JP2017212554A - Encoder, decoder and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coding performance, by reducing entropy efficiently in intra-prediction.SOLUTION: An encoder 1 includes an intra-prediction unit 14a for generating a prediction image by using intra-prediction mode, a residual signal generation unit 14b for generating a residual signal by the difference of a prediction image and an original image, an inversion unit 14c1 for inverting the residual signal to at least one of horizontal direction and vertical direction, when at least one of the right side and underside is included in the position of a reference pixel used for generation of the prediction image, and an orthogonal transformation unit 14c2 for selecting orthogonal transformation processing to be applied among a prescribed orthogonal transformation processing group, according to the intra-prediction mode and the position of the reference pixel used for generation of the prediction image, and applying the selected orthogonal transformation processing to the inverted residual signal.SELECTED DRAWING: Figure 2

Description

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

  In a moving picture (video) coding system represented by H.265 / HEVC (High Efficiency Video Coding), inter prediction using temporal correlation between frames and intra prediction using spatial correlation within a frame are used. After generating a residual signal by performing prediction while switching between types of predictions, a stream obtained by performing orthogonal transform processing, loop filter processing, and entropy coding processing is output.

  In intra prediction in HEVC, 35 types of intra prediction modes including Planar prediction, DC prediction, and direction prediction are prepared, and intra prediction is performed using adjacent decoded reference pixels according to the intra prediction mode determined by the encoder. Configured to do. Hereinafter, unless otherwise specified, the description “reference pixel” indicates a decoded reference pixel.

  Here, in intra prediction in HEVC, a specified value (10) for a CU that does not have an adjacent reference pixel, such as an encoding target block (hereinafter referred to as “CU: Coding Unit”) located at the upper left in a frame. In the case of a bit moving image, “512”) is embedded to create a reference pixel used when generating a predicted image.

  Further, in the conventional HEVC, since the encoding process is performed in the order of raster scan from the upper left, the reference pixel may not be decoded. In such a case, a predicted image is generated using a value obtained by extrapolating the nearest decoded reference pixel by zero order.

  In particular, in conventional intra prediction in HEVC, reference pixels located on the lower left side or upper right side of a CU are often not decoded by encoding processing in raster scan order. In such a case, reference pixels that are not decoded are used. If direction prediction is performed from the direction in which the image exists, the prediction accuracy is lowered and the coding efficiency is reduced.

  In order to solve such a problem, in intra prediction, a raster scan order (for example, Z-type) is used as an encoding process order for a plurality of transform blocks (hereinafter referred to as “TU: Transform Unit”) existing in a CU. In addition, there is known a technique for improving the prediction accuracy by providing a degree of freedom in the encoding order such as U type and X type (see Non-Patent Document 1).

  In addition, intra prediction used in HEVC is prediction using upper or left reference pixels that are spatially adjacent to each other, and the accuracy of a prediction pixel near the reference pixel is high, and the prediction is a position far from the reference pixel. Pixel accuracy tends to be low (see FIG. 10).

  In the drawings of the present specification, the arrow indicating the direction (prediction direction) of the intra prediction mode is assumed to be directed from the pixel subject to intra prediction to the reference pixel, as described in the HEVC standard (the same applies hereinafter). .

  In the conventional HEVC, using such a property, a discrete sine transform (DST) or a discrete cosine transform (DCT) is performed from the left side and the upper side where the reference pixel is located in the horizontal direction and the vertical direction. The orthogonal transformation process is applied to reduce the entropy of the residual signal.

  In particular, as shown in FIG. 11, the shape of the impulse response of the DST has an asymmetric shape in which one of the end points is closed and the other of the end points is widened. By applying DST according to 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 an optimal orthogonal transform process that concentrates the energy of the residual signal more (can reduce entropy). .

  On the other hand, there is a problem that increasing the number of types of bases for orthogonal transform processing increases the amount of information necessary for transmission and storage of flag information indicating which orthogonal transform processing has been applied.

  In order to prevent such a problem, the technique described in Non-Patent Document 2 is configured to select an orthogonal transform process for a residual signal obtained by intra prediction according to an intra prediction mode.

  The reason 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, and by limiting the options to orthogonal transformation processing that has a statistically high entropy reduction effect, It is possible to reduce the amount of information necessary for transmission and accumulation of flag information indicating the basis of the applied orthogonal transform processing.

