JP2008283402A - Image processing apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a suitable prediction mode from many prediction modes by suppressing processing loads when performing intra-frame prediction encoding. <P>SOLUTION: A block divider 11 divides an encoding object block into sub blocks in two or more sizes. A measuring unit 12 calculates the feature quantity of the image of the sub block and determines a prediction block size to be used when performing the intra-frame prediction encoding of the encoding object block on the basis of the feature quantity. A prediction mode judging unit 14, 16 or 18 sets the prediction mode of a prediction image for the infra-frame prediction encoding on the basis of the feature quantity of the sub block smaller than the prediction block size. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to video encoding.

  As a moving image encoding method, an intra-frame encoding method such as Motion JPEG or Digital Video, or H.261, H.263, MPEG-1, or MPEG-2 using inter-frame predictive encoding is used. It has been known. In recent years, encoding schemes such as H.264 are also known. These are internationally standardized by ISO (International Organization for Standardization) and ITU (International Telecommunication Union).

  The intra-frame coding method is a method of performing coding independently for each frame, and is easy to manage the frame, so that it is most suitable for an apparatus that requires editing of moving images and special reproduction. In addition, the inter-frame predictive coding scheme has a feature of high-efficiency coding because it uses inter-frame prediction based on the image difference between frames.

  The H.264 method encodes the difference image between the current block image and the predicted image block image for both intra-frame coding and inter-frame prediction coding, thereby enabling more efficient coding than the conventional coding method. Is realized.

  H.264 intra-frame coding is a method that uses a predicted image for an m × n pixel block (usually 16 × 16 pixels) to be encoded as an encoded image in the same frame as the encoding target block. Intra prediction is performed using the decoded pixel (local decoded image).

  In the case of H.264, there are a plurality of prediction modes used for intra prediction. In intra-frame predictive coding based on intra prediction, a prediction image is generated for a block to be encoded using one intra prediction mode, and a difference image between the prediction image and the block image and information indicating the intra prediction mode are encoded. By doing so, encoding is performed.

  In intra prediction in H.264, spatial prediction is performed using pixels of a locally decoded image around a block to be encoded, and a predicted image corresponding to the block to be encoded is generated.

  1 and 2 are diagrams for explaining the intra prediction mode.

  For example, there are four types of intra prediction modes for a block of 16 × 16 pixels. FIG. 1A shows a vertical prediction mode (prediction mode 0), and a prediction image of a coding target block is generated using 16 decoded pixels adjacent on the coding target block.

  FIG. 1B shows a horizontal prediction mode (prediction mode 1), and a prediction image corresponding to the encoding target block is generated using 16 decoded pixels adjacent to the left of the encoding target block.

  FIG. 1 (c) shows a DC prediction mode (prediction mode 2), which generates a predicted image of the encoding target block using 32 decoded pixels adjacent to the left and above the encoding target block. That is, the average value of 32 pixels is used as the prediction pixel of the encoding target block.

  FIG. 1 (d) shows a planar prediction mode (prediction mode 3), which generates a predicted image of the encoding target block using 32 decoded pixels adjacent to the left and above the encoding target block.

  Nine types of intra prediction modes exist for a 4 × 4 pixel block. FIG. 2 (a) shows the vertical prediction mode (prediction mode 0), and a prediction image of the encoding target block is generated using four decoding pixels adjacent on the encoding target block.

  FIG. 2B shows a horizontal prediction mode (prediction mode 1), and a prediction image of the encoding target block is generated using four decoded pixels adjacent to the left of the encoding target block.

  FIG. 2 (c) shows a DC prediction mode (prediction mode 2), and a prediction image of the encoding target block is generated using eight decoded pixels adjacent to the left and above the encoding target block. That is, the average value of eight pixels is used as the prediction pixel of the encoding target block.

  Furthermore, as shown in FIGS. 2 (d) to (i), the diagonally lower left direction (prediction mode 3), the diagonally lower right direction (prediction mode 4), the diagonally lower right direction (prediction mode 5), and the horizontal slightly downward direction (prediction) Mode 6), diagonally slightly lower left (prediction mode 7), horizontal slightly upward (prediction mode 8). That is, there are a total of nine types of intra prediction modes, that is, prediction modes in eight prediction directions and DC prediction modes.

