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 of a left side of the extension region, second information indicating a width of a right side of the extension region, or third information indicating a height 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, the second information or the third 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 of a left side of the extension region, second information indicating a width of a right side of the extension region, or third information indicating a height 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, of the second information or the third 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 of a left side of the extension region, second information indicating a width of a right side of the extension region, or third information indicating a height 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, the second information or the third information is encoded into the bitstream.