Image data encoding/decoding method and apparatus

A method of encoding a 360-degree image, the method comprising:

• generating a predicted image, syntax information for the predicted image being encoded into a bitstream;
• acquiring a residual image based on the predicted image;
• and
• encoding the residual image into the bitstream by transforming and quantizing the residual image,
• wherein the residual image and the predicted image being used to reconstruct a decoded image which is used to produce a 360-degree image corresponding to a projection format,
• wherein the generating of the predicted image comprises:
• obtaining a reference image among previous images and by performing image expansion on the reference image;
• and
• generating a predicted image with reference to the reference image on which the image expansion is performed,
• wherein the reference image on which the image expansion is performed includes an expansion region,
• wherein a size of the expansion region is determined as a value indicated by size information encoded into the bitstream,
• wherein a number of syntax elements for the size information varies according to the projection format, the projection format being one among a plurality of projection formats including an ERP format in which the 360-degree image is projected in a two-dimensional plane and a CMP format in which the 360-degree image is projected in a cube,
• wherein sample values in the expansion region are determined according to a padding method selected among a plurality of padding methods, and
• wherein the padding method for a right side of the expansion region is determined separately from the padding method for a left side of the expansion region, information explicitly indicating the padding method for the right side and the padding method for the left side being encoded into the bitstream.

A method of transmitting a bitstream that is generated by a method of encoding a 360-degree image, the method comprising:

• generating a predicted image, syntax information for the predicted image being encoded into a bitstream;
• acquiring a residual image based on the predicted image;
• encoding the residual image into the bitstream by transforming and quantizing the residual image;
• and
• transmitting the bitstream,
• wherein the residual image and the predicted image being used to reconstruct a decoded image which is used to produce a 360-degree image corresponding to a projection format,
• wherein the generating of the predicted image comprises:
• obtaining a reference image among previous images and by performing image expansion on the reference image;
• and
• generating a predicted image with reference to the reference image on which the image expansion is performed,
• wherein the reference image on which the image expansion is performed includes an expansion region,
• wherein a size of the expansion region is determined as a value indicated by size information encoded into the bitstream,
• wherein a number of syntax elements for the size information varies according to the projection format, the projection format being one among a plurality of projection formats including an ERP format in which the 360-degree image is projected in a two-dimensional plane and a CMP format in which the 360-degree image is projected in a cube,
• wherein sample values in the expansion region are determined according to a padding method selected among a plurality of padding methods, and
• wherein the padding method for a right side of the expansion region is determined separately from the padding method for a left side of the expansion region, information explicitly indicating the padding method for the right side and the padding method for the left side being encoded into the bitstream.