  In addition, for an 8 × 8 pixel block, nine types of intra prediction modes exist as in the 4 × 4 pixel block. As described above, H.264 that performs complicated intra prediction realizes higher efficiency encoding than the conventional encoding scheme.

  The purpose of the intra prediction process is to finally determine the prediction mode. In order to find the prediction mode that minimizes the prediction error indicated by the difference pixel between the prediction image and the image of the encoding target block, it is only necessary to calculate the prediction error for all prediction modes and find the prediction mode with the smallest prediction error. In order to further improve the accuracy, the generated code amount is calculated for all prediction modes, and the prediction mode with the minimum code amount may be searched.

  However, in order to search for a prediction mode with the smallest prediction error or generated code amount, in other words, to improve the image quality, calculating the prediction error or generated code amount of a large number of prediction modes until the prediction mode is determined. The processing load is increased, making real-time processing difficult. On the other hand, if the intra prediction process is easily omitted, the prediction accuracy is lowered and the code amount cannot be reduced, and as a result, the image quality is lowered.

JP2004-304724 INTERNATIONAL STANDARD ISO / IEC, 14496-10: Information technology-Coding of audio-visual objects―Part 10: Advanced video coding

  An object of the present invention is to set a suitable prediction mode from a large number of prediction modes while suppressing the processing load when performing intraframe prediction encoding.

  The present invention has the following configuration as one means for achieving the above object.

  An image processing apparatus according to the present invention is an image processing apparatus that encodes a frame of a moving image in block units, a dividing unit that divides an encoding target block into a plurality of sub-blocks, and an image of the sub-block. Calculating means for calculating a feature amount of the subblock, determining means for determining a prediction block size when intra-frame predictive coding is performed on the encoding target block based on the feature amount, and features of sub-blocks smaller than the prediction block size And setting means for setting a prediction mode of a prediction image used for the intra-frame prediction encoding based on the amount.

  An image processing method according to the present invention is an image processing method for encoding a frame of a moving image in units of blocks, wherein the encoding target block is divided into a plurality of sub-blocks, and the feature amount of the image of the sub-block And calculating a prediction block size when the encoding target block is subjected to intraframe prediction encoding based on the feature amount, and determining the intraframe prediction code based on a subblock feature amount smaller than the prediction block size. The prediction mode of the prediction image used for conversion is set.

  ADVANTAGE OF THE INVENTION According to this invention, when performing intra-frame prediction encoding, a suitable prediction mode can be set from many prediction modes, suppressing processing load.

  Hereinafter, image processing according to an embodiment of the present invention will be described in detail with reference to the drawings. In the following, a 16 × 16 pixel block will be described, but the same processing can be performed for a 4 × 4 pixel block and an 8 × 8 pixel block.

[Device configuration]
FIG. 3 is a block diagram illustrating a configuration example of an H.264 encoder according to the embodiment. The encoder encodes a frame of a moving image divided into encoded blocks in units of blocks.

  The subtractor 101 calculates a difference between an image of a block to be encoded (hereinafter referred to as the current block) of a frame to be encoded (hereinafter referred to as the current frame) and a predicted image, and outputs a difference image. An orthogonal transform (DCT) unit 102 orthogonally transforms the difference image. The quantization unit 103 quantizes the orthogonal transform coefficient. The variable length coding unit 104 generates a code from the quantized orthogonal transform coefficient using Huffman coding or arithmetic coding.

  For generation of a predicted image, an image obtained by locally decoding already encoded data (hereinafter referred to as a locally decoded image) is used. The inverse quantization unit 106 inversely quantizes the quantized orthogonal transform coefficient. The inverse DCT unit 107 performs inverse DCT on the orthogonal transform coefficient obtained by inverse quantization to generate a local decoded image. In the case of inter-frame predictive coding, the adder 117 adds the image output from the inverse DCT unit 107 and the predicted image. The block distortion removing unit 111 suppresses visual degradation that easily occurs when the quantization step called block distortion is large. The above decoding process is also called local decoding. A frame memory (FM) 113 temporarily stores locally decoded images.

