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, the method comprising:
receiving a bitstream obtained by encoding the 360-degree image;
generating a predicted image with reference to syntax information acquired from the received bitstream;
acquiring a decoded image by combining the generated predicted image with a residual image acquired by inversely quantizing and inversely transforming the bitstream; and
reconstructing the decoded image to produce a 360-degree image corresponding to a projection format,
wherein the generating of the predicted image comprises:
obtaining a reference image acquired by restoring the bitstream 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 obtained from the bitstream, and
the size information comprises first height information on a top side of the expansion region and second height information on a bottom side of the expansion region, a syntax element for the first height information being different from a syntax element for the second height information,
wherein sample values in the expansion region are determined according to a padding method selected among a plurality of padding methods, and
the padding method for the top side of the expansion region is determined separately from the padding method for the bottom side of the expansion region, information explicitly indicating the padding method for the top side and the padding method for the bottom side being obtained from the bitstream.
2 . 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,
the size information comprises first height information on a top side of the expansion region and second height information on a bottom side of the expansion region, a syntax element for the first height information being different from a syntax element for the second height information,
wherein sample values in the expansion region are determined according to a padding method selected among a plurality of padding methods, and
the padding method for the top side of the expansion region is determined separately from the padding method for the bottom side of the expansion region, information explicitly indicating the padding method for the top side and the padding method for the bottom side being encoded into the bitstream.
3 . 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, and
the size information comprises first height information on a top side of the expansion region and second height information on a bottom side of the expansion region, a syntax element for the first height information being different from a syntax element for the second height information,
wherein sample values in the expansion region are determined according to a padding method selected among a plurality of padding methods, and
the padding method for the top side of the expansion region is determined separately from the padding method for the bottom side of the expansion region, information explicitly indicating the padding method for the top side and the padding method for the bottom side being encoded into the bitstream.