JP2013090015A - Intra prediction apparatus, encoder, decoder and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intra prediction apparatus which improves accuracy of an intra prediction by using a prediction formula considering a correlation between a prediction target block and a reference pixel adjacent to the prediction target block.SOLUTION: An intra prediction apparatus 1 comprises: a primary prediction image generation part 10 for generating a prediction image of a primary component signal on the basis of a primary prediction mode; a reference pixel selection part 11 for determining a position of a reference pixel to be used to derive coefficients of a prediction formula in accordance with a prediction direction indicated by the primary prediction mode and for generating reference pixel position information indicating the position of the reference pixel; a coefficient derivation part 14 for deriving the coefficients of the predication formula from a pixel of the primary component signal and a pixel of a secondary component signal which are indicated by the reference pixel position information; and a first secondary prediction image generation part 15 for generating a prediction image of the secondary component signal by performing an intra predication of the secondary component signal by using the prediction formula for which the coefficients are substituted.

Description

  The present invention relates to an intra prediction device, an encoding device, a decoding device, and a program that perform intra prediction (intra-screen prediction) in units of blocks and generate a prediction image of a prediction symmetric block.

  MPEG-4 AVC / H. In the H.264 system (ISO / IEC 14496-10 / ITU-T Rec. H.264), when a prediction target block (encoding target block) is encoded by intra prediction, a decoded surrounding block is used. It is known that intra prediction is performed to generate a predicted image, and the difference between the original image and the predicted image is encoded (see, for example, Non-Patent Document 1). In intra prediction, an optimal prediction direction is selected from the preset prediction directions and prediction is performed, and an intra prediction mode (hereinafter also simply referred to as “prediction mode”) indicating the selected prediction direction is encoded. And transmit.

  MPEG-4 AVC / H. Intra prediction in the H.264 scheme is performed in units of 4 × 4 pixels, 8 × 8 pixels, or 16 × 16 pixels, and an optimal prediction mode is selected from a plurality of preset prediction modes. FIG. 8 shows MPEG-4 AVC / H. FIG. 3 is a diagram illustrating an intra prediction mode when performing intra prediction in units of 8 × 8 pixels in the H.264 scheme. In the figure, a hatched circle indicates a decoded pixel, a white circle indicates a prediction target pixel, and an arrow indicates a prediction direction. The prediction mode 0 in FIG. 8 (a) is vertical prediction, the prediction mode 1 in FIG. 8 (b) is horizontal prediction, the prediction mode 2 in FIG. 8 (c) is DC prediction, and the prediction mode 3 in FIG. 8 (d). In diagonally lower left direction prediction, in prediction mode 4 in FIG. 8 (e), diagonal lower right direction prediction, in prediction mode 5 in FIG. 8 (f), vertical right direction prediction, in prediction mode 6 in FIG. 8 (g), horizontal. In the downward prediction, the prediction mode 7 in FIG. 8H performs vertical left prediction, and the prediction mode 8 in FIG. 8I performs horizontal upward prediction. Thus, the prediction mode is associated with the prediction direction. Note that the prediction modes 0 to 8 are set for the intra prediction of the luminance signal, but only the prediction modes 0 to 3 are set for the intra prediction of the color difference signal.

  It is known that intra-prediction is also performed in the HEVC (High-Efficiency Video Coding) system, which is being standardized as a next-generation compression encoding system (see, for example, Non-Patent Document 2). FIG. 9 is a diagram illustrating an intra prediction mode in the HEVC method disclosed in Non-Patent Document 2. For convenience of drawing, the arrow in FIG. 8 indicates the prediction direction, but the arrow in FIG. 9 indicates the reference direction (the direction opposite to the prediction direction). Also, the numbers in FIG. 9 represent the prediction mode. The prediction mode of the HEVC system is MPEG-4 AVC / H. Compared to 9 types of H.264 system, it is increased to 34 types.

  Also, in encoding a color image (RGB image or YCbCr image), for example, when encoding a YCbCr image, one luminance signal (Y) and two color difference signals (Cb, Cr) are encoded. At this time, in addition to the technique of performing intra prediction using the same component signal in the same screen as described above, a technique of performing intra prediction using different component signals (luminance signal and color difference signal) in the same screen is known. (For example, see Non-Patent Document 3). In the technique described in Non-Patent Document 3, a prediction formula for predicting a color difference signal is derived from a luminance signal, and a color difference signal is predicted from a decoded luminance signal using the derived prediction formula. Note that it is not necessary to transmit the prediction formula to the decoding side.

FIG. 10 is a diagram for describing intra prediction using a prediction formula between different component signals. When the image size of the luminance signal and the image size of the color difference signal are different, the luminance signal is down-sampled so as to have the same image size as the color difference signal. In FIG. 10, a signal Rec _L ′ is generated by down-sampling the luminance signal Rec _L of 2N × 2N pixels so as to have the same image size as the color difference signal Rec _C of N × N pixels.

Then, the decoded pixel Rec _C (i) adjacent to the prediction target block of the color difference signal and the decoded pixel Rec _L ′ () of the luminance signal at the position corresponding to the pixel (the same position between different component signals). i) and the following equations (1) and (2) are used to derive the coefficients α and β used in the prediction equation. By substituting the coefficients α and β derived into the prediction equation of the following equation (3), the prediction value Pred _C of the color difference signal can be calculated from the luminance signal. Here, I represents the number of adjacent pixels (reference pixels), and i represents the number of adjacent pixels. As shown in FIG. 10, when the size of the prediction target block is 8 × 8 pixels, I = 16 and i = 0 to 15. In addition, intra prediction is performed for each of the color difference signals Cb and Cr using the equations (1) to (3).