  The intra prediction unit 110 receives an image of the current block and a locally decoded image located in the vicinity of the current block from the FM 113 for intra prediction of intraframe prediction encoding, and generates a prediction image. The motion compensation unit 112 inputs an image of the current block and a local decoded image of a frame in the vicinity of the current frame from the FM 113 for inter-frame predictive coding, and calculates the relative motion amount (hereinafter referred to as motion) of the object between the blocks. Vector) and a predicted image is generated.

  When encoding, the variable length encoding unit 104 also encodes additional information such as mode determination in intra prediction and motion vector in interframe prediction. The buffer unit 114 monitors the generated code amount, outputs the state to the rate control unit 115, and outputs a code at a predetermined transmission rate. The rate control unit 115 sets a quantization step for performing coarse quantization in the quantization unit 103 when the generated code amount> the target value, and performs a quantization step for performing fine quantization when the generated code amount <the target value. The generated code amount is controlled by setting in the quantization unit 103.

  The mode determination unit 105 determines whether the current frame is subjected to intraframe prediction encoding or interframe prediction encoding, and controls the switches 108 and 109 according to the determination result. In the case of an intra picture (I picture) to be subjected to intraframe prediction encoding, a prediction image of the intra prediction unit 110 is input to the subtractor 101 via the switch 109. The switch 108 is open. On the other hand, in the case of a prediction picture (P picture) or a bidirectional prediction picture (B picture) to be subjected to interframe prediction encoding, a prediction image of the motion compensation unit 110 is input to the subtractor 101 via the switch 109. Also, the predicted image of the motion compensation unit 110 is input to the adder 117 via the switch 108.

  As described above, the H.264 method encodes the difference image between the current block image and the predicted image block image in both intra-frame coding and inter-frame prediction coding.

  FIG. 11 is a block diagram for explaining an example in which the encoder is realized by the computer apparatus 1100.

  The CPU 1000 executes an operating system (OS) and various programs stored in a ROM of the memory 1001 and a hard disk drive (HDD) 1006 using the RAM of the memory 1001 as a work memory. Then, various components to be described later are controlled via the system bus 1002, and a program for realizing the function as the encoder of the embodiment is executed, thereby functioning as the encoder shown in FIG.

  A network interface (I / F) 1007 is an interface with the network 1008. The input device 1003 is a video input device such as a mouse, a keyboard, or a video camera. The output device 1004 is a recording device that records video on various recording media.

  The computer device 1100 displays video data input from the input device 1003 or video data stored in the HDD 1006 on the monitor 1005. Alternatively, the video data is encoded and output to the output device 1004 or transmitted to the server or client via the network 1008.

[Intra prediction section]
FIG. 4 is a block diagram illustrating a configuration example of the intra prediction unit 110.

  The block divider 11 inputs an image of the current block (hereinafter, the current image) and divides it into sub-blocks having block sizes of 2 × 2, 4 × 4, and 8 × 8 pixels. The measuring instrument 12 inputs 4 × 4, 8 × 8 pixel images and threshold values α, β, γ, measures the feature amount of the current block, determines the predicted block size, and determines the feature amount and block size. Output information. Since the threshold values α, β, and γ depend on the input image, it is preferable to obtain them statistically or empirically. For example, when the target image is a substantially flat image, α is 1200, β is 2500, γ is 90, and the like. The selector 13 operates a mode determiner and a predictor corresponding to the block size determination information of the measuring device 12.

  The 4 × 4 mode determiner 14 receives the feature amount from the measuring device 12 and determines the prediction mode in the 4 × 4 block size. The 4 × 4 predictor 15 generates a 4 × 4 pixel size predicted image from the local decoded image of the FM 113 according to the prediction mode determined by the 4 × 4 mode determiner 13, and indicates information indicating the 4 × 4 prediction mode. Output a predicted image. That is, information indicating 16 sets of 4 × 4 prediction modes and a prediction image are output per current block. The 4 × 4 mode determiner 14 and the 4 × 4 predictor 15 are operated by the selector 13 when the block size determination information indicates 4 × 4.

