Title of Invention: PREDICTION IMAGE GENERATION METHOD, IMAGE CODING METHOD, IMAGE DECODING METHOD, AND PREDICTION IMAGE GENERATION APPARATUS Abstract: An image decoding device is provided for decoding a current block using a coded bitstream. The image decoding device includes a processor and a memory coupled to the processor. The processor of the image coding device performs operations, including obtaining a first data to determine a number of first points in a first picture to predict the current block, the first picture including the current block. The processor also performs selecting motion information for each of the first points, the motion information being one of candidates where the number of selected motion information being equal to the number of the first points determined by the first data. The processor further performs generating a prediction image to decode the current block based on the selected motion information. Detailed Description: This is a continuation application of U.S. patent application Ser. No. 15/785,756, filed Oct. 17, 2017, which is a continuation application of U.S. application Ser. No. 14/630,120, filed Feb. 24, 2015, which claims the benefit of U.S. Provisional Application No. 61/954,759, filed Mar. 18, 2014, and priority to Japanese Application No. 434.298.3887, filed Nov. 13, 2014. The disclosure of each of the above-identified documents, including the specification, drawings, and claims is incorporated herein by reference in their entirety. BACKGROUND OF THE INVENTION 1. Field of the Invention The present disclosure relates to a prediction image generation method, an image coding method, an image decoding method, and a prediction image generation apparatus. 2. Description of the Related Art In order to improve coding efficiency, various studies have been made regarding an HEVC (High Efficiency Video Coding) standard which is the latest video coding standard (see, for example, NPL 1). This scheme is one of ITU-T (International Telecommunication Union Telecommunication Standardization Sector) standards called H.26x and one of ISO/IEC (International Organization for Standardization/International Electrotechnical Communication) standards called MPEG-x (Moving Picture Experts Group-x), and has been studied as a successor to the video coding standard called H.264/AVC (Advanced Video Coding) or MPEG-4 AVC. In a prediction image generation process that is used during the coding in both AVC and HEVC, only pixel information on an adjacent block is used in intra prediction, and only parallel translation is used in inter prediction. CITATION LIST Non-Patent Literature NPL 1: Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11 12th Meeting: Geneva, CH, 14-23 Jan. 2013 JCTVC-L1003_v34.doc, High Efficiency Video Coding (HEVC) text specification draft 10 (for FDIS & Last Call) http://phenix.it-sudparis.eu/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L 1003-v34.zip SUMMARY OF THE INVENTION There is a demand for improving the coding efficiency in the prediction image generation method, the image coding method, and the image decoding method. An object of the present disclosure is to provide a motion prediction method, an image coding method, or an image decoding method capable of improving the coding efficiency. One aspect of the present disclosure provides a prediction image generation method for generating a prediction image of a target block, the prediction image generation method including: an extraction step of extracting a plurality of first feature points each of which has a local feature quantity, the plurality of first feature points being included in a reconstructed image; a search step of searching a corresponding point from the plurality of first feature points, the corresponding point having a local feature quantity similar to a local feature quantity of a second feature point corresponding to the target block, a relationship between the corresponding point and the second feature point being expressed by information including a non-parallel translation component; and a generation step of generating the prediction image from the reconstructed image based on the relationship. Note that these general or specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM (Compact Disc-Read Only Memory), or using any given combination of a system, a method, an integrated circuit, a computer program, and a computer-readable recording medium. The present disclosure can provide a prediction image generation method, an image coding method or an image decoding method capable of improving the coding efficiency. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a configuration of an image coding apparatus according to a first exemplary embodiment; FIG. 2 is a flowchart illustrating an example of an image coding process according to the first exemplary embodiment; FIG. 3 is a flowchart illustrating an example of a prediction block generation process according to the first exemplary embodiment; FIG. 4 is a flowchart illustrating an example of an intra prediction process according to the first exemplary embodiment; FIG. 5 is a flowchart illustrating an example of a feature point use intra prediction process of the first exemplary embodiment; FIG. 6 is a flowchart illustrating an example of an in-block mode intra prediction process of the first exemplary embodiment; FIG. 7 is a view illustrating an example of an in-block mode prediction image generation process of the first exemplary embodiment; FIG. 8 is a flowchart illustrating an example of an in-block mode feature-point-related information coding process of the first exemplary embodiment; FIG. 9 is a flowchart illustrating an example of a surrounding block mode intra prediction process of the first exemplary embodiment; FIG. 10 is a view illustrating an example of a surrounding block mode prediction image generation process of the first exemplary embodiment; FIG. 11 is a flowchart illustrating an example of a surrounding block mode feature-point-related information coding process of the first exemplary embodiment; FIG. 12 is a view illustrating extraction range information of the first exemplary embodiment; FIG. 13 is a flowchart illustrating an example of an inter prediction process of the first exemplary embodiment; FIG. 14 is a flowchart illustrating an example of a feature point use inter prediction process of the first exemplary embodiment; FIG. 15 is a flowchart illustrating an example of the in-block mode inter prediction process of the