Image decoding device, image decoding method and program

Abstract

To improve encoding efficiency.SOLUTION: An image decoding device 200 includes a first intra-frame prediction unit 204 for generating a first predicted pixel based on decoded pixels and control information, a second intra-frame prediction unit 205 for generating a second predicted pixel by referring to a plurality of the decoded pixels based on common control information, an accumulation unit 208 for accumulating the decoded pixels, an inter-frame prediction unit 206 for generating a third predicted pixel based on the accumulated decoded pixels and control information, and an adder 207 for adding a prediction residual and the first to third predicted pixels to obtain a decoded pixel.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image decoding device, an image decoding method, and a program. [Background technology]

[0002] Non-Patent Documents 1 to 3 disclose intra block copy (IBC).

[0003] In IBC, pixels are referenced from the decoded pixel area of ​​the frame to be decoded and used as predicted pixels for the block to be decoded. Specifically, in IBC, pixels are copied from the reference block indicated by the block vector of the block to be decoded and used as predicted pixels.

[0004] Non-Patent Document 4 discloses that IBC holds two block vectors. When IBC holds two block vectors, it predicts a current block to be decoded, which is used as a prediction pixel, by referencing pixels from a decoded pixel area and taking a simple average. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] ITU-T H.266 / VVC [Non-Patent Document 2] X. [Non-Patent Document 3] M. Coban et al., “Algorithm description of Enhanced Compression Model 8 (ECM 8)”, JVET-AC2025, 2023 [Non-Patent Document 4] Y. Kidani et al., “Non-EE2: Bi-predictive IBC for natural and screen content”, JVET-AD0134, 2023 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Non-Patent Documents 1 to 3, there is only one block vector, so there is a problem that the prediction accuracy of the referenced pixel is not necessarily high.

[0007] In Non-Patent Document 4, by dividing the block vector into two, the respective reference pixels are averaged, so that when the prediction residuals of the two reference pixels are independent of each other, the variance of the prediction residuals of the reference pixels can be halved, and as a result, the prediction accuracy is improved, and the above-mentioned problem can be partially improved. However, since it is a simple average, there is still room for improvement in the coding performance.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide an image decoding device, an image decoding method, and a program with high coding efficiency. [Means for solving the problem]

[0009] A first feature of the present invention is an image decoding device comprising: a decoding unit that decodes control information and quantized values; an inverse quantization unit that inversely quantizes the quantized values ​​to obtain transform coefficients; an inverse transform unit that inversely transforms the transform coefficients to obtain predictive residuals; a first intra-frame prediction unit that generates a first predicted pixel based on decoded pixels and the control information; a second intra-frame prediction unit that generates a second predicted pixel by referencing a plurality of the decoded pixels based on the common control information; a storage unit that accumulates the decoded pixels; an inter-frame prediction unit that generates a third predicted pixel based on the accumulated decoded pixels and the control information; and an adder that adds the predictive residual and the first to third predicted pixels to obtain the decoded pixel.

[0010] A second feature of the present invention is an image decoding method comprising the steps of: decoding control information and quantization values; inversely quantizing the quantization values ​​to obtain transform coefficients; inversely transforming the transform coefficients to obtain predictive residuals; generating a first predicted pixel based on decoded pixels and the control information; generating a second predicted pixel by referencing a plurality of the decoded pixels based on the common control information; accumulating the decoded pixels; generating a third predicted pixel based on the accumulated decoded pixels and the control information; and obtaining the decoded pixel by adding the predictive residuals to the first to third predicted pixels.

