Image encoding method and image decoding method

Abstract

To provide an image coding and image decoding method with high coding efficiency.SOLUTION: An image coding method includes: a first step of selecting one or more motion reference blocks from coded pixel blocks having motion information; a second step of selecting, from the motion reference blocks, one or more usable blocks that have different types of motion information from each other and are pixel blocks having candidates for motion information to be applied to a coding target block; a third step of selecting one selection block from the usable blocks; a fourth step of creating a prediction image of the coding target block by using the motion information of the selection block; a fifth step of coding a prediction error between the prediction image and an original image; and a sixth step of referring to a code table predetermined according to the number of usable blocks to code selection information for specifying the selection block.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention relates to encoding and decoding methods for moving and still images. [Background technology]

[0002] In recent years, video coding methods with significantly improved coding efficiency have been recommended by the ITU-T and ISO / IEC in the form of ITU-T Rec. H.264 and ISO / IEC 14496-10 (hereinafter referred to as H.264). In H.264, prediction, transformation, and entropy coding processes are performed in rectangular block units (e.g., 16×16 pixel block units, 8×8 pixel block units, etc.). In the prediction process, motion compensation is performed on a rectangular block to be coded (a target block), in which temporal prediction is performed by referencing a previously coded frame (a reference frame). This motion compensation requires coding motion information, including a motion vector as spatial shift information between the target block and a reference block in the reference frame, and sending the coded information to the decoding side. Furthermore, when motion compensation is performed using multiple reference frames, reference frame numbers must also be coded along with the motion information. This may result in an increase in the amount of code associated with the motion information and reference frame numbers.

[0003] One example of a method for calculating a motion vector in motion compensation prediction is a direct mode in which a motion vector to be assigned to a block to be coded is derived from motion vectors assigned to already coded blocks, and a predicted image is generated based on the derived motion vector (see Patent Documents 1 and 2). In the direct mode, the amount of coding required for motion information can be reduced because the motion vector is not coded. The direct mode is adopted in, for example, H.264 / AVC. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4020789 [Patent Document 2] U.S. Patent No. 7,233,621 Summary of the Invention [Problem to be solved by the invention]

[0005] In direct mode, the motion vector of the current block is predicted and generated using a fixed method in which the motion vector is calculated from the median value of the motion vectors of the blocks that have already been coded and are adjacent to the current block, which means that there is little flexibility in calculating the motion vector.

[0006] To increase the degree of freedom in motion vector calculation, a method has been proposed in which one of multiple coded blocks is selected and the motion vector is assigned to the block to be coded. In this method, selection information identifying the selected block must always be transmitted so that the decoding side can identify the selected coded block. Therefore, when selecting one of multiple coded blocks to assign to the block to be coded, there is a problem that the amount of coding related to the selection information increases.

[0007] The present invention has been made to solve the above problems, and has as its object to provide an image coding and decoding method with high coding efficiency. [Means for solving the problem]

[0008] An image encoding method according to one embodiment of the present invention includes a first step of selecting at least one motion reference block from among encoded pixel blocks having motion information; a second step of selecting at least one available block from the motion reference blocks, which is a pixel block having candidate motion information to be applied to a block to be encoded, the pixel block having different motion information from each other; a third step of selecting one selected block from among the available blocks; a fourth step of generating a predicted image of the block to be encoded using the motion information of the selected block; a fifth step of encoding a prediction error between the predicted image and an original image; and a sixth step of encoding selection information that identifies the selected block by referring to a code table predetermined according to the number of available blocks.

[0009] An image decoding method according to another embodiment of the present invention includes a first step of selecting at least one motion reference block from decoded pixel blocks having motion information; a second step of selecting at least one available block from the motion reference blocks, which is a pixel block having candidate motion information to be applied to a block to be decoded, the candidate block having different motion information; a third step of obtaining selection information for identifying the selected block by decoding input encoded data with reference to a code table predetermined according to the number of available blocks; a fourth step of selecting one selected block from the available blocks according to the selection information; a fifth step of generating a predicted image of the block to be decoded using the motion information of the selected block; a sixth step of decoding a prediction residual of the block to be decoded from the encoded data; and a seventh step of obtaining a decoded image from the predicted image and the prediction residual. [Effects of the Invention]

[0010] According to the present invention, it is possible to improve coding efficiency. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a block diagram schematically illustrating a configuration of an image encoding device according to a first embodiment. [Figure 2A] 2 is a diagram showing an example of the size of a macroblock, which is a processing unit for encoding in the image decoding section shown in FIG. 1. FIG. [Figure 2B] 1. FIG. 4 is a diagram showing another example of the size of a macroblock, which is a processing unit for encoding by the image decoding unit shown in FIG. [Figure 3] 2 is a diagram showing an order in which the image encoding unit shown in FIG. 1 encodes pixel blocks in a frame to be encoded. [Figure 4] 2 is a diagram showing an example of a motion information frame held by a motion information memory shown in FIG. 1. FIG. [Figure 5] 2 is a flowchart showing an example of a procedure for processing the input image signal of FIG. 1. [Figure 6A] 2 is a diagram showing an example of inter prediction processing executed by the motion compensation unit of FIG. 1. FIG. [Figure 6B] 1. FIG. 4 is a diagram showing another example of the inter prediction process performed by the motion compensation unit of FIG. [Figure 7A] FIG. 10 is a diagram showing an example of the size of a motion compensation block used in inter prediction processing. [Figure 7B] FIG. 10 is a diagram showing another example of the size of a motion compensation block used in inter prediction processing. [Figure 7C] FIG. 10 is a diagram showing yet another example of the size of a motion compensation block used in inter prediction processing. [Figure 7D] FIG. 10 is a diagram showing another example of the size of a motion compensation block used in inter prediction processing. [Figure 8A] FIG. 10 is a diagram showing an example of the arrangement of spatial and temporal motion reference blocks. [Figure 8B] FIG. 10 is a diagram showing another example of the arrangement of spatial motion reference blocks. [Figure 8C] 8C is a diagram showing the relative position of a spatial motion reference block with respect to the encoding target block shown in FIG. 8B. [Figure 8D] FIG. 10 is a diagram showing another example of the arrangement of time-direction motion reference blocks. [Figure 8E] FIG. 10 is a diagram showing yet another example of the arrangement of time-direction motion reference blocks. [Figure 8F] FIG. 10 is a diagram showing yet another example of the arrangement of time-direction motion reference blocks. [Figure 9] 10 is a flowchart showing an example of a method by which an available block acquisition unit in FIG. 1 selects available blocks from among motion reference blocks. [Figure 10] 10 is a diagram showing an example of available blocks selected from the motion reference blocks shown in FIG. 8 according to the method of FIG. 9. FIG. [Figure 11] 2 is a diagram showing an example of available block information output by an available block acquisition unit in FIG. 1; FIG. [Figure 12A] 1. FIG. 4 is a diagram showing an example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 12B] 1. FIG. 4 is a diagram showing another example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 12C] 1. FIG. 9 is a diagram showing yet another example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 12D] 1. FIG. 4 is a diagram showing another example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 12E] 1. FIG. 9 is a diagram showing yet another example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 12F] 1. FIG. 4 is a diagram showing another example of determination of identity of motion information between blocks by the available block acquisition unit of FIG. [Figure 13] FIG. 2 is a block diagram illustrating a schematic configuration of a prediction unit in FIG. [Figure 14] 14 is a diagram showing a group of motion information output by the time direction motion information acquisition unit in FIG. 13. FIG. [Figure 15] 14 is an explanatory diagram illustrating an interpolation process with small pixel accuracy that can be used in the motion compensation process by the motion compensation unit of FIG. 13. FIG. [Figure 16]14 is a flowchart showing an example of the operation of the prediction unit in FIG. 13. [Figure 17] 14 is a diagram showing how the motion compensation unit in FIG. 13 copies motion information of a time-direction motion reference block to a current block to be coded. [Figure 18] 2 is a block diagram showing a schematic configuration of a variable-length coding unit in FIG. 1. FIG. [Figure 19] FIG. 10 is a diagram illustrating an example of generating syntax according to available block information. [Figure 20] FIG. 10 is a diagram showing an example of binarization of selected block information syntax corresponding to available block information. [Figure 21] FIG. 10 is an explanatory diagram illustrating scaling of motion information. [Figure 22] FIG. 1 is a diagram illustrating a syntax structure according to an embodiment. [Figure 23A] FIG. 2 is a diagram illustrating an example of a macroblock layer synctas according to the first embodiment. [Figure 23B] FIG. 10 is a diagram showing another example of a macroblock layer synctas according to the first embodiment. [Figure 24A] FIG. 10 is a diagram showing mb_type in the case of B slices in H.264 and a code table corresponding to the mb_type. [Figure 24B] FIG. 2 is a diagram illustrating an example of a code table according to the embodiment. [Figure 24C] FIG. 10 is a diagram showing mb_type in the case of P slices in H.264 and a code table corresponding to the mb_type. [Figure 24D] FIG. 10 is a diagram showing another example of a code table according to the embodiment. [Figure 25A] FIG. 10 is a diagram illustrating an example of mb_type in a B slice and a code table corresponding to the mb_type according to an embodiment. [Figure 25B] FIG. 10 is a diagram illustrating another example of mb_type in a P slice and a code table corresponding to the mb_type according to an embodiment. [Figure 26] FIG. 10 is a block diagram schematically illustrating the configuration of an image encoding device according to a second embodiment. [Figure 27]FIG. 27 is a block diagram schematically illustrating the configuration of a prediction unit in FIG. 26. [Figure 28] FIG. 28 is a block diagram schematically illustrating a configuration of the second prediction unit in FIG. 27. [Figure 29] FIG. 27 is a block diagram showing a schematic configuration of a variable-length coding unit in FIG. 26. [Figure 30A] FIG. 10 is a diagram illustrating an example of macroblock layer syntax according to the second embodiment. [Figure 30B] FIG. 10 is a diagram illustrating another example of macroblock layer syntax according to the second embodiment. [Figure 31] FIG. 10 is a block diagram schematically illustrating an image decoding device according to a third embodiment. [Figure 32] FIG. 32 is a block diagram showing in more detail the coded data decoding unit shown in FIG. 31. [Figure 33] FIG. 32 is a block diagram showing in more detail the prediction unit shown in FIG. 31. [Figure 34] FIG. 10 is a block diagram schematically showing an image decoding device according to a fourth embodiment. [Figure 35] FIG. 34 is a block diagram showing in more detail the coded data decoding unit shown in FIG. 33. [Figure 36] FIG. 34 is a block diagram showing in more detail the prediction unit shown in FIG. 33. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an image encoding and decoding method and apparatus according to an embodiment of the present invention will be described with reference to the drawings as necessary. Note that in the following embodiments, parts with the same numbers perform similar operations, and redundant description will be omitted.

[0013] (First embodiment) Fig. 1 shows a schematic configuration of an image coding device according to a first embodiment of the present invention. As shown in Fig. 1, this image coding device includes an image coding unit 100, a coding control unit 150, and an output buffer 120. This image coding device may be realized by hardware such as an LSI chip, or may be realized by causing a computer to execute an image coding program.

