Abstract: An encoder includes: circuitry; and memory coupled to the circuitry. In operation, the circuitry: derives a base motion vector to be used in predicting a current block to be encoded; derives a first motion vector different from the base motion vector; derives a motion vector difference based on a difference between the base motion vector and the first motion vector; determines whether the motion vector difference is greater than a threshold; modifies the first motion vector when the motion vector difference is determined to be greater than the threshold, and does not modify the first motion vector when the motion vector difference is determined not to be greater than the threshold; and encodes the current block using the first motion vector modified or the first motion vector not modified.

Abstract: An image coding method includes: deriving a candidate for a motion vector predictor from a co-located motion vector; adding the candidate to a list; selecting the motion vector predictor from the list; and coding a current block and coding a current motion vector, wherein the deriving includes: deriving the candidate by a first derivation scheme in the case of determining that each of a current reference picture and a co-located reference picture is a long-term reference picture; and deriving the candidate by a second derivation scheme in the case of determining that each of the current reference picture and the co-located reference picture is a short-term reference picture.

Abstract: An encoder capable of properly handling an image to be encoded or decoded includes processing circuitry and memory connected to the processing circuitry. Using the memory, the processing circuitry: obtains parameters including at least one of (i) one or more parameters related to a first process for correcting distortion in an image captured with a wide angle lens and (ii) one or more parameters related to a second process for stitching a plurality of images; generates an encoded image by encoding a current image to be processed that is based on the image or the plurality of images; and writes the parameters into a bitstream including the encoded image.

Abstract: An encoder determines, based on a width and a height of a block, whether or not to disable a prediction mode in which the block is split along a partitioning line defined by a distance and an angle and then prediction is performed; and encodes the block with the prediction mode disabled or not disabled according to a result of the determination on whether or not to disable the prediction mode. Here, the distance is the shortest distance between the center of the block and the partitioning line, and the angle is an angle representing a direction from the center of the block toward the partitioning line in the shortest distance. The encoder determines to disable the prediction mode when (i) a width-to-height ratio is at least 8 or (ii) a height-to-width ratio is at least 8.

Abstract: An encoder includes circuitry and memory connected to the circuitry. The circuitry: derives an absolute value of a sum of gradient values in first and second ranges; derives, as a first parameter, a total sum of absolute values of sums of gradient values derived respectively for pairs of relative pixel positions; derives a pixel difference value between pixel values in the first and second ranges; inverts or maintains a plus or minus sign of the pixel difference value, according to a plus or minus sign of the sum of the gradient values indicating the sum of the gradient values in the first and second ranges; derives, as a second parameter, a total sum of pixel difference values each having the plus or minus sign inverted or maintained, the pixel difference values derived respectively for the relative pixel positions; and generates a prediction image using the first and second parameters.

Abstract: An encoder according to one aspect of the present disclosure encodes a block of an image, and includes a processor and memory connected to the processor. Using the memory, the processor partitions a block into a plurality of sub blocks and encodes a sub block included in the plurality of sub blocks in an encoding process including at least a transform process or a prediction process. The block is partitioned using a multiple partition including at least three odd-numbered child nodes and each of a width and a height of each of the plurality of sub blocks is a power of two.

Abstract: Provided is an encoder which includes circuitry and memory. The circuitry encodes an image block using the memory. In encoding the image block, the circuitry: obtains one or more size parameters related to a size of the image block; determines whether the one or more size parameters and one or more thresholds satisfy a determined relationship; encodes a split parameter when the one or more size parameters and the one or more thresholds are determined to satisfy the determined relationship, the split parameter indicating whether the image block is to be split into a plurality of partitions including a non-rectangular partition; and encodes the image block after splitting the image block into the plurality of partitions when the split parameter indicates that the image block is to be split into the plurality of partitions.

Abstract: An encoder determines, based on a width and a height of a block, whether or not to disable a prediction mode in which the block is split along a partitioning line defined by a distance and an angle and then prediction is performed; and encodes the block with the prediction mode disabled or not disabled according to a result of the determination on whether or not to disable the prediction mode. Here, the distance is the shortest distance between the center of the block and the partitioning line, and the angle is an angle representing a direction from the center of the block toward the partitioning line in the shortest distance. The encoder determines to disable the prediction mode when (i) a width-to-height ratio is at least 8 or (ii) a height-to-width ratio is at least 8.

Abstract: An image coding method includes: deriving a candidate for a motion vector predictor from a co-located motion vector; adding the candidate to a list; selecting the motion vector predictor from the list; and coding a current block and coding a current motion vector, wherein the deriving includes: deriving the candidate by a first derivation scheme in the case of determining that each of a current reference picture and a co-located reference picture is a long-term reference picture; and deriving the candidate by a second derivation scheme in the case of determining that each of the current reference picture and the co-located reference picture is a short-term reference picture.

Abstract: Provided is an encoder which includes circuitry and memory. Using the memory, the circuitry splits an image block into a plurality of partitions, obtains a prediction image for a partition, and encodes the image block using the prediction image. When the partition is not a non-rectangular partition, the circuitry obtains (i) a first prediction image for the partition, (ii) a gradient image for the first prediction image, and (iii) a second prediction image as the prediction image using the first prediction image and the gradient image. When the partition is a non-rectangular partition, the circuitry obtains the first prediction image as the prediction image without using the gradient image.

