicted image includes at least one of the right side and the lower side. and flipped in at least one of the vertical directions.

In step S103, the encoding device 1 selects an orthogonal transformation process to be applied from a predefined orthogonal transformation process group according to the intra prediction mode and the position of the reference pixel used to generate the predicted image, The selected orthogonal transformation process is performed on the inverted residual signal.

In step S104, the encoding device 1 performs a quantization process on the signal that has been subjected to the orthogonal transform process, and generates quantized transform coefficients.

In step S105, the encoding device 1 performs entropy encoding processing on the flag information including the intra prediction mode and the quantized transform coefficients, and outputs the result as a stream.

Furthermore, the decoding device 3 according to the present embodiment is configured to decode an original image in units of frames constituting a moving image by dividing it into CUs. Further, the decoding device 3 according to this embodiment is configured to be able to divide a CU into a plurality of TUs, similarly to the encoding device 1 according to this embodiment.

As shown in FIG. 7, the decoding device 3 according to this embodiment includes an entropy decoding section 31, a decoding order control section 32, a sequentially decoded image generation section 33, and a memory 34.

The entropy decoding unit 31 is configured to decode transform coefficients, flag information, etc. from the stream output from the encoding device 1 by performing entropy decoding processing on the stream output from the encoding device 1. ing. Here, the transform coefficients are quantized transform coefficients obtained by the encoding device 1 as a signal encoded by dividing an original image in units of frames into CUs.

The decoding order control unit 32 is configured to determine the decoding order of TUs within a CU based on the intra prediction mode.

Specifically, the decoding order control unit 32 uses a flag output by the entropy decoding unit 31 indicating whether TU division has been performed (whether a CU is divided into a plurality of TUs) and an intra prediction mode. The decoding order of TUs within a CU is determined according to the direction.

For example, like the encoding order control unit 13, the decoding order control unit 32, when the CU is divided into a plurality of TUs and the direction of the intra prediction mode is from the lower left to the upper right, Decoding order is lower left TU in CU → lower right TU in CU → upper left TU in CU → upper right TU in CU, or lower left TU in CU → upper left TU in CU → within CU The decoding process may be performed in a predefined decoding order from the lower right TU of the CU to the upper right TU of the CU.

The sequential decoded image generation unit 33 is configured to generate decoded images (decoded images for each TU) based on the decoding order determined by the decoding order control unit 32 and the method of dividing the CU into TUs.

Specifically, when a CU is divided into a plurality of TUs, the sequential decoded image generation unit 33 generates quantized images output by the entropy decoding unit 31 according to the decoding order determined by the decoding order control unit 32. The decoded image is generated by sequentially performing inverse quantization processing, inverse orthogonal transformation processing, and intra prediction on the obtained transform coefficients.

As shown in FIG. 7, the sequential decoded image generation section 33 includes an intra prediction section 33a, an inverse quantization/inverse transformation section 33b, and a decoded image generation section 33c.

The intra prediction unit 33a may be configured to generate a predicted image using the intra prediction mode output by the entropy decoding unit 31 according to the decoding order determined by the decoding order control unit 32.

The inverse quantization/inverse transform unit 33b performs an inverse quantization process and an inverse transform process (for example, inverse orthogonal transform process) on the quantized transform coefficients outputted by the entropy decoding unit 31, thereby obtaining a residual difference. configured to generate a signal.

As shown in FIG. 8, the inverse quantization/inverse transform section 33b includes an inverse quantization section 33b1, an inverse orthogonal transform section 33b2, and an inverse orthogonal transform section 33b3.

The dequantization unit 33b1 is configured to perform dequantization processing on the quantized transform coefficients output by the entropy decoding unit 31.

The inverse orthogonal transform section 33b2 is configured to perform an inverse orthogonal transform process on the signal (transform coefficient) output from the inverse quantization section 33b1.