[0014] An original image (input image signal) 10, which is a moving image or a still image, is input to the image encoding unit 100, for example, in units of pixel blocks obtained by dividing the original image. As will be described in detail later, the image encoding unit 100 compression-encodes the input image signal 10 to generate coded data 14. The generated coded data 14 is temporarily stored in an output buffer 120 and sent to a storage system (storage media) or a transmission system (communication line), not shown, at an output timing managed by an encoding control unit 150.

[0015] The encoding control unit 150 controls the overall encoding process of the image encoding unit 100, such as feedback control of the amount of generated code, quantization control, prediction mode control, and entropy encoding control. Specifically, the encoding control unit 150 provides encoding control information 50 to the image encoding unit 100 and appropriately receives feedback information 51 from the image encoding unit 100. The encoding control information 50 includes prediction information, motion information 18, quantization parameter information, etc. The prediction information includes prediction mode information and block size information. The motion information 18 includes a motion vector, a reference frame number, and a prediction direction (unidirectional prediction, bidirectional prediction). The quantization parameter information includes quantization parameters such as a quantization width (quantization step size) and a quantization matrix. The feedback information 51 includes the amount of code generated by the image encoding unit 100 and is used, for example, to determine the quantization parameter.

[0016] The image encoding unit 100 encodes the input image signal 10 in units of pixel blocks (e.g., macroblocks, sub-blocks, single pixels, etc.) obtained by dividing an original image. Therefore, the input image signal 10 is sequentially input to the image encoding unit 100 in units of pixel blocks obtained by dividing the original image. In this embodiment, the encoding process is performed in units of macroblocks, and a pixel block (macroblock) to be encoded that corresponds to the input image signal 10 is simply referred to as a block to be encoded. Furthermore, an image frame including the block to be encoded, i.e., an image frame to be encoded, is referred to as a frame to be encoded.

[0017] Such a target block for encoding may be, for example, a 16x16 pixel block as shown in Figure 2A, or a 64x64 pixel block as shown in Figure 2B. The target block for encoding may also be a 32x32 pixel block, an 8x8 pixel block, or the like. The shape of the macroblock is not limited to the square shape shown in Figures 2A and 2B, but may be set to any shape, such as a rectangle. Furthermore, the processing unit is not limited to a pixel block such as a macroblock, but may be a frame or a field.

[0018] The encoding process for each pixel block in the encoding target frame may be performed in any order. For simplicity of explanation, in this embodiment, as shown in Fig. 3, it is assumed that the encoding process is performed on the pixel blocks row by row from the upper left pixel block to the lower right pixel block of the encoding target frame, i.e., in raster scan order.

[0019] The image coding unit 100 shown in FIG. 1 includes a prediction unit 101, a subtractor 102, a transform / quantization unit 103, a variable-length coding unit 104, an inverse quantization / inverse transform unit 105, an adder 106, a frame memory 107, a motion information memory 108, and an available block acquisition unit 109.

[0020] In the image encoding unit 100, an input image signal 10 is input to a prediction unit 101 and a subtractor 102. The subtractor 102 receives the input image signal 10 and also receives a predicted image signal 11 from the prediction unit 101, which will be described later. The subtractor 102 calculates the difference between the input image signal 10 and the predicted image signal 11 to generate a prediction error image signal 12.

[0021] The transform / quantization unit 103 receives the prediction error image signal 12 from the subtractor 102 and performs a transform process on the received prediction error image signal 12 to generate transform coefficients. The transform process is, for example, an orthogonal transform such as a discrete cosine transform (DCT). In other embodiments, the transform / quantization unit 103 may generate transform coefficients using techniques such as a wavelet transform and independent component analysis instead of the discrete cosine transform. Furthermore, the transform / quantization unit 103 quantizes the generated transform coefficients based on a quantization parameter provided by the encoding control unit 150. The quantized transform coefficients (transform coefficient information) 13 are output to the variable-length coding unit 104 and the inverse quantization / inverse transform unit 105.

[0022] The inverse quantization and inverse transform unit 105 inverse quantizes the quantized transform coefficients 13 according to the quantization parameters provided by the encoding control unit 150, i.e., the same quantization parameters as those used by the transform and quantization unit 103. Next, the inverse quantization and inverse transform unit 105 performs inverse transform on the inversely quantized transform coefficients to generate a decoded prediction error signal 15. The inverse transform process performed by the inverse quantization and inverse transform unit 105 is the same as the inverse transform process of the transform and quantization unit 103. For example, the inverse transform process is an inverse discrete cosine transform (IDCT) or an inverse wavelet transform.

[0023] The adder 106 receives the decoded prediction error signal 15 from the inverse quantization and inverse transform unit 105, and also receives the predicted image signal 11 from the prediction unit 101. The adder 106 adds the decoded prediction error signal 15 and the predicted image signal 11 to generate a locally decoded image signal 16. The generated locally decoded image signal 16 is stored in a frame memory 107 as a reference image signal 17. The reference image signal 17 stored in the frame memory 107 is read out and referred to by the prediction unit 101 when encoding a subsequent block to be encoded.

[0024] The prediction unit 101 receives a reference image signal 17 from the frame memory 107 and also receives available block information 30 from an available block acquisition unit 109 (described later). Furthermore, the prediction unit 101 receives reference motion information 19 from a motion information memory 108 (described later). Based on the reference image signal 17, the reference motion information 19, and the available block information 30, the prediction unit 101 generates a predicted image signal 11, motion information 18, and selected block information 31 for the current block to be coded. Specifically, the prediction unit 101 includes a motion information selection unit 118 that generates the motion information 18 and the selected block information 31 based on the available block information 30 and the reference motion information 19, and a motion compensation unit 113 that generates the predicted image signal 11 based on the motion information 18. The predicted image signal 11 is sent to the subtractor 102 and the adder 106. The motion information 18 is stored in the motion information memory 108 for subsequent prediction processing of the current block to be coded. Furthermore, the selected block information 31 is sent to the variable-length coding unit 104. The prediction unit 101 will be described in detail later.

[0025] The motion information memory 108 temporarily stores the motion information 18 as reference motion information 19. Fig. 4 shows an example of the configuration of the motion information memory 108. As shown in Fig. 4, the motion information memory 108 holds reference motion information 19 on a frame-by-frame basis, and the reference motion information 19 forms a motion information frame 25. The motion information memory 108 sequentially inputs motion information 18 related to coded blocks, and as a result, the motion information memory 108 holds a plurality of motion information frames 25 with different coding times.

[0026] The reference motion information 19 is stored in the motion information frame 25 in predetermined block units (e.g., 4x4 pixel block units). The motion vector block 28 shown in FIG. 4 is a pixel block of the same size as the current block to be coded, the available block, and the selected block, e.g., a 16x16 pixel block. A motion vector is assigned to each of the motion vector blocks 28, for example, for each 4x4 pixel block. Inter-prediction processing using the motion vector block is referred to as motion vector block prediction processing. The reference motion information 19 stored in the motion information memory 108 is read by the prediction unit 101 when generating the motion information 18. The motion information 18 held by the available block, as described below, refers to the reference motion information 19 stored in the area of ​​the motion information memory 108 where the available block is located.

[0027] The motion information memory 108 is not limited to storing the reference motion information 19 in units of 4x4 pixel blocks, and may store the reference motion information 19 in other pixel block units. For example, the pixel block unit for the reference motion information 19 may be one pixel or a 2x2 pixel block. The shape of the pixel block for the reference motion information 19 is not limited to a square, and may be any shape.

[0028] The available block acquisition unit 109 in Fig. 1 acquires reference motion information 19 from the motion information memory 108, and selects available blocks that can be used for prediction processing by the prediction unit 101 from among multiple blocks that have already been coded, based on the acquired reference motion information 19. The selected available blocks are sent to the prediction unit 101 and the variable-length coding unit 104 as available block information 30. Encoded blocks that are candidates for selecting available blocks are called motion reference blocks. Methods for selecting motion reference blocks and available blocks will be described in detail later.

[0029] In addition to the transform coefficient information 13, the variable-length coding unit 104 receives selected block information 31 from the prediction unit 101, coding parameters such as prediction information and quantization parameters from the coding control unit 150, and available block information 30 from the available block acquisition unit 109. The variable-length coding unit 104 performs entropy coding (e.g., equal-length coding, Huffman coding, or arithmetic coding) on ​​the quantized transform coefficients 13, selected block information 31, available block information 30, and coding parameters to generate coded data 14. The coding parameters include all parameters required for decoding, such as information on the transform coefficients and information on quantization, in addition to the selected block information 31 and prediction information. The generated coded data 14 is temporarily stored in an output buffer 120 and then transmitted to a storage system or a transmission system (not shown).

[0030] 5 shows a processing procedure for an input image signal 10. As shown in FIG. 5, first, a predicted image signal 11 is generated by a prediction unit 101 (step S501). In generating the predicted image signal 11 in step S501, one of available blocks described later is selected as a selected block, and the predicted image signal 11 is created using selected block information 31, motion information of the selected block, and a reference image signal 17. A subtractor 102 calculates the difference between the predicted image signal 11 and the input image signal 10, and a prediction error image signal 12 is generated (step S502).

[0031] Next, the prediction error image signal 12 is subjected to orthogonal transform and quantization by the transform / quantization unit 103, thereby generating transform coefficient information 13 (step S503). The transform coefficient information 13 and selected block information 31 are sent to the variable-length coding unit 104, where they are subjected to variable-length coding, thereby generating coded data 14 (step S504). Also, in step S504, the code table is switched in accordance with the selected block information 31 so that the code table has a number of entries equal to the number of available blocks, and the selected block information 31 is variable-length coded. A bit stream 20 of coded data is sent to a storage system or a transmission path (not shown).

[0032] The transform coefficient information 13 generated in step S503 is inverse quantized and inverse transformed by the inverse quantization and inverse transform unit 105 to generate a decoded prediction error signal 15 (step S505). The decoded prediction error signal 15 is added to the reference image signal 17 used in step S501 to generate a locally decoded image signal 16 (step S506), which is stored in the frame memory 107 as a reference image signal (step S507).

[0033] Next, each component of the image encoding unit 100 described above will be described in more detail. The image encoding unit 100 in Fig. 1 is provided with a plurality of prediction modes, each of which differs in the method of generating a predicted image signal 11 and the motion compensation block size. The methods by which the prediction unit 101 generates the predicted image signal 11 can be broadly divided into intra-prediction (intra-frame prediction), which generates a predicted image using a reference image signal 17 related to a frame (or field) to be encoded, and inter-prediction (inter-frame prediction), which generates a predicted image using a reference image signal 17 related to one or more already-encoded reference frames (reference fields). The prediction unit 101 selectively switches between intra-prediction and inter-prediction to generate the predicted image signal 11 of a block to be encoded.

[0034] FIG. 6A shows an example of inter prediction by the motion compensation unit 113. In inter prediction, as shown in FIG. 6A, a predicted image signal 11 is generated using a reference image signal 17 for a block 24 that is spatially shifted from a block (also referred to as a predicted block) 23 in a reference frame one frame before the current frame, which has already been coded, and is located at the same position as the current block, according to a motion vector 18a included in the motion information 18. That is, the predicted image signal 11 is generated using a reference image signal 17 for the block 24 in the reference frame, which is identified by the position (coordinates) of the current block and the motion vector 18a included in the motion information 18. In inter prediction, motion compensation with fractional pixel accuracy (e.g., half-pixel accuracy or quarter-pixel accuracy) is possible, and interpolated pixel values ​​are generated by filtering the reference image signal 17. For example, H.264 allows interpolation up to quarter-pixel accuracy for luminance signals. When quarter-pixel accuracy motion compensation is performed, the amount of information in the motion information 18 is four times that of integer pixel accuracy.

