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 for the 2-dimensional 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 for the 2-dimensional 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 the extension region or second information indicating a height of the extension region, independently of a size of the 2-dimensional image,
wherein the first information comprises left size information for specifying the width of the extension region on a left side of the face and right size information for specifying the width of the extension region on a right side of the face,
wherein the extension region is not included in the image with the 3-dimensional projection structure,
wherein at least one of the identification information, the first information or the second information is obtained from the bitstream,
wherein the prediction image is generated by selecting one prediction mode among a plurality of prediction modes including intra prediction and inter prediction, and performing prediction based on the selected prediction mode, and
information on the selected prediction mode is obtained from the bitstream.
2. 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 the extension region or second information indicating a height of the extension region, independently of a size of the 2-dimensional image,
wherein the first information comprises left size information for specifying the width of the extension region on a left side of the face and right size information for specifying the width of the extension region on a right side of the face,
wherein the extension region is not included in the image with the 3-dimensional projection structure,
wherein at least one of the identification information, the first information or the second information is encoded into the bitstream, and
wherein the prediction image is generated by selecting one prediction mode among a plurality of prediction modes including intra prediction and inter prediction, and performing prediction based on the selected prediction mode, and
information on the selected prediction mode is encoded into the bitstream.
3. A method of transmitting a bitstream that is generated by a method for encoding a 360-degree image, comprising:
transmitting the bitstream to an image decoding apparatus;
wherein the method for encoding a 360-degree image comprises:
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 the extension region or second information indicating a height of the extension region, independently of a size of the 2-dimensional image,
wherein the first information comprises left size information for specifying the width of the extension region on a left side of the face and right size information for specifying the width of the extension region on a right side of the face,
wherein the extension region is not included in the image with the 3-dimensional projection structure,
wherein at least one of the identification information, the first information or the second information is encoded into the bitstream, and
wherein the prediction image is generated by selecting one prediction mode among a plurality of prediction modes including intra prediction and inter prediction, and performing prediction based on the selected prediction mode, and
information on the selected prediction mode is encoded into the bitstream.