JP2018166306A - Coding apparatus, imaging apparatus, coding method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for suppressing deterioration in image quality while suppressing an increase in storage capacity used by storing a reference image when resolution of a coding target image increases.SOLUTION: The coding apparatus is so configured that, when a resolution in a first direction of a coding target image is a first resolution, selecting means selects a reference image such that a temporal distance between the coding target image and a reference image is within a first distance, and motion vector detecting means searches a search range of a motion vector in a second direction orthogonal to the first direction as a first search range. When the resolution in the first direction of the coding target image is a second resolution higher than the first resolution, the selecting means selects the reference image such that the temporal distance between the coding target image and the reference image is within a second distance shorter than the first distance, and the motion vector detection means searches a search range of the motion vector in the second direction as a second search range narrower than the first search range.SELECTED DRAWING: Figure 10

Description

  The present invention relates to an encoding device, an imaging device, an encoding method, and a program.

  In recent years, 4k televisions and 4k video cameras have become widespread, and the resolution of moving images has been increasing. Along with this, the amount of pixel data processed by the system is increasing. H. is an international standard encoding standard for moving images. In coding schemes such as H.264 and HEVC (High Efficiency Video Coding), a technique called motion vector detection is used. Motion vector detection is performed by detecting motion between an image to be encoded and an encoded reference image that is temporally different from the image to be encoded, and performing video compression based on the motion information. Increases efficiency.

  In this motion vector detection, motion is detected for each block to be encoded within a predetermined search range. A wider search range improves the accuracy of motion vector detection, but increases the circuit scale and processing amount. On the other hand, when a search range narrower than the original motion of the subject is set, since the motion cannot be tracked, the accuracy of motion vector detection is lowered, leading to image quality degradation.

  Therefore, setting the search range appropriately is a very important element for motion vector detection, and a technique has been proposed in which the search range is changed according to the frame rate of the input image (see Patent Document 1). .

  When motion vector detection is performed by hardware processing, the search range portion of the reference image placed in the external memory is read out and held in the internal memory, and motion vector detection is performed. As a configuration of the internal memory for storing the reference image, a line buffer that holds data for the horizontal resolution of the image in the horizontal direction is often used. This is because when reading a reference image from an external memory, if the necessary reference image is read for each coding block without using a line buffer, it is necessary to read the same pixel over and over again. This is because the image data reading bus bandwidth is wasted.

  When such a line buffer is used, the horizontal size of the line buffer corresponds to the horizontal resolution of the image, and the vertical size corresponds to the vertical search range in motion vector detection.

JP 2010-239230 A

  The horizontal size of the reference image storage line buffer used for motion vector detection depends on the horizontal resolution of the image. Therefore, it is necessary to increase the size of the line buffer in the horizontal direction as the resolution of moving images increases.

  However, if the horizontal size is increased while maintaining the vertical size of the line buffer, the storage capacity of the line buffer increases, leading to an increase in circuit scale and cost. On the other hand, if the horizontal size is increased while maintaining the storage capacity of the line buffer in order to suppress an increase in circuit scale, the vertical size is reduced. As a result, the searchable range in the vertical direction in motion vector detection is narrowed, which may lead to image quality degradation.

  The present invention has been made in view of such a situation. When the resolution of an image to be encoded increases, a technique for suppressing image quality deterioration while suppressing an increase in storage capacity used by storing a reference image. The purpose is to provide.

  In order to solve the above-described problem, the present invention is an encoding apparatus that performs motion compensation prediction encoding on an encoding target image included in a moving image in units of blocks, and selects a reference image from the moving image A selection unit; a detection unit that detects a motion vector of an encoding target block of the encoding target image by searching a part of the reference image; and the encoding target block is encoded based on the motion vector And when the resolution in the first direction of the encoding target image is the first resolution, the selection unit is configured to select a temporal interval between the encoding target image and the reference image. The reference image is selected so that a short distance is within the first distance, and the detection unit uses the motion vector search range in the second direction orthogonal to the first direction as the first search range. Search And when the resolution in the first direction of the encoding target image is a second resolution higher than the first resolution, the selection unit is configured to select between the encoding target image and the reference image. The reference image is selected so that a temporal distance of the second image is within a second distance shorter than the first distance, and the detection means sets the motion vector search range in the second direction to the second distance. An encoding apparatus is provided that performs the search as a second search range narrower than one search range.

  Other features of the present invention will become more apparent from the accompanying drawings and the following description of the preferred embodiments.