[0011] A third feature of the present invention is a program for causing a computer to function as an image decoding device, the image decoding device comprising: a decoding unit that decodes control information and quantized values; an inverse quantization unit that inversely quantizes the quantized values ​​to obtain transform coefficients; an inverse transform unit that inversely transforms the transform coefficients to obtain predictive residuals; a first intra-frame prediction unit that generates a first predicted pixel based on decoded pixels and the control information; a second intra-frame prediction unit that generates a second predicted pixel by referencing a plurality of the decoded pixels based on the common control information; a storage unit that accumulates the decoded pixels; an inter-frame prediction unit that generates a third predicted pixel based on the accumulated decoded pixels and the control information; and an adder that adds the predictive residual and the first to third predicted pixels to obtain the decoded pixel. Effect of the Invention

[0012] According to the present invention, it is possible to provide an image decoding device, an image decoding method, and a program with high coding efficiency. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of functional blocks of an image decoding device 200 according to an embodiment. [Diagram 2]FIG. 2 is a diagram illustrating an example of a BV input to the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Diagram 3] FIG. 3 is a diagram showing an example of the relationship between BV, BVP, and BVD when two BVs exist in a conventional method. [Figure 4] FIG. 4 is a diagram for explaining an example of a method for deriving a BVP in the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Diagram 5] FIG. 5 is a diagram illustrating an example of a method for deriving the BVD in the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of a method for deriving the BVD in the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Figure 7] FIG. 7 is a diagram illustrating an example of a method for deriving the BVD in the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Figure 8] FIG. 8 is a diagram illustrating an example of a method for deriving the BVD in the second intra-frame predictor 205 of the image decoding device 200 according to an embodiment. [Figure 9] FIG. 9 is a flowchart showing an example of a method for setting a correction method on a sequence basis. [Figure 10] FIG. 10 is a flowchart showing an example of a method for applying two IBC BVP modes on a block-by-block basis. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the components in the following embodiments can be appropriately replaced with existing components, and various variations including combinations with other existing components are possible. Therefore, the description of the following embodiments does not limit the content of the invention described in the claims.

[0015] First Embodiment An image decoding device 200 according to this embodiment will be described below with reference to Figures 1 to 10. Figure 1 is a diagram showing an example of functional blocks of the image decoding device 200 according to this embodiment.

[0016] As shown in FIG. 1, the image decoding device 200 includes a code input unit 210, a decoding unit 201, an inverse quantization unit 202, an inverse transformation unit 203, a first intra-frame prediction unit 204, a second intra-frame prediction unit 205, an inter-frame prediction unit 206, an adder 207, an accumulation unit 208, and an image output unit 220.

[0017] The code input unit 210 is configured to obtain code information coded by an image coding device.

[0018] The decoding unit 201 is configured to decode the control information and the quantized value from the code information input from the code input unit 210. For example, the decoding unit 201 is configured to output the control information and the quantized value by performing variable length decoding on the code information.

[0019] Here, the quantized value is sent to the inverse quantization unit 202, and the control information is sent to the first intra-frame prediction unit 204, the second intra-frame prediction unit 205, and the inter-frame prediction unit 206. Note that such control information includes information necessary for controlling the first intra-frame prediction unit 204, the second intra-frame prediction unit 205, the inter-frame prediction unit 206, etc., and may include header information such as a sequence parameter set, a picture parameter set, a picture header, a slice header, etc.

[0020] The inverse quantization unit 202 is configured to inverse quantize the quantized values ​​sent from the decoding unit 201 to generate transform coefficients. The transform coefficients are sent to the inverse transform unit 203.

[0021] The inverse transform unit 203 is configured to inversely transform the transform coefficients sent from the inverse quantization unit 202 to generate prediction residuals. The prediction residuals are sent to an adder 207.

[0022] The first intra-frame prediction unit 204 is configured to generate a first predicted pixel to be added to the prediction residual by the adder 207, based on the decoded pixel obtained via the adder 207 and the control information decoded by the decoding unit 201. The first predicted pixel is sent to the adder 207.

[0023] The inter-frame prediction unit 206 is configured to generate a third predicted pixel to be added to the prediction residual by the adder 207, based on the decoded pixel obtained by referring to the storage unit 208 and the control information decoded by the decoding unit 201. The third predicted pixel is sent to the adder 207.