  The 8 × 8 mode determiner 16 receives the feature amount from the measuring device 12 and determines the prediction mode in the 8 × 8 block size. The 8 × 8 predictor 17 generates an 8 × 8 pixel size predicted image from the FM 113 local decoded image according to the prediction mode determined by the 8 × 8 mode determiner 16, and indicates the 8 × 8 prediction mode. Output a predicted image. That is, for each current block, information indicating four sets of 4 × 4 prediction modes and a prediction image are output. The 8 × 8 mode determiner 16 and the 8 × 8 predictor 17 are operated by the selector 13 when the block size determination information indicates 8 × 8.

  The 16 × 16 mode determiner 18 receives the feature amount from the measuring device 12 and determines the prediction mode in the 16 × 16 block size. The 16 × 16 predictor 19 generates a 16 × 16 pixel size predicted image from the locally decoded image of the FM 113 according to the prediction mode determined by the 16 × 16 mode determiner 18, and indicates information indicating the 16 × 16 prediction mode. Output a predicted image. The 16 × 16 mode determiner 18 and the 16 × 16 predictor 19 are operated by the selector 13 when the block size determination information indicates 16 × 16.

Measuring Instrument FIG. 5 is a block diagram showing a configuration example of the measuring instrument 12.

  As will be described in detail later, the feature calculator 20 calculates the sum of pixel values of 4 × 4 pixel blocks (hereinafter referred to as 4 × 4 sub-blocks), that is, 16 sub-blocks, and distributes the 16 sums. Calculate the value A. Further, the sum of pixel values of an 8 × 8 pixel block (hereinafter, 8 × 8 sub-block), that is, four sub-blocks is calculated, and a variance value B of the four sums is calculated.

  Although details will be described later, the threshold comparator 21 determines the predicted block size by comparing the feature amounts (variance values A and B) input from the feature calculator 20 with the threshold values α and β, and block size determination information The threshold value γ is output. As will be described in detail later, the feature calculator 22 calculates and outputs a feature amount that depends on the predicted block size.

[Operation of intra prediction unit]
FIG. 6 is a flowchart for explaining the operation of the intra prediction unit 110, and shows processing for one block.

  The intra prediction unit 110 inputs the current image and threshold values α, β, and γ (S10), and the block divider 11 divides the current image into 2 × 2, 4 × 4, and 8 × 8 sub-blocks (S11). . Then, the feature amounts (variance values A and B) of the 4 × 4 and 8 × 8 sub-blocks are calculated, and the predicted block size is determined from the feature amounts and the threshold values α and β (S12). The block size determination information is input to the selector 13, and the feature value and the threshold γ are input to the 4 × 4 mode determiner 14, the 8 × 8 mode determiner 16, and the 16 × 16 mode determiner 18 (S13).

  Next, the intra prediction unit 110 determines whether or not the block size determination information indicates 4 × 4 (S14), and when 4 × 4 is indicated, for the 16 4 × 4 sub-blocks, the intra prediction unit 110 determines whether the block size determination information indicates 4 × 4 or not. Processing by the 4 × 4 mode determiner 14 and the 4 × 4 predictor 15 is performed (S16).

  Further, the intra prediction unit 110 determines whether or not the block size determination information indicates 8 × 8 (S15), and when 8 × 8 is indicated, for the 8 × 8 sub-blocks, the 8 Processing by the × 8 mode determiner 16 and the 8 × 8 predictor 17 is performed (S17).

  If the block size determination information does not indicate 4 × 4 or 8 × 8, the intra prediction unit 110 performs the above 16 × 16 mode determination unit 18 and 16 × 16 prediction on the current block of 16 × 16 pixels. The processing by the device 19 is performed (S18).

FIG. 7 is a flowchart for explaining the operation of the measuring instrument 12.