Satoshi Okubo and three others, “Revised third edition H.264 / AVC textbook”, Impress R & D, December 26, 2008 T. Wiegand, W-J Han, B Bross, J-R.Ohm, G.J.Sullivan, “WD3: Working Draft 3 of High-Efficiency Video Coding”, JCTVC-E603 JCT-VC E266 Chroma intra prediction by reconstructed luma samples (Samusung, LG)

  In the technique of performing intra prediction using a prediction formula between different component signals in the same screen as described above, it is assumed that a correlation between a prediction target block (encoding target block) and an adjacent pixel adjacent to the prediction target block is high. Intra prediction is performed. However, in general, the correlation between the prediction target block and adjacent pixels is not necessarily high, and when the correlation between the two is low, intra prediction with high accuracy (reliability) cannot be performed.

  In order to solve the above problem, an object of the present invention is to improve the accuracy of intra prediction by performing intra prediction using a prediction formula that takes into account the correlation between a prediction target block and adjacent pixels of the prediction target block. It is an object to provide an intra prediction device, an encoding device, a decoding device, and a program capable of performing the above.

  An encoded component signal (for example, luminance signal) is defined as a primary component signal, and one or more other component signals (for example, color difference signals) to be predicted are defined as secondary component signals. In order to solve the above-described problem, the intra prediction apparatus according to the present invention derives a prediction formula using adjacent pixels used for intra prediction of a primary component signal. In many intra predictions, a prediction that the same value continues in one specific direction is used, so that the position of an adjacent pixel having a high correlation with the prediction target block can be estimated from the selected prediction mode of intra prediction. Therefore, a prediction formula suitable for prediction of a prediction target block can be derived by using only adjacent pixels that exist in a direction opposite to the prediction direction with respect to the prediction target block.

  That is, the intra prediction apparatus according to the present invention has encoded a video signal having a primary component signal (for example, a luminance signal) and a secondary component signal (for example, a color difference signal) composed of one or more other component signals. An intra-prediction device that performs intra-prediction of a secondary component signal using a prediction formula represented by a primary component signal and a coefficient based on a primary prediction mode determined from a plurality of predetermined intra-prediction modes A primary prediction image generation unit that generates a prediction image of a primary component signal, and determines a position of a reference pixel used for deriving a coefficient of the prediction formula according to a prediction direction indicated by the primary prediction mode, and determines the position of the reference pixel Generate reference pixel position information to indicate Derived from a pixel of the light source pixel, a pixel of the primer component signal and a pixel of the secondary component signal indicated by the reference pixel position information, and the coefficient deriving unit. A first secondary predicted image generation unit configured to perform intra prediction of the secondary component signal using a prediction formula into which a coefficient is substituted and generate a predicted image of the secondary component signal.

  Furthermore, in the intra prediction device according to the present invention, the reference pixel selection unit has a range in which an angle in a counterclockwise direction with respect to a vertically downward direction of the prediction direction indicated by the primary prediction mode includes 0 degrees. When the angle is equal to or larger than the first angle and smaller than the second angle, the position of the reference pixel is set to a row of pixels adjacent to the upper side of the prediction target block (in the example illustrated in FIG. 2 described later, adjacent pixels a1 to a8). When the angle in the counterclockwise direction with respect to the vertically downward direction of the prediction direction indicated by the primary prediction mode is a range including 45 degrees, and is less than the second angle and less than the third angle. , The position of the reference pixel is a part of the pixels in the one row and a part of a column of pixels adjacent to the left side of the prediction target block (in the example shown in FIG. 2 described later, adjacent pixels b1 to b8), The primary prediction mode If the angle in the counterclockwise direction with respect to the vertical downward direction of the prediction direction indicated by is within the range including 0 degrees and is less than or equal to the third angle and less than the fourth angle, the position of the reference pixel Is the one row of pixels.

  Furthermore, in the intra prediction device according to the present invention, a second secondary prediction image generation unit that generates a prediction image of a secondary component signal based on a secondary prediction mode determined from a plurality of predetermined intra prediction modes; Secondary prediction that selects and outputs either one of the predicted image of the secondary component signal generated by the first secondary predicted image generation unit and the predicted image of the secondary component signal generated by the second secondary predicted image generation unit And an image selection unit.

  Moreover, in order to solve the said subject, the encoding apparatus which concerns on this invention is provided with the intra prediction apparatus mentioned above, It is characterized by the above-mentioned.

  Moreover, in order to solve the said subject, the decoding apparatus which concerns on this invention is provided with the intra prediction apparatus mentioned above.

  Moreover, in order to solve the said subject, the program which concerns on this invention makes a computer function as an intra prediction apparatus mentioned above, an encoding apparatus, or a decoding apparatus.

  According to the present invention, it is possible to improve the accuracy of intra prediction by performing intra prediction using a prediction formula that takes into account the correlation between a prediction target block and a reference pixel adjacent to the prediction target block. .

It is a block diagram which shows the 1st structural example of the intra prediction apparatus by the side of an encoding which concerns on one Example of this invention. It is a figure which shows the reference pixel used when deriving the coefficient of a prediction formula. It is a block diagram which shows the 2nd structural example of the intra prediction apparatus by the side of an encoding which concerns on one Example of this invention. It is a block diagram which shows the structural example of the encoding apparatus which concerns on one Example of this invention. It is a block diagram which shows the 1st structural example of the intra prediction apparatus by the side of a decoding which concerns on one Example of this invention. It is a block diagram which shows the 2nd structural example of the intra prediction apparatus by the side of decoding which concerns on one Example of this invention. It is a block diagram which shows the structural example of the decoding apparatus which concerns on one Example of this invention. MPEG4 AVC / H. It is a figure which shows the intra prediction mode in H.264 system. It is a figure which shows the intra prediction mode in a HEVC system. It is a figure explaining the intra prediction using the prediction formula between different component signals.

  An intra prediction apparatus according to the present invention uses a prediction formula represented by a primary component signal and a coefficient for a video signal having a primary component signal and a secondary component signal composed of one or more other component signals. Perform intra prediction of the signal. In the embodiments of the present invention described below, a case where the primary component signal is a luminance signal and the secondary component signal is a color difference signal will be described as an example. The color difference signal is composed of a Cb signal and a Cr signal, and intra prediction is performed using a prediction formula for each of the color difference signals Cb and Cr. However, in the following embodiments, the present invention is applied to both the color difference signals Cb and Cr. Since they are possible, they are referred to as color difference signals without distinction.