Mochizuki et al., “Applied Intra Prediction Method Based on Average Coordinates”, Information Processing Society of Japan, Vol. 2012-AVM-77, No. 12 X.Zhao, J.Chen, M.Karkzewicz, “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, a base group (orthogonal transformation process) that can be selected according to the intra prediction mode without considering the position of the reference pixel used in the intra prediction mode. Group) is determined.

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

  Therefore, in the technique described in Non-Patent Document 2, when intra prediction using the right and lower reference pixels is performed, if the orthogonal transform processing group that can be selected only in the intra prediction mode is switched, The orthogonal transform processing to be applied is selected from the options that are not statistically highly effective in reducing entropy, and there is a problem that entropy increases and coding performance may be degraded.

  Therefore, the present invention has been made to solve the above-described problem, and an encoding device, a decoding device, and a program capable of efficiently reducing entropy and improving encoding performance in intra prediction. The purpose is to provide.

  A first feature of the present invention is an encoding device configured to divide and encode an original image in frame units constituting a moving image into encoding target blocks, and uses an intra prediction mode. An intra prediction unit configured to generate a prediction image, and a residual signal configured to generate a residual signal based on a difference between the prediction image generated by the intra prediction unit and the original image When at least one of the right side and the lower side is included in the position of the reference pixel used to generate the prediction image and the generation unit, the residual signal generated by the residual signal generation unit is at least in the horizontal direction and the vertical direction. Orthogonal transformation processing prescribed in advance according to the reversing unit configured to be reversed to one side, the intra prediction mode, and the position of the reference pixel used for generating the predicted image An orthogonal transformation unit configured to perform the selected orthogonal transformation process on the residual signal inverted by the inversion unit. The gist.

  A second feature of the present invention is a decoding apparatus configured to divide a frame-unit original image constituting a moving image into decoding target blocks and decode the predicted image using an intra prediction mode. An intra prediction unit configured to generate an inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient, the intra prediction mode, and the predicted image In accordance with the position of the reference pixel used for generation of, the inverse orthogonal transform processing to be applied is selected from the predetermined inverse orthogonal transform processing group, the signal output from the inverse quantization unit, A signal output from the inverse orthogonal transform unit when the selected inverse orthogonal transform unit configured to perform the inverse orthogonal transform process and at least one of the right side and the lower side are included in the position of the reference pixel The horizontal And it summarized in that comprising a reversing unit configured to invert at least one of the vertical direction.

  A third feature of the present invention is an encoding device configured to divide and encode an original image in frame units constituting a moving image into encoding target blocks, and uses an intra prediction mode. An intra prediction unit configured to generate a prediction image, and a residual signal configured to generate a residual signal based on a difference between the prediction image generated by the intra prediction unit and the original image According to the generation unit, the intra prediction mode, and the position of the reference pixel used to generate the predicted image, the orthogonal transform process to be applied is selected from the predefined orthogonal transform process group. An orthogonal transform unit, and the orthogonal transform unit includes a residual signal generated by the residual signal generation unit when at least one of a right side and a lower side is included in the position of the reference pixel. For the signal, on which is obtained by inverting at least one of the base of the horizontal and vertical directions, and summarized in that is configured to perform the orthogonal transform processing selected.

  A fourth feature of the present invention is a decoding apparatus configured to divide a frame-unit original image constituting a moving image into decoding target blocks and decode the prediction image using an intra prediction mode. An intra prediction unit configured to generate an inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient, the intra prediction mode, and the predicted image An inverse orthogonal transform unit configured to select an inverse orthogonal transform process to be applied from a group of inverse orthogonal transform processes defined in advance according to the position of a reference pixel used for generating The inverse orthogonal transform unit includes at least one of a horizontal direction and a vertical direction with respect to a signal output from the inverse quantization unit when at least one of a right side and a lower side is included in the position of the reference pixel. Base of On obtained by inverting the, and summarized in that is configured to perform the inverse orthogonal transform processing selected.

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

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

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

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

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

  The encoding apparatus 1 according to the present embodiment is configured to divide and encode a frame-unit original image constituting a moving image into CUs. Also, the encoding device 1 according to the present embodiment may be configured to be able to divide a CU into a plurality of TUs. Hereinafter, in the present embodiment, a case in which a CU is divided into a plurality of TUs will be described as an example. However, the present invention does not divide a CU into a plurality of TUs, and the position of the reference pixel of the CU is lower. It is also applicable to cases that include the side or right side.