[0024] The storage unit 208 is configured to cumulatively store the decoded pixels sent from the adder 207. The inter-frame prediction unit 206 refers to the decoded pixels via the storage unit 208.

[0025] The adder 207 is configured to add the prediction residual sent from the inverse transform unit 203 to any one of the first to third predicted pixels sent from the first intra-frame prediction unit 204, the second intra-frame prediction unit 205, and the inter-frame prediction unit 206 to obtain a decoded pixel. The decoded pixel is sent to the image output unit 220, the storage unit 208, the first intra-frame prediction unit 204, and the second intra-frame prediction unit 205.

[0026] (Second frame intra prediction unit 205) Hereinafter, a method for deriving the second predicted pixel by the second intra-frame predictor 205 will be described.

[0027] The role of the second intra-frame prediction unit 205 is to derive one or more block vectors (hereinafter referred to as BV) for the block to be decoded, and to predict the pixels of the block referenced by the BV (second intra-frame prediction), in order to compensate the block to be decoded with high accuracy in the downstream adder 207.

[0028] An example of such second frame prediction is intra block copy (hereinafter, referred to as IBC) disclosed in Non-Patent Document 4.

[0029] In the following, as an example, a case will be described in which two BVs are input to the second intra-frame prediction unit 205 in IBC BVP mode as shown in FIG.

[0030] First, the BV is expressed as a combination of the block vector prediction (hereinafter, abbreviated as BVP) and the block vector difference (hereinafter, abbreviated as BVD) of the BV, as shown in the following equation.

[0031] BV=BVP+BVD At this time, the image coding apparatus constructs a BVP candidate list using BVs held by neighboring blocks and BVs used in the past as BVP candidates, and signals the BVP as an index of the BVP candidate list.

[0032] On the other hand, BVD is derived and signaled as the difference of BVP over BV, ie, BVD=BV-BVP.

[0033] In addition, in the conventional method, when two BVs exist, they are encoded (decoded) independently, as shown in FIG. 3, so it is necessary to signal BVP1, BVP2, BVD1, and BVD2.

[0034] The second intra-frame predictor 205 is configured to combine the BVPs into one BVP when two BVs exist.

[0035] As shown in Figure 4, when two BVs are BV1 and BV2, the second intra-frame prediction unit 205 may be configured to set the BVP candidate that minimizes the sum of the difference from BV1 and the difference from BV2 as the BVP, for example, as shown in the following equation.

[0036] BVP=argmin(|BV1-BVP|+|BV2-BVP|) In the example of FIG. 4, BVP1 in FIG. 3 minimizes the above sum more than BVP2 in FIG. 3, so BVP1 in FIG. 3 is drawn as the BVP in FIG.

[0037] According to this configuration, the number of BVP signaling lines is reduced from two to one, which has the effect of improving coding efficiency.

[0038] Since BVD1 and BVD2 are each derived from one BVP and signaled as BVD1=BV1-BVP and BVD2=BV2-BVP, decoding section 201 decodes BV1 and BV2 using the following equation.

[0039] BV1=BVP+BVD1 BV2=BVP+BVD2 At this time, the second intra-frame predictor 205 can decode either BVD1 or BVD2 based on the other. For example, the shorter of BVD1 and BVD2 may be decoded first, and the other may be decoded using the length of the shorter decoded bit.

[0040] In this case, by encoding the shorter of BVD1 and BVD2, it is possible to omit the signaling indicating the length of BVD. That is, the second intra-frame prediction unit 205 may be configured to omit decoding the signaling indicating the length of BVD.

[0041] As shown in Figure 5, to explain a numerical example, when BVD1 = (-9, -12) and BVD2 = (4, -3), the second intra-frame prediction unit 205 may be configured to decode the shorter BVD2, and then decode (-6, -8) as BVDD, which is obtained by removing the length 5 of BVD2 from BVD1 = (-9, -12), and decode the other BVD1 by adding the length 5 of BVD2 to the extension of (-6, -8).