  The measuring device 12 inputs the sub-block and the threshold values α, β, and γ (S100), the feature calculator 20 calculates the variance value A (S101), and calculates the variance value B (S102). Then, the threshold value comparator 21 compares the variance value A with the threshold value α (S103), and if A> α, outputs block size determination information indicating 4 × 4 and the threshold value γ (S105). Then, by the feature calculator 22, the sum of the pixel values of each of the 64 2 × 2 pixel sub-blocks (hereinafter referred to as 2 × 2 sub-blocks) and the four 2 × 2 sub-blocks adjacent to each other vertically and horizontally The variance value C is calculated, and the sum and the variance value C are output (S106). Note that 16 variance values C are output for the current block.

  When A ≦ α, the measuring device 12 compares the variance value B with the threshold value β (S104), and if B <β, outputs the block size determination information indicating 8 × 8 and the threshold value γ (S107). Then, the feature amount calculator 22 calculates the sum of the pixel values of each of the 16 4 × 4 sub-blocks and the variance value D between the four 4 × 4 sub-blocks adjacent to the top, bottom, left, and right. The value D is output (S108). Note that four variance values D are output for the current block.

  If A ≦ α and B ≧ β, the measuring device 12 outputs block size determination information indicating 16 × 16 and a threshold value γ (S109). Then, the sum of the pixel values of each of the four 8 × 8 sub-blocks calculated by the feature amount calculator 20 and the variance value B are output (S110). One variance value B is output for the current block.

FIG. 8 is a flowchart for explaining the operation of the 4 × 4 prediction mode determiner 14.

The 4 × 4 prediction mode determination unit 14 inputs the threshold value γ (S200), and resets the counter i to 0 (S201). Then, the sum of pixel values a, b, c, d of the four 2 × 2 sub-blocks included in the i-th 4 × 4 sub-block and the variance value C [i] between these sub-blocks are input ( S202). The relationship between the sums a, b, c, d and the sub-blocks is as follows.
┌─┬─┐
│ a│ b│
├─┼─┤
│ c│ d│
└─┴─┘

Next, the 4 × 4 prediction mode determiner 14 compares γ and C [i] (S203), and outputs a prediction mode 2 if C [i] <γ (S205). On the other hand, if γ ≧ C [i], the following comparison is performed (S204).
| a-b | + | c-d |> | a-c | + | b-d |… (1)

  If Expression (1) is true, the 4 × 4 prediction mode determiner 14 generates a prediction image of prediction modes 1, 6, 8, 3, 4 (horizontal emphasis) from the locally decoded image of FM 113 (S206). ), The prediction mode is selected and output (S207). If the expression (1) is false, a prediction image of prediction modes 0, 5, 7, 3, 4 (vertical importance) is generated from the FM 113 local decoded image (S208), and the prediction mode is selected. Output (S209). In these cases, prediction images of the above five types of prediction modes are generated, and for example, the sum of absolute differences with the image of the current block is calculated, and the prediction mode with the smallest sum of absolute differences is selected.

  Next, the counter i is incremented (S210). If i <16, the process returns to step S202, and the above process is repeated until i = 16.

FIG. 9 is a flowchart for explaining the operation of the 8 × 8 prediction mode determiner 16.

  The 8 × 8 prediction mode determiner 16 inputs the threshold value γ (S300), and resets the counter i to 0 (S301). Then, the sum of pixel values a, b, c, d of the four 4 × 4 sub-blocks included in the i-th 8 × 8 sub-block and the variance value D [i] between these sub-blocks are input ( S302).

  Next, the 8 × 8 prediction mode determiner 16 compares γ and D [i] (S303), and outputs a prediction mode 2 if D [i] <γ (S305). On the other hand, if γ ≧ D [i], the comparison of Expression (1) is performed (S304).

  If Expression (1) is true, the 8 × 8 prediction mode determiner 16 generates prediction images of prediction modes 1, 6, 8, 3, and 4 (horizontal emphasis) from the locally decoded image of FM 113 (S306). ), The prediction mode is selected and output (S307). If the expression (1) is false, a prediction image of prediction modes 0, 5, 7, 3, 4 (vertical importance) is generated from the FM 113 local decoded image (S308), and the prediction mode is selected. Output (S309). In these cases, prediction images of the above five types of prediction modes are generated, and for example, the sum of absolute differences with the image of the current block is calculated, and the prediction mode with the smallest sum of absolute differences is selected.

