Methods, apparatuses, and programs for encoding and decoding picture

A picture decoding method for generating a prediction signal using spatial inter-pixel prediction and decoding a picture using a prediction residual signal which is a difference between the prediction signal and an original signal, the picture decoding method comprising:

• a step of decoding an intra-prediction residual signal, an intra-prediction mode, and a size of an intra-prediction block in an input encoded stream;
• a step of identifying a reference pixel of intra-prediction based on the intra-prediction mode and the size of the intra-prediction block;
• a step of setting a tap length of an interpolation filter necessary for generating the reference pixel of the intra-prediction based on one or both of a size of a block which is a processing unit of coding, transform, or prediction and a quantization parameter of the block for the reference pixel;
• a step of performing a filtering process which generates the reference pixel using the interpolation filter corresponding to the set tap length;
• a step of generating an intra-prediction signal corresponding to the decoded intra-prediction mode using the generated reference pixel;
• and
• a step of generating a decoded signal of a decoding target region using the generated intra-prediction signal and the intra-prediction residual signal.

A picture encoding apparatus which generates a prediction signal using spatial inter-pixel prediction and encodes a picture using a prediction residual signal which is a difference between the prediction signal and an original signal, the picture encoding apparatus comprising:

• a tap length setting unit which sets a tap length of an interpolation filter necessary for generating a reference pixel of intra-prediction based on one or both of a size of a block which is a processing unit of coding, transform, or prediction and a quantization parameter of the block for the reference pixel;
• a filtering processing unit which performs a filtering process which generates the reference pixel using the interpolation filter corresponding to the set tap length;
• a prediction signal generating unit which generates an intra-prediction signal corresponding to a designated intra-prediction mode using the generated reference pixel;
• a prediction residual signal generating unit which generates an intra-prediction residual signal representing a difference between the generated intra-prediction signal and the original signal;
• and
• a prediction residual signal encoding unit which encodes the intra-prediction residual signal.

A picture decoding apparatus which generates a prediction signal using spatial inter-pixel prediction and decodes a picture using a prediction residual signal which is a difference between the prediction signal and an original signal, the picture decoding apparatus comprising:

• a decoding unit which decodes an intra-prediction residual signal, an intra-prediction mode, and a size of an intra-prediction block in an input encoded stream;
• an identifying unit which identifies a reference pixel of intra-prediction based on the intra-prediction mode and the size of the intra-prediction block;
• a tap length setting unit which sets a tap length of an interpolation filter necessary for generating the reference pixel of the intra-prediction based on one or both of a size of a block which is a processing unit of coding, transform, or prediction and a quantization parameter of the block for the reference pixel;
• a filtering processing unit which performs a filtering process which generates the reference pixel using the interpolation filter corresponding to the set tap length;
• a prediction signal generating unit which generate an intra-prediction signal corresponding to the decoded intra-prediction mode using the generated reference pixel;
• and
• a decoded signal generating unit which generates a decoded signal of a decoding target region using the generated intra-prediction signal and the intra-prediction residual signal.