  According to the present invention, when the resolution of a moving image increases, it is possible to suppress deterioration in image quality while suppressing an increase in storage capacity used by storing a reference image.

The block diagram which shows the structure of the imaging device 100 containing an encoding apparatus. The figure which shows the example of a GOP structure. The figure which shows the example of a structure using TemporalID. The figure which shows the search range of an encoding object block (CTU (Coding Tree Unit)) and motion vector detection. The figure which shows the search range of the motion vector detection corresponding to the encoding object CTU next to CTU401. The figure which shows the search range of the motion vector detection corresponding to CTU (43,0) which becomes a search range to the right end of a screen. The figure which shows the search range of the motion vector detection corresponding to CTU (0, 1). The figure which shows the search range of the motion vector detection corresponding to CTU (43, 5) from which the search range of the upper and lower sides of encoding object CTU becomes equal, and becomes a search range to the upper end of a screen. The figure which shows the search range of the motion vector detection corresponding to CTU (0, 6). 6 is a flowchart of encoding processing executed by the imaging apparatus 100.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention. Moreover, it is possible to appropriately combine the features described in different embodiments.

[First Embodiment]
FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus 100 including an encoding apparatus. In the following description, it is assumed that the imaging apparatus 100 is compatible with HEVC. However, the encoding method of the present embodiment is not limited to HEVC, and can be applied to any encoding method involving motion compensation prediction encoding. It is.

  The captured image is input to the imaging unit 102 through the lens 101. The imaging unit 102 converts the image into digital pixel data and sends it to the development processing unit 103. The development processing unit 103 performs image processing such as debayer processing, scratch correction, noise removal, enlargement / reduction processing, and color conversion processing to the YCbCr format. An image in a format that can be subjected to compression encoding after image processing is input to the encoding frame buffer 104. The imaging apparatus 100 uses this image as an encoding target image. The reference frame buffer 105 stores a reference image. The encoding block buffer 106 acquires the encoding target image stored in the encoding frame buffer 104 for each block and stores it as an encoding target block.

  The reference line buffer 107 acquires a reference image necessary for motion vector detection from the reference frame buffer 105 and stores it. Note that the reference image (buffer image) simultaneously held by the reference line buffer 107 is not the entire reference image but a part thereof (details will be described later with reference to FIGS. 4 to 9).

  The encoding frame buffer 104 and the reference frame buffer 105 are implemented using a DRAM (Dynamic Random Access Memory) (not shown). Also, the encoding block buffer 106 and the reference line buffer 107 are implemented using a memory different from the encoding frame buffer 104 and the reference frame buffer 105. For example, the encoding frame buffer 104 and the reference frame buffer 105 are implemented using an unillustrated SRAM (Static Random Access Memory).

  The motion prediction unit 108 performs motion vector detection by performing block matching between the encoding target block stored in the encoding block buffer 106 and the reference image stored in the reference line buffer 107. The motion prediction unit 108 takes a pixel difference between the encoding target block and a reference image (prediction image) at a position corresponding to the detected motion vector, and outputs the difference image to the orthogonal transformation unit 109. In addition, the motion prediction unit 108 outputs the predicted image to the motion compensation unit 116 in order to create a local decoded image.

  The orthogonal transform unit 109 performs discrete cosine transform on the difference image output from the motion prediction unit 108, generates a transform coefficient, and outputs the transform coefficient to the quantization unit 110.

  The quantization unit 110 quantizes the transform coefficient output from the orthogonal transform unit 109 according to the quantization step size output from the quantization control unit 111. The quantized transform coefficient is output to the variable length encoding unit 112 for generating an encoded stream, and is output to the inverse quantization unit 114 for generating a local decoded image.

  The variable length coding unit 112 performs zigzag scanning, alternate scanning, and the like on the quantized transform coefficients to perform variable length coding. In addition, the variable length coding unit 112 performs variable length coding on coding method information such as motion vectors, quantization step sizes, block division information, and parameters for adaptive offset processing with respect to variable length coded transform coefficients. Is added to generate an encoded stream. The generated encoded stream is recorded on the recording medium 113. In addition, the variable length coding unit 112 calculates a generated code amount for each block at the time of coding and outputs it to the quantization control unit 111.

  The quantization control unit 111 uses the generated code amount output from the variable length encoding unit 112 to determine a quantization step size so as to be a target code amount, and outputs the quantization step size to the quantization unit 110.