first exemplary embodiment; FIG. 16 is a view illustrating an example of the in-block mode prediction image generation process of the first exemplary embodiment; FIG. 17 is a flowchart illustrating an example of the surrounding block mode inter prediction process of the first exemplary embodiment; FIG. 18 is a view illustrating an example of the surrounding block mode prediction image generation process of the first exemplary embodiment; FIG. 19 is a flowchart illustrating an example of a motion information use inter prediction process according to a second exemplary embodiment; FIG. 20 is a flowchart illustrating an example of a motion estimation process of the second exemplary embodiment; FIG. 21 is a block diagram illustrating a configuration of an image decoding apparatus according to a third exemplary embodiment; FIG. 22 is a flowchart illustrating an example of an image decoding process of the third exemplary embodiment; FIG. 23 is a flowchart illustrating an example of a prediction information decoding process of the third exemplary embodiment; FIG. 24 is a flowchart illustrating an example of a feature-point-related information decoding process of the third exemplary embodiment; FIG. 25 is a flowchart illustrating an example of the in-block mode feature-point-related information decoding process of the third exemplary embodiment; FIG. 26 is a flowchart illustrating an example of the surrounding block mode feature-point-related information decoding process of the third exemplary embodiment; FIG. 27 is a flowchart illustrating an example of a prediction block generation process of the third exemplary embodiment; FIG. 28 is a flowchart illustrating an example of an intra prediction image generation process of the third exemplary embodiment; FIG. 29 is a flowchart illustrating an example of a feature point use intra prediction process of the third exemplary embodiment; FIG. 30 is a flowchart illustrating an example of the in-block mode intra prediction image generation process of the third exemplary embodiment; FIG. 31 is a flowchart illustrating an example of the surrounding block mode intra prediction image generation process of the third exemplary embodiment; FIG. 32 is a flowchart illustrating an example of an inter prediction image generation process of the third exemplary embodiment. FIG. 33 is a flowchart illustrating an example of a feature point use intra prediction process of the third exemplary embodiment; FIG. 34 is a flowchart illustrating an example of the in-block mode inter prediction image generation process of the third exemplary embodiment; FIG. 35 is a flowchart illustrating an example of the surrounding block mode inter prediction image generation process of the third exemplary embodiment; FIG. 36 is a flowchart illustrating an example of a prediction image generation process of the third exemplary embodiment; FIG. 37 is an entire configuration diagram illustrating a content supply system that implements a content distribution service; FIG. 38 is an entire configuration diagram of a digital broadcasting system; FIG. 39 is a block diagram illustrating a configuration example of a television; FIG. 40 is a block diagram illustrating a configuration example of an information playback/recording unit that reads and writes information from and to a recording medium which is of an optical disk; FIG. 41 is a view illustrating a structural example of the recording medium that is of the optical disk; FIG. 42A is a view illustrating an example of a mobile phone; FIG. 42B is a block diagram illustrating a configuration example of the mobile phone; FIG. 43 is a view illustrating a structure of multiplexed data; FIG. 44 is a schematic diagram illustrating how to multiplex each stream in the multiplexed data; FIG. 45 is a view illustrating how to store a video stream in a PES packet sequence in more detailed; FIG. 46 is a view illustrating structures of a TS (Transport Stream) packet and a source packet in the multiplexed data; FIG. 47 is a view illustrating a data configuration of a PMT; FIG. 48 is a view illustrating an internal configuration of multiplexed data information; FIG. 49 is a view illustrating an internal configuration of stream attribute information; FIG. 50 is a view illustrating steps of identifying video data; FIG. 51 is a block diagram illustrating a configuration example of an integrated circuit that implements a video coding method and a video decoding method according to each of the exemplary embodiments; FIG. 52 is a view illustrating a configuration that switches a driving frequency; FIG. 53 is a view illustrating steps of identifying the video data to switch the driving frequency; FIG. 54 is a view illustrating an example of a lookup table in which a video data standard and a driving frequency are associated with each other; FIG. 55A is a view illustrating an example of a configuration in which a signal processor module is shared; and FIG. 55B is a view illustrating another example of a configuration in which the signal processor module is shared. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Underlying Knowledge of Present Disclosure In the conventional image coding scheme, the pixel information on the adjacent block is used to generate the prediction image in the intra prediction, and the information on the parallel translation is used in the inter prediction. For this reason, in the intra prediction, even if a similar region exists in the identical image, the information on the region cannot be used in the case that the region is not located in surroundings of the target block. In the inter prediction, even if the images are similar to each other by performing a deformation such as scaling and rotation, the information on the similar image cannot be used. Additionally, a technique of using high-order motion information such as an affine transform is discussed in the inter prediction. Therefore, the scaling or the rotation deformation of a subject can be expressed by applying a geometric transform to the motion information. Therefore, quality of the generated prediction image is improved. The coding efficiency is improved by increasing a prediction unit. However, in the affine transform, at least six-dimensional information is required because three kinds of deformations of the scaling, the rotation, and shear are required to be expressed in addition to the parallel translation. At least eight-dimensional information is required to express a projection transform. Thus, in the case