  In the present embodiment, a specified value (“512” for a 10-bit moving image) is used for an encoding target CU that does not have an adjacent decoded reference pixel, such as the CU positioned at the upper left in the frame. Since the reference pixels used when generating the predicted image are created by the process of filling in, the pixels adjacent to the left side of the CU to be encoded can be set as reference pixels.

  As illustrated in FIG. 1, the encoding device 1 according to the present embodiment includes an intra prediction mode determination unit 11, a TU partition determination unit 12, a coding order control unit 13, a sequential local decoded image generation unit 14, A memory 15 and an entropy encoding unit 16 are provided.

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

  The TU partition determination unit 12 is configured to determine whether to divide a CU into a plurality of TUs. In this embodiment, as a method of dividing a CU into a plurality of TUs, a case of four divisions is described as an example. However, regarding the number of divisions and division shapes when a CU is divided into a plurality of TUs. However, it is not limited to such a case.

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

  For example, when the TU partition determination unit 12 determines to divide a CU into a plurality of TUs, the coding order control unit 13 determines the direction of the intra prediction mode determined by the intra prediction mode determination unit 11 from the lower left. When the direction is toward the upper right (that is, when direction prediction is performed from the lower left toward the upper right), the encoding order of the TU in the CU is not the conventional raster scan order, but the lower left TU in the 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 → Lower right TU in CU → Of the encoding order of the upper right TU in the CU, a predetermined encoding order may be adopted.

  The sequential local decoded image generation unit 14 is configured to generate a local decoded image (decoded image 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, the sequential local decoded image generation unit 14 follows the encoding order determined by the encoding order control unit 13 when the TU division determination unit 12 determines to divide a CU into a plurality of TUs. The local decoded image is generated sequentially.

  As shown in FIG. 1, the sequential local decoded image generation unit 14 includes an intra prediction unit 14a, a residual signal generation unit 14b, an orthogonal transform / quantization unit 14c, an inverse quantization unit / inverse orthogonal transform unit 14d, And a local decoded image generation unit 14e.

  The intra prediction unit 14a is configured to generate a prediction 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 generate the predicted image using the reference pixel.

  Furthermore, the intra prediction unit 14a may be configured to generate a prediction 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 transform / quantization unit 14c is configured to perform orthogonal transform processing and quantization processing on the residual signal generated by the residual signal generation unit 14b to generate a quantized transform coefficient. .

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

  The reversing unit 14c1 includes a case where at least one of the right side and the lower side is included in the position of the reference pixel used for generating the predicted image (when the predicted image is generated using the reference pixel adjacent to at least one of the right side and the lower side). In addition, the residual signal generated by the residual signal generator 14b is inverted in at least one of the horizontal direction and the vertical direction.

  For example, the inversion 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 a predicted image is generated using a reference pixel adjacent to the lower side). It may be.

  Alternatively, the inversion 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). May be.

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

  Specifically, the orthogonal transform unit 14c2 is applied from among the orthogonal transform processing groups (orthogonal transform base groups) defined in advance according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. The orthogonal transform process is selected, and the selected orthogonal transform process is performed on the residual signal inverted by the inversion unit 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.

  In addition, although this embodiment demonstrates the example using the intra prediction mode in HEVC shown in FIG. 3, this invention is applicable also to the example where 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 transform coefficients using orthogonal transform processing. By concentrating the energy of the residual signal by the orthogonal transform process, it is possible to improve the encoding efficiency in the subsequent entropy encoding process.

  HEVC is prepared as an orthogonal transform process to which DCT and DST can be applied, and the orthogonal transform process is performed while switching according to the block size and the prediction mode.

  Here, the orthogonal transformation process is not limited to DST, DCT, or the like, but may be a transformation process (including an integer for speeding up) applied to the residual signal for the purpose of concentrating energy. Any conversion process may be used.

  Increasing the types of orthogonal transform processing that can be selected increases the possibility of selecting an orthogonal transform process that concentrates more energy for residual signals with various energy distributions. The amount of information required to transmit and store flag information indicating whether to apply the conversion process increases.

  The energy distribution of the residual signal is statistically correlated with the distance from the reference pixel used for intra prediction. For this reason, the energy distribution of the residual signal is different between the intra prediction mode using only the left reference pixel and the intra prediction mode using the left and upper reference pixels.

  Therefore, the technique described in Non-Patent Document 2 uses an orthogonal transform that can be selected according to the direction of the intra prediction mode using the correlation between the bias of the energy distribution of the residual signal and the direction of the intra prediction mode. The processing group is configured to be switched.