[Intra prediction device on the encoding side]
FIG. 1 is a block diagram illustrating a first configuration example of an encoding-side intra prediction apparatus according to an embodiment of the present invention. As illustrated in FIG. 1, the intra prediction apparatus 1 on the encoding side includes a luminance prediction image generation unit (primary prediction image generation unit) 10, a reference pixel selection unit 11, a downsampling unit 12, a memory 13, and coefficients. A derivation unit 14 and a first color difference prediction image generation unit (first secondary prediction image generation unit) 15 are provided.

  The intra prediction apparatus 1 on the encoding side performs intra prediction on the color difference signal after performing intra prediction on the luminance signal for each predetermined unit block (for example, macroblock). In order to clarify this point, in FIG. 1A, only the processing unit that performs intra prediction on the luminance signal is shown by a solid line, and in FIG. 1B, only the processing unit that performs intra prediction on the color difference signal is shown by a solid line. Yes. That is, as illustrated in FIG. 1A, the intra prediction device 1 performs intra prediction on the input luminance signal in units of blocks by the luminance prediction image generation unit 10, and the luminance prediction mode that is a luminance signal prediction mode, A luminance prediction image that is a prediction image of the luminance signal is generated. Thereafter, as shown in FIG. 1B, the reference color selection unit 11, the downsampling unit 12, the memory 13, the coefficient derivation unit 14, and the first color difference prediction image generation unit 15 are processed in block units for the input color difference signal. Intra prediction is performed to generate a color difference prediction image that is a prediction image of the color difference signal. In addition, when the intra prediction apparatus 1 is incorporated in an encoding apparatus, each local decoded image is input into the intra prediction apparatus 1 as a luminance signal and a color difference signal, as will be described later.

  The luminance predicted image generation unit 10 refers to an image of a block (hereinafter referred to as “reference block”) that is a block around the prediction target block and has a prediction mode determined for the luminance signal (primary component signal) in advance. A luminance prediction mode (primary prediction mode) that is an optimal prediction mode is determined from a plurality of determined prediction modes, and the determined luminance prediction mode is output to the outside. The luminance signal input to the luminance predicted image generation unit 10 and the luminance prediction mode output from the luminance predicted image generation unit 10 are also used for intra prediction of the color difference signal performed thereafter.

  The luminance predicted image generation unit 10 can determine the luminance prediction mode by a known method. For example, a prediction image is obtained based on each prediction mode, and a luminance prediction mode that minimizes the coding cost is determined by RD optimization (Rate-Distortion Optimization). MPEG4 AVC / H. When the intra prediction is performed in units of 8 × 8 pixels using the H.264 method, the luminance prediction mode of the prediction target block is determined from the prediction modes 0 to 8 illustrated in FIG. 8, and when the intra prediction is performed using the HEVC method, The luminance prediction mode of the prediction target block is determined from the prediction modes 0 to 33 shown in FIG.

  In addition, the predicted brightness image generation unit 10 generates a predicted brightness image that is a predicted image based on the determined brightness prediction mode, and outputs the generated predicted brightness image to the outside. For example, when the luminance prediction mode is the prediction mode 0 illustrated in FIG. 8, the luminance prediction image generation unit 10 determines the pixels adjacent to the upper side of the prediction target block as the prediction values of the pixels in the same column of the prediction target block. A luminance prediction image is generated.

  The reference pixel selection unit 11 acquires the luminance prediction mode generated by the luminance prediction image generation unit 10 for the luminance signal block at the same position in the same frame as the prediction target block of the color difference signal. Then, the position of the reference pixel used when deriving the coefficients α and β of the prediction formula is determined according to the prediction direction indicated by the acquired luminance prediction mode, and reference pixel position information indicating the position of the determined reference pixel is generated. And output to the coefficient deriving unit 14.

  FIG. 2 is a diagram illustrating reference pixels used when deriving the coefficients α and β of the prediction formula. Here, a case where the block size of the prediction target block is 8 × 8 pixels, that is, a case where intra prediction is performed in units of 8 × 8 pixels is shown. At this time, adjacent pixels adjacent to the upper side of the prediction target block are a1 to a8, and adjacent pixels adjacent to the left side of the prediction target block are b1 to b8. The reference pixel selection unit 11 determines the positions of the reference pixels used when deriving the coefficients α and β according to the prediction direction indicated by the prediction mode of the luminance signal input from the luminance prediction image generation unit 10 as the adjacent pixels a1 to a1. Select from a8 and b1 to b8.

For example, MPEG4 AVC / H. In the H.264 system, when the prediction modes 0 to 8 shown in FIG. 8 are set in advance, the reference pixel selection unit 11 determines the position of the reference pixel as follows. The angle in the counterclockwise direction with respect to the vertical downward direction of the prediction direction is −45 degrees when the prediction direction is diagonally downward left, 0 degrees when downward, 45 degrees when diagonally downward right, and rightward At 90 degrees.
When the prediction mode of the luminance signal is a prediction mode (prediction mode 2) in which the average value of the reference pixels is a prediction value, all of the adjacent pixels a1 to a8 and b1 to b8 are determined as reference pixels.
When the angle of the prediction direction indicated by the prediction mode of the luminance signal in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 0 degree (the first angle is less than the second angle) ( In the prediction modes 3, 7, 0), adjacent pixels a1 to a8 are determined as reference pixels.
The angle of the prediction direction indicated by the luminance signal prediction mode in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 45 degrees (more than the second angle and less than the third angle). In (prediction modes 5, 4, 6), adjacent pixels a1 to a4 and b1 to b4 are determined as reference pixels.
When the angle of the prediction direction indicated by the prediction mode of the luminance signal in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 90 degrees (more than the third angle and less than the fourth angle). In (prediction modes 1 and 8), adjacent pixels b1 to b8 are determined as reference pixels.