that the high-order motion information is used, there is generated a problem in that a calculation quantity necessary for a motion information estimation process increases. In exemplary embodiments, the problem is solved by applying a technology used in computer vision. Nowadays, various feature point and feature quantity extraction techniques typified by SIFT (Scale-Invariant Feature Transform) and ORB (Oriented FAST and Rotated BREIF) are proposed with the progress of the technology concerning the computer vision. In the feature point and feature quantity extraction techniques, a feature point is extracted with respect to an edge or corner portion in the high-reliability image, and information called a feature quantity is generated using a size or distribution of pixel information and gradient information on surroundings of the extracted feature point. Hereinafter, the feature quantity is also referred to as a local feature quantity. The feature quantity extraction techniques frequently have a feature that the technique is robust to the scaling and the rotation. Therefore, the feature point information includes parameters called a rotation quantity (rotation angle) and a scale value. The feature quantities at the feature points are compared to each other, and a relationship called a corresponding point is set for a small Euclid distance between the feature quantities. A feature point matching process of searching the corresponding point from a feature point group is also used in a process of generating a panoramic image. In the prediction image generation technique, the prediction image can be generated with higher accuracy than the existing technique by applying the technology concerning the feature quantities. One aspect of the present disclosure provides a prediction image generation method for generating a prediction image of a target block, the prediction image generation method including: an extraction step of extracting a plurality of first feature points each of which has a local feature quantity, the plurality of first feature points being included in a reconstructed image; a search step of searching a corresponding point from the plurality of first feature points, the corresponding point having a local feature quantity similar to a local feature quantity of a second feature point corresponding to the target block, a relationship between the corresponding point and the second feature point being expressed by information including a non-parallel translation component; and a generation step of generating the prediction image from the reconstructed image based on the relationship. Therefore, in the prediction image generation method, the prediction image can be generated using the image of a reference region to which a deformation including the non-parallel translation component such as scaling and rotation is added using the feature point and the feature quantity. Therefore, the prediction image generation method can improve the coding efficiency. For example, the second feature point may be included in the target block, and the prediction image may be generated using a pixel value of a region including the corresponding point in the reconstructed image in the generation step. For example, the second feature point may be a feature point in surroundings of the target block, and the prediction image may be generated using a pixel value of a region that does not include the corresponding point in the reconstructed image in the generation step. For example, the reconstructed image may be a reconstructed image of a target picture including the target block. For example, the reconstructed image may be a reconstructed image of a picture different from a target picture including the target block. Another aspect of the present disclosure provides an image coding method in which the prediction image generation method is performed, the image coding method including an image coding step of coding the target block using the prediction image. Therefore, in the image coding method, a reference region to which a deformation including the non-parallel translation component is added using the feature point and the feature quantity, and the prediction image can be generated using the image of the reference region. Therefore, the prediction image generation method can improve the coding efficiency. For example, the image coding method may further include a feature point information coding step of coding feature point information identifying the second feature point in a plurality of third feature points corresponding to the target block. At this point, the plurality of third feature points may be extracted in the extraction step, and the second feature point may be selected from the plurality of third feature points in the search step. For example, the feature point information may indicate a coordinate of the second feature point. For example, the feature point information may indicate a rotation quantity or a scale value which is possessed by the second feature point. For example, the image coding method may further include a corresponding point information coding step of coding corresponding point information identifying the corresponding point in the plurality of first feature points. For example, the corresponding point information may indicate a coordinate of the second feature point. For example, in the feature point information coding step, indexes may be allocated to the plurality of first feature points in a predetermined sequence, and the corresponding point information may indicate the index allocated to the corresponding point. For example, in the generation step, an initial value of a motion estimation process may be set based on the relationship, and the prediction image may be generated by performing the motion estimation process using the initial value. Still another aspect of the present disclosure provides an image decoding method in which the prediction image generation method is performed, the image decoding method including an image decoding step of decoding the target block using the prediction image. Therefore, in the image coding method, a reference region to which a deformation including the non-parallel translation component is added using the feature point and the feature quantity, and the prediction image can be generated using the image of the reference region. Therefore, the prediction image generation method can improve the coding efficiency. For example, the image decoding method may further include