  4 (a) and 4 (b), as an example of the energy distribution of the residual signal, intra prediction mode 2 in HEVC (intra prediction mode using only reference pixels located on the left side) and intra prediction mode 18 (left side). And the difference in energy distribution of the residual signal in the intra prediction mode using the reference pixel located on the upper side).

  Thus, for the residual signals having different energy distributions, the orthogonal transformation process having a statistically high entropy reduction effect is different.

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

  According to this technique, by switching the applicable orthogonal transform processing group according to the direction of the intra prediction mode, which of the applied orthogonal transform processing is efficiently concentrated while statistical energy distribution of the residual signal is efficiently concentrated. It is possible to reduce the information amount of the flag indicating whether or not.

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

  The energy distribution of the residual signal by the direction prediction in the intra prediction mode 2 using the reference pixels located on the left side and the lower side (see FIG. 5) uses the reference pixels located on the left side and the upper side shown in FIG. The energy distribution is the same as that obtained by inverting the residual signal obtained by the direction prediction in the intra prediction mode 18 in the vertical direction.

  That is, when the direction prediction in the intra prediction mode 2 is performed, the left and lower sides are included as the positions of the reference pixels, and obtained when the residual signal is inverted in the vertical direction and the orthogonal transformation process is applied. The energy distribution of the orthogonal transform coefficient is the case where the left and upper sides are included as the position of the reference pixel when performing the direction prediction in the intra prediction mode 18, and the residual signal is not inverted in the horizontal direction and the vertical direction. This is the same as the energy distribution of the orthogonal transform coefficient obtained when the orthogonal transform process is applied (see FIGS. 4B and 5).

  Since the energy distribution of the orthogonal transform coefficient obtained by the orthogonal transform process on the residual signal by the direction prediction in the intra prediction mode 2 differs depending on the position of the reference pixel used for the intra prediction, the orthogonality applicable only based on the intra prediction mode. By determining the transform processing group, entropy may increase and coding performance may be degraded.

  Therefore, when the residual signal is inverted in at least one of the horizontal direction and the vertical direction according to the position of the reference pixel in the intra prediction, the orthogonal transform unit 14c2 selects according to the direction of the applied intra prediction mode and the position of the reference pixel. A possible orthogonal transform processing group is determined.

  That is, when the intra prediction mode belongs to category B, the orthogonal transform unit 14c2 is configured to select an orthogonal transform process to be applied from a group of orthogonal transforms defined in advance according to the direction of the intra prediction mode. May be.

  For example, when the intra prediction mode is 18, the orthogonal transform unit 14c2 is configured to select an orthogonal transform process to be applied from a group of orthogonal transforms defined in advance according to the direction of the intra prediction mode 18. May be.

  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 transform unit 14c2 performs orthogonality defined in advance according to the direction of the intra prediction mode. The orthogonal transform process to be applied may be selected from the 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 orthogonal transform unit 14c2 has a group of orthogonal transforms that are defined in advance according to the direction of the intra prediction mode 2. May be configured to select an orthogonal transform process to be applied.

  Alternatively, when the intra prediction mode belongs to the category C and the right side is not included as the position of the reference pixel, the orthogonal transform unit 14c2 uses the orthogonality defined in advance according to the direction of the intra prediction mode. The orthogonal transform process to be applied may be selected from the 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 orthogonal transform unit 14c2 determines the orthogonal transform group defined in advance according to the direction of the intra prediction mode 34. May be configured to select an orthogonal transform process to be applied.

  Also, the orthogonal transform unit 14c2 applies the orthogonal transform that is applied from the orthogonal transform group that is defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the vertical direction when the lower side is included in the position of the reference pixel. It may be configured to select a process.

  Here, “invert the direction of the intra prediction mode in the vertical direction” means to convert between the directions of the intra prediction modes 2 to 9 and the directions of the intra prediction modes 18 to 11 in the example of FIG. 3. That is, it means that the direction of each intra prediction mode is converted to the direction of the intra prediction mode having a line-symmetric 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 transform unit 14c2 responds to the direction obtained by inverting the direction of the intra prediction mode in the vertical direction. The orthogonal transformation processing to be applied may be selected from among the orthogonal transformation groups defined in advance.

  For example, when the intra prediction mode is 2 and the lower side is included as the position of the reference pixel, the orthogonal transform unit 14c2 rotates the direction of the intra prediction mode 2 in the vertical direction (intra prediction mode). The orthogonal transformation processing to be applied may be selected from among the orthogonal transformation groups defined in advance according to the (18 directions).