  Next, the counter i is incremented (S310), and if i <4, the process returns to step S302, and the above process is repeated until i = 4.

FIG. 10 is a flowchart for explaining the operation of the 16 × 16 prediction mode determiner 18.

  The 16 × 16 prediction mode determiner 18 inputs a threshold value γ (S401). Then, the sum a, b, c, d of the pixel values of the four 8 × 8 sub-blocks included in the 16 × 16 sub-block and the variance value B between these sub-blocks are input (S402).

  Next, the 16 × 16 prediction mode determiner 18 compares γ and B (S403), and outputs a prediction mode 0 if B <γ (S405). On the other hand, if γ ≧ D [i], the comparison of Expression (1) is performed (S404).

  If Equation (1) is true, the 16 × 16 prediction mode determiner 18 generates a prediction image of prediction modes 1 and 3 (horizontal emphasis) from the FM 113 local decoded image (S406), and selects the prediction mode And output (S407). If the expression (1) is false, a prediction image of prediction modes 2 and 3 (vertical importance) is generated from the locally decoded image of the FM 113 (S408), and the prediction mode is selected and output (S409). In these cases, a prediction image of the above two types of prediction modes is generated, for example, the sum of absolute differences with the image of the current block is calculated, and the prediction mode with the smallest sum of absolute differences is selected.

  As described above, when a suitable prediction mode is selected from a large number of prediction modes, it is possible to reduce the processing amount and improve the prediction accuracy, thereby improving the image quality.

  The image processing according to the second embodiment of the present invention will be described below. Note that the same reference numerals in the second embodiment denote the same parts as in the first embodiment, and a detailed description thereof will be omitted.

[Intra prediction section]
FIG. 12 is a block diagram illustrating a configuration example of the intra prediction unit 110 according to the second embodiment. The difference from the configuration shown in FIG. 4 is that measuring device 12 receives quantization parameter QP from rate control section 115.

Measuring Instrument FIG. 13 is a block diagram showing a configuration example of the measuring instrument 12.

  The QP memory 23 stores quantization parameters for the immediately preceding frame. The threshold value corrector 24 inputs the quantization step of the current block, and corrects the threshold values α and β from the quantization step of the current block and the quantization step for one frame stored in the memory 23.

[Operation of intra prediction unit]
The overall operation of the intra prediction unit 110 is the same as that of the first embodiment (FIG. 6) except that the quantization step is input in addition to the current image and the threshold values α, β, γ in step S10, and thus detailed description thereof is omitted. To do. The operation of the measuring instrument 12 is the same as that of the first embodiment (FIG. 7) except that the threshold values α and β are corrected by the quantization step in step S100, and thus detailed description thereof is omitted.

Threshold Correction The threshold corrector 24 corrects the thresholds α and β according to equation (2) (S100).
α = α × (1 + QP / QP ')
β = β × (1 + QP / QP ')… (2)
Where QP is the quantization step of the current block
QP 'is the quantization step of the block corresponding to the current block of the previous frame

  Note that the size of the current block may differ between frames. Therefore, the quantization steps QP used for the calculation of Expression (2) are all converted to 16 × 16. Specifically, the average value for 16 4 × 4 sub-blocks in the case of 4 × 4, and the average value for four 8 × 8 sub-blocks in the case of 8 × 8 blocks.

  That is, the threshold values α and β are increased by the equation (2). Therefore, as moving picture encoding progresses, it becomes easier to select a block size of 8 × 8 rather than 4 × 4 and 16 × 16 rather than 8 × 8, and by encoding with a larger block size, The generated code amount is suppressed. In particular, when QP> QP ′, which indicates a tendency to increase the amount of generated code, compared to the case of QP <QP ′, which indicates a tendency to increase the amount of generated code, the increase tendency of α and β is increased and larger. Give priority to block-size encoding. In other words, when the two quantization steps QP and QP ′ show a tendency to suppress the generated code amount, the threshold corrector 24 increases the thresholds α and β to induce the predicted block size to a larger size.