[0035] Note that inter prediction is not limited to the example in which a reference frame of one frame before is used as shown in FIG. 6A , and any coded reference frame may be used as shown in FIG. 6B . When reference image signals 17 relating to multiple reference frames at different temporal positions are stored, information indicating the temporal position of the reference image signal 17 from which the predicted image signal 11 was generated is represented by a reference frame number. The reference frame number is included in the motion information 18. The reference frame number can be changed in units of regions (pictures, blocks, etc.). That is, a different reference frame can be used for each pixel block. As an example, when a coded reference frame of one frame before is used for prediction, the reference frame number of this region is set to 0, and when a coded reference frame of two frames before is used for prediction, the reference frame number of this region is set to 1. As another example, when only one frame's worth of reference image signal 17 is stored in the frame memory 107 (the number of reference frames is 1), the reference frame number is always set to 0.

[0036] Furthermore, in inter prediction, a block size suitable for the current block can be selected from among multiple motion compensation blocks. That is, the current block can be divided into multiple small pixel blocks, and motion compensation can be performed for each small pixel block. Figures 7A to 7C show the size of motion compensation blocks in units of macroblocks, while Figure 7D shows the size of motion compensation blocks in units of subblocks (pixel blocks of 8x8 pixels or less). As shown in Figure 7A, if the current block is 64x64 pixels, a 64x64 pixel block, a 64x32 pixel block, a 32x64 pixel block, or a 32x32 pixel block can be selected as the motion compensation block. As shown in Figure 7B, if the current block is 32x32 pixels, a 32x32 pixel block, a 32x16 pixel block, a 16x32 pixel block, or a 16x16 pixel block can be selected as the motion compensation block. Furthermore, as shown in Figure 7C, if the current block to be coded is 16x16 pixels, the motion compensation block can be set to a 16x16 pixel block, a 16x8 pixel block, an 8x16 pixel block, an 8x8 pixel block, etc. Furthermore, as shown in Figure 7D, if the current block to be coded is 8x8 pixels, the motion compensation block can be selected to be an 8x8 pixel block, an 8x4 pixel block, a 4x8 pixel block, or a 4x4 pixel block, etc.

[0037] As described above, small pixel blocks (e.g., 4x4 pixel blocks) in a reference frame used for inter prediction have motion information 18, allowing optimal motion compensation block shapes and motion vectors to be used in accordance with local characteristics of the input image signal 10. Furthermore, the macroblocks and sub-macroblocks shown in Figures 7A to 7D can be arbitrarily combined. If the current block to be coded is a 64x64 pixel block as shown in Figure 7A, blocks ranging from 64x64 to 16x16 pixels can be used hierarchically by selecting one of the block sizes shown in Figure 7B for each of the four 32x32 pixel blocks obtained by dividing the 64x64 pixel block. Similarly, if block sizes up to those shown in Figure 7D are selectable, block sizes ranging from 64x64 to 4x4 can be used hierarchically.

[0038] Next, the motion reference block will be described with reference to FIGS. 8A to 8F. The motion reference blocks are selected from the coded regions (blocks) in the current frame and the reference frame according to a method agreed upon by both the image coding device of FIG. 1 and an image decoding device (described later). FIG. 8A shows an example of the arrangement of motion reference blocks selected according to the position of the current block. In the example of FIG. 8A, nine motion reference blocks A to D and TA to TE are selected from the coded regions in the current frame and the reference frame. Specifically, four blocks A, B, C, and D adjacent to the left, above, right-top, and top-left of the current block are selected as motion reference blocks from the current frame, and block TA, which is located at the same position as the current block, and four pixel blocks TB, TC, TD, and TE adjacent to the right, below, left, and above block TA are selected as motion reference blocks from the reference frame. In this embodiment, the motion reference blocks selected from the current frame are referred to as spatial motion reference blocks, and the motion reference blocks selected from the reference frame are referred to as temporal motion reference blocks. The symbol p assigned to each motion reference block in FIG. 8A indicates the index of the motion reference block. The indexes are numbered in the order of the motion reference blocks in the time direction and the space direction, but this is not limiting, and the order does not necessarily have to be different as long as the indexes do not overlap. For example, the motion reference blocks in the time direction and the space direction may be numbered out of order.

[0039] The spatial direction motion reference block is not limited to the example shown in Figure 8A, but may be a block (for example, a macroblock or a sub-macroblock) to which pixels a, b, c, and d adjacent to the encoding target block belong, as shown in Figure 8B. In this case, the relative positions (dx, dy) of each pixel a, b, c, and d from the upper left pixel e in the encoding target block are set as shown in Figure 8C. Here, in the examples shown in Figures 8A and 8B, the macroblock is shown as an NxN pixel block.

[0040] 8D, all blocks A1 to A4, B1, B2, C, and D adjacent to the current block may be selected as spatial motion reference blocks. In the example of FIG. 8D, the number of spatial motion reference blocks is eight.

[0041] Furthermore, the time-direction motion reference blocks may be arranged such that the blocks TA to TE partially overlap each other as shown in FIG. 8E, or may be arranged spaced apart as shown in FIG. 8F. In FIG. 8E, the overlapping portions of the time-direction motion reference blocks TA and TB are indicated by diagonal lines. Furthermore, the time-direction motion reference blocks are not necessarily limited to the block at a position corresponding to the encoding target block (Collocate position) and its surrounding blocks, but may be blocks arranged at any position within the reference frame. For example, a block within the reference frame identified by the position of the reference block and the motion information 18 of any encoded block adjacent to the encoding target block may be set as a central block (e.g., block TA), and this central block and its surrounding blocks may be selected as time-direction motion reference blocks. Furthermore, the time-direction reference blocks do not have to be arranged at equal intervals from the central block.

[0042] In any of the above cases, as long as the number and positions of spatial and temporal motion reference blocks are predetermined between the encoding device and the decoding device, the number and positions of the motion reference blocks may be set in any manner. Furthermore, the size of the motion reference block does not necessarily have to be the same as the size of the block to be encoded. For example, as shown in FIG. 8D, the size of the motion reference block may be larger or smaller than the block to be encoded. Furthermore, the motion reference block is not limited to a square shape, and may be set to any shape, such as a rectangle. Furthermore, the motion reference block may be set to any size.

[0043] Furthermore, the motion reference blocks and available blocks may be arranged in only one of the temporal direction and the spatial direction. Furthermore, the motion reference blocks and available blocks in the temporal direction may be arranged according to the type of slice, such as a P slice or a B slice, or the motion reference blocks and available blocks in the spatial direction may be arranged.

[0044] 9 shows a method by which the available block acquisition unit 109 selects available blocks from among the motion reference blocks. The available blocks are blocks for which motion information can be applied to the block to be coded, and have different motion information from each other. The available block acquisition unit 109 refers to the reference motion information 19, and determines whether each motion reference block is an available block according to the method shown in FIG. 9, and outputs available block information 30.

[0045] As shown in Fig. 9, first, a motion reference block with index p of zero is selected (S800). In the explanation of Fig. 9, it is assumed that motion reference blocks with index p of 0 to M-1 (M indicates the number of motion reference blocks) are processed in order. In addition, the explanation will be made assuming that the usability determination process for motion reference blocks with index p of 0 to p-1 has been completed, and the index of the motion reference block to be determined as usable or not is p.

[0046] The available block acquisition unit 109 determines whether or not the motion reference block p has motion information 18, i.e., whether or not at least one motion vector is assigned (S801). If the motion reference block p does not have a motion vector, i.e., if the temporal motion reference block p is a block in an I-slice that does not have motion information, or if all the subpixel blocks in the temporal motion reference block p are intra-prediction coded, the process proceeds to step S805. In step S805, the motion reference block p is determined to be an unavailable block.

[0047] If the motion reference block p has motion information in step S801, the process proceeds to step S802. The available block acquisition unit 109 selects the motion reference block q (available block q) that has already been selected as an available block. Here, q is a value smaller than p. Subsequently, the available block acquisition unit 109 compares the motion information 18 of the motion reference block p with the motion information 18 of the available block q and determines whether they have the same motion information (S803). If it is determined that the motion information 18 of the motion reference block p is the same as the motion information 18 of the motion reference block q selected as the available block, the process proceeds to step S805, and the motion reference block p is determined to be an unavailable block.

[0048] For all available blocks q that satisfy q < p, if it is determined in step S803 that the motion information 18 of the motion reference block p is not the same as the motion information 18 of the available block q, the process proceeds to step S804. In step S804, the available block acquisition unit 109 determines that the motion reference block p is an available block.

[0049] When it is determined that the motion reference block p is an available block or an unavailable block, the available block acquisition unit 109 determines whether the availability determination has been executed for all motion reference blocks (S806). If there is a motion reference block for which the availability determination has not been executed, for example, if p < M - 1, the process proceeds to step S807. Subsequently, the available block acquisition unit 109 increments the index p by 1 (step S807) and executes steps S801 to S806 again. When the availability determination is executed for all motion reference blocks in step S806, the availability determination process ends.

[0050] By performing the above-described availability determination process, it is determined whether each motion reference block is an available block or an unavailable block. The available block acquisition unit 109 generates available block information 30 including information about the available blocks. By selecting available blocks from the motion reference blocks in this way, the amount of information in the available block information 30 is reduced, and as a result, the amount of encoded data 14 can be reduced.

[0051] FIG. 10 shows an example of the results of performing the availability determination process on the motion reference blocks shown in FIG. 8A. In FIG. 10, two spatial motion reference blocks (p=0, 1) and two temporal motion reference blocks (p=5, 8) are determined to be available blocks. FIG. 11 shows an example of available block information 30 related to the example of FIG. 10. As shown in FIG. 11, the available block information 30 includes the index, availability, and motion reference block name of the motion reference block. In the example of FIG. 11, the indexes p=0, 1, 5, 8 are available blocks, and the number of available blocks is four. The prediction unit 101 selects an optimal available block from these available blocks as a selected block and outputs information about the selected block (selected block information) 31. The selected block information 31 includes the number of available blocks and the index value of the selected available block. For example, if the number of available blocks is four, the corresponding selected block information 31 is coded by the variable-length coding unit 104 using a code table with a maximum of four entries.

[0052] 9, if at least one of the blocks in the temporal motion reference block p is an intra-prediction coded block, the available block acquisition unit 109 may determine that the motion reference block p is an unavailable block. That is, the process may proceed to step S802 only if all the blocks in the temporal motion reference block p are coded using inter-prediction.

[0053] 12A to 12E show an example in which the motion information 18 of the motion reference block p and the motion information 18 of the available block q are determined to be the same in the comparison of the motion information 18 in step S803. Each of FIGS. 12A to 12E shows multiple shaded blocks and two white blocks. For simplicity of explanation, FIGS. 12A to 12E assume that the motion information 18 of these two white blocks is compared without considering the shaded blocks. It is assumed that one of the two white blocks is the motion reference block p, and the other is the motion reference block q that has already been determined to be available (available block q). Unless otherwise specified, either of the two white blocks may be the motion reference block p.