[0042] Alternatively, when the length of BVD2 is a decimal number, the second intra-frame prediction unit 205 may simplify the process by using coordinates that are integers as a reference.

[0043] For example, on the image encoding device side, from a total of eight possibilities, including four possibilities of positive / negative inversion of the x and y components of BVD2 and four possibilities of permutation of the x and y components, the point BVDP that is the smallest distance from BVD1 is selected, and the difference BVDD between BVD1 and BVDP is encoded.

[0044] On the image decoding device 200 side, BVD1 is derived by adding BVDD and BVDP.

[0045] As shown in Figure 6, using a numerical example, when BVD1 = (-9, -12) and BVD2 = (5, -3), among the BVDP candidates for BVD2, (5, -3), (5, 3), (-5, -3), (-5, 3), (-3, 5), (-3, -5), (3, 5), and (3, -5), the one with the smallest distance from BVD1, (-3, -5), is selected, and BVDD = (-6, -7), which is the difference between BVD1 = (-9, -12) and BVDP = (-3, -5), is signaled.

[0046] Here, the BVDP may or may not be signaled.

[0047] If not signaled, the BVDP that minimizes the difference between the pixel referenced using the 8 or 4 possible points of the BVDP and the pixel referenced by BVD2 can be adopted.

[0048] In either case, the amount of BVD coding is reduced, resulting in improved coding efficiency.

[0049] In addition to the above-mentioned processing, the second intra-frame predictor 205 may be configured to combine the BVDs into one BVD when two BVs exist.

[0050] Specifically, the second intra-frame prediction unit 205 is configured to decode a vector BVD that connects the midpoint of two BVs from the BVP, and to search for a correction vector BVR centered on the midpoint.

[0051] For example, as shown in FIG. 7, when two BVs are BV1 and BV2, first, the second intra-frame predictor 205 decodes a BVD that satisfies the following formula.

[0052] BVD=(BV1+BV2) / 2-BVP Secondly, the second intra-frame predictor 205 searches for a combination that minimizes the pixel difference when the pixels are moved point-symmetrically by the same correction vector BVR with the midpoint (BVP+BVD) as the center.

[0053] Third, the second intra-frame predictor 205 derives BV1 and BV2 using the following equation.

[0054] BV1=BVP+BVD+BVR BV2=BVP+BVD-BVR According to this configuration, the number of BVPs and BVDs is reduced from two to one, thereby improving the coding efficiency.

[0055] At this time, in order to reduce the effort required for searching for the correction vector BVR, the second intra-frame predictor 205 may decode information related to the BVR.

[0056] For example, the second intra-frame predictor 205 can decode the BVR itself. In this case, the BVD and the BVR are expressed by the following equations.

[0057] BVD=(BV1+BV2) / 2-BVP BVR=(BV1-BV2) / 2 When BV1 and BV2 are sufficiently similar, the amount of code for BVR is reduced compared to the amount of code for BV1 and BV2, resulting in improved coding efficiency.

[0058] Alternatively, the image coding device may code only the length |BVR| of the BVR, the angle ∠BVR, the x coordinate of the BVR, or the y coordinate of the BVR.

[0059] When encoding only |BVR|, the BVR search range is limited to the circumference of |BVR|, when encoding only ∠BVR, the BVR search range is limited to the line of ∠BVR, and when encoding only the x or y coordinate of the BVR, the BVR search range is limited to the corresponding straight line, thereby reducing the decoding processing time.

[0060] Furthermore, if the midpoint of two BVs cannot be represented with the resolution of the BVs, the midpoint may be quantized in order to maintain the resolution of the midpoint.

[0061] For example, when BV has integer precision and BV1 and BV2 are even and odd numbers, respectively, the midpoint cannot be expressed as an integer, so the second intra-frame prediction unit 205 rounds the BV to an integer of the same resolution by quantization, and then derives BVD.

