JP2013098970A - Image decoding apparatus, inverse orthogonal conversion method, program and image coding apparatus - Google Patents

Abstract

Encoding efficiency is improved by making it possible to select a DST for blocks other than 4 × 4 while suppressing an increase in processing amount.
An image decoding apparatus that performs intra prediction using a plurality of prediction directions, comprising: a transform block that is target data for inverse orthogonal transform; and a prediction block that indicates a block used in the intra prediction. A determination unit that determines whether or not a condition related to the block size is satisfied, an inverse discrete cosine transform based on a determination result by the determination unit, and an inverse discrete cosine transform for a preset horizontal / vertical direction depending on a prediction direction And / or a control unit that controls which of the inverse discrete sine transforms is performed, and an inverse transform unit that performs an inverse orthogonal transform process controlled by the control unit on the transform block.
[Selection] Figure 11

Description

  The present invention relates to an image decoding apparatus, an inverse orthogonal transform control method, a program, and an image encoding apparatus that perform intra prediction using a plurality of prediction directions.

  In recent years, with the advance of multimedia, there are many opportunities to handle moving images. Image data has a large amount of information, and a moving image, which is a set of images, has an information amount exceeding 1 Gbit / sec in high-definition (1920 × 1080) broadcasting, which is the mainstream of television broadcasting.

  Therefore, the moving image data is H.264. H.264 / AVC (Advanced Video Coding) and standardization work HEVC (High Efficiency Video Coding) and the like are used for transmission and storage by compressing the amount of information.

  HEVC does not simply divide the screen into blocks that are encoding units from the upper left as in the conventional encoding technique, but newly adopts hierarchical division to enable block division of a plurality of hierarchies. A coding unit divided into a plurality of blocks is also called a CU (Coding Unit) or a coding block.

  FIG. 1 is a diagram illustrating an example of block division by HEVC. As shown in FIG. 1, in HEVC, an image can be divided into 4 × 4, 8 × 8, 16 × 16, 32 × 32, etc. and encoded.

  In HEVC, in order to efficiently express the prediction error signal, the CU can be divided into layers and divided into conversion units. The transform unit is also called a TU (Transform Unit) or transform block.

  FIG. 2 is a diagram illustrating a relationship between a CU and a TU. As shown in FIG. 2, for example, for a 32 × 32 CU, a TU with 0 layer division is the same block as a 32 × 32 CU, and a TU with 1 layer division is a block divided into 16 × 16 It is. In addition, a TU with two hierarchical divisions is a block divided into 8 × 8.

  Since TUs are hierarchically divided according to the size of CUs, the TU sizes in each layer are different depending on the size of CUs.

  In HEVC, a CU is divided into prediction units that are a plurality of types of rectangular areas, and prediction processing is performed in each prediction unit. This prediction unit is also referred to as a PU (Prediction Unit) or a prediction block.

  FIG. 3 is a diagram illustrating an example of a prediction block used in inter-screen prediction or intra-screen prediction. As shown in FIG. 3, a CU can be divided into four types of PUs. For example, a 2N × 2N CU is divided into a 2N × 2N PU, an N × N PU, an N × 2N PU, and a 2N × N PU. There are various types of PUs depending on the size of the CU.

  Here, in the intra-frame coding (intra coding) for the divided blocks, spatial signal prediction within the screen is performed, and this technique is called intra-frame prediction (intra prediction). There are a plurality of methods for intra prediction that are being studied in HEVC.

  As one of the methods, a technique for predicting the signal of the encoded block with reference to the already encoded and decoded signal around the encoded block will be described. The encoder uses a signal known by the decoder as a signal to be used for prediction. For this reason, the encoder includes a local decoder that performs processing equivalent to that of the decoder, and the encoded signals are sequentially decoded.

  Therefore, the predetermined signal located around the signal of the encoding block to be encoded has already been decoded by the local decoder. In the case of HEVC, as in the conventional encoding process, the blocks located on the left and upper side of the encoding block to be encoded have already been decoded, and the signal of the encoding block is predicted using the decoded signal. To do.

  The basic principle of this prediction is H.264. Signal prediction is performed in the same manner as H.264 / AVC intra prediction (Non-Patent Document 1). In HEVC, the direction of signal prediction is H.264. H.264 / AVC, and signal prediction in 33 directions is performed at the maximum.

  FIG. 4 is a diagram illustrating a prediction direction of intra prediction by HEVC. As shown in FIG. 4, in HEVC, intra prediction is performed using 33 prediction directions.

  In the case of a video signal, since the correlation between adjacent pixels is high on average, according to this prediction, the signal adjacent to the reference signal has high prediction accuracy, and the signal located farther from the reference signal has lower prediction accuracy.

  The difference between the reference signal by prediction and the original signal is called a prediction error signal, and the prediction error signal is encoded by orthogonal transform. In the conventional encoding technique, two-dimensional DCT (Discrete Cosine Transform) or integerized two-dimensional DCT is used as orthogonal transform.

  In HEVC, a plurality of orthogonal transforms depending on the prediction mode of intra prediction can be selected in addition to DCT. As the orthogonal transformation, switching between DCT and discrete sine transform type VII (hereinafter referred to as DST) is performed.

  Therefore, in HEVC, a combination of different orthogonal transforms can be selected for a two-dimensional signal in the horizontal direction and the vertical direction. In general, when the number of options is increased, an identification flag for transmitting to the decoder which orthogonal transform has been selected is required. However, this identification flag becomes additional information, and the efficiency of information amount reduction by encoding is reduced.