[0054] 12A shows an example in which both the motion reference block p and the available block q are spatial blocks. In the example of FIG. 12A, if the motion information 18 of blocks A and B is the same, it is determined that the motion information 18 is the same. In this case, the sizes of blocks A and B do not need to be the same.

[0055] 12B shows an example in which one of the motion reference block p and the available block q is a spatial block A, and the other is a temporal block TB. In FIG. 12B, the temporal block TB contains one block having motion information. If the motion information 18 of the temporal block TB is the same as the motion information 18 of the spatial block A, it is determined that the motion information 18 is the same. In this case, the sizes of the blocks A and TB do not need to be the same.

[0056] 12C shows another example in which one of the motion reference block p and the available block q is a spatial block A, and the other is a temporal block TB. Fig. 12C shows a case in which the temporal block TB is divided into a plurality of small blocks, each of which has motion information 18. In the example of Fig. 12C, all of the blocks having motion information 18 have the same motion information 18, and if this motion information 18 is identical to the motion information 18 of the spatial block A, it is determined that the motion information 18 is identical. In this case, the sizes of the blocks A and TB do not need to be identical.

[0057] 12D shows an example in which the motion reference block p and the available block q are both temporal blocks. In this case, if the motion information 18 of blocks TB and TE is the same, it is determined that the motion information 18 is the same.

[0058] 12E shows another example in which the motion reference block p and the available block q are both temporal blocks. Fig. 12E shows a case in which the temporal blocks TB and TE are each divided into a plurality of small blocks, each of which has a plurality of small blocks having motion information 18. In this case, the motion information 18 is compared for each small block within the block, and if the motion information 18 is the same for all the small blocks, it is determined that the motion information 18 of block TB and the motion information 18 of block TE are the same.

[0059] 12F shows another example in which the motion reference block p and the available block q are both temporal blocks. Fig. 12F shows a case in which a temporal block TE is divided into a plurality of small blocks, and the block TE has a plurality of small blocks each having motion information 18. If all the motion information 18 of the block TE is the same motion information 18 and is the same as the motion information 18 of the block TD, it is determined that the motion information 18 of the block TD and the TE is the same.

[0060] In this way, in step S803, it is determined whether the motion information 18 of the motion reference block p and the motion information 18 of the available block q are the same. In the examples of Figures 12A to 12F, the number of available blocks q to be compared with the motion reference block p is 1, but if the number of available blocks q is 2 or more, the motion information 18 of the motion reference block p may be compared with the motion information 18 of each available block q. Furthermore, if scaling, which will be described later, is applied, the motion information 18 after scaling becomes the motion information 18 described above.

[0061] Note that the determination that the motion information of the motion reference block p and the motion information of the available block q are identical is not limited to the case where the motion vectors included in the motion information are completely identical. For example, if the norm of the difference between the two motion vectors is within a predetermined range, the motion information of the motion reference block p and the motion information of the available block q may be considered to be substantially identical.

[0062] Fig. 13 shows a more detailed configuration of the prediction unit 101. As described above, the prediction unit 101 receives the available block information 30, the reference motion information 19, and the reference image signal 17 as input, and outputs the predicted image signal 11, the motion information 18, and the selected block information 31. As shown in Fig. 13, the motion information selection unit 118 includes a spatial motion information acquisition unit 110, a temporal motion information acquisition unit 111, and a motion information changeover switch 112.

[0063] The spatial direction motion information acquisition unit 110 receives as input available block information 30 and reference motion information 19 related to spatial direction motion reference blocks. The spatial direction motion information acquisition unit 110 outputs motion information 18A including motion information possessed by each available block located in the spatial direction and index values ​​of the available blocks. When the information shown in FIG. 11 is input as the available block information 30, the spatial direction motion information acquisition unit 110 generates two motion information outputs 18A, and each motion information output 18A includes an available block and the motion information 19 possessed by this available block.

[0064] The temporal motion information acquisition unit 111 receives input of available block information 30 and reference motion information 19 related to a temporal motion reference block. The temporal motion information acquisition unit 111 outputs, as motion information 18B, the motion information 19 of the available temporal motion reference block identified by the available block information 30 and the index value of the available block. The temporal motion reference block is divided into a plurality of subpixel blocks, each of which has motion information 19. As shown in FIG. 14, the motion information 18B output by the temporal motion information acquisition unit 111 includes a group of motion information 19 of each subpixel block in the available block. When the motion information 18B includes a group of motion information 19, motion compensation prediction can be performed on the current block to be coded in units of the subpixel blocks into which the current block to be coded is divided. When the information shown in FIG. 11 is input as the available block information 30, the temporal motion information acquisition unit 111 generates two motion information outputs 18B, each of which includes an available block and a group of motion information 19 of the available block.

[0065] The time direction motion information acquisition unit 111 may also find the average value or representative value of the motion vectors included in the motion information 19 of each pixel sub-block, and output the average value or representative value of the motion vectors as the motion information 18B.

[0066] The motion information changeover switch 112 in Figure 13 selects one appropriate available block as a selected block based on the motion information 18A and 18B output from the spatial motion information acquisition unit 110 and the temporal motion information acquisition unit 111, and outputs the motion information 18 (or a group of motion information 18) corresponding to the selected block to the motion compensation unit 113. The motion information changeover switch 112 also outputs selected block information 31 regarding the selected block. The selected block information 31 includes the index p or the name of the motion reference block, and is also simply referred to as selection information. The selected block information 31 is not limited to the index p and the name of the motion reference block, and may be any information as long as it can identify the position of the selected block.

[0067] The motion information changeover switch 112 selects, as the selected block, an available block that minimizes the coding cost derived by the cost formula shown in the following formula 1, for example.

number

[0068] Here, J denotes the coding cost, and D denotes the coding distortion representing the sum of squared errors between the input image signal 10 and the reference image signal 17. Furthermore, R denotes the code amount estimated by provisional coding, and λ denotes a Lagrange coefficient determined by the quantization width, etc. Instead of using Equation 1, the coding cost J may be calculated using only the code amount R or the coding distortion D, or the cost function of Equation 1 may be created using an approximate value of the code amount R or the coding distortion D. Furthermore, the coding distortion D is not limited to the sum of squared errors, but may also be the sum of absolute differences (SAD) of prediction errors. The code amount R may be limited to the code amount related to the motion information 18. Furthermore, the example in which the available block with the smallest coding cost is selected as the selected block is not limited to the example in which the available block with the smallest coding cost is selected as the selected block. Alternatively, one available block having a value within a certain range equal to or greater than the smallest coding cost may be selected as the selected block.

[0069] The motion compensation unit 113 derives the position of a pixel block from which the reference image signal 17 is extracted as the predicted image signal 11, based on the motion information (or a group of motion information) of the selected block selected by the motion information selection unit 118. When a group of motion information is input to the motion compensation unit 113, the motion compensation unit 113 divides the pixel block from which the reference image signal 17 is extracted as the predicted image signal 11 into small pixel blocks (for example, 4×4 pixel blocks) and applies the corresponding motion information 18 to each of these small pixel blocks, thereby obtaining the predicted image signal 11 from the reference image signal 17. The position of the block from which the predicted image signal 11 is obtained is a position shifted in the spatial direction from the small pixel block in accordance with the motion vector 18a included in the motion information 18, as shown in FIG. 4A for example.

[0070] The motion compensation process for the current block to be coded can be the same as that of H.264. Here, as an example, a quarter-pixel precision interpolation method will be specifically described. In quarter-pixel precision interpolation, if each component of the motion vector is a multiple of 4, the motion vector indicates an integer pixel position. Otherwise, the motion vector indicates a predicted position corresponding to the fractional precision interpolation position.

number

[0071] Here, x and y indicate vertical and horizontal indices indicating the start position (e.g., the upper left vertex) of the block to be predicted, and x_pos and y_pos indicate the corresponding prediction position in the reference image signal 17. (mv_x, mv_y) indicate a motion vector with quarter-pixel accuracy. Next, for the determined pixel position, a prediction pixel is generated by filling or interpolating the corresponding pixel position in the reference image signal 17. FIG. 15 shows an example of prediction pixel generation in H.264. In FIG. 15, squares indicated by capital letters (hatched squares) indicate pixels at integer positions, and shaded squares indicate interpolated pixels at half-pixel positions. Furthermore, white squares indicate interpolated pixels corresponding to quarter-pixel positions. For example, in FIG. 15, half-pixel interpolation corresponding to the positions of the letters b and h is calculated using the following Equation 3:

number

[0072] Here, the alphabets (e.g., b, h, C1, etc.) shown in Equation 3 and the following Equation 4 indicate pixel values ​​of pixels assigned the same alphabet in FIG. 16. Also, ">>" indicates a right shift operation, and ">> 5" corresponds to division by 32. That is, the interpolated pixel at the 1 / 2 pixel position is calculated using a 6-tap FIR (Finite Impulse Response) filter (tap coefficients: (1, -5, 20, 20, -5, 1) / 32).

[0073] Furthermore, the interpolation process for 1 / 4 pixels corresponding to the positions of the letters a and d in FIG. 15 is calculated using the following formula 4.

number

[0074] In this way, the interpolated pixel at the 1 / 4 pixel position is calculated using a 2-tap average filter (tap coefficients: (1 / 2, 1 / 2)). The interpolation process for the 1 / 2 pixel corresponding to the alphabet j located between the four integer pixel positions is generated using 6 taps in both the vertical direction and the horizontal direction. Interpolated pixel values ​​are generated in a similar manner for pixel positions other than those described above.

[0075] The interpolation process may be performed using other interpolation coefficients, not limited to the examples of Equation 3 and Equation 4. The interpolation coefficients may be fixed values ​​provided by the encoding control unit 150, or may be optimized for each frame based on the above-mentioned encoding cost, and the optimized interpolation coefficients may be used to generate the interpolation coefficients.

[0076] Furthermore, in this embodiment, the motion reference block is described as a macroblock (e.g., 16x16 pixel block) unit for motion vector block prediction. However, the prediction process may be performed not only in macroblock units but also in 16x8 pixel block units, 8x16 pixel block units, 8x8 pixel block units, 8x4 pixel block units, 4x8 pixel block units, or 4x4 pixel block units. In this case, information about the motion vector block is derived in pixel block units. Furthermore, the prediction process may be performed in units larger than 16x16 pixel blocks, such as 32x32 pixel block units, 32x16 pixel block units, or 64x64 pixel block units.

[0077] When substituting a reference motion vector in a motion vector block as a motion vector for a small pixel block in the block to be encoded, (A) the negative value (inverse vector) of the reference motion vector may be substituted, or (B) a weighted average value, median value, maximum value, or minimum value using the reference motion vector corresponding to the small block and the reference motion vectors adjacent to this reference motion vector may be substituted.

