JP2018182393A - Video encoding apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an encoding structure having high encoding efficiency using a low operation amount.SOLUTION: A video encoding apparatus generates a reference group including predetermined three or more continuous frames from a frame group acquired from input video information, calculates an evaluation value associated with an error between frames on the basis of an initial frame and a last frame of the reference group generated, and any one determination target frame between the initial frame and the last frame, determines whether or not to couple a reference relationship between a determination target frame, and the initial frame and the last frame on the basis of a relative value of other evaluation value using a reference of an evaluation value between the determination target frame and the initial frame among evaluation values calculated, or on the basis of the relative value and the evaluation values between the determination target frame and both of the initial frame and the last frame, and selects a picture type of the frame included in the frame group on the basis of the determination result.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a video coding apparatus.

  As a standard for video coding, H.3. H.264 / AVC (Advanced Video Coding) and H.264. A video coding scheme called H.265 / HEVC (High Efficiency Video Coding) has been formulated. In HEVC, a plurality of picture types are defined: I (Intra) picture which is an intra picture, P (Predictive) picture which is an inter picture, and B (Bi-directional predictive) picture. Each frame is assigned one of the picture types.

  The I picture is usually a picture type defined every several frames, and is a picture type to which only the intra prediction mode predicted from encoded pixels in the encoding target frame is applied. P picture and B picture are picture types to which an intra prediction mode or an inter prediction mode of predicting from a coded frame is selectively applied. P pictures use past frames in time series as reference frames, while B pictures use past and future frames as reference frames.

  A group of frames from I picture to the next I picture is called GOP (Group Of Picture), and coding structures such as I picture intervals and reference structures can be freely set for each GOP. As a typical coding structure, there are a coding structure for low delay coding shown in FIG. 17 and a coding structure for random access coding shown in FIG. 18, and in general, random access coding is better in coding efficiency. Is said to be high.

  In determining the coding structure, coding efficiency can be improved by adaptively setting the I picture or P picture interval according to the video to be coded. For example, as shown in FIG. 19, for a sequence of video frames having a scene change in the middle of the video, the I picture or P picture is adaptively adapted to the scene change rather than the fixed I picture or P picture interval. The coding efficiency is improved by selecting the frame.

  In addition, coding efficiency can be improved by adaptively changing the reference structure, such as hierarchically setting reference structures as shown in FIG. 20 and FIG. For example, when adaptive structure 1 shown in FIG. 20 is compared with adaptive structure 2 shown in FIG. 21, since adaptive structure 2 shown in FIG. Since the distance is smaller, improvement in coding efficiency is expected.

  A method of selecting a coding structure having higher coding efficiency has also been proposed (see, for example, Non-Patent Documents 1 and 2). The following describes two representative proposed techniques. In the technique shown in Non-Patent Document 1, the coding structure is determined according to the following procedure. The original image is reduced to half size in the vertical and horizontal directions (step Sx1). The first frame is encoded as an I picture, and is set as a reference frame (step Sx2). For each frame up to N frames ahead, the cost for the case of P picture is calculated, and the frame for which the calculated cost is minimum is taken as a P picture. Here, the cost is the sum of all the blocks of the smaller encoding cost when encoding each encoding block of the frame according to the intra prediction mode and the inter prediction mode (step Sx3).

  Between the reference frame and the frame selected as the P picture in step Sx3, an intermediate frame referencing them is defined. For a frame located between the reference frame and the intermediate frame, the cost is calculated in the case where these frames are B pictures that reference the reference frame and the intermediate frame. In addition, with respect to a frame located between the intermediate frame and the P picture, the cost is calculated in the case where these frames are B pictures that refer to the intermediate frame and the P picture. A combination that minimizes the calculated cost is selected as a final coding structure (step Sx4). Assuming that the frame used as the P picture in step Sx3 is a reference frame, steps Sx3 and Sx4 are repeatedly executed to adaptively determine the coding structure.

In the technique described in Non-Patent Document 2, the coding structure is determined according to the following procedure. The first frame is encoded as an I picture (step Sy1). Motion search is performed between the I picture and the next frame, and the motion vector of each coding block is S ₁ (k) (where 1 ≦ k ≦ N _blk : N _blk is the number of blocks in the frame) (Step Sy2).

A motion search is performed between the nth frame (n ≧ 3) and the first frame, and the motion vector of each coding block divided by the interframe distance is S _n (k) To do (step Sy3). The average of the motion vector difference (E = S (S ₁ −S _n ) / N _blk ) is calculated (step Sy 4). A predetermined threshold value is th, and if E <th, the nth frame is B picture, otherwise it is P picture (step Sy 5).

“VideoLAN, a project and a non-profit organization”, [online], VideoLAN Organization, [search on March 17, 2017], Internet (URL: https://www.videolan.org/developers/x265.html ) Adriana Dumitras and Barry G. Haskell, “I / P / B FRAME TYPE DECISION BY COLLINEARITY OF DISPLACEMENTS”, 2004 International Conference on Image Processing (ICIP), p2769-p2772

  However, as shown in the above-described procedure, in the technique described in Non-Patent Document 1, although the reduced image is used, processing close to actual coding is performed on a plurality of combinations. In addition, there are combinations in which calculation results are wasted, and as a result, there is a problem that the method has a large amount of calculation. Further, in the technology described in Non-Patent Document 1, it is premised that two layers are allocated as the hierarchy of B pictures, and if it is intended to apply a deeper hierarchical structure with good coding efficiency to this technology, the number of combinations is There is a problem that the

  Even in the technique described in Non-Patent Document 2, there is a combination in which the calculation result in the determination is wasted, so there is a problem that the amount of calculation is large. Moreover, in the technique described in Non-Patent Document 2, there is a problem that only one layer can be applied as the layer of the B picture. Further, in the technique described in Non-Patent Document 2, only the motion vector is used for determination, so it is not possible to accurately determine a complex video, and there is a problem that the coding efficiency is poor.

  In view of the above circumstances, the present invention aims to provide a technique capable of obtaining a coding structure with high coding efficiency with a small amount of calculation.

  One aspect of the present invention is a video encoding apparatus for performing inter-frame predictive coding, which includes, from a frame group acquired from input video information, a reference group including three or more consecutive frames determined in advance. The reference group generation unit to generate, the first and last frames of the reference group generated by the reference group generation unit, and any one determination target frame between the first and last frames, Among the evaluation values calculated by the evaluation value calculation unit, an evaluation value calculation unit that calculates an evaluation value regarding an error between the frames, and the evaluation value between the determination target frame and the first frame among the evaluation values calculated Prior to the evaluation value based on the relative value of the evaluation value of the frame, or based on the relative value and the evaluation value between the determination target frame and both the first and last frames. An evaluation value determination unit that determines whether or not the reference relationship between the determination target frame and the first and last frames is combined, and the determination result of the evaluation value determination unit based on the determination results of the frames And a picture type selection unit that selects a picture type.

  One embodiment of the present invention is the video encoding device described above, wherein the evaluation value calculation unit is configured to calculate a first one-way evaluation value regarding an error between the frames between the determination target frame and the first frame. And a second one-way evaluation value regarding the inter-frame error between the determination target frame and the last frame, the inter-frame between the determination target frame and both the first and last frames. The evaluation value determination unit selects a smaller one of the second one-way evaluation value and the two-way evaluation value, and calculates the evaluation value of the selected evaluation value. The relative value is calculated as a relative value with respect to the first one-way evaluation value, and the determination target frame and the first are determined based on the calculated relative value and a predetermined relative evaluation threshold value. Last fray It determines whether to combine the reference relationship with the arm.

  One embodiment of the present invention is the above-described video encoding device, wherein the predetermined relative evaluation threshold is larger than a first relative evaluation threshold and a first relative evaluation threshold. And the evaluation value determination unit determines whether the relative value is less than the first relative evaluation threshold, the determination target frame and the first and last frames. It is determined whether or not the reference relationship with the frame is combined, and it is determined that the relative value is not less than the first relative evaluation threshold and the reference frame of the determination target frame is not the first and last frames. In the case where the relative value is a value within a range defined by the first relative evaluation threshold and the second relative evaluation threshold, the bidirectional evaluation value and the predetermined absolute evaluation threshold And the judgment target frame And it determines whether to combine the reference relationship between the first and last frame.

  One embodiment of the present invention is the above-described video encoding apparatus, wherein the reference group generation unit determines whether the first frame or the last frame of the reference group determined to be combined by the evaluation value determination unit is A new reference group including the reference group and a number of consecutive frames including the reference group and greater than the predetermined number of three or more is generated so as to be the determination target frame, and the evaluation value calculation unit The evaluation value regarding the error between the frames is calculated based on the first and last frames of the new reference group and the determination target frame, and the evaluation value determination unit calculates the evaluation value calculation unit. Among the evaluation values, the phases of other evaluation values based on the evaluation value between the frame to be judged of the new reference group and the first frame The determination target frame and the first and last frames based on the value or the relative value and the evaluation value between the determination target frame of the new reference group and both the first and last frames It is determined whether or not to combine the reference relationships of.

  One embodiment of the present invention is the video encoding device described above, wherein when the reference group generation unit generates another reference group adjacent to the reference group, the last frame of the reference group is the Generating the reference group including the predetermined number of consecutive frames of the predetermined number or more of the predetermined number of overlapping frames so as to become the first frame of another adjacent reference group; When the evaluation value determination unit determines that the reference relationship between the frame to be determined and the first and last frames is to be combined in both, the adjacent two reference groups are combined to generate the new reference group. The overlapping frames are taken as the determination target frames.

One embodiment of the present invention is the video encoding device described above, wherein the reference group generation unit
The generation of the new reference group is repeated according to the value of the number of layers of the coding structure to be defined in advance.

  One embodiment of the present invention is the video encoding device described above, wherein the picture type selection unit acquires the frame group from the input video information, and selects the first frame of the acquired frame group as an I picture. The picture type selection unit, when it is determined that the combination determination unit combines the reference relationship between the determination target frame and the first and last frames, the determination target frame is the first And the last frame as a reference frame, and the frames not selected as the I picture or the B picture are selected as the P picture, and the selected frames in the display order of the frame group The frame of the previous P picture closest to the And, if there is no the frame of the most recent past of the P-picture to the frame selected, the frame of the I picture, and the reference frame of the frame that was selected.