  The inverse quantization unit 114 performs inverse quantization on the quantized transform coefficient output from the quantization unit 110 to generate a transform coefficient for local decoding. The transform coefficient is output to the inverse orthogonal transform unit 115.

  The inverse orthogonal transform unit 115 performs inverse discrete cosine transform on the transform coefficient output from the inverse quantization unit 114 to generate a difference image. The generated difference image is output to the motion compensation unit 116.

  The motion compensation unit 116 adds the predicted image output from the motion prediction unit 108 and the difference image output from the inverse orthogonal transform unit 115 to generate image data for local decoding. The generated image data is output to the deblocking filter unit 117.

  The deblocking filter unit 117 applies a deblocking filter to the image data output from the motion compensation unit 116. The image after the deblocking filter is output to the adaptive offset processing unit 118.

  The adaptive offset processing unit 118 selects one of band offset processing, edge offset processing, or no processing, and determines a band position, an edge direction, an offset value, and the like for performing the adaptive offset processing. Then, the adaptive offset processing unit 118 stores, in the reference frame buffer 105, a local decoded image obtained by performing the adaptive offset processing on the image after the deblocking filter. The adaptive offset processing unit 118 generates a parameter for adaptive offset processing such as a band position, an edge direction, and an offset value as an encoded stream, which variable length code has been selected as the adaptive offset processing. To the conversion unit 112. By such an operation, an encoded stream and a local decoded image are created.

  The search range control unit 119 determines a vertical search range for motion vector detection based on the resolution information of the input image. The encoding control unit 120 determines a reference relationship between an encoding target image and an image (reference image) referred to at the time of motion detection, that is, a GOP (Group of Pictures) structure, based on the resolution information of the input image. Also, the encoding control unit 120 controls the encoding process by controlling each unit of the imaging apparatus 100 according to a control program stored in a ROM (not shown).

  FIG. 2 is a diagram illustrating an example of a GOP structure. In FIG. 2, “I”, “P”, and “B” represent an I picture, a P picture, and a B picture, respectively. Each picture is arranged in the display order. In FIG. 2A, a P picture 201 refers to an I picture 202 eight frames before, and this reference is the maximum reference distance in time. A GOP structure in which the maximum reference distance in time is 8 pictures is defined as “M = 8”. At this time, the B picture 203 refers to the P picture 201 or the I picture 202. The B picture 204 refers to the I picture 202 or the B picture 203. The B picture 205 refers to the P picture 201 or the B picture 203. The B picture 206 refers to the I picture 202 or the B picture 204. The B picture 207 refers to the B picture 203 or the B picture 204. The B picture 208 refers to the B picture 203 or the B picture 205. The B picture 209 refers to the P picture 201 or the B picture 205.

  In FIG. 2B, a P picture 210 refers to the previous I picture 211, and this reference is the maximum reference distance in time. A GOP structure in which the maximum reference distance in time is four pictures is defined as “M = 4”. At this time, the B picture 212 refers to the P picture 210 or the I picture 211. The B picture 213 refers to the I picture 211 or the B picture 212. The B picture 214 refers to the P picture 210 or the B picture 212.

  In FIG. 2C, the P picture 215 refers to the previous I picture 216, and this reference is the maximum reference distance in time. A GOP structure in which the maximum reference distance in time is three pictures is defined as “M = 3”. At this time, the B picture 217 and the B picture 218 refer to the P picture 215 or the I picture 216.

  In FIG. 2D, the P picture 219 refers to the previous I picture 220, and this reference is the maximum reference distance in time. The GOP structure in which the maximum reference distance in time is two pictures is defined as “M = 2”. At this time, the B picture 221 refers to the P picture 219 or the I picture 220.

  Thus, the temporal distance between the encoding target image and the reference image is within a distance defined by the value of M. In the examples of FIGS. 2A to 2D, the reference destination of the P picture is the maximum reference distance in terms of time. However, the GOP structure may be configured such that the reference destination of the B picture is the maximum reference distance in time. Moreover, although only the case of M = 2, 3, 4, and 8 was illustrated, the reference distance is not limited to these, and a GOP structure with other reference distances (for example, M = 5 and M = 9) can be used. It is.

  In HEVC, a time hierarchical structure can be used. By assigning a temporal ID (time identifier) to the stream according to this time hierarchical structure, a moving image can be output at a corresponding time resolution. For example, a 30p or 15p stream can be extracted from a 60p (p: progressive) stream encoded at 60 frames per second.