[0078] FIG. 16 schematically illustrates the operation of the prediction unit 101. As illustrated in FIG. 16, first, a reference frame (motion reference frame) including a temporal reference motion block is acquired (step S1501). The motion reference frame is typically the reference frame that is the closest temporal distance from the current frame to be coded and is a temporally older reference frame. For example, the motion reference frame is a frame coded immediately before the current frame to be coded. In another example, any reference frame whose motion information 18 is stored in the motion information memory 108 may be acquired as the motion reference frame. Next, the spatial motion information acquisition unit 110 and the temporal motion information acquisition unit 111 each acquire the available block information 30 output from the available block acquisition unit 109 (step S1502). Next, the motion information changeover switch 112 selects one of the available blocks as a selected block, for example, according to Equation 1 (step S1503). Next, the motion compensation unit 113 copies the motion information of the selected block to the current block to be coded (step S1504). At this time, if the selected block is a spatial reference block, the motion information 18 of this selected block is copied to the encoding reference block, as shown in Fig. 17. Also, if the selected block is a temporal reference block, a group of motion information 18 of this selected block is copied to the encoding target block together with position information. Next, motion compensation is performed using the copied motion information 18 or the group of motion information 18 by the motion compensation unit 113, and the predicted image signal 11 and the motion information 18 used for motion compensated prediction are output.

[0079] FIG. 18 shows a more detailed configuration of the variable-length coding unit 104. As shown in FIG. 18, the variable-length coding unit 104 includes a parameter coding unit 114, a transform coefficient coding unit 115, a selected block coding unit 116, and a multiplexing unit 117. The parameter coding unit 114 codes parameters required for decoding, such as prediction mode information, block size information, and quantization parameter information, excluding the transform coefficient information 13 and the selected block information 31, to generate coded data 14A. The transform coefficient coding unit 115 codes the transform coefficient information 13 to generate coded data 14B. Furthermore, the selected block coding unit 116 codes the selected block information 31 with reference to the available block information 30 to generate coded data 14C.

[0080] When the available block information 30 includes an index and the availability of a motion reference block corresponding to the index, as shown in Fig. 19, unavailable motion reference blocks are excluded from a plurality of preset motion reference blocks, and only available motion reference blocks are converted into a syntax (stds_idx). In Fig. 19, five of nine motion reference blocks are unavailable, so the syntax stds_idx is assigned to the remaining four motion reference blocks in order starting from 0. In this example, the selected block information to be coded is selected from four available blocks, not nine, so the amount of code to be assigned (number of bins) can be reduced on average.

[0081] FIG. 20 shows an example of a code table indicating the syntax stds_idx and binary information (bin) of the syntax stds_idx. As shown in FIG. 18, the fewer the number of available motion reference blocks, the smaller the average number of bins required to encode the syntax stds_idx. For example, if the number of available blocks is four, the syntax stds_idx can be represented by three bits or less. The binary information (bin) of the syntax stds_idx may be binarized so that all stds_idx has the same number of bins for each number of available blocks, or may be binarized according to a binarization method determined by pre-learning. Furthermore, multiple binarization methods may be prepared and switched appropriately for each block to be encoded.

[0082] Entropy coding (e.g., equal-length coding, Huffman coding, or arithmetic coding) can be applied to these coding units 114, 115, and 116, and the generated coded data 14A, 14B, and 14C are multiplexed by a multiplexing unit 117 and output.

[0083] In this embodiment, an example is described in which a frame coded one frame before the frame to be coded is used as a reference frame, but the motion vector may be scaled (or normalized) using the motion vector and reference frame number in the reference motion information 19 held by the selected block, and the reference motion information 19 may be applied to the block to be coded.

[0084] This scaling process will be specifically described with reference to Fig. 21. tc shown in Fig. 21 indicates the temporal distance (POC (number indicating display order) distance) between the encoding target frame and the motion reference frame, and is calculated using the following formula 5. tr[i] shown in Fig. 21 indicates the temporal distance between the motion reference frame and frame i referenced by the selected block, and is calculated using the following formula 6.

number

[0085] Here, curPOC indicates the POC (Picture Order Count) of the frame to be coded, colPOC indicates the POC of the motion reference frame, and refPOC indicates the POC of frame i referenced by the selected block. Clip(min, max, target) is a clip function that outputs min if target is less than min, or max if target is greater than max, and outputs target otherwise. DiffPicOrderCnt(x, y) is a function that calculates the difference between two POCs.

[0086] If the motion vector of the selected block is MVr=(MVr_x, MVr_y) and the motion vector to be applied to the current block is MV=(MV_x, MV_y), the motion vector MV is calculated by the following Equation 7.

number

[0087] Here, Abs(x) is a function that extracts the absolute value of x. In this way, in motion vector scaling, the motion vector MVr assigned to the selected block is converted into the motion vector MV between the encoding target frame and the first motion reference frame.

[0088] Further examples of motion vector scaling are described below. First, for each slice or frame, a scaling factor (DistScaleFactor[i]) is calculated for all possible time distances tr of the motion reference frame according to the following formula 8. The number of scaling factors is equal to the number of frames referenced by the selected block, i.e., the number of reference frames.

number

[0089] The calculation of tx shown in Equation 8 may be made into a table in advance.

[0090] When scaling each block to be coded, the motion vector MV can be calculated using only multiplication, addition, and shift operations by using the following formula 9.

number

[0091] When such scaling processing is performed, the scaled motion information 18 is applied to the processing of the prediction unit 101 and the available block acquisition unit 109. When scaling processing is performed, the reference frame referred to by the block to be coded becomes a motion reference frame.

[0092] Fig. 22 shows the syntax structure in the image encoding unit 100. As shown in Fig. 22, the syntax mainly includes three parts: a high-level syntax 901, a slice-level syntax 904, and a macroblock-level syntax 907. The high-level syntax 901 holds syntax information for layers higher than the slice level. The slice-level syntax 904 holds information required for each slice, and the macroblock-level syntax 907 holds data required for each macroblock shown in Figs. 7A to 7D.

[0093] Each part contains more detailed syntax. High-level syntax 901 includes sequence- and picture-level syntax such as sequence parameter set syntax 902 and picture parameter set syntax 903. Slice-level syntax 904 includes slice header syntax 905 and slice data syntax 906. Furthermore, macroblock-level syntax 907 includes macroblock layer syntax 908 and macroblock prediction syntax 909.

[0094] Figures 23A and 23B show examples of macroblock layer syntax. available_block_num shown in Figures 23A and 23B indicates the number of available blocks, and if this value is greater than 1, selected block information needs to be coded. Furthermore, stds_idx indicates selected block information, and is coded using a code table according to the number of available blocks described above.

[0095] 23A shows the syntax for encoding selected block information after mb_type. stds_idx is encoded when the mode indicated by mb_type is a specified size or a specified mode (TARGET_MODE) and available_block_num is greater than 1. For example, stds_idx is encoded when motion information of the selected block is available for block sizes of 64x64 pixels, 32x32 pixels, or 16x16 pixels, or in direct mode.

[0096] Fig. 23B shows the syntax for encoding selected block information before mb_type. If available_block_num is greater than 1, stds_idx is encoded. If available_block_num is 0, conventional motion compensation, such as that used in H.264, is performed, so mb_type is encoded.

[0097] Note that between the rows of the tables shown in Figures 23A and 23B, syntax elements not specified in the present invention may be inserted, and descriptions related to other conditional branching may also be included. Alternatively, syntax tables may be divided and integrated into multiple tables. Furthermore, the same terminology does not necessarily have to be used, and may be changed as desired depending on the form of use. Furthermore, each syntax element described in the macroblock layer syntax may be changed as specified in the macroblock data syntax described below.

[0098] Furthermore, by utilizing information about stds_idx, it is possible to reduce the amount of information about mb_type. FIG. 24A shows mb_type and a code table corresponding to mb_type for B slices in H.264. N shown in FIG. 24A is a value representing the size of the block to be coded, such as 16, 32, or 64, and M is half the value of N. Therefore, when mb_type is 4 to 21, the block to be coded is a rectangular block. Furthermore, L0, L1, and Bi in FIG. 24A indicate unidirectional prediction (List0 direction only), unidirectional prediction (List1 direction only), and bidirectional prediction, respectively. When the block to be coded is a rectangular block, mb_type includes information indicating which of L0, L1, and Bi predictions has been performed for each of the two rectangular blocks in the block to be coded. Furthermore, B_Sub indicates that the above processing is performed on each of the pixel blocks obtained by dividing a macroblock into four. For example, if the current block to be coded is a 64×64 pixel macroblock, the macroblock is divided into four to obtain four 32×32 pixel blocks, each of which is further assigned an mb_type and coded.

[0099] Here, when the selected block indicated by stds_idx is Spatial Left (a pixel block adjacent to the left side of the encoding target block), motion information of the pixel block adjacent to the left side of the encoding target block is used as motion information of the encoding target block. Therefore, stds_idx has the same meaning as performing prediction on the encoding target block using horizontally long rectangular blocks indicated by mb_type=4, 6, 8, 10, 12, 14, 16, 18, 20 in FIG. 24A. On the other hand, when the selected block indicated by stds_idx is Spatial Up, motion information adjacent to the upper side of the encoding target block is used as motion information of the encoding target block. Therefore, stds_idx has the same meaning as performing prediction on the vertically long rectangular blocks indicated by mb_type=5, 7, 9, 11, 13, 15, 17, 19, 21 in FIG. 24A. Therefore, by using stds_idx, it is possible to create a code table as shown in FIG. 24B, in which the columns of mb_type=4 to 21 in FIG. 24A are reduced. Similarly, with regard to the mb_type for P slices in H.264 shown in FIG. 24C and the code table corresponding to the mb_type, it is possible to create a code table with a reduced number of mb_types as shown in FIG. 24D.

[0100] Also, stds_idx information may be included in mb_type information for encoding. FIG. 25A shows an example of a code table when stds_idx information is included in mb_type information, and shows an example of a code table corresponding to mb_type for a B slice. B_STDS_X (X=0, 1, 2) in FIG. 25A indicates a mode corresponding to stds_idx, and B_STDS_X is added by the number of available blocks (in FIG. 25A, the number of available blocks is 3). Similarly, another example of mb_type for a P slice is shown in FIG. 25B. The description of FIG. 25B is omitted because it is the same as that for a B slice.

[0101] The order of mb_type and the binarization method (binning) are not limited to the examples shown in Figures 25A and 25B, and mb_type may be encoded according to other orders and binarization methods. B_STDS_X and P_STDS_X do not need to be consecutive and may be placed between each mb_type. In addition, the binarization method (binning) may be designed based on a selection frequency learned in advance.

[0102] In this embodiment, the present invention can also be applied to extended macroblocks in which motion compensation prediction is performed on a group of multiple macroblocks. Furthermore, in this embodiment, any scanning order for encoding may be used. For example, the present invention can be applied to line scanning or Z scanning.

[0103] As described above, the image coding device according to this embodiment selects available blocks from a plurality of motion reference blocks, generates information for specifying the motion reference block to be applied to the block to be coded according to the number of selected available blocks, and codes this information. Therefore, the image coding device according to this embodiment can reduce the amount of coding related to the motion vector information while performing motion compensation in units of small pixel blocks that are smaller than the block to be coded, thereby achieving high coding efficiency.