  Alternatively, the orthogonal transform unit 14c2 applies the orthogonal transform that is applied from the orthogonal transform group that is defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the horizontal direction when the right side is included in the position of the reference pixel. It may be configured to select a process.

  Here, “invert the direction of the intra prediction mode in the horizontal direction” means to convert between the directions of the intra prediction modes 18 to 25 and the directions of the intra prediction modes 34 to 27 in the example of FIG. That is, it means that the direction of each intra prediction mode is converted to the direction of the intra prediction mode having a line-symmetric 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 transform unit 14c2 responds to the direction obtained by inverting the direction of the intra prediction mode in the horizontal direction. The orthogonal transformation processing to be applied may be selected from among the orthogonal transformation groups defined in advance.

  For example, when the intra prediction mode is 34 and the right side is included as the position of the reference pixel, the orthogonal transform unit 14c2 reverses the direction of the intra prediction mode 34 in the horizontal direction (intra prediction mode). The orthogonal transformation processing to be applied may be selected from among the orthogonal transformation groups defined in advance according to the (18 directions).

  The quantization unit 14c3 is configured to perform a quantization process on the signal output from the orthogonal transform unit 14c2 and generate a quantized transform coefficient.

  The inverse quantization unit / inverse orthogonal transform unit 14d performs the inverse quantization process and the inverse orthogonal transform process on the quantized transform coefficient generated by the orthogonal transform / quantization unit 14c again to generate a residual signal. Configured to generate.

  The local decoded image generation unit 14e generates a local decoded image by adding the prediction 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 local decoded image generated by the sequential local decoded image generation unit 14 so that it can be used as a reference image.

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

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

  As illustrated 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 uses the reference pixel to determine the predicted image. And a residual signal is generated based on the difference between the predicted image and the original image.

  In step S102, the encoding device 1 uses the residual signal generated by the residual signal generation unit 14b in the horizontal direction when at least one of the right side and the lower side is included in the position of the reference pixel used for generating the predicted image. And reverse in at least one of the vertical directions.

  In step S103, the encoding apparatus 1 selects an orthogonal transform process to be applied from a group of orthogonal transform processes defined in advance according to the intra prediction mode and the position of a reference pixel used for generating a 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 subjected to the orthogonal transform process, and generates a quantized transform coefficient.

  In step S105, the encoding apparatus 1 performs entropy encoding processing on the flag information including the intra prediction mode and the like and the quantized transform coefficient, and outputs the stream.

  In addition, the decoding device 3 according to the present embodiment is configured to decode a frame-unit original image constituting a moving image by dividing it into CUs. Also, the decoding device 3 according to the present embodiment is configured to be able to divide a CU into a plurality of TUs, similarly to the encoding device 1 according to the present embodiment.

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

  The entropy decoding unit 31 is configured to decode transform coefficients, flag information, and the like 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 coefficient is a quantized transform coefficient obtained by the encoding apparatus 1 as a signal encoded by dividing an original image in frame units into CUs.

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

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

  For example, the decoding order control unit 32, like the coding order control unit 13, is a case where the CU is divided into a plurality of TUs and the direction of the intra prediction mode is a direction from the lower left to the upper right. Decoding order of 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 → in CU The decoding processing may be performed in a predetermined decoding order among the decoding order of the upper right TU → the upper right TU in the CU.

  The sequential decoded image generation unit 33 is configured to generate a decoded image (decoded image 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 the CU is divided into a plurality of TUs, the sequential decoded image generation unit 33 performs the quantization output from 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 transform processing, and intra prediction on the transform coefficients.

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

  The intra prediction unit 33a may be configured to generate a prediction 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, an inverse orthogonal transform process) on the quantized transform coefficient output from the entropy decoding unit 31, thereby obtaining a residual. It is configured to generate a signal.

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

  The inverse quantization unit 33b1 is configured to perform an inverse quantization process on the quantized transform coefficient output by the entropy decoding unit 31.