  Therefore, in order to suppress this reduction in coding efficiency, the transform block is limited to a block size of 4 × 4 and 8 × 8, and DCT and DST in the horizontal direction and the vertical direction according to the prediction direction of intra prediction. There is a technique in which which is used for encoding is set in advance (Non-Patent Documents 2 and 3).

  As a result, a table describing combinations of DCT and DST set in advance is prepared in both the encoder and the decoder, so that an identification flag becomes unnecessary, and a decrease in encoding efficiency can be prevented. .

Supervised by Satoshi Okubo, “Revised Third Edition H.264 / AVC Textbook”, Impress R & D, p. 264-268, January 1, 2009 Ankur Saxena, `` CE7: Mode-dependent DCT / DST without 4 * 4 full matrix multiplication for intra prediction (JCTVC-E125) '', Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11 5th Meeting: Geneva, CH, 16-23 March, 2011 Ankur Saxena, `` CE7: Mode-dependent 8x8 DCT / DST for Intra Prediction (JCTVC-F282) '', Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO / IEC JTC1 / SC29 / WG11 6th Meeting: Torino, IT, 14-22 July, 2011

  However, the nature of the prediction error signal is lost as the block size increases and the number of pixels adjacent to the reference signal decreases with respect to the number of pixels constituting this block. For this reason, the improvement effect of the encoding efficiency by selecting DST is limited to a relatively small block. Therefore, the selection of DST is limited to 4 × 4 blocks as in the technique described in Non-Patent Document 2.

  In addition, as a method for enabling selection of DST, in Non-Patent Document 3, since it is applied to all 8 × 8 transform blocks, the processing amount increases, and the effect of coding efficiency due to the increase in processing amount. There is a problem that there are few.

  Accordingly, an image decoding apparatus that has been made in view of the above-described problem and can improve the coding efficiency by making it possible to select a DST for blocks other than 4 × 4 while suppressing an increase in processing amount. An object of the present invention is to provide an inverse orthogonal transform control method, a program, and an image encoding device.

  An image decoding apparatus according to an aspect of the present invention is an image decoding apparatus that performs intra prediction using a plurality of prediction directions, and is used in a transform block that is target data of inverse orthogonal transform and the intra prediction. A determination unit that determines whether or not a prediction block indicating a block satisfies a condition regarding a block size, and an inverse discrete cosine transform and a preset value depending on the prediction direction based on a determination result by the determination unit A control unit that controls whether to perform inverse discrete cosine transform and / or inverse discrete sine transform for horizontal and vertical directions, and inverse orthogonal transform processing controlled by the control unit to the transform block And an inverse conversion unit for performing.

  In addition, the condition is that the size of the transform block is 8 × 8, the number of layer divisions from an encoded block obtained by dividing an image into a predetermined size is 0, and the control unit satisfies the condition: The inverse discrete cosine transform and / or the inverse discrete sine transform may be controlled to be performed by the inverse transform unit.

  Further, the condition is that the size of the prediction block and the size of the transform block are equal to or less than 8 × 8, and the control unit performs the inverse discrete cosine transform and / or inverse when the condition is satisfied. Control may be performed so that the inverse transformation unit performs processing of discrete sine transformation.

  The condition is that the prediction block is a rectangle having a long side of 16 or less, and the control unit performs the inverse discrete cosine transform and / or inverse discrete sine transform processing when the condition is satisfied. It may be controlled to perform.

  Further, in the inverse orthogonal transform control method according to another aspect of the present invention, the transform block that is the target data of the inverse orthogonal transform and the prediction block indicating the block used in the intra-screen prediction satisfy a condition regarding the block size. A determination step for determining whether or not, and an inverse discrete cosine transform for the horizontal and vertical directions set in advance depending on the prediction direction used in the intra prediction based on the determination result of the determination step And / or a computer executing a control step for controlling which of the inverse discrete sine transform is performed, and an inverse transform step for performing the inverse orthogonal transform process controlled by the control step on the transform block. To do.

  Further, the program according to another aspect of the present invention determines whether or not a transform block that is data to be subjected to inverse orthogonal transform and a prediction block indicating a block used in the intra-screen prediction satisfy a condition regarding a block size. A determination step, and an inverse discrete cosine transform and an inverse discrete cosine transform and / or inverse with respect to a preset horizontal / vertical direction depending on a prediction direction used in intra prediction based on a determination result of the determination step The computer executes a control step for controlling which of the discrete sine transform is performed and an inverse transform step for performing the inverse orthogonal transform controlled by the control step on the transform block.

  An image encoding apparatus according to another aspect of the present invention includes a prediction block that is included in an encoding target block in which an image is divided into a predetermined size and indicates a block used for the intra prediction, and the encoding target block Is determined based on the determination result by the determination unit, the determination unit determines whether or not the transform block divided into one or more by the hierarchical division satisfies the condition regarding the block size, and in the prediction direction A control unit that controls whether to perform discrete cosine transform and / or discrete sine transform in a preset horizontal / vertical direction depending on the orthogonal transform processing controlled by the control unit. And a conversion unit for the block.

  According to the present invention, encoding efficiency can be improved by making it possible to select a DST for blocks other than 4 × 4 while suppressing an increase in processing amount.