[0104] (Second embodiment) FIG. 26 shows an image encoding device according to a second embodiment of the present invention. In the second embodiment, differences and operations from the first embodiment will be mainly described. As shown in FIG. 26, an image encoding unit 200 according to this embodiment differs from the first embodiment in the configuration of a prediction unit 201 and a variable-length encoding unit 204. As shown in FIG. 27, the prediction unit 201 includes a first prediction unit 101 and a second prediction unit 202, and selectively switches between the first and second prediction units 101 and 202 to generate a predicted image signal 11. The first prediction unit 101 has the same configuration as the prediction unit 101 according to the first embodiment (FIG. 1), and generates the predicted image signal 11 according to a prediction method (first prediction method) that performs motion compensation using motion information 18 of a selected block. The second prediction unit 202 generates the predicted image signal 11 according to a prediction method (second prediction method) such as H.264 that performs motion compensation using a single motion vector for a block to be encoded. The second prediction unit 202 generates a predicted image signal 11B using the input image signal 10 and a reference image signal 17 from the frame memory.

[0105] Fig. 28 schematically shows the configuration of the second prediction unit 202. As shown in Fig. 28, the second prediction unit 202 includes a motion information acquisition unit 205 that generates motion information 21 using an input image signal 10 and a reference image signal 17, and a motion compensation unit 113 (Fig. 1) that generates a predicted image signal 11A using the reference image signal 17 and the motion information 21. The motion information acquisition unit 205 determines a motion vector to be assigned to a block to be coded, for example, by block matching, based on the input image signal 10 and the reference image signal 17. The matching evaluation criterion uses a value obtained by accumulating, for each pixel, the difference between the input image signal 10 and the interpolated image after matching.

[0106] The motion information acquisition unit 205 may determine an optimal motion vector using a value obtained by converting the difference between the predicted image signal 11 and the input image signal 10. Alternatively, the optimal motion vector may be determined by taking into consideration the magnitude of the motion vector and the code amount of the motion vector and the reference frame number, or by using Equation 1. The matching method may be performed based on search range information provided from outside the image encoding device, or may be performed hierarchically for each pixel precision. Alternatively, the motion information provided by the encoding control unit 150 may be output 21 from the motion information acquisition unit 205 without performing a search process.

[0107] The prediction unit 101 in FIG. 27 further includes a prediction method switching switch 203 that selects and outputs either a predicted image signal 11A from the first prediction unit 101 or a predicted image signal 11B from the second prediction unit 202. For example, the prediction method switching switch 203 calculates a coding cost for each of the predicted image signals 11A and 11B using the input image signal 10, for example, according to Equation 1, and selects one of the predicted image signals 11A and 11B so as to reduce the coding cost, and outputs it as the predicted image signal 11. Furthermore, the prediction method switching switch 203 outputs, together with motion information 18 and selected block information 31, prediction switching information 32 that indicates whether the output predicted image signal 11 was output from the first prediction unit 101 or the second prediction unit 202. The output motion information 18 is coded by a variable-length coding unit 204 and then multiplexed with coded data 14.

[0108] FIG. 29 schematically illustrates the configuration of the variable-length coding unit 204. The variable-length coding unit 204 illustrated in FIG. 29 includes a motion information coding unit 217 in addition to the configuration of the variable-length coding unit 104 illustrated in FIG. 18. Furthermore, unlike the selection block coding unit 116 illustrated in FIG. 18, the selection block coding unit 216 illustrated in FIG. 29 encodes prediction switching information 32 to generate coded data 14D. When the prediction process is performed by the first prediction unit 101, the selection block coding unit 216 further encodes available block information 30 and selected block information 31. The encoded available block information 30 and selected block information 31 are included in the coded data 14D. When the prediction process is performed by the second prediction unit 202, the motion information coding unit 217 encodes motion information 18 to generate coded data 14E. The selected block coding unit 216 and the motion information coding unit 217 each determine whether the prediction process was performed by the first prediction unit 101 or the second prediction unit 202 based on prediction switching information 32 indicating whether the predicted image was generated by motion compensation prediction using the motion information of the selected block.

[0109] The multiplexing unit 117 receives the coded data 14A, B, D, and E from the parameter coding unit 114, the transform coefficient coding unit 115, the selected block coding unit 216, and the motion information coding unit, and multiplexes the received coded data 14A, B, D, and E.

[0110] 30A and 30B each show an example of macroblock layer syntax according to this embodiment. In FIG. 30A, available_block_num indicates the number of available blocks. If this value is greater than 1, the selected block encoder 216 encodes the selected block information 31. Furthermore, stds_flag is a flag indicating whether motion information of the selected block was used as motion information for the current block in motion compensation prediction, i.e., a flag indicating whether the prediction method switch 203 selected the first predictor 101 or the second predictor 202. If the number of available blocks is greater than 1 and stds_flag is 1, this indicates that the motion information of the selected block was used for motion compensation prediction. Furthermore, if stds_flag is 0, the motion information of the selected block is not used, and the information in the motion information 18 is encoded directly or as a predicted differential value, as in H.264. Furthermore, stds_idx indicates the selected block information. The code table corresponding to the number of available blocks is as described above.

[0111] 30A shows the syntax for encoding selected block information after mb_type. stds_flag and stds_idx are encoded only when the mode indicated by mb_type is a specified size or mode. For example, stds_flag and stds_idx are encoded when motion information of the selected block is available for block sizes of 64x64, 32x32, or 16x16, or in direct mode.

[0112] Figure 30B shows the syntax when the selection block information is coded before mb_type. For example, if stds_flag is 1, mb_type does not need to be coded. If stds_flag is 0, mb_type is coded.

[0113] As described above, the image coding device according to the second embodiment selectively switches between the first prediction unit 101 according to the first embodiment and the second prediction unit 202 that uses a prediction method such as H.264 to compress and code an input image signal so as to reduce coding costs. Therefore, the image coding device according to the second embodiment has improved coding efficiency compared to the image coding device according to the first embodiment.

[0114] (Third embodiment) Fig. 31 schematically illustrates an image decoding device according to the third embodiment. As shown in Fig. 31, this image decoding device includes an image decoding unit 300, a decoding control unit 350, and an output buffer 308. The image decoding unit 300 is controlled by the decoding control unit 350. The image decoding device according to the third embodiment corresponds to the image coding device according to the first embodiment. That is, the decoding process by the image decoding device of Fig. 31 has a complementary relationship with the coding process by the image coding process of Fig. 1. The image decoding device of Fig. 31 may be realized by hardware such as an LSI chip, or may be realized by causing a computer to execute an image decoding program.

[0115] The image decoding device of Fig. 31 includes a coded sequence decoding unit 301, an inverse quantization and inverse transform unit 302, an adder 303, a frame memory 304, a prediction unit 305, a motion information memory 306, and an available block acquisition unit 307. In the image decoding unit 300, coded data 80 from a storage system or a transmission system (not shown) is input to the coded sequence decoding unit 301. This coded data 80 corresponds to, for example, the coded data 14 sent in a multiplexed state from the image coding device of Fig. 1.

[0116] In this embodiment, a pixel block (for example, a macroblock) to be decoded is simply referred to as a current block to be decoded, and an image frame including the current block to be decoded is referred to as a current frame to be decoded.

[0117] The coded sequence decoding unit 301 performs decoding by parsing the code sequence based on the syntax for each frame or field. Specifically, the coded sequence decoding unit 301 sequentially performs variable-length decoding on the coded sequence of each syntax, and decodes coding parameters related to the block to be decoded, including transform coefficient information 33, selected block information 61, and prediction information such as block size information and prediction mode information.

[0118] In this embodiment, the decoding parameters include the transform coefficients 33, selected block information 61, and prediction information, and also include all parameters required for decoding, such as information on the transform coefficients and information on quantization. The prediction information, information on the transform coefficients, and information on quantization are input to the decoding control unit 350 as control information 71. The decoding control unit 350 provides each unit of the image decoding unit 300 with decoding control information 70, which includes parameters required for decoding, such as the prediction information and quantization parameters.

[0119] Furthermore, as will be explained later, the coded data decoding unit 301 simultaneously decodes the coded data 80 to obtain prediction information and selected block information 61. The motion information 38 including the motion vector and the reference frame number does not need to be decoded.

[0120] The transform coefficients 33 decoded by the coded stream decoding unit 301 are sent to the inverse quantization and inverse transform unit 302. Various pieces of information related to quantization decoded by the coded stream decoding unit 301, i.e., quantization parameters and quantization matrices, are provided to the decoding control unit 350 and loaded into the inverse quantization and inverse transform unit 302 for inverse quantization. The inverse quantization and inverse transform unit 302 inversely quantizes the transform coefficients 33 according to the loaded information related to quantization, and then performs inverse transform processing (e.g., inverse discrete cosine transform) to obtain a prediction error signal 34. The inverse transform processing by the inverse quantization and inverse transform unit 302 in FIG. 31 is the inverse transform of the transform processing by the transform and quantization unit in FIG. 1. For example, when a wavelet transform is performed by the image encoding device (FIG. 1), the inverse quantization and inverse transform unit 302 performs the corresponding inverse quantization and inverse wavelet transform.

[0121] The prediction error signal 34 restored by the inverse quantization and inverse transform unit 302 is input to the adder 303. The adder 303 adds the prediction error signal 34 to a predicted image signal 35 generated by a prediction unit 305 (described later) to generate a decoded image signal 36. The generated decoded image signal 36 is output from the image decoding unit 300 and temporarily stored in an output buffer 308, and then output in accordance with an output timing managed by a decoding control unit 350. The decoded image signal 36 is also stored in a frame memory 304 as a reference image signal 37. The reference image signal 37 is sequentially read out from the frame memory 304 frame by frame or field by field, and input to the prediction unit 305.

[0122] The available block acquisition unit 307 receives reference motion information 39 from a motion information memory 306 (described later) and outputs available block information 60. The operation of the available block acquisition unit 307 is similar to that of the available block acquisition unit 109 (FIG. 1) described in the first embodiment.

[0123] The motion information memory 306 receives motion information 38 from the prediction unit 305 and temporarily stores it as reference motion information 39. The motion information memory 306 temporarily saves the motion information 38 output from the prediction unit 305 as reference motion information 39. FIG. 4 shows an example of the motion information memory 306. The motion information memory 306 holds multiple motion information frames 26 with different encoding times. Motion information 38 or a group of motion information 38 that have been decoded are saved as reference motion information 39 in the motion information frame 26 corresponding to the decoding time. In the motion information frame 26, the reference motion information 39 is saved in units of, for example, 4×4 pixel blocks. The reference motion information 39 saved in the motion information memory 306 is read and referenced by the prediction unit 305 when generating motion information 38 for the block to be decoded.

[0124] Next, the motion reference blocks and available blocks according to this embodiment will be described. A motion reference block is a candidate block selected from an already decoded region according to a predetermined method by the image encoding device and image decoding device. FIG. 8A shows an example of available blocks. In FIG. 8A, a total of nine motion reference blocks are arranged: four motion reference blocks in the frame to be decoded and five motion reference blocks in the reference frame. Motion reference blocks A, B, C, and D in the frame to be decoded in FIG. 8A are adjacent blocks to the left, above, upper right, and upper left of the block to be decoded. In this embodiment, a motion reference block selected from a frame to be decoded that includes a block to be decoded is referred to as a spatial motion reference block. Furthermore, a motion reference block TA in a reference frame is a pixel block located at the same position as the block to be decoded in the reference frame, and pixel blocks TB, TC, TD, and TE adjacent to this motion reference block TA are selected as the motion reference block. A motion reference block selected from pixel blocks in a reference frame is referred to as a temporal motion reference block. Moreover, the frame in which the time-direction motion reference block is located is called a motion reference frame.