  One embodiment of the present invention is the above-described video encoding apparatus, wherein the predetermined number of three or more is three.

  According to the present invention, it is possible to obtain a coding structure with high coding efficiency with a small amount of calculation.

It is a block diagram which shows the structure of the video coding apparatus in the 1st Embodiment of this invention. It is a block diagram which shows the structure of the encoding structure construction part of the embodiment. It is a flow chart which shows a flow of coding structure construction processing of the embodiment. It is a flowchart which shows the flow of the joint determination process of the embodiment. It is a figure (the 1) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure (the 2) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure (the 3) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure (the 4) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure which shows the specific example of the coupling determination process of the embodiment. It is a figure which shows the evaluation value calculated in the specific example of the joint determination process of the embodiment. It is a block diagram which shows the structure of the encoding structure construction part of the 2nd Embodiment of this invention. It is a flowchart (the 1) which shows the flow of the encoding structure construction process of the embodiment. It is a flowchart (the 2) which shows the flow of the encoding structure construction process of the embodiment. It is a figure (the 1) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure (the 2) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure (the 3) which shows the specific example of the encoding structure construction process of the embodiment. It is a figure which shows the coding structure of the low delay coding in inter prediction coding. It is a figure which shows the coding structure of the random access coding in inter prediction coding. It is a figure which shows the difference of the fixed structure and the adaptive structure in inter prediction coding. It is a figure (the 1) for demonstrating the adaptive structure in inter prediction coding. It is a figure (the 2) for demonstrating the adaptive structure in inter prediction coding.

First Embodiment
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a video encoding device 1 according to the first embodiment of the present invention. The video coding apparatus 1 includes a coding structure construction unit 10, a subtractor 11, an orthogonal transformation / quantization unit 12, a variable length encoding unit 13, an inverse quantization / inverse orthogonal transformation unit 14, an adder 15, an intra prediction unit And 16, a loop filter unit 17, a decoded picture storage unit 18, an inter prediction unit 19, and an intra / inter switching unit 20.

  The encoding structure construction unit 10 fetches input video information from the outside, selects frames of the number according to the size of a predetermined GOP from the fetched input video information, and generates a frame group. Further, the coding structure construction unit 10 selects a picture type of each frame of the generated frame group, a reference structure, and the like, and constructs a coding structure. Also, the coding structure construction unit 10 outputs a coding target frame in units of CU (Coding Unit) blocks in accordance with the coding order indicated by the constructed coding structure.

  The subtractor 11 includes the image information of the encoding target frame output from the encoding structure construction unit 10, and the predicted image information output from the intra prediction unit 16 or the inter prediction unit 19 via the intra / inter switching unit 20. Calculate the difference of Further, the subtractor 11 outputs difference image information based on the calculated difference to the orthogonal transformation / quantization unit 12.

  The orthogonal transformation / quantization unit 12 performs orthogonal transformation and quantization on the difference image information output from the subtractor 11, and outputs the result to the variable-length coding unit 13 and the inverse quantization / inverse orthogonal transformation unit 14. The variable-length coding unit 13 performs variable-length coding on the quantization coefficient output from the orthogonal transformation / quantization unit 12 to generate coded data, and outputs the generated coded data to the outside.

  The inverse quantization / inverse orthogonal transformation unit 14 performs inverse quantization and inverse orthogonal transformation on the quantization coefficient output from the orthogonal transformation / quantization unit 12 to decode difference image information, and outputs the decoded image information to the adder 15 Do. The adder 15 outputs the decoded difference image information output from the inverse quantization / inverse orthogonal transform unit 14 and the predicted image information output from the intra prediction unit 16 or the inter prediction unit 19 via the intra / inter switching unit 20. Calculate the sum of The adder 15 also outputs decoded image information based on the calculated sum to the intra prediction unit 16 and the loop filter unit 17.

  The intra prediction unit 16 generates intra prediction image information of the encoding target block included in the encoding target frame, using the decoded image information output from the adder 15 as a reference frame.

  The loop filter unit 17 applies a loop filter to the decoded image information output from the adder 15, and writes and stores the decoded image information to which the loop filter is applied in the decoded picture storage unit 18. The inter prediction unit 19 uses the decoded image information stored in the decoded picture storage unit 18 as a reference frame, and inter prediction image information of the coding target block included in the coding target frame output from the coding structure construction unit 10 Generate

  The intra / inter switching unit 20 switches between the intra prediction unit 16 and the inter prediction unit 19 according to the prediction mode of the encoding target block, and outputs the intra prediction image information output by the intra prediction unit 16 or the inter prediction unit The inter-prediction image information output by 19 is output to the subtractor 11 and the adder 15.

  With the above-described configuration, the video encoding device 1 generates a frame group from input video information captured from the outside, and performs raster scan for each encoding target frame of the generated frame group to generate a CU block. The video encoding device 1 repeatedly encodes each of the generated CU blocks as an encoding target block in raster scan order, and outputs encoded data for each encoding target block. The video encoding device 1 encodes the encoding target input video information by repeatedly performing this process on frames included in all frame groups generated from the input video information.

  In the process of encoding, in order to encode the P picture frame in the inter prediction unit 19, it is necessary to store in advance in the decoded picture storage unit 18 a reference frame for the P picture frame. In addition, in order to encode a B picture frame, two reference frames for the B picture frame need to be stored in the decoded picture storage unit 18 in advance. The coding structure construction unit 10 constructs a coding structure that satisfies the requirements of the order of coding.

  FIG. 2 is a block diagram showing the configuration of the coding structure construction unit 10. As shown in FIG. The coding structure construction unit 10 includes a coding target frame selection unit 101, an I picture selection unit 102, a reference group generation unit 103, a combination determination unit 104, a picture type selection unit 105, a picture type storage unit 106, and a block output unit 107. Equipped with

  The encoding target frame selection unit 101 selects the number of frames according to the predetermined GOP size from the input video information, generates a frame group, and outputs the frame group to the I picture selection unit 102 and the block output unit 107. The I picture selection unit 102 selects the first frame of the frame group as the I picture, and outputs the frame group to the reference group generation unit 103 with the first frame as the start frame.

  The reference group generation unit 103 selects a predetermined number (for example, three) of consecutive frames starting from the first frame of the frame group, and sets the selected combination of the predetermined number of consecutive frames as the first reference group. Generate Further, the reference group generation unit 103 selects a predetermined number of continuous frames from the frame as the starting point thereafter, and generates a combination of the selected predetermined number of continuous frames as a reference group. Further, when it is determined that the two adjacent reference groups are to be combined by the combination determination unit 104, the reference group generation unit 103 combines the two adjacent reference groups to generate a new reference group.

  In addition, the reference group generation unit 103 performs combined determination of information of the generated reference group, that is, image information of frames included in the reference group, and information such as frame numbers identifying frames of frames included in the reference group Output to the unit 104 and the picture type selection unit 105.

  The combination determination unit 104 determines whether or not to combine frames included in the reference group generated and output by the reference group generation unit 103. Here, combining the frames included in the reference group means making the determination target frame, which is a frame between the first and last frames, a B picture in which the first and last frames are reference frames. The combination determination unit 104 includes an evaluation value calculation unit 110, an evaluation value determination unit 111, and a determination result storage unit 112.

  The evaluation value calculation unit 110 calculates the evaluation value of the reference group generated by the reference group generation unit 103. Here, the evaluation value is a value of three inter costs calculated as follows. The inter cost is, for example, an evaluation value regarding an error in the case of performing motion search between frames, and for example, the minimum value of the sum of absolute errors is applied, and this evaluation value is RD (Rate-Distortion) cost The coding cost is different from the coding cost which can not be obtained unless coding is actually performed. Here, the minimum value of the absolute error sum represents the smallest value among the values obtained by detecting a plurality of motion vectors and calculating the absolute error sum for each motion vector.

  First, the first frame, the determination target frame between the first and last frames, and the last frame are respectively S frame, M frame, and E frame. When the reference group includes a predetermined number (for example, three) of consecutive frames, the determination target frame is an intermediate frame, and when two adjacent reference groups are combined as described later, the determination target frame Is the last frame of the previous reference group in display order.

  The sum (hereinafter, referred to as the L0 cost) of all the blocks in the unidirectional inter cost when the S frame is used as the reference frame in a predetermined block size unit predetermined for the M frame is calculated. Next, the sum (hereinafter, referred to as L1 cost) of all the blocks of the unidirectional inter cost when the E frame is used as the reference frame in a predetermined block size unit predetermined for M frames is calculated. Furthermore, the sum (hereinafter referred to as the Bi cost) of all blocks of the bidirectional inter cost when the S frame and the E frame are used as reference frames in predetermined block size units predetermined for M frames is calculated.

  The evaluation value determination unit 111 determines whether to combine the frames of the reference group based on the L0 cost, the L1 cost, and the Bi cost calculated by the evaluation value calculation unit 110, that is, refers to the M frame and the S frame and the E frame. A combination determination process is performed to determine whether to use a B picture as a frame. The evaluation value determination unit 111 writes the determination result in the determination result storage unit 112 in association with the information indicating the reference group, and outputs the determination result to the picture type selection unit 105. The determination result storage unit 112 stores the determination result determined by the evaluation value determination unit 111 for each reference group.

  The picture type selection unit 105 selects a picture type of a frame included in the reference group generated by the reference group generation unit 103 according to the determination result output from the connection determination unit 104. Further, when the reference group generation unit 103 determines that the three consecutive frames can not be selected, the picture type selection unit 105 selects the remaining frames as P pictures. In addition, after selecting the picture types for all frames, the picture type selection unit 105 selects the frame selected as the P picture and the frame selected as the past P picture closest to the frame in the display order Select as the frame reference frame.

  Here, the closest past P picture in display order is the closest P picture with a number smaller than the frame to which the reference frame is assigned, in the case where a sequential number is assigned in display order from the first frame to be I picture. It is. Also, if there is no closest past P picture in display order, the picture type selection unit 105 selects an I picture as a reference frame.

