JP2008193501A - Image encoding device and image encoding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform encoding in a prediction mode having high encoding efficiency. <P>SOLUTION: Arithmetic processing can be reduced and real time encoding can be performed by preferentially selecting an intra prediction mode determined in an encoded block located at the same position of an encoding target block in an encoded picture temporally closest from an encoding target picture as an intra prediction mode for the encoding target block and performing intra prediction. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image encoding device and an image encoding method, and more particularly to a technique suitable for use in encoding / decoding a moving image by intra prediction.

  In recent years, the digitalization of information related to multimedia has been rapidly progressing, and the demand for higher image quality of video information has increased accordingly. As a specific example, in the broadcasting media, it can be mentioned that a transition from the conventional SD (Standard Definition) method of 720 × 480 pixels to the HD (High Definition) method of 1920 × 1080 pixels is being performed. .

  However, this demand for high image quality has a problem of simultaneously increasing digital data. In order to solve this problem, a compression encoding technique and a decoding technique exceeding the conventional performance are required. In response to these demands, standardization of an encoding / compression method using inter-frame prediction using correlation between images is underway by activities of ITU-T SG16 and ISO / IEC JTC1 / SC29 / WG11.

  Among these, H.264 is an encoding method that is said to realize the most efficient encoding at present. H.264 / MPEG-4 PART10 (AVC) (hereinafter referred to as H.264). In addition, as one of the newly introduced technologies, intra prediction has been introduced in which intra-frame correlation is used to predict pixel values in the same frame using intra-frame pixel values.

  In intra prediction, there are a plurality of prediction block sizes and prediction directions (hereinafter referred to as intra prediction modes). For example, intra 16 × 16 prediction that determines a prediction direction based on block data of “16 × 16 pixels” has four types of prediction directions. In addition, there are nine types of prediction directions in intra 4 × 4 prediction that determines a prediction direction based on block data of “4 × 4 pixels”.

  H. H.264 realizes highly efficient coding by selecting the most appropriate one of these intra prediction modes. In general, a method of trying an intra prediction process and selecting an optimal intra prediction mode is used. Furthermore, Patent Document 1 proposes a method for selecting an optimal intra prediction mode using shooting information. Patent Document 2 proposes a method for determining an image pattern and selecting an optimal intra prediction mode.

JP 2006-217158 A JP 2006-005659 A

  As described above, in order to obtain an optimal intra prediction mode in the intra prediction, it is necessary to select an optimal intra prediction mode. For this purpose, H.264 provided by ITU-T SG16 and ISO / IEC. In the H.264 reference software model JM (Joint Model), calculation is performed for all intra prediction modes, and an optimal intra prediction mode is selected.

  However, enormous processing time is required to perform operations for all intra prediction modes determined by intra 16 × 16 prediction and intra 4 × 4 prediction for the current block. For this reason, it has been difficult to perform the encoding process in real time especially for P pictures and B pictures for which a motion vector needs to be calculated in addition to the selection of the intra prediction mode.

  In addition, since an increase in calculation load leads to an increase in power consumption, in the case of a mobile device such as a video camera, there is a problem that the operable time of the device is shortened. Furthermore, in the method of Patent Document 1, acquisition of photographing information is essential, and in the method of Patent Document 2, there is a problem that means for determining an image pattern is necessary.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to enable encoding in a prediction mode with good encoding efficiency with a smaller calculation amount than in the past.

