Image encoding/decoding method and device
The video encoding/decoding method and device according to the present invention can determine an intra prediction mode of a chroma block, specify a luminance area for inter-component reference of the chroma block, downsample the specified luminance area, derive parameters for the inter-component reference of the chroma block, apply the parameters to the downsampled luminance area, and thereby predict the chroma block.
1 . An image decoding method, comprising:
determining an intra prediction mode of a chroma block;
determining a neighboring region for inter-component reference of the chroma block based on the intra prediction mode, the neighboring region including at least one of a top neighboring region or a left neighboring region adjacent to a luma block corresponding to the chroma block;
deriving down-sampled neighboring luma samples by down-sampling neighboring luma samples in the neighboring region,
deriving a parameter for the inter-component reference of the chroma block based on the down-sampled neighboring luma samples; and
predicting the chroma block based on the parameter for the inter-component reference,
wherein deriving the parameter for the inter-component reference comprises:
classifying the down-sampled neighboring luma samples into a first group and a second group, the first group including down-sampled neighboring luma samples having relatively large values and the second group including down-sampled neighboring luma samples having relatively small values; and
calculating a maximum value by averaging the down-sampled neighboring luma samples included in the first group and a minimum value by averaging the down-sampled neighboring luma samples included in the second group,
wherein the parameter for the inter-component reference is derived based on a difference between the maximum value and the minimum value,
wherein the parameter for the inter-component reference includes at least one of a weight or an offset,
wherein when the top neighboring region belongs to a different coding tree unit from the luma block, only three neighboring luma samples are used to derive one down-sampled neighboring luma sample, and
wherein when the top neighboring region belongs to a same coding tree unit as the luma block, five or six neighboring luma samples are used to derive the one down-sampled neighboring luma sample.
2 . The method of claim 1 , wherein the intra prediction mode of the chroma block is derived based on an index and a predetermined group configured with inter-component reference-based prediction modes, and
wherein the inter-component reference-based prediction modes includes a first mode which refers to both left and top neighboring regions adjacent to the chroma block, a second mode which refers to only the left neighboring region adjacent to the chroma block and a third mode which refers to only the top neighboring region adjacent to the chroma block.
3 . The method of claim 1 ,
wherein the top neighboring region includes N sample lines and the left neighboring luma region includes M sample lines, and
wherein N is set to a different value than M.
4 . The method of claim 1 , wherein the down-sampling is performed by using only a neighboring luma sample at a specific position and neighboring samples adjacent to the neighboring luma sample.
5 . The method of claim 4 , wherein the specific position is determined based on a position of one or more samples selected among a plurality of samples belonging to a neighboring region of the chroma block.
6 . The method of claim 5 , wherein the selected one or more pixels are representative of one or more samples positioned at every predetermined interval in the neighboring region of the chroma block.
7 . The method of claim 4 , wherein the neighboring samples include a sample positioned in at least one of a left, right, top, bottom, top-left, bottom-left, top-right, or bottom-right direction of the neighboring luma sample at the specific position.
8 . An image encoding method, comprising:
determining an intra prediction mode for a chroma block;
determining a neighboring region for inter-component reference of the chroma block based on the intra prediction mode, the neighboring region including at least one of a top neighboring region or a left neighboring region adjacent to a luma block corresponding to the chroma block;
deriving down-sampled neighboring luma samples by down-sampling neighboring luma samples in the neighboring region,
deriving a parameter for the inter-component reference of the chroma block based on the down-sampled neighboring luma samples; and
predicting the chroma block based on the parameter for the inter-component reference,
wherein deriving the parameter for the inter-component reference comprises:
classifying the down-sampled neighboring luma samples into a first group and a second group, the first group including down-sampled neighboring luma samples having relatively large values and the second group including down-sampled neighboring luma samples having relatively small values; and
calculating a maximum value by averaging the down-sampled neighboring luma samples included in the first group and a minimum value by averaging the down-sampled neighboring luma samples included in the second group,
wherein the parameter for the inter-component reference is derived based on a difference between the maximum value and the minimum value,
wherein the parameter for the inter-component reference includes at least one of a weight or an offset,
wherein when the top neighboring region belongs to a different coding tree unit from the luma block, only three neighboring luma samples are used to derive one down-sample neighboring luma sample, and
wherein when the top neighboring region belongs to a same coding tree unit as the luma block, five or six neighboring luma samples are used to derive the one down-sample neighboring luma sample.
9 . The method of claim 8 , wherein the intra prediction mode of the chroma block is derived based on an index and a predetermined group configured with inter-component reference-based prediction modes, and
wherein the inter-component reference-based prediction modes includes a first mode which refers to both left and top neighboring regions adjacent to the chroma block, a second mode which refers to only the left neighboring region adjacent to the chroma block and a third mode which refers to only the top neighboring region adjacent to the chroma block.
10 . The method of claim 8 , wherein the top neighboring region includes N sample lines and the left neighboring region includes M sample lines, and
wherein N is set to a different value than M.
11 . The method of claim 8 , wherein the down-sampling is performed by using only a neighboring luma sample at a specific position and neighboring samples adjacent to the neighboring luma sample.
12 . The method of claim 11 , wherein the specific position is determined based on a position of one or more samples selected among a plurality of samples belonging to a neighboring region of the chroma block.