In the HEVC system, when the prediction modes 0 to 33 shown in FIG. 9 are set in advance, MPEG4 AVC / H. As in the case of the H.264 system, the reference pixel selection unit 11 selects the position of the reference pixel as follows.
When the prediction mode of the luminance signal is a prediction mode in which the average value of the reference pixels is a prediction value (prediction mode 2), all of the adjacent pixels a1 to a8 and b1 to b8 are determined as reference pixels.
When the angle of the prediction direction indicated by the prediction mode of the luminance signal in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 0 degree (the first angle is less than the second angle) ( In prediction modes 6, 25, 13, 24, 5, 23, 12, 22, 0, 21, 11, 20, 4), adjacent pixels a1 to a8 are determined as reference pixels.
The angle of the prediction direction indicated by the luminance signal prediction mode in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 45 degrees (more than the second angle and less than the third angle). In (prediction modes 19, 10, 18, 3, 26, 14, 27), adjacent pixels a1 to a4 and b1 to b4 are determined as reference pixels.
When the angle of the prediction direction indicated by the prediction mode of the luminance signal in the counterclockwise direction with respect to the vertical downward direction is within a predetermined range including 90 degrees (more than the third angle and less than the fourth angle). In (prediction modes 7, 28, 15, 29, 1, 30, 16, 31, 8, 32, 17, 33, 9), adjacent pixels b1 to b8 are determined as reference pixels.

  In addition, when intra prediction with directionality is not used (for example, when intra DC prediction using the average value of the reference pixels described above or motion compensation prediction is used), the adjacent pixel a1 is used. All of .about.a8 and b1 to b8 are determined as reference pixels. In the example described above, the angle of the prediction direction indicated by the luminance prediction mode is classified into three: a predetermined range including 270 degrees, a predetermined range including 315 degrees, and a predetermined range including 0 degrees. The position of the reference pixel may be determined by fine classification.

  The downsampling unit 12 downsamples the image size of the luminance signal input from the outside to the same image size as the color difference signal, and outputs the downsampled luminance signal to the memory 13. For example, when the format of Y, Cb, and Cr is 4: 2: 2, the image size of the luminance signal is downsampled to ½ in the horizontal direction. When the format of Y, Cb, and Cr is 4: 1: 1, the image size of the luminance signal is downsampled to 1/4 in the horizontal direction. When the format of Y, Cb, and Cr is 4: 2: 0, the luminance signal image size is down-sampled to 1/2 in the horizontal direction and down-sampled to 1/2 in the vertical direction. Note that when the format of Y, Cb, and Cr is 4: 4: 4, downsampling is not performed.

  The memory 13 stores a color difference signal input from the outside and a downsampled luminance signal input from the downsampling unit 12.

Based on the reference pixel position information input from the reference pixel selection unit 11, the coefficient deriving unit 14 corresponds to the decoded pixel Rec _C (i) adjacent to the prediction target block of the color difference signal from the memory 13 and the pixel. And the decoded pixel Rec _L ′ (i) of the luminance signal at the position to be obtained, the coefficients α and β are derived by the above equations (1) and (2), and the derived coefficients α and β are used as the first color difference. It outputs to the prediction image generation part 15.

In the conventional technique of performing intra prediction using a prediction formula, all of the adjacent pixels a1 to a8 and b1 to b8 of the prediction target block are used as Rec _C (i) and Rec _L ′ (i), and the above formula ( 1) The coefficients α and β were derived from (2). However, in the intra prediction apparatus 1 according to the present invention, only the reference pixels selected by the reference pixel selection unit 11 among the adjacent pixels a1 to a8 and b1 to b8 as Rec _C (i) and Rec _L ′ (i). In order to derive the coefficients α and β using the above equations (1) and (2), the above prediction equation (3) is obtained by considering the correlation between the prediction target block and the adjacent pixels of the prediction target block. It can be.

The first color difference predicted image generation unit 15 uses the coefficients α and β input from the coefficient derivation unit 14 and the downsampled luminance signal Rec _L ′ [x, y] acquired from the memory 13 as described above. A color difference image which is a predicted image of the color difference signal is generated by the prediction formula of Expression (3), and the generated color difference image is output to the outside.

  FIG. 3 is a block diagram showing a second configuration example of the encoding-side intra prediction apparatus according to an embodiment of the present invention. As illustrated in FIG. 3, the intra prediction apparatus 2 on the encoding side includes a luminance predicted image generation unit 10, a reference pixel selection unit 11, a downsampling unit 12, a memory 13, a coefficient derivation unit 14, a first A color difference prediction image generation unit 15, a second color difference prediction image generation unit (second secondary prediction image generation unit) 16, and a color difference prediction image selection unit 17 are provided. The intra prediction device 2 of the second configuration example further includes a second color difference prediction image generation unit 16 and a color difference prediction image selection unit 17 as compared with the intra prediction device 1 of the first configuration example shown in FIG. The points to be provided are different, but the other points are the same. Therefore, the same components as those of the intra prediction apparatus 2 of the first configuration example shown in FIG. In FIG. 3, all the processing blocks are indicated by solid lines. However, after performing intra prediction on the luminance signal for each predetermined unit block (for example, macro block), the point of performing intra prediction on the color difference signal is as follows. This is the same as the intra prediction apparatus 1 of the first configuration example shown in FIG.

  The first color difference predicted image generation unit 15 outputs the generated color difference predicted image to the color difference predicted image selection unit 17 instead of the outside.

  The second color difference prediction image generation unit 16 refers to the image of the reference block for the color difference signal, determines a color difference prediction mode that is an optimal prediction mode from a plurality of predetermined prediction modes, and determines the determined color difference prediction mode. It outputs to the color difference prediction image selection part 17. The second color difference prediction image generation unit 16 can determine the color difference prediction mode by a known method. For example, a prediction image is obtained based on each prediction mode, and a color difference prediction mode that minimizes the coding cost is determined by RD optimization. For example, MPEG4 AVC / H. When the intra prediction is performed in units of 8 × 8 pixels by the H.264 method, the color difference prediction mode of the prediction target block is determined from the prediction modes illustrated in FIG. 8, and the intra prediction by the HEVC method is illustrated in FIG. 9. The color difference prediction mode of the prediction target block is determined from the prediction modes.