An image encoding apparatus according to the present invention is an image encoding apparatus that performs intra-frame prediction for each block composed of a plurality of pixels defined in a picture to be encoded, and performs encoding according to a plurality of types of prediction modes. An intra-prediction unit capable of executing an intra-prediction process; and a prediction mode selection unit that selects a prediction mode used by the intra-prediction unit. The prediction mode selection unit is temporally closest to the encoding target picture. In the encoded picture, the prediction mode corresponding to the prediction block size determined by the encoded block at the same position as the encoding target block is preferentially selected during the intra prediction process of the encoding target block. It is characterized by doing.
Another feature of the image coding apparatus according to the present invention is that the image coding apparatus performs coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded. Intra prediction means capable of executing intra-screen prediction processing according to a plurality of types of prediction modes, and prediction mode selection means for selecting a prediction mode used by the intra prediction means, wherein the prediction mode selection means includes a code The prediction mode determined by the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture is prioritized in the intra prediction process of the encoding target block It is characterized by selecting automatically.
Another feature of the image coding apparatus of the present invention is that the image coding apparatus performs coding by performing intra prediction for each block composed of a plurality of pixels defined in the picture to be coded. Intra prediction means capable of executing intra-screen prediction processing according to a plurality of types of prediction modes, and prediction mode selection means for selecting a prediction mode used by the intra prediction means, wherein the prediction mode selection means includes a code In the encoded picture that is closest in time to the encoding target picture, the predicted block size determined by the encoded block at the position shifted by the amount corresponding to the amount of motion between pictures from the same position as the encoding target block The corresponding prediction mode is preferentially selected during the intra-screen prediction process of the encoding target block.
Another feature of the image coding apparatus of the present invention is that the image coding apparatus performs coding by performing intra prediction for each block composed of a plurality of pixels defined in the picture to be coded. Intra prediction means capable of executing intra-screen prediction processing according to a plurality of types of prediction modes, and prediction mode selection means for selecting a prediction mode used by the intra prediction means, wherein the prediction mode selection means includes a code The prediction mode determined by the encoded block at the position shifted by the amount corresponding to the amount of motion between the pictures from the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture, The selection is performed preferentially during the intra-frame prediction process of the encoding target block.
Another feature of the image coding apparatus of the present invention is that the image coding apparatus performs coding by performing intra prediction for each block composed of a plurality of pixels defined in the picture to be coded. A prediction mode selection unit that selects a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra prediction, and an encoding target according to the prediction mode candidate selected by the prediction mode selection unit Intra prediction means for performing an intra-screen prediction process of the block to calculate a prediction error due to the prediction mode candidate, and finally, based on the calculation result of the intra prediction means, the prediction mode candidate with the smallest prediction error is determined. Prediction mode determining means for determining as a correct prediction mode, and the prediction mode selecting means is a temporally closest code from the picture to be encoded. In reduction already picture and selects the encoding target block and a candidate of the prediction modes including the prediction mode determined by the encoded blocks in the same position.
Another feature of the image coding apparatus of the present invention is that the image coding apparatus performs coding by performing intra prediction for each block composed of a plurality of pixels defined in the picture to be coded. A prediction mode selection unit that selects a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra prediction, and an encoding target according to the prediction mode candidate selected by the prediction mode selection unit Intra prediction means for performing an intra-screen prediction process of the block to calculate a prediction error due to the prediction mode candidate, and finally, based on the calculation result of the intra prediction means, the prediction mode candidate with the smallest prediction error is determined. Prediction mode determining means for determining as a correct prediction mode, and the prediction mode selecting means is a temporally closest code from the picture to be encoded. In the encoded picture, the prediction mode candidate is selected including the prediction mode determined by the encoded block at a position shifted by the amount corresponding to the motion amount between pictures from the same position as the encoding target block. It is characterized by that.

The image encoding method of the present invention is an image encoding method for performing encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded. A step of selecting a predetermined number of prediction mode candidates from among the prediction modes, and performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidates, thereby performing prediction based on the prediction mode candidates A step of calculating an error, and a step of determining a prediction mode candidate having the smallest prediction error as a final prediction mode based on a result of the calculation, and selecting the prediction mode candidate The prediction mode determined by the encoded block in the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture. Including de and selects candidates of the prediction mode.
Another feature of the image coding method of the present invention is that the image coding method performs coding by performing intra prediction for each block composed of a plurality of pixels defined in the picture to be coded. A step of selecting a predetermined number of prediction mode candidates from among a plurality of types of prediction modes related to the intra prediction, and performing an intra prediction process of the encoding target block according to the selected prediction mode candidates Calculating a prediction error due to the prediction mode candidate, and determining a prediction mode candidate with the smallest prediction error as a final prediction mode based on the result of the calculation, In the step of selecting a prediction mode candidate, in the encoded picture that is temporally closest to the encoding target picture, between the pictures from the same position as the encoding target block. Characterized in that including the prediction mode determined by the encoded blocks in shifted by positions an amount corresponding to the motion amount selecting the candidate of the prediction mode.

The program of the present invention is a program for causing a computer to execute an image encoding method for performing encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded. A process of selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to intra prediction, and performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidates, Calculating a prediction error due to the prediction mode candidate, and determining a prediction mode candidate with the smallest prediction error as a final prediction mode based on a result of the calculation, In the prediction mode candidate selection step, the encoding target block in the encoded picture temporally closest to the encoding target picture is selected. Including click and prediction mode determined in encoded blocks in the same position, characterized in that to be executed by a computer to select a candidate of the prediction mode.
Another feature of the program of the present invention is that it causes a computer to execute an image coding method for performing coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded. And a coding target block according to the step of selecting a predetermined number of prediction mode candidates from among a plurality of types of prediction modes related to the intra-screen prediction, and the selected prediction mode candidates And calculating a prediction error due to the prediction mode candidate, and determining a prediction mode candidate with the smallest prediction error as a final prediction mode based on the result of the calculation. In the step of causing the computer to execute the process and selecting the prediction mode candidate, the encoded picture that is temporally closest to the encoding target picture is used. In which the prediction mode candidate is selected including the prediction mode determined by the encoded block at the position shifted by the amount corresponding to the amount of motion between pictures from the same position as the encoding target block. It is made to perform.

  According to the present invention, it is possible to select an appropriate intra prediction mode without performing calculations for all intra prediction modes. As a result, encoding can be performed in a prediction mode with good encoding efficiency, arithmetic processing can be reduced, and real-time encoding can be performed. In addition, power consumption can be greatly reduced.

(First embodiment)
Hereinafter, a preferred first embodiment of an image encoding device according to the present invention will be described in detail with reference to FIGS.
FIG. 1 is a block diagram illustrating a configuration example of an image encoding device according to the present embodiment. As shown in FIG. 1, the image coding apparatus according to this embodiment includes a frame memory 101 and a post-filter reference frame memory 102.