Specifically, like the orthogonal transform unit 14c2, the inverse orthogonal transform unit 33b2 selects one of the predefined inverse orthogonal transform groups according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. It is configured to select an inverse orthogonal transform process to be applied from among them, and perform the selected inverse orthogonal transform process on the signal output from the inverse quantizer 33b1.

That is, when the intra prediction mode belongs to category B, the inverse orthogonal transform unit 33b2 selects an inverse orthogonal transform process to be applied from among the inverse orthogonal transform group defined in advance according to the direction of the intra prediction mode. It may be configured as follows.

For example, when the intra prediction mode is 18, the inverse orthogonal transform unit 33b2 selects an inverse orthogonal transform process to be applied from among an inverse orthogonal transform group predefined according to the direction of the intra prediction mode 18. may be configured.

Alternatively, when the intra prediction mode belongs to category A and the lower side is not included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 predefines the direction of the intra prediction mode. The inverse orthogonal transform processing to be applied may be selected from among the inverse orthogonal transform group.

For example, when the intra prediction mode is 2 and the lower side is not included as the position of the reference pixel, the inverse orthogonal transform unit 33b2 converts the inverse orthogonal transform that is predefined according to the direction of the intra prediction mode 2. The inverse orthogonal transform processing to be applied may be selected from among the transform group.

Alternatively, when the intra prediction mode belongs to category C and the right side is not included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 predefines the direction of the intra prediction mode according to the direction of the intra prediction mode. The inverse orthogonal transform processing to be applied may be selected from among the inverse orthogonal transform group.

For example, when the intra prediction mode is 34 and the right side is not included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 performs an inverse orthogonal transformation that is predefined according to the direction of the intra prediction mode 34. The inverse orthogonal transform processing to be applied may be selected from among the transform group.

Further, when the position of the reference pixel includes the lower side, the inverse orthogonal transform unit 33b2 applies an inverse orthogonal transform from among a predefined inverse orthogonal transform group according to the direction in which the direction of the intra prediction mode is vertically reversed. It may be configured to select inverse orthogonal transformation processing.

That is, when the intra prediction mode belongs to category A and the lower side is included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 reverses the direction of the intra prediction mode in the vertical direction. Accordingly, the inverse orthogonal transform process to be applied may be selected from a predefined group of inverse orthogonal transforms.

For example, when the intra prediction mode is 2 and the lower side is included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 converts the direction of the intra prediction mode 2 into a direction that is vertically reversed (intra prediction The inverse orthogonal transform process to be applied may be selected from a predefined group of inverse orthogonal transforms depending on the direction of mode 18).

Alternatively, when the position of the reference pixel includes the right side, the inverse orthogonal transform unit 33b2 applies an inverse orthogonal transform from among a predefined inverse orthogonal transform group according to the direction in which the direction of the intra prediction mode is horizontally reversed. It may be configured to select inverse orthogonal transformation processing.

That is, when the intra prediction mode belongs to category C and the right side is included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 reverses the direction of the intra prediction mode in the horizontal direction. Accordingly, the inverse orthogonal transform process to be applied may be selected from a predefined group of inverse orthogonal transforms.

For example, when the intra prediction mode is 34 and the right side is included as the position of the reference pixel, the inverse orthogonal transformation unit 33b2 converts the direction of the intra prediction mode 34 into a horizontal direction (intra prediction The inverse orthogonal transform process to be applied may be selected from a predefined group of inverse orthogonal transforms depending on the direction of mode 18).

The inversion unit 33b3 is configured to invert the signal output from the inverse orthogonal transformation unit 33b2 in at least one of the horizontal direction and the vertical direction when the reference pixel position includes at least one of the right side and the bottom side. There is.

Specifically, the inverter 33b3 may be configured to invert the signal output from the inverse orthogonal transformer 33b2 in the vertical direction when the lower side is included in the position of the reference pixel.

Alternatively, the inverting unit 33b3 may be configured to horizontally invert the signal output from the inverse orthogonal transform unit 33b2 when the right side is included in the position of the reference pixel.