[0125] The spatial motion reference block is not limited to the example shown in Fig. 8A, and a pixel block to which pixels a, b, c, and d adjacent to the block to be decoded belong may be selected as the spatial motion reference block as shown in Fig. 8B. In this case, the relative positions (dx, dy) of pixels a, b, c, and d with respect to the upper left pixel in the block to be decoded are shown in Fig. 8C.

[0126] 8D, all pixel blocks A1 to A4, B1, B2, C, and D adjacent to the block to be decoded may be selected as spatial motion reference blocks. In FIG. 8D, the number of spatial motion reference blocks is eight.

[0127] Furthermore, the temporal motion reference blocks TA to TE may partially overlap each other as shown in FIG. 8E, or may be spaced apart as shown in FIG. 8F. Furthermore, the temporal motion reference block does not necessarily have to be located in the block at the collocate position or its surroundings, but may be a pixel block at any position within the motion reference frame. For example, by using motion information of an already decoded block adjacent to the block to be decoded, the reference block indicated by the motion vector included in the motion information may be selected as the center of the motion reference block (e.g., block TA). Furthermore, the temporal reference blocks do not have to be arranged at equal intervals.

[0128] In the above-described method for selecting a motion reference block, the number and positions of the motion reference blocks may be selected from any number and positions as long as information regarding the number and positions of spatial and temporal motion reference blocks is shared between the image decoding device and the image decoding device. Furthermore, the size of the motion reference block does not necessarily have to be the same as the size of the block to be decoded. For example, as shown in FIG. 8D, the size of the motion reference block may be larger or smaller than the size of the block to be decoded, or may be any size. Furthermore, the shape of the motion reference block is not limited to a square, and may be a rectangle.

[0129] Next, we will explain available blocks. Available blocks are pixel blocks selected from among motion reference blocks, and are pixel blocks for which motion information can be applied to the block to be decoded. Available blocks have different motion information from one another. Available blocks are selected by executing the available block determination process shown in FIG. 9 on a total of nine motion reference blocks in the frame to be decoded and the reference frame, as shown in FIG. 8A, for example. FIG. 10 shows the results of executing the available block determination process shown in FIG. 9. In FIG. 10, hatched pixel blocks indicate unavailable blocks, and white blocks indicate available blocks. That is, two of the spatial motion reference blocks and two of the temporal motion reference blocks are determined to be available blocks, for a total of four. The motion information selection unit 314 in the prediction unit 305 selects an optimal available block as a selected block from among these available blocks arranged in the temporal and spatial directions, according to the selected block information 61 received from the selected block decoding unit 323.

[0130] Next, we will explain the available block acquisition unit 307. The available block acquisition unit 307 has the same function as the available block acquisition unit 109 in the first embodiment, and acquires reference motion information 39 from the motion information memory 306, and outputs available block information 60, which is information indicating an available block or an unavailable block for each motion reference block.

[0131] The operation of the available block acquisition unit 307 will be described with reference to the flowchart of Fig. 9. First, the available block acquisition unit 307 determines whether or not a motion reference block (index p) has motion information (step S801). That is, in step S801, it is determined whether or not at least one subpixel block in the motion reference block p has motion information. If it is determined that the motion reference block p does not have motion information, that is, if the temporal motion reference block is a block in an I-slice without motion information, or if all subpixel blocks in the temporal motion reference block have been intra-prediction decoded, the process proceeds to step S805. In step S805, this motion reference block p is determined to be an unavailable block.

[0132] If it is determined in step S801 that the motion reference block p has motion information, the available block acquisition unit 307 selects a motion reference block q (referred to as available block q) that has already been determined to be an available block (step S802). Here, q is a value smaller than p. Next, the available block acquisition unit 307 compares the motion information of this motion reference block p with the motion information of the available block q for all q to determine whether the motion reference block p has the same motion information as the available block q (S803). If the motion reference block p has the same motion vector as the available block q, the process proceeds to step S805, where the available block acquisition unit 307 determines that the motion reference block p is an unavailable block. If the motion reference block p has motion information that is different from all of the available blocks q, the available block acquisition unit 307 determines that the motion reference block p is an available block in step S804.

[0133] By performing the above-described available block determination process on all motion reference blocks, it is determined whether each motion reference block is available or unavailable, and available block information 60 is generated. An example of the available block information 60 is shown in Fig. 11. As shown in Fig. 11, the available block information 60 includes the index p and availability of the motion reference block. In Fig. 11, the available block information 60 indicates that the motion reference blocks with index p of 0, 1, 5, and 8 have been selected as available blocks, and the number of available blocks is 4.

[0134] 9, if at least one of the blocks in the temporal motion reference block p is an intra-prediction coded block, the available block acquisition unit 307 may determine that the motion reference block p is an unavailable block. That is, the process may proceed to step S802 only if all the blocks in the temporal motion reference block p are coded using inter-prediction.

[0135] 12A to 12E show an example in which the motion information 38 of the motion reference block p and the motion information 38 of the available block q are determined to be the same in the comparison of the motion information 38 in step S803. Each of FIGS. 12A to 12E shows multiple shaded blocks and two white blocks. For simplicity of explanation, FIGS. 12A to 12E assume that the motion information 38 of these two white blocks is compared without considering the shaded blocks. It is assumed that one of the two white blocks is the motion reference block p, and the other is the motion reference block q (available block q) that has already been determined to be available. Unless otherwise specified, either of the two white blocks may be the motion reference block p.

[0136] 12A shows an example in which both the motion reference block p and the available block q are spatial blocks. In the example of FIG. 12A, if the motion information 38 of blocks A and B is the same, it is determined that the motion information 38 is the same. In this case, the sizes of blocks A and B do not need to be the same.

[0137] 12B shows an example in which one of the motion reference block p and the available block q is a spatial block A, and the other is a temporal block TB. In FIG. 12B, the temporal block TB contains one block having motion information. If the motion information 38 of the temporal block TB is the same as the motion information 38 of the spatial block A, it is determined that the motion information 38 is the same. In this case, the sizes of the blocks A and TB do not need to be the same.

[0138] 12C shows another example in which one of the motion reference block p and the available block q is a spatial block A, and the other is a temporal block TB. FIG. 12C shows a case in which the temporal block TB is divided into a plurality of small blocks, each of which has motion information 38. In the example of FIG. 12C, all of the blocks having motion information 38 have the same motion information 38, and if this motion information 38 is identical to the motion information 38 of the spatial block A, it is determined that the motion information 38 is identical. In this case, the sizes of the blocks A and TB do not need to be identical.

[0139] 12D shows an example in which the motion reference block p and the available block q are both temporal blocks. In this case, if the motion information 38 of blocks TB and TE is the same, it is determined that the motion information 38 is the same.

[0140] 12E shows another example in which the motion reference block p and the available block q are both temporal blocks. Fig. 12E shows a case in which the temporal blocks TB and TE are each divided into a plurality of small blocks, each of which has a plurality of small blocks having motion information 38. In this case, the motion information 38 is compared for each small block within the block, and if the motion information 38 is the same for all the small blocks, it is determined that the motion information 38 of block TB and the motion information 38 of block TE are the same.

[0141] 12F shows another example in which the motion reference block p and the available block q are both temporal blocks. Fig. 12F shows a case in which a temporal block TE is divided into a plurality of small blocks, and the block TE has a plurality of small blocks each having motion information 38. If all the motion information 38 of the block TE is the same motion information 38 and is the same as the motion information 38 of the block TD, it is determined that the motion information 38 of the block TD and the block TE are the same.

[0142] In this way, in step S803, it is determined whether the motion information 38 of motion reference block p and the motion information 38 of available block q are the same. In the examples of Figures 12A to 12F, the number of available blocks q to be compared with motion reference block p is 1, but if the number of available blocks q is 2 or more, the motion information 38 of motion reference block p may be compared with the motion information 38 of each available block q. Furthermore, when scaling, which will be described later, is applied, the motion information 38 after scaling becomes the motion information 38 described above.

[0143] Note that the determination that the motion information of the motion reference block p and the motion information of the available block q are identical is not limited to the case where the motion vectors included in the motion information are completely identical. For example, if the norm of the difference between the two motion vectors is within a predetermined range, the motion information of the motion reference block p and the motion information of the available block q may be considered to be substantially identical.

[0144] Fig. 32 is a block diagram showing in more detail the coded sequence decoding unit 301. As shown in Fig. 32, the coded sequence decoding unit 301 includes a separator 320 that separates coded data 80 into syntax units, a transform coefficient decoder 322 that decodes transform coefficients, a selected block decoder 323 that decodes selected block information, and a parameter decoder 321 that decodes parameters related to prediction block size and quantization, etc.

[0145] The parameter decoding unit 321 receives coded data 80A including parameters related to the prediction block size and quantization from the separating unit, and decodes the coded data 80A to generate control information 71. The transform coefficient decoding unit 322 receives coded transform coefficients 80B from the separating unit 320, and decodes the coded transform coefficients 80B to obtain transform coefficient information 33. The selected block decoding unit 323 receives coded data 80C related to the selected block and available block information 60 as input, and outputs selected block information 61. The input available block information 60 indicates the availability of each motion reference block, as shown in FIG. 11 .

[0146] Next, the prediction unit 305 will be described in detail with reference to FIG. 33, the prediction unit 305 includes a motion information selection unit 314 and a motion compensation unit 313, and the motion information selection unit 314 includes a spatial motion information acquisition unit 310, a temporal motion information acquisition unit 311, and a motion information changeover switch 312. The prediction unit 305 basically has the same configuration and functions as the prediction unit 101 described in the first embodiment.

[0147] The prediction unit 305 receives available block information 60, selected block information 61, reference motion information 39, and reference image signal 37 as input, and outputs a predicted image signal 35 and motion information 38. The spatial motion information acquisition unit 310 and temporal motion information acquisition unit 311 have the same functions as the spatial motion information acquisition unit 110 and temporal motion information acquisition unit 111 described in the first embodiment, respectively. The spatial motion information acquisition unit 310 uses the available block information 60 and reference motion information 39 to generate motion information 38A including motion information and indexes of each available block located in the spatial direction. The temporal motion information acquisition unit 311 uses the available block information 60 and reference motion information 39 to generate motion information (or a group of motion information) 38B including motion information and indexes of each available block located in the temporal direction.

[0148] The motion information changeover switch 312 selects one of the motion information 38A from the spatial motion information acquisition unit 310 and the motion information (or a group of motion information) 38B from the temporal motion information acquisition unit 311 in accordance with the selected block information 61, and obtains motion information 38. The selected motion information 38 is sent to the motion compensation unit 313 and the motion information memory 306. The motion compensation unit 313 performs motion compensation prediction in accordance with the selected motion information 38, in the same way as the motion compensation unit 113 described in the first embodiment, and generates a predicted image signal 35.

[0149] The motion vector scaling function of the motion compensation unit 313 is the same as that described in the first embodiment, so a description thereof will be omitted.