  Also, the motion prediction unit 103, motion compensation unit 104, intra prediction unit 105, orthogonal transform unit 106, quantization unit 107, entropy coding unit 108, inverse quantization unit 109, inverse orthogonal transform unit 110, switch 111, subtractor 112 and an adder 113. Further, a pre-filter reference frame memory 114, a loop filter 115, and an intra prediction mode storage unit 116 are provided.

First, a method for encoding an input image in the image encoding apparatus of the present embodiment configured as described above will be described.
Input images are stored in the frame memory 101 in the display order, and the encoding target blocks are rearranged in the encoding order to the motion prediction unit 103, the intra prediction unit 105, and the subtractor 112, and sequentially transmitted.

  The subtractor 112 subtracts the predicted image block transmitted from the switch 111 from the encoding target block transmitted from the frame memory 101, and outputs image residual data. A method for generating a predicted image block will be described later.

  The orthogonal transform unit 106 performs orthogonal transform processing on the image residual data output from the subtractor 112 and transmits transform coefficients to the quantization unit 107. The quantization unit 107 quantizes the orthogonal transform unit transform coefficient using a predetermined quantization parameter, and transmits the quantized unit to the entropy coding unit 108 and the inverse quantization unit 109.

  The entropy coding unit 108 inputs the transform coefficient quantized by the quantization unit 107, performs entropy coding such as CAVLC (Context-Based Adaptive Variable Length), CABAC (Context-based Adaptive Binary Arithmetic Coding), Output as encoded data. Next, a method for generating reference image data using the transform coefficient quantized by the quantization unit 107 will be described.

  The inverse quantization unit 109 performs inverse quantization on the quantized transform coefficient transmitted from the quantization unit 107. The inverse orthogonal transform unit 110 performs inverse orthogonal transform on the transform coefficient inversely quantized by the inverse quantization unit 109, generates decoded residual data, and transmits the decoded residual data to the adder 113.

  The adder 113 adds decoded residual data and predicted image data described later to generate reference image data, and stores the reference image data in the pre-filter reference frame memory 114. Also, it is transmitted to the loop filter 115. The loop filter 115 filters the reference image data to remove noise, and stores the filtered reference image data in the filtered reference frame memory 102.

Next, a method for generating the predicted image data using the input image data, the pre-filter reference image data, and the post-filter reference image data will be described.
The motion prediction unit 103 uses the coding target block transmitted from the frame memory 101 and the filtered reference image data transmitted from the filtered reference frame memory 102, and the amount of motion in the filtered reference image data of the coding target block Is detected. Then, the detected motion vector is transmitted to the motion compensation unit 104 together with the filtered reference frame image data number.

  The motion compensation unit 104 refers to the reference frame image indicated by the filtered reference frame image data number in the filtered reference frame memory 102 using the motion vector transmitted from the motion prediction unit 103. Then, predicted image data of each block is generated and transmitted to the switch 111.

  On the other hand, the intra prediction unit 105 uses intra-frame prediction using the encoding target block transmitted from the frame memory 101 and the peripheral pixels of the already encoded target block transmitted from the pre-filter reference frame memory 114 ( Intra prediction). Then, an appropriate intra prediction mode is selected from a plurality of intra prediction modes to generate predicted image data, which is transmitted to the switch 111 and information on the selected prediction mode is stored in the intra prediction mode storage unit 116. A method for selecting an appropriate intra prediction mode, which is a feature of the present embodiment, will be described in detail later.

  The switch 111 selects an appropriate prediction image from the prediction image data transmitted from the motion compensation unit 104 and the intra prediction unit 105 and transmits the selected prediction image to the subtractor 112. As a method for selecting an appropriate prediction image, for example, a method of selecting a smaller sum of absolute values of image residuals of an encoding target block and reference image data may be used. In the apparatus, the selection method is not limited.

Next, a method of generating a predicted image using a prediction mode that can be used by the intra prediction unit 105 will be described with reference to FIG.
First, a method for generating a predicted image in a prediction mode that can be selected by intra 16 × 16 prediction will be described. Here, the pixel data belonging to the encoding target block is P (x, y). Note that x and y indicate the position in the row direction and the column direction of matrix pixel data constituting the block, and are integers from 0 to 15.

  The pixel data adjacent to the encoding target block are P (x, −1) and P (−1, y). Also, the pixel data is determined to be “unavailable” when it belongs to a different picture or a different slice from the encoding target block.

(Prediction mode 0):
Prediction mode 0 is vertical (vertical) prediction, and is applied when P (x, −1) is “available”. In this case, in vertical (vertical) prediction, pixel data Pred (x, y) of the predicted image data PI is generated as shown in Equation 1.

(Prediction mode 1):
Prediction mode 1 is horizontal (horizontal) prediction and is applied when P (−1, y) is “available”. In this case, in horizontal (horizontal) prediction, pixel data Pred (x, y) of the predicted image data PI is generated as shown in Equation 2.

(Prediction mode 2):
Prediction mode 2 is DC prediction. In intra 16 × 16 prediction, pixel data Pred (x, y) of predicted image data PI is generated as shown in Equation 3. First, when all of P (x, −1) and P (−1, y) are “available”, the pixel data Pred (x, y) of the predicted image data PI is used for intra 16 × 16 prediction. It is generated as shown in Equation 3.