  In addition, the second color difference predicted image generation unit 16 generates a color difference predicted image that is a predicted image based on the determined color difference prediction mode, and outputs the generated color difference predicted image to the color difference predicted image selection unit 17.

  The color difference prediction image selection unit 17 is one of the color difference prediction image input from the first color difference prediction image generation unit 15 and the color difference prediction image input from the second color difference prediction image generation unit 16, for example, R−. The color difference prediction image whose encoding cost is reduced by D optimization is selected, and the selected color difference prediction image is output to the outside. The conventional MPEG4 AVC / H. By replacing one of the prediction modes set in advance in the H.264 system or the HEVC system with a prediction mode based on the prediction formula, the number of modes may not be increased compared to the conventional system.

  As described above, the intra prediction apparatuses 1 and 2 on the encoding side generate reference pixel position information according to the prediction direction indicated by the luminance prediction mode generated by the luminance predicted image generation unit 10 by the reference pixel selection unit 11, The coefficient derivation unit 14 derives the coefficients α and β of the prediction formula from the luminance signal pixel and the color difference signal pixels indicated by the reference pixel position information, and the first color difference prediction image generation unit 15 substitutes the coefficients α and β. A color difference prediction image is generated by performing intra prediction of a color difference signal using a prediction formula. Therefore, the intra prediction devices 1 and 2 can perform intra prediction considering the correlation between the prediction target block and the reference pixel adjacent to the prediction target block, and can improve the accuracy of intra prediction. Become.

  The intra prediction device 2 on the encoding side includes a second color difference prediction image generation unit 16 that generates a color difference prediction image based on a color difference prediction mode determined from a plurality of predetermined prediction modes, and a first color difference prediction. A color difference prediction image selection unit 17 that selects and outputs one of the color difference prediction image generated by the image generation unit 15 and the color difference prediction image generated by the second color difference prediction image generation unit 16; . For this reason, the intra-prediction device 2 uses a color difference prediction image based on a prediction formula in consideration of the correlation and the conventional MPEG4 AVC / H. Since it is possible to select a suitable one of the color difference prediction images by the H.264 method, the accuracy of intra prediction can be further improved.

  It should be noted that a computer can be suitably used to function as the intra prediction devices 1 and 2 described above, and such a computer can store a program describing processing contents for realizing each function of the intra prediction devices 1 and 2. It can be realized by storing the program in a storage unit of the computer and reading and executing the program by the CPU of the computer.

[Encoding device]
Next, an encoding apparatus provided with the intra prediction apparatus 1 or 2 described above will be described. FIG. 4 is a block diagram showing a configuration of an encoding apparatus according to an embodiment of the present invention. In this example, MPEG-4 AVC / H. The example which applied intra prediction apparatus 1 or 2 to the encoding apparatus of H.264 system is shown. As illustrated in FIG. 4, the encoding device 20 includes a subtraction unit 21, an orthogonal transformation unit 22, a quantization unit 23, an inverse quantization unit 24, an inverse orthogonal transformation unit 25, an addition unit 26, and a memory. 27, intra prediction apparatuses 1 and 2, a motion compensation unit 28, a changeover switch 29, and a variable length coding unit 30. The encoding device 20 encodes the color difference signal after encoding the luminance signal for each predetermined unit block (for example, macroblock). Therefore, it should be noted that each processing block of the encoding device 20 described below processes the color difference signal after processing the luminance signal.

  The subtracting unit 21 is a video signal (luminance signal or color difference signal) composed of a luminance signal and a color difference signal, and a prediction image (luminance prediction image) input from the intra prediction devices 1 and 2 or the motion compensation unit 28 via the changeover switch 29. Or the color difference prediction image), and the difference image is output to the orthogonal transform unit 22.

  The orthogonal transform unit 22 performs orthogonal transform on the difference image input from the subtraction unit 21 in units of blocks, and outputs the obtained orthogonal transform coefficients to the quantization unit 23.

  The quantization unit 23 selects a quantization table for the orthogonal transform coefficient input from the orthogonal transform unit 22 and performs a quantization process. The quantized orthogonal transform coefficient is converted into an inverse quantization unit 24 and a variable length code. To the conversion unit 30.

  The inverse quantization unit 24 performs inverse quantization processing on the quantized orthogonal transform coefficient input from the quantization unit 23 and outputs the obtained orthogonal transform coefficient to the inverse orthogonal transform unit 25.

  The inverse orthogonal transform unit 25 performs an inverse orthogonal transform (for example, IDCT; Inverse Discrete Cosine Transform) process on the orthogonal transform coefficient input from the inverse quantization unit 24 and outputs an inversely orthogonally transformed image to the addition unit 26. To do.

  The adding unit 26 performs the inverse orthogonal transform image input from the inverse orthogonal transform unit 25 and the predicted image (luminance predicted image or color difference) input from the intra prediction devices 1 and 2 or the motion compensation unit 28 via the changeover switch 29. The predicted image) is added to generate a local decoded image, and the generated local decoded image is output to the memory 27. Since the encoding device 20 processes the luminance signal and then the color difference signal, when encoding the nth block of the color difference signal, the memory 27 stores the (n−1) th block of the color difference signal. The local decoded images up to and the local decoded image up to the nth block of the luminance signal are stored.

  The intra prediction devices 1 and 2 refer to the locally decoded image stored in the memory 27, generate the luminance signal intra prediction image as described above, and then generate the color difference signal intra prediction image. The generated intra prediction image is output to the subtraction unit 21 and the addition unit 26 via the changeover switch 29. Also, the intra prediction device 1 generates a luminance prediction mode and outputs it to the variable length coding unit 30, and the intra prediction device 2 generates a luminance prediction mode and a color difference prediction mode and outputs them to the variable length coding unit 30.