  FIG. 3 shows an example of a configuration using TemporalID. In this example, a moving image is encoded in four layers having different Temporal IDs in the GOP structure of M = 8 shown in FIG. For example, the I picture 202, the B pictures 203, 204, 205, and the P picture 201 can be reproduced by taking out and reproducing the stream of the portion of TemporalID = 0, 1, 2. That is, it is possible to extract and reproduce only the 30p portion from the 60p stream. At this time, the temporal ID is 0 for the picture having the maximum temporal reference distance (here, P picture 201).

  Next, a method for storing a reference image in the reference line buffer 107 (buffer memory) will be described. Here, an example will be described in which the resolution of the encoding target image is 1920 × 1080, the horizontal search range for motion vector detection is ± 512 pixels, and the vertical search range is ± 128 lines.

  FIG. 4 shows an encoding target block (CTU (Coding Tree Unit)) and a search range for motion vector detection. The CTU size is 32 × 32 pixels. A CTU when the horizontal CTU position is x and the vertical CTU position is y is expressed as CTU (x, y).

  A CTU 401 is a CTU at the head of a picture and corresponds to CTU (0, 0). In this case, the reference image 402 serving as a search range for motion vector detection has 544 pixels in the horizontal direction of 0 to 543 and 160 lines in the vertical direction of 0 to 159. The encoding control unit 120 acquires the reference image 402 from the reference frame buffer 105 and stores it in the reference line buffer 107 before encoding the CTU 401.

  FIG. 5 is a diagram illustrating a search range of motion vector detection corresponding to the next CTU 401 to be encoded. The CTU 501 corresponds to CTU (1, 0). In this case, the reference image 502 serving as a search range for motion vector detection has 576 pixels in the horizontal direction of 0 to 575 and 160 lines in the vertical direction of 0 to 159. Prior to encoding of the CTU 501, reference images in the horizontal direction 0 to 543 are already stored in the reference line buffer 107. Therefore, the encoding control unit 120 acquires only the reference image 503 in the horizontal direction 544 to 575 that is newly required from the reference frame buffer 105 and stores it in the reference line buffer 107.

  Next, encoding of CTU (43, 0) in which the search range is up to the right end of the screen will be described with reference to FIG. FIG. 6 shows the search range of motion vector detection at this time. The CTU 601 corresponds to the CTU (43, 0). The reference image 602 serving as the search range for motion vector detection at this time has 1056 pixels in the horizontal direction from 864 to 1919 and 160 lines in the vertical direction from 0 to 159. The reference image 603 is a portion of 0 to 863 in the horizontal direction and 0 to 159 in the vertical direction. This portion is outside the search range of the CTU 601, but is necessary when detecting the motion vector of the next CTU line. It has been retained.

  With reference to FIG. 7, encoding of CTU (0, 1), which is the next CTU line, will be described. FIG. 7 shows the search range of motion vector detection at this time. The CTU 701 corresponds to CTU (0, 1). The reference image 702 serving as a search range for motion vector detection at this time has 544 pixels in the horizontal direction of 0 to 543 and 192 lines in the vertical direction of 0 to 191. At the start of encoding of the CTU 701, the reference image in the vertical direction 0 to 159 has already been stored in the reference line buffer 107 because it has been used for previous encoding. Therefore, the encoding control unit 120 acquires only the reference images 703 in the horizontal direction 0 to 543 and the vertical directions 160 to 191 that are newly required from the reference frame buffer 105 and stores them in the reference line buffer 107.

  Next, the encoding of CTU (43, 5) in which the upper and lower search ranges of the encoding target CTU are equal and the search range is the search range will be described with reference to FIG. FIG. 8 shows the search range of motion vector detection at this time. The CTU 801 corresponds to the CTU (43, 5). The reference image 802 serving as a search range for motion vector detection at this time has 1056 pixels in the horizontal direction from 864 to 1919 and 288 lines in the vertical direction from 0 to 287. At this time, the reference line buffer 107 stores a reference image of 0 to 1919 in the horizontal direction which is the same as the resolution of the encoding target image and 0 to 287 in the vertical direction corresponding to the search range.

