In-loop filtering-based image coding apparatus and method

1. A decoding apparatus for image decoding, the decoding apparatus comprising:

a memory; and

at least one processor connected to the memory, the at least one processor configured to:

obtain image information including residual information through a bitstream;

derive quantized transform coefficients based on the residual information;

derive transform coefficients based on a dequantization process for the quantized transform coefficients;

derive residual samples based on an inverse transform process for the transform coefficients;

generate reconstructed samples based on the residual samples, wherein the reconstructed samples include reconstructed luma samples and reconstructed chroma samples;

derive ALF filter coefficients for an adaptive loop filtering (ALF) process of the reconstructed chroma samples;

generate filtered reconstructed chroma samples based on the reconstructed chroma samples and the ALF filter coefficients;

derive cross-component filter coefficients for cross-component filtering; and

generate modified filtered reconstructed chroma samples based on the reconstructed luma samples, the filtered reconstructed chroma samples, and the cross-component filter coefficients,

wherein the image information includes header information and an adaptation parameter set (APS) including ALF data,

wherein the cross-component filter coefficients are derived based on the ALF data,

wherein the header information includes a first flag related to whether a cross-component adaptive loop filter (CCALF) is enabled for a Cb color component of the filtered reconstructed chroma samples,

wherein based on the determination that a value of the first flag is 1, the header information includes information related to an identifier of the APS for deriving the cross-component filter coefficients for the Cb color component,

wherein the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include a Cb filter signal flag related to whether the cross-component filters for the Cb color component are signaled,

wherein based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information related to the number of cross-component filters for the Cb color component,

wherein based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information on absolute values of the cross-component filter coefficients for the Cb color component and information on signs of the cross-component filter coefficients for the Cb color component, and

wherein the cross-component filter coefficients for the Cb color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cb color component and the information on the signs of the cross-component filter coefficients for the Cb color component.

2. An encoding apparatus for image encoding, the encoding apparatus comprising:

a memory; and

at least one processor connected to the memory, the at least one processor configured to:

generate residual samples for a current block;

derive transform coefficients based on a transform process for the residual samples;

derive quantized transform coefficients based on a quantization process for the transform coefficients;

generate residual information indicating the quantized transform coefficients;

generate reconstructed samples based on the residual information;

generate adaptive loop filter (ALF)-related information and cross-component ALF (CCALF)-related information for the reconstructed samples; and

encode image information including the residual information, the ALF-related information, and the CCALF-related information,

wherein the image information includes header information and an adaptation parameter set (APS) including ALF data,

wherein the header information includes a first flag related to whether the CCALF is enabled for a Cb color component of the filtered reconstructed chroma samples,

wherein cross-component filter coefficients are represented based on the ALF data,

wherein based on the determination that a value of the first flag is 1, the header information includes information related to an identifier of the APS for deriving the cross-component filter coefficients for the Cb color component,

wherein the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include a Cb filter signal flag related to whether cross-component filters for the Cb color component are signaled,

wherein based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information related to the number of cross-component filters for the Cb color component,

wherein based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information on absolute values of the cross-component filter coefficients for the Cb color component and information on signs of the cross-component filter coefficients for the Cb color component, and

wherein the cross-component filter coefficients for the Cb color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cb color component and the information on the signs of the cross-component filter coefficients for the Cb color component.

3. A non-transitory computer-readable storage medium storing a bitstream generated by the encoding apparatus for image encoding of claim 2 .

4. An apparatus for transmitting data for an image, the apparatus comprising:

at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on generating residual samples for a current block, deriving transform coefficients based on a transform process for the residual samples, deriving quantized transform coefficients based on a quantization process for the transform coefficients, generating residual information indicating the quantized transform coefficients, generating reconstructed samples based on the residual information, generating adaptive loop filter (ALF)-related information and cross-component ALF (CCALF)-related information for the reconstructed samples, and encoding image information including the residual information, the ALF-related information, and the CCALF-related information; and

a transmitter configured to transmit the data comprising the bitstream,

wherein the image information includes header information and an adaptation parameter set (APS) including ALF data,

wherein the header information includes a first flag related to whether the CCALF is enabled for a Cb color component of the filtered reconstructed chroma samples,

wherein cross-component filter coefficients are represented based on the ALF data,

wherein based on the determination that a value of the first flag is 1, the header information includes information related to an identifier of the APS for deriving the cross-component filter coefficients for the Cb color component,

wherein the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include a Cb filter signal flag related to whether cross-component filters for the Cb color component are signaled,

wherein based on the Cb filter signal flag, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information related to the number of cross-component filters for the Cb color component,

wherein based on the information related to the number of cross-component filters for the Cb color component, the ALF data included in the APS for deriving the cross-component filter coefficients for the Cb color component include information on absolute values of the cross-component filter coefficients for the Cb color component and information on signs of the cross-component filter coefficients for the Cb color component, and

wherein the cross-component filter coefficients for the Cb color component are derived based on the information on the absolute values of the cross-component filter coefficients for the Cb color component and the information on the signs of the cross-component filter coefficients for the Cb color component.