Abstract: An image encoder includes circuitry, and a memory connected to the circuitry. The circuitry, in operation, determines a first region and a second region in an input image, generates a first image from the input image by applying a first prefilter to the first region and a second prefilter to the second region, determines a first parameter relating to the first region and a second parameter relating to the second region, and generates a bitstream by encoding the first region based on the first parameter, encoding the second region based on the second parameter, encoding the first prefilter or a first postfilter corresponding to the first prefilter, and encoding the second prefilter or a second postfilter corresponding to the second prefilter.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. The circuitry, in operation, generates a first coefficient value by applying a CCALF (cross component adaptive loop filtering) process to a first reconstructed image sample of a luma component, and 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 modifies the first coefficient value by performing an arithmetic right shift by 7 bits on the first coefficient value. The circuitry generates a third coefficient value by adding the modified 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: 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. In operation, the circuitry: derives a motion vector of a current block by referring to at least one reference picture different from a picture to which the current block belongs; performs a mode for estimating, for each sub-block unit of sub-blocks obtained by splitting the current block, a surrounding region of the motion vector to correct the motion vector; determines whether to apply deblocking filtering to each of boundaries between neighboring ones of the sub-blocks; and applies the deblocking filtering to the boundary, based on a result of the determination.

Abstract: When intra prediction is to be used, an encoder determines whether an adaptive basis selection mode is to be used and whether a size of the current block matches a determined size. When the adaptive basis selection mode is to be used and the size matches the determined size, the encoder fixes the first transform basis for the current block to a first determined transform basis in the adaptive basis selection mode, and generates first transform coefficients by performing first transform of residual signals of the current block using the first determined transform basis; quantizes the first transform coefficients when an intra prediction mode for the current block is a determined mode; and generates second transform coefficients by performing second transform of the first transform coefficients using a second transform basis, and quantizes the second transform coefficients, when the intra prediction mode is not the determined mode.

Abstract: An encoder which encodes a video including a plurality of pictures includes circuitry and memory. Using the memory, the circuitry performs: encoding a first picture among the plurality of pictures; and performing (i) a first operation for encoding a parameter set for a second picture which follows the first picture in coding order among the plurality of pictures after encoding the first picture, and encoding the second picture after encoding the parameter set, or (ii) a second operation for encoding the second picture without encoding the parameter set after encoding the first picture. The circuitry performs the first operation when the second picture is a determined picture, in the performing of the first operation or the second operation.

Abstract: An encoding method includes determining video format information, (i) setting each of all frames or all fields which are included in the video, as a picture, regardless of whether the video format is the interlace format or the progressive format, (ii) setting a POC indicating display order to each of all of the set pictures one by one, the POC being different each other, and encoding a picture to be encoded which is the frame or the field with reference to a picture previously encoded before encoding the picture to be encoded. In the encoding, the video is encoded with a syntax structure which is not dependent on the video format, the video format information is encoded in a header of a sequence which is a unit of the video, and the encoded bit stream is generated.

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: A decoder comprises circuitry and memory. The circuitry, using the memory, in operation, determines a number of first pixels and a number of second pixels used in a deblocking filter process, wherein the first pixels are located at an upper side of a block boundary and the second pixels are located at a lower side of the block boundary, and performs the deblocking filter process on the block boundary. The number of the first pixels and the number of the second pixels are selected from among candidates, wherein the candidates include at least 4 and M larger than 4. Response to a location of the block boundary being a predetermined location, the number of the first pixels used in the deblocking filter process is limited to be 4.

Abstract: An encoder including circuitry and memory coupled to the circuitry. In both of a first case where an orthogonal transform is performed and a second case where the orthogonal transform is skipped, when a number of CABAC processes is within an allowable range, the circuitry: encodes a plurality of coefficient information flags by CABAC; and encodes a remainder value of the coefficient; and when the number of CABAC processes is not within the allowable range, the circuitry: skips the encoding of the plurality of coefficient information flags, wherein in the first case, the circuitry: converts the coefficient to a second coefficient by using a poszero value that is determined using a plurality of surrounding coefficients; and encodes a value of the second coefficient, and wherein in the second case, the circuitry: encodes the value of the coefficient.

Abstract: An image decoding device includes circuitry and a memory connected to the circuitry, in which in operation, the circuitry acquires a first image and a plurality of first filter sets by decoding a bitstream, generates and outputs a second image by selecting one first filter set from the plurality of first filter sets based on usage information indicating an image usage, and applying the first filter set having been selected to the first image.

