INTER-IMAGE COMPONENT PREDICTION METHOD, AND IMAGE ENCODING AND DECODING METHOD AND DEVICE USING SAME
An image encoding and decoding method comprises the steps of: determining an inter-component prediction mode of a chrominance component block on the basis of an inter-component prediction mode list and predetermined index information; determining a reference sample for inter-component prediction of the chrominance component block on the basis of the determined inter-component prediction mode; deriving the parameters of a linear prediction model by using the reference sample; and performing inter-component prediction for the chrominance component block by using the parameters of the linear prediction model.
1 . An image decoding method, comprising:
determining an inter-component prediction mode of a chroma component block based on an inter-component prediction mode list and predetermined index information, wherein the inter-component prediction mode list is configured with k inter-component prediction modes;
downsampling reference samples for inter-component prediction of the chroma component block based on the determined inter-component prediction mode, the reference samples belonging to at least one of a left neighboring block or a top neighboring block of a luma component block corresponding to the chroma component block;
classifying the downsampled reference samples into a first group and a second group, wherein the first group represents a minimum value group of first downsampled reference samples having relatively small values among the downsampled reference samples and the second group represents a maximum value group of second downsampled reference samples having relatively large values among the downsampled reference samples;
obtaining a first average value between the first downsampled reference samples in the first group and a second average value between the second downsampled reference samples in the second group;
calculating a difference between the first average value and the second average value;
deriving a parameter of a linear prediction model based on the difference between the first average value of the first group and the second average value of the second group; and
performing the inter-component prediction on the chroma component block based on the parameter of the linear prediction model,
wherein a filter for the downsampling is variably determined based on whether a top boundary of the luma component block is on a top boundary of a coding tree unit (CTU) to which the luma component block belongs.
2 . The method of claim 1 , wherein the downsampling is selectively performed for a reference sample at a specific position.
3 . The method of claim 2 , wherein the specific position is determined based on encoding information on at least one of the chroma component block or the luma component block.
4 . The method of claim 3 , wherein the downsampling is performed based on a neighboring sample adjacent to the reference sample at the specific position in at least one of a vertical direction, a horizontal direction or a diagonal direction.
5 . The method of claim 4 , wherein the downsampling is performed based on at least one of availability of a neighboring block of the luma component block, a CTU related parameter or a predetermined flag, and
wherein the flag represents whether a sample of the chroma component block has a position shifted by a predetermined distance from a corresponding sample position of the luma component block.
6 . An image encoding method, comprising:
determining an inter-component prediction mode of a chroma component block from an inter-component prediction mode list including k inter-component prediction modes;
downsampling reference samples for inter-component prediction of the chroma component block based on the determined inter-component prediction mode, the reference samples belonging to at least one of a left neighboring block or a top neighboring block of a luma component block corresponding to the chroma component block;
classifying the downsampled reference samples into a first group and a second group, wherein the first group represents a minimum value group of first downsampled reference samples having relatively small values among the downsampled reference samples and the second group represents a maximum value group of second downsampled reference samples having relatively large values among the downsampled reference samples;
obtaining a first average value between the first downsampled reference samples in the first group and a second average value between the second downsampled reference samples in the second group;
calculating a difference between the first average value and the second average value;
deriving a parameter of a linear prediction model based on the difference between the first average value of the first group and the second average value of the second group; and
performing the inter-component prediction on the chroma component block based on the parameter of the linear prediction model,
wherein a filter for the downsampling is variably determined based on whether a top boundary of the luma component block is on a top boundary of a coding tree unit (CTU) to which the luma component block belongs.
7 . The method of claim 6 , wherein the downsampling is selectively performed for a reference sample at a specific position.
8 . The method of claim 7 , wherein the specific position is determined based on encoding information on at least one of the chroma component block or the luma component block.
9 . The method of claim 8 , wherein the downsampling is performed based on a neighboring sample adjacent to the reference sample at the specific position in at least one of a vertical direction, a horizontal direction or a diagonal direction.
10 . The method of claim 9 , wherein the downsampling is performed based on at least one of availability of a neighboring block of the luma component block, a CTU related parameter or a predetermined flag, and
wherein the flag represents whether a sample of the chroma component block has a position shifted by a predetermined distance from a corresponding sample position of the luma component block.
11 . A non-transitory computer-readable storage medium for storing a bitstream generated by an image encoding method,
the image encoding method comprising:
determining an inter-component prediction mode of a chroma component block from an inter-component prediction mode list including k inter-component prediction modes;
downsampling reference samples for inter-component prediction of the chroma component block based on the determined inter-component prediction mode, the reference samples belonging to at least one of a left neighboring block or a top neighboring block of a luma component block corresponding to the chroma component block;
classifying the downsampled reference samples into a first group and a second group, wherein the first group represents a minimum value group of first downsampled reference samples having relatively small values among the downsampled reference samples and the second group represents a maximum value group of second downsampled reference samples having relatively large values among the downsampled reference samples;
obtaining a first average value between the first downsampled reference samples in the first group and a second average value between the second downsampled reference samples in the second group;
calculating a difference between the first average value and the second average value;
deriving a parameter of a linear prediction model based on the difference between the first average value of the first group and the second average value of the second group; and
performing the inter-component prediction on the chroma component block based on the parameter of the linear prediction model,
wherein a filter for the downsampling is variably determined based on whether a top boundary of the luma component block is on a top boundary of a coding tree unit (CTU) to which the luma component block belongs.