[0150] Fig. 22 shows the syntax structure in the image decoding unit 300. As shown in Fig. 22, the syntax mainly includes three parts: a high-level syntax 901, a slice-level syntax 904, and a macroblock-level syntax 907. The high-level syntax 901 holds syntax information for layers higher than the slice level. The slice-level syntax 904 holds information required for each slice, and the macroblock-level syntax 907 holds data required for each macroblock shown in Figs. 7A to 7D.

[0151] Each part contains more detailed syntax. High-level syntax 901 includes sequence- and picture-level syntax such as sequence parameter set syntax 902 and picture parameter set syntax 903. Slice-level syntax 904 includes slice header syntax 905 and slice data syntax 906. Furthermore, macroblock-level syntax 907 includes macroblock layer syntax 908 and macroblock prediction syntax 909.

[0152] Figures 23A and 23B show examples of macroblock layer syntax. available_block_num shown in Figures 23A and 23B indicates the number of available blocks, and if this value is greater than 1, it is necessary to decode selected block information. Furthermore, stds_idx indicates selected block information, and is coded using a code table according to the number of available blocks described above.

[0153] 23A shows the syntax for decoding selected block information after mb_type. When the prediction mode indicated by mb_type is a predetermined size or a predetermined mode (TARGET_MODE) and when available_block_num is greater than 1, stds_idx is decoded. For example, when motion information of the selected block is available for a block size of 64x64 pixels, 32x32 pixels, or 16x16 pixels, or in direct mode, stds_idx is coded.

[0154] Fig. 23B shows the syntax for decoding selected block information before mb_type. If available_block_num is greater than 1, stds_idx is decoded. If available_block_num is 0, conventional motion compensation, such as that used in H.264, is performed, so mb_type is coded.

[0155] Between the rows of the tables shown in Figures 23A and 23B, syntax elements not specified in the present invention may be inserted, and descriptions related to other conditional branching may also be included. Alternatively, syntax tables may be divided and integrated into multiple tables. Furthermore, the same terminology does not necessarily have to be used, and may be changed as desired depending on the form of use. Furthermore, each syntax element described in the macroblock layer syntax may be changed as specified in the macroblock data syntax described below.

[0156] As described above, the image decoding device according to this embodiment decodes images coded by the image coding device according to the first embodiment. Therefore, the image decoding according to this embodiment can reproduce high-quality decoded images from relatively small amounts of coded data.

[0157] (Fourth embodiment) Fig. 34 schematically illustrates an image decoding device according to the fourth embodiment. As shown in Fig. 34, the image decoding device includes an image decoding unit 400, a decoding control unit 350, and an output buffer 308. The image decoding device according to the fourth embodiment corresponds to the image coding device according to the second embodiment. In the fourth embodiment, differences in parts and operations from the third embodiment will be mainly described. As shown in Fig. 34, the image decoding unit 400 according to this embodiment differs from the third embodiment in a coded sequence decoding unit 401 and a prediction unit 405.

[0158] The prediction unit 405 of this embodiment selectively switches between a prediction method (first prediction method) that performs motion compensation using motion information possessed by the selected block and a prediction method (second prediction method) that performs motion compensation using one motion vector for the block to be decoded, such as H.264, to generate a predicted image signal 35.

[0159] FIG. 35 is a block diagram showing the coded sequence decoding unit 401 in more detail. The coded sequence decoding unit 401 shown in FIG. 35 includes a motion information decoding unit 424 in addition to the components of the coded sequence decoding unit 301 shown in FIG. 32. Furthermore, unlike the selected block decoding unit 323 shown in FIG. 32, the selected block decoding unit 423 shown in FIG. 35 decodes coded data 80C related to a selected block to obtain prediction switching information 62. The prediction switching information 62 indicates whether the prediction unit 101 in the image coding device of FIG. 1 used the first or second prediction method. If the prediction switching information 62 indicates that the prediction unit 101 used the first prediction method, i.e., if the block to be decoded was coded using the first prediction method, the selected block decoding unit 423 decodes the selected block information in the coded data 80C to obtain selected block information 61. If the prediction switching information 62 indicates that the prediction unit 101 used the second prediction method, i.e., if the block to be decoded is coded using the second prediction method, the selected block decoding unit 423 does not decode the selected block information, and the motion information decoding unit 424 decodes the coded motion information 80D to obtain motion information 40.

[0160] FIG. 36 is a block diagram showing the prediction unit 405 in more detail. The prediction unit 405 shown in FIG. 34 includes a first prediction unit 305, a second prediction unit 410, and a prediction method switching switch 411. The second prediction unit 410 performs motion compensation prediction similar to that performed by the motion compensation unit 313 in FIG. 33 using the motion information 40 decoded by the coded sequence decoding unit 401 and the reference image signal 37, to generate a predicted image signal 35B. The first prediction unit 305 is the same as the prediction unit 305 described in the third embodiment, and generates the predicted image signal 35B. Furthermore, the prediction method switching switch 411 selects either the predicted image signal 35B from the second prediction unit 410 or the predicted image signal 35A from the first prediction unit 305 based on prediction switching information 62, and outputs the selected signal as the predicted image signal 35 of the prediction unit 405. At the same time, the prediction method changeover switch 411 sends the motion information used in the selected first predictor 305 or second predictor 410 to the motion information memory 306 as motion information 38 .

[0161] Next, the syntax structure of this embodiment will be described, focusing on the differences from the third embodiment.

[0162] 30A and 30B each show an example of macroblock layer syntax according to this embodiment. In FIG. 30A, available_block_num indicates the number of available blocks. If this value is greater than 1, the selected block decoding unit 423 decodes the selected block information in the coded data 80C. Furthermore, stds_flag is a flag indicating whether the motion information of the selected block was used as the motion information of the block to be decoded in motion compensation prediction, i.e., a flag indicating whether the prediction method switching switch 411 selected the first predictor 305 or the second predictor 410. If the number of available blocks is greater than 1 and stds_flag is 1, this indicates that the motion information of the selected block was used in motion compensation prediction. If stds_flag is 0, the motion information of the selected block is not used, and the motion information is coded directly or using a predicted differential value, as in H.264. Furthermore, stds_idx indicates the selected block information. The code table corresponding to the number of available blocks is as described above.

[0163] 30A shows the syntax for decoding selected block information after mb_type. stds_flag and stds_idx are decoded only when the prediction mode indicated by mb_type is a specified block size or mode. For example, when the block size is 64x64, 32x32, or 16x16, or in direct mode, stds_flag and stds_idx are decoded.

[0164] Figure 30B shows the syntax for decoding selected block information before mb_type. For example, if stds_flag is 1, mb_type does not need to be decoded. If stds_flag is 0, mb_type is decoded.

[0165] As described above, the image decoding device according to this embodiment decodes images coded by the image coding device according to the second embodiment. Therefore, the image decoding according to this embodiment can reproduce high-quality decoded images from relatively small amounts of coded data.

[0166] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be deleted from all of the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined.

[0167] As an example, the same effect can be obtained by modifying the first to fourth embodiments described above as follows.

[0168] (1) In the first to fourth embodiments, a frame to be processed is divided into rectangular blocks such as 16×16 pixel blocks, and encoding or decoding is performed in an order from the pixel block in the upper left corner of the screen to the pixel block in the lower right corner, as shown in FIG. 4 . However, the encoding or decoding order is not limited to this example. For example, the encoding or decoding order may be from the lower right corner of the screen to the upper left corner, or from the upper right corner to the lower left corner. Furthermore, the encoding or decoding order may be a spiral order from the center of the screen to the periphery, or from the periphery to the center.

[0169] (2) In the first to fourth embodiments, the luminance signal and the color difference signal are not separated, and only one color signal component is used. However, different prediction processes may be used for the luminance signal and the color difference signal, or the same prediction process may be used. When different prediction processes are used, the prediction method selected for the color difference signal is encoded / decoded in the same manner as for the luminance signal.

[0170] It goes without saying that the present invention can be similarly implemented even if various modifications are made without departing from the spirit of the present invention. [Industrial Applicability]

[0171] INDUSTRIAL APPLICABILITY The image encoding / decoding method according to the present invention can improve encoding efficiency and has industrial applicability. [Explanation of symbols]

[0172] 10...input image signal, 11...prediction image signal, 12...prediction error image signal, 13...quantized transform coefficient, 14...encoded data, 15...decoded prediction error signal, 16...locally decoded image signal, 17...reference image signal, 18...motion information, 20...bitstream, 21...motion information, 25, 26...information frame, 30...available block information, 31...selected block information, 32...prediction switching information, 33...transform coefficient information, 34...prediction error signal, 35...prediction image signal, 36...decoded image signal, 37...reference image signal, 38...motion information, 39...reference motion information, 40...motion information, 50...encoding control information , 51...feedback information, 60...available block information, 61...selected block information, 62...prediction switching information, 70...decoding control information, 71...control information, 80...encoded data, 100...image encoding unit, 101...prediction unit, 102...subtractor, 103...transformation and quantization unit, 104...variable length encoding unit, 105...inverse quantization and inverse transform unit, 106...adder, 107...frame memory, 108...information memory, 109...available block acquisition unit, 110...spatial direction motion information acquisition unit, 111...temporal direction motion information acquisition unit, 112...information changeover switch, 113...motion compensation unit, 114... parameter coding unit, 115...transform coefficient coding unit, 116...selected block coding unit, 117...multiplexing unit, 118...motion information selection unit, 120...output buffer, 150...coding control unit, 200...image coding unit, 201...prediction unit, 202...second prediction unit, 203...prediction method changeover switch, 204...variable length coding unit, 205...motion information acquisition unit, 216...selected block coding unit, 217...motion information coding unit, 300...image decoding unit, 301...code string decoding unit, 301...code string decoding unit, 302...inverse quantization and inverse transform unit, 303...adder, 304...frame memory, 305...prediction measurement unit, 306... information memory, 307... available block acquisition unit, 308... output buffer, 310... spatial direction motion information acquisition unit, 311... temporal direction motion information acquisition unit, 312... motion information changeover switch, 313... motion compensation unit, 314... information selection unit, 320... separation unit, 321... parameter decoding unit, 322... transform coefficient decoding unit, 323... selected block decoding unit, 350... decoding control unit, 400... image decoding unit, 401... coded sequence decoding unit, 405... prediction unit, 410... second prediction unit, 411... prediction method changeover switch, 423... selected block decoding unit, 424... information decoding unit,901...High-level syntax, 902...Sequence parameter set syntax, 903...Picture parameter set syntax, 904...Slice level syntax, 905...Slice header syntax, 906...Slice data syntax, 907...Macroblock level syntax, 908...Macroblock layer syntax, 909...Macroblock prediction syntax.

Claims

[Claim 1] a circuit for transmitting the encoded data; the encoded data includes identification information for identifying a selected block; the identification information is generated by determining whether a plurality of candidate blocks having a predetermined positional relationship with respect to a target block are available in a predetermined order according to the positional relationship, and selecting one of the candidate blocks determined to be available as the selected block; the plurality of candidate blocks include a block adjacent to the upper left of the target block and a block adjacent to the top of the target block, the determining step includes determining the block adjacent to an upper left of the target block after determining the block adjacent to an upper left of the target block, and determining the candidate block as available if the candidate block has motion information that does not match motion information corresponding to a candidate block already determined as available. Transmitting device.

Images