Image data encoding/decoding method and apparatus
Disclosed are methods and apparatuses for decoding an image. A method includes receiving a bitstream obtained by encoding the image; dividing a first coding block into a plurality of second coding blocks; generating a prediction block of a second coding block based on syntax information obtained from the bitstream; and reconstructing the second coding block based on the prediction block and a residual block of the second coding block, the residual block being obtained by performing a dequantization and an inverse-transform on quantized transform coefficients from the bitstream. The first coding block has a recursive division structure. The first coding block is divided based on at least one of a quad tree division, a binary tree division or a triple tree division.
1. A method of decoding a 360-degree image performed by an image decoding apparatus, the method comprising:
receiving a bitstream in which the 360-degree image is encoded, the bitstream including data of an expanded 2-dimensional image, the expanded 2-dimensional image including a 2-dimensional image and a predetermined expansion region, and the 2-dimensional image being projected from an image with a 3-dimensional projection structure and including one or more faces;
generating a predicted image by performing prediction based on information on the prediction included in the bitstream; and
reconstructing the expanded 2-dimensional image based on the predicted image and a residual image,
wherein a size of the expansion region is determined based on first width information of the expansion region on a left side of the face and second width information of the expansion region on a right side of the face, both the first width information and the second width information being obtained from the bitstream,
wherein sample values of the expansion region are determined differently according to a padding method selected from a plurality of padding methods,
wherein the sample values of the expansion region are determined by horizontally copying the sample values of the face according to the padding method selected from the plurality of padding methods,
wherein the size of the expansion region is determined based on size information obtained from the bitstream,
wherein the predicted image is added to the residual image to reconstruct the expanded 2-dimensional image,
wherein the number of syntax elements for the size information is determined differently based on a projection format for the 3-dimensional projection structure, 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 the residual image is obtained by decoding residual information included in the bitstream, and
wherein the 3-dimensional projection structure is selectively determined based on identification information, among a plurality of pre-defined projection formats including the ERP format in which the 360-degree image is projected in the two-dimensional plane and the CMP format in which the 360-degree image is projected in the cube.
2. A method of encoding a 360-degree image performed by an image encoding apparatus, the method comprising:
obtaining a 2-dimensional image projected from an image with a 3-dimensional projection structure and including at least one face;
obtaining an expanded 2-dimensional image including the 2-dimensional image and a predetermined expansion region;
generating a predicted image by performing prediction, information on the prediction being encoded into the bitstream; and
encoding data of the expanded 2-dimensional image into the bitstream based on the predicted image and a residual image,
wherein a size of the expansion region is encoded based on first width information of the expansion region on a left side of the face and second width information of the expansion region on a right side of the face, both the first width information and the second width information being encoded into the bitstream,
wherein sample values of the expansion region are determined differently according to a padding method selected from a plurality of padding methods,
wherein the sample values of the expansion region are determined by horizontally copying the sample values of the face according to the padding method selected from the plurality of padding methods,
wherein size information on the size of the expansion region is encoded into the bitstream,
wherein the residual image is obtained based on the expanded 2-dimensional image and the predicted image, and
wherein the number of syntax elements for the size information is determined differently based on a projection format for the 3-dimensional projection structure, 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 residual information is included in the bitstream by encoding the residual image, and
wherein the 3-dimensional projection structure is selectively determined based on identification information, among a plurality of pre-defined projection formats including the ERP format in which the 360-degree image is projected in the two-dimensional plane and the CMP format in which the 360-degree image is projected in the cube.
3. A method of transmitting a bitstream performed by a transmitting apparatus, comprising:
transmitting the bitstream to an image decoding apparatus,
wherein the bitstream is generated by performing
obtaining a 2-dimensional image projected from an image with a 3-dimensional projection structure and including at least one face;
obtaining an expanded 2-dimensional image including the 2-dimensional image and a predetermined expansion region;
generating a predicted image by performing prediction, information on the prediction being encoded into the bitstream; and
encoding data of the expanded 2-dimensional image into the bitstream based on the predicted image and a residual image,
wherein a size of the expansion region is encoded based on first width information of the expansion region on a left side of the face and second width information of the expansion region on a right side of the face, both the first width information and the second width information being encoded into the bitstream,
wherein sample values of the expansion region are determined differently according to a padding method selected from a plurality of padding methods,
wherein the sample values of the expansion region are determined by horizontally copying the sample values of the face according to the padding method selected from the plurality of padding methods,
wherein size information on the size of the expansion region is encoded into the bitstream,
wherein the residual image is obtained based on the expanded 2-dimensional image and the predicted image, and
wherein the number of syntax elements for the size information is determined differently based on a projection format for the 3-dimensional projection structure, 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 residual information is included in the bitstream by encoding the residual image, and
wherein the 3-dimensional projection structure is selectively determined based on identification information, among a plurality of pre-defined projection formats including the ERP format in which the 360-degree image is projected in the two-dimensional plane and the CMP format in which the 360-degree image is projected in the cube.