a feature point information decoding step of decoding feature point information identifying the second feature point in a plurality of third feature points corresponding to the target block. At this point, the plurality of third feature points may be extracted in the extraction step, and the second feature point may be selected from the plurality of third feature points using the feature point information in the search step. For example, the feature point information may indicate a coordinate of the second feature point. For example, the feature point information may indicate a rotation quantity or a scale value which is possessed by the second feature point. For example, the image decoding method may further include a corresponding point information decoding step of decoding corresponding point information identifying the corresponding point in the plurality of first feature points. At this point, the corresponding point may be searched from the plurality of first feature points using the corresponding point information in the search step. For example, in the feature point information decoding step, indexes may be allocated to the plurality of first feature points in a predetermined sequence, and the corresponding point information may indicate the index allocated to the corresponding point. Yet another aspect of the present disclosure provides a prediction image generation apparatus that generates a prediction image of a target block, the prediction image generation apparatus including: an extraction unit that extracts a plurality of first feature points each of which has a local feature quantity, the plurality of first feature points being included in a reconstructed image; a search unit that searches a corresponding point from the plurality of first feature points, the corresponding point having a local feature quantity similar to a local feature quantity of a second feature point corresponding to the target block, a relationship between the corresponding point and the second feature point being expressed by information including a non-parallel translation component; and a generation unit that generates the prediction image from the reconstructed image based on the relationship. Therefore, in the prediction image generation apparatus, a reference region to which a deformation including the non-parallel translation component is added using the feature point and the feature quantity, and the prediction image can be generated using the image of the reference region. Therefore, the prediction image generation apparatus can improve the coding efficiency. Note that these general or specific aspects may be implemented using a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or using any given combination of a system, a method, an integrated circuit, a computer program, and a computer-readable recording medium. Exemplary embodiments will be described in detail below with reference to the drawings as needed. However, the detailed description of the well-known item and the overlapping description of the substantially identical configuration are occasionally neglected. This is because unnecessary redundancy of the following description is avoided to facilitate easy understanding of those skilled in the art. Note that each of the following exemplary embodiments illustrates a specific example of the present disclosure. Numerical values, shapes, materials, elements, arranged positions and connection forms of the elements, steps, the order of the steps, and the like of the following exemplary embodiments are described only by way of example, but do not restrict the present disclosure. Also, among elements described in the following exemplary embodiments, elements that are not included in an independent claim which represents the highest-order concept are described as optional elements. First Exemplary Embodiment An image coding apparatus in which an image coding method according to a first exemplary embodiment is used will be described. The image coding apparatus of the first exemplary embodiment performs an intra prediction process and an inter prediction process using a local feature quantity. Therefore, the image coding apparatus generates a prediction image using a reference block expressed by information including a non-parallel translation component except a parallel translation component, so that the coding efficiency can be improved. FIG. 1 is a block diagram illustrating an example of image coding apparatus 100 of the first exemplary embodiment. Image coding apparatus 100 includes feature quantity extraction unit 101, block division unit 102, subtractor 103, frequency transform unit 104, quantization unit 105, entropy coding unit 106, inverse quantization unit 107, inverse frequency transform unit 108, adder 109, feature quantity extraction unit 110, intra prediction unit 111, loop filter 112, feature quantity extraction unit 113, frame memory 114, inter prediction unit 115, and switching unit 116. Image coding apparatus 100 codes input image 121 to generate bitstream 126. FIG. 2 is a flowchart of an image coding process performed by image coding apparatus 100 of the first exemplary embodiment. Feature quantity extraction unit 101 extracts a feature point included in input image 121 that is of a still or video image including at least one picture and a feature quantity of the feature point by a feature point and feature quantity extraction technique typified by the SIFT (S101). Image coding apparatus 100 divides input image 121 into coding blocks 122 that are of coding process units (S102). For each coding block 122, intra prediction unit 111 or inter prediction unit 115 generates prediction block 134 using decoded block 129 or decoded image 131 (S103). The detailed process is described later. Subtractor 103 generates difference block 123 that is of a difference between coding block 122 and prediction block 134 (S104). Frequency transform unit 104 performs a frequency transform on difference block 123 to generate coefficient block 124. Quantization unit 105 quantizes coefficient block 124 to generate coefficient block 125 (S105). Entropy coding unit 106 performs entropy coding on coefficient block 125 to generate bitstream 126 (S106). In order to generate decoded block 129 and decoded image 131 to be used in the generation of prediction block 134 of the subsequent block or picture, inverse quantization unit 107 performs inverse quantization on coefficient block 125 to generate coefficient block 127. Inverse frequency