  The picture type storage unit 106 stores the information indicating the picture type of the I picture in association with the information indicating the frame selected as the I picture by the I picture selecting unit 102. Further, the picture type storage unit 106 stores information indicating the picture type of the B picture or P picture selected by the picture type selection unit 105 in association with the information indicating each frame together with the information indicating the reference frame.

  The block output unit 107 receives the frame group output from the encoding target frame selection unit 101, temporarily writes it in the internal storage area, and stores it. Further, when the selection of the picture type is completed and the coding structure is determined, the block output unit 107 reads the frames from the internal storage area in the order based on the defined coding structure, and raster scans each of the read frames It decomposes | disassembles into CU block in order of, and it outputs as an encoding object block.

(Coding structure construction processing of the first embodiment)
Next, processing by the coding structure construction unit 10 of the first embodiment will be described. FIG. 3 is a flowchart showing a flow of coding structure construction processing by the coding structure construction unit 10. Further, FIG. 4 is a flowchart showing a flow of a subroutine of connection determination processing by the connection determination unit 104 called in the coding structure construction processing.

  The encoding target frame selection unit 101 selects a number of frames according to a predetermined GOP size from input video information to generate a frame group, and generates the generated frame group to the I picture selection unit 102 and the block output unit 107. Output. The I picture selection unit 102 selects the picture type of the first frame of the frame group as an I picture, and writes and stores information indicating that the frame is selected as an I picture in the picture type storage unit 106. Further, the I picture selection unit 102 sets the first frame as the start frame, and outputs the frame group to the reference group generation unit 103 (step S101).

  The reference group generation unit 103 determines whether or not three continuous frames can be selected from the frame group starting from the start point frame (step S102). If the reference group generation unit 103 determines that three consecutive frames can be selected (YES in step S102), the reference group generation unit 103 selects three consecutive frames in the display order A, B, and so on. Generate a reference group to be included as a C frame. The determination target frame in the reference group is a B frame.

  The reference group generation unit 103 outputs the generated reference group to the combination determination unit 104 and the picture type selection unit 105 (step S105). The connection determination unit 104 performs connection determination processing with the A, B, and C frames included in the reference group output from the reference group generation unit 103 as S, M, and E frames (step S106).

(Coupling determination processing by the combining determination unit)
In the subroutine of the connection determination process shown in FIG. 4, the evaluation value calculation unit 110 calculates three evaluation values of L0 cost, L1 cost, and Bi cost based on the S frame, M frame, and E frame (step S201). .

  The evaluation value determination unit 111 selects the smaller one of the Bi cost and the L1 cost (step S202), and divides the selected value by L0 to calculate a relative value (step S203). When the values of the Bi cost and the L1 cost are the same, either one may be selected, so either one is selected. The processes of steps S202 and S203 can be expressed by the following equation (1).

  Relative value = min (Bi cost, L1 cost) / L0 cost (1)

  The evaluation value determination unit 111 determines the magnitude of the calculated relative value based on predetermined relative evaluation threshold values Th_min and Th_max (step S204). When it is determined that the calculated relative value is less than the value of Th_min (step S204: <Th_min), the evaluation value determination unit 111 outputs “True” indicating that the frames included in the reference group are combined (step S204: <Th_min) Step S205). On the other hand, when the evaluation value determination unit 111 determines that the calculated relative value exceeds the value of Th_max (step S 204:> Th_max), “False” indicating that frames included in the reference group are not combined. Are output (step S206).

  On the other hand, when the evaluation value determination unit 111 determines that the calculated relative value is equal to or greater than the value of Th_min and equal to or less than the value of Thmax (step S204: ThTh_min and ≦ Th_max), the magnitude of the value of the Bi cost Is determined based on a predetermined absolute evaluation threshold Th_abs (step S207). When it is determined that the value of the Bi cost is less than the value of Th_abs (step S207: <Th_abs), the evaluation value determination unit 111 outputs “True” indicating that frames included in the reference group are combined (step S207: <Th_abs) Step S208). On the other hand, when it is determined that the value of Bi cost is equal to or greater than the value of Th_abs (step S207: ≧ Th_abs), the evaluation value determination unit 111 outputs “False” indicating that the frames included in the reference group are not combined ( Step S206).

  The evaluation value determination unit 111 writes information of “True” or “False” indicating the determination result in association with the information indicating the reference group in the process of steps S205, S206, and S208 and stores the information in the determination result storage unit 112. Then, the subroutine of connection determination processing is ended.

  Returning to FIG. 3, the picture type selection unit 105 determines the determination result output by the combination determination unit 104 (step S107). When the determination result is “False” (Step S107-False), the picture type selection unit 105 selects the picture type of the B frame of the reference group as a P picture and information indicating that the B frame is selected as a P picture. The picture type storage unit 106 is written and stored. The picture type selection unit 105 outputs, to the reference group generation unit 103, information in which the B frame is the start frame (step S108). When the reference group generation unit 103 receives the information that uses the B frame output from the picture type selection unit 105 as the start frame, the reference group generation unit 103 proceeds to the process of step S102 with the B frame as the start frame.

  On the other hand, when the determination result is "True" (step S107-True), the picture type selection unit 105 selects the picture type of the B frame as the B picture with the A frame and the C frame as reference frames, Information indicating that it is selected as a picture, and information indicating that the A frame and the C frame are reference frames are written and stored in the picture type storage unit 106. Further, the picture type selection unit 105 selects the picture type of the C frame as a P picture, and writes and stores information indicating that the C frame is selected as a P picture in the picture type storage unit 106. The picture type selection unit 105 outputs the information indicating the reference group of which the determination result is “True” to the reference group generation unit 103 (step S109).

  The reference group generation unit 103 refers to the determination result storage unit 112 of the connection determination unit 104 when the information indicating the reference group whose determination result output by the picture type selection unit 105 is “True” is received. Based on the information stored in the determination result storage unit 112, the reference group generation unit 103 determines whether the determination result of the reference group immediately before the reference group being processed is "True" in the display order. It is determined (step S110).

  When the reference group generation unit 103 determines that the determination result of the reference group immediately before the reference group being processed is not “True” in display order (step S110-NO), the C frame is set as the start frame ((step S110) Step S116) The processing proceeds to step S102.

  The reference group generation unit 103 generates a new reference group when it is determined that the determination result of the reference group immediately before the reference group being processed is "True" in the display order (step S110-YES). Do. That is, the reference group generation unit 103 sets the first frame and the last frame of the previous reference group as an α frame and a β frame, respectively, and the last frame of the reference group being processed as a γ frame. , Γ frame is generated. The β frame is also the first A frame of the reference group being processed, and is a determination target frame in the reference group. The reference group generation unit 103 outputs the generated information on the new reference group to the combination determination unit 104 and the picture type selection unit 105 (step S111).

  The combination determination unit 104 performs combination determination processing on the α, β, and γ frames included in the reference group output by the reference group generation unit 103. The evaluation value calculation unit 110 performs the connection determination process shown in FIG. 4 with each of the α, β and γ frames as an S, M and E frame (step S112).

  The picture type selection unit 105 determines the determination result output from the combination determination unit 104 (step S113). If the determination result is "False" (step S113-False), the picture type selection unit 105 starts the γ frame which is the last frame of the new reference group, that is, the C frame of the reference group in process before combining The information indicating the setting is output to the reference group generation unit 103 (step S115). The reference group generation unit 103 receives the information indicating that the C frame output from the picture type selection unit 105 is the start frame, sets the C frame as the start frame (step S116), and proceeds to the process of step S102.

  On the other hand, when the determination result is "True" (step S113-True), the picture type selection unit 105 selects the picture type of the β frame as a B picture with the α frame and the γ frame as reference frames, Information indicating that it is selected as a picture, and information indicating that the α frame and the γ frame are reference frames are written and stored in the picture type storage unit 106. In addition, the picture type selection unit 105 selects the picture type of the γ frame as a P picture, and writes and stores information indicating that the γ frame is selected as a P picture in the picture type storage unit 106 (step S114).

  The picture type selection unit 105 outputs, to the reference group generation unit 103, information indicating that the γ frame which is the last frame of the new reference group, that is, the C frame of the reference group being processed before combining is used as the start frame. (Step S115). The reference group generation unit 103 receives the information indicating that the C frame output from the picture type selection unit 105 is the start frame, sets the C frame as the start frame (step S116), and proceeds to the process of step S102.

  On the other hand, when it is determined in step S102 that the reference group generation unit 103 can not select three consecutive frames (step S102-NO), instruction information for selecting the remaining frames of the frame group as P pictures Is output to the picture type selection unit 105.

  The picture type selection unit 105 receives the instruction information from the reference group generation unit 103, selects the picture type of the remaining frame as a P picture, and stores information indicating that the remaining frame is selected as a P picture. The part 106 is written and stored (step S103). For each of the frames selected as a P picture, the picture type selection unit 105 selects, as a reference frame, a frame of the past P picture closest to the frame in display order. If there is no closest past P picture in display order, the I picture is selected as the reference frame of the frame. The picture type selection unit 105 writes and stores information on the reference frame selected for each P picture in the picture type storage unit 106 (step S104).

  As a result, the picture type storage unit 106 stores the information of the coding structure finally constructed. The block output unit 107 temporarily stores the frame group received from the encoding target frame selection unit 101 in an internal storage area, and internally stores the frames in the order based on the encoding structure stored in the picture type storage unit 106. Read the frame from the storage area of The block output unit 107 decomposes each of the read frames into CU blocks in raster scan order and outputs the CU block as an encoding target block, and the coding structure construction unit 10 ends the processing for one frame group.

(Specific Example of Encoding Structure Processing of First Embodiment)
Next, with reference to FIG. 5 to FIG. 8, an example in the case of applying the coding structure construction process of the first embodiment shown in FIG. 3 to the frame group shown in FIG. 5A will be described. The encoding target frame selection unit 101 generates a frame group shown in FIG. 5A from the input video information. The frame group includes a scene change in the frames of frame number 8 and frame number 9.

  As shown in FIG. 5B, the I picture selection unit 102 selects the picture type of the frame with frame number 0 as an I picture, and information indicating that the frame is selected as an I picture is stored in the picture type storage unit 106. Write to and memorize. Also, the I picture selection unit 102 sets the frame of frame number 0 as the start frame (step S101).