Abstract: An encoder includes circuitry and a memory coupled to the circuitry. The circuitry, in operation, determines whether or not a ternary split process of splitting a block into three sub blocks in a first direction parallel to a first longer side of the block is allowed by comparing a size of a second shorter side of the block to a minimum threshold value. The circuitry, responsive to the ternary split process being allowed, writes, into a bitstream, a split direction parameter indicative of a splitting direction. The circuitry, in operation, splits the block into a plurality of sub blocks in a direction indicated by the split direction parameter; and encodes the plurality of sub blocks. The minimum threshold value corresponds to a minimum size supported in a transform process.

Abstract: Various embodiments provide an encoder that performs an up-conversion and a down-conversion on a first quantization matrix to generate a second quantization matrix, and quantizes transform coefficients of a current block using the second quantization matrix. The first quantization matrix has a first number of rows and a first number of columns equal to the first number of rows, and the second quantization matrix has a second number of rows and a second number of columns different from the second number of rows. In the up-conversion, the circuitry generates the second quantization matrix such that one of the second number of rows or the second number of columns is larger than the first number of rows. In the down-conversion, the circuitry generates the second quantization matrix such that the other of the second number of rows or the second number of columns is smaller than the first number of rows.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. In operation, the circuitry: performs quantization on a plurality of transform coefficients of a current block to be encoded, using a quantization matrix when orthogonal transform is performed on the current block and secondary transform is not performed on the current block; and performs quantization on the plurality of transform coefficients of the current block without using the quantization matrix when orthogonal transform is not performed on the current block and when both orthogonal transform and secondary transform are performed on the current block.

Abstract: An encoder is an encoder that encodes a block in a picture using a prediction image of the block, and includes circuitry and memory. Using the memory, the circuitry: calculates a first average pixel value which is an average pixel value of first reference samples out of the first reference samples and second reference samples, The first reference samples are referable and located outside the block and adjacent to a first side of the block. The second reference samples are referable and located outside the block and adjacent to a second side of the block. When generating the prediction image, the circuitry applies the same prediction pixel value to inner samples among current samples to be processed that are included in the block. The inner samples constitute a quadrilateral region including at least two current samples in each of a horizontal direction and a vertical direction.

Abstract: An encoder includes circuitry and memory connected to the circuitry. In operation, the circuitry: corrects a base motion vector using a correction value for correcting the base motion vector in a predetermined direction; and encodes a current partition to be encoded in an image of a video, using the base motion vector corrected. The correction value is specified by a first parameter and a second parameter, the first parameter indicating a table to be selected from among a plurality of tables each including values, the second parameter indicating one of the values included in the table to be selected indicated by the first parameter. In each of the plurality of tables, a smaller value among the values is assigned a smaller index. Each of the plurality of tables includes a different minimum value among the values.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. In operation, the circuitry: derives a motion vector of a current block by referring to at least one reference picture different from a picture to which the current block belongs; performs a mode for estimating, for each sub-block unit of sub-blocks obtained by splitting the current block, a surrounding region of the motion vector to correct the motion vector; determines whether to apply deblocking filtering to each of boundaries between neighboring ones of the sub-blocks; and applies the deblocking filtering to the boundary, based on a result of the determination.

Abstract: An encoder includes memory and circuitry. The circuitry, using the memory, (i) selects a mode from among a plurality of modes each for deriving a motion vector, and derives a motion vector for a current block via the selected mode, and (ii) performs inter prediction encoding on the current block, using the derived motion vector, via one of a skip mode and a non-skip mode different from the skip mode. The plurality of modes include a plurality of first modes each for predicting the motion vector for the current block based on an encoded block neighboring the current block without encoding information indicating a motion vector into a stream. When a second mode included in the plurality of first modes is selected, the current block is encoded via the non-skip mode regardless of presence or absence of a residual coefficient.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. In operation, the circuitry: encodes one or more pictures which have common time information and each of which is included in a different layer; adds the one or more pictures into one access unit in a bitstream; and adds, into the bitstream, a first flag indicating that a total number of access units present in the bitstream is one.

Abstract: An encoder includes circuitry and memory coupled to the circuitry. In operation, the circuitry: encodes pictures in an encoding order according to temporal scalability that specifies temporal layers; adds, to a bitstream, information indicating whether CPB removal timings of lower pictures in one or more first temporal layers lower than or equal to a lower temporal layer lower than a higher temporal layer among the temporal layers in a first case in which the one or more first temporal layers are to be decoded are identical to CPB removal timings of the lower pictures in a second case in which second temporal layers lower than or equal to the higher temporal layer are to be decoded; and sets, in the information, a value indicating that the CPB removal timings in the first case are identical to the CPB removal timings in the second case.