[0062] Here, when rounding to the first decimal place, the four possibilities for each x and y are rounded to one point, so the second intra-frame prediction unit 205 searches for coordinates that minimize the error with the reference destination of the former BV to derive the other BV that is different from the BV used to derive the BVD.

[0063] As shown in Figure 8, using a numerical example, when BV1 = (-10, 6) and BV2 = (-3, 9), the second intra-frame prediction unit 205 quantizes the midpoint to (-7, 8) so that the decimal point is rounded off, and the residual with BV1 is BVR = (-3, -2).

[0064] If the midpoint after quantization is (-7,8), the coordinates of the candidate midpoints to which -BVR should be applied to derive BV2 are four points: (-7,8), (-6,8), (-7,7), and (-6,7).Therefore, the second intra-frame prediction unit 205 applies -BVR to each of these points to derive the coordinates that minimize the reference error.

[0065] That is, the second intra-frame predictor 205 calculates the error between (-4,10), (-3,10), (-4,9), and (-3,9) and (-10,6), and sets the minimum coordinate as BV2.

[0066] According to this configuration, the resolution of the BVD and BVR is not increased, and therefore, improvement in coding efficiency is expected.

[0067] Note that the effect of simplifying the processing can be obtained by limiting the target to which the processing of the second intra-frame predictor 205 is applied to blocks of a specific size.

[0068] Hereinafter, the control information decoded by the decoding unit 201 for the second intra-frame prediction will be described.

[0069] The input code information may include a sequence parameter set (SPS) that summarizes control information for each sequence.

[0070] The input coded information may also include a picture parameter set (PPS) or a picture header (PH) that summarizes control information for each picture.

[0071] Furthermore, the input coded information may include a slice header (SH) that summarizes control information for each slice.

[0072] A method for setting the correction method on a sequence-by-sequence basis will be described below. Figure 9 shows a flowchart illustrating an example of such a method.

[0073] As shown in FIG. 9, in step S101, the decoding unit 201 determines whether or not sps_biibc_enabled_flag is 1 in the sequence parameter set.

[0074] Here, sps_biibc_enabled_flag is a syntax element that controls the presence or absence of bi-predictive IBC. When sps_biibc_enabled_flag is 1, this indicates that the bi-predictive IBC is enabled, and when sps_biibc_enabled_flag is 0, this indicates that the bi-predictive IBC is disabled.

[0075] If sps_biibc_enabled_flag is 1, the operation proceeds to step S102, and if sps_biibc_enabled_flag is 0, the operation ends.

[0076] In step S202, the decoding unit 201 decodes sps_biibc_mode.

[0077] Here, sps_biibc_mode is a syntax element that controls the bi-prediction IBC method.

[0078] By using sps_biibc_mode, the bi-predictive IBC method can be changed according to image characteristics on a sequence-by-sequence basis, which is expected to maximize coding efficiency.

[0079] For example, for sequences composed of CG, the pixel distribution is often composed of the same values, so the search range of the bi-predictive IBC can be set to be narrower, whereas for sequences composed of natural images, the pixel distribution is diverse, so the search range of the bi-predictive IBC can be set to be wider, thereby maximizing coding efficiency.

[0080] When the correction method is set on a picture-by-picture basis, the decoding unit 201 similarly decodes pps_biibc_enabled_flag and pps_biibc_mode in the picture parameter set or the picture header.

[0081] By using pps_biibc_mode, the correction method can be changed on a picture-by-picture basis according to the image characteristics, which is expected to maximize coding efficiency.

[0082] For example, for pictures composed of CG, the pixel distribution is often composed of the same values, so the search range of the bi-predictive IBC can be set to be narrower, whereas for pictures composed of natural images, the pixel distribution is diverse, so the search range of the bi-predictive IBC can be set to be wider, thereby maximizing coding efficiency.

[0083] When the correction method is set on a slice-by-slice basis, the decoding unit 201 similarly decodes sh_biibc_enabled_flag and sh_biibc_mode in the slice header.