  The reference group generation unit 103 selects three consecutive frames of frame numbers 0, 1 and 2 with the frame of frame number 0 as the start frame (step S102-YES). The reference group generation unit 103 generates a reference group 301 including the frames of frame numbers 0, 1 and 2 as frames A, B and C, and the information of the generated reference group 301 is combined determination unit 104 and picture type selection unit 105. Output (step S105). The determination target frame in the reference group 301 is the frame of frame number 1.

  The combination determination unit 104 performs the combination determination process shown in FIG. 4 on the reference group 301. Here, it is assumed that the evaluation value determination unit 111 outputs "True" because there is no scene change (step S106). . Since the determination result output from the connection determination unit 104 is “True” (step S 107 -True), the picture type selection unit 105 sets the frame types of frame number 1 to frame number 0 and frame number 2. It is selected as a B picture to be a reference frame. The picture type selection unit 105 writes in the picture type storage unit 106 information indicating that the frame of frame number 2 has been selected as a B picture, and information indicating that the frames of frame number 0 and frame number 2 are reference frames. Remember.

  In addition, the picture type selection unit 105 selects the picture type of the frame of frame number 2 as a P picture, and writes information indicating that the frame of frame number 2 is selected as a P picture into the picture type storage unit 106 for storage. . The picture type selection unit 105 outputs information indicating the reference group 301 whose determination result is “True” to the reference group generation unit 103 (step S109).

  As shown in FIG. 5C, the reference group generation unit 103 refers to the determination result storage unit 112, and there is no reference group one before the reference group 301 (step S110-NO). The frame of No. 2 is set as the starting point frame (step S116), and three consecutive frames of frame numbers 2, 3 and 4 are selected (step S102--YES). The reference group generation unit 103 generates the reference group 302 including the frames of frame numbers 2, 3 and 4 as the frames A, B and C, and the generated information of the reference group 302 is combined determination unit 104 and picture type selection unit 105. Output (step S105). In the reference group 302, the determination target frame is a frame of frame number 3.

  The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group 302. Also here, since there is no scene change, the evaluation value determination unit 111 outputs "True" (step S106). . Since the determination result output from the connection determination unit 104 is “True” (step S 107 -True), the picture type selection unit 105 sets the picture types of the frame of frame number 3 to the frames of frame numbers 2 and 4. It is selected as a B picture to be a reference frame. The picture type selection unit 105 writes in the picture type storage unit 106 information indicating that the frame of frame number 3 has been selected as a B picture, and information indicating that the frames of frame numbers 2 and 4 are reference frames. Remember.

  Also, the picture type selection unit 105 selects the picture type of frame number 4 as a P picture, and writes and stores information indicating that the frame of frame number 4 is selected as a P picture in the picture type storage unit 106. The picture type selection unit 105 outputs the information indicating the reference group 302 whose determination result is “True” to the reference group generation unit 103 (step S109).

  As shown in FIG. 6D, the reference group generation unit 103 refers to the determination result storage unit 112 and determines that the determination result of the reference group 301 immediately before the reference group 302 is “True”. (Step S110-YES). The reference group generation unit 103 generates a reference group 303 including the frames of frame numbers 0, 2 and 4 as the frames α, β and γ. The determination target frame in the reference group 303 is the frame of frame number 2. The reference group generation unit 103 outputs the generated information of the reference group 303 to the combination determination unit 104 and the picture type selection unit 105 (step S111).

  The connection determination unit 104 performs the connection determination process illustrated in FIG. 4 on the reference group 303. Also here, since there is no scene change, the evaluation value determination unit 111 outputs “True” (step S112). . Since the determination result is "True" (step S113-True), the picture type selection unit 105 selects the picture type of the frame of frame number 2 as a B picture with the frames of frame number 0 and frame number 4 as the reference frame. Do.

  In the picture type storage unit 106, information indicating that the frame of frame number 2 is a P picture has already been written. Therefore, the picture type selection unit 105 uses the picture type storage unit 106 as information indicating that the frame of frame number 2 has been selected as a B picture, and information indicating that the frames of frame numbers 0 and 4 are reference frames. Are overwritten and stored (step S114). The picture type selection unit 105 outputs, to the reference group generation unit 103, information indicating frame number 4 that is the next start frame (step S115).

  As shown in FIG. 6E, the reference group generation unit 103 selects three consecutive frames of frame numbers 4, 5 and 6 with the frame of frame number 4 as the starting point frame (step S116). S102-YES). The reference group generation unit 103 generates the reference group 304 including the frames of frame numbers 4, 5 and 6 as the frames A, B and C, and the information of the generated reference group 304 is combined determination unit 104 and picture type selection unit 105. Output (step S105). The determination target frame in the reference group 304 is the frame of frame number 5.

  The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group 304. Also here, since there is no scene change, the evaluation value determination unit 111 outputs "True" (step S106). . Since the determination result output from the connection determination unit 104 is “True” (step S 107 -True), the picture type selection unit 105 sets the frame types of frame number 5 and frame number 6 as the picture type of the frame of frame number 5. It is selected as a B picture to be a reference frame. The picture type selection unit 105 writes in the picture type storage unit 106 information indicating that the frame of frame number 5 has been selected as a B picture, and information indicating that the frames of frame numbers 4 and 6 are reference frames. Remember.

  Also, the picture type selection unit 105 selects the picture type of frame number 6 as a P picture, and writes and stores information indicating that the frame of frame number 6 is selected as a P picture in the picture type storage unit 106. The picture type selection unit 105 outputs the information indicating the reference group 304 whose determination result is “True” to the reference group generation unit 103 (step S109).

  As shown in FIG. 6F, the reference group generation unit 103 refers to the determination result storage unit 112 and determines that the determination result of the reference group 303 immediately before the reference group 304 is “True”. (Step S110-YES). The reference group generation unit 103 generates a reference group 305 including the frames of frame numbers 0, 4 and 6 as the frames α, β and γ. The determination target frame in the reference group 305 is the frame of frame number 4. The reference group generation unit 103 outputs the generated information of the reference group 305 to the combination determination unit 104 and the picture type selection unit 105 (step S111).

  The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group 305. Also here, since there is no scene change, the evaluation value determination unit 111 outputs "True" (step S112). . Since the determination result is “True” (step S 113 -True), the picture type selection unit 105 selects the picture type of the frame of frame number 4 as the B picture with the frames of frame number 0 and frame number 6 as reference frames. Do.

  Information indicating that the frame of frame number 4 is a P picture has already been written in the picture type storage unit 106. Therefore, the picture type selection unit 105 uses the picture type storage unit 106 as information indicating that the frame of frame number 4 is selected as a B picture, and information indicating that the frames of frame number 0 and frame number 6 are reference frames. Are overwritten and stored (step S114). The picture type selection unit 105 outputs, to the reference group generation unit 103, information indicating the frame number 6 that is the next starting point frame (step S115).

  As shown in FIG. 7G, the reference group generation unit 103 selects three consecutive frames of frame numbers 6, 7 and 8 with the frame of frame number 6 as the starting point frame (step S116). S102-YES). The reference group generation unit 103 generates a reference group 306 including the frames of frame numbers 6, 7 and 8 as frames A, B and C, and the information of the generated reference group 306 is combined determination unit 104 and picture type selection unit 105. Output (step S105). In the reference group 306, the determination target frame is the frame of frame number 7.

  The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group 306. Also here, since there is no scene change, the evaluation value determination unit 111 outputs "True" (step S106). . Since the determination result output from the connection determination unit 104 is “True” (step S 107 -True), the picture type selection unit 105 sets the picture types of the frame of frame number 7 as the frame numbers 6 and 8. It is selected as a B picture to be a reference frame. The picture type selection unit 105 writes in the picture type storage unit 106 information indicating that the frame of frame number 7 has been selected as a B picture, and information indicating that the frames of frame numbers 6 and 8 are reference frames. Remember.

  In addition, the picture type selection unit 105 selects the picture type of frame number 8 as a P picture, and writes and stores information indicating that the frame of frame number 8 is selected as a P picture in the picture type storage unit 106. The picture type selection unit 105 outputs the information indicating the reference group 306 whose determination result is “True” to the reference group generation unit 103 (step S109).

  As shown in FIG. 7H, the reference group generation unit 103 refers to the determination result storage unit 112, and determines that the determination result of the reference group 305 immediately before the reference group 306 is "True". (Step S110-YES). The reference group generation unit 103 generates a reference group 307 including the frames of frame numbers 0, 6, and 8 as the frames α, β, and γ. In the reference group 307, the determination target frame is a frame of frame number 6. The reference group generation unit 103 outputs the generated information of the reference group 307 to the combination determination unit 104 and the picture type selection unit 105 (step S111).

  The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group 307. Also here, since there is no scene change, the evaluation value determination unit 111 outputs "True" (step S112). . Since the determination result is “True” (step S 113 -True), the picture type selection unit 105 selects the picture type of the frame of frame number 6 as the B picture with the frames of frame number 0 and frame number 8 as the reference frame Do.

  In the picture type storage unit 106, information indicating that the frame of frame number 6 is a P picture has already been written. Therefore, the picture type selection unit 105 uses the picture type storage unit 106 as information indicating that the frame of frame number 6 has been selected as a B picture, and information indicating that the frames of frame number 0 and frame number 8 are reference frames. Are overwritten and stored (step S114). The picture type selection unit 105 outputs, to the reference group generation unit 103, information indicating the frame number 8 that is the next start point frame (step S115).

  As shown in FIG. 7I, the reference group generation unit 103 selects three consecutive frames of frame numbers 8, 9, and 10, using the frame of frame number 8 as the starting point frame (step S116). S102-YES). The reference group generation unit 103 generates the reference group 308 including the frames of frame numbers 8, 9, and 10 as the frames A, B, and C, and the information of the generated reference group 308 is combined determination unit 104 and picture type selection unit 105. Output (step S105). In the reference group 308, the determination target frame is the frame of frame number 9.