(Prediction mode 3):
The prediction mode 3 is plane prediction, and is applied when all of P (x, −1) and P (−1, y) are “available”. In this case, in the plane prediction, the pixel data Pred (x, y) of the predicted image data PI is generated as shown in Equation 6.

Next, a method for generating predicted block data in a prediction mode that can be selected by intra 4 × 4 prediction will be described with reference to FIG.
FIG. 4 is a diagram for explaining the positional relationship between pixel data a to p belonging to a 4 × 4 block that is an encoding process target for intra 4 × 4 prediction and pixel data A to M belonging to the periphery of the block data. FIG. Predicted image data PI is generated based on the predicted values of the pixel data a to p. The pixel data A to M are determined to be “unavailable” when they belong to a different picture or a different slice from the block to be processed.

(Prediction mode 0):
The prediction mode 0 is vertical (vertical) prediction, and is applied when all of the pixel data A, B, C, and D shown in FIG. 4 are “available”. In this case, the vertical prediction generates prediction values of the pixel data a to p of the encoding target block using the pixel data A, B, C, and D as shown in Equation 7.

(Prediction mode 1):
The prediction mode 1 is horizontal prediction and is applied when all of the pixel data I, J, K, and L shown in FIG. 4 are “available”. In this case, the horizontal prediction generates prediction values of the encoding target block pixel data a to p using the pixel data I, J, K, and L as shown in Equation 8.

(Prediction mode 2):
The prediction mode 2 is DC prediction, and when all of the pixel data A, B, C, D, I, J, K, and L shown in FIG. Predicted values of data a to p are generated as shown in Equation 9 using pixel data A, B, C, D, I, J, K, and L.

  If all of the pixel data A, B, C, and D shown in FIG. 4 are not “available”, the predicted values of the encoding target block pixel data a to p are set as the pixel data A, B, C, It is generated as shown in Equation 10 using D.

  If all of the pixel data I, J, K, and L shown in FIG. 4 are not “available”, the predicted values of the encoding target block pixel data a to p are set as the pixel data I, J, K, It is generated as shown in Equation 11 using L.

  When all of the pixel data A, B, C, D, I, J, K, and L shown in FIG. 4 are not “available”, the predicted value “128” of the encoding target block pixel data a to p is “128”. Is used.

(Prediction mode 3):
The prediction mode 3 is D, Igonal_Down_Left prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. . In this case, the D and Iagonal_Down_Left prediction is performed by using the pixel data A, B, C, D, I, J, K, L, and M as the prediction values of the encoding target block pixel data a to p as shown in Expression 12. Generate.

(Prediction mode 4):
The prediction mode 4 is D, Igonal_Down_Right prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. .
In this case, the prediction values of the encoding target block pixel data a to p are generated as in Expression 13 using the pixel data A, B, C, D, I, J, K, L, and M.

(Prediction mode 5):
The prediction mode 5 is D, Iagonal_Vertical_Right prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. .
In this case, the prediction values of the encoding target block pixel data a to p are generated as in Expression 14 using the pixel data A, B, C, D, I, J, K, L, and M.

(Prediction mode 6):
The prediction mode 6 is Horizontal_Down prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. In this case, the prediction values of the encoding target block pixel data a to p are generated as in Expression 15 using the pixel data A, B, C, D, I, J, K, L, and M.

(Prediction mode 7):
The prediction mode 7 is Vertical_Left prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. In this case, the prediction values of the encoding target block pixel data a to p are generated as in Expression 16 using the pixel data A, B, C, D, I, J, K, L, and M.

(Prediction mode 8):
The prediction mode 8 is Horizontal_Up prediction, and is applied when all of the pixel data A, B, C, D, I, J, K, L, and M shown in FIG. 4 are “available”. In this case, the prediction values of the encoding target block pixel data a to p are generated as in Expression 17 using the pixel data A, B, C, D, I, J, K, L, and M.

  In addition, mode 1 of intra 16 × 16 prediction is a mode having high correlation (weighting) in the horizontal direction, and mode 0 is a mode having high correlation (weighting) in the vertical direction. Modes 2 and 3 are modes in which weighting in the horizontal and vertical directions is hardly performed.

  Intra 4 × 4 prediction modes 1, 6, and 8 are modes with high correlation (weighting) in the horizontal direction, and modes 0, 5, and 7 are modes with high correlation (weighting) in the vertical direction. is there. Modes 2, 4, and 3 are modes in which weighting in the horizontal and vertical directions is hardly performed.

  Next, the process of selecting the above-described intra prediction mode, which is the most characteristic part of the present embodiment, will be described with reference to the block diagram of the intra prediction unit in FIG. 2 and the flowchart in FIG. In this embodiment, it is assumed that prediction error calculation in all prediction modes cannot be performed in order to perform real-time encoding.

  FIG. 2 is a block diagram illustrating a configuration example of the intra prediction unit 105 according to the present embodiment. As illustrated in FIG. 2, the intra prediction unit 105 according to the present embodiment includes an intra 16 × 16 prediction unit 201, an intra 4 × 4 prediction unit 202, and an intra prediction mode determination unit 203. Furthermore, the intra 16 × 16 mode-specific cost storage unit 204, the intra 4 × 4 mode-specific cost storage unit 205, the intra 16 × 16 best mode determination unit 206, the intra 4 × 4 best mode determination unit 207, and the intra best prediction mode determination unit. 208. The “cost” referred to here is a so-called evaluation value obtained by calculation for each mode.