  Hereinafter, image processing according to the third embodiment of the present invention will be described. Note that the same reference numerals in the third embodiment denote the same parts as in the first and second embodiments, and a detailed description thereof will be omitted.

[Intra prediction section]
FIG. 14 is a block diagram illustrating a configuration example of the intra prediction unit 110 according to the third embodiment. The difference from the configuration shown in FIG. 4 is that measuring instrument 12 inputs the predicted code amount of the current frame and the generated code amount of the previous frame from rate control section 115.

Measuring Instrument FIG. 15 is a block diagram showing a configuration example of the measuring instrument 12.

  The threshold value corrector 25 corrects the threshold values α and β from the predicted code amount of the current frame and the generated code amount of the previous frame.

[Operation of intra prediction unit]
The overall operation of the intra prediction unit 110 is the same as that of the first embodiment (FIG. 6) except that the prediction code amount and the generated code amount are input in addition to the current image and the threshold values α, β, γ in step S10. Detailed description is omitted. The operation of the measuring instrument 12 is the same as that of the first embodiment (FIG. 7) except that the threshold values α and β are corrected by the predicted code amount and the generated code amount in step S100, and thus detailed description thereof is omitted.

Threshold Correction The threshold corrector 25 corrects the thresholds α and β using equation (3) (S100).
α = α × (1 + R / R ')
β = β × (1 + R / R ') (3)
Here, R ′ is the generated code amount of the previous frame
R is the predicted code amount of the current frame

Note that when the unit of the predicted code amount R is the code amount of one frame and the generated code amount R ′ is a cumulative value of the generated code amount of the encoded block of the current block, the predicted code amount R is Convert to the number of encoded blocks.
R = R × Ne / Na (4)
Where Ne is the number of encoded blocks in the frame
Na is the total number of blocks in the frame

  That is, the threshold values α and β are increased by the equation (3). Therefore, as moving picture encoding progresses, it becomes easier to select a block size of 8 × 8 rather than 4 × 4 and 16 × 16 rather than 8 × 8, and by encoding with a larger block size, The generated code amount is suppressed. In particular, compared to the case of R <R ′ where the generated code amount shows a decreasing tendency, when R> R ′ where the generated code amount shows an increasing tendency, the increasing tendency of α and β is strengthened, and a larger block. Prioritize size encoding. In other words, when the predicted code amount R and the generated code amount R ′ show an increasing tendency of the code amount, the threshold corrector 25 increases the thresholds α and β to induce the predicted block size to a larger size.

[Modification]
In each of the above-described embodiments, an example in which the block size is three types has been described. However, the block size is limited, and 8 × 8 and 16 × 16 except for 4 × 4 may be processed, or 8 The processing target may be 4 × 4 and 16 × 16 except for × 8.

  In addition, in steps S206 and S207 in FIG. 8 and steps S306 and S307 in FIG. 9, an example in which the prediction modes 1, 6, 8, 3, and 4 with emphasis on the horizontal are shown, but for simplification, Only prediction modes 1, 6, and 7 may be used. Similarly, steps S208 and S209 in FIG. 8 and steps S308 and S309 in FIG. 9 show examples targeting the prediction modes 0, 5, 7, 3, and 4 that emphasize verticality. However, only prediction modes 1, 6, and 7 may be used.

[Other embodiments]
Note that the present invention can be applied to a system including a plurality of devices (for example, a computer, an interface device, a reader, a printer, etc.), but an apparatus (for example, a copier, a facsimile machine, a control device) including a single device. Etc.).

  Another object of the present invention is to supply a storage medium storing a computer program for realizing the functions of the above embodiments to a system or apparatus, and the computer (CPU or MPU) of the system or apparatus executes the computer program. But it is achieved. In this case, the software read from the storage medium itself realizes the functions of the above embodiments, and the computer program and the computer-readable storage medium storing the computer program constitute the present invention. .