  The combination determination unit 104 performs the combination determination process illustrated in FIG. 4 on the reference group 308. As shown in FIG. 5A, since there is a scene change between frame number 8 and frame number 9, it is assumed here that the evaluation value determination unit 111 outputs "False" (step S106). The picture type selection unit 105 selects the picture type of the frame with the frame number 9 as the P picture because the determination result output from the connection determination unit 104 is “False” (step S 107 -False). The picture type selection unit 105 writes and stores information indicating that the frame of frame number 9 is selected as a P picture in the picture type storage unit 106. The picture type selection unit 105 sets the frame of frame number 9 as the start frame (step S108).

  As shown in FIG. 8 (j), the reference group generation unit 103 can not select three consecutive frames starting from the frame of frame number 9 (step S102-NO). The reference group generation unit 103 outputs, to the picture type selection unit 105, instruction information for selecting the picture type of the frame of frame number 10 which is the remaining frame as a P picture. The picture type selection unit 105 receives the instruction information, selects the frame of frame number 10 as a P picture, and writes information indicating that the frame of frame number 10 is selected as a P picture in the picture type storage unit 106. It memorizes (Step S103).

  The picture type selection unit 105 refers to the information stored in the picture type storage unit 106, and for the frame of frame numbers 8, 9, and 10 selected as a P picture, the closest past P picture in display order The frame of is selected as the reference frame. When there is no closest past P picture in display order, a frame of I picture is selected as a reference frame. The picture type selection unit 105 writes and stores information indicating the selected reference frame in the picture type storage unit 106 (step S104).

  As for the frame of frame number 8, there is no closest past P picture in display order, so the frame of I picture of frame number 0 is the reference frame. For the frame of frame number 9, the closest past P picture in display order is the frame of frame number 8. For the frame of frame number 10, the closest past P picture in display order is the frame of frame number 9.

  When the coding structure constructed based on the information stored in the picture type storage unit 106 is hierarchized, the coding structure has a hierarchical structure of B pictures of four layers as shown in FIG. .

(Specific example of combination determination processing)
Next, an example of the connection determination process by the connection determination unit 104 will be described with reference to FIGS. 9 and 10. FIG. 9 shows an example of S, M and E frames to which the connection determination process is applied. FIG. 9 (i) is an example in which there are no scene changes in three frames of S, M and E frames. Is an example in which there is a scene change between M frame and E frame, and (iii) is an example in which there is a scene change between S frame and M frame. FIGS. 9 (iv) and (v) are examples in which there is a scene change in part from S frame to E frame.

  In this example, it is assumed that “0.8” and “1.2” are defined as the relative evaluation threshold Th_min and Th_max, and “350” is defined as the absolute evaluation threshold Th_abs.

  In the case of FIG. 9I, the evaluation value calculation unit 110 of the connection determination unit 104 sets “150”, “150”, and “100” as evaluation values of L0, L1, and Bi costs, respectively, as shown in FIG. Is calculated (step S201). If Formula (1) is applied by the evaluation value determination part 111, it will become relative value = min (100,150) / 150 = 100/150 = 2/3 (step S202, S203). Since 2/3 <0.8 (step S204, <Th_min), the evaluation value determination unit 111 outputs "True" (step S205).

  In the case of FIG. 9 (ii), the evaluation value calculation unit 110 of the connection determination unit 104 sets “150”, “500”, and “400” as evaluation values of L0, L1, and Bi costs, respectively, as shown in FIG. Is calculated (step S201). If Formula (1) is applied by the evaluation value determination part 111, it will become relative value = min (400,500) / 150 = 400/150 = 8/3 (step S202, S203). Since 8/3> 1.2 (step S204,> Th_max), the evaluation value determination unit 111 outputs "False" (step S206).

  In the case of FIG. 9 (iii), the evaluation value calculation unit 110 of the connection determination unit 104 sets “500”, “150”, and “400” as evaluation values of L0, L1, and Bi costs, respectively, as shown in FIG. Is calculated (step S201). If Formula (1) is applied by the evaluation value determination part 111, it will become relative value = min (400,150) /500=150/500=0.3 (step S202, S203). Since 0.3 <0.8 (step S204, <Th_min), the evaluation value determination unit 111 outputs "True" (step S205).

  In the case of FIG. 9 (iv), the evaluation value calculation unit 110 of the connection determination unit 104 sets “300”, “400”, and “300” as evaluation values of L0, L1, and Bi costs, respectively, as shown in FIG. Is calculated (step S201). If Formula (1) is applied by the evaluation value determination part 111, it will become relative value = min (300,400) / 300 = 300/300 = 1 (step S202, S203). Since 0.8 ≦ 1 ≦ 1.2 (step S204, ThTh_min and ≦ Th_max), the evaluation value determination unit 111 determines the value of the Bi cost based on the absolute evaluation threshold (step S207). ). Since the value of Bi cost is “300” <Th_abs “350” (step S207, <Th_abs), the evaluation value determination unit 111 outputs “True” (step S208).

  In the case of FIG. 9 (v), the evaluation value calculation unit 110 of the connection determination unit 104 sets “400”, “500”, and “400” as evaluation values of L0, L1, and Bi costs, respectively, as shown in FIG. Is calculated (step S201). When the expression (1) is applied by the evaluation value determination unit 111, the relative value = min (400, 500) / 400 = 400/400 = 1 is obtained (steps S202 and S203). Since 0.8 ≦ 1 ≦ 1.2 (step S204, ThTh_min and ≦ Th_max), the evaluation value determination unit 111 determines the value of the Bi cost based on the absolute evaluation threshold (step S207). ). Since the value of the Bi cost "400" ThTh_abs "350" (step S207, ThTh_abs), the evaluation value determination unit 111 outputs "False" (step S206).

  According to the configuration of the first embodiment, in the coding structure construction unit 10, the coding target frame selection unit 101 selects a number of frames according to the size of the GOP determined in advance from the input video information, and sets the frame group. Generate The I picture selection unit 102 selects the first frame of the frame group as an I picture and uses it as a start frame. The reference group generation unit 103 selects three continuous frames starting from the start frame, and generates a reference group using the selected three frames as A, B, and C frames. The evaluation value calculation unit 110 of the combination determination unit 104 calculates three evaluation values of L0 cost, L1 cost, and Bi cost based on the A, B, and C frames included in the reference group. The evaluation value determination unit 111 selects the smaller one of the Bi cost and the L1 cost, and makes a determination based on the relative value based on the value of the L0 cost and the predetermined relative evaluation threshold values Th_min and Th_max. It is determined whether or not the reference relationship between the B frame, which is the target frame, and the A and C frames is combined. In addition, when the relative value is within the range not less than the value of Th_min and not more than the value of Th_max, the evaluation value determining unit 111 further determines the value of Bi cost based on the absolute evaluation threshold Th_abs. It is determined whether or not the reference relationship between the B frame, which is the determination target frame, and the A and C frames is combined. If the evaluation value determination unit 111 determines that the reference relationship between the B frame and the A and C frames is combined, the picture type selection unit 105 selects the B frame as a B picture having the A and C frames as reference frames. . That is, the encoding structure construction unit 10 does not perform an operation to perform actual coding, but calculates three evaluation values based on three frames, and calculates 3 based on the calculated 3 evaluation values. It is determined whether or not reference relationships of two frames are to be combined. For this reason, in the coding structure construction unit 10 of the first embodiment, it is possible to obtain a coding structure with high coding efficiency with a small amount of calculation.

  Further, the reference group generation unit 103 combines two adjacent reference groups of which the evaluation value determination unit 111 determines that the reference relationship between the determination target frame and the first and last frames are combined Repeat creating a new reference group. In the connection determination unit 104, the reference group generation unit 103 performs connection determination processing based on the newly generated α, β, and γ frames of the reference group. As a result, in the coding structure construction unit 10 of the first embodiment, it is possible to construct a coding structure of two or more deep layers, and it becomes possible to improve the coding efficiency. There is. For example, as described above, the example of FIG. 8 (k) indicates that it is possible to construct a coding structure having a hierarchical structure of B pictures of four layers.

Second Embodiment
FIG. 11 is a block diagram showing the configuration of the coding structure construction unit 10a in the second embodiment of the present invention. The coding structure construction unit 10 a is a functional unit to be applied replacing the coding structure construction unit 10 of the video coding device 1 according to the first embodiment. When the coding structure construction unit 10a of the second embodiment is applied, the code of the video coding apparatus is represented by "1a" instead of "1". In the second embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and components different from those of the coding structure construction unit 10 of the first embodiment will be described below.

  The coding structure construction unit 10a includes a coding target frame selection unit 101, an I picture selection unit 102a, a reference group generation unit 103a, a combination determination unit 104, a picture type selection unit 105a, a picture type storage unit 106, a block output unit 107, And a reference group storage unit 108.

In the coding structure construction unit 10a, the I picture selection unit 102a selects the first frame of the frame group as an I picture. The reference group generation unit 103a sets an initial value to i = 0 and j = 0, and a reference group including three frames of frame numbers “2j”, “2j + 2 ⁱ ”, and “2j + 2 ^{(i + 1)} ” from the frame group Repeat while j is less than N / 2, adding 1 to j, until it can not be generated. Here, the value of N is the maximum value of the frame numbers assigned to the frames included in the frame group, and is a value obtained by subtracting “1” from the number of frames in the frame group.

In addition, the reference group generation unit 103a sets three frames as A, B, and C frames in each of the combinations of the selected frame numbers “2 ^j ”, “2 j + 2 ⁱ ”, and “2 j + 2 ^{(i + 1)} ”. Create a reference group Ref [i] [j] indexed by i and j, including B, C, C frames (however, if generating a reference group including A, B, C frames, i = 0) Fixed, only j is a variable). Further, the reference group generation unit 103a writes the generated reference group Ref [0] [j] in the reference group storage unit 108 and stores the reference group Ref [0] [j].

  Further, the reference group generation unit 103 a sets the initial value to i = 1, j = 0, and the connection determination unit 104 in both of the reference groups Ref [i−1] [j] and Ref [i−1] [j + 1]. Is repeated while j is less than N / 2 while 2 is added to j, while i is 1 and depth_max is added. Repeat for less than. Here, depth_max is a value indicating the number of layers of the coding structure to be constructed, which is predetermined, and in the case of three layers, depth_max is "3".