In this configuration, a process for selecting the intra prediction mode will be described.
First, the prediction mode stored in the intra prediction mode storage unit 116 outside the intra prediction unit 105 is transmitted to the intra prediction mode determination unit 203 for each intra 16 × 16 block size and intra 4 × 4 block size. Note that the prediction mode transmitted from the intra prediction mode storage unit 116 is a prediction mode used in the block at the same position of the temporally closest picture that has been encoded and decoded (step S301 in FIG. 3).

  The correlation between pictures that are close in time is high, and there is a high possibility that image data at the same position has not changed significantly. Therefore, when encoding is performed in the prediction mode used in the block at the same position of the temporally closest picture that has been encoded and decoded, there is a high possibility that the encoding efficiency is good. For these reasons, the prediction mode used in the block at the same position of the temporally closest picture that has been encoded and decoded as a candidate for the intra prediction mode to be selected first is used.

  Note that if there is no picture that has been encoded and decoded, such as the first I picture (slice), any prediction mode may be selected as a candidate for the intra prediction mode first. Alternatively, it is not necessary to perform inter prediction, and it can be compensated by calculating more prediction modes than P and B pictures in I pictures (slices) that have more processing time than P and B pictures (slices). Good.

  The intra prediction mode determination unit 203 instructs the intra 16 × 16 prediction unit 201 and the intra 4 × 4 prediction unit 202 to perform the prediction error calculation in the prediction mode transmitted from the intra prediction mode storage unit 116. Also, pixel data required in the prediction mode transmitted from the intra prediction mode storage unit 116 is stored in the pre-filter reference frame memory 114 outside the intra prediction unit 105, and the intra 16 × 16 prediction unit 201 and intra 4 × 4 prediction are used. The unit 202 is instructed to transmit.

  The intra 16 × 16 prediction unit 201 and the intra 4 × 4 prediction unit 202 use the predicted image data transmitted from the pre-filter reference frame memory 114 outside the intra prediction unit 105 to convert each prediction block data by the above method. Generate.

  Subsequently, the prediction error Cost in the prediction mode set using the encoding target data transmitted from the frame memory 101 outside the intra prediction unit 105 and the header data added by the entropy encoding unit 108 is expressed as “ Calculation is performed using “Expression 18”. Further, the cost by cost and the prediction mode at that time are transmitted to and stored in the cost storage unit 204 by intra 16 × 16 mode and the cost storage unit 205 by intra 4 × 4 mode (step S302 in FIG. 3).

In Equation 18, “n” takes a value of “16” or “4” depending on whether the prediction is intra 16 × 16 or intra 4 × 4. Org (i, j) is the pixel value at the pixel position (i, j) when the upper left of the encoding target data is (0, 0) and the lower right is (n, n), Pred (mode, i). , J) is the pixel value at the pixel position (i, j) of the predicted image data. SAD ₀ (mode) represents the number of bits of the header data, and QP ₀ is a coefficient that associates the quantization parameter QP with the quantization scale actually used for quantization.

  Subsequently, until the prediction error calculation of the set prediction mode reaches a predetermined number of times, the intra prediction mode determination unit 203 sets a prediction mode different from the selected prediction mode to the intra 16 × 16 prediction unit 201, intra Transmit to the 4 × 4 prediction unit 202. Then, the processing in step S302 is repeated (step S303 and step S304 in FIG. 3). However, the number of transmissions is set to be smaller than the number of prediction error calculations in all prediction modes. Further, in this case, the prediction mode is the prediction mode used in the block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture.

  When the prediction error calculation for the set prediction mode reaches a predetermined number of times, the intra 16 × 16 mode cost storage unit 204 and the intra 4 × 4 mode cost storage unit 205 store the stored prediction mode and prediction error Cost. Send. In this embodiment, the information is transmitted to the intra 16 × 16 best mode determination unit 206 and the intra 4 × 4 best mode determination unit 207.

  The intra 16 × 16 best mode determination unit 206 and the intra 4 × 4 best mode determination unit 207 select the prediction mode with the smallest prediction error Cost from the transmitted prediction modes as the best mode by prediction size. And it transmits to the intra best prediction mode determination part 208 with the prediction error Cost (step S305 of FIG. 3). Further, the prediction mode is simultaneously transmitted and stored for each prediction size in the intra prediction mode storage unit 116 (step S306 in FIG. 3).

  The intra best prediction mode determination unit 208 adds the prediction error Cost transmitted from the intra 4 × 4 best mode determination unit 207 until it reaches “16 × 16 block size” (that is, 16 × 16 / (4 × 4) = add 16 times). Thereafter, the prediction error Cost transmitted from the intra 16 × 16 best mode determination unit 206 is compared with the sum of the 16 prediction errors Cost transmitted from the intra 4 × 4 best mode determination unit 207. Then, the prediction size mode with the smaller error value is determined as the final intra prediction mode (step S307).

