Method and apparatus for reconstructing 360-degree image according to projection format
Disclosed are methods and apparatuses for image data encoding/decoding. A method for decoding a 360-degree image includes the steps of: receiving a bitstream obtained by encoding a 360-degree image; generating a prediction image by making reference to syntax information obtained from the received bitstream; adding the generated prediction image to a residual image obtained by dequantizing and inverse-transforming the bitstream, so as to obtain a decoded image; and reconstructing the decoded image into a 360-degree image according to a projection format. Therefore, the performance of image data compression can be improved.
1. A method for decoding a 360-degree image, the method comprising:
receiving a bitstream in which the 360-degree image is encoded, the bitstream including data of an extended 2-dimensional image, the extended 2-dimensional image including a 2-dimensional image and a predetermined extension region, and the 2-dimensional image being from an image with a 3-dimensional projection structure and including one or more faces;
generating a prediction image by referring to syntax information obtained from the received bitstream;
obtaining a decoded image by adding the generated prediction image to a residual image, the residual image being obtained by inverse-quantizing and inverse transforming quantized transform coefficients from the bitstream; and
reconstructing the decoded image into the 360-degree image according to a projection format,
wherein the projection format is selectively determined based on identification information, among a plurality of pre-defined projection formats including an ERP format in which the 360-degree image is projected in a two-dimensional plane or a CMP format in which the 360-degree image is projected in a cube,
wherein a size of the extension region is variably determined based on at least one of first information indicating a width on a left side of the extension region or second information indicating a width on a right side of the extension region, independently of a size of the 2-dimensional image,
wherein the extension region is not included in the image with the 3-dimensional projection structure, and
wherein at least one of the identification information, the first information or the second information is obtained from the bitstream.
2. The method of claim 1 , wherein reconstructing the decoded image comprises:
obtaining, from the bitstream, arrangement information according to a regional packing, the arrangement information specifying one of a plurality of conversion types pre-defined in a decoding apparatus; and
rearranging at least one of a plurality of faces in the decoded image according to the arrangement information.
3. The method of claim 2 , wherein the pre-defined conversion types include at least one of 90-degree rotation, 180-degree rotation, 270-degree rotation, horizontal flipping, or vertical flipping.
4. The method of claim 1 , wherein the extension region is adjacent to a boundary of at least one of the faces.
5. The method of claim 4 , wherein the boundary of the face is discontinuous in the 2-dimensional image and continuous in the image with the 3-dimensional projection structure.
6. A method for encoding a 360-degree image, the method comprising:
generating a bitstream in which the 360-degree image is encoded, the bitstream including data of an extended 2-dimensional image, the extended 2-dimensional image including a 2-dimensional image and a predetermined extension region, and the 2-dimensional image being from an image with a 3-dimensional projection structure and including one or more faces;
wherein the bitstream comprises syntax information, the syntax information being referred to for generating a prediction image,
the bitstream comprises quantized transform coefficients, the quantized transform coefficients being inverse-quantized and inverse transformed for obtaining a residual image,
the prediction image is added to the residual image for obtaining a decoded image, and
the decoded image is reconstructed into the 360-degree image according to a projection format,
wherein the projection format is selectively determined based on identification information, among a plurality of pre-defined projection formats including an ERP format in which the 360-degree image is projected in a two-dimensional plane or a CMP format in which the 360-degree image is projected in a cube,
wherein a size of the extension region is variably determined based on at least one of first information indicating a width on a left side of the extension region or second information indicating a width on a right side of the extension region, independently of a size of the 2-dimensional image,
wherein the extension region is not included in the image with the 3-dimensional projection structure, and
wherein at least one of the identification information, the first information or the second information is encoded into the bitstream.
7. A method of transmitting a bitstream, the method comprising:
transmitting the bitstream to an image decoding apparatus;
wherein the bitstream is generated by encoding a 360-degree image, the bitstream including data of an extended 2-dimensional image, the extended 2-dimensional image including a 2-dimensional image and a predetermined extension region, and the 2-dimensional image being from an image with a 3-dimensional projection structure and including one or more faces;
wherein the bitstream comprises syntax information, the syntax information being referred to for generating a prediction image,
the bitstream comprises quantized transform coefficients, the quantized transform coefficients being inverse-quantized and inverse transformed for obtaining a residual image,
the prediction image is added to the residual image for obtaining a decoded image, and
the decoded image is reconstructed into the 360-degree image according to a projection format,
wherein the projection format is selectively determined based on identification information, among a plurality of pre-defined projection formats including an ERP format in which the 360-degree image is projected in a two-dimensional plane or a CMP format in which the 360-degree image is projected in a cube,
wherein a size of the extension region is variably determined based on at least one of first information indicating a width on a left side of the extension region or second information indicating a width on a right side of the extension region, independently of a size of the 2-dimensional image,
wherein the extension region is not included in the image with the 3-dimensional projection structure, and
wherein at least one of the identification information, the first information or the second information is encoded into the bitstream.