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

  Specifically, similarly to the orthogonal transform unit 14c2, the inverse orthogonal transform unit 33b2 includes a group of inverse orthogonal transform groups that are defined in advance according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. The inverse orthogonal transform process to be applied is selected, and the selected inverse orthogonal transform process is performed on the signal output from the inverse quantization unit 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 groups 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 the inverse orthogonal transform groups defined in advance according to the direction of the intra prediction mode 18. It 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 transform unit 33b2 is defined in advance according to the direction of the intra prediction mode. An inverse orthogonal transform process to be applied may be selected from 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 is the inverse orthogonal defined in advance according to the direction of the intra prediction mode 2. The inverse orthogonal transform process to be applied may be selected from 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 transform unit 33b2 is defined in advance according to the direction of the intra prediction mode. An inverse orthogonal transform process to be applied may be selected from 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 transform unit 33b2 performs the inverse orthogonal defined in advance according to the direction of the intra prediction mode 34. The inverse orthogonal transform process to be applied may be selected from the transform group.

  Further, when the lower side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 applies the inverse orthogonal transform group defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the vertical direction. It may be configured to select an inverse orthogonal transform process.

  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 transform unit 33b2 sets the direction of the intra prediction mode in the direction inverted in the vertical direction. Accordingly, an inverse orthogonal transform process to be applied may be selected from a group of inverse orthogonal transforms defined in advance.

  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 transform unit 33b2 reverses the direction of the intra prediction mode 2 in the vertical direction (intra prediction). It may be configured to select an inverse orthogonal transform process to be applied from a group of inverse orthogonal transforms defined in advance according to the direction of the mode 18).

  Alternatively, when the right side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 applies the inverse orthogonal transform group defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the horizontal direction. It may be configured to select an inverse orthogonal transform process.

  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 transform unit 33b2 sets the direction of the intra prediction mode in the direction reversed in the horizontal direction. Accordingly, an inverse orthogonal transform process to be applied may be selected from a group of inverse orthogonal transforms defined in advance.

  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 transform unit 33b2 reverses the direction of the intra prediction mode 34 in the horizontal direction (intra prediction It may be configured to select an inverse orthogonal transform process to be applied from a group of inverse orthogonal transforms defined in advance according to the direction of the mode 18).

  The inversion unit 33b3 is configured to invert the signal output from the inverse orthogonal transform unit 33b2 to 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. Yes.

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

  Alternatively, the inversion unit 33b3 may be configured to invert the signal output from the inverse orthogonal transform unit 33b2 in the horizontal direction 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 prediction image generated by the intra prediction unit 33a and the residual signal generated by the inverse quantization / inverse conversion unit 33b.

  The memory 34 is configured to hold the decoded image generated by the sequential decoded image generation unit 33 so that it can be used as a reference image 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 illustrated in FIG. 9, in step S201, the decoding device 3 generates a prediction image using the intra prediction mode.

  In step S202, the decoding device 3 performs an inverse quantization process on the quantized transform coefficient.

  In step S203, the decoding device 3 selects an inverse orthogonal transform process to be applied from among the inverse orthogonal transform groups defined in advance according to the intra prediction mode and the position of the reference pixel used for generating the predicted image, The selected inverse orthogonal transform process is performed on the signal subjected to the inverse quantization process.

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

  According to the encoding device 1 and the decoding device 3 according to the present embodiment, different orthogonal transform processing groups differ depending on not only the direction of the intra prediction mode but also the position of the reference pixel with respect to the residual signal obtained by intra prediction. Can be switched and used, and entropy can be reduced, thereby improving the coding efficiency.

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

  The encoding device 1 according to the present embodiment does not include the inverting unit 14c1, and the decoding device 3 according to the present embodiment does not include the inverting unit 33b3.

  In the encoding device 1 according to the present embodiment, the orthogonal transform unit 14c2 applies the predetermined orthogonal transform processing group according to the intra prediction mode and the position of the reference pixel used to generate the predicted image. An orthogonal transformation process is selected.

  Here, when at least one of the right side and the lower side is included in the position of the reference pixel, the orthogonal transform unit 14c2 applies the horizontal direction and the vertical direction to the residual signal generated by the residual signal generation unit 14b. The selected orthogonal transformation process is performed after inverting at least one of the bases.

  Specifically, the orthogonal transform unit 14c2 selects from the orthogonal transform processing group defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the vertical direction when the position of the reference pixel includes the lower side. The orthogonal transformation process to be applied may be selected, the vertical base may be inverted with respect to the residual signal, and the selected orthogonal transformation process may be performed.

  Alternatively, when the right side is included in the position of the reference pixel, the orthogonal transform unit 14c2 applies the orthogonal transform applied from the orthogonal transform processing group that is defined in advance according to the direction in which the direction of the intra prediction mode is reversed in the horizontal direction. It may be configured to select the transform process, invert the horizontal base 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 is applied from among the inverse orthogonal transform processing groups defined in advance according to the intra prediction mode and the position of the reference pixel used for generating the predicted image. The inverse orthogonal transform process is selected.