[0084] By using sh_biibc_mode, the correction method can be changed according to the image characteristics on a slice-by-slice basis, which is expected to maximize coding efficiency.

[0085] For example, for slice regions composed of CG, the pixel distribution is often composed of the same values, so the search range of the bi-predictive IBC can be set to be narrower, whereas for slice regions composed of natural images, the pixel distribution is diverse, so the search range of the bi-predictive IBC can be set to be wider, thereby maximizing coding efficiency.

[0086] By setting only the upper layers, it is possible to suppress an increase in the amount of code, and by setting the lower layers as well and then prioritizing the settings in the lower layers, adaptive control is possible.

[0087] Alternatively, if the correction method is set in advance, decoding of the correction method itself can be omitted.

[0088] In the above example, the method of setting the bi-predictive IBC method on a sequence basis, a picture basis, or a slice basis has been described, but the method may be directly selected on a block basis (described later) without setting these. In this case, the increase in header information described above can be avoided.

[0089] A method for applying two IBC BVP modes on a block-by-block basis will be described below. Figure 10 shows a flowchart of an example of such a method.

[0090] As shown in FIG. 10, in step S201, the decoding unit 201 determines whether any one of sps_biibc_enabled_flag, pps_biibc_enabled_flag, and sh_biibc_enabled_flag is 1 or not.

[0091] If neither is 1, the operation ends, and if either is 1, the operation proceeds to step S202.

[0092] In step S202, the decoding unit 201 determines whether the current block to be decoded is in two-line IBC BVP mode.

[0093] If Yes, the operation proceeds to step S203; if No, the operation ends.

[0094] In step S203, the decoding unit 201 decodes cu_biibc_mode, which is a control signal indicating that the current block is in the two-line IBC BVP mode.

[0095] In step S204, the decoding unit 201 decodes the control signal representing the BVP.

[0096] In step S205, the decoding unit 201 decodes the control signal representing the BVD in accordance with cu_biibc_mode.

[0097] Alternatively, the decoding unit 201 decodes either cu_bvd1 or cu_bvd2 and a control signal representing BVDD.

[0098] In another modified example, the decoder 201 decodes a control signal representing a BVR or a control signal that reduces the effort required to search for a BVR, according to cu_biibc_mode.

[0099] According to this embodiment, by unifying at least one of BVP and BVD in decoding BV of bi-predictive IBC, decoding can be performed with a relatively small amount of code, and coding efficiency can be improved.

[0100] The above-described image decoding device 200 may be realized as a program that causes a computer to execute each function (each process). [Industrial Applicability]

[0101] According to this embodiment, for example, it is possible to improve the overall service quality in video communication, which makes it possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation." [Explanation of symbols]

[0102] 200...Image decoding device 201…Decoding section 202...Inverse quantization section 203…Inverse conversion section 204...First frame intra prediction unit 205...Second frame intra prediction unit 206...Interframe prediction unit 207…Adder 208…Storage section 210...Code input section 220...Image output unit

Claims

1. An image decoding device, comprising: a decoding unit for decoding the control information and the quantization value; an inverse quantization unit that inversely quantizes the quantized values ​​to generate transform coefficients; an inverse transform unit that inversely transforms the transform coefficients to generate prediction residuals; a first intra-frame prediction unit that generates a first predicted pixel based on a decoded pixel and the control information; a second intra-frame prediction unit that generates a second predicted pixel by referring to a plurality of the decoded pixels based on the common control information; a storage unit that stores the decoded pixels; an inter-frame prediction unit that generates a third predicted pixel based on the accumulated decoded pixels and the control information; an adder that adds the prediction residual and the first to third predicted pixels to obtain the decoded pixel.

2. 2 . The image decoding device according to claim 1 , wherein the second intra-frame predictor combines block vector predictions into one when two block vectors exist.