  As described above, in the image encoding device according to the present embodiment, a predetermined number of intra prediction modes are selected from a plurality of types of intra prediction modes for each block including a plurality of pixels defined in the encoding target picture. Select a prediction mode candidate. Then, a prediction mode selection unit that performs a prediction error calculation and selects a prediction mode with a small error value of the calculation result is provided. The prediction mode selection means uses a prediction size mode with the smallest prediction error value as an intra prediction mode in a block that is in the same position as the encoding target block in the encoded picture that is temporally closest to the encoding target picture. select. The prediction mode selection means is a block at the same position of the encoded picture that is temporally closest to the encoding target picture, and uses the prediction mode with the smallest prediction error as an intra prediction mode candidate of the encoding target block. Select with priority.

  As in this embodiment, when encoding is performed in the prediction mode used in the block at the same position of the encoded picture that is closest in time, there is a high possibility that the encoding efficiency is good. For this reason, in the present embodiment, the prediction mode used in the block at the same position of the encoded picture that is temporally closest is preferentially selected as a candidate. Thereby, high encoding efficiency can be maintained even when prediction error calculation cannot be performed in real time in all prediction modes. Further, when prediction error calculation in all prediction modes can be performed in real time, the number of prediction error calculations can be reduced, and the power consumption of the image coding apparatus can be reduced.

(Second Embodiment)
Next, another embodiment of the image coding apparatus according to the present invention will be described in detail with reference to the block diagram of FIG. 5, the flowchart of FIG. 6, and the characteristic diagram of FIG. However, the image coding apparatus according to the second embodiment shown in FIG. 5 has substantially the same structure as that of the first embodiment, except that a global vector calculation unit 501 is provided.

  In addition, the intra prediction unit 105 according to the second embodiment has the same structure as that of the first embodiment. However, in this embodiment, the point that a prediction mode candidate is selected using a global vector is the first. Different from the first embodiment. Note that the operations of the components other than the intra prediction unit 105 and the global vector calculation unit 501 are the same as those in the first embodiment, and thus description thereof is omitted.

  The global vector calculation unit 501 receives the encoded and decoded picture that is temporally closest to the encoding target picture (hereinafter referred to as a reference picture) from the filtered reference frame memory 102 and simultaneously frames the encoding target picture in the frame. Receive from the memory 101. Then, a global vector indicating a spatial position difference of the encoding target picture with respect to the reference picture is calculated using all the pixel values of the encoding target picture and all of the pixel values of the reference picture. For example, calculation is performed using an evaluation function such as the following MSE (Mean Square Error) (Equation 19), MAE (Mean Absolute Error) (Equation 20), or MAD (Mean Absolute difference).

Here, S _cur indicates the (m, n) -th pixel value in the encoding target picture, and S _ref indicates the (m, n) -th pixel value in the reference picture. (I, j) indicate the spatial position of the encoding target picture with respect to the reference picture.

  FIG. 7 shows an example of a global vector selection method when the MAE value is taken as an example. The reference frame is shifted one pixel at a time in a predetermined direction, and the average of the sum of MAE values is taken for each pixel moving distance. The amount of movement when the average MAE value is the minimum is the global vector selection criterion. For example, if this process is executed also in another direction orthogonal to a predetermined direction and a movement amount that minimizes the average MAE value is obtained in this direction, a global vector is determined from the two movement amounts and the movement direction. (Step S601 in FIG. 6).

  In this embodiment, one global vector is calculated using all pixel values of one picture. In addition to this, for example, the picture may be divided into a plurality of areas, for example, by dividing the picture into three equal parts in the vertical direction and three parts in the horizontal direction to obtain nine global vectors, and the global vector may be calculated in each area. . The global vector calculation unit 501 transmits the calculated global vector to the intra prediction mode storage unit 116.

  The intra prediction mode storage unit 116 first transmits the stored prediction modes to the intra prediction mode determination unit 203 for each intra 16 × 16 prediction size and intra 4 × 4 prediction size. Note that the prediction mode to be transmitted is the prediction mode used in the block located at a position shifted by the global vector from the block located at the same position in the encoded picture that is closest in time (step S602 in FIG. 6).

  Even when the picture is close in time, for example, when there is a large movement such as when the imaging device is panning, the correlation is low even for the block at the same position of the closest picture. Even in such a case, it is possible to select a highly correlated block by correcting the position of the encoding target block by the amount of motion between pictures using a global vector.

  For the above reasons, the prediction mode used in the block shifted by the global vector from the block at the same position of the encoded picture closest in time is used as the candidate of the intra prediction mode to be selected first.

  In addition, when there is no already encoded picture such as the first I picture, an arbitrary prediction mode may be selected as a candidate for an intra prediction mode first. Alternatively, there is no need for intra prediction, and I picture (slice) that has more processing time than P and B pictures (slices) can be compensated by calculating more prediction modes than P and B pictures. Good.

  Further, when the position of the block points out of the picture as a result of shifting the position by the global vector, for example, the same position of the encoded picture that is closest in time as described in the first embodiment is used. The prediction mode used in a certain block may be used. Moreover, although the prediction mode used by the adjacent block may be used, the method is not ask | required. Since the subsequent processing is the same as that of the first embodiment, description thereof is omitted.

  In addition to the prediction mode used in the present embodiment, the prediction mode used in the block located at the same position of the encoded picture closest in time described in the first embodiment may be used. In that case, the order in which the prediction mode of the present embodiment and the prediction mode of the first embodiment are selected does not matter. Of course, when the prediction modes selected by the two methods are the same, the processing after the prediction error calculation may be performed once.