  Next, encoding of CTU (0, 6), which is the next CTU line, will be described with reference to FIG. FIG. 9 shows the search range of motion vector detection at this time. The CTU 901 corresponds to CTU (0, 6). The reference image 902 serving as a search range for motion vector detection at this time has 544 pixels in the horizontal direction of 0 to 543 and 288 lines in the vertical direction of 32 to 319. The reference images 903 in the horizontal direction 0 to 1919 and the vertical direction 0 to 31 do not become the search range in subsequent CTUs. For this reason, the encoding control unit 120 sets a part of the SRAM in which the reference image 903 has been stored as an empty area, and stores a newly required reference image in this part. That is, the encoding control unit 120 uses the reference line buffer 107 to store the reference image 904 in the horizontal direction 0 to 543 and the vertical direction 288 to 319 that are newly required, using the SRAM of the part in which the reference image 903 is stored. To store.

  Thus, the reference line buffer 107 is used so that the horizontal size matches the horizontal resolution of the encoding target image, and the vertical size matches the maximum search range (including the vertical CTU size) in the vertical direction. . When the resolution of the encoding target image is 1920 × 1080 and the CTU size is 32 × 32, the horizontal size of the reference line buffer 107 is 1920 pixels that is the horizontal resolution of the encoding target image. The vertical size of the reference line buffer 107 is 288 lines in total because the vertical search range (excluding the vertical CTU size) is ± 128 lines and 256 lines, and the vertical CTU size is 32 lines. The maximum size of the buffer image stored in the reference line buffer 107 in the horizontal direction is 1920 pixels corresponding to the horizontal resolution.

  Next, a case where the resolution of the encoding target image is increased will be described. In the above description, consider a case where the resolution which was 1920 × 1080 has increased to 3840 × 2160. In order to increase the horizontal size from 1920 pixels to 3840 pixels while maintaining the storage capacity of the reference line buffer 107, it is necessary to decrease the vertical size from 288 lines to 144 lines. In this case, the maximum search range in the vertical direction (including the vertical CTU size) is also reduced from 288 lines to 144 lines. As a result, the search range in the vertical direction becomes narrower than the original movement of the subject, and the possibility that the movement cannot be tracked increases, which may lead to image quality degradation.

  In order to compensate for the reduction in the search range in the vertical direction, the encoding control unit 120 shortens the maximum time distance of the reference image for motion vector detection by changing the GOP structure. For example, consider a case where the GOP structure when the resolution is 1920 × 1080 is M = 8. In this case, when the resolution increases to 3840 × 2160, the encoding control unit 120 changes the GOP structure to M = 4. When the time distance of the reference image is halved, the movement of the corresponding subject is also halved. Accordingly, it is possible to compensate for the halving of the vertical search range accompanying the halving of the vertical size of the reference line buffer 107.

  Here, it is assumed that a change in the spatial search range due to a change in pixel density is not considered. Regardless of the pixel density, even if the comparison is made only with the number of pixels in the search range, the search range is reduced as the resolution of the encoding target image increases, and the number of pixels in the search range is reduced by reducing the time distance of the reference image. Can be compensated for.

  Further, the reduction rate of the maximum time distance of the reference image does not necessarily match the reduction rate of the size of the reference line buffer 107 in the vertical direction. For example, even by changing the GOP structure from M = 8 to M = 7, the reduction in the vertical size of the reference line buffer 107 can be compensated to some extent.

  FIG. 10 is a flowchart of the encoding process executed by the imaging apparatus 100. Unless otherwise specified, the processing of each step in this flowchart is realized by the encoding control unit 120 controlling each unit of the imaging apparatus 100 according to the control program.

  In S1001, the encoding control unit 120 checks the horizontal resolution of the encoding target image. If the horizontal resolution is 1920, the process proceeds to S1002, and if the horizontal resolution is 3840, the process proceeds to S1004.

  In S1002, the encoding control unit 120 sets the GOP structure to M = 8. In S1003, the encoding control unit 120 sets the vertical search range to 288 lines.

  In S1004, the encoding control unit 120 sets the GOP structure to M = 4. In S1005, the encoding control unit 120 sets the vertical search range to 144 lines.

  In S1006, the encoding control unit 120 encodes the encoding target image. At this time, the encoding control unit 120 performs motion vector detection (selection of a reference image, storage of a reference image in the reference line buffer 107, etc.) using the GOP structure and vertical search range set above.

  As described above, according to the first embodiment, when the horizontal resolution of the encoding target image increases, the imaging apparatus 100 reduces the search range in the vertical direction in motion vector detection and temporally compares the reference image. Reduce the maximum distance. As a result, when the resolution of the encoding target image increases, it is possible to suppress image quality deterioration while suppressing an increase in storage capacity used by storing the reference image.