3. The image decoding device according to claim 1, characterized in that the second intra-frame prediction unit selects a block vector prediction candidate that minimizes the sum of the difference from the first block vector and the difference from the second block vector as the block vector prediction.

4. 2 . The image decoding device according to claim 1 , wherein the second intra-frame prediction section derives a first block vector difference and a second block vector difference from one block vector prediction.

5. 2. The image decoding device according to claim 1, wherein the second intra-frame prediction unit decodes one of two block vector differentials by using a length of the other block vector differential.

6. The image decoding device according to claim 5 , wherein the second intra-frame prediction section omits decoding of signaling indicating whether the first block vector difference and the second block vector difference are long or short.

7. 6. The image decoding device according to claim 5, wherein the second intra-frame predictor uses, as a reference, coordinates that are integers when the length of the one block vector difference is a decimal number.

8. 8. The image decoding device according to claim 7, wherein the second intra-frame prediction section decodes a difference between a point having a minimum distance from the one block vector difference and the one block vector difference.

9. The image decoding device described in claim 8, characterized in that the second intra-frame prediction unit does not decode the signaling of the minimum point, but instead adopts the point at which the difference between the pixel referenced using the point that is likely to be the minimum point and the pixel referenced by the one of the block vector differentials is the smallest as the minimum point.

10. 2 . The image decoding device according to claim 1 , wherein the second intra-frame predictor combines block vector differences into one block vector when two block vectors exist.

11. 2. The image decoding device according to claim 1, wherein the second intra-frame predictor decodes a vector connecting midpoints of two block vectors from a block vector prediction.

12. 2. The image decoding device according to claim 1, wherein the second intra-frame predictor searches for a correction vector centered on a midpoint between two block vectors.

13. 13. The image decoding device according to claim 12, wherein the second intra-frame prediction section searches for a combination that minimizes a pixel difference when only the correction vector is moved point-symmetrically.

14. The image decoding device according to claim 12 , wherein the second intra-frame prediction section decodes information relating to the correction vector.

15. The image decoding device according to claim 14, characterized in that the second intra-frame prediction unit decodes the correction vector itself, the length of the correction vector, the angle of the correction vector, and part of the coordinates of the correction vector as information regarding the correction vector.

16. The image decoding device according to claim 11 , wherein the second intra-frame predictor quantizes the midpoint.

17. The image decoding device described in claim 16, characterized in that the second intra-frame prediction unit searches for coordinates that minimize an error between a block vector different from a block vector used to derive the block vector difference and the reference destination of the block vector used to derive the block vector difference.

18. 2. The image decoding device according to claim 1, wherein the process of the second intra-frame prediction section is applied only to blocks of a specific size.

19. 1. An image decoding method, comprising: decoding the control information and the quantized values; dequantizing the quantized values ​​to obtain transform coefficients; inverse transforming the transform coefficients to obtain a prediction residual; generating a first predicted pixel based on the decoded pixel and the control information; generating a second predicted pixel by referring to a plurality of the decoded pixels based on the common control information; storing the decoded pixels; generating a third predicted pixel based on the accumulated decoded pixels and the control information; and adding the prediction residual to the first to third predicted pixels to obtain the decoded pixel.

20. A program for causing a computer to function as an image decoding device, The image decoding device comprises: a decoding unit for decoding the control information and the quantization value; an inverse quantization unit that inversely quantizes the quantized values ​​to generate transform coefficients; an inverse transform unit that inversely transforms the transform coefficients to generate prediction residuals; a first intra-frame prediction unit that generates a first predicted pixel based on a decoded pixel and the control information; a second intra-frame prediction unit that generates a second predicted pixel by referring to a plurality of the decoded pixels based on the common control information; a storage unit that stores the decoded pixels; an inter-frame prediction unit that generates a third predicted pixel based on the accumulated decoded pixels and the control information; an adder that adds the prediction residual and the first to third predicted pixels to obtain the decoded pixel.

Images