  In addition, the reference group generation unit 103a is configured to set the first of Ref [i-1] [j] and the first of Ref [i-1] [j] in each of the detected combinations of the reference groups Ref [i-1] [j] Three frames of the last frame and the last frame of Ref [i-1] [j + 1] are selected as α, β and γ frames. Further, the reference group generation unit 103a writes and stores a new reference group including the selected α, β, and γ frames as a reference group Ref [i] “j / 2” in the reference group storage unit 108.

The picture type selection unit 105a selects the picture type of the frame included in the reference group Ref [i] [j] according to the determination result output from the combination determination unit 104. If the picture type selection unit 105a determines that the reference group generation unit 103a can not select the frames with frame numbers “2j”, “2j + 2 ⁱ ”, and “2j + 2 ^{(i + 1)} ”, the remaining frames are P pictures. To be selected.

  Further, after selecting the picture types for all the frames, the picture type selection unit 105a selects the frame selected as the P picture, and the frame selected as the past P picture closest to the frame in the display order Select as the frame reference frame. When there is no closest past P picture in display order, a frame of I picture is selected as a reference frame of the frame. The reference group storage unit 108 stores the reference group Ref [i] [j] generated by the reference group generation unit 103a.

(Coding structure construction processing of the second embodiment)
Next, processing by the coding structure construction unit 10a of the second embodiment will be described. 12 and 13 are flowcharts showing the flow of coding structure construction processing by the coding structure construction unit 10. The processes shown in FIGS. 12 and 13 are continuous processes in which the processes are connected at a point indicated by a symbol A. The processing up to the point indicated by symbol A shown in FIG. 12 is the processing of constructing the coding structure of the first layer indicated by i = 0, and the processing shown in FIG. 13 is i = 1, 2 This is processing for constructing the coding structure of the second and third layers shown.

  The encoding target frame selection unit 101 selects a number of frames according to a predetermined GOP size from input video information and generates a frame group. The encoding target frame selection unit 101 assigns a frame number from “0” to the generated frame group in display order, and outputs the frame group to the I picture selection unit 102 a and the block output unit 107. The I picture selection unit 102a selects the picture type of the first frame of the frame group, that is, the frame of frame number 0 as an I picture. The I picture selection unit 102a writes and stores information indicating that the frame of frame number 0 has been selected as an I picture in the picture type storage unit 106 (step S301).

The reference group generation unit 103a sets i = 0 and j = 0 (step S302), and can select three frames of frame numbers “2j”, “2j + 2 ⁱ ”, and “2j + 2 ^{(i + 1)} ” from the frame group. It is determined (step S303).

  When the reference group generation unit 103a determines that three frames can be selected (YES in step S303), the reference group generation unit 103a includes three frames in the display order as A, B, and C frames. Generate reference group Ref [0] [j]. The reference group generation unit 103a writes and stores the generated reference group Ref [0] [j] in the reference group storage unit 108 (step S305). The determination target frame in the reference group is a B frame.

  When the information on the reference group Ref [0] [j] is written to the reference group storage unit 108 by the reference group generation unit 103a, the connection determination unit 104 causes the A included in the written reference group Ref [0] [j] to The combination determination process shown in FIG. 4 is performed with the B, C, and C frames as S, M, and E frames (step S306).

  The picture type selection unit 105a determines the determination result output from the combination determination unit 104 (step S307). When the determination result is “False” (Step S307—False), the picture type selection unit 105a selects the picture types of the B frame and the C frame of the reference group Ref [0] [j] as a P picture. The picture type selection unit 105a writes and stores information indicating that the B and C frames of the reference group Ref [0] [j] are selected as the P picture in the picture type storage unit 106 (step S308).

  On the other hand, when the determination result is “True” (step S 307 -True), the picture type selection unit 105 a sets the picture types of B frames of the reference group Ref [0] [j] as A frame and C frame. Select as B picture. The picture type selection unit 105 a receives information indicating that the B frame of the reference group Ref [0] [j] has been selected as the B picture, and information indicating that the A frame and the C frame are reference frames. Write to 106 for storage. Also, the picture type selection unit 105a selects the picture type of the C frame of the reference group Ref [0] [j] as a P picture. The picture type selection unit 105a writes and stores information indicating that the C frame of the reference group Ref [0] [j] has been selected as a P picture in the picture type storage unit 106 (step S309).

  After the processes of steps S308 and S309, the picture type selection unit 105a outputs instruction information for continuing the process to the reference group generation unit 103a. The reference group generation unit 103a adds “1” to the value of j (step S310), and determines whether the value of j is less than N / 2 (step S311). When the reference group generation unit 103a determines that the value of j is less than N / 2 (YES in step S311), the processing from step S303 is repeated. On the other hand, when the reference group generation unit 103a determines that the value of j is not less than N / 2 (step S311-NO), the reference group generation unit 103a starts the processing illustrated in FIG.

  On the other hand, when the reference group generation unit 103a determines that three frames can not be selected (step S303-NO), the instruction information for selecting the remaining frames of the frame group as P pictures is the picture type selection unit 105a. Output to The picture type selection unit 105a receives the instruction information from the reference group generation unit 103a, selects the picture type of the remaining frame as a P picture, and stores information indicating that the remaining frame is selected as a P picture. The part 106 is written and stored (step S304). The reference group generation unit 103a outputs the instruction information to the picture type selection unit 105a, and thereafter, starts the processing illustrated in FIG. 13 via the portion indicated by the symbol A.

  As shown in FIG. 13, the reference group generation unit 103 a sets i = 1, j = 0 (step S 312), refers to the determination result storage unit 112 of the connection determination unit 104, and selects the reference group Ref [i−1] [ It is determined whether both j] and the determination results of Ref [i-1] [j + 1] are "True" (step S313). When the reference group generation unit 103a determines that the determination results of both the reference group Ref [i-1] [j] and Ref [i-1] [j + 1] are not “True” (step S313-NO), the process is performed. Proceed to step S318.

  On the other hand, when the reference group generation unit 103a determines that the determination results of both the reference group Ref [i-1] [j] and Ref [i-1] [j + 1] are “True” (step S313-YES) , Select the three frames of the first and last frame of reference group Ref [i-1] [j] and the last frame of reference group Ref [i-1] [j + 1] as α, β, γ frames . The reference group generation unit 103a generates a reference group Ref [i] [j / 2] including the selected α, β, and γ frames, and generates the reference group Ref [i] [j / 2] as a reference group storage unit. It writes in 108 and makes it memorize (Step S314).

  When the information on the reference group Ref [i] [j / 2] is written to the reference group storage unit 108 by the reference group generation unit 103a, the connection determination unit 104 writes the written reference group Ref [i] [j / 2]. The combination determination process shown in FIG. 4 is performed with the .alpha., .Beta., And .gamma. Frames included in the frame being S, M, and E frames (step S315).

  The picture type selection unit 105a determines the determination result output from the combination determination unit 104 (step S316). If the determination result is “False” (step S316-False), the picture type selection unit 105a outputs, to the reference group generation unit 103a, instruction information that causes the process to proceed to step S318.

  On the other hand, when the determination result is "True" (step S316-True), the picture type selection unit 105a refers to the .alpha. Frame and the .gamma. Frame as the picture type of the .beta. Frame of the reference group Ref [i] [j / 2]. It is selected as a B picture. The picture type selection unit 105a uses the information indicating that the β frame of the reference group Ref [i] [j / 2] has been selected as the B picture, and the information indicating that the α frame and the γ frame are reference frames. The information is written in the storage unit 106 and stored. Also, the picture type selection unit 105a selects the picture type of the γ frame of the reference group Ref [i] [j / 2] as a P picture. The picture type selection unit 105 a writes and stores information indicating that the γ frame of the reference group Ref [i] [j / 2] is selected as the P picture in the picture type storage unit 106. The picture type selection unit 105a outputs instruction information for advancing the process to step S318 to the reference group generation unit 103a (step S317).

  The reference group generation unit 103a adds “2” to the value of j (step S318), and determines whether the value of j is less than N / 2 (step S319). If the reference group generation unit 103a determines that the value of j is less than N / 2 (YES in step S319), the processing from step S313 is repeated.

On the other hand, when it is determined that the value of j is not less than N / 2 (step S319-NO), the reference group generation unit 103a adds “1” to the value of i and sets j = 0 (step S320).
The reference group generation unit 103a determines whether the value of i is less than depth_max (here, depth_max = 3) (step S321). If the reference group generation unit 103a determines that the value of i is less than depth_max (YES in step S321), the process from step S313 is repeated. On the other hand, when it is determined that the value of i is not less than depth_max (step S 321 -NO), the reference group generation unit 103 a outputs, to the picture type selection unit 105 a, instruction information for selecting the reference frame for the P picture frame. .

  In response to the instruction information, the picture type selection unit 105a selects, for each of the frames selected as a P picture, a past P picture frame closest to the frame in display order as a reference frame of the frame. When there is no closest past P picture in display order, a frame of I picture is selected as a reference frame of the frame. The picture type selection unit 105a writes and stores information on the reference frame selected for each P picture in the picture type storage unit 106 (step S322).

  As a result, the picture type storage unit 106 stores the information of the coding structure finally constructed. The block output unit 107 temporarily stores the frame group received from the encoding target frame selection unit 101 in an internal storage area, and internally stores the frames in the order based on the encoding structure stored in the picture type storage unit 106. Read the frame from the storage area of The block output unit 107 decomposes each of the read frames into CU blocks in raster scan order and outputs the CU block as an encoding target block, and the coding structure construction unit 10a ends the processing for one frame group.

(Specific Example of Encoding Structure Construction Process of Second Embodiment)
Next, referring to FIG. 14 to FIG. 16, an example in the case of applying the coding structure construction process of the second embodiment shown in FIG. 12 and FIG. 13 to the frame group shown in FIG. explain. The encoding target frame selection unit 101 generates a frame group shown in FIG. 14A from the input video information. The frame group includes a scene change in the frames of frame number 4 and frame number 5.