transform unit 108 performs inverse frequency transform on coefficient block 127 to restore difference block 128 (S107). Adder 109 adds prediction block 134 used in Step S103 and difference block 128 to generate decoded block 129 (reconstructed image) (S108). Decoded block 129 is used in an intra prediction process performed by intra prediction unit 111. By a technique similar to that in Step S101, feature quantity extraction unit 110 extracts the feature point included in decoded block 129 that is of a decoding result of an already-coded region in input image 121 at that time and the feature quantity of the feature point (S109). The extracted feature point and feature quantity are used in the intra prediction. Image coding apparatus 100 determines whether the coding process of the whole of one image is completed (S110). When the coding process of the whole of one image is completed (Yes in S110), loop filter 112 performs a filtering process such as a deblocking filter on a plurality of decoded blocks 129 included in the one image in order to relieve image quality degradation caused by a block deformation, and generates decoded image 131 (S111). Feature quantity extraction unit 113 extracts the feature point of decoded image 131 and the feature quantity of the feature point using the technique similar to that in Steps S101 and 5109 (S112). The extracted feature point and feature quantity are used in the inter prediction. Frame memory 114 stores decoded image 131 therein. Decoded image 131 is used in an inter prediction process performed by inter prediction unit 115. Image coding apparatus 100 repeatedly performs a series of processes until the coding process to whole input image 121 that is of an input video image is completed (S113). The inverse quantization and inverse frequency transform in Step S105 may sequentially be performed as a separate process or collectively be performed. Similarly the inverse quantization and inverse frequency transform in Step S107 may sequentially be performed as a separate process or collectively be performed. The quantization refers to a process in which values sampled at predetermined intervals are digitized while associated with respective predetermined levels. The inverse quantization refers to a process in which each value obtained through quantization is returned to a value in the original interval. In the data compression field, the quantization refers to a process in which values are classified into coarser intervals than the original ones, whereas the inverse quantization refers to a process in which values in coarser intervals are re-classified into the original finer intervals. In the codec technology field, the quantization and the inverse quantization are sometimes called rounding or scaling. The prediction block generation process in Step S103 will be described in detail below with reference to a flowchart in FIG. 3. Intra prediction unit 111 generates prediction block 130 through the intra prediction process (S121). Inter prediction unit 115 generates prediction block 132 through the inter prediction process (S122). Switching unit 116 performs a cost calculation on each of prediction blocks 130 and 132 obtained in Steps S121 and S122 using an R-D optimization model (the following (Eq. 1)), selects a technique less costly, namely, a technique having higher coding efficiency, and outputs the prediction block corresponding to the selected technique as prediction block 134 (S123). [Mathematical formula 1] Cost=D+λ× (Eq. 1) In (Eq. 1), D denotes coding distortion and is, for example, a sum of absolute values of differences between an original pixel value of a pixel in a coding-target block and a value of a corresponding pixel in the generated prediction image. R denotes a generated code quantity and is, for example, a code quantity necessary for the coding of motion information used to generate the prediction block. λ denotes the Lagrange multiplier. Therefore, an appropriate prediction mode is selected from among intra prediction and inter prediction, so that the coding efficiency can be improved. In advance of the processes in Steps S121 and S122, image coding apparatus 100 may decide which one of the prediction processes is used, and perform only the process corresponding to the decided prediction process. Therefore, a processing quantity for the prediction image generation process can be reduced. Image coding apparatus 100 performs coding on information indicating which one of the intra prediction and the inter prediction is used. As used herein, the coding means that the information is provided to the coding information, in other words, a coded bitstream including the information is generated. The intra prediction process in Step S121 will be described in detail below with reference to a flowchart in FIG. 4. Intra prediction unit 111 generates the prediction block by performing the intra prediction process adopted in H.264/AVC and H.265/HEVC in which information on the adjacent already-coded block is used (S141). Hereinafter, the process is referred to as usual intra prediction. Intra prediction unit 111 generates the prediction block through the intra prediction process in which a corresponding point of a feature point is used (S142). Hereinafter, the process is referred to as feature point use intra prediction. Intra prediction unit 111 performs the process similar to that in Step S123 on the prediction blocks generated in Steps S141 and S142, selects the technique having the higher coding efficiency in the techniques of Steps S141 and S142, and outputs the prediction block corresponding to the selected technique as prediction block 130 (S143). In advance of the processes in Steps S141 and S142, intra prediction unit 111 may decide which one of the prediction processes is used, and perform only the process corresponding to the decided prediction process. Therefore, a processing quantity for the prediction image generation process can be reduced. Image coding apparatus 100 performs the coding on information indicating which one of the usual intra prediction process and the feature point use intra prediction process is used. The feature point use intra prediction process in Step S142 will be described in detail below with reference to a flowchart in FIG. 5. Intra prediction unit 111 generates the prediction block by performing the intra prediction process in which the feature point included in a target block that is of a target in the prediction process is used (S161). Hereinafter, the