The refinement of a lower-pel resolution motion estimation vector is made more effective by preceding the actual refinement with a determination of a context out of a set of context candidates based on coding costs of a set of lower-pel resolution vectors within a neighborhood of the lower-pel resolution motion estimation vector, wherein each context candidate is associated with a ranking among a set of higher-pel resolution candidate vectors surrounding the lower-pel resolution motion estimation vector. The actual refinement of the lower-pel resolution motion estimation vector to obtain the higher-pel resolution motion estimation vector may thus use the ranking associated with the context determined: sequentially arranged accordingly, the set of higher-pel resolution candidate vectors may be tested sequentially.

The refinement of a lower-pel resolution motion estimation vector is made more effective by preceding the actual refinement with a determination of a context out of a set of context candidates based on coding costs of a set of lower-pel resolution vectors within a neighborhood of the lower-pel resolution motion estimation vector, wherein each context candidate is associated with a ranking among a set of higher-pel resolution candidate vectors surrounding the lower-pel resolution motion estimation vector. The actual refinement of the lower-pel resolution motion estimation vector to obtain the higher-pel resolution motion estimation vector may thus use the ranking associated with the context determined: sequentially arranged accordingly, the set of higher-pel resolution candidate vectors may be tested sequentially.

An image coding method includes selecting two or more transform components from among a plurality of transform components that include a translation component and non-translation components, the two or more transform components serving as reference information that represents a reference destination of a current block; coding selection information that identifies the two or more transform components that have been selected from among the plurality of transform components; and coding the reference information of the current block by using reference information of a coded block different from the current block.

An image coding method includes selecting two or more transform components from among a plurality of transform components that include a translation component and non-translation components, the two or more transform components serving as reference information that represents a reference destination of a current block; coding selection information that identifies the two or more transform components that have been selected from among the plurality of transform components; and coding the reference information of the current block by using reference information of a coded block different from the current block.

An index, indicating a vector representing a spatial relationship between a block to be encoded and at least one block spatially at the periphery of the block to be encoded, is encoded in a case where an coding mode to encode the block to be encoded is a first coding mode, and an index, indicating a vector representing a spatial relationship between the block to be encoded and at least one block spatially at the periphery of the block to be encoded, and a vector correlated with a block within an image that is different from the image to be encoded, is encoded in a case where the coding mode to encode the block to be encoded is a second coding mode.

An index, indicating a vector representing a spatial relationship between a block to be encoded and at least one block spatially at the periphery of the block to be encoded, is encoded in a case where an coding mode to encode the block to be encoded is a first coding mode, and an index, indicating a vector representing a spatial relationship between the block to be encoded and at least one block spatially at the periphery of the block to be encoded, and a vector correlated with a block within an image that is different from the image to be encoded, is encoded in a case where the coding mode to encode the block to be encoded is a second coding mode.

Innovations in encoder-side decisions that use the results of hash-based block matching when setting parameters are presented. For example, some of the innovations relate to ways to select motion vector precision depending on the results of hash-based block matching. Other innovations relate to ways to selectively disable sample adaptive offset filtering depending on the results of hash-based block matching. Still other innovations relate to ways to select which reference pictures to retain in a reference picture set depending on the results of hash-based block matching.

A method for encoding a current frame of a video includes jointly determining respective motion models for reference frames and encoding the current frame using the respective motion models. The reference frames are used for encoding the current frame. Jointly determining respective motion models for reference frames includes determining respective aggregated residuals for combinations of candidate motion models and selecting the combination of candidate motion models that corresponds to the smallest aggregated residual. The respective motion models correspond to the candidate motion models of the selected combination.

An index, indicating a vector representing a spatial relationship between a block to be encoded and at least one block spatially at the periphery of the block to be encoded, is encoded in a case where an coding mode to encode the block to be encoded is a first coding mode, and an index, indicating a vector representing a spatial relationship between the block to be encoded and at least one block spatially at the periphery of the block to be encoded, and a vector correlated with a block within an image that is different from the image to be encoded, is encoded in a case where the coding mode to encode the block to be encoded is a second coding mode.

An index, indicating a vector representing a spatial relationship between a block to be encoded and at least one block spatially at the periphery of the block to be encoded, is encoded in a case where an coding mode to encode the block to be encoded is a first coding mode, and an index, indicating a vector representing a spatial relationship between the block to be encoded and at least one block spatially at the periphery of the block to be encoded, and a vector correlated with a block within an image that is different from the image to be encoded, is encoded in a case where the coding mode to encode the block to be encoded is a second coding mode.