The figure which shows an example of the block division | segmentation by HEVC. The figure which shows the relationship between CU and TU. The block diagram which shows an example of a structure of an intra estimation part. The figure which shows the prediction direction of the intra prediction by HEVC. The figure which shows the relationship between a prediction block, a conversion block, and prediction efficiency. 1 is a block diagram illustrating an example of a schematic configuration of an image encoding device according to Embodiment 1. FIG. The block diagram which shows an example of a structure of an orthogonal transformation part. The flowchart which shows an example of orthogonal transformation control processing (the 1). The flowchart which shows an example of orthogonal transformation control processing (the 2). The flowchart which shows an example of orthogonal transformation control processing (the 3). FIG. 6 is a block diagram illustrating an example of a configuration of an image decoding device according to a second embodiment. The block diagram which shows an example of a structure of an inverse orthogonal transformation part. FIG. 9 is a block diagram illustrating an example of a configuration of an image processing apparatus according to a third embodiment.

  First, the premise of each embodiment described below will be described. As described above, switching between DCT and DST depending on the prediction direction of intra prediction shows an effect on the smallest block size, and shows an effect on a block having a size exceeding 4 × 4. Not exclusively.

  Here, the prediction direction of intra prediction is determined by a prediction block including one or a plurality of transform blocks. The prediction block represents a prediction target block used in, for example, intra prediction. One or a plurality of transform blocks included in the same prediction block performs prediction in the same prediction direction.

  On the other hand, when the prediction block includes a plurality of transform blocks, the prediction accuracy by the prediction method selected for each transform block varies. Therefore, when encoding is performed with a combination of DCT and DST that is uniformly predetermined according to the prediction direction, encoding efficiency may or may not be improved.

  For this reason, the prediction that shows the effect when the improvement efficiencies in the respective transform blocks are averaged is selected, but the optimum prediction is not necessarily performed in each transform block. In such a conversion block, DST does not always show the effect as expected.

  In view of this, the inventors of the present invention, when the trend of the prediction error signal is uniform in the transform block in the prediction block, the tendency of the prediction error signal using the directionality of the signal is approximated to the signal assumed by the DST. I thought that it was guaranteed with a high probability.

  That is, if the DST can be selected only when the tendency of the prediction error signal is uniform in the transform block in the prediction block, the coding efficiency can be improved efficiently. The case where the tendency of the prediction error signal is uniform among the transform blocks in the prediction block is, for example, a case where the block sizes of the prediction block and the transform block match. The block size at this time is 8 × 8 or 4 × 4.

  In addition, even when the prediction block is rectangular, considering that the prediction block is divided into different prediction blocks because the pattern of each prediction block is different, there is a tendency of the prediction error signal in the transform blocks in these prediction blocks. It may be uniform. Hereinafter, the tendency of the prediction error signal is also referred to as prediction efficiency.

  FIG. 5 is a diagram illustrating the relationship among the prediction block, the transform block, and the prediction efficiency. The arrow shown in FIG. 5 represents the prediction direction. FIG. 5A shows a case where the prediction block pu11 and the transform block tu11 have the same size. In the example shown in FIG. 5A, the prediction block pu11 and the transform block tu11 have the same size, so the prediction efficiency is uniform. Therefore, in the case shown in FIG. 5A, it is only necessary to select DCT and DST depending on the prediction direction.

  FIG. 5B shows a case where the prediction block pu21 is divided into four transform blocks tu21 to 24. In the example shown in FIG. 5B, since the prediction efficiency varies, the prediction block is divided. In the case shown in FIG. 5B, a normal DCT may be used.

  FIG. 5C shows an example in which the prediction blocks pu31 and 32 are divided. In the case of FIG. 5C, although the prediction directions are different between the prediction block pu31 and the prediction block pu32, this increases the possibility that the prediction efficiency is uniform in each prediction block. Therefore, DCT and DST depending on the prediction direction may be selected for the transform blocks tu31 and 32 in the prediction block pu31 and the transform blocks tu33 and 34 in the prediction block pu32 illustrated in FIG. .

  Embodiments based on the above assumption will be described in detail below with reference to the accompanying drawings.

[Example 1]
<Configuration>
FIG. 6 is a block diagram illustrating an example of a schematic configuration of the image encoding device 10 according to the first embodiment. In the example illustrated in FIG. 6, the image encoding device 10 includes a preprocessing unit 100, a prediction error signal generation unit 101, an orthogonal transformation unit 102, a quantization unit 103, an entropy coding unit 104, an inverse quantization unit 105, and an inverse orthogonal. Conversion unit 106, decoded image generation unit 107, deblocking filter unit 108, loop filter unit 109, decoded image storage unit 110, intra prediction unit 111, inter prediction unit 112, motion vector calculation unit 113, encoding control and header generation unit 114 and a predicted image selection unit 115. An outline of each part will be described below.

  The preprocessing unit 100 rearranges the pictures in accordance with the picture type, and sequentially outputs the picture type and the frame image for each frame. The preprocessing unit 100 also performs block division and the like.

  The prediction error signal generation unit 101 acquires block data obtained by dividing an encoding target image of input moving image data into blocks such as 32 × 32, 16 × 16, and 8 × 8 pixels.

  The prediction error signal generation unit 101 generates a prediction error signal based on the block data and the block data of the prediction image output from the prediction image selection unit 115. The prediction error signal generation unit 101 outputs the generated prediction error signal to the orthogonal transformation unit 102.

  The orthogonal transform unit 102 performs orthogonal transform processing on the input prediction error signal. The orthogonal transform unit 102 can perform orthogonal transform on the prediction error signal in the case of intra prediction using a combination of DCT and DST depending on the prediction direction. Details of the orthogonal transform unit 102 will be described later with reference to FIG. The orthogonal transform unit 102 outputs a signal separated into horizontal and vertical frequency components by the orthogonal transform process to the quantization unit 103.