prediction process is referred to as an in-block mode. Intra prediction unit 111 performs the intra prediction process in which the feature point existing in the already-coded region in surroundings of the target block is used (S162). Hereinafter, the prediction process is referred to as a surrounding block mode. Intra prediction unit 111 performs the process similar to that in Step S123 on each of the prediction blocks generated in Steps S161 and S162, and selects the technique having the higher coding efficiency in the in-block mode and the surrounding block mode (S163). In advance of the processes in Steps S161 and S162, intra prediction unit 111 may decide which one of the prediction modes is used, and perform only the process corresponding to the decided prediction process. Therefore, a processing quantity for the prediction image generation process can be reduced. The in-block mode intra prediction process in Step S161 will be described in detail below with reference to a flowchart in FIG. 6. Intra prediction unit 111 extracts the feature point existing in the target block from the feature point of the input image 121, the feature point of the input image 121 being obtained in Step S101 (S181). When the feature point exists (Yes in S182), intra prediction unit 111 performs a corresponding point search process (S183). Specifically, intra prediction unit 111 searches the corresponding point that is of the feature point having the feature quantity similar to the feature quantity of the feature point extracted in Step S181 from the feature points extracted from the decoded block of the already-coded region in the same image as the target block, the feature point being obtained in Step S109. As used herein, for example, the similarity means a small Euclid distance between the feature quantities. When the corresponding point exists in Step S183 (Yes in S184), intra prediction unit 111 performs the prediction image generation process using the information between the corresponding points (S185). FIG. 7 is a view illustrating the prediction image generation process, and illustrating target image 150 including target block 153 that is of a prediction process target. Target image 150 is already coded, and includes already-coded region 151 where decoded block 129 is generated and uncoded region 152 where the coding is not performed. Intra prediction unit 111 sets a region including target block 153 around feature point 154 extracted in Step S181 to prediction target region 155. Intra prediction unit 111 also sets a region around corresponding point 156 corresponding to feature point 154 extracted in Step S183 to reference region 157 used in the prediction image generation. Then, intra prediction unit 111 generates the prediction image (prediction block) using pixel information on reference block 158, which is included in reference region 157 and is the image located at a position corresponding to a position of target block 153 in prediction target region 155. At this point, local feature quantity extraction techniques, such as SIFT and ORB, which are used to decide reference region 157 as the feature point extraction technique, are robust to the scaling and the rotation. Therefore, as illustrated in FIG. 7, intra prediction unit 111 can generate the prediction image in consideration of the rotation and enlargement of prediction target region 155. Specifically, each feature point has information on the rotation quantity and scale value in addition to coordinate information. Intra prediction unit 111 transforms reference block 158 based on a difference between the rotation quantity and scale value of feature point 154 and the rotation quantity and scale value of corresponding point 156 to generate the prediction image (prediction block). In the case that reference region 157 includes an outside of target image 150, intra prediction unit 111 may perform a padding process in which a region having no piece of pixel information is generated by copying the pixel information near a terminal end of the image. Therefore, reference region 157 can be set by a simple process, and quality degradation of the prediction image can be suppressed. Instead of the padding process, intra prediction unit 111 may perform a folding process in which the pixel information outside a screen is generated by folding the pixel information inside the image with the terminal end as an axis. Alternatively, intra prediction unit 111 may paint pixels outside the image with a predetermined value. In the former, quality of the prediction image can be improved because detailed information on the image can be used. In the latter, an increase in processing amount can be suppressed because of the simple process of substituting a fixed value. Intra prediction unit 111 provides feature-point-related information to coding information (S186). When the feature point does not exist in the target block (No in S182), or when the corresponding point does not exist (No in S184), intra prediction unit 111 performs an exception process in the case that the corresponding point does not exist (S187). Specifically, intra prediction unit 111 sets a cost value of the exception process to the maximum value. For example, intra prediction unit 111 sets D and R in (Eq. 1) to infinite. Therefore, the technique in Step S161 is not selected in Step S163. The method for providing the feature-point-related information to the coding information in Step S186 will be described in detail below with reference to a flowchart in FIG. 8. At this point, the feature-point-related information includes corresponding point information that is of information on the corresponding point and feature point information that is of information on the feature point in the target block. Intra prediction unit 111 provides corresponding point information that is of the information necessary to search the corresponding point to the coding information (S201). Specifically, target point information indicates a coordinate of the corresponding point corresponding to the feature point included in the target block. Intra prediction unit 111 determines whether feature point information that is of the information on the feature point included in the target block is matched with a defined value (S202). As used therein, the feature point information means the coordinate of the feature point in the block, the rotation quantity and scale value possessed by the feature point, and the like. For example, the defined value