Image decoding device, method, and program with prediction refinement optical flow

An image decoding method comprising:

• decoding a first flag which is included in a sequence parameter set and controls enabling/disabling of PROF (Prediction Refinement with Optical Flow) processing from encoded data;
• decoding a second flag indicating whether or not a flag indicating enabling/disabling of the PROF processing is included in a low order header of a picture parameter set from the sequence parameter set additionally in a case where the first flag indicates enabling of the PROF processing in units of sequences;
• decoding a third flag which is included in a low order header of the picture parameter set and indicates enabling/disabling of the PROF processing from the encoded data in a case where the second flag indicates that the flag indicating enabling/disabling of the PROF processing is included in the low order header of a picture parameter set;
• determining non-application conditions of the PROF processing for each block;
• determining not to apply the PROF processing to a block that meets at least one of the non-application conditions of the PROF processing and generating a prediction signal without performing the PROF processing;
• calculating “diffMV” corresponding to each pixel position in each sub-block to which a block that doesn't meet any of the non-application conditions of the PROF processing is divided, and performing correction of the prediction signal by executing the PROF processing with the “diffMV”,
• the non-application conditions of the PROF processing include a condition that the first flag indicates disabling of the PROF processing in units of sequences,
• the non-application conditions of the PROF processing include a condition that the third flag indicates disabling of the PROF processing, and
• the non-application conditions of the PROF processing include a condition that “fallbackMode” is applied to a block.

A program stored on a non-transitory computer-readable medium for causing a computer to execute:

• decoding a first flag which is included in a sequence parameter set and controls enabling/disabling of PROF (Prediction Refinement with Optical Flow) processing from encoded data;
• decoding a second flag indicating whether or not a flag indicating enabling/disabling of the PROF processing is included in a low order header of a picture parameter set from the sequence parameter set additionally in a case where the first flag indicates enabling of the PROF processing in units of sequences;
• decoding a third flag which is included in a low order header of the picture parameter set and indicates enabling/disabling of the PROF processing from the encoded data in a case where the second flag indicates that the flag indicating enabling/disabling of the PROF processing is included in the low order header of a picture parameter set;
• determining non-application conditions of the PROF processing for each block;
• determining not to apply the PROF processing to a block that meets at least one of the non-application conditions of the PROF processing and generating a prediction signal without performing the PROF processing;
• calculating “diffMV” corresponding to each pixel position in each sub-block to which a block that doesn't meet any of the non-application conditions of the PROF processing is divided, and performing correction of the prediction signal by executing the PROF processing with the “diffMV”,
• the non-application conditions of the PROF processing include a condition that the first flag indicates disabling of the PROF processing in units of sequences,
• the non-application conditions of the PROF processing include a condition that the third flag indicates disabling of the PROF processing, and
• the non-application conditions of the PROF processing include a condition that “fallbackMode” is applied to a block.