The decoded image generation unit 33c is configured to generate a decoded image by adding the predicted image generated by the intra prediction unit 33a and the residual signal generated by the inverse quantization/inverse transformation unit 33b.

The memory 34 is configured to hold decoded images generated by the sequential decoded image generation unit 33 so that they can be used as reference images for intra prediction and inter prediction.

FIG. 9 shows a flowchart for explaining an example of the operation of the decoding device 3 according to the present embodiment.

As shown in FIG. 9, in step S201, the decoding device 3 generates a predicted image using intra prediction mode.

In step S202, the decoding device 3 performs inverse quantization processing on the quantized transform coefficients.

In step S203, the decoding device 3 selects an inverse orthogonal transform process to be applied from a predefined inverse orthogonal transform group according to the intra prediction mode and the position of the reference pixel used to generate the predicted image, The selected inverse orthogonal transform process is performed on the signal that has been subjected to the inverse quantization process.

In step S204, the decoding device 3 inverts the signal subjected to the inverse orthogonal transform process in at least one of the horizontal direction and the vertical direction when the position of the reference pixel includes at least one of the right side and the lower side.

According to the encoding device 1 and the decoding device 3 according to the present embodiment, different orthogonal transformation processing groups are applied to the residual signal obtained by intra prediction, depending on not only the direction of the intra prediction mode but also the position of the reference pixel. This makes it possible to switch between the two, reduce entropy, and improve coding efficiency.

(Second embodiment)
The encoding device 1 and decoding device 3 according to the second embodiment of the present invention will be described below, focusing on the differences from the encoding device 1 and decoding device 3 according to the above-described first embodiment.

The encoding device 1 according to this embodiment does not include the inversion section 14c1, and the decoding device 3 according to this embodiment does not include the inversion section 33b3.

In the encoding device 1 according to the present embodiment, the orthogonal transformation unit 14c2 applies one orthogonal transformation processing from among a predefined orthogonal transformation processing group according to the intra prediction mode and the position of the reference pixel used for generating the predicted image. It is configured to select orthogonal transformation processing.

Here, when the position of the reference pixel includes at least one of the right side and the bottom side, the orthogonal transformation unit 14c2 transforms the residual signal generated by the residual signal generation unit 14b in the horizontal direction and the vertical direction. The selected orthogonal transformation processing is performed after inverting at least one of the bases.

Specifically, when the lower side is included in the position of the reference pixel, the orthogonal transformation unit 14c2 selects one of the predefined orthogonal transformation processing groups according to the direction in which the intra prediction mode direction is vertically reversed. It may be configured to select an orthogonal transform process to be applied, invert the base in the vertical direction with respect to the residual signal, and then perform the selected orthogonal transform process.

Alternatively, when the right side is included in the position of the reference pixel, the orthogonal transformation unit 14c2 applies orthogonal transformation processing from among a predefined orthogonal transformation processing group according to the direction in which the direction of the intra prediction mode is horizontally reversed. It may be configured to select a transform process, invert the base in the horizontal direction for the residual signal, and then perform the selected orthogonal transform process.

In the decoding device 3 according to the present embodiment, the inverse orthogonal transform unit 33b2 applies an inverse orthogonal transform process from among a predefined group of inverse orthogonal transform processes according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. It is configured to select the inverse orthogonal transform processing to be performed.

Here, when the position of the reference pixel includes at least one of the right side and the bottom side, the inverse orthogonal transformation unit 33b2 transforms the signal output from the inverse quantization unit 33b1 in at least one of the horizontal direction and the vertical direction. After inverting the basis of , the selected orthogonal transformation process is performed.

Specifically, when the lower side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 performs an inverse orthogonal transform processing group predefined according to the direction in which the intra prediction mode direction is vertically reversed. It is configured to select an inverse orthogonal transform process to be applied from among them, invert the base in the vertical direction with respect to the signal output from the inverse quantizer 33b1, and then apply the selected inverse orthogonal transform process. Good too.