  Here, the inverse orthogonal transform unit 33b2 performs at least one of the horizontal direction and the vertical direction on the signal output from the inverse quantization unit 33b1 when at least one of the right side and the lower side is included in the position of the reference pixel. The selected orthogonal transformation process is performed after inverting the base of.

  Specifically, when the lower side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 is a group of inverse orthogonal transform processing groups defined in advance according to the direction in which the direction of the intra prediction mode is inverted in the vertical direction. The inverse orthogonal transform process to be applied is selected, the vertical base is inverted with respect to the signal output from the inverse quantization unit 33b1, and the selected inverse orthogonal transform process is performed. Also good.

  Or, when the right side is included in the position of the reference pixel, the inverse orthogonal transform unit 33b2 is applied from among the inverse orthogonal transform processing groups defined in advance according to the direction in which the direction of the intra prediction mode is reversed in the horizontal direction. It is also possible to select the inverse orthogonal transform process to be performed, invert the horizontal base on the signal output from the inverse quantization unit 33b1, and then perform the selected inverse orthogonal transform process.

(Other embodiments)
As described above, the present invention has been described by using the above-described embodiment. However, it should not be understood that the description and drawings constituting a part of the disclosure in the embodiment limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  Further, although not particularly mentioned in the above-described embodiment, a program for causing a computer to execute each process performed by the above-described encoding device 1 and decoding device 3 may be provided. Such a program may be recorded on a computer-readable medium. If a computer readable medium is used, such a program can be installed in the 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.

  Alternatively, a chip configured by a memory that stores a program for realizing at least a part of the functions in the encoding device 1 and the decoding device 3 and a processor that executes the program stored in the memory may be provided. Good.

DESCRIPTION OF SYMBOLS 1 ... Coding apparatus 11 ... Intra prediction mode determination part 12 ... TU division | segmentation determination part 13 ... Coding order control part 14 ... Sequential local decoded image generation part 14a ... Intra prediction part 14b ... Residual signal generation part 14c ... Orthogonal transformation * Quantization unit 14c1 ... Inversion unit 14c2 ... Orthogonal transformation unit 14c3 ... Quantization unit 14d ... Inverse quantization unit / inverse orthogonal transformation unit 14e ... Local decoded image generation unit 15 ... Memory 16 ... Entropy encoding unit 3 ... Decoding device 31 ... Entropy decoding unit 32 ... decoding order control unit 33 ... sequential local 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 (14)