  As shown in FIG. 14B, after the frame of frame number 0 is selected as an I picture by the I picture selection unit 102a, the reference group generation unit 103a includes the frame of frame number (0, 1, 2). The reference group Ref [0] [0] is written to the reference group storage unit 108 (steps S303 and S305). The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group Ref [0] [0] written in the reference group storage unit 108. Here, since there is no scene change, the connection determination unit 104. It is assumed that the evaluation value determination unit 111 of “No” outputs “True” (step S315).

  Since the determination result output from the connection determination unit 104 is “True”, the picture type selection unit 105 a uses the picture type of the frame of frame number 1 as the frame of frame number 0 and the frame of frame number 2 as the reference frame To be selected. The picture type selection unit 105 writes in the picture type storage unit 106 information indicating that the frame of frame number 2 has been selected as a B picture, and information indicating that the frames of frame number 0 and frame number 2 are reference frames. Remember.

  Further, the picture type selection unit 105a selects the picture type of the frame of frame number 2 as a P picture and writes information indicating that the frame of frame number 2 is selected as a P picture into the picture type storage unit 106 and stores the information. (Step S309).

  The reference group generation unit 103a adds 1 to j while the value of j is less than N / 2, and the reference group Ref [0] [1] including the frame of the frame number (2, 3, 4), the frame number Reference group Ref [0] [2] including frames of (4, 5, 6), reference group Ref [0] [3] including frames of frame numbers (6, 7, 8), frame numbers (8, 9 , 10) are written in the reference group storage unit 108 and stored therein. The connection determination unit 104 performs the connection determination process illustrated in FIG. 4 each time a new reference group is written to the reference group storage unit 108. As a result, as shown in FIG. 14B, for the reference group Ref [0] [2] including the scene change, “False” is output as the determination result, and for all other than the reference group Ref [0] [2] Will output "True".

  As a result, the picture type selection unit 105a selects a picture type as shown in FIG. 14B for the frames of frame numbers 1 to 10. That is, each of the reference groups Ref [0] [0], Ref [0] [1], Ref [0] [3], and Ref [0] [4] determined to be “True” by the connection determination unit 104. The B frame of the determination target frame is selected as a B picture referring to each of the A and C frames, and the C frame is selected as a P picture. On the other hand, the frames of the reference group Ref [0] [2] determined to be “False” by the combining determination unit 104, the B frame and the C frame are selected as P pictures.

  As shown in FIG. 13, the reference group generation unit 103a sets i = 1, j = 0 (step S312), and firstly, the reference group Ref [0 stored in the determination result storage unit 112 of the connection determination unit 104. Reference is made to the judgment results of reference group Ref [0] [1] and reference group Ref [0] [1]. Since the determination results of both the reference group Ref [0] [0] and the reference group Ref [0] [1] are “True” (YES in step S313), the reference group generation unit 103a selects the reference group Ref [0]. Reference group Ref [0] including the first and last frames of [0] and the last frame of reference group Ref [0] [1], that is, frames of frame numbers 0, 2 and 4 as α, β, and γ frames. 1] Generate [0].

  As shown in FIG. 15C, the reference group generation unit 103a writes and stores the generated reference group Ref [1] [0] in the reference group storage unit 108 (step S314). The connection determination unit 104 performs the connection determination process shown in FIG. 4 on the reference group Ref [1] [0] written in the reference group storage unit 108. Here, since there is no scene change, the evaluation value determination unit It is assumed that 111 outputs "True" (step S315). Since the determination result is “True” (step S316-True), the picture type selection unit 105a sets the picture type of the frame of frame number 2 which is the determination target frame of the reference group Ref [1] [0] to frame number 0 And a frame of frame number 4 is selected as a B picture as a reference frame.

  In the picture type storage unit 106, information indicating that the frame of frame number 2 is a P picture has already been written. Therefore, the picture type selection unit 105 a receives information indicating that the frame of frame number 2 has been selected as a B picture, and information indicating that the frames of frame numbers 0 and 4 are reference frames. Overwrite and store them.

  Further, the picture type selection unit 105a selects the picture type of the frame of frame number 4 that is a γ frame as a P picture. Although information indicating that the picture of frame number 4 is a P picture has already been written in the picture type storage unit 106, the picture type selection unit 105a has selected the frame of frame number 4 as a P picture. The information indicating that is written over the picture type storage unit 106 and stored (step S317).

  The reference group generation unit 103a adds 2 to the value of j to set j = 2 (step S318), and since the value of j is less than N / 2 (N = 10) (step S319-YES), the connection determination is performed. The determination results of the reference group Ref [0] [2] and the reference group Ref [0] [3] stored in the determination result storage unit 112 of the unit 104 are referred to. Since the determination result of the reference group Ref [0] [2] is “False”, the reference group generation unit 103a determines the determination results of the reference group Ref [0] [2] and the reference group Ref [0] [3]. It is determined that both are not "True" (step S313-NO). Therefore, the reference group Ref [1] [1] shown for convenience of explanation in FIG. 15C is not generated by the reference group generation unit 103a.

  The reference group generation unit 103a adds 2 to the value of j to set j = 4 (step S318), and since the value of j is less than N / 2 (N = 10) (step S319-YES), the reference group An attempt is made to refer to the determination results of Ref [0] [4] and the reference group Ref [0] [5]. However, since the reference group Ref [0] [5] does not exist, the reference group generation unit 103a determines that the determination results of both the reference group Ref [0] [4] and the reference group Ref [0] [5] It is determined that it is not "True" (step S313-NO). The reference group generation unit 103a adds 2 to the value of j to set j = 6 (step S318), and the value of j is not less than N / 2 (N = 10) (step S319-NO). “1” is added to the value to set i = 1 and j = 0 (step S320).

  Since the value of i is less than depth_max (depth_max = 3) (step S 321 -YES), the reference group generation unit 103 a uses the reference group Ref [1] stored in the determination result storage unit 112 of the connection determination unit 104. It is attempted to refer to the determination results of [0] and the reference group Ref [1] [1]. However, as described above, since the reference group Ref [1] [1] is not generated, the reference group generation unit 103a is configured to compare the reference group Ref [0] [4] and the reference group Ref [0] [5]. It is determined that the determination results are not both "True" (step S313-NO). Therefore, the reference group Ref [2] [0] shown for convenience of description in FIG. 15D is not generated by the reference group generation unit 103a.

  Thereafter, the processes of steps S318 and S319 are repeated until j is not less than N / 2, and further, "1" is added to the value of i in step S320, and i = 2, j = 0. Since the value of i is less than depth_max (step S 321 -YES), the process is continued, but as described above, the reference group Ref [2] [0] shown in FIG. Since it is not generated by 103a, the determination in step S313 is "NO". Again, the processing in steps S318 and S319 is repeated until j is not less than N / 2, and “1” is added to the value of i in step S320, i = 3, j = 0. Since the value of i is not less than depth_max (NO in step S 321), the reference group generation unit 103 a outputs, to the picture type selection unit 105 a, instruction information for selecting the reference frame for the P picture frame.

  In response to the instruction information, the picture type selection unit 105a selects, for each of the frames selected as a P picture, a past P picture frame closest to the frame in display order as a reference frame of the frame. When there is no closest past P picture in display order, a frame of I picture is selected as a reference frame of the frame. The picture type selection unit 105a writes and stores information on the reference frame selected for each P picture in the picture type storage unit 106 (step S322). As a result, the picture type storage unit 106 stores the coding structure having a hierarchical structure of B pictures of two layers, as shown in FIG.

With the configuration of the second embodiment described above, in the coding structure construction unit 10a, the coding target frame selection unit 101 selects a number of frames according to the size of the GOP determined in advance from the input video information, and sets the frame group. Generate The I picture selection unit 102a selects the first frame of the frame group as an I picture. The reference group generation unit 103a sets i = 0 and j = 0, and repeatedly adds “1” to j from the frame group with the frame numbers “2j”, “2j + 2 ⁱ ”, and “2j + 2 ^{(i + 1)} ”. A reference group Ref [0] [j] is generated which includes the selected three frames as A, B and C frames. The evaluation value calculation unit 110 of the combination determination unit 104 calculates three evaluation values of L0 cost, L1 cost, and Bi cost based on the A, B, and C frames included in the reference group. The evaluation value determination unit 111 selects the smaller one of the Bi cost and the L1 cost, and makes a determination based on the relative value based on the value of the L0 cost and the predetermined relative evaluation threshold values Th_min and Th_max. It is determined whether or not the reference relationship between the B frame, which is the target frame, and the A and C frames is combined. In addition, when the relative value is within the range not less than the value of Th_min and not more than the value of Th_max, the evaluation value determining unit 111 further determines the value of Bi cost based on the absolute evaluation threshold Th_abs. It is determined whether or not the reference relationship between the B frame, which is the determination target frame, and the A and C frames is combined. When the evaluation value determination unit 111 determines that the reference relationship between the B frame and the A and C frames is combined, the picture type selection unit 105a selects the B frame as a B picture having the A and C frames as reference frames. . That is, the coding structure construction unit 10a does not carry out an operation to perform actual coding, but calculates three evaluation values based on three frames, and calculates 3 based on the calculated 3 evaluation values. It is determined whether or not reference relationships of two frames are to be combined. For this reason, in the coding structure construction unit 10a of the second embodiment, it is possible to obtain a coding structure with high coding efficiency with a small amount of calculation.

  Further, the reference group generation unit 103a combines two adjacent reference groups determined by the evaluation value determination unit 111 to combine the reference relationship between the determination target frame and the first and last frames, and determines an overlapping frame as a determination target frame. Repeat creating a new reference group. In the connection determination unit 104, the reference group generation unit 103a performs connection determination processing based on the newly generated α, β, and γ frames of the reference group. As a result, in the coding structure construction unit 10a of the second embodiment, it is possible to construct a coding structure of two or more deep layers, which makes it possible to improve the coding efficiency. There is.

  In addition, in the coding structure construction units 10 and 10a according to the first and second embodiments, the minimum value of the absolute error sum in the case of performing the motion search between the frames is calculated as the evaluation value. Since it is not, it is possible to perform the joint determination with high accuracy even for a complex input video. Therefore, the coding structure construction units 10 and 10a according to the first and second embodiments can obtain a coding structure with high coding efficiency with a small amount of calculation.