  The motion compensation unit 28 refers to past and / or future pictures (frames) stored in the memory 27 with respect to the video signal, and performs an SSD (Sum of Squared Difference) method or an SAD (Sum of Absolute Intensity Difference) method. A motion vector is generated by block matching using, and the generated motion vector is output to the variable length encoding unit 30. Block matching is performed with decimal pixel accuracy by, for example, interpolation processing using a parabolic fitting function.

  The motion compensation unit 28 performs motion compensation on the decoded image stored in the memory 27 using the generated motion vector to generate an inter prediction image (inter prediction), and generates the inter prediction image. The inter prediction image is output to the subtraction unit 21 and the addition unit 26 via the changeover switch 29.

  The changeover switch 29 switches between the intra prediction image input from the intra prediction devices 1 and 2 and the inter prediction image input from the motion compensation unit 28, and outputs the result to the subtraction unit 21 and the addition unit 26.

  The variable length encoding unit 30 scans the quantized orthogonal transform coefficient input from the quantization unit 23 to perform variable length encoding processing, and outputs the obtained encoded data to the outside. The variable length coding unit 30 also performs variable length coding processing on the prediction mode input from the intra prediction apparatuses 1 and 2 and the motion vector information input from the motion compensation unit 28, and obtains encoded data obtained. Is output to the outside.

  Thus, since the encoding apparatus 20 includes the intra prediction apparatus 1 or 2, the accuracy of intra prediction can be improved, and accordingly, the encoding efficiency can be improved.

  Note that a computer can be suitably used to cause the above-described encoding device 20 to function, and such a computer stores a program that describes processing contents for realizing each function of the encoding device 20 in the storage of the computer. The program can be realized by reading out and executing the program by the CPU of the computer.

[Intra prediction device on decoding side]
Next, the decoding side intra prediction apparatus will be described. FIG. 5 is a block diagram illustrating a first configuration example of the decoding-side intra prediction apparatus according to an embodiment of the present invention. As illustrated in FIG. 5, the decoding-side intra prediction device 3 includes a luminance predicted image generation unit 10, a reference pixel selection unit 11, a downsampling unit 12, a memory 13, a coefficient derivation unit 14, and a first color difference. A predicted image generation unit 15.

  The intra prediction apparatus 3 on the decoding side performs intra prediction on the color difference signal after performing intra prediction on the luminance signal for each predetermined unit block (for example, macroblock). In order to clarify this point, in FIG. 5A, only the processing unit that performs intra prediction on the luminance signal is shown by a solid line, and in FIG. 5B, only the processing unit that performs intra prediction on the color difference signal is shown by a solid line. Yes. That is, as illustrated in FIG. 5A, the intra prediction device 3 performs intra prediction on the input luminance signal by the luminance prediction image generation unit 10 in units of blocks, and obtains a luminance prediction image that is a prediction image of the luminance signal. Generate. Thereafter, as shown in FIG. 1B, the reference color selection unit 11, the downsampling unit 12, the memory 13, the coefficient derivation unit 14, and the first color difference prediction image generation unit 15 are processed block by block with respect to the input color difference signal. Intra prediction is performed to generate a color difference prediction image that is a prediction image of the color difference signal. In addition, when the intra prediction apparatus 3 is incorporated in a decoding apparatus, each decoded image is input to the intra prediction apparatus 3 as a luminance signal and a color difference signal as described later.

  The decoding-side intra prediction device 3 illustrated in FIG. 5 is different from the encoding-side intra prediction device 1 illustrated in FIG. 1 in that the luminance prediction image generation unit 10 does not generate the luminance prediction mode and reference pixel selection. The difference is that the unit 11 generates reference pixel position information using the luminance prediction mode input from the outside, but the functions of the other blocks are the same as those of the intra prediction apparatus 1 on the encoding side.

  That is, the luminance predicted image generation unit 10 generates a luminance predicted image based on the luminance prediction mode acquired from the encoding side, and outputs the generated luminance predicted image to the outside. The luminance signal and the luminance prediction mode input to the luminance predicted image generation unit 10 are also used for intra prediction of the color difference signal performed thereafter.

  The reference pixel selection unit 11 selects the position of the reference pixel used when deriving the coefficients α and β of the prediction formula based on the luminance prediction mode acquired from the encoding side, and indicates the reference pixel selection position The position information is output to the coefficient deriving unit 14.

  The downsampling unit 12 downsamples the image size of the luminance signal acquired from the encoding side to the same image size as the color difference signal acquired from the encoding side, and outputs the downsampled luminance signal to the memory 13. The memory 13 stores the color difference signal and the downsampled luminance signal input from the downsampling unit 12.

Based on the reference pixel position information input from the reference pixel selection unit 11, the coefficient deriving unit 14 corresponds to the decoded pixel Rec _C (i) adjacent to the prediction target block of the color difference signal from the memory 13 and the pixel. And the decoded pixel Rec _L ′ (i) of the luminance signal at the position to be obtained, the coefficients α and β are derived by the above equations (1) and (2), and the derived coefficients α and β are used as the first color difference. It outputs to the prediction image generation part 15. The color difference prediction image generation unit 15 uses the coefficients α and β input from the coefficient derivation unit 14 and the downsampled luminance signal Rec _L ′ [x, y] acquired from the memory 13 to A color difference prediction image is generated by the prediction formula 3), and the generated color difference prediction image is output to the outside.

