Image encoding/decoding method and device using lossless color transform, and method for transmitting bitstream
Provided are an image encoding/decoding method and device. The image decoding method performed by the image decoding device, according to the present disclosure, may comprise the steps of: determining a residual sample of a current block; and resetting the value of the residual sample on the basis of whether a color space transform is applied. The step for resetting the value of the residual block may be performed on the basis of a half value of a chroma residual sample value.
1 . An image decoding method performed by an image decoding apparatus, the method comprising:
deriving a transform coefficient for each of a luma component block, a chroma Cb component block, and a chroma Cr component block based on a quantization parameter for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
deriving a residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on the transform coefficient;
modifying a value of the residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on color space transform information; and
reconstructing the luma component block, the chroma Cb component block, and the chroma Cr component block based on the residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
wherein the quantization parameter is derived by using a quantization parameter offset and further comparing with a lower limit value, and
wherein the value of each residual sample is modified based on a half value of the residual sample for the chroma Cb component block.
2 . The method of claim 1 ,
wherein a value of the quantization parameter offset is derived as a different value for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on the color space transform information.
3 . The method of claim 1 ,
wherein a value of the quantization parameter offset for the luma component block is derived as −5 based on the color transform information.
4 . The method of claim 1 ,
wherein a value of the quantization parameter offset for the chroma Cb component block is derived as 1 based on the color transform information.
5 . The method of claim 1 ,
wherein a value of the quantization parameter offset for the chroma Cr component block is derived as 3 based on the color transform information.
6 . The method of claim 1 ,
wherein the value of each residual sample is modified further based on a value of the residual sample for the luma component block.
7 . The method of claim 1 ,
wherein the half value of the residual sample for the chroma Cb component block is obtained based on a right shift operation for the value of the residual sample for the chroma Cb component block.
8 . The method of claim 1 ,
wherein the value of the residual sample for the luma component block is modified based on adding the half value of the residual sample for the chroma Cb component block.
9 . The method of claim 8 ,
wherein the half value of the residual sample for the chroma Cb component block added to the value of the residual sample for the luma component block is derived based on subtracting the value of the residual sample for the chroma Cb component block obtained by a right shift operation from the value of the residual sample for the chroma Cb component block.
10 . The method of claim 1 ,
wherein the value of the residual sample for the chroma Cb component block is modified based on subtracting both the half value of the residual sample for the chroma Cb component block and the half value of the residual sample for the chroma Cr component block from the value of the residual sample for the luma component block.
11 . The method of claim 10 ,
wherein the half value of the residual sample for the chroma Cb component block is derived based on a value obtained by a right shift operation for the value of the residual sample for the chroma Cb component block,
wherein the half value of the residual sample for the chroma Cr component block is derived based on a value obtained by a right shift operation for the value of the residual sample for the chroma Cr component block.
12 . The method of claim 1 ,
wherein the value of the residual sample for the chroma Cr component block is modified based on subtracting the half value of the residual sample for the chroma Cb component block from the value of the residual sample for the luma component block and adding the half value of the residual sample for the chroma Cr component block.
13 . The method of claim 1 ,
wherein the residual sample for the luma component block (r y ), the residual sample for the chroma Cb component block (r Cb ), and the residual sample for the chroma Cr component block (r Cr ) are modified based on:
tmp
=
r
Y
[
x
]
[
y
]
-
(
r
Cb
[
x
]
[
y
]
≫
1
)
r
Y
[
x
]
[
y
]
=
tmp
+
r
Cb
[
x
]
[
y
]
r
Cb
[
x
]
[
y
]
=
tmp
-
(
r
Cr
[
x
]
[
y
]
≫
1
)
r
Cr
[
x
]
[
y
]
=
r
Cb
[
x
]
[
y
]
+
r
Cr
[
x
]
[
y
]
.
14 . An image encoding method performed by an image encoding apparatus, the method comprising:
deriving a transform coefficient for each of a luma component block, a chroma Cb component block, and a chroma Cr component block based on a quantization parameter for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
deriving a residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on the transform coefficient;
modifying a value of the residual block for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on color space transform information; and
reconstructing the luma component block, the chroma Cb component block, and the chroma Cr component block based on the residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
wherein the quantization parameter is derived by using a quantization parameter offset and further comparing with a lower limit value, and
wherein the value of each residual sample is modified based on a half value of the residual sample for the chroma Cb component block.
15 . A non-transitory computer-readable recording medium storing a bitstream generated by an image encoding method, the method comprising:
deriving a transform coefficient for each of a luma component block, a chroma Cb component block, and a chroma Cr component block based on a quantization parameter for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
deriving a residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on the transform coefficient;
modifying a value of the residual block for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on color space transform information; and
reconstructing the luma component block, the chroma Cb component block, and the chroma Cr component block based on the residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
wherein the quantization parameter is derived by using a quantization parameter offset and further comparing with a lower limit value, and
wherein the value of each residual sample is modified based on a half value of the residual sample for the chroma Cb component block.
16 . A transmitting method of a bitstream comprising:
deriving a transform coefficient for each of a luma component block, a chroma Cb component block, and a chroma Cr component block based on a quantization parameter for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
deriving a residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on the transform coefficient;
modifying a value of the residual block for each of the luma component block, the chroma Cb component block, and the chroma Cr component block based on color space transform information;
reconstructing the luma component block, the chroma Cb component block, and the chroma Cr component block based on the residual sample for each of the luma component block, the chroma Cb component block, and the chroma Cr component block;
encoding the bitstream based on the reconstructed luma component block, the reconstructed chroma Cb component block, and the reconstructed chroma Cr component block; and
transmitting the bitstream,
wherein the quantization parameter is derived by using a quantization parameter offset and further comparing with a lower limit value, and
wherein the value of each residual sample is modified based on a half value of the residual sample for the chroma Cb component block.