Abstract: A decoder includes memory and a processor coupled to the memory and configured to: generate a first coefficient value by applying a CCALF (cross component adaptive loop filtering) process to a first reconstructed image sample of a luma component; clip the first coefficient value such that the clipped first coefficient value is within a first range from ?27 to 27?1; generate a second coefficient value by applying an ALF (adaptive loop filtering) process to a second reconstructed image sample of a chroma component; clip the second coefficient value such that the clipped second coefficient value is within a second range different from the first range; generate a third coefficient value by adding the clipped first coefficient value to the clipped second coefficient value; and generate a third reconstructed image sample of the chroma component using the third coefficient value.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. The circuitry determines whether to split a current luma virtual pipeline decoding unit (VPDU) into smaller blocks. When it is determined not to split the current luma VPDU into smaller blocks, the circuitry predicts a block of chroma samples without using luma samples. When it is determined to split the luma VPDU into smaller blocks, the circuitry predicts the block of chroma samples using luma samples. The circuitry encodes the block using the predicted chroma samples.

Abstract: An image coding method includes: writing, into a sequence parameter set, buffer description defining information for defining a plurality of buffer descriptions; selecting one of the buffer descriptions for each processing unit that is a picture or a slice, and writing buffer description selecting information for specifying the selected buffer description, into a first header of the processing unit which is included in the coded bitstream; and coding the processing unit using the selected buffer description, and the buffer description defining information includes long-term information for identifying, among a plurality of reference pictures indicated in the buffer descriptions, a reference picture to be assigned as a long-term reference picture.

Abstract: An encoder according to one aspect of the present disclosure encodes a block of an image, and includes a processor and memory connected to the processor. Using the memory, the processor partitions a block into a plurality of sub blocks and encodes a sub block included in the plurality of sub blocks in an encoding process including at least a transform process or a prediction process. The block is partitioned using a multiple partition including at least three odd-numbered child nodes and each of a width and a height of each of the plurality of sub blocks is a power of two.

Abstract: An image encoder includes circuitry and a memory, wherein the circuitry, in operation, determines whether inter prediction is to be applied to a current block; in response to determining that the inter prediction is to be applied to the current block, performs a partition prediction process; and, in response to determining that the inter prediction is not to be applied, encodes the current block without using the partition prediction process. The partition prediction process includes predicting first values of a set of pixels between a first partition and a second partition in the current block, using a first motion vector for the first partition; predicting second values of the set of pixels, using a second motion vector for the second partition; weighting the first values and the second values; and generating a prediction image for the current block using the weighted first values and the weighted second values.

Abstract: An image encoder or decoder includes circuitry and a memory coupled to the circuitry. The circuitry, in operation, predicts a first set of samples for a first partition of a current picture with one or more motion vectors including a first motion vector and predicts a second set of samples for a first portion of the first partition with one or more motion vectors from a second partition different from the first partition. The samples of the first set of samples of the first portion of the first partition and of the second set of samples of the first portion of the first partition are weighted. A motion vector for the first portion of the first partition is stored which is based on one or both of the first motion vector and the second motion vector. The first partition is encoded or decoded using at least the weighted samples of the first portion of the first partition.

Abstract: An encoder includes circuitry and a memory coupled to the circuitry, wherein the circuitry, in operation, performs a partition process. The partition process includes calculating first values of a set of pixels between a first partition and a second partition in a current block, using a first motion vector for the first partition; calculating second values of the set of pixels, using a second motion vector for the second partition; and calculating third values of the set of pixels by weighting the first values and the second values. When a ratio of a width to a height of the current block is larger than 4 or a ratio of the height to the width of the current block is larger than 4, the circuitry disables the partition process.

Abstract: An image coding method includes: selecting a first picture from plural pictures; setting a first temporal motion vector prediction flag which is associated with the first picture and is a temporal motion vector prediction flag indicating whether or not temporal motion vector prediction is to be used, to indicate that the temporal motion vector prediction is not to be used, and coding the first temporal motion vector prediction flag; coding the first picture without using the temporal motion vector prediction; and coding a second picture which follows the first picture in coding order, with referring to a motion vector of a picture preceding the first picture in coding order being prohibited.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. The circuitry, in response to a first reconstructed image sample being located outside a virtual boundary, duplicates a reconstructed sample located inside and adjacent to the virtual boundary to generate the first reconstructed image sample. The circuitry generates a first coefficient value by applying a CCALF (cross component adaptive loop filtering) process to the first reconstructed image sample of a luma component. The circuitry generates a second coefficient value by applying an ALF (adaptive loop filtering) process to a second reconstructed image sample of a chroma component. The circuitry generates a third coefficient value by adding the first coefficient value to the second coefficient value, and encodes a third reconstructed image sample of the chroma component using the third coefficient value.

Abstract: An encoder includes circuitry and memory connected to the circuitry. In operation, the circuitry corrects a base motion vector using a correction value in a fixed direction; and encodes a current partition by using the corrected base motion vector corrected. The correction value is specified by an index indicating one of correction values included in a table. The table is selected from among a plurality of tables, wherein the correction values in one of the plurality of tables have different increments from the correction values in another one of the plurality of tables.