  By using the method of the first embodiment in combination, the effects described in the first embodiment can be expected in addition to the effects in the present embodiment. Further, it is preferable to always select one prediction mode as a prediction mode candidate other than the prediction mode selected by the method of the first and second embodiments.

  If encoding is performed only with the prediction mode selected by the method of the first and second embodiments, only two prediction modes are selected for all pictures, and as a result, there is a possibility that the encoding efficiency may be lowered. is there. In this way, by selecting the prediction mode, it is possible to prevent the prediction mode from being the same for all pictures.

(Other embodiments according to the present invention)
The prediction mode selection means and prediction mode determination means constituting the image encoding apparatus in the above-described embodiment of the present invention can be realized by operating a program stored in a RAM or ROM of a computer. Also, the prediction mode selection step and the prediction mode determination step of the image encoding method can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable storage medium storing the program are included in the present invention.

  Further, the present invention can be embodied as a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system composed of a plurality of devices, or may be applied to an apparatus composed of a single device.

  In the present invention, a software program (in the embodiment, a program corresponding to the flowcharts shown in FIGS. 3 and 6) for realizing the functions of the above-described embodiments may be directly applied to the system or apparatus. Alternatively, it may be achieved by supplying from a remote location and the computer of the system or apparatus reads and executes the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention.

  In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Examples of the storage medium for supplying the program include a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, MO, CD-ROM, CD-R, and CD-RW. Moreover, a magnetic tape, a non-volatile memory card, ROM, DVD (DVD-ROM, DVD-R), etc. are also included.

  As another program supply method, the program can be supplied by connecting to a homepage on the Internet using a browser of a client computer and downloading the computer program of the present invention from the homepage. Alternatively, it can be supplied by downloading a compressed file including an automatic installation function to a storage medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  In addition, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and key information for decryption is downloaded from a homepage via the Internet to users who have cleared predetermined conditions. Let It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. In addition, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.

  Further, the program read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, the CPU of the function expansion board or function expansion unit performs part or all of the actual processing based on the instructions of the program, and the functions of the above-described embodiments are realized by the processing.

It is a block diagram which shows the structure of the outline of the image coding apparatus in 1st Embodiment of this invention. It is a block diagram which shows the structure of the outline of the intra estimation part of the image coding apparatus in 1st Embodiment of this invention. It is a flowchart explaining operation | movement of the intra estimation part of the image coding apparatus which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the prediction mode of intra prediction in embodiment of this invention. It is a block diagram which shows the schematic structure of the image coding apparatus in 2nd Embodiment of this invention. It is a flowchart explaining operation | movement of the intra estimation part of the image coding apparatus which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the determination method of the global vector which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

101 Frame memory 102 Reference frame memory after filtering 103 Motion prediction unit 104 Motion compensation unit 105 Intra prediction unit 106 Orthogonal transformation unit 107 Quantization unit 108 Entropy coding unit 109 Inverse quantization unit 110 Inverse orthogonal transformation unit 111 Switch 112 Subtractor 113 Adder 114 Pre-filter reference frame memory 115 Loop filter 116 Intra prediction mode storage unit 201 Intra 16 × 16 prediction unit 202 Intra 4 × 4 prediction unit 203 Intra prediction mode determination unit 204 Intra 16 × 16 mode-specific cost storage unit 205 Intra 4 X4 mode cost storage unit 206 intra 16 × 16 best mode determination unit 207 intra 4 × 4 best mode determination unit 208 intra best mode determination unit 501 global vector operation unit

Claims (17)