of the coordinate is a coordinate in the center of the target block, the rotation quantity has the defined value of 0 degree, and the scale value has the defined value of 1. When all the pieces of feature point information included in the target block are matched with the defined values (Yes in S202), intra prediction unit 111 turns off a detailed information flag indicating that the detailed information on the feature point exists, and intra prediction unit 111 provides the detailed information flag to the coding information (S203). When at least one of the pieces of feature point information included in the target block is not matched with the defined value (No in S202), intra prediction unit 111 turns on the detailed information flag, and intra prediction unit 111 provides the detailed information flag to the coding information (S204). Intra prediction unit 111 provides pieces of detailed information such as the coordinate and rotation quantity of the feature point included in the target block to the coding information (S205). The corresponding point information in Step S201 is not limited to the above information. The corresponding point information may be an index that can uniquely decide the corresponding point from the feature point group (feature points extracted from the whole already-coded region) including the corresponding point. For example, the index is set such that the value of the feature point decreases as the feature point comes close to the target block. Alternatively, the index is set such that the value of the feature point decreases with increasing reliability corresponding to the feature quantity. Although two-dimensional information is required for the use of the coordinate, the corresponding point can be indicated by one-dimensional information for the use of the index. The defined value in Step S202 is not limited to the above value. For example, the defined value of the coordinate may be a coordinate at an upper left end of the target block. The defined value of the rotation quantity may be a rotation quantity in the whole image. The detailed information may indicate an absolute value or relative value of the coordinate, rotation quantity, or scale value. That is, the detailed information may indicate a difference between the defined value of the coordinate, rotation quantity, or scale value and the coordinate, rotation quantity, or scale value of the feature point used. Alternatively, the detailed information may indicate a difference in coordinate, rotation quantity, or scale value between the corresponding point and the feature point. The defined value in Step S202 may be a defined value of the above difference. Although the process of determining whether all the elements such as the coordinate, the rotation quantity, and the scale value are matched with the defined values is described as the determination process in Step S202, intra prediction unit 111 may perform the determination of each element, and code a flag of each element. Alternatively, intra prediction unit 111 may group the plurality of elements into some groups, perform the determination in each group, and code a flag of each group. For at least two flags, intra prediction unit 111 performs the processes in Steps S202 to 5205 times for the number of flags. For example, intra prediction unit 111 may code the flag for the coordinate information and the flag for the information on the rotation quantity and scale value. Therefore, the setting is flexibly performed during the coding, so that the coding efficiency can be improved. The surrounding block mode intra prediction process in Step S162 will be described in detail below with reference to a flowchart in FIG. 9. Intra prediction unit 111 extracts the feature point included in an adjacent region, which is of the decoded image of the already-coded region adjacent to the target block, from the feature point obtained in Step S109 (S221). When at least one feature point can be extracted in Step S221 (Yes in S222), intra prediction unit 111 extracts the feature point extracted from the decoded image of the already-coded region in the same image as the target block in the feature points obtained in Step S109 with respect to extracted at least the one feature point, and intra prediction unit 111 searches the corresponding point in the extracted feature points (S223). When at least one corresponding point exists in Step S223 (Yes in S224), intra prediction unit 111 generates the prediction image from the corresponding point information (S225). FIG. 10 is a view illustrating this process, and illustrating target image 150 including target block 153 that is of the prediction process target. Target image 150 is already coded, and includes already-coded region 151 where decoded block 129 is generated and uncoded region 152 where the coding is not performed. Intra prediction unit 111 selects at least one feature point 164 from the feature point group, which is obtained in Step S221 and exists in the surrounding region of the target block, and sets prediction target region 165 including both feature point 164 and target block 153. Intra prediction unit 111 sets the region including corresponding point 166 of feature point 164 included in prediction target region 165 to reference region 167. In setting reference region 167, intra prediction unit 111 performs geometric transforms such as an affine transform using the plurality of corresponding points 166. Therefore, the coding efficiency is improved because the quality of the prediction image is improved. Then, intra prediction unit 111 generates the prediction image (prediction block) using pixel information on reference block 168, which is included in reference region 167 and is the image located at the position corresponding to the position of target block 153 in prediction target region 165. Intra prediction unit 111 needs not to generate the prediction image using all the feature point at which the corresponding points are found, but may change a combination of the corresponding points used and decide a combination of the corresponding points having the best coding efficiency. Therefore, the coding efficiency is further improved. In the case that reference region 167 includes the outside of target image 150, intra prediction unit 111 may perform an out-of-region process such as the padding process described in Step S185. Therefore, the coding efficiency is improved. Then intra prediction unit 111 provides the feature-point-related