  In the coding structure construction units 10 and 10a according to the first and second embodiments, as described with reference to FIG. 4, before performing the absolute evaluation of the Bi cost using the threshold for absolute evaluation in step S207, In step S204, relative evaluation is performed based on the L0 cost. Therefore, robust determination can be realized. On the other hand, in the technique described in Non-Patent Document 1, absolute evaluation is performed using only the minimum value of the coding cost as the evaluation value. Therefore, when the method of the technique described in Non-Patent Document 1 is applied to the frames shown in FIGS. 9 (ii) and (iii), assuming that the inter cost is sufficiently large, the same “150” value is obtained in both cases. It will be calculated. Therefore, in the technique described in Non-Patent Document 1, as in the evaluation value determination unit 111 of the first and second embodiments, it is assumed that the method of FIG. 9 (ii) is not combined, and the method of FIG. You can not make different decisions to combine.

  When combining is performed in both of FIG. 9 (ii) and (iii), in FIG. 9 (iii), since there is a merit in referring to the E frame which is the same scene in M frame, combining is considered effective. On the other hand, in FIG. 9 (ii), since the M frame and the E frame are different scenes, there is a high possibility of an erroneous determination. On the contrary, in the case of not combining, there is a high possibility that the determination in FIG. As described above, in the evaluation value determination unit 111 in the first and second embodiments, it is assumed that the method of FIG. 9 (ii) is not combined and the determination of combining the method of FIG. 9 (iii) is performed. As it can, coding efficiency can be improved in either case. This is an evaluation that reflects the merit of combining when the correlation with the E frame is high, that is, when the L1 cost or the Bi cost is sufficiently smaller than the L0 cost, when focusing on the M frame. It is because

  In the first and second embodiments described above, the connection determination unit 104 sets three frames, which are the determination target frames of the reference group generated by the reference group generation unit 103 and 103a, and the first and last frames. Although it is premised that the connection determination processing is performed, the configuration of the present invention is not limited to the embodiment. For example, the present invention may be applied to the technology described in Non-Patent Document 1. As described above, in the technique described in Non-Patent Document 1, intermediate frames that reference these are defined between a reference frame and a selected P frame. For the frame located between the reference frame and the intermediate frame, the cost is calculated in the case where these frames are B pictures that reference the reference frame and the intermediate frame. Further, with respect to a frame located between the intermediate frame and the P picture, the cost is calculated in the case where these frames are B pictures that reference the reference frame and the intermediate frame. Then, a combination that minimizes the calculated cost is selected as the final coding structure. Instead of these costs, the joint determination unit 104 may be applied to the technique in Non-Patent Document 1, and the coding structure may be constructed using the three evaluation values calculated by the joint determination unit 104.

  In the first and second embodiments described above, a B frame is selected as a P picture, a C frame is selected as a P picture, and a γ frame is selected as a P picture according to the result of connection determination. Also, when three frames can not be selected, the remaining frames are selected as P pictures, but the configuration of the present invention is not limited to this embodiment. For example, a frame to be a P picture may be selected in advance at an interval determined in advance from the I picture, or after all frames to be a B picture have been selected as a result of the combination determination, Frames other than the frame may be P pictures.

  In the first and second embodiments described above, three consecutive frames are generated as a reference group, but three or more frames may be generated.

  In the first and second embodiments described above, adjacent reference groups are generated so that one overlapping frame is included in adjacent reference groups, but one or more frames overlap. Adjacent reference groups may be generated. When a plurality of frames overlap, the determination target frame is selected from any of the overlapping frames.

  Also, in the first and second embodiments described above, the reference group generation unit 103, 103a generates a new reference group based on the determination result of the adjacent reference groups, and constructs a coding structure of two or more layers. However, processing for constructing only one layer may be performed.

  Further, in the first and second embodiments described above, the reference group generation unit 103, 103a combines the past adjacent reference groups in display order to generate a new reference group, but the present invention The embodiment of the invention is not limited to the embodiment. For example, adjacent reference groups in the future may be combined in display order, or adjacent reference groups in both the past and the future may be combined.

  In the first and second embodiments described above, the evaluation value determination unit 111 performs determination based on Th_min and Th_max, which are relative evaluation thresholds, and Th_abs, which is an absolute evaluation threshold. In this determination, the evaluation value determination unit 111 makes a determination based on whether it is less than Th_min, whether it exceeds Th_max, and whether it is less than Th_abs. The determination as to whether it is exceeded is an example, and it may be determined based on whether it is Th_min or less, Th_max or more, or Th_abs or less.

  The video encoding devices 1 and 1a in the first and second embodiments described above may be realized by a computer. In that case, a program for realizing this function may be recorded in a computer readable recording medium, and the program recorded in the recording medium may be read and executed by a computer system. Here, the “computer system” includes an OS and hardware such as peripheral devices. The term "computer-readable recording medium" refers to a storage medium such as a flexible disk, a magneto-optical disk, a ROM, a portable medium such as a ROM or a CD-ROM, or a hard disk built in a computer system. Furthermore, “computer-readable recording medium” dynamically holds a program for a short time, like a communication line in the case of transmitting a program via a network such as the Internet or a communication line such as a telephone line. It may also include one that holds a program for a certain period of time, such as volatile memory in a computer system that becomes a server or a client in that case. Further, the program may be for realizing a part of the functions described above, or may be realized in combination with the program already recorded in the computer system. It may be realized using a programmable logic device such as an FPGA (Field Programmable Gate Array).

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within the scope of the present invention.

10 Coding structure construction unit 101 Coding target frame selection unit 102 I picture selection unit 103 Reference group generation unit 104 Connection determination unit 105 Picture type selection unit 106 Picture type storage unit , 107 ... block output unit, 110 ... evaluation value calculation unit, 111 ... evaluation value determination unit, 112 ... determination result storage unit

Claims (8)

A video coding apparatus that performs interframe prediction coding, comprising:
A reference group generation unit that generates a reference group including a predetermined number of continuous frames of three or more from a frame group acquired from input video information;
Based on the first and last frames of the reference group generated by the reference group generation unit and any one determination target frame between the first and last frames, an evaluation value regarding the error between the frames is calculated. An evaluation value calculation unit to calculate;
Among the evaluation values calculated by the evaluation value calculation unit, based on relative values of other evaluation values based on the evaluation value between the determination target frame and the first frame, or with the relative value An evaluation value that determines whether or not the reference relationship between the determination target frame and the first and last frames is to be combined based on the determination target frame and the evaluation value between both the first and last frames. A judgment unit,
A picture type selection unit that selects a picture type of the frame included in the frame group based on the determination result of the evaluation value determination unit;
A video coding apparatus comprising: The evaluation value calculation unit
A first one-way evaluation value regarding the inter-frame error between the determination target frame and the first frame, and a second one regarding the error between the determination target frame and the last frame Calculating a one-way evaluation value and a two-way evaluation value regarding an error between the frames between the determination target frame and both the first and last frames;
The evaluation value determination unit
The smaller one of the second one-way evaluation value and the two-way evaluation value is selected, and the relative value of the selected one of the evaluation values relative to the first one-way evaluation value is selected. A value is calculated, and it is determined whether or not the reference relationship between the frame to be determined and the first and last frames is combined based on the calculated relative value and a predetermined relative evaluation threshold value. The video encoding device according to Item 1. The predetermined relative evaluation threshold includes a first relative evaluation threshold and a second relative evaluation threshold larger in value than the first relative evaluation threshold.
The evaluation value determination unit
It is determined whether or not the reference relationship between the frame to be determined and the first and last frames is combined based on whether or not the relative value is less than the first relative evaluation threshold.
When it is determined that the relative value is not less than the first relative evaluation threshold and the reference frame of the determination target frame is not the first and last frames, the relative value is for the first relative evaluation. In the case of the value of the range defined by the threshold value and the second relative evaluation threshold value, the determination target frame and the first and last frames are determined based on the bidirectional evaluation value and a predetermined absolute evaluation threshold value. The video encoding apparatus according to claim 2, wherein it is determined whether or not to combine reference relationships with frames. The reference group generation unit
From the three or more predetermined number of sheets including the reference group such that the first frame or the last frame of the reference group determined to be combined by the evaluation value determination unit becomes the determination target frame Generate a new reference group including a large number of consecutive frames,
The evaluation value calculation unit
The evaluation value regarding the error between the frames is calculated based on the first and last frames of the new reference group and the determination target frame,
The evaluation value determination unit
Among the evaluation values calculated by the evaluation value calculation unit, a relative value of another evaluation value based on the evaluation value between the determination target frame of the new reference group and the first frame or the relative value of the evaluation value The reference relationship between the determination target frame and the first and last frames is determined based on the relative value and the evaluation value between the determination target frame of the new reference group and both the first and last frames. The video coding apparatus according to any one of claims 1 to 3, which determines whether or not to combine. The reference group generation unit
When generating another reference group adjacent to the reference group, the three predetermined frames are overlapped such that the last frame of the reference group is the first frame of the other adjacent reference group Generating the reference group including the above number of consecutive frames,
When it is determined that the evaluation value determination unit combines the reference relationship between the determination target frame and the first and last frames in both two adjacent reference groups, the adjacent two reference groups are combined to each other. 5. The video encoding apparatus according to claim 4, wherein the new reference group is generated, and the overlapping frame is set as the determination target frame. The reference group generation unit
The video coding apparatus according to claim 5, wherein generation of the new reference group is repeated according to a value of the number of layers of the coding structure to be defined in advance. The picture type selection unit
And an I picture selection unit that acquires the frame group from the input video information and selects the first frame of the acquired frame group as an I picture,
The picture type selection unit
When the combination determination unit determines that the reference relationship between the determination target frame and the first and last frames is to be combined, the determination target frame is selected as a B picture having the first and last frames as reference frames,
The frame not selected as the I picture or the B picture is selected as the P picture, and the frame of the past P picture closest to the selected frame is selected in the display order of the frame group The reference frame of the frame, when there is no previous frame of the P picture closest to the selected frame, the frame of the I picture is the reference frame of the selected frame. 6. The video encoding device according to any one of 6.   The video encoding apparatus according to any one of claims 1 to 7, wherein the number of the predetermined three or more sheets is three.

Images