In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
Intra-prediction means capable of executing intra-screen prediction processing according to multiple types of prediction modes;
Prediction mode selection means for selecting a prediction mode used by the intra prediction means,
The prediction mode selection means includes a prediction mode corresponding to a prediction block size determined by a coded block at the same position as the coding target block in a coded picture temporally closest to the coding target picture, An image encoding apparatus, wherein the image encoding device is preferentially selected during an intra-screen prediction process of the encoding target block. In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
Intra-prediction means capable of executing intra-screen prediction processing according to multiple types of prediction modes;
Prediction mode selection means for selecting a prediction mode used by the intra prediction means,
The prediction mode selection means selects the prediction mode determined by the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture. An image encoding apparatus that is preferentially selected during intra prediction processing.   The prediction mode selection means selects a prediction mode determined by a coded block in the same position as the coding target picture in a coded picture temporally closest to the coding target picture. The image encoding apparatus according to claim 1 or 2, wherein the image encoding apparatus is first selected as a block prediction mode candidate.   The prediction mode selection means includes at least one prediction mode other than the prediction mode determined by the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture. The image encoding apparatus according to any one of claims 1 to 3, wherein a prediction mode is selected as a prediction mode candidate of the encoding target block.   5. The apparatus according to claim 1, further comprising: a prediction mode determination unit that determines a prediction mode having the smallest prediction error among the plurality of prediction modes selected by the prediction mode selection unit as a final prediction mode. The image encoding device according to any one of the above. In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
Intra-prediction means capable of executing intra-screen prediction processing according to multiple types of prediction modes;
Prediction mode selection means for selecting a prediction mode used by the intra prediction means,
The prediction mode selection means is a coded block at a position shifted from the same position as the coding target block by an amount corresponding to the amount of motion between pictures in a coded picture that is temporally closest to the coding target picture. An image encoding apparatus, wherein the prediction mode corresponding to the prediction block size determined in (1) is preferentially selected during the intra-screen prediction process of the encoding target block. In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
Intra-prediction means capable of executing intra-screen prediction processing according to multiple types of prediction modes;
Prediction mode selection means for selecting a prediction mode used by the intra prediction means,
The prediction mode selection means is a coded block at a position shifted from the same position as the coding target block by an amount corresponding to the amount of motion between pictures in a coded picture that is temporally closest to the coding target picture. The image coding apparatus characterized by preferentially selecting the prediction mode determined in (4) during the intra-frame prediction process of the coding target block.   The prediction mode selection unit encodes a coded picture closest in time to the coding target picture at a position shifted from the same position as the coding target block by an amount corresponding to a motion amount between pictures. The image encoding apparatus according to claim 6 or 7, wherein a prediction mode determined by a completed block is first selected as a prediction mode candidate of the encoding target block.   The prediction mode selection unit encodes a coded picture that is temporally closest to the coding target block at a position shifted from the same position as the coding target block by an amount corresponding to a motion amount between pictures. The image according to any one of claims 6 to 8, wherein at least one prediction mode is selected as a prediction mode candidate of the encoding target block, in addition to the prediction mode determined by a completed block. Encoding device.   10. A prediction mode determining means for determining a prediction mode with the smallest prediction error among a plurality of prediction modes selected by the prediction mode selection means as a final prediction mode. The image encoding device according to any one of the above. In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
A prediction mode selection means for selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra prediction;
Intra prediction means for performing an intra-screen prediction process of the encoding target block according to a prediction mode candidate selected by the prediction mode selection means, and calculating a prediction error due to the prediction mode candidate;
A prediction mode determination unit that determines a prediction mode candidate with the smallest prediction error as a final prediction mode based on a calculation result of the intra prediction unit;
The prediction mode selection means includes the prediction mode determined by the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture. An image encoding apparatus characterized by selecting a candidate. In an image encoding apparatus that performs encoding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be encoded,
A prediction mode selection means for selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra prediction;
Intra prediction means for performing an intra-screen prediction process of the encoding target block according to a prediction mode candidate selected by the prediction mode selection means, and calculating a prediction error due to the prediction mode candidate;
A prediction mode determination unit that determines a prediction mode candidate with the smallest prediction error as a final prediction mode based on a calculation result of the intra prediction unit;
The prediction mode selection means is encoded in a position that is shifted by an amount corresponding to the amount of motion between pictures from the same position as the encoding target block in the encoded picture that is temporally closest to the encoding target picture. An image encoding apparatus that selects a prediction mode candidate including a prediction mode determined in a block. In an image coding method for performing coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded,
Selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra-screen prediction;
Performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidate, and calculating a prediction error due to the prediction mode candidate;
Determining a prediction mode candidate with the smallest prediction error as a final prediction mode based on a result of the calculation,
In the step of selecting the prediction mode candidate, the prediction mode determined in the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture is included. An image encoding method, wherein the prediction mode candidate is selected. In an image coding method for performing coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded,
Selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra-screen prediction;
Performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidate, and calculating a prediction error due to the prediction mode candidate;
Determining a prediction mode candidate with the smallest prediction error as a final prediction mode based on a result of the calculation,
In the step of selecting the prediction mode candidate, in the encoded picture temporally closest to the encoding target picture, the position is shifted from the same position as the encoding target block by an amount corresponding to the amount of motion between pictures. An image coding method comprising: selecting a prediction mode candidate including a prediction mode determined by a certain encoded block. A program for causing a computer to execute an image coding method for performing coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded,
Selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra-screen prediction;
Performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidate, and calculating a prediction error due to the prediction mode candidate;
Based on the result of the operation, causing the computer to execute a step of determining a prediction mode candidate with the smallest prediction error as a final prediction mode,
In the step of selecting the prediction mode candidate, the prediction mode determined in the encoded block at the same position as the encoding target block in the encoded picture temporally closest to the encoding target picture is included. A program causing a computer to execute a selection of the prediction mode candidates. A program for causing a computer to execute an image coding method for performing coding by performing intra prediction for each block composed of a plurality of pixels defined in a picture to be coded,
Selecting a predetermined number of prediction mode candidates from a plurality of types of prediction modes related to the intra-screen prediction;
Performing an intra-screen prediction process of the encoding target block according to the selected prediction mode candidate, and calculating a prediction error due to the prediction mode candidate;
Based on the result of the calculation, causing the computer to execute a step of determining a prediction mode candidate with the smallest prediction error as a final prediction mode,
In the step of selecting the prediction mode candidate, in the encoded picture temporally closest to the encoding target picture, the position is shifted from the same position as the encoding target block by an amount corresponding to the amount of motion between pictures. A program for causing a computer to execute the selection of a prediction mode candidate including a prediction mode determined by a certain encoded block.   A computer-readable recording medium storing the program according to claim 15 or 16.

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