information, which is of the information on the feature point necessary for the process in Step S225, to the coding information (S226). When the feature point does not exist in the region adjacent to the target block (No in S222), or when the corresponding point does not exist (No in S224), intra prediction unit 111 performs the exception process in the case that the corresponding point does not exist (S227). The process in Step S227 is similar to the process in Step S187, and is performed such that the technique in Step S162 is not selected. The process of providing the feature-point-related information to the coding information in Step S226 will be described in detail below with reference to a flowchart in FIG. 11. At this point, the feature-point-related information includes extraction range information indicating extraction region 175 including feature points 174 in the surroundings of target block 153, number information indicating the number of feature points used in feature points 174 extracted in the extraction region 175, and feature point designating information designating the feature point used in feature points 174 extracted in extraction region 175. Intra prediction unit 111 provides the extraction range information necessary to designate extraction region 175 that is of a rectangular region including all feature points 174 in the surroundings of target block 153 used in Step S225 to the coding information (S241). For example, the extraction range information is information defining a width and a height of extraction region 175, and the extraction range information includes information indicating width 171 and height 172 in FIG. 12. Intra prediction unit 111 provides the number information indicating the number of feature points (corresponding points) used in Step S225 to the coding information (S242). In other words, the number information indicates the number of feature points (corresponding points) included in a set of feature points used. When all feature points 174 extracted in extraction region 175 designated by the information in Step S241 are used (Yes in S243), intra prediction unit 111 turns off the detailed information flag indicating that the detailed information on the feature point exists, and intra prediction unit 111 provides the detailed information flag to the coding information (S244). On the other hand, when all the feature points extracted in extraction region 175 are used (No in S243), intra prediction unit 111 turns on the detailed information flag, and intra prediction unit 111 provides the detailed information flag to the coding information (S245). Intra prediction unit 111 provides the pieces of feature point designating information, which designates the feature point used in feature points 174 extracted in extraction region 175, for the number of feature points to the coding information (S246). For example, the feature point designating information is information indicating the coordinate of the feature point. The coding process in Steps S241, S242, and Steps S243 to S246 is not limited to the above order, but may properly be changed. The width and height of extraction region 175 in Step S241 may be designated in units of coding blocks, images, or sequences. A fixed value may be used as the width and height of extraction region 175. In the case that the width and height are changed in units of blocks, the range is flexibly set, so that the quality of the prediction image can be improved. In the case that the width and height are designated in units of images, the coding efficiency is improved because the coding information decreases. Different values may be set to the width and height of extraction region 175, or an identical value may be set to the width and the height. In the case that the different values are set to the width and height, the effective feature point is easily selected, so that the quality of the prediction image can be improved. On the other hand, in the case that the identical value is set to the width and the height, a code quantity can be reduced because of only one piece of information necessary for the coding. The extraction range information in Step S241 may indicate the number of pixels corresponding to the width and height, or indicate the number of already-coded blocks corresponding to the width and height. In this case, the number of blocks in a width direction and the number of blocks in a height direction may separately be designated, or an identical value may be used as the number of blocks in the width direction and the number of blocks in the height direction. The code quantity can be reduced because the use of the number of blocks can express distance information such as the width by a smaller value. The inter prediction process in Step S122 performed by inter prediction unit 115 will be described in detail below with reference to a flowchart in FIG. 13. Inter prediction unit 115 generates the prediction image by performing the inter prediction process using motion information used in H.264/AVC or H.265/HEVC that is of the existing video coding scheme (S261). Hereinafter, the process is referred to as usual inter prediction. Inter prediction unit 115 generates the prediction image by performing the inter prediction process in which the feature point is used (S262). Hereinafter, the process is referred to as feature point use inter prediction. Intra prediction unit 115 performs the process similar to that in Step S123 on each of the prediction images obtained in Steps S261 and S262, thereby selecting the technique having the higher coding efficiency (S263). The feature point use inter prediction process in Step S262 will be described in detail below with reference to a flowchart in FIG. 14. Inter prediction unit 115 generates the prediction image by performing the inter prediction process in which the feature point included in the target block is used (S281). Hereinafter, the prediction process is referred to as an in-block mode. Inter prediction unit 115 performs the inter prediction process in which the feature point existing in the already-coded region in the surroundings of the target block is used (S282). Hereinafter, the prediction process is referred to as a surrounding block mode. Inter prediction unit 115 performs the process similar to that in Step S123 on each of the prediction images generated in Steps S281 and S282, thereby selecting the technique having the higher coding efficiency (S283).
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