An encoding device configured to divide and encode an original image of a frame unit constituting a moving image into encoding target blocks,
An intra prediction unit configured to generate a prediction image using the intra prediction mode;
A residual signal generation unit configured to generate a residual signal based on a difference between the predicted image generated by the intra prediction unit and the original image;
When the position of the reference pixel used for generating the predicted image includes at least one of the right side and the lower side, the residual signal generated by the residual signal generation unit is inverted to at least one of the horizontal direction and the vertical direction. An inversion part configured as follows:
According to the intra prediction mode and the position of the reference pixel used for generating the predicted image, an orthogonal transform process to be applied is selected from a group of orthogonal transform processes defined in advance, and is inverted by the inversion unit. An encoding apparatus comprising: an orthogonal transform unit configured to perform the selected orthogonal transform process on a residual signal. The inversion unit 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 the lower side is included in the position of the reference pixel, the orthogonal transform unit applies from among the orthogonal transform processing groups defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the vertical direction. The encoding apparatus according to claim 1, wherein the encoding apparatus is configured to select the orthogonal transform process. The inversion unit is configured to invert the residual signal in a horizontal direction when the right side is included in the position of the reference pixel,
When the right side is included in the position of the reference pixel, the orthogonal transform unit applies from among the orthogonal transform processing groups defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the horizontal direction. The encoding apparatus according to claim 1, wherein the encoding apparatus is configured to select the orthogonal transform process. A decoding device configured to divide and decode an original image of a frame unit constituting a moving image into encoding target blocks,
An intra prediction unit configured to generate a prediction image using the intra prediction mode;
An inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient;
According to the intra prediction mode and the position of the reference pixel used for generation of the predicted image, an inverse orthogonal transform process to be applied is selected from a predetermined inverse orthogonal transform process group, and the inverse quantization unit An inverse orthogonal transform unit configured to perform the selected inverse orthogonal transform process on the output signal;
An inversion unit configured to invert a signal output from the inverse orthogonal transform unit in at least one of a horizontal direction and a vertical direction when at least one of the right side and the lower side is included in the position of the reference pixel; A decoding apparatus comprising: When the lower side is included in the position of the reference pixel, the inverse orthogonal transform unit includes the inverse orthogonal transform processing group that is defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the vertical direction. Configured to select the inverse orthogonal transform process to apply;
The said inversion part is comprised so that the signal output from the said inverse orthogonal transformation part may be inverted in a perpendicular direction, when the lower side is contained in the position of the said reference pixel, The said output part is characterized by the above-mentioned. Decoding device. The inverse orthogonal transform unit, when the right side is included in the position of the reference pixel, from among the inverse orthogonal transform processing group defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the horizontal direction Configured to select the inverse orthogonal transform process to apply;
The said inversion part is comprised so that the signal output from the said inverse orthogonal transformation part may be reversed in a horizontal direction, when the right side is contained in the position of the said reference pixel, The Claim 4 or 5 characterized by the above-mentioned. The decoding device according to 1. An encoding device configured to divide and encode an original image of a frame unit constituting a moving image into encoding target blocks,
An intra prediction unit configured to generate a prediction image using the intra prediction mode;
A residual signal generation unit configured to generate a residual signal based on a difference between the predicted image generated by the intra prediction unit and the original image;
An orthogonal transform unit configured to select an orthogonal transform process to be applied from a group of orthogonal transform processes defined in advance according to the intra prediction mode and the position of a reference pixel used for generating the predicted image. And
The orthogonal transform unit may include at least one of a horizontal direction and a vertical direction with respect to the residual signal generated by the residual signal generation unit when at least one of the right side and the lower side is included in the position of the reference pixel. An encoding device is configured to perform the selected orthogonal transformation process after inverting the base of.   When the lower side is included in the position of the reference pixel, the orthogonal transform unit applies from among the orthogonal transform processing groups defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the vertical direction. 8. The apparatus according to claim 7, wherein the orthogonal transform process is selected, the selected orthogonal transform process is performed after the vertical base is inverted with respect to the residual signal. The encoding device described.   When the right side is included in the position of the reference pixel, the orthogonal transform unit applies from among the orthogonal transform processing groups defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the horizontal direction. The orthogonal transform processing is selected, and the horizontal transform base is inverted with respect to the residual signal, and then the selected orthogonal transform processing is performed. 8. The encoding device according to 8. A decoding device configured to divide and decode an original image of a frame unit constituting a moving image into encoding target blocks,
An intra prediction unit configured to generate a prediction image using the intra prediction mode;
An inverse quantization unit configured to perform an inverse quantization process on the quantized transform coefficient;
Inverse configured to select an inverse orthogonal transform process to be applied from a group of inverse orthogonal transform processes defined in advance according to the intra prediction mode and the position of a reference pixel used to generate the predicted image. An orthogonal transformation unit,
When the reference pixel includes at least one of a right side and a lower side in the position of the reference pixel, the inverse orthogonal transform unit outputs at least one base in the horizontal direction and the vertical direction with respect to the signal output from the inverse quantization unit. The decoding apparatus is configured to perform the selected inverse orthogonal transform process after inverting.   When the lower side is included in the position of the reference pixel, the inverse orthogonal transform unit includes the inverse orthogonal transform processing group that is defined in advance according to a direction obtained by inverting the direction of the intra prediction mode in the vertical direction. The inverse orthogonal transform process to be applied is selected, the vertical base is inverted with respect to the signal output from the inverse quantization unit, and the selected inverse orthogonal transform process is performed. The decoding apparatus according to claim 10, wherein:   The inverse orthogonal transform unit, when the right side is included in the position of the reference pixel, from among the inverse orthogonal transform processing group defined in advance according to the direction obtained by inverting the direction of the intra prediction mode in the horizontal direction The inverse orthogonal transform process to be applied is selected, the horizontal base is inverted with respect to the signal output from the inverse quantization unit, and the selected inverse orthogonal transform process is performed. The decoding device according to claim 10 or 11, wherein   The program for functioning a computer as an encoding apparatus as described in any one of Claims 1 thru | or 3, 7 thru | or 9.   A program for causing a computer to function as the decoding device according to any one of claims 4 to 6, 10 to 12.