  Further, the above functions are not only realized by the execution of the computer program. That is, according to the instruction of the computer program, the operating system (OS) running on the computer and / or the first, second, third,... This includes cases where functions are realized.

  The computer program may be written in a memory of a device such as a function expansion card or unit connected to the computer. That is, the case where the CPU or the like of the first, second, third,... Device performs part or all of the actual processing according to the instruction of the computer program, thereby realizing the above functions.

  When the present invention is applied to the storage medium, the storage medium stores a computer program corresponding to or related to the flowchart described above.

The figure explaining intra prediction mode, The figure explaining intra prediction mode, Block diagram showing a configuration example of an H.264 encoder of the embodiment, A block diagram showing a configuration example of an intra prediction unit, Block diagram showing a configuration example of a measuring instrument, A flowchart for explaining the operation of the intra prediction unit; Flowchart explaining the operation of the measuring device, A flowchart for explaining the operation of the 4 × 4 prediction mode determiner, A flowchart for explaining the operation of the 8 × 8 prediction mode determiner, A flowchart for explaining the operation of the 16 × 16 prediction mode determiner, A block diagram for explaining an example in which an encoder is realized by a computer device; Block diagram showing a configuration example of the intra prediction unit of the second embodiment, Block diagram showing a configuration example of a measuring instrument, Block diagram showing a configuration example of the intra prediction unit of the third embodiment, It is a block diagram which shows the structural example of a measuring device.

Claims (11)

An image processing apparatus that encodes a frame of a moving image in units of blocks,
Dividing means for dividing the block to be encoded into a plurality of sub-blocks of a plurality of sizes;
Calculating means for calculating the feature quantity of the image of the sub-block;
A determination unit that determines a prediction block size in the case of performing intra-frame prediction encoding on the encoding target block based on the feature amount;
An image processing apparatus, comprising: a setting unit configured to set a prediction mode of a prediction image used for the intra-frame prediction encoding based on a feature amount of a sub-block smaller than the prediction block size.   2. The image processing apparatus according to claim 1, further comprising generating means for generating the predicted image in accordance with the set prediction mode.   The setting means includes first determination means for determining a prediction direction to be emphasized, and second determination means for determining a prediction mode to be set from prediction modes corresponding to the prediction direction to be emphasized. The image processing device according to claim 1 or 2.   The image according to any one of claims 1 to 3, wherein the determining unit determines the predicted block size by comparing a feature amount of a plurality of sub-blocks of a plurality of sizes with a threshold value. Processing equipment.   The determination means includes an input means for inputting a quantization step of the encoding target block, a quantization step of a block corresponding to the encoding target block of the previous frame, and the threshold value by the two quantization steps. 5. The image processing apparatus according to claim 4, further comprising correction means for correcting.   6. The correction unit according to claim 5, wherein when the two quantization steps show a tendency to suppress the generated code amount, the correction unit increases the threshold value to induce the prediction block size to a larger size. Image processing apparatus.   The determination unit includes an input unit that inputs a predicted code amount of a frame to be encoded and a generated code amount of a previous frame, and a correction unit that corrects the threshold based on the predicted code amount and the generated code amount. 5. The image processing apparatus according to claim 4, wherein the image processing apparatus is characterized.   8. The correction means, when the prediction code amount and the generated code amount indicate an increase tendency of the code amount, increasing the threshold value to induce the prediction block size to a larger size. The image processing apparatus described in 1. An image processing method for encoding a frame of a moving image in units of blocks,
Divide the target block into sub-blocks of multiple sizes,
Calculating the feature quantity of the image of the sub-block;
Based on the feature amount, determine a prediction block size when the encoding target block is subjected to intraframe prediction encoding,
An image processing method, wherein a prediction mode of a prediction image used for the intraframe prediction encoding is set based on a feature amount of a sub-block smaller than the prediction block size.   9. A computer program for controlling a computer device to function as each unit of the image processing device according to any one of claims 1 to 8.   11. A computer-readable storage medium in which the computer program according to claim 10 is recorded.

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