  Note that FIG. 10 shows only cases where the horizontal resolution is 1920 and 3840, but the horizontal resolution of the present embodiment is not limited to this. Also, regarding the GOP structure and the vertical search range, what is shown in FIG. 10 is merely an example, and the present embodiment is not limited to the configuration of FIG. Further, the relationship between the horizontal and the vertical explained in FIG. 10 can be exchanged. That is, when the reference line buffer 107 is a vertical line buffer, the encoding control unit 120 confirms the vertical resolution in S1001. Then, the encoding control unit 120 sets the horizontal search range in S1004 and S1005 so that the horizontal search range is reduced as the vertical resolution increases. When generalized, the encoding control unit 120 reduces the search range in the second direction orthogonal to the first direction in motion vector detection as the resolution in the first direction of the encoding target image increases, The maximum value of the temporal distance of the reference image is decreased. The greater the degree of reduction of the search range, the more the storage capacity of the reference line buffer 107 is suppressed. Also, the greater the degree of decrease in the maximum value of the temporal distance of the reference image, the greater the degree that the search range can be compensated.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

  DESCRIPTION OF SYMBOLS 104 ... Encoding frame buffer, 105 ... Reference frame buffer, 106 ... Encoding block buffer, 107 ... Reference line buffer, 108 ... Motion estimation part, 109 ... Orthogonal transformation part, 110 ... Quantization part, 112 ... Variable length encoding Unit, 120 ... encoding control unit

Claims (9)

An encoding device that performs motion compensation prediction encoding on a block-by-block basis for an encoding target image included in a moving image,
Selecting means for selecting a reference image from the moving images;
Detecting means for detecting a motion vector of an encoding target block of the encoding target image by searching a part of the reference image;
Encoding means for encoding the encoding target block based on the motion vector;
With
When the resolution in the first direction of the encoding target image is the first resolution,
The selection means selects the reference image so that a temporal distance between the encoding target image and the reference image is within a first distance,
The detection means performs the search using a search range of the motion vector in a second direction orthogonal to the first direction as a first search range,
When the resolution in the first direction of the encoding target image is a second resolution higher than the first resolution,
The selection unit selects the reference image so that a temporal distance between the encoding target image and the reference image is within a second distance shorter than the first distance;
The encoding device characterized in that the detection means performs the search using a search range of the motion vector in the second direction as a second search range narrower than the first search range. Control means for controlling a buffer memory to store a buffer image including the part of the reference image corresponding to the motion vector search range;
The encoding apparatus according to claim 1, wherein the detection unit detects the motion vector by searching the part of the reference image stored in the buffer memory. The encoding apparatus according to claim 2, wherein the maximum size of the buffer image in the first direction corresponds to the resolution in the first direction of the encoding target image. The ratio between the first distance and the second distance is equal to the ratio between the first search range and the second search range. 4. The encoding device described. The encoding means is configured to perform encoding with a temporal hierarchical structure,
The resolution of the encoding target image in the first direction is the first resolution, and the temporal distance between the encoding target image and the reference image is the first distance; and When the resolution of the encoding target image in the first direction is the second resolution and the temporal distance between the encoding target image and the reference image is the second distance. The encoding apparatus according to claim 1, wherein the encoding target image belongs to the lowest time hierarchy. The encoding apparatus according to claim 1, wherein the first direction is a horizontal direction and the second direction is a vertical direction. The encoding device according to any one of claims 1 to 6,
Imaging means for generating the moving image;
An imaging apparatus comprising: An encoding method executed by an encoding device that performs motion compensation prediction encoding on a block-by-block basis for an encoding target image included in a moving image,
A selection step of selecting a reference image from the moving image;
Detecting a motion vector of an encoding target block of the encoding target image by searching a part of the reference image; and
An encoding step of encoding the encoding target block based on the motion vector;
With
When the resolution in the first direction of the encoding target image is the first resolution,
The selection step selects the reference image so that a temporal distance between the encoding target image and the reference image is within a first distance,
The detection step performs the search using a search range of the motion vector in a second direction orthogonal to the first direction as a first search range,
When the resolution in the first direction of the encoding target image is a second resolution higher than the first resolution,
The selection step selects the reference image so that a temporal distance between the encoding target image and the reference image is within a second distance shorter than the first distance,
The encoding method, wherein the detection step performs the search with a search range of the motion vector in the second direction as a second search range narrower than the first search range.   The program for functioning a computer as each means of the encoding apparatus of any one of Claims 1 thru | or 6.

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