Alternatively, when the right side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 applies an inverse orthogonal transform processing group predefined according to the direction in which the direction of the intra prediction mode is horizontally reversed. The configuration may be such that the inverse orthogonal transform processing is selected, the base in the horizontal direction is inverted for the signal output from the inverse quantization unit 33b1, and then the selected inverse orthogonal transform processing is performed.

(Other embodiments)
As mentioned above, the present invention has been explained using the embodiments described above, but the statements and drawings that form part of the disclosure in these embodiments should not be understood as limiting the present invention. Various alternative embodiments, implementations, and operational techniques will be apparent to those skilled in the art from such disclosure.

Further, although not specifically mentioned in the above-described embodiment, a program that causes a computer to execute each process performed by the above-described encoding device 1 and decoding device 3 may be provided. Moreover, such a program may be recorded on a computer-readable medium. Computer readable media allow such programs to be installed on a computer. Here, the computer-readable medium on which such a program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or a DVD-ROM, for example.

Alternatively, a chip may be provided that includes a memory that stores a program for realizing at least some of the functions in the encoding device 1 and decoding device 3 described above, and a processor that executes the program stored in the memory. good.

1... Encoding device 11... Intra prediction mode determining unit 12... TU division determining unit 13... Encoding order control unit 14... Sequentially locally decoded image generating unit 14a... Intra prediction unit 14b... Residual signal generating unit 14c... Orthogonal transform/ Quantization section 14c1...Inversion section 14c2...Orthogonal transformation section 14c3...Quantization section 14d...Inverse quantization section/inverse orthogonal transformation section 14e...Local decoded image generation section 15...Memory 16...Entropy encoding section 3...Decoding device 31... Entropy decoding unit 32...Decoding order control unit 33...Sequential locally decoded image generation unit 33a...Intra prediction unit 33b...Inverse quantization/inverse transformation unit 33b1...Inverse quantization unit 33b2...Inverse orthogonal transformation unit 33b3...Inversion unit 33c...Decoding Image generation unit 34...memory

Claims (6)

An encoding device that divides and encodes an original image in units of frames constituting a moving image into blocks,
an intra prediction unit that generates a predicted image corresponding to a target block to be encoded using an intra prediction mode indicating the type of intra prediction processing;
a residual signal generation unit that generates a residual signal based on a difference between the predicted image generated by the intra prediction unit and the target block;
An orthogonal transformation process is applied from a predefined orthogonal transformation processing group according to the intra prediction mode and the position of the decoded reference pixel that can be used to generate the predicted image, which is determined according to the block coding order. An encoding device comprising : a conversion unit that selects a conversion process. The transform unit applies one orthogonal transform process to be applied to each target block from among a group of orthogonal transform processes including DCT and DST, according to the position of the reference pixel and the intra prediction mode. The encoding device according to claim 1, which selects the encoding device. A decoding device that decodes in blocks obtained by dividing an original image in frames constituting a moving image,
an entropy decoding unit that decodes an intra prediction mode indicating the type of intra prediction processing;
an intra prediction unit that uses the intra prediction mode to generate a predicted image corresponding to a block to be decoded;
an inverse quantization unit that performs inverse quantization processing on the quantized transform coefficients;
Inverse orthogonal transform processing is applied from among a predefined group of inverse orthogonal transformation processes according to the intra prediction mode and the position of decoded reference pixels that can be used to generate the predicted image, which is determined according to the block decoding order. A decoding device comprising: an inverse transform unit that selects orthogonal transform processing . The inverse transform unit selects one inverse orthogonal transform process to be applied to each target block from a group of inverse orthogonal transform processes including inverse DCT and inverse DST, according to the position of the reference pixel and the intra prediction mode. The decoding device according to claim 3, wherein the decoding device selects two inverse orthogonal transform processes. A program for causing a computer to function as the encoding device according to claim 1. A program for causing a computer to function as the decoding device according to claim 3 .

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