  FIG. 6 is a block diagram illustrating a second configuration example of the decoding-side intra prediction apparatus according to an embodiment of the present invention. As illustrated in FIG. 6, the decoding-side intra prediction device 4 includes a luminance predicted image generation unit 10, a reference pixel selection unit 11, a downsampling unit 12, a memory 13, a coefficient derivation unit 14, and a first color difference. A prediction image generation unit 15, a second color difference prediction image generation unit 16, and a color difference prediction image selection unit 17 are provided. Compared with the decoding-side intra prediction device 3 of the first configuration example illustrated in FIG. 5, the decoding-side intra prediction device 4 of the second configuration example has a second color difference prediction image generation unit 16 and color difference prediction. The difference is that the image selection unit 17 is further provided, but the other points are the same. Therefore, the same components as those of the decoding-side intra prediction device 3 of the first configuration example shown in FIG. In FIG. 6, all processing blocks are indicated by solid lines. However, after performing intra prediction for a luminance signal for each predetermined unit block (for example, a macroblock), the point of performing intra prediction for a color difference signal is as follows. This is the same as the intra prediction apparatus 3 of the first configuration example on the decoding side shown in FIG.

  The first color difference predicted image generation unit 15 outputs the generated color difference predicted image to the color difference predicted image selection unit 17 instead of the outside.

  The second color difference prediction image generation unit 16 generates a color difference prediction image based on the color difference prediction mode acquired from the encoding side, and outputs the generated color difference prediction image to the color difference prediction image selection unit 17.

  The color difference prediction image selection unit 17 is input from the encoding side among the color difference prediction image input from the first color difference prediction image generation unit 15 and the color difference prediction image input from the second color difference prediction image generation unit 16. Either one is selected based on the color difference prediction mode and output to the outside. That is, when the color difference prediction mode is a prediction mode for generating a color difference prediction image using a prediction formula, the color difference prediction image input from the first color difference prediction image generation unit 15 is selected, and the other prediction modes are selected. If it is, the color difference prediction image input from the second color difference prediction image generation unit 16 is selected. When the color difference prediction mode is a prediction mode for generating a color difference prediction image using a prediction formula, the second color difference prediction image generation unit 16 does not generate a color difference prediction image, and other prediction modes are used. If there is a color difference prediction image, the first color difference prediction image generation unit 15 may not generate the color difference prediction image.

  As described above, the decoding-side intra prediction devices 3 and 4 indicate the luminance prediction mode generated by the luminance-predicted image generation unit 10 by the reference pixel selection unit 11 in the same manner as the encoding-side intra prediction devices 1 and 2. The reference pixel position information is generated according to the prediction direction, and the coefficient deriving unit 14 derives the coefficients α and β of the prediction formula from the pixel of the luminance signal and the color difference signal indicated by the reference pixel position information, and the first color difference prediction The image generation unit 15 generates a color difference prediction image by performing intra prediction of the color difference signal using a prediction formula into which the coefficients α and β are substituted. For this reason, the intra prediction apparatuses 3 and 4 can perform the intra prediction which considered the correlation with a prediction object block and the reference pixel adjacent to this prediction object block, and can improve the accuracy of intra prediction. Become.

  The decoding-side intra prediction device 4 includes a second color difference prediction image generation unit 16 that generates a color difference prediction image based on a color difference prediction mode determined from a plurality of predetermined intra prediction modes, and a first color difference prediction. A color difference prediction image selection unit 17 that selects and outputs one of the color difference prediction image generated by the image generation unit 15 and the color difference prediction image generated by the second color difference prediction image generation unit 16; . For this reason, the intra-prediction device 4 uses a color difference prediction image based on a prediction formula in consideration of the correlation and the conventional MPEG4 AVC / H. Since it is possible to select a suitable one of the color difference prediction images by the H.264 method, the accuracy of intra prediction can be further improved.

  It should be noted that a computer can be suitably used to function as the above-described intra prediction devices 3 and 4, and such a computer can store a program describing processing contents for realizing each function of the intra prediction devices 3 and 4. It can be realized by storing the program in a storage unit of the computer and reading and executing the program by the CPU of the computer.

[Decoding device]
Next, a decoding apparatus provided with the intra prediction apparatus 3 or 4 described above will be described. FIG. 7 is a block diagram showing a configuration of a decoding apparatus according to an embodiment of the present invention. In this example, MPEG-4 AVC / H. An example in which the intra prediction device 3 or 4 is applied to a H.264 decoding device is shown. As illustrated in FIG. 7, the decoding device 40 includes a variable length decoding unit 41, an inverse quantization unit 42, an inverse orthogonal transform unit 43, an addition unit 44, a memory 45, intra prediction devices 3 and 4, A motion compensation unit 46 and a changeover switch 47 are provided. The decoding device 40 performs decoding on the color difference signal after decoding the luminance signal for each predetermined unit block (for example, macroblock). Therefore, it should be noted that each processing block of the decoding device 40 described below processes the color difference signal after processing the luminance signal.

  The variable length decoding unit 41 performs a variable length decoding process on the encoded orthogonal transform coefficient and outputs it to the inverse quantization unit 42, and performs a variable length decoding process on the encoded prediction mode to perform the intra length conversion. It outputs to the prediction apparatuses 3 and 4, performs a variable length decoding process with respect to the encoded motion vector, and outputs it to the motion compensation part 46. FIG.

  The inverse quantization unit 42 performs an inverse quantization process on the quantized orthogonal transform coefficient input from the variable length decoding unit 41 and outputs the orthogonal transform coefficient of the obtained difference image to the inverse orthogonal transform unit 43. .

  The inverse orthogonal transform unit 43 performs inverse orthogonal transform (for example, IDCT) on the orthogonal transform coefficient of the difference image input from the inverse quantization unit 42 and outputs the obtained difference image to the addition unit 44.

  The adding unit 44 adds the difference image obtained from the inverse orthogonal transform unit 43 and the prediction image input from the intra prediction devices 3 and 4 or the motion compensation unit 46 via the changeover switch 47, and stores the decoded image in the memory 45. And output to the outside. When decoding a block having a luminance signal, the memory 45 stores a decoded image up to the previous block of the luminance signal. When a block having a color difference signal is decoded, a decoded image up to the previous block of the color difference signal and a decoded image of a luminance signal of the same frame are stored.