  The quantization unit 103 quantizes the output signal from the orthogonal transform unit 102. The quantization unit 103 reduces the code amount of the output signal by quantization, and outputs this output signal to the entropy encoding unit 104 and the inverse quantization unit 105.

  The entropy coding unit 104 entropy codes and outputs the output signal from the quantization unit 103, the motion vector information output from the motion vector calculation unit 113, the filter coefficient from the loop filter unit 109, and the like. Entropy coding is a method of assigning variable-length codes according to the appearance frequency of symbols.

  The inverse quantization unit 105 dequantizes the output signal from the quantization unit 103 and then outputs the output signal to the inverse orthogonal transform unit 106. The inverse orthogonal transform unit 106 performs an inverse orthogonal transform process on the output signal from the inverse quantization unit 105 and then outputs the output signal to the decoded image generation unit 107. By performing decoding processing by the inverse quantization unit 105 and the inverse orthogonal transform unit 106, a signal having the same level as the prediction error signal before encoding is obtained.

  The decoded image generation unit 107 adds the block data of the image subjected to motion compensation by the inter prediction unit 112 and the prediction error signal decoded by the inverse quantization unit 105 and the inverse orthogonal transform unit 106. The decoded image generation unit 107 outputs the decoded image block data generated by the addition to the deblocking filter unit 108.

  The deblocking filter unit 108 applies a filter for reducing block distortion to the decoded image output from the decoded image generation unit 107 and outputs the filtered image to the loop filter unit 109.

  The loop filter unit 109 is, for example, an ALF (Adaptive Loop Filter), and performs a filtering process using a decoded image subjected to the deblocking filtering process and an input image. For example, a Wiener filter is used for the filter processing, but other filters may be used.

  In addition, the loop filter unit 109 divides the input image into groups for each predetermined size, and generates an appropriate filter coefficient for each group. The loop filter unit 109 divides the decoded image subjected to the deblocking filter processing into groups for each predetermined size, and performs filter processing for each group using the generated filter coefficients. The loop filter unit 109 outputs the filter processing result to the decoded image storage unit 110 and accumulates it as a reference image. The predetermined size is, for example, an orthogonal transformation size.

  The decoded image storage unit 110 stores the input block data of the decoded image as new reference image data, and outputs the data to the intra prediction unit 111, the inter prediction unit 112, and the motion vector calculation unit 113.

  The intra prediction unit 111 generates a predicted image from the already-encoded reference pixels for the processing target block of the encoding target image. The intra prediction unit 111 performs prediction using a plurality of prediction directions and determines an optimal prediction direction. Prediction information including information on the determined prediction direction and prediction block is output to the orthogonal transform unit 102.

  The inter prediction unit 112 performs motion compensation on the reference image data acquired from the decoded image storage unit 110 with the motion vector provided from the motion vector calculation unit 113. Thereby, block data as a motion-compensated reference image is generated.

  The motion vector calculation unit 113 obtains a motion vector using the block data in the encoding target image and the reference image acquired from the decoded image storage unit 110. The motion vector is a value indicating a spatial deviation in units of blocks obtained using a block matching technique for searching for a position most similar to the processing target block from the reference image in units of blocks.

  The motion vector calculation unit 113 outputs the obtained motion vector to the inter prediction unit 112, and outputs motion vector information including information indicating the motion vector and the reference image to the entropy coding unit 104.

  The block data output from the intra prediction unit 111 and the inter prediction unit 112 are input to the predicted image selection unit 115.

  The predicted image selection unit 115 selects one of the block data acquired from the intra prediction unit 111 and the inter prediction unit 112 as a predicted image. The selected prediction image is output to the prediction error signal generation unit 101.

  The encoding control and header generation unit 114 performs overall encoding control and header generation. The encoding control and header generation unit 114 notifies the intra prediction unit 111 of the presence / absence of slice division, the deblocking filter unit 108 notifies the deblocking filter presence / absence, and the motion vector calculation unit 113 provides a reference image. Notification of restrictions, etc.

  The encoding control and header generation unit 114 generates header information using the control result. The generated header information is output to the entropy encoding unit 104, and is output as a stream together with image data and motion vector data.

<Configuration of orthogonal transform unit>
Next, the configuration of the orthogonal transform unit 102 will be described. FIG. 7 is a block diagram illustrating an example of the configuration of the orthogonal transform unit 102. An orthogonal transform unit 102 shown in FIG. 7 shows a configuration for orthogonal transform for a prediction error signal of intra prediction according to the present invention.

  The orthogonal transform unit 102 illustrated in FIG. 7 includes a determination unit 201, a control unit 202, and a transform unit 203. The determination unit 201 acquires prediction information, and determines whether the prediction block and the transform block satisfy a condition regarding the block size. This condition is a condition for making the tendency of the prediction error signal uniform in the transform block in the prediction block.

For example, the following three conditions can be considered.
・ Condition 1
The size of the transform block is 8 × 8, and the layer division from the coding block is 0 times. Condition 2
The size of the prediction block and the size of the transform block are equal to or less than 8 × 8. Condition 3
The prediction block is a rectangle having a long side of 16 or less (for example, 16 × 8, 8 × 16). In condition 1, in the case of intra coding, the block relationship is CU ≧ PU ≧ TU, and the TU hierarchy Since the division counts the number of hierarchical divisions from the CU, if the TU is 8 × 8 and the hierarchical division number is 0, CU = PU = TU. Therefore, condition 1 is a condition for determining whether the prediction block and the transform block have an 8 × 8 size.