  The intra prediction devices 3 and 4 receive the decoded image stored in the memory 45, generate an intra prediction image of the luminance signal based on the prediction mode input from the variable length decoding unit 41, and then perform intra prediction of the color difference signal. Generate an image. The generated intra predicted image is output to the adding unit 44 via the changeover switch 47.

  The motion compensation unit 46 refers to the decoded frame image stored in the memory 45, generates an inter prediction image using the motion vector obtained from the variable length decoding unit 41, and switches the generated inter prediction image via the changeover switch 47. To the adder 44.

  The changeover switch 47 switches between the intra prediction image input from the intra prediction devices 3 and 4 and the inter prediction image input from the motion compensation unit 46 and outputs the switched image to the addition unit 44.

  Thus, since the decoding apparatus 40 includes the intra prediction apparatus 3 or 4, the accuracy of intra prediction can be improved, and the image quality of the decoded image can be improved accordingly.

  Note that a computer can be suitably used to cause the above-described decryption device 40 to function, and such a computer stores a program describing processing contents for realizing each function of the decryption device 40 in a storage unit of the computer. This can be realized by storing the program and executing it by the CPU of the computer.

  Although the above embodiments have been described as representative examples, it will be apparent to those skilled in the art that many changes and substitutions can be made within the spirit and scope of the invention. Therefore, the present invention should not be construed as being limited by the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims.

  For example, in the above-described embodiment, the case where the primary component signal is a luminance signal and the secondary component signal is a color difference signal has been described as an example. However, when the input video signal is an RGB signal, the primary component signal is Is the G signal, the secondary component signal is the R signal and the B signal, and intra prediction of the R signal and the B signal can be performed from the G signal using the prediction formula. In addition, even when the input video is composed of a large number of component signals such as a multispectral signal, intra prediction of the secondary component signal can be performed from the primary component signal using the prediction formula.

  In the above-described embodiment, the case where the primary component signal has a higher resolution than the secondary component signal (the number of pixels) is taken as an example, and thus the downsampling unit 12 is provided. However, the primary component signal has a lower resolution than the secondary component signal ( In the case where the number of pixels is small), by providing an upsampling unit instead of the downsampling unit 12, it is possible to similarly perform intra prediction of the secondary component signal from the primary component signal using the prediction formula.

  As described above, according to the present invention, it is possible to improve the accuracy of the intra prediction accuracy. Therefore, the present invention is useful for any application that encodes or decodes a video signal by intra prediction.

DESCRIPTION OF SYMBOLS 1, 2 Coding side intra prediction apparatus 3,4 Decoding side intra prediction apparatus 10 Luminance prediction image generation part (primary prediction image generation part)
DESCRIPTION OF SYMBOLS 11 Reference pixel selection part 12 Downsampling part 13 Memory 14 Coefficient derivation | leading-out part 15 1st color difference prediction image generation part (1st secondary prediction image generation part)
16 2nd color difference prediction image generation part (2nd secondary prediction image generation part)
17 Color difference prediction image selection unit 20 Encoding device 21 Subtraction unit 22 Orthogonal transformation unit 23 Quantization unit 24, 42 Inverse quantization unit 25, 43 Inverse orthogonal transformation unit 26, 44 Addition unit 27, 45 Memory 28, 46 Motion compensation unit 29, 47 changeover switch 30 variable length encoding unit 40 decoding device 41 variable length decoding unit

Claims (8)

For a video signal having a primary component signal and a secondary component signal composed of one or more other component signals, intra prediction of the secondary component signal is performed using a coded primary component signal and a prediction formula represented by a coefficient. An intra prediction device for performing
A primary prediction image generation unit that generates a prediction image of a primary component signal based on a primary prediction mode determined from a plurality of predetermined intra prediction modes;
A reference pixel selection unit that determines a position of a reference pixel used for deriving a coefficient of the prediction formula according to a prediction direction indicated by the primary prediction mode, and generates reference pixel position information indicating the position of the reference pixel;
A coefficient deriving unit for deriving a coefficient of the prediction formula from the pixel of the primer component signal and the pixel of the secondary component signal indicated by the reference pixel position information;
A first secondary predicted image generation unit configured to perform intra prediction of the secondary component signal using a prediction formula into which the coefficient derived by the coefficient deriving unit is substituted, and generate a predicted image of the secondary component signal;
An intra prediction apparatus comprising: The reference pixel selection unit includes:
When the angle in the counterclockwise direction with respect to the vertical downward direction of the prediction direction indicated by the primary prediction mode is a range including 0 degrees, the reference angle is greater than or equal to the first angle and less than the second angle. The pixel position is a row of pixels adjacent to the upper side of the prediction target block,
When the angle of the anticlockwise direction with respect to the vertical downward direction of the prediction direction indicated by the primary prediction mode is a range including 45 degrees, the angle is greater than or equal to the second angle and less than the third angle, The position of the reference pixel is a part of the pixels in the one row and a part of a column of pixels adjacent to the left side of the prediction target block,
In the case where the angle of the counterclockwise direction with respect to the vertical downward direction of the prediction direction indicated by the primary prediction mode is a range including 90 degrees, the angle is equal to or greater than the third angle and less than the fourth angle. The intra prediction apparatus according to claim 1, wherein a position of a reference pixel is the pixel in the row. A second secondary predicted image generation unit that generates a predicted image of the secondary component signal based on a secondary prediction mode determined from a plurality of predetermined intra prediction modes;
One of the predicted image of the secondary component signal generated by the first secondary predicted image generation unit and the predicted image of the secondary component signal generated by the second secondary predicted image generation unit are selected and output. A secondary predicted image selection unit;
The intra prediction apparatus according to claim 1, further comprising:   An encoding apparatus comprising the intra prediction apparatus according to any one of claims 1 to 3.   A decoding apparatus comprising the intra prediction apparatus according to any one of claims 1 to 3.   The intra prediction program for functioning a computer as an intra prediction apparatus as described in any one of Claim 1 to 3.   An encoding program for causing a computer to function as the encoding device according to claim 4. A decoding program for causing a computer to function as the decoding device according to claim 5.

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