  Condition 2 is a condition for determining whether the size of the prediction block is the same as the size of the transform block and whether the size is the same at 8 × 8, 4 × 4.

  Condition 3 is a condition for determining whether the prediction block is a rectangle (long side is 16 or less) and the transform block is 4 × 4 or 8 × 8. If the prediction block is a rectangle, the transform block is necessarily divided into squares. Therefore, as a condition, it is only necessary to determine whether the prediction block is a rectangle (long side ≦ 16). Further, if the rectangle is limited to a rectangle having a long side of 16 or less, the block size of the conversion block is reduced, and the DST effect is easily exhibited.

  The determination unit 201 is set to determine any one of the conditions 1 to 3, and outputs a determination result as to whether or not the condition is satisfied to the control unit 202. Note that the determination unit 201 may determine by combining conditions 1 and 3 and conditions 2 and 3.

  The control unit 202 acquires a determination result from the determination unit 201, and performs DCT processing on the prediction error signal based on the determination result, or processes a combination of DCT / DST in the horizontal and vertical directions depending on the prediction direction. Control what to do.

  When the determination result indicates that the condition is satisfied, the control unit 202 instructs the prediction direction dependent DCT / DST unit 205 to process the prediction error signal. If the determination result indicates that the condition is not satisfied, the control unit 202 instructs the DCT unit 204 to process the prediction error signal.

  The transform unit 203 performs orthogonal transform on the prediction error signal of intra coding. The conversion unit 203 includes a DCT unit 204 and a prediction direction dependent DCT / DST unit 205.

  The DCT unit 204 performs horizontal and vertical DCT processing on the prediction error signal, and outputs an orthogonally transformed signal to the quantization unit 103.

  The prediction direction dependent DCT / DST unit 205 performs DCT and / or DST processing on the horizontal direction and the vertical direction according to the prediction direction determined by the intra prediction unit 111. The prediction direction dependent DCT / DST unit 205 holds a table indicating whether DCT or DST is applied in the horizontal direction or DCT or DST is applied in the vertical direction according to the prediction direction.

  Therefore, when the prediction direction dependent DCT / DST unit 205 knows the prediction direction, it can determine the orthogonal transformation applied in the horizontal direction and the orthogonal transformation applied in the vertical direction with reference to the table. The prediction direction dependent DCT / DST unit 205 outputs the orthogonally transformed signal to the quantization unit 103.

  As a result, it is possible to select a DST for a transform block that has a relatively small block size and is predicted to have a uniform prediction efficiency in the prediction block.

  In the example illustrated in FIG. 7, the determination unit 201 and the control unit 202 are described as being included in the orthogonal transform unit 102. However, the determination unit 201 and the control unit 202 are orthogonally transformed independently of the orthogonal transform unit 102. You may comprise as a control part.

<Operation>
Next, the operation of the image encoding device 10 in the first embodiment will be described. Below, the orthogonal transformation control process in each case of conditions 1-3 is demonstrated.

  FIG. 8 is a flowchart illustrating an example of orthogonal transform control processing (part 1). The process shown in FIG. 8 is an orthogonal transform control process in which whether or not the condition 1 is satisfied is determined for one transform block.

  In step S100, the determination unit 201 determines whether the transform block has a 4 × 4 size. If the size is 4 × 4 (step S100—YES), the process proceeds to step S103, and if the size is not 4 × 4 (step S100—NO), the process proceeds to step S101. In step S101, the determination unit 201 determines whether or not the transform block has an 8 × 8 size. If the size is 8 × 8 (step S101—YES), the process proceeds to step S102, and if the size is not 8 × 8 (step S101—NO), the process proceeds to step S104.

  In step S102, the determination unit 201 determines whether or not the hierarchical division of the transform block is zero. If the hierarchy division is 0 times (step S102—YES), the process proceeds to step S103, and if the hierarchy division is not 0 times (step S102—NO), the process proceeds to step S104.

  In step S103, the control unit 202 controls the prediction direction dependent DCT / DST unit 205 to be used for the prediction error signal of the transform block.

  In step S104, the control unit 202 controls the DCT unit 204 to be used for the prediction error signal of the transform block.

  In step S105, the transform unit 203 performs orthogonal transform processing on the prediction error signal of the transform block using either the DCT unit 204 or the prediction direction dependent DCT / DST unit 205 that has been determined to be used.

  FIG. 9 is a flowchart illustrating an example of orthogonal transform control processing (part 2). The process shown in FIG. 9 is an orthogonal transform control process in which whether a condition 2 is satisfied is determined for one transform block.

  In step S201, the determination unit 201 determines whether or not the prediction block and the transform block have the same size of 8 × 8 or less. If it is the same size of 8 × 8 or less (step S201—YES), the process proceeds to step S202, and if it is not the same size of 8 × 8 or less (step S201—NO), the process proceeds to step S203.

  In step S202, the control unit 202 controls the prediction direction dependent DCT / DST unit 205 to be used for the prediction error signal of the transform block.

  In step S203, the control unit 202 controls the DCT unit 204 to be used for the prediction error signal of the transform block.

  In step S204, the transform unit 203 performs orthogonal transform processing on the prediction error signal of the transform block using either the DCT unit 204 or the prediction direction dependent DCT / DST unit 205 that has been determined to be used.

  FIG. 10 is a flowchart illustrating an example of orthogonal transform control processing (part 3). The process illustrated in FIG. 10 is an orthogonal transform control process in which whether a condition 3 is satisfied is determined for one transform block.

  In step S301, the determination unit 201 determines whether the prediction block is a rectangle (long side is 16 or less). If the long side is a rectangle of 16 or less (step S301-YES), the process proceeds to step S302, and if the long side is not the size of a rectangle of 16 or less (step S301-NO), the process proceeds to step S303. In step S301, the determination unit 201 may determine whether or not the prediction block is a 16 × 8 or 8 × 16 rectangle and the transform block is 8 × 8. If the transform block is necessarily divided in size, the prediction efficiency in the prediction block may be uniform.

  In step S302, the control unit 202 controls the prediction direction dependent DCT / DST unit 205 to be used for the prediction error signal of the transform block.

  In step S303, the control unit 202 controls the DCT unit 204 to be used for the prediction error signal of the transform block.

  In step S304, the transform unit 203 performs orthogonal transform processing on the prediction error signal of the transform block using either the DCT unit 204 or the prediction direction dependent DCT / DST unit 205 that has been determined to be used.

  By making the DST selectable for a transform block that can effectively use DST by the above orthogonal transform control processing, encoding efficiency can be improved.

  As described above, according to the first embodiment, encoding efficiency can be improved by making it possible to select DST for blocks other than 4 × 4 while suppressing an increase in processing amount.

[Example 2]
Next, the image decoding device 30 according to the second embodiment will be described. The image decoding device 30 according to the second embodiment is a device that decodes the bitstream encoded by the image encoding device 10 according to the first embodiment.

  FIG. 11 is a block diagram illustrating an example of a schematic configuration of the image decoding device 30 according to the second embodiment. As illustrated in FIG. 11, the image decoding device 30 includes an entropy decoding unit 301, an inverse quantization unit 302, an inverse orthogonal transform unit 303, an intra prediction unit 304, a decoded information storage unit 305, an inter prediction unit 306, and a predicted image selection unit. 307, a decoded image generation unit 308, a deblocking filter unit 309, a loop filter unit 310, and a frame memory 311. An outline of each part will be described below.

  When a bit stream is input, the entropy decoding unit 301 performs entropy decoding corresponding to the entropy encoding of the image encoding device 10. The prediction error signal decoded by the entropy decoding unit 301 is output to the inverse quantization unit 302. Also, the decoded filter coefficient, the decoded motion vector in the case of inter prediction, and the like are output to the decoded information storage unit 305.

  In the case of intra prediction, the entropy decoding unit 301 notifies the intra prediction unit 304 to that effect. In addition, the entropy decoding unit 301 notifies the prediction image selection unit 307 whether the decoding target image is inter predicted or intra predicted.

  The inverse quantization unit 302 performs an inverse quantization process on the output signal from the entropy decoding unit 301. The inversely quantized output signal is output to the inverse orthogonal transform unit 303.

  The inverse orthogonal transform unit 303 performs an inverse orthogonal transform process on the decoded block of the output signal from the inverse quantization unit 302 to generate a residual signal. In the case of intra prediction, the inverse orthogonal transform unit 303 controls whether to perform inverse DCT (IDCT) processing or inverse DCT / inverse DST (IDST) processing determined depending on the prediction direction. Details of the inverse orthogonal transform unit 303 will be described later with reference to FIG. The residual signal is output to the decoded image generation unit 308.

  The intra prediction unit 304 generates a predicted image using a plurality of prediction directions from the peripheral pixels already decoded of the decoding target image acquired from the frame memory 311. Information on the prediction direction and the prediction block used to generate the prediction image is output to the inverse orthogonal transform unit 303 as prediction information.

  The decoding information storage unit 305 stores decoding information such as filter coefficients, motion vectors, and division modes of the decoded loop filter.

  The inter prediction unit 306 performs motion compensation on the reference image data acquired from the frame memory 311 using the motion vector and the division mode acquired from the decoded information storage unit 305. Thereby, block data as a motion-compensated reference image is generated.

  The predicted image selection unit 307 selects either the intra predicted image or the inter predicted image. The selected block data is output to the decoded image generation unit 308.

  The decoded image generation unit 308 adds the predicted image output from the predicted image selection unit 307 and the residual signal output from the inverse orthogonal transform unit 303 to generate a decoded image. The generated decoded image is output to the deblocking filter unit 309.

  The deblocking filter unit 309 applies a filter for reducing block distortion to the decoded image output from the decoded image generation unit 308 and outputs the filtered image to the loop filter unit 310.

  The loop filter unit 310 performs filter processing for each predetermined size of the decoded image using the filter coefficient acquired from the decoded information storage unit 305. The predetermined size is, for example, an inverse orthogonal transform size. The decoded image after the loop filter processing is output to the frame memory 311. Note that the decoded image after the loop filter may be output to a display device or the like.

  The frame memory 311 stores a decoded image that serves as a reference image. The decoded information storage unit 305 and the frame memory 311 are configured separately, but they may be the same storage unit.

<Configuration of inverse orthogonal transform unit>
Next, the configuration of the inverse orthogonal transform unit 303 will be described. FIG. 12 is a block diagram illustrating an example of the configuration of the inverse orthogonal transform unit 303. The inverse orthogonal transform unit 303 illustrated in FIG. 12 includes a determination unit 401, a control unit 402, and an inverse transform unit 403.

  The determination unit 401 has the same function as the determination unit 201 shown in FIG. Note that the determination unit 401 performs determination for each transform block under the same conditions as the determination unit 201 of the image encoding device 10.

  Based on the determination result of the determination unit 401, the control unit 402 controls whether the IDCT unit 403 performs processing or the prediction direction dependent IDCT / IDST unit 404 performs processing.

  If the determination result indicates that the condition is satisfied, the control unit 402 instructs the prediction direction dependent IDCT / IDST unit 405 to process the dequantized signal. If the determination result indicates that the condition is not satisfied, the control unit 402 instructs the IDCT unit 404 to process the dequantized signal.

  The inverse transform unit 403 performs inverse orthogonal transform on the inversely quantized signal of the transform block. The inverse transform unit 403 includes an IDCT unit 404 and a prediction direction dependent IDCT / IDST unit 405.

  The IDCT unit 404 performs horizontal and vertical IDCT processing on the inversely quantized signal, and outputs an inverse orthogonal transformed signal to the decoded image generation unit 308.

  The prediction direction dependent IDCT / IDST unit 405 performs IDCT and / or IDST processing on the horizontal and vertical directions of the dequantized signal according to the prediction direction decoded and extracted by the intra prediction unit 304. The prediction direction dependent IDCT / IDST unit 405 holds a table indicating whether IDCT or IDST is applied in the horizontal direction or IDCT or IDST is applied in the vertical direction, depending on the prediction direction. This table is the same table as the image encoding measure 10.

  Therefore, when the prediction direction dependent IDCT / IDST unit 405 knows the prediction direction, the prediction direction dependent IDCT / IDST unit 405 can determine the inverse orthogonal transform applied in the horizontal direction and the inverse orthogonal transform applied in the vertical direction with reference to the table. The prediction direction dependent IDCT / IDST unit 405 outputs the inversely orthogonally transformed signal to the decoded image generation unit 308.

  Thereby, the determination unit 401 and the control unit 402 can perform processing similar to the processing of the image encoding device 10. Note that the determination unit 401 and the control unit 402 may be configured as an inverse orthogonal transform control unit independently of the inverse orthogonal transform unit 303.

<Operation>
The inverse orthogonal transform processing in the image decoding device 30 is basically the same as the processing shown in FIGS. The difference is that the orthogonal transform becomes an inverse orthogonal transform.

  As described above, according to the second embodiment, the bitstream encoded by the image encoding device 10 according to the first embodiment can be appropriately decoded.

[Example 3]
FIG. 13 is a block diagram illustrating an example of the configuration of the image processing apparatus 50 according to the third embodiment. An image processing apparatus 50 illustrated in FIG. 13 is an example of an apparatus in which the image encoding process described in the first embodiment or the image decoding process described in the second embodiment is implemented by software.

  As illustrated in FIG. 13, the image processing apparatus 50 includes a control unit 501, a main storage unit 502, an auxiliary storage unit 503, a drive device 504, a network I / F unit 506, an input unit 507, and a display unit 508. These components are connected to each other via a bus so as to be able to transmit and receive data.

  The control unit 501 is a CPU that controls each device, calculates data, and processes in a computer. In addition, the control unit 501 performs an operation for executing an image encoding process program including an orthogonal transform control process stored in the main storage unit 502 or the auxiliary storage unit 503 or an image decoding process program including an inverse orthogonal transform control process. Device. The control unit 501 receives data from the input unit 507 and the storage device, calculates and processes the data, and then outputs the data to the display unit 508 and the storage device.

  The control unit 501 can realize the processing described in each embodiment by executing a program of image encoding processing including orthogonal transformation control processing or image decoding processing including inverse orthogonal transformation control processing.

  The main storage unit 502 is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like. The main storage unit 502 is a storage device that stores or temporarily stores programs and data such as OS (Operating System) and application software which are basic software executed by the control unit 501.

  The auxiliary storage unit 503 is an HDD (Hard Disk Drive) or the like, and is a storage device that stores data related to application software or the like.

  The drive device 504 reads the program from the recording medium 505, for example, a flexible disk, and installs it in the storage unit.

  A predetermined program is stored in the recording medium 505, and the program stored in the recording medium 505 is installed in the image processing apparatus 50 via the drive device 504. The installed predetermined program can be executed by the image processing apparatus 50.

  The network I / F unit 506 has a communication function connected via a network such as a LAN (Local Area Network) or a WAN (Wide Area Network) constructed by a data transmission path such as a wired and / or wireless line. This is an interface between the device and the image processing apparatus 50.

  The input unit 507 includes a keyboard having cursor keys, numeric input, various function keys, and the like, a mouse for selecting keys on the display screen of the display unit 508, a slice pad, and the like. The input unit 507 is a user interface for a user to give an operation instruction to the control unit 501 or input data.

  The display unit 508 is configured by a CRT (Cathode Ray Tube), an LCD (Liquid Crystal Display), or the like, and performs display according to display data input from the control unit 501.

  The decoded image storage unit 111 illustrated in FIG. 6 is realized by, for example, the main storage unit 502 or the auxiliary storage unit 503, and configurations other than the decoded image storage unit 111 illustrated in FIG. 6 include, for example, a control unit 501 and a work memory. This can be realized by the main storage unit 502.

  Further, the decoding information storage unit 305 and the frame memory 311 illustrated in FIG. 11 are realized by, for example, the main storage unit 502 or the auxiliary storage unit 503, and configurations other than the decoding information storage unit 305 and the frame memory 311 illustrated in FIG. It can be realized by the control unit 501 and the main storage unit 502 as a work memory.

  The program executed by the image processing apparatus 50 has a module configuration including each unit described in the first and second embodiments. As actual hardware, when the control unit 501 reads out and executes a program from the auxiliary storage unit 503, one or more of the above-described units are loaded onto the main storage unit 502, and one or more of the units are main. It is generated on the storage unit 502.

  As described above, the image encoding process described in the first embodiment and the image decoding process described in the second embodiment may be realized as a program for causing a computer to execute. The processing described in each embodiment can be realized by installing this program from a server or the like and causing the computer to execute the program.

  It is also possible to record the program in the recording medium 505 and cause the computer or portable terminal to read the recording medium 505 on which the program is recorded, thereby realizing the above-described filtering process. The recording medium 505 is a recording medium that records information optically, electrically, or magnetically, such as a CD-ROM, a flexible disk, or a magneto-optical disk, and information is electrically stored such as a ROM or flash memory. Various types of recording media such as a semiconductor memory for recording can be used. Further, the processes described in the above embodiments may be implemented in one or a plurality of integrated circuits.

  Note that the image processing device 50 according to the third embodiment has functions as the image encoding device 10 and the image decoding device 30 as described above.

  Each embodiment has been described in detail above. However, the present invention is not limited to the specific embodiment, and various modifications and changes other than the above-described modification are possible within the scope described in the claims. .

DESCRIPTION OF SYMBOLS 10 Image coding apparatus 30 Image decoding apparatus 50 Image processing apparatus 101 Predictive image generation part 102 Orthogonal transformation part 103 Quantization part 104 Entropy encoding part 105 Inverse quantization part 106 Inverse orthogonal transformation part 107 Decoded image generation part 108 Deblocking filter Unit 109 loop filter unit 110 decoded image storage unit 111 intra prediction unit 112 inter prediction unit 113 motion vector calculation unit 114 encoding control and header generation unit 115 prediction image selection unit 201 determination unit 202 control unit 203 conversion unit 204 DCT unit 205 prediction Direction dependent DCT / DST unit 303 Inverse orthogonal transform unit 401 Determination unit 402 Control unit 403 Inverse transform unit 404 IDCT unit 405 Prediction dependent IDCT / IDST unit 501 Control unit 502 Main storage unit 503 Auxiliary storage unit 504 Drive device

Claims (7)

An image decoding device that performs intra prediction using a plurality of prediction directions,
A determination unit that determines whether or not a transform block that is data to be subjected to inverse orthogonal transform and a prediction block indicating a block used in the intra-screen prediction satisfy a condition related to a block size;
Based on the determination result by the determination unit, any one of inverse discrete cosine transform and inverse discrete cosine transform and / or inverse discrete sine transform with respect to a preset horizontal / vertical direction depending on the prediction direction is performed. A control unit for controlling
An inverse transform unit that performs an inverse orthogonal transform process controlled by the control unit on the transform block;
An image decoding apparatus comprising: The condition is that the size of the transform block is 8 × 8, and the number of hierarchical divisions from an encoded block obtained by dividing an image by a predetermined size is 0,
The controller is
The image decoding apparatus according to claim 1, wherein when the condition is satisfied, the inverse transform unit controls the inverse discrete cosine transform and / or inverse discrete sine transform processing. The condition is that the size of the prediction block and the size of the transform block are equal to or less than 8 × 8,
The controller is
The image decoding apparatus according to claim 1, wherein when the condition is satisfied, the inverse transform unit controls the inverse discrete cosine transform and / or inverse discrete sine transform processing. The condition is that the prediction block is a rectangle having a long side of 16 or less,
The controller is
The image decoding apparatus according to claim 1, wherein when the condition is satisfied, the inverse transform unit controls the inverse discrete cosine transform and / or inverse discrete sine transform processing. A determination step of determining whether a transform block that is target data of inverse orthogonal transform and a prediction block indicating a block used in the intra prediction satisfy a condition regarding a block size;
Based on the determination result of the determination step, inverse discrete cosine transform, and inverse discrete cosine transform and / or inverse discrete sine transform with respect to a preset horizontal / vertical direction depending on a prediction direction used in intra prediction. A control step for controlling which of the processing is performed;
An inverse orthogonal transform control method in which a computer executes an inverse transform step of performing an inverse orthogonal transform process controlled by the control step on the transform block. A determination step of determining whether a transform block that is target data of inverse orthogonal transform and a prediction block indicating a block used in the intra prediction satisfy a condition regarding a block size;
Based on the determination result of the determination step, inverse discrete cosine transform, and inverse discrete cosine transform and / or inverse discrete sine transform with respect to a preset horizontal / vertical direction depending on a prediction direction used in intra prediction. A control step for controlling which of the processing is performed;
A program for causing a computer to execute an inverse transform step of performing an inverse orthogonal transform controlled by the control step on the transform block. An image encoding device that performs intra prediction using a plurality of prediction directions,
A prediction block indicating a block used for the intra prediction, and a transform block obtained by dividing the coding target block into one or a plurality of layers by hierarchical division are included in the coding target block divided into a predetermined size. A determination unit for determining whether or not a condition regarding the block size is satisfied;
Control whether to perform discrete cosine transform or discrete cosine transform and / or discrete sine transform with respect to a preset horizontal / vertical direction depending on the prediction direction based on the determination result by the determination unit A control unit,
A transform unit that performs orthogonal transform processing controlled by